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See discussions, st ats, and author pr ofiles f or this public ation at : .researchgate.ne t/public ation/335404336 MECHANICAL AND MICRO-STRUCTURE CHARACTERIZATION OF STEEL FIBER- REINFORCED GEOPOLYMER CONCRETE Conf erence Paper · May 2019 CITATIONS 2READS2 author s: Some o f the author s of this public ation ar e also w orking on these r elat ed pr ojects: Geopolymer s for W ater Purific ation View pr oject Progressiv e collapse analysis of RC struct ures View pr oject S. A. Elkholy Fayoum Univ ersity 68 PUBLICA TIONS    226 CITATIONS     SEE PROFILE Hilal El-Hassan Unit ed Ar ab Emir ates Univ ersity 97 PUBLICA TIONS    1,067 CITATIONS     SEE PROFILE All c ontent f ollo wing this p age was uplo aded b y S. A. Elkholy on 23 Dec ember 2021. The user has r equest ed enhanc ement of the do wnlo aded file. Performance Evaluation and Microstructure Characterization of Steel Fiber –Reinforced Alkali-Activated Slag Concrete Incorporating Fly Ash Hilal El-Hassan, Ph.D., M.ASCE1; and Said Elkholy, Ph.D.2 Abstract: This paper investigates the performance of steel fiber –reinforced alkali-activated slag concrete incorporating different fly ash replacement percentages. Three different molarities of sodium hydroxide (SH) were combined with sodium silicate to activate the bindingphase. Double hooked-end steel fibers were incorporated into the alkali-activated mix in varying volumetric proportions up to 3% to enhance its ductility. Blended binder, alkali-activator solution, dune sand, and coarse aggregate contents were proportioned and samples were cured at ambient conditions. Results showed that higher slag content, molarity of SH, and fiber addition led to less-workable concretes but withimproved mechanical properties, especially at early ages. Fly ash replacement of 25% could enhance mechanical performance after 28 days. Analytical models correlating mechanical properties were developed for alkali-activated slag concretes with fly ash. Scanning electron microscopy, differential scanning calorimetry, and Fourier transform infrared spectroscopy highlighted the coexistence of calcium alumi-nosilicate hydrate and sodium aluminosilicate hydrate gels. DOI: 10.1061/(ASCE)MT.1943-5533.0002872 .© 2019 American Society of Civil Engineers. Author keywords: Fiber-reinforced concrete; Mechanical properties; Rheological properties; Microstructure analysis; Analytical models. Introduction The concrete industry has been facing global pressure to reduce its greenhouse gas emissions and consumption of natural resources. To alleviate these environmental concerns, scientists and environ- mentalists recommend the replacement of cement by supplemen-tary cementitious materials (SCMs). If integrated into concrete mixes, they have the dual benefit of reducing cement usage while also usefully disposing of solid industrial byproducts. Fly ash (FA) and ground granulated blast furnace slag (referred to hereafter as slag) are industrial byproducts of the combustion of coal and pro- duction of steel, respectively. With their pozzolanic properties and global abundance, they are highlighted as primary replacements ofordinary portland cement (OPC) in concrete. Fly ash –based geopolymer concretes exhibit promising per- formance as an alternative to conventional concrete. However, their activation depends on curing at elevated temperatures. Such energy-intensive curing is considered a hindrance to its adoption by the concrete industry. In comparison, alkali-activated slag mortars and concretes cured in ambient conditions have been reported to exhibit limited workability but high compressive strengths up to 150 MPa ( Aydın and Baradan 2014 ;El-Hassan and Ismail 2018 ; El-Hassan et al. 2018 ). However, they experience deterioration that is attributed to the development of microcracks over time(Collins and Sanjayan 2001 ). Ballekere Kumarappa et al. ( 2018 ) explained that such shrinkage-induced microcracks are directly re-lated to the properties of the alkali-activator solution. The differentmicrostructures of fly ash geopolymer and alkali-activated slagconcretes partially explain these results. The main reaction product of the former is a three-dimensional sodium aluminosilicate hydrate (N─A─S─H) gel, resulting from the dissolution of SiO 2(Nath et al. 2016 ;Palomo et al. 1999 ;Škvára et al. 2009 ), while those of the latter are phases of hydrotalcite and calcium silicate hydrateswith traces of aluminum (C ─A─S─H) gel ( Ismail et al. 2014 ;Sun et al. 2018 ). Researchers have investigated the incorporation of slag in fly ash–based geopolymers to eliminate the need for heat curing. Research findings have highlighted an increase in mechanicalperformance but a decrease in slump/flow and setting times(Nath and Sarker 2014 ;Saha and Rajasekaran 2017 ;van Deventer et al. 2015 ;Yang et al. 2012 ). These blended geopolymers offer good resistance to water permeation, abrasion, acid and sulfate at-tack, elevated temperatures, corrosion, and fire ( Bernal et al. 2012 ; Karahan and Yakupo ğlu 2011 ;Shi 2003 ;van Deventer et al. 2015 ; Zhang et al. 2018 ). However, the chemical composition of slag seems to affect the hydration kinetics and strength development,especially the quantities of magnesia and alumina ( Winnefeld et al. 2015 ). While extensive work has been conducted on fly ash –based geopolymers incorporating slag (slag-to-fly ash ratio between 0and 1), limited work has been performed on alkali-activated slagconcretes with fly ash (slag-to-fly ash ratio >1)(Rodrigue et al. 2018 ;Wardhono et al. 2015 ). The effect of fly ash replacement on the microstructure of alkali-activated slag concrete has alsonot yet been investigated. Despite their superior performance, geopolymer and alkali- activated concretes have shown little resistance to cracking dueto their brittle nature. For application in the construction industry,their tensile and flexural properties should be improved. Steel fibershave been proposed for their ability to reduce crack propagation and cause more ductile behavior. Recent studies investigated the1Assistant Professor, Dept. of Civil and Environmental Engineering, United Arab Emirates Univ., P.O. Box 15551, Al Ain, United Arab Emirates (corresponding author). ORCID: Email: helhassan@uaeu.ac.ae 2Assistant Professor, Dept. of Civil and Environmental Engineering, United Arab Emirates Univ., P.O. Box 15551, Al Ain, United Arab Emirates; Associate Professor, Fayoum Univ., Fayoum 63514, Egypt. Note. This manuscript was submitted on June 11, 2018; approved on April 17, 2019; published online on July 26, 2019. Discussion period open until December 26, 2019; separate discussions must be submitted for individual papers. This paper is part of the Journal of Materials in Civil Engineering , © ASCE, ISSN 0899-1561. © ASCE 04019223-1 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2019, 31(10): 04019223 Downloaded from ascelibrary.org by United Arab Emirates University on 10/29/19. Copyright ASCE. For personal use only; all rights reserved. mechanical properties of steel fiber –reinforced geopolymer and alkali-activated composites. An increase in the modulus of elastic- ity and the compressive, tensile, and flexural strength was reportedupon using steel fibers in fly ash –based geopolymer with dosages up to 1% by volume ( Ganesan et al. 2015 ). Geopolymers incorpo- rating slag and palm oil fuel ash (POFA) or silica fume reported enhanced mechanical properties, including tensile and flexural strength, first crack load, and impact resistance upon the additionof 0.5% and 2% steel fibers ( Al-Majidi et al. 2017 ;Aydın and Baradan 2013 ;Islam et al. 2017 ). Bernal et al. ( 2010 ), Beglarigale et al. ( 2016 ), and Guo and Pan ( 2018 ) noted a significant improve- ment in the performance of alkali-activated slag mortar and con- crete with the use of 0.5% steel fibers by volume. Yet, no work has been conducted on the addition of steel fibers (up to 3%) tofly ash –slag blended alkali-activated concrete. Summarizing the review, while many authors have investigated the development and performance of steel fiber –reinforced geopol- ymer and alkali-activated concrete made with single binders (slagor fly ash), very few studies have examined the mechanical proper- ties and microstructure characteristics of blended alkali-activated concretes. In this research, steel fiber –reinforced alkali-activated slag concrete blended with fly ash and cured under ambient con- ditions were produced. Different blends of fly ash with slag wereused (fly ash ∶slag of 50∶50,25∶75, and 0∶100) and served to elimi- nate heat curing and age-related microcrack development while promoting the adoption of alkali-activated concrete by the con-struction industry for in situ applications. Unlike past research with the highest fiber volume fraction used being 2%, in this work, fibers were added up to dosages of 3% to transform the ceramic-like brittle behavior of alkali-activated concretes into a more duc- tile one. Three different molar concentrations of sodium hydroxide (SH) were used to assess its combined effect with fiber incorpo- ration. While past work utilized manufactured crushed fine sand,this study employed desert dune sand as a sustainable fine aggre- gate. The performance of alkali-activated concretes made withdifferent blends of slag and fly ash were evaluated in terms offresh properties, such as workability, and hardened properties, in-cluding modulus of elasticity and compressive, tensile, and flexu-ral strengths. An analytical study relating mechanical properties to codified and literature equations was also performed. Such a correlation has not been established for steel fiber –reinforced alkali-activated slag concrete (with and without fly ash), and itis important to provide a prediction of mechanical performancewithout the need for conducting extensive experimental testing.The microstructure of plain alkali-activated concretes has alsobeen analyzed by differential scanning calorimetry (DSC), Fouriertransform infrared spectroscopy (FTIR), and scanning electronmicroscopy (SEM). Experimental Program Materials Class F ( ASTM 2015a ) fly ash and slag were used in this study as the blended alkali-activated binding material. The specific gravityand Blaine fineness of fly ash were determined to be 2.32 and3,680 cm 2=g, respectively, while those of slag were 2.70 and 4,250 cm2=g, respectively. Figs. 1and2present the particle size distribution, SEM micrograph, and X-ray diffraction (XRD) spec-trum of fly ash and slag, respectively. Crushed stone was used ascoarse aggregate with a nominal maximum size of 10 mm, densityof1,660 kg=m 3, and water absorption of 0.7%. Prior to incorpo- ration into alkali-activated concrete mixes, the aggregates were pre-pared to surface-saturated dry (SSD) condition. Desert dune sand served as fine aggregate. Its specific gravity and unit weight were 2.57 and 1,670 kg=m 3, respectively. Fig. 3shows the particle size (b) (a) (c) 020406080100 0.1 1 10 100Percentage passing (%) Particle size (µm)Fly ash 10 20 30 40 50 60Intensity (counts) Position (2 θ)Q: Quartz M: Mullite H: Hematite QQ MM HQ QQ Q Fig. 1. (a) Particle size distribution; (b) SEM micrograph; and (c) XRD spectrum of fly ash. © ASCE 04019223-2 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2019, 31(10): 04019223 Downloaded from ascelibrary.org by United Arab Emirates University on 10/29/19. Copyright ASCE. For personal use only; all rights reserved. distribution, scanning electron micrograph, and X-ray diffraction spectrum. The chemical compositions of as-received fly ash, slag, and dune sand are shown in Table 1. An alkali-activator solution was prepared as a mixture of sodium silicate (SS) and SH.The mass chemical composition of the Grade N SS solution was 26.3% SiO 2, 10.3% Na 2O, and 63.4% H 2O. The SH solution was formulated to molarities of 8, 10, and 14 by dissolving97%–98% pure NaOH flakes in tap water. Past work by(b) (a) (c) 020406080100Percentage passing (%) Particle size (µm)Slag 1 10 100 10 20 30 40 50 60Intensity (counts) Position (2 θ)Q: Quartz M: Mullite G: Gehlenite GQ QGM Fig. 2. (a) Particle size distribution; (b) SEM micrograph; and (c) XRD spectrum of slag. (b) (a) (c)020406080100Percentage passing (%) Particle size (µm)Dune sand 10 100 1000 10 20 30 40 50 60Intensity (counts) Position (2 θ)Q Q C Q QCFA FQ: Quartz C: Calcite F: Iron oxide A: Aluminum oxide Fig. 3. (a) Particle size distribution; (b) SEM micrograph; and (c) XRD spectrum of dune sand. © ASCE 04019223-3 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2019, 31(10): 04019223 Downloaded from ascelibrary.org by United Arab Emirates University on 10/29/19. Copyright ASCE. For personal use only; all rights reserved. Kanesan et al. ( 2017 ), Patankar et al. ( 2014 ), and Sani et al. (2016 ) showed that a molarity below 8 and above 14 reduced the reaction efficiency, while a molarity of 10 acted as a bettermedian than 12. Double hooked-end steel fibers with a specificgravity of 7.9, an aspect ratio of 65, and length of 35 mm wereused. To ensure sufficient workability for mixes with high steelfiber content, a polycarboxylic ether polymer –based superplasti- cizer (SP) was used. It has been reported that such SPs can im-prove the workability of alkali-activated composites withoutcompromising the mechanical properties ( Montes et al. 2012 ; Palacios and Puertas 2005 ). Alkali-Activated Concrete Mix Design A total of seventeen (17) alkali-activated concrete mixes were pre- pared with varying fly ash replacement proportions (0%, 25%, and50%), SH molar concentrations (8, 10, and 14 M), and fiber volumefractions (0%, 1%, 2%, and 3%), as shown in Table 2. Mixtures were designated as GX-YM-ZSF, where X is the slag content (per-centage of binder by mass), Y is the molar concentration of SH, andZ is the steel fiber volume fraction (%). For instance, Mix 9, des-ignated as G75-8M-1.0SF, represents a concrete mix made with aslag:fly ash ratio of 75:25, 8 M sodium hydroxide solution, andsteel fiber volume fraction of 1%. Binder, aggregate and activatorsolution contents were optimized based on previous work con-ducted by the authors ( El-Hassan and Ismail 2018 ;Ismail and El-Hassan 2018 ). For all mixes, the total binder, dune sand, andcoarse aggregate contents were 500, 550, and 1,100 kg=m 3, respec- tively. An alkali-activator solution-to-binder ratio of 0.40 was se-lected with a SS-to-SH ratio of 2.5. The SP content was 2% bybinder mass, except for samples made with equal proportions offly ash and slag, where no SP was added. Steel fibers were incor-porated into the mix in the range of 0 –2% for samples with 14 M SH and up to 3% for 8 M SH. Preliminary test trials showed thatmixes with higher SH molar concentration had reduced workabilityand compactability due to an increased viscosity and thus could notincorporate more than 2% steel fibers (see the section “Workabil- ity”). Other than Mixes 1 –6, all concretes were made with a slag ∶fly ash ratio of 75∶25due to the superior performance after 28 days (see the section “Results and Discussion ”). Also, it should be noted that Mixes 13 and 14 (G75-10M-0.0SF and G75-10M-2.0SF)served as median samples with 10 M SH to assess the effect of SHmolar concentration on the performance of steel fiber –reinforced alkali-activated slag/fly ash blended concrete. Sample Preparation Concrete samples were cast under ambient conditions (temperature of24°C/C62°C and relative humidity of 50% /C65%). The alkali- activator solution was prepared 24 h prior to casting to allow fordissipation of heat associated with the exothermic chemical reac-tions of SH flakes with water and SH solution with SS solution. Thedry components, comprising slag, fly ash, dune sand, and coarseaggregates, were mixed in a pan mixer for 3 min. The preparedsolution was gradually incorporated into the dry components andmixed for another 3 min to ensure homogeneity and uniformity.Superplasticizer was added a few seconds after the activatorsolution. Freshly mixed alkali-activated concrete samples wereprepared as 100×200mm (diameter ×height) cylinders for com- pressive strength testing, 150×300mm (diameter ×height) cylin- ders for tensile splitting testing, and 100×100×500mm prisms for flexural strength testing. One additional cylindrical sample(100mm diameter ×200mm height) was prepared for micro- structure testing. Specimens were cast into two to three layers, compact-vibrated for 10 s on a vibrating table, left to rest for 24 hat ambient conditions, and then demolded. So-produced concreteswere kept under ambient conditions until testing age to simulateon-site construction scenarios.Table 1. Chemical composition of as-received materials OxideMaterial (%) Slag Fly ash Dune sand CaO 42.0 3.3 14.1 SiO 2 34.7 48.0 64.9 Al2O3 14.4 23.1 3.0 MgO 6.9 1.5 1.3Fe 2O3 0.8 12.5 0.7 Na2O 0.0 0.0 0.4 K2O 0.0 0.0 1.1 Loss on ignition 1.1 1.1 0.0 Others 0.2 10.5 15.5 Table 2. Mix proportion of alkali-activated concrete (kg =m3) Mix No. Mix designationBinder Aggregate Activator SPSteel fiber volume (%) Fly ash Slag Dune sand Coarse SS SH (molarity) 1 G50-14M-0.0SF 250 250 550 1,100 143 57 (14M) 0 0.0 2 G50-14M-2.0SF 250 250 550 1,100 143 57 (14M) 0 2.0 3 G75-14M-0.0SF 125 375 550 1,100 143 57 (14M) 10 0.0 4 G75-14M-2.0SF 125 375 550 1,100 143 57 (14M) 10 2.0 5 G100-14M-0.0SF 0 500 550 1,100 143 57 (14M) 10 0.0 6 G100-14M-2.0SF 0 500 550 1,100 143 57 (14M) 10 2.07 G75-8M-0.0SF 125 375 550 1,100 143 57 (8M) 10 0.0 8 G75-8M-0.5SF 125 375 550 1,100 143 57 (8M) 10 0.5 9 G75-8M-1.0SF 125 375 550 1,100 143 57 (8M) 10 1.0 10 G75-8M-1.5SF 125 375 550 1,100 143 57 (8M) 10 1.5 11 G75-8M-2.0SF 125 375 550 1,100 143 57 (8M) 10 2.012 G75-8M-3.0SF 125 375 550 1,100 143 57 (8M) 10 3.0 13 G75-10M-0.0SF 125 375 550 1,100 143 57 (10M) 10 0.0 14 G75-10M-2.0SF 125 375 550 1,100 143 57 (10M) 10 2.0 15 G75-14M-0.5SF 125 375 550 1,100 143 57 (14M) 10 0.5 16 G75-14M-1.0SF 125 375 550 1,100 143 57 (14M) 10 1.017 G75-14M-1.5SF 125 375 550 1,100 143 57 (14M) 10 1.5 © ASCE 04019223-4 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2019, 31(10): 04019223 Downloaded from ascelibrary.org by United Arab Emirates University on 10/29/19. Copyright ASCE. For personal use only; all rights reserved. Performance Evaluation The workability of fresh alkali-activated slag/fly ash blended concrete was characterized by the slump of ASTM C143 ( ASTM 2015c ). The mechanical performance of plain and steel fiber – reinforced concrete samples was evaluated following standardizedprocedures. ASTM C39 ( ASTM 2015b ) was employed to measure the compressive strength at 1, 7, and 28 days. The static chord modu- lus of elasticity was determined as per the procedure of ASTM C469 (ASTM 2014 ). In this test, a 500-kN compression load cell was used to record the applied compressive load, while four 60-mm-longstrain gauges were attached at midheight of the cylinder on diamet- rically opposite points. The tensile strength of 28-day specimens was measured indirectly following the method of tensile splitting strength of ASTM C496 ( ASTM 2011 ). The flexural strength (also referred to as the modulus of rupture) was calculated by performing four-pointloading tests on 28-day concrete prism samples as per ASTM C78 (ASTM 2016 ). For each experimental performance test, three repli- cates were prepared to obtain an average. Analytical Techniques The mechanical performance of alkali-activated slag concrete made with up to 50% fly ash replacement can only be properly under- stood through microstructure analysis. With limited information available in the literature, the microstructure of untested alkali-activated slag concrete with different fly ash replacement percent- ages was analyzed at the ages of 7 and 28 days. Three specimens were tested for each experimental test to ensure credibility andconsistency of results. Differential scanning calorimetry was per- formed using a DSC-Q200 calorimeter (TA Instruments, New Castle, Delaware) at a heating rate of 10°C=min in a constant flow of nitrogen gas ( 50mL=min). Concrete samples were finely ground and sieved through an 80- μm sieve to remove coarse particles. The obtained powder specimen was weighed (10 mg) and packed into aluminum crucibles for DSC testing. Fourier transform infrared spectroscopy was conducted using a Varian 3100 FT-IR spectrometer (Walnut Creek, California) in transmittance mode at a resolution of 1cm −1from 400 to 4,000 cm−1. Concrete samples, similar to those used in DSC test- ing, were mixed with potassium bromide at a ratio of 3:1, by mass, and pelletized for FTIR testing. Scanning electron microscopy was performed using a JEOL- JSM 6390A microscope (Tokyo) with energy dispersive X-ray(EDX). Concrete chunks (25 mm in diameter) were obtained from the core of untested original alkali-activated concrete specimens, sputter-coated with a thin gold layer (99% purity) to ensure con- ductivity, and examined in high-vacuum SEM mode.Results and Discussion Workability The slump values, characterizing the workability, of plain and steel fiber–reinforced alkali-activated concrete are shown in Fig. 4.A s illustrated in Fig. 4(a), the replacement of slag by 25% and 50% fly ash increased the slump by 17 and 45 mm, representing increases of74% and 196%, respectively. This improvement in workability isattributed to the lubricating effect of spherical fly ash particles,which produced less interparticle frictional forces ( Sun et al. 2003 ). The addition of 2% steel fibers by volume resulted in zero slump for 75% and 100% slag concrete samples. The slump was 10 mm for concretes with a fly ash content of 50%. Fig.4(b)shows that plain concrete samples made with a slag ∶fly ash ratio of 75∶25and 8, 10, and 14 M SH solution observed slumps of 60, 52, and 40 mm, respectively. As the molarity increased, a13% and 33% reduction in slump was noted. This is owed to the higher viscosity of the produced activator solution. The incor- poration of steel fibers caused a significant decrease in the work-ability. On average, every 0.5% steel volume fraction additionreduced the slump by 11 mm as a result of more mortar adheringto the fibers, which caused an increase in viscosity and decrease inslump ( Chen and Liu 2005 ). A zero slump was noted for 14-M-SH samples made with 2% steel fibers by volume. Evidently, with higher SH molar concentration, a less workable and compactableconcrete was produced, to the extent that only up to 2% steel fiberscould be incorporated. Further additions of steel fibers (3%) wasthus not possible in 14-M-SH concretes. Compressive Strength The compressive strength of alkali-activated concrete samples was tested at the ages of 1, 7, and 28 days. Fig. 5(a)presents the com- pressive strength development of 14-M-SH concretes incorporating0%, 25%, and 50% fly ash and 0% and 2% steel fiber reinforce- ment. At an early age of 1 and 7 days, the compressive strength decreased as the fly ash content increased from 0% to 50%. Thisis mainly due to a slower fly ash polymerization reaction at ambienttemperatures ( Ismail et al. 2014 ). In comparison, samples with high slag content have a larger reactant surface area (i.e., more ac-tivation sites), leading to an accelerated reaction of calcium and production of aluminosilicate hydrate and calcium silicate hydrate gels ( Al-Majidi et al. 2016 ;Chi 2012 ;Davidovits 2008 ;Palomo et al. 1999 ). However, at a later age of 28 days, the compressive strength slightly increased as the fly ash content increased from 0%to 25% but decreased when the content was further increased to50%. Apparently, fly ash contributes to later strength through(b) (a)01020304050607080 02 0 4 0 6 0Slump (mm) Fly Ash Content (%)SF=0% SF=2%01234Slump (mm) Steel Fiber Volume (%)8M 10M 14M Fig. 4. Workability of alkali-activated slag concretes with different: (a) fly ash content; and (b) volumetric fiber fractions. © ASCE 04019223-5 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2019, 31(10): 04019223 Downloaded from ascelibrary.org by United Arab Emirates University on 10/29/19. Copyright ASCE. For personal use only; all rights reserved. the development of N ─A─S─H gel, while slag is the main con- tributor to early-age strength with the formation of C ─A─S─H gel. Similar findings have been reported by Ismail et al. ( 2014 ). It is also worth noting that the highest increase in strength between7 and 28 days was 23.8% and 19.5% for samples with 50% and75% slag, respectively. Nevertheless, 50% slag replacement byfly ash could hinder the development of strength, remaining 12% lower than its 25% fly ash concrete counterpart. Furthermore, the addition of 2% steel fibers increased the compressive strengthby 20% –52% (average of 33.3%), with highest increase reported for alkali-activated concrete mixes with 25% fly ash. The compressive strength development of plain and steel fiber – reinforced alkali-activated slag concrete with 25% fly ash and 8 M SH is shown in Fig. 5(b). On average, 78% and 89% of the 28-day compressive strength was obtained at 1 and 7 days of age, respec-tively. As for 14-M-SH concretes of Fig. 5(c), an average of 81% and 97% of the respective 28-day compressive strength wasreached within 1 and 7 days. This is a clear indication of the rapid strength development of alkali-activated slag/fly ash blended con- crete. Temuujin et al. ( 2009 ) reported that such a phenomenon is mainly due to the high SH concentration, which improves theefficiency of activation reaction and increases the early-age com- pressive strength. Fig. 5(d) shows the strength development of 0.0% and 2.0% steel fiber –reinforced concretes made with a slag ∶fly ash ratio of 75∶25and different SH molar concentrations (8, 10, and 14 M). A superior performance can be noted with higher concentrationof SH solution. It is believed that the increase in SH molarity provides more sodium ions that could balance the charges, thusforming aluminosilicate networks in the alkali-activated mix (Sathonsaowaphak et al. 2009 ). On the other hand, a low molarity of SH could limit the activation reaction due to less leaching ofsilica and alumina from the source material ( Alonso and Palomo 2001 ). The addition of steel fibers to the alkali-activated slag/fly ash blended concrete created a significant variation in the developmentof compressive strength. The strength index, shown in Eq. ( 1), was used to evaluate the increase in strength owing to the incorporationof different volumes of steel fibers. Thus, the strength index plottedin Fig. 6is the relative increase in strength of steel fiber –reinforced concretes compared to their unreinforced counterparts Strength index ð%Þ¼½ ð fcf−f0cpÞ=f0cp/C138ð 1Þ where f0 cf= average compressive strength of fiber-reinforced alkali-activated concrete; and f0cp= average compressive strength of plain alkali-activated concrete. Fig.6(a)presents the compressive strength increase due to the addition of 2% steel fibers to alkali-activated slag concretes madewith different fly ash replacement percentages and a 14-M-SHsolution. For 1- and 7-day samples, the strength increased inthe range of 20% –39% and 36% –52%, respectively, with highest value associated with 25% fly ash concretes (G75-14M-2.0SF).Among mixes with 0% and 25% fly ash replacement (G100-14M-0.0SF and G75-14M-0.0SF), the latter was weaker at 1 and7 days [Fig. 5(a)]. Thus, the addition of steel fiber contributed more to its strength, owing to a less dense matrix at an early age. Similar conclusions were noted for samples after 28 days, with an increase(b) (a) (c) (d) 01020304050607080 G50-14M- 0.0SF G75-14M- 0.0SF G100-14M- 0.0SF G50-14M- 2.0SF G75-14M- 2.0SF G100-14M- 2.0SFCompressive Strength (MPa) Mix Designation1-day 7-day 28-day SF = 0.0%SF=2.0%G75-8M- 0.0SF G75-8M- 0.5SF G75-8M- 1.0SF G75-8M- 1.5SF G75-8M- 2.0SF G75-8M- 3.0SFCompressive Strength (MPa) Mix Designation1-day 7-day 28-dayG75-14M- 0.0SF G75-14M- 0.5SF G75-14M- 1.0SF G75-14M- 1.5SF G75-14M- 2.0SFCompressive Strength (MPa) Mix Designation1-day 7-day 28-dayG75-8M- 0.0SF G75-10M- 0.0SF G75-14M- 0.0SF G75-8M- 2.0SF G75-10M- 2.0SF G75-14M- 2.0SFCompressive Strength (MPa) Mix Designation1-day 7-day 28-day Fig. 5. Strength development of alkali-activated concrete made with (a) 14-M-SH solution and different fly ash content and SF ratios; (b) 8-M-SH solution and different SF ratios; (c) 14-M-SH solution and different SF ratios; and (d) different molarities of SH solution. © ASCE 04019223-6 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2019, 31(10): 04019223 Downloaded from ascelibrary.org by United Arab Emirates University on 10/29/19. Copyright ASCE. For personal use only; all rights reserved. in strength between 23% and 30%. This shows that the effect of steel fibers was less significant at a later age of 28 days due to a densified alkali-activated structure, reduced porosity, and en- hanced binding ability of the aluminosilicate hydrate and calcium silicate hydrate gels, as discussed later in the microstructure analy- sis sections. As shown in Fig. 6(b), the addition of steel fibers led to an increase in the load carrying capacity of 8M-SH concretes. An increase between 7% and 22% was observed after 1 day when 0.5% –3% steel fibers were added (G75-8M-0.5SF, G75-8M- 1.0SF, G75-8M-1.5SF, G75-8M-2.0SF, and G75-8M-3.0SF). At 7 and 28 days, up to 25% improvement in compressive strength was recorded with 3% steel fibers (G75-8M-3.0SF). At these ages, the effect was much less apparent with low steel fiber volume fractions of 0.5% and 1% (G75-8M-0.5SF and G75-8M-1.0SF). This shows that the incorporation of steel fibers could significantly enhance the compressive strength of 25∶75fly ash ∶slag blended alkali-activated concretes if more than 1.5% by volume was added to the mix. This is mainly due to the ability of steel fibers to restrain the expansion of cracks, reduce the stress concentration within cracks, and delay the growth of cracks by redirecting them ( Afroughsabet and Ozbakkaloglu 2015 ). Analogous findings have been reported by Aydın and Baradan ( 2013 ). Similar observations can be noted for 14-M-SH alkali-activated concrete in Fig. 6(c). At 1 and 7 days of age, the addition of steel fibers enhanced the compressive strength by 7% –39% and 1% – 46%, respectively. It was less effective at 28 days with an increase of 13% –30% owing to a superior alkali-activated matrix. Fig. 6(d) examines the strength increase in 75∶25slag∶fly ash alkali-activated concrete made with 2.0% steel fiber volume fraction and different molarities of SH solution (G75-8M-2.0SF,G75-10M-2.0SF, and G75-14M-2.0SF). It is clear that incorporat- ing steel fibers could further improve the compressive strength of samples with higher SH molar concentration. Nonetheless, its ef-fect was more significant at an early age of 1 day. The respectiveincrease of G75-8M-2.0SF, G75-10M-2.0SF, and G75-14M-2.0SF was 12.6%, 21.8%, and 32.8% after 1 day and 7.0%, 17.9%, and 20.4% after 7 days. This is possibly due to the increase in activationreaction efficiency at a later age of 28 days to the extent that theaddition of steel fibers caused limited improvement to compressive strength. While 1- and 7-day results are novel, the 28-day findings are not unexpected. Indirect Tensile Strength The 28-day tensile strength of steel fiber –reinforced alkali- activated slag concrete incorporating fly ash was measured indirectly as the tensile splitting strength ( f sp). The effect of fly ash replacement and steel fiber addition on fspis shown in Fig.7(a). Values ranged between 3.53 and 3.81 MPa for plain sam- ples and between 4.16 and 4.64 MPa for steel fiber –reinforced counterparts (SF ¼2.0%). The substitution of slag with 25% fly ash resulted in a slight increase in the 28-day tensile strength.Apparently, the mechanical performance was enhanced with an intermix of sodium aluminosilicate hydrate (N ─A─S─H) and cal- cium aluminosilicate hydrate (C ─A─S─H) gels from the alkali ac- tivation of fly ash and slag. This intermix has been reported todensify the concrete matrix and increase the strength ( Brough and Atkinson 2002 ). The addition of steel fibers led to a significant increase in tensile strength, with the highest increase of 22% rep-resenting that of mix with 75% slag and 25% fly ash. It is clear thatwhile steel fibers could enhance the mechanical performance of (b) (a) (d) (c)01020304050 0 1 02 03 04 05 06 0Strength Index (%) Fly Ash Content (%)1-day 7-day 28-day01020304050 0.0 1.0 2.0 3.0 4.0Strength Index (%) Steel Fiber Volume (%)1-day 7-day 28-day0.0 0.5 1.0 1.5 2.0 2.5Strength Index (%) Steel Fiber Volume (%)1-day 7-day 28-day6 8 10 12 14 16Strength Index (%) Molarity of SH solution (M)1-day 7-day 28-day Fig. 6. Strength index of alkali-activated concretes over time: (a) 2.0% SF with different slag-to-fly ash ratio and 14-M-SH solution; (b) 8-M-SH; (c) 14-M-SH; and (d) 2.0% SF with different molarities of SH. © ASCE 04019223-7 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2019, 31(10): 04019223 Downloaded from ascelibrary.org by United Arab Emirates University on 10/29/19. Copyright ASCE. For personal use only; all rights reserved. alkali-activated slag concrete, they were most effective in mixes with 25% fly ash replacement. It is also worth noting that speci- mens with 50% fly ash were somewhat weaker than the others owing to a slower activation chemical reaction of fly ash at ambienttemperatures ( Palomo et al. 1999 ). Fig.7(b) presents the tensile splitting strength as a function of steel fiber volume fraction in 8-, 10-, and 14-M-SH concretes (75%slag and 25% fly ash). It can be seen that the 14-M-SH concretesamples were consistently superior to counterparts made with alower molarity of SH. This is mainly due to the enhanced perfor-mance of the activation matrix made with a higher SH molar con-centration, which is also reflected in the compressive strengthresults. Specimens with 8 M SH increased by 14%, 17%, 24%,29%, and 31% when 0.5%, 1%, 1.5%, 2%, and 3% steel fibers wereadded, respectively. Clearly, the contribution of steel fibers to ten-sile strength was more significant at higher fiber dosages. On theother hand, 14-M-SH counterparts increased by 13%, 16%, 17%,and 22% for similar steel fibers volume fractions. The effect of steelfibers on splitting tensile strength seemed to be similar regardless ofthe molarity of SH solution. It is also worth noting that the tensilesplitting strength was approximately 5% –8% of the compressive strength. A previous study reported similar results due to the incor-poration of steel fibers in fly ash –based geopolymer concrete (Islam et al. 2017 ). The tensile splitting strength of concrete is typically estimated using codified and previously published equations, including thosein AS3600 ( Standards Australia 2009 ), ACI Commitee 318 ( ACI 2014 ), CEB-FIP ( 1990 ), Choi and Yuan ( 2005 ), Xu and Shi ( 2009 ), Perumal ( 2015 ), Ahmed and Shah ( 1985 ), and ACI Committee 363 ( ACI 1992 ). Such equations, shown in Table 3, were applied to determine the tensile splitting strengths of plain and steelfiber–reinforced alkali-activated concretes incorporating slag and fly ash using the average 28-day compressive strength. The asso-ciated plots are shown in Fig. 8(a). The equations provided by ACI Commitee 318 ( ACI 2014 ) and Ahmed and Shah ( 1985 ) are suitable for 10-M-SH and 14-M-SH steel fiber –reinforced con- crete mixes but slightly overestimate the tensile strength for plaincounterparts owing to its ceramic-like brittleness. Apparently, theaddition of steel fibers modified the tensile behavior of these mixesand rendered them more similar to that of conventional concrete.Furthermore, the AS3600 ( Standards Australia 2009 ) equation could be employed to predict the performance of plain 8-M-SHconcretes only. Nevertheless, it is should be noted that the ACICommitee 318 ( ACI 2014 ) equation could be used for all alkali- activated concrete mixes produced in this work if such a codifiedequation were to be multiplied by a factor α. To determine the value ofα, the regression equations were obtained based on plotted trend lines, as shown in Fig. 8(b). Each regression equation can accu- rately predict the tensile splitting strength of alkali-activated slagconcretes produced in this work with R 2>0.90. Thus, a modified version of the ACI Commitee 318 ( ACI 2014 ) equation is proposed in the form of Eq. ( 2), where αis 1 for 10-M-SH and 14-M-SH samples and 0.75 for 8-M-SH specimens: fsp¼0.56αffiffiffiffiffi f0cp ð2Þ The tensile splitting behavior of 8-, 10-, and 14-M-SH alkali- activated concrete was significantly improved due to the incorpo- ration of steel fibers. The postcracking behavior was also affected as shown in Fig. 9. The tensile strength development in plain con- cretes could be associated to the formation of alkali-activationproducts in the matrix with limited postcracking performance. (b) (a)0123456 0 1 02 03 04 05 06 0Tensile Splitting Strength (MPa) Fly Ash Content (%)SF=0% SF=2%0.0 0.5 1.0 1.5 2.0 2.5 3.0Splitting Tensile Strength (MPa) Steel Fiber Volume (%)8M 10M 14M Fig. 7. Splitting tensile strength of alkali-activated slag concrete with different: (a) fly ash content; and (b) molar concentration of SH solution. Table 3. Published equations relating mechanical properties Reference Tensile splitting strength ( fsp) Flexural strength ( fr) Modulus of elasticity ( Ec) ACI Commitee 318 ( ACI 2014 ) 0.56f00.5c 0.62f00.5c 0.043w1.5f00.5c AS3600 ( Standards Australia 2009 ) 0.36f00.5c 0.60f00.5c 0.024w1.5ðf00.5cþ0.12Þ CEB-FIP ( 1990 ) 0.3f00.67c 0.81f00.5c 9,979 .4f00.33c Choi and Yuan ( 2005 ) 0.6f00.5c —— Xu and Shi ( 2009 ) 0.21f00.83c 0.39f00.59c — Perumal ( 2015 ) 0.188f00.84c 0.259f00.843c — Ahmed and Shah ( 1985 ) 0.46f00.55c 0.44f00.5c 3.38w2.5f00.65c Dilli et al. ( 2015 ) —— 10,750 ðf0c=10Þ0.5 Mendis ( 2003 ) —— 0.043w1.5ð1:1−0.002f0cÞf00.5c ACI Committee 363 ( ACI 1992 ) 0.59f00.5c 0.94f00.5c 3,320 f00.5cþ6,900 Note: w= density of concrete (kg =m3); and f0c= compressive strength (MPa). © ASCE 04019223-8 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2019, 31(10): 04019223 Downloaded from ascelibrary.org by United Arab Emirates University on 10/29/19. Copyright ASCE. For personal use only; all rights reserved. Nevertheless, the tensile splitting strength and the postcracking performance were enhanced with higher steel fiber volume frac- tions. It is believed that the incorporation of ever more fibers increased the energy requirements for crack propagation and bridged microcracks. Hence, the fracture process seemed to bearrested or retarded, producing an alkali-activated concrete with higher splitting tensile load capacity and improved postcrackingperformance. Flexural Strength The flexural strength of alkali-activated slag concretes made with different fly ash replacement percentages and steel fiber volumefractions is shown in Fig. 10(a) . Values ranged from 3.99 to 4.31 MPa for plain concretes and from 4.72 to 5.27 MPa for steelfiber–reinforced equivalents. A similar trend to tensile splitting strength is noted, whereby the highest flexural strength was thatof alkali-activated slag concrete mix with 25% fly ash replacement.Also, the addition of steel fibers enhanced the flexural performanceby up to 22%. Fig.10(b) presents the flexural strength ( f r) of plain and steel fiber–reinforced alkali-activated concrete after 28 days. An increase in flexural strength can be noted upon the incorporation of steelfibers. For 8-M-SH samples, a volumetric addition of fiber up to1.5% could enhance the flexural capacity by 16%. However, theeffect of fiber addition was more pronounced at higher dosagesof 2% and 3%. The associated increase in strength was 23% and25%, respectively. Apparently, crack propagation through alkali-activated concrete was retarded or arrested due to the incorporationof 2% –3% steel fibers. Similar results were presented for steel fiber–reinforced fly ash-based geopolymer concretes ( Bernal et al. 2010 ). An increase of 19% was also reported for 10-M-SH con- cretes upon the addition of 2.0% steel fiber volume fraction. In con-trast, a near-linear relation between the volume fraction of steelfibers and flexural strength increase was noted for 14-M-SH sam-ples. On average, the flexural strength increased by 7% for every0.5% volume fraction of steel fiber added. A comparison betweenalkali-activated concretes with constant steel fiber content and dif-ferent molarity of SH (8M-2.0SF, 10M-2.0SF, and 14M-2.0SF)showed that a higher molarity resulted in further increases in flexu-ral strength. Others reported that the compression zone of concreteprisms placed under flexural loading played an insignificant role infailure ( Gencel et al. 2011 ). On the other hand, the tension zone was critical to the development of flexural strength. It is thus believed that the addition of steel fibers could allow alkali-activated concrete to withstand more crack generation in the tension zone and, as such,result in a higher flexural strength. Codified and past literature equations, shown in Table 3, from AS3600 ( Standards Australia 2009 ), ACI Commitee 318 ( ACI 2014 ), Ahmed and Shah ( 1985 ), Xu and Shi ( 2009 ), Perumal (2015 )(CEB-FIP 1990 ), and ACI Committee 363 ( ACI 1992 ) were employed to predict the flexural strength of steel fiber –reinforced alkali-activated concrete. The results displayed in Fig. 11(a) show that the equations of ACI Commitee 318 ( ACI 2014 ) and ACI Committee 363 ( ACI 1992 ) provide the closest prediction with rea- sonable accuracy. Plain alkali-activated concrete samples were gen-erally lower than predictions provided by most codified equationsdue to its ceramic-like brittle behavior. However, it is possible toapply a modification factor, α, to the ACI Commitee 318 ( ACI 2014 ) equation based on the molarity of SH. To obtain the value ofα, the plots of linear regression analyses equations were devel- oped, as shown in Fig. 11(b) . Accordingly, Eq. ( 3) is proposed as a modified version of the ACI Commitee 318 ( ACI 2014 ) equa- tion to accurately predict ( R 2>0.90) the flexural strength, with α being 0.75 for 8-M-SH and 1 for 10- and 14-M-SH alkali-activatedconcretes: f r¼0.62αffiffiffiffiffi f0cp ð3Þ(a) (b) 234567 6.5 7.0 7.5 8.0 8.5Splitting Tensile Strength (MPa) Compressive Strength, √f'c (MPa) 8M 10M 14M AS3600 (2009) ACI Committee 318 (2014) CEB-FIP (1990) Choi and Yuan (2005) Xu and Shi (2009) Perumal (2015) Ahmed and Shah (1985) ACI Committee 363 (1992) fsp= 0.42 √f'cfsp= 0.55 √f'cfsp= 0.56 √f'c6.5 7.0 7.5 8.0 8.5Splitting Tensile Strength (MPa) Compressive Strength, √f'c (MPa)8M 10M 14M Fig. 8. Relationship between splitting tensile and compressive strength: (a) in comparison to literature and codified equations; and(b) using linear regression analysis. 050100150200Applied Load (kN) Loading Time (s)0.00% vf 0.50% vf 1.00% vf 2.00% vf Fig. 9. Development of splitting tensile load over time of 14-M alkali- activated slag concretes with 25% fly ash. © ASCE 04019223-9 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2019, 31(10): 04019223 Downloaded from ascelibrary.org by United Arab Emirates University on 10/29/19. Copyright ASCE. For personal use only; all rights reserved. Modulus of Elasticity The modulus of elasticity ( Ec) is the ability of a material to sustain induced stress while increasing the strain within the elastic limit.Table 4shows the experimentally determined modulus of elas- ticity for produced alkali-activated slag concretes after 28 days. The replacement of slag by 25% fly ash resulted in higher E c.H o w - ever, further replacement up to 50% reduced the modulus. Theseresults are well aligned with those of other mechanical properties.The experimental modulus of steel fiber –reinforced alkali-activated concrete made with 8-M-SH solution could reach 28.5 GPa com- pared to 25.5 GPa for nonreinforced counterparts, representing an 11.8% increase due to the addition of 3% steel fiber by volume. However, the modulus was almost unchanged when less than 1.5% steel fiber was added. An increase in the modulus of 9.2% was also noted for 10-M-SH alkali-activated concrete upon the incorporation of 2% steel fibers by volume. This shows that steel fibers can enhance the elastic behavior of alkali-activated concrete.For 14-M-SH, 100% slag concrete samples, the modulus increased by 14.4% when 2% fiber volume fraction was incorporated into the mix. The effect of adding steel fibers seemed to be more significant in alkali-activated slag concrete with 25% fly ash and 14-M-SH solution. Fig.12(a) shows a comparison between the experimental results and prediction equations provided by AS3600 ( Standards Australia 2009 ), ACI Commitee 318 ( ACI 2014 ), Dilli et al. ( 2015 ), Ahmed and Shah ( 1985 ), ACI Committee 363 ( ACI 1992 ), Mendis ( 2003 ), and CEB-FIP ( 1990 ). Most equations seem to overestimate the modulus of elasticity of 8-M-SH concretes, except for that given(b) (a)0123456 0 1 02 03 04 05 06 0Flexural Strength (MPa) Fly Ash Content (%)SF=0% SF=2%0.0 1.0 2.0 3.0 4.0Flexural Strength (MPa) Steel Fiber Volume (%)8M 10M 14M Fig. 10. Flexural strength of alkali-activated slag concrete with different: (a) fly ash contents; and (b) SH molar concentrations. (a) (b) 012345678910 6.5 7.0 7.5 8.0 8.5Flexural Strength (MPa) Compressive Strength, √f'c (MPa) 8M 10M 14M AS3600 (2009) ACI Committee 318 (2014) Ahmed and Shah (1985) Xu and Shi (2009) Perumal (2015) CEB-FIP (1990) ACI Committee 363 (1992) fr= 0.46 √f'c fr= 0.61 √f'c fr= 0.62 √f'c 6.5 7.0 7.5 8.0 8.5Flexural Strength (MPa) Compressive Strength, √f'c (MPa)8M 10M 14M Fig. 11. Relationship between flexural and compressive strength: (a) in comparison to literature and codified equations; and (b) using linearregression analysis.Table 4. Modulus of elasticity of alkali-activated concrete samples Mix No. Mix designationModulus of elasticity Experimental PredictedPercentage increaseaPercentage differenceb 1 G50-14M-0.0SF 33.5 34.5 — −3.0 2 G50-14M-2.0SF 37.8 38.2 12.8 −1.1 3 G75-14M-0.0SF 36.8 36.8 — 0.0 4 G75-14M-2.0SF 42.1 42.0 14.4 0.2 5 G100-14M-0.0SF 35.8 36.2 — −1.0 6 G100-14M-2.0SF 40.5 40.8 13.1 −0.7 7 G75-8M-0.0SF 25.5 25.5 — 0.0 8 G75-8M-0.5SF 25.6 25.6 0.4 0.0 9 G75-8M-1.0SF 25.7 25.7 0.8 0.0 10 G75-8M-1.5SF 26.5 26.4 3.9 0.411 G75-8M-2.0SF 27.6 27.7 8.2 −0.4 12 G75-8M-3.0SF 28.5 28.5 11.8 0.0 13 G75-10M-0.0SF 35.7 35.7 — 0.0 14 G75-10M-2.0SF 39.0 38.8 9.2 0.5 15 G75-14M-0.5SF 39.0 39.1 6.0 −0.3 16 G75-14M-1.0SF 40.0 40.2 8.7 −0.5 17 G75-14M-1.5SF 40.5 40.3 10.1 0.5 aPercentage increase of steel fiber –reinforced concrete with respect to plain counterparts. bPercentage difference between experimental and predicted modulus of elasticity values. © ASCE 04019223-10 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2019, 31(10): 04019223 Downloaded from ascelibrary.org by United Arab Emirates University on 10/29/19. Copyright ASCE. For personal use only; all rights reserved. by Dilli et al. ( 2015 ) and AS3600 ( Standards Australia 2009 ). This is in agreement with work reported by Pan et al. ( 2011 ), whereby the modulus of plain fly ash –based geopolymer concrete was 27% lower than conventional cement-based counterparts. To accurately predict the modulus of elasticity from the compressive strength,linear regression analysis was employed. The regression equationsand trend lines are shown in Fig. 12(b) . Based on these equations, it is possible to apply a modification factor, α, of 0.75 to the ACI Commitee 318 ( ACI 2014 ) equation to be suitable for 8-M-SHmixes. The case was different with 10- and 14-M-SH samples. The equation proposed by ACI Commitee 318 ( ACI 2014 ) could accurately predict E c(α¼1). It is thus proposed that Eq. ( 4)b e employed to estimate the modulus of elasticity, with αbeing 0.75 for 8-M-SH and 1 for 10- and 14-M-SH alkali-activated concretes: Ec¼5:056αffiffiffiffiffi f0cp ð4Þ Because concrete is a heterogeneous material, its elastic modu- lus depends on its different components. Although the compositionis dissimilar to conventional concrete, the ACI Commitee 318 ( ACI 2014 ) equation may be used with some modification for 8-M-SH alkali-activated slag concrete. Table 4presents the percentage dif- ference between moduli obtained from the prediction equation andexperimental testing. Besides the correlation coefficient exceeding0.97, the difference ranged between −3%andþ1%. This indicates an excellent performance of the regression model, with the pre-dicted modulus being similar to the experimental values. DSC Analysis The microstructure of alkali-activated slag concretes with 0% –50% fly ash replacement was analyzed at the ages of 7 and 28 days tostudy the development of reaction products. Such a comparativeanalysis has not yet been performed and is critical to correlating the microstructure to the mechanical performance. The DSC ther- mograms of 7-day alkali-activated slag concretes incorporating upto 50% fly ash are shown in Fig. 13(a) . A broad endotherm between 110°C and 130°C is detected in samples made with equal propor-tions of slag and fly ash (G50). It is associated with the decompo-sition of alkali-activation reaction products as combined water insodium aluminosilicate hydrate (N ─A─S─H) gel ( Colella 1999 ) or as interstitial water ( Perera et al. 2006 ). At lower fly ash replace- ments (0% and 25%), the peak shifted toward higher temperatures,became narrower, and increased in intensity. This providesevidence of the formation of calcium aluminosilicate hydrate(C─A─S─H) gel ( Al-Majidi et al. 2016 ;Nath and Kumar 2013 ) and explains the higher 7-day strength of alkali-activated concretesmade with 100% slag. Fig. 13(b) presents the DSC thermograms of concretes after 28 days. The endotherm in the range of 120°C –140°C in concrete made with 25% fly ash was more intense than samples with 0% and50% fly ash. Compared to 7-day equivalents, these peaks had ahigher intensity and narrower shape, indicating the progressionof the activation reaction and the formation of C ─A─S─H gel (Al-Majidi et al. 2016 ;Nath and Kumar 2013 ). Nevertheless, N─A─S─H gel could also be detected within the same endotherm (Colella 1999 ). Clearly, an intermix of reaction products between N─A─S─H and C ─A─S─H existed at a later age of 28 days,(a) (b) 01020304050 0 1 02 03 04 05 0Predicted Ec (GPa) Experimental Ec (GPa)ACI Committee 318 (2014) ACI Committee 363 (1992) Dilli, Atahan and Sengül (2015) Ahmed and Shah (1985) Mendis (2003) AS3600 (2009) CEB-FIP (1990) Ec= 3.8027 √f'cEc= 5.1063 √f'c Ec= 5.0913 √f'c6.0 6.5 7.0 7.5 8.0 8.5Modulus of Elasticity (GPa) Compressive Strength0.5(MPa0.5)8M 10M 14M Fig. 12. (a) Predicted versus experimental modulus of elasticity; and (b) relationship between modulus of elasticity and compressivestrength using linear regression analysis. (b) (a)50 100 150 200 250 300 350 400 450 500Heat Flow (mW) Temperature (°C)G50 G75 G100 50 100 150 200 250 300 350 400 450 500Heat Flow (mW) Temperature (°C)G50 G75 G100 Fig. 13. DSC thermograms of (a) 7-day; and (b) 28-day alkali-activated concretes. © ASCE 04019223-11 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2019, 31(10): 04019223 Downloaded from ascelibrary.org by United Arab Emirates University on 10/29/19. Copyright ASCE. For personal use only; all rights reserved. providing superior mechanical performance. Also, a broad endo- thermic shoulder was identified in 100% slag specimens at around400°C corresponding to the decomposition of a hydrotalcite-typephase ( Ben Haha et al. 2011a ,b). It has been reported that hydro- talcite may have a higher pore-filling ability and, thus, could pro-duce a denser and stronger concrete structure ( Ben Haha et al. 2011a ,b). Yet, the intensity of this band decreased with more than 25% fly ash replacement, confirming the reduced compressive strength. FTIR Analysis Fig. 14(a) presents the FTIR spectra of alkali-activated slag con- crete with different fly ash replacement percentages. Samples with 100% slag show a broad transmittance band in the range of600–700cm −1, signifying the stretching vibrations of Al ─O bonds in the AlO 4groups, which could possibly indicate the formation of C─A─S─H gel ( Jiao et al. 2018 ;Puertas and Torres-Carrasco 2014 ). The higher intensity of this band in 100% slag concrete compared to counterparts blended with fly ash explains the higher7-day strength of the former concrete. This is in good agreementwith DSC analysis results. Bending vibrations of O ─Ha t 1,600 –1,700 cm −1and stretching vibrations of H ─OH groups at 3,200 –3,600 cm−1(Ismail et al. 2014 ) decreased with higher slag replacement by fly ash, indicating a lower degree of reaction. As aresult, their mechanical performance was inferior to 100% slagconcretes. Fig.14(b) presents the FTIR spectra of concretes after 28 days. Compared to 7-day samples, the intensity of bands increasedthroughout the spectra. This signifies that larger quantities of reac-tion products had developed during subsequent curing. A narrow-shaped asymmetric vibration of Si ─O─Si is detected between 895 and 1,050 cm −1in the 100% slag concretes, indicating the formation of an ordered calcium-based structure ( Nath 2018 ). In comparison, concrete mixes with 25% fly ash noted a similar vi-bration of Si ─O─Si but at higher wavelengths of 900–1,100 cm −1, centered at 946cm−1. Similar findings have been reported else- where ( Al Bakri et al. 2012 ;Ismail et al. 2014 ;Rosas et al. 2014 ; Škvára et al. 2009 ). This shift in wavelength is due to the simulta- neous activation of fly ash and slag, creating a more cross-linkedgel structure, comprising an intermix of reaction products ofN─A─S─H and C ─A─S─H. As a result, the activation reaction accelerated and the compressive strength increased. For concreteswith 50% fly ash, the Si ─O─Si vibration became broader and fur- ther shifted toward higher wavelengths. Ismail et al. ( 2014 ) ex- plained this higher wavelength as being due to the presence of unreacted fly ash components. Consequently, its mechanical per- formance was inferior to its counterparts with low fly ash content(0% and 25%). In addition, the broad band at 1,400 cm −1repre- sents O ─C─Oi nC O2− 3(Ismail et al. 2014 ;Samantasinghar and Singh 2018 ), which indicates the formation of carbonation products from the reaction of alkali-activated slag with CO 2in the air over the duration of curing ( Zhang et al. 2017 ). It should also be noted that water peaks ( 1,600 –1,700 cm−1and3,200 –3,600 cm−1) were highest in the sample with 75% slag and 25% fly ash. Accordingly, its mechanical properties were superior to 50% and 100% slag sam- ples. This is in agreement with the findings of DSC analysis. SEM Analysis The morphology of alkali-activated slag concretes with different fly ash replacements was characterized using SEM with EDX. Fig. 15(a) shows the micrograph of 7-day concrete samples with 100% slag. A dense matrix can be noted by randomly distributedfibrous spherical shapes. Microcracks with an average width of5μm spread on the sphere ’s surface. Work by Beglarigale and Yazici ( 2014 ), El-Hassan et al. ( 2018 ), and Yaz ıcı(2012 ) confirmed that such spherical shapes are associated with calcium aluminosil-icate hydrate (C ─A─S─H) gel. The effect of replacing 25% slag by fly ash on the microstructure is shown in Fig. 15(b) . While the spherical shapes are still evident in the matrix, they are smaller.EDX analysis shows higher Ca/Si and Si/Al ratios with largerspheres, which indicate more calcium hydrates and silicate phases,respectively. With more phases being produced, the matrix densi-fies, creating a higher-strength concrete ( Brough and Atkinson 2002 ). Further replacement of slag by fly ash up to 50% created a much different microstructure, as seen in Fig. 15(c) . Microgaps are detected in a matrix intermixed with angular slag and sphericalfly ash particles, creating a more porous microstructure and weakerconcrete. EDX analysis of this concrete (50% fly ash replacement)in Fig. 15(d) highlights the formation of a compound with calcium, silicon, sodium, aluminum, and oxygen, signifying an intermixof C─A─S─H and N ─A─S─H gels. Yet, it should be noted that the latter seems to dominate the former given the low calciumcontent. Accordingly, while C ─A─S─H is known to be a strength- contributing product, the weaker aluminosilicate compound gov-erned the mechanical performance of alkali-activated concretemixes with 50% fly ash. Fig.16shows the micrographs of alkali-activated slag concrete samples after 28 days. In general, the microstructure did notsignificantly change between 7 and 28 days. Fig. 16(a) presents a fibrous spherical shape similar to that noted at 7 days. In com-parison, concretes with 25% fly ash showed a smaller sphericalshape covered in white dots, which may possibly be developed N─A─S─H gel particles, as shown in Fig. 16(b) . The 28-day concrete sample with 50% fly ash replacement is presented in(b) (a)500 1000 1500 2000 2500 3000 3500 4000 Transmittance (%) Wavelength (cm-1)G50 G75 G100 500 1000 1500 2000 2500 3000 3500 4000 Transmittance (%) Wavelength (cm-1)G50 G75 G100 Fig. 14. FTIR spectra of (a) 7-day; and (b) 28-day alkali-activated concretes. © ASCE 04019223-12 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2019, 31(10): 04019223 Downloaded from ascelibrary.org by United Arab Emirates University on 10/29/19. Copyright ASCE. For personal use only; all rights reserved. Fig. 15. SEM micrograph of 7-day alkali-activated concretes with (a) 100% slag; (b) 75% slag and 25% fly ash; (c) 50% slag and 50% fly ash; and (d) EDX spectrum of 50∶50slag∶fly ash sample. Fig. 16. SEM micrograph of 28-day alkali-activated concretes with (a) 100% slag; (b) 75% slag and 25% fly ash; (c) 50% slag and 50% fly ash; and (d) EDX spectrum of 50∶50slag∶fly ash sample. © ASCE 04019223-13 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2019, 31(10): 04019223 Downloaded from ascelibrary.org by United Arab Emirates University on 10/29/19. Copyright ASCE. For personal use only; all rights reserved. Fig. 16(c) . Most slag and fly ash particles are integrated into the matrix, producing an intermix of activation and hydration products,as noted in the EDX analysis in Fig. 16(d) . A comparison between the EDX spectra of 7- and 28-day alkali-activated slag concrete with 50% fly ash replacement was carried out. The Ca/Si andSi/Al ratios increased from 0.29 and 2.50 to 0.56 and 3.40, re-spectively, during subsequent curing. This indicates further de-velopment of calcium hydrates and silicate phases, respectively,providing evidence of the 23.8% increase in compressive strength from 7 to 28 days. Nevertheless, some microcracks still exist in the 28-day microstructure of 50∶50slag∶fly ash concrete due to solu- tion evaporation and slow polymerization reaction of fly ash inambient conditions. This explains its inferior compressive strengthat 28 days. Conclusions The effects of slag replacement by fly ash, sodium hydroxidemolarity, and steel fiber incorporation on the rheology, mechanicalperformance, and microstructure characteristics of alkali-activatedslag concrete containing dune sand were investigated. What followsare the key findings of the study: 1. The replacement of slag by fly ash led to an increase in work- ability due to its more spherical shape, causing less interparticlefriction. The molarity of SH solution was inversely proportionalto workability. An average 23% decrease in slump was notedupon increasing the molarity of SH from 8 to 14 M, owingto a more viscous alkaline activator solution. Further, for every0.5% of steel fiber added to the concrete, an average 11-mm reduction in slump was noted. Concrete samples made with 14 M SH could not incorporate more than 2% steel fiber volumefraction. 2. At 1 and 7 days, the addition of fly ash resulted in a decrease in mechanical properties, i.e., modulus of elasticity, compressive,tensile, and flexural strength, owing to the slow activation of flyash in ambient conditions. After 28 days, alkali-activated slagconcrete samples with 25% fly ash had superior strength, withan intermix of activation and hydration products. Higher molarconcentration of sodium hydroxide resulted in better mechanicalperformance. This was mainly due to the availability of moresodium ions that could balance the charges, thereby formingaluminosilicate networks in the alkali-activated matrix. 3. The compressive strength rapidly developed, with, on average, 78% and 89% of the 28-day compressive strength being ob-tained at the ages of 1 and 7 days. The addition of steel fiberscould increase the compressive strength by up to 39% and 52%for 1- and 7-day samples. Its effect, however, was less signifi-cant (23% –30% increase) for 28-day samples. With a densified alkali-activated structure and enhanced binding ability of thealuminosilicate hydrate and calcium silicate hydrate gels, thealkali-activated matrix gained sufficient strength to the extentthat steel fibers caused limited improvement. 4. The tensile splitting and flexural strength could increase by up to 31% and 25%, respectively, upon the addition of steel fibers,with more contribution at higher dosages. Its effect was morepronounced in concretes made with 25% fly ash replacement,especially at an early age and 8-M-SH concrete samples witha weaker alkali-activated matrix. Clearly, adding steel fibersincreased the energy requirements for crack propagation andbridged microcracks in the alkali-activated concretes, resultingin a delayed fracture process and improved postcracking perfor-mance. The tensile and flexural behavior of these steel fiber – reinforced mixes was similar to that of conventional concrete.5. Experimental results of the modulus of elasticity of alkali- activated concretes showed a gradual increase as more steel fibers were incorporated. The increase could reach up to 12%,10%, and 14% for 8-M-, 10-M-, and 14-M-SH samples, respec-tively. The effect of adding steel fibers seemed to be more sig-nificant in alkali-activated slag concrete with 25% fly ash and14-M-SH solution. 6. Published and codified equations relating the modulus of elasticity and the tensile splitting and flexural strength to compressive strength could be suitable for predicting, withreasonable accuracy, the mechanical properties of steel fiber – reinforced alkali-activated slag concretes. In fact, ACI Commit-tee 318 ( ACI 2014 ) equations for f r,fsp, and Eccould be employed as-is for 10- and 14-M-SH alkali-activated concretes,regardless of the steel fiber volume fraction and slag:fly ash ra-tio. However, a modification factor was introduced to ACI 318prediction equations for 8-M-SH samples. This factor, α, was found to be 0.75. 7. Microstructure analysis was performed on plain alkali-activated slag concretes with different fly ash replacements using DSC, FTIR, and SEM. At 7 days, calcium aluminosilicatehydrate (C ─A─S─H) gel was found to be the dominant, strength-contributing reacti on product. Sodium aluminosili- cate (N ─A─S─H) gel was reported, but in small quantities due to the slower activation reaction of fly ash particles in am-bient conditions. Water peaks in FTIR and endothermic bands inDSC were more intense with higher slag content, indicating ahigher degree of activation reaction. This provides evidence ofthe superior performance of 100% slag at 7 days. After 28 days,N─A─S─H further developed and was identified using SEM as white nanosized dots on the surface of the activated matrix,being most prevalent in samples with 25% fly ash replacement.As such, these samples ( 75∶25slag∶fly ash) had superior perfor- mance at 28 days of age. Based on the current study, the mechanical performance of alkali-activated slag concrete cured in ambient conditions improvedwith the replacement of slag by 25% fly ash and the addition ofsteel fibers. ACI Committee 318 equations could be employed,with a newly proposed modification factor, for plain and steelfiber–reinforced alkali-activated slag/fly ash blended concretes. A more in-depth study of the pore structure, fiber –matrix interfacial properties, and mechanism of fiber reinforcement in alkali-activated concretes should be conducted in the future. Acknowledgments The authors are grateful to the United Arab Emirates University (UAEU), Al Ain, UAE, for the financial support through Grants 31N282 and 31N305. The assistance of students and laboratorystaff at UAEU is gratefully acknowledged.

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 04 Issue: 08 | Aug -2017 www.irjet.net p -ISSN: 2395 -0072 © 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 18 EXPERIMENTAL STUDY ON MECHANICAL PROPERTIES OF FLY ASH AND GGBS BASED GEOPOLYMER CONCRETE Ajay Takekar1, Prof.G.R.Patil2 1 PG Student, Department of Civil Engineering, JSPM’s Rajarshi Shahu college of Engg., Pune, MH, India 2 Professor, Department of Civil Engineering, JSPM’s Rajarshi Shahu college of Engg., Pune, MH, India --------------------------------------------------------------------- ***--------------------------------------------------------------------- Abstract - The present investigation aims at studying the mechanical properties of fly ash and GGBS based geopolymer concrete. In this study, fly ash was replaced at different levels (0%, 25%, 50%, 75% and 100%) by GGBS. Sodium hydroxide (14 M) and Sodium silicate solution is used as alkaline activator in 1:1 ratio. M -25 grade of geopolymer concrete is tested for mechan ical properties Viz, compressive strength, split tensile strength and flexural strength at 3,7 and 28 day and compared with normal OPC M -25 grade concrete and also the effect of ambient curing and oven curing is studied. The result shows that replacement o f fly ash by GGBS eliminates heat curing of geopolymer concrete. Geopolymer concrete shows better result than normal conventional concrete. Rate of gain of strength of geopolymer concrete is high at early stage however geopolymer concrete is more advantage ous, economical and ecofriendly. This experimental investigation is for research purpose for strength properties of geopolymer concrete using fly ash and ground granulated furnace slag (GGBS). Key Words : Geopolymer Concrete, Fly ash, Ground granulated fur nace slag (GGBS), Alkaline solutions, oven curing, ambient curing, compressive strength, Split tensile strength, Flexural strength. 1. INTRODUCTION The major problem the world is facing today is environmental pollution. In the construction industry main ly the production of Portland cement causes emission of pollutants results in environmental pollution. It is widely known that the production of Portland cement consumes considerable energy and at the same time contributes a large volume of CO2 to the atmo sphere. However, Portland cement is still the main binder in concrete construction prompting a search for more environmentally friendly materials .One possible alternative is the use of alkali -activated binder using industrial by -products containing sil icate materials. Davidovits proposed that an alkaline liquid which can react with the silicon (Si) and aluminum (Al) in a source material of geological origin or industrial by product can be used to produce binders. Since chemical reaction in this process is of polymerization therefore, he termed it as “Geopolymer” [2,3]. Thus geopolymer constitutes of two main compounds namely source materials and alkaline liquids. The alkaline liquids are f rom soluble alkali metals which are mainly sodium or potassium based. Sodium hydroxide (NaOH) or Potassium Hydroxide (KOH) and Sodium silicate or Potassium silicate are most widely used alkaline liquid. The primary difference between concrete produced usin g Portland cement and geopolymer concrete is the binder. Geopolymer consists of silicon and aluminum atoms bonded via oxygen into a polymer network. Geopolymer are prepared by dissolution and poly condensation reactions between alumino silicate binder and an alkaline silicate solution such as a mixture of an alkali metal silicate and metal hydroxide is obtained. The most common industrial by -products used as binder materials are fly ash (FA) and ground granulated blast furnace slag (GGBS). GGBS has been widely used as a cement replacement material due to its latent hydraulic properties, while fly ash has been used as a pozzolanic material to enhance the physical, chemical and mechanical properties of cement and concrete. Increasing emphasis on the environmental impacts of construction materials such as Portland cement has provided immense thrust in recent years to the increased utilization of waste and by -product materials in concretes. Activation of alumina silicate materials such as fly ash, b last furnace slag, and metakaolin using alkaline solutions to produce binders free of Portland cement is a major advancement towards increasing the beneficial use of industrial waste products and reducing the adverse impacts of cement production. It has been reported that fly ash and ground granulated blast furnace slag (GGBS) are very effective as starting materials for cement - free binder concretes because of the soluble silica and alumina contents in these materials that undergo dissolution, p olymerization with the alkali, condensation on particle surfaces, and solidification that eventually provides strength and stability to these matrices. Investigation and discussions for mix design code for geopolymer concrete are in process to add up in IS standards. However in this study mix design for geopolymer concrete is used from theory of mix design proposed by Subash V.Patankar. International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 04 Issue: 08 | Aug -2017 www.irjet.net p -ISSN: 2395 -0072 © 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 19 2. EXPERIMENTAL WORK Entire experimental work carried out is briefly explained as follows. 2.1 Materials Fly ash used in this study is low calcium class F Fly ash from Dirk India private limited under the name of the product POZZOCRETE 60. Ground granulated blast furnace slag (GGBS) used is obtained from JSW cements. The chemical and physical properties of GGBS a nd Fly Ash used are shown in the Table 1 and Table 2 respectively. The most commonly used alkaline activators are a mixture of sodium hydroxide (NaOH) with sodium silicate (Na2SiO3). For preparation of alkaline liquids, sodium hydroxide with 98% purity in the form of flakes and sodium silicate were obtained from local manufacturer. Locally available 20 mm crushed aggregates have been used as coarse aggregates. Locally available river sand is used as fine aggregate in the mixes. Crushed granite stones of size 20mm are used as coarse aggregate. As per IS: 2386 (Part III) -1963, the bulk specific gravity in oven dry condition and water absorption of the coarse aggregate are 2.58 and 0.3% respectively. The fineness modulus of 20mm coarse aggregates are 6.68. A s per IS: 2386 (Part III) -1963, the bulk specific gravity in oven dry condition and water absorption of the sand are 2.62 and 1% respectively. The fineness modulus of sand is 2.47. TABLE 1 . Chemical properties of Fly Ash and GGBS TABLE 2. Physical properties of Fly Ash and GGBS Properties Class F fly Ash GGBS Specific Gravity 2.24 2.86 Fineness (m²/kg) 360 400 2.2 Specimen Details and its Schedule Specimen size and its number are determined Table 3. Schedule of Specimen As per the respective IS guidelines used for determining mechanical properties of Concrete. Thus total 99 cubes + 66 beams + 66 cylinders = 231 specimens are casted and tested as per their IS provisions. Cubes are tested as per IS 516 -1959. Chemical Composition Class F fly ash GGBS % silica (SiO 2) 65.6 30.61 % Alumina (Al 2O3) 28.0 16.24 % Iron oxide (Fe 2O3) 3.0 0.584 % Lime (CaO) 1.0 34.48 % Magnesia (MgO) 1.0 6.79 % Titanium (TiO 2) 0.5 - % Sulpher Trioxide (SO 3) 0.2 1.85 Loss on Ignition 0.29 2.1 Concrete Designation Concrete Grade Binding Material Curing Type Cube (Compressive Strength) Beam (flexural Strength) Cylinder (Split Tensile Strength) 3 Day Test 7 Day Test 28 Day Test 7 Day Test 28 Day Test 7 Day Test 28 Day Test Batch -O M25 OPC -43 Cement -100% Water curing 3 3 3 3 3 3 3 Batch -A G25 Fly Ash -100% GGBS - 0 % Hot Curing 3 3 3 3 3 3 3 Ambient Curing 3 3 3 3 3 3 3 Batch -B G25 Fly Ash - 75 % GGBS - 25 % Hot Curing 3 3 3 3 3 3 3 Ambient Curing 3 3 3 3 3 3 3 Batch -C G25 Fly Ash - 50 % GGBS - 50 % Hot Curing 3 3 3 3 3 3 3 Ambient Curing 3 3 3 3 3 3 3 Batch -D G25 Fly Ash - 25 % GGBS - 75 % Hot Curing 3 3 3 3 3 3 3 Ambient Curing 3 3 3 3 3 3 3 Batch -E G25 Fly Ash - 0 % GGBS - 100 % Hot Curing 3 3 3 3 3 3 3 Ambient Curing 3 3 3 3 3 3 3 International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 04 Issue: 08 | Aug -2017 www.irjet.net p -ISSN: 2395 -0072 © 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 20 Beams are tested according to IS 516 -1959 provisions and cylinders are tested according to IS 5816 -1999 provisions. 2.3 Mix Design Mix design of geopolymer concrete of G -25 grade is made according to theory of mix design proposed by Subash V.Patankar . Alkaline liquid ratio is kept constant at 1. The sodium hydroxide solution of 14 M concentration is used and it is kept constant throughout investigation. Cubes of size 150 mm × 150 mm × 150 mm are used for compressive strength test. Beams of size 100 mm × 100 mm × 500 mm are used to determine flexural strength and cylinder of 150 mm (dia) × 300 mm are used to determine split tensile strength. Table 4. Mix proportions of Geopolymer Concrete (G -25) FA or GGBS Sand Coarse Agg. (20mm) NaOH Na 2SiO 3 Water Kg/m³ 587.3 Kg/m³ 1283.08 Kg/m³ 70.88 Kg/m³ 70.88 Kg/m³ 82.42 Kg/m³ 1 1.45 3.16 0.35 0.20 2.4 Curing In this experimental work effect of oven curing and ambient curing on mechanical properties of geopolymer concrete is also studied. After casting the test specimens, specimens are demoulded after 24 hours and kept for oven curing at 60°C for 24 hours and then after are kept at ambient surroundings while some specimens are directly kept for ambient curing. 2.4 Testing of Specimens Specimens are tested at 3, 7 and 28 day of testing for compressive strength, flexural strength and split tensile strength. 2.4.1 Compressive Strength testing of Cubes Cubes as casted of size 150 x 150 x 150 mm were tested using Compression testing machine (CTM) of capacity 250 ton, capable of giving load at the rate of 140 kg/sq.cm/min. Testing of the cubes was done at the age of 3rd, 7th and 28th day. Cubes were placed in the machine between wiped and cleaned loading sur faces and load is given approximately at the rate of 140 kg/sq.cm/min. and ultimate crushing load is noted to calculate crushing strength of concrete according to IS: 516 -1959. The measuring strength of specimen is calculated by dividing the maximum load applied to the specimen during the test by the cross section area. Fck= = =………N/mm² (Eq.1) Fig.1 Compressive testing 2.4.2 Split Tensile Testing of Cylinder Cylinders as casted of size 150 mm (dia) × 300 mm were tested using CTM machine of capacity 250 ton, capable of giving load at the rate of 140 kg/sq.cm/min. Testing of the cubes was done at the age of 7th and 28th day. The cylinders were placed in the machine between wiped and cleaned loading surfaces and load is given approximately at the rate of 140 kg/sq.cm/min. and ultimate crushing load is noted to calculate crushing strength of concrete according to IS: 516 -1959. The measuring strength of specimen is calculated by dividin g the two times maximum load applied to the specimen during the test by the cross section area Ft= =…….. N/mm² (Eq.2) Fig.2 Split tensile testing International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 04 Issue: 08 | Aug -2017 www.irjet.net p -ISSN: 2395 -0072 © 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 21 2.4.2 Flexural Testing of Beams Beams casted as of size 100 mm × 100 mm × 500 mm are tested for flexural strength under the UTM machine of 600 KN capacity as per the guidelines given in IS 516 -1959.The flexural strength of beam is calculated by following equation Fb= ……….N/mm² (Eq.3) 3. RESULTS AND DISCUSSION All the specimens are tested according to their respective IS provisions and results are shown as below, Table 6. Compressive Strength Results Batc h 3 Day Result (N/mm²) 7 Day Result (N/mm²) 28 Day Result (N/mm²) Ambient Curing Oven Curing Ambient Curing Oven Curing Ambient Curing Oven Curing Batc h- O 11.81 - 19.17 - 26.67 - Batc h- A 5.71 12 8.33 14.8 9 14.66 19.33 Batc h- B 20.94 26.60 25.48 38.3 3 32.64 41.04 Batc h- C 29.65 32.81 33.12 40.0 7 39.52 43.24 Batc h- D 37.55 40.56 41.57 46.1 1 47.91 50.47 Batc h- E 40.13 41.86 43.75 48.4 9 47.98 53.11 Fig.3 3 Day Compressive Strength Fig.4 7 Day Compressive Strength Fig.5 28 Day Compressive Strength The Above graph shows Compressive Strength results of concrete. From the graph it is clearly seen that Fly ash based geopolymer concrete doesn’t show good strength but however GGBS based geopolymer concrete shows the best resul t of compressive strength. Also, oven cured specimens shows more strength than the ambient cured specimens. From the above results batch B gives optimum mix design with satisfactory results however Batch E gives the highest strength for the mix design combination.From Batch B onwards we can replace Conventional Concrete by geopolymer concrete since it is giving better results than it. Fig.6 7 Day Split Tensile Strength in N/mm² International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 04 Issue: 08 | Aug -2017 www.irjet.net p -ISSN: 2395 -0072 © 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 22 Fig.7 28 Day Split Tensile Strength in N/mm² The above graph shows the results of Split tensile strength of concrete. From the graph it is clearly seen that split tensile strength increases as we increase replacement of fly ash by GGBS. The highest split strength is achieved in Batch E that is in GGB S based geopolymer concrete giving highest strength. From the graph it is seen that oven cured specimen gives more strength than ambient cured specimen. Also early stage strength gain is high in geopolymer concrete than the normal conventional concrete. Table 7. Flexural Strength Results Batch 7 Day Result (KN) 28 Day Result (KN) Ambient Cured Oven Cured Ambient Cured Oven Cured Batch - O 10.38 - 13.50 - Batch - A 8.85 9.12 9.25 9.90 Batch - B 10.11 10.83 12.20 12.94 Batch - C 12.84 13.08 14.92 15.20 Batch - D 13.08 14.80 15.46 16.10 Batch -E 14.40 15.08 16.46 17.10 Flexural strength of geoplymer concrete gives much more flexural strength than the conventional concrete from Batch B onwards. Also the same nature that oven cure specimen gives more strength than the ambient cured specimen. Highest flexural strength from above is given by GGBS based g eopolymer concrete that by Batch E. Fly ash based geopolymer concrete strength results are less than the normal conventional concrete. Flexural strength result is shown as load taken in KN. Fig.8 7 Day Flexural Strength Results in KN Fig.9 28 Day Flexural Strength Results in KN Failure of geopolymer concrete and conventional concrete was brittle failure. Flexural strength of geopolymer concrete is more than the conventional concrete except in Batch A. however the same nature of being more st rength in oven cured than the ambient cured is found. Maximum of flexural strength is achieved in Batch E that GGBS based and oven cured specimen. 4. CONCLUSIONS Based on above experimental work carried out, following conclusions are made 1) It is observed that an increasing trend has been observed in compressive strength of GPC mixes up to full replacement level of fly ash by GGBS. 2) The rate of gain in compressive strength, split tensile strength and flexural strength of geopolymer concrete is very fast at 7 days curing period and the rate gets reduces with age. 3) Almost 90 % of strength is achieved at 7th day. Therefore speedy construction is possible with geopolymer concrete. 4) Oven curing gives higher result than ambient curing International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 04 Issue: 08 | Aug -2017 www.irjet.net p -ISSN: 2395 -0072 © 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 23 5) Addition of GGBS eliminate the necessity of oven curing. 6) The geopolymer concrete using GGBS as a sole binder achieves more strength than that of normal control concrete when oven curing is done. A higher concentration of GGBS result in higher compressive strength, split tensile strength and flexural strength of geopolymer concrete. 7) High Strength Concrete is achieved by using geopolymer concrete. 8) Fly ash and GGBS based geopolymer concrete can be used for structural use. 9) Mix design with 75% fly ash and 25% GGBS as binding ma terial gives economic design with better strength. 10) However GGBS based geopolymer concrete give best results in all aspect. 11) Thus Geopolymer concrete can be recommended as an innovative construction material for the use of construction. ACKNOWLEDGEMENT I wish to express my deep sense of gratitude to my guide and PG co coordinator Prof.G.R.Patil, Department of Civil Engineering, for his valuable time, sustained guidance and useful suggestions, which helped me in completing the work, in time. Last, but not the least, I would like to express my heartfelt thanks to my beloved parents for their blessings, my friends/classmates for their help and wishes for the successful completion of this work. REFERENCES Malhotra V. M., 2002, Introduction: Sustainable development and concrete technology, ACI Concrete International, 24(7). The Proceedings of Geopolymer 2005 World Congress , 4th Int. Conference on geopolymers, edited by J. Davidovits, Geopolymer Institute, France 2006 Davidovits J, 1994, “Propertie s of Geopolymer cement,”, Proceedings first international conference on Alkaline cements and concretes, scientific research institute on binders and materials”, Kiev state technical university, Kiev, Ukraine, pp. 131 -149. D. Hardjito and B. V. Rangan, 2005,”Development & Properties of Low calcium Fly ash based Geopolymer concrete” Research report Curtin University, Australia. Adam, A.A, 2009, “Strength and Durability Properties of Alkali Activated Slag and Fly Ash -Based Geopolymer Concrete”, Thesis. RMIT University. Talling, B and Brandstetr, J.,1989,“ Present state and future of alkali -activated slag concretes, Proceedings of the Third International Conference, Trondheim, Norway ”ACI SP -114, Vol. 2, pp 1519 -1546 Subash V.Patankar, Springer India 2015, advances in structural Engineering DOI 10.1007/978 -81-322 -2187 - 6_123. BIOGRAPHIES Ajay M. Takekar (PG 2nd year student) Department of Civil (Structural) Engg. JSPM’ s Rajarshi Shahu college of Engineering, Tathawade,pune -411033 Prof.G.R.Patil (Guide & PG coordinator) Department of Civil (Structural) Engg. JSPM’s Rajarshi Shahu college of Engineering, Tathawade, Pune -411033

See discussions, st ats, and author pr ofiles f or this public ation at : .researchgate.ne t/public ation/316566650 Mechanical Properties of Geopolymer Concrete Composites Article    in  Mat erials T oday: Pr oceedings · Dec ember 2017 DOI: 10.1016/ j.matpr .2017.02.175 CITATIONS 37READS 3,922 2 author s: Some o f the author s of this public ation ar e also w orking on these r elat ed pr ojects: Strength and dur ability st udies of multi blended c oncr etes c ontaining fly ash and silic a fume View pr oject Thesis View pr oject Kolli R amujee VNR V ignana Jy othi Instit ute of Engineering & T echnolog y 21 PUBLICA TIONS    92 CITATIONS     SEE PROFILE Pothar aju Malasani GITAM Univ ersity 34 PUBLICA TIONS    151 CITATIONS     SEE PROFILE All c ontent f ollo wing this p age was uplo aded b y Kolli R amujee on 10 Mar ch 2018. The user has r equest ed enhanc ement of the do wnlo aded file. Available online at www.sciencedirect.com ScienceDirect Materials Today: Proceedings 4 (2017) 2937 –2945 www.materialstoday.com/proceedings 2214 -7853©2017 Elsevier Ltd. All rights reserved . Selection and peer -review under responsibility of Conference Committee Members of 5th International Conference of Materials Processing and Characterization (ICMPC 2016) . 5th International Conference of Materials Processing and Characterization (ICMPC 2016) Mechanical Properties of Geopolymer Concrete Composites Kolli.Ramujeea, M.PothaRajub a Professor, VNR Vignana Jyothi Institute of Engineering & Tahnology,Bachupally,Hyderabad -500090, India bProfessor of Civil Engineering,GITAM University,Rushikonda,Vishakapatnam -530045,India Abstract The increasing demand of environment friendly constructi on has been the driving force for developing sustainable and economical building materials. The critical aspects influencing the development are performance of the materials under different and special user conditions, economic aspects as well as environme ntal impact aspects. Cement is an energy consuming and high green house gas emitting product. Geopolymers are gaining increased interest as binders with low CO 2-emission in comparison to Portland cement. In the present investigation, the mechanical propert ies of flyash based geopolymer concrete(GPC) were studied. Experimentally measured values of the compressive strength and split tensile strength of GPC specimens made from low, medium and higher grades compared with reference to the control mixes(OPC). The regression model analysis was carried out to study the relationship between the Compressive strength and Split tensile strength and It was found that the mechanical behaviour of GPC is similar to that of ordinary Portland cement(OPC) concrete. ©201 7 Elsevier Ltd. All rights reserved . Selection and peer -review under responsibility of Conference Committee Members of 5th International Conference of Materials Processing and Characterization (ICMPC 2016) . Keywords: Geopolymers; OPC concrete;class -F flyash;Alkaline actvators; Strength,Correlation 1. Introduction Increasing emphasis on the environmental impacts of construction materials such as Portland cement has provided immense thrust in recent years to the increased utilization of waste and by -product materials in concretes. Activation of aluminosilicate materi als such as fly ash, blast furnace slag, and metakaolin using alkaline solutions to produce 2938 Kolli.Ramujee and M.PothaRaju / Materials Today: Proceedings 4 (2017) 2937– 2945 binders free of Portland cement is a major advancement towards increasing the beneficial use of industrial waste products and reducing the adverse impacts of cement production. These alkali -activated binder systems appear in the vast available body of literature in a variety of names: alkali- activated cement (predominantly used for binders containing large amounts of calcium such as slags), geopolymer [2 –6], inor ganic polymer , hydroceramic, or low temperature aluminosilicate glass . They are sometimes called polysialates also because of the polymeric silicon –oxygen –aluminum framework . In general, concretes made using alkali activation of the starting aluminosilicate material do not contain Portland cement at all, and hence they are referred to generically as cement - free binder concretes in this study. The concretes containing alkali -aluminosilicate gel as the binder has been shown to have high compressi ve strengths, and resistance to fire, and chemical attack [10 –13]. The starting material and activating agent type and concentration are the most important parameters that influence the properties of the alkali - activated end product [14,15] . The production of cement -free binders requires a starting material containing aluminum and silicon species that are soluble in highly alkaline solutions. Previous studies have shown that the amount of vitreous silica and alumina present in the starting material plays a significant role in activation reactions and the properties of the reaction product [10,16] . The presence of calcium oxide in the source material also influences the properties, especially because of the formation of more than one reaction product . Sodium hydroxide and sodium silicate are the more commonly used alkaline activating agents [18–20] even though few studies have also been carried out with potassium hydroxide or sodium carbonate as the activating agent .In the present investigation, Geo polymer concrete is manufactured using source materials that are rich in silica and alumina. While the cement -based concrete utilizes the formation of calcium -silica hydrates (CSHs) for matrix formation and strength, geopolymers involve the chemical reacti on of alumino -silicate oxides with alkali polysilicates yielding polymeric Si– O–Al bonds. 2.0 Source materials and mixture proportions 2.1. Materials used In this experimental work, fly ash is used as the source material to make geopolymer paste as the b inder, to produce concrete. The manufacture of geopolymer concrete is carried out using the usual concrete technology methods. The role and influence of aggregates are considered to be same as in the Portland cement concrete.The mass of combined aggregate s may be taken to be between 75% and 80% of the mass of the Geopolymer concrete. Sodium -based activators were chosen because they were cheaper than Potassium -based activators. The sodium hydroxide was used, in flake or pellet form. It is recommended that the alkaline liquid is prepared by mixing both the solutions together at least 24 hours prior to use. The mass of NaOH solids in a solution varied depending onthe concentration of the solution expressed in terms of Molarity, M. The concentration of sodium hydroxide solution (NaOH) liquid measured in terms of Molarity(M), in the range of 8 to 16 M. The mass of water is the major component in both the alkaline solutions. In order to improve the workability, high performance Polycarboxylic based super plasticizer purchased from BASF under trade name GLENIUM B233 has been added to the mixture. The primary difference between Geopolymer concrete and Portland cement concrete is the binder. The silicon and aluminium oxides in the low – calcium fly ash reacts with th e alkaline liquid to form the geopolymer paste that binds the loose coarse and fine aggregates and other unreacted materials to form the geopolymer concrete. As in the case of Portland cement concrete the coarse and fine aggregates occupy about 75% to 80% of the mass of Geopolymer concrete. This component of Geopolymer concrete mixtures can be designed using the tools currently available for Portland cement concrete. The compressive strength and workability of geopolymer concrete are influenced by the proportions and properties of the constituent materials that make the geopolymer paste. 2.2 Mixture Proportions The mix proportions for Geopolymer concretes of three grades namely G20,G40 & G60 were arrived based on the Kolli.Ramujee and M.PothaRaju / Materials Today: Proceedings 4 (2017) 2937 –2945 2939 trial mixes carried out by the author i n the laboratory and for control mix the corresponding grades were taken in equivalent mix proportions of geopolymer concrete. the details of properties of materials ( table 1to 5) and the the mix proportions for GPC of three grades((shown in tab le .6 ) and the control mix proportions were given in table7. Table 1. Chemical composition of flyash(%mass) Oxides Percentage SiO2 Al203 Fe2O3 CaO MgO K2O+Na 2O SO 3 Loss on ignition 60.54 5.87 0.38 0.23 Table 2. Properties of Sodium Hydroxide (NaOH) Property Fine Aggregate Coarse Aggregate Specific gravity Water absorption Fineness modulus Bulk density Kg/m3 Source 2.78 0.50% 7.21 Crushed granite stone 2.63 1% 2.40 River sand Table 3 . Properties of Sodium silicate solution Property Value Specific gravity Molar mass (gr/mol) Na2O ( by mass) SiO 2 ( by mass) Weight of solids (by mass) Water ( by mass) Weight ratio (SiO 2 to Na 2O) Molar ratio 1.6 14.70% 29.40% 44.1% 55.90% 2.06 2940 Kolli.Ramujee and M.PothaRaju / Materials Today: Proceedings 4 (2017) 2937– 2945 Table 4. Properties of Sodium hydroxide(NaOH) Property value Molar mass Appearance Density Melting point Boiling point Amount of heat liberatedhen dissolved in water 40 gr/mol White solid 2.1gr/cc 3180C 13900C 266 cal/gr Table 5 . Properties of Cement Property Value Standard consistency Initial setting time Final setting time Specific gravity Soundness Compressive strength (MPa) 7 days 28 days 32% 115 min 240 min 1mm 40.1 Table 6. Mix proportions for various grades of Geopolymer concrete Grade of GPC G20 G40 G60 Fly ash (kg/m3) Fine Aggregate (kg/m3) Coarse Aggregate (kg/m3) NaOH(kg/m3) (M) Concentration Na2SiO 3(kg/m3) Extra water (kg/m3) Super plasticizer (GLENIUM)(kg/m3) Ratio of Mixture proportions Liquid/binder ratio Water/geopolymer Solids ratio Workability (Slump) 327 1248 54.33( 8M) 108.67 ----- 1:2.05:3.81 0.31 100 mm 394.3 1201.2 45.06(16M) -- 1:1.64:3.04 0.21 50mm 408.9 1294.0 40.89(16M) -- 1:1.35:3.16 0.158 50mm Kolli.Ramujee and M.PothaRaju / Materials Today: Proceedings 4 (2017) 2937 –2945 2941 Table 7. Mix proportions of OPC Conventional concrete expressed as Equivalent Proportions of GPC Grade of concrete M20 M40 M60 Cement (kg/m3) Fine Aggregate(kg/m3) Coarse Aggregate(kg/m3) Water(kg/m3) SP(kg/m3) Mix Proportion 327 1248 2 1:2.05:3.81 394.3 1201.2 4 1:1.64:3.04 408.9 1294.0 143.11 1:1.35:3.16 W/C ratio 0.50 0.40 0.35 2.2 Specimen preparation The sodium hydroxide flakes were dissolved in distilled water to make a solution with a desired concentration at least one day prior to use. The fly ash and the aggregates were first mixed together in a 80 litre pan mixer shown in fig.1 for about three minutes. The sodium hydroxide and the sodium silicate solutions were mixed together and then added to the dry materials and mixed for about four minutes shon in fig.2 , then the super plasticizer of required dosage was added. Even though af ter addition of super plasticizer, the required slump is not achieved ,then the extra water was added to the mix. After mixing , the slump of the fresh geopolymer concrete was determined in accordance with slump test . After determination of slump , the fresh concrete was cast into the mould. The specimens were compacted with three layer placing and tamping using a rod. This was followed by an additional vibration of 10 seconds using a vibrating table. Fig.1 Pan mixer used for mixing GPC Fig.2 addition of Alkaline liquids to the Mix 2.3. Curing regime The specimens were wrapped with thin vinyl sheet to avoid loss of water due to evaporation, All the specimens were then transferred to an oven set at a temperature of 60 °C and stored for 24 hours. After curing ,the specimens were allowed to cool in air ,demoulded and kept in open until the day of testing. Both types of heat curing and 2942 Kolli.Ramujee and M.PothaRaju / Materials Today: Proceedings 4 (2017) 2937– 2945 ambient curing were adopted. In case of heat curing shown in fig.3 , the specimens were cured in an oven and in ambient curing the specimens were left to air for required period. For each grade of Geopolymer concrete mix about 7 mix proportions were considered and the mix which exhibited the required compressive strength consistently at 28 days un der both curing conditions was adopted for further investigations. Fig.3 Hot Air Oven for curing GPC Fig.4 Computerized 100 T UTM for testing 2.4.Strength tests The compressive strength and split tensile strength tests on GPC concretes for G20,G40 and G60 grades and their counterparts i.e control mixes have been carried out shown in fig.4 .A summary of the mechanical properties measured for each of the sample is presented in the Table No.8. 3.0 Results Table: 8 Mechanical proper ties of Geopolymer concrete & OPC concrete S. N o Mix designaton Compressive Strength (MPa) Split Tensile strength (MPa) Heat cured specimens @ 28 days 1 MH2G 20 30.4 1.97 2 31.2 2.34 3 32.4 2.68 4 MH2G 40 50.0 3.02 5 49.69 2.98 6 52.28 3.45 7 MH2G 60 71.2 4.20 8 70.6 4.20 9 71.4 4.60 Control mix water cured @ 28 days 10 M1M20 27.5 2.21 11 M1M40 48.8 3.54 12 M1M60 68.6 4.52 Kolli.Ramujee and M.PothaRaju / Materials Today: Proceedings 4 (2017) 2937 –2945 2943 4.0 D iscussions The cube compressive strength ranged from 30.4Mpa to 71.4Mpa for GPC specimens under heat cured conditions are shown in Table 8.,where as for control mix the results varied from 27.5Mpa to 68.6Mpa is also shown in table 8. The split tensile strength values for GPC for heat cured were shown in the table 8.I t has been widely reported that splitting tensile strength can be estimated from compressive strength of concrete through various empirical relations proposed by different concrete institutes and researchers . These empirical relations can be summarized by the following general equ ation: f ts = A( fck)B where f ts is splitting tensile strength, MPa; f ck iscompressive strength, MPa; A and B are regression coefficients. A Regression model analysis was carried out using MATLAB software for analyzing the results between the compressive strength and split tensile strength . Correlation between the split tensile strength (f ts) and compressive strength of GPC is also analysed by regression analysis was shown in fig.3, by regression analysis the following empirical relation can be expressed as f st = 0.08 f cs0.92 with R2of this proposed relation as 0.80 suggests variabi lity among the relation may be due to various factor which were affecting the properties of GPC with heat curing and ambient curing condtions. However , the relationship was supported by the following empirical formula suggested by ACI318- 99 , Fig. 5, f st = 0.095 f cs0.89 Fig.5 Relationship between compressive strength and split tensile strength 2944 Kolli.Ramujee and M.PothaRaju / Materials Today: Proceedings 4 (2017) 2937– 2945 5.0 C onclusions Based on the applicability evaluation and empirical relations to GPC and the regression analysis on experimental data of mechanical properties of Geopolymer Concrete , the following conclusions can be drawn. 1) The GPC attains its target strength much faster under heat cured condition compared to ambient cured condition.. 2) The GPC under heat cured conditio n exhibited almost same split tensile strength as that of corresponding strengths of OPC concrete. 3) The Relationship between Split tensile strength and compressive strength of GPC can be expressed using regression model analysis that resembles that given b y ACI -318-99 for Ordinary concrete. 4) Mechanical behavior of Geopolymer concrete is similar to that of OPC concrete. 5) Geopolymer concrete exhibits some of the characteristics required for an Engineered material based on its mechanical properties and behavio r.

Construction and Building Materials 301 (2021) 124380 Available online 31 July 2021 0950-0618/© 2021 Elsevier Ltd. All rights reserved.Influence of molarity and alkali mixture ratio on ambient temperature 303007, India bDepartment of Civil Engineering, Malaviya National Institute of Technology, Jaipur 302017, India ARTICLE INFO Keywords: Construction and demolition waste Molarity Alkali mixture Geopolymer mortar ANOVA ABSTRACT Generation of an enormous amount of construction and demolition (C&D) waste due to rapid growth in the infrastructure segment globally is a matter of dire concern for the present decade due to poorly managed disposal to re-utilization. The present study focuses on the formulation of an effective utilization regime of C&D waste (cement concrete) for its re-consumption as geopolymer mortar. Formulation of different molarities of sodium hydroxide (6 M to 16 M) and alkali mixture ratio of sodium silicate to sodium hydroxide solution (1.5, 2.5 and 3.5) have been done and cured for 90D at controlled ambient temperature. The samples were tested for fresh and hardened properties. The effect of silicate modulus and Na2O% with different alkali proportions on the hardened properties were studied. The results reveals that the optimum compressive strength of 20.7 MPa is achieved at a silicate modulus of 1.54 and Na2O% of 12.5%. Further microstructural analysis (mineralogical, elemental, thermal and bonding types) has been done to better comprehend the interactive performance of C&D waste with the change in alkali quantities. The physicochemical and microanalysis reveals that molarity, dissolution of aluminosilicates, and mineralogical compositions are the main factors governing the outcomes while keeping the curing regime at ambient temperature. 1.Introduction The construction industry is closely related to any country ’s socio- economic growth. It showcases the prosperity and livelihood of the countrymen. When we closely observe the construction industry, the foremost thing is the construction materials, and the most used con- struction material is cement concrete. Cement concrete is the second- highest utilized material after water throughout the globe . Also, it is a fact that Ordinary Portland Cement (OPC) production is an energy- intensive process and contributes approximately 5–8% of the total anthropogenic CO2 (major greenhouse gas) emission globally per annum . The total CO2 emission from cement production can further be bifurcated into CO2 emitted from cement clinker production (50–60%) and the burning of fossil fuel (40%) . Other than the OPC production to manufacture concrete, a substantial amount of natural aggregates (NA) are also consumed, which leads to the scarcity of natural aggregate and increases its overall cost . Other than the shortage of natural aggregate and emission of CO2 due to OPC manufacturing, continuous repair and rehabilitation of old structures generate a considerable amount of construction and demolition (C&D) waste . Due to the vast heterogeneity of the C&D waste, it is typically tough to recycle, and unmanaged dumping of the C&D waste occupies a massive area for landfills and creates an envi- ronmental concern due to the different levels of contamination of waste [5,6] . Therefore, reuse of the C&D waste is encouraged by various government agencies throughout the globe, and a considerable amount of research works have already been conducted utilizing C&D as a partial to complete replacement of NA in cement concrete production [7-9] . However, due to the adhesion of old mortar with the recycled aggregate (RA), the quality of the RA is much inferior to the NA and subsequently resulted in at least 10–40% strength reduction with about 50% increased water absorption and drying shrinkage [10-13] . Addi- tionally, utilization of RA, as a replacement of NA, reduces the bulk density, specific gravity, and compressive strength, limiting its con- sumption to the non-structural application or non-important structural part like base course filling work. The non-structural applications also create environmental hazards due to leaching out of the contaminants and altering the surrounding earth ’s pH level . Geopolymers, a series of inorganic polymers generated from alumi - nosilicate sources in a concentrated alkali environment, make their way in the effective utilization of C&D waste. The most often used waste *Corresponding author. E-mail address: san.civil@gmail.com (S. Shrivastava). Contents lists available at ScienceDirect Construction and Building Materials u{�~zkw! s{yo| kro>! ÐÐÐ1ow �o�to~1m{y2w {mk�o2m{zl� twnyk�! Received 8 January 2021; Received in revised form 20 July 2021; Accepted 26 July 2021 Construction and Building Materials 301 (2021) 124380 2materials in the production of geopolymers are fly ash and slag. Recently, building and demolition wastes such as cement concrete, clay brick, and glass have also been investigated. [4,15-19] . In a highly concentrated alkali environment (either sodium (Na-) or potassium (K-) based), the silica (Si) and alumina (Al) from the aluminosilicate source precipitate and form the Si-O-Al-O monomers . The entire geo- polymerization process begins with the dissolution of Si and Al, followed by the production of oligo-sialate monomers, and finally, the develop - ment of geopolymers by reticulation, networking, and solidification. . Eq 1 and 2 represent the chemical reactions behind geo- polymerization . Researchers have proved that geopolymers have shown superior quality in both mechanical and durability aspects over cement mixtures , leading to sustainable development and a greener environment by utilizing the industry-generated wastes. Further, the wastes having a considerable amount of calcium enhance the geo- polymer ’s mechanical properties due to the coexistence of C-S-H gel and the sialate bond (Si-O-Al-O) [23,24] . Focusing on utilizing different types of C&D wastes, researchers have used waste cement concrete as a precursor for producing geopolymers. Still, it was either a binary or ternary blend mixture. Zaharaki et al., in their study, examined both sole recycled cement concrete based geopolymers and four other C&D waste blended geopolymers and they found that upon heat curing at 80 •C for 24 hrs, the control mix (10 M NaOH solution) was able to achieve a compressive strength of 8 MPa only . While substituting the recy- cled cement concrete content with other precursors (slag, tiles, and red clay bricks), only 10% of recycled cement concrete content gives an optimum compressive strength of 75 MPa at the same curing condition. Allahverdi and Najafi examined a binary blend of waste brick with waste concrete, and they encountered a maximum compressive strength of 16.5 MPa at 28D with 8% Na2O content when the optimum amount of waste concrete was 60% of the total precursor . Another researcher H. M. Khater utilized crushed walls which contains bricks with adhered cement mortar (55% wt.), waste concrete (40% wt.), and hydrated lime (5% wt.) to assess the effect of calcium content on geopolymerization as a precursor and reported 5 MPa 28D compressive strength at ambient temperature curing . Minimal investigations have been reported utilizing waste cement concrete as a sole precursor for geopolymer production. Robayo-Salazar et al. reported a compressive strength of 7.5 MPa with only NaOH (6% Na2O) and 25 MPa with NaOH and Na2SiO3 mixture having silicate modulus of 11.11 at 25 •C temperature . Whereas utilizing 100% concrete waste as a precursor for geopolymer, Zaharaki et al. reported a compressive strength of 7.8 MPa with 10 M NaOH solution at ambient temperature curing . In contrast, V˘asquez et al. reported a compressive strength of 25 MPa at ambient temperature. Interestingly, the compressive strength reduces from 37 MPa at 7D to 25 MPa at 28D when heat cured at a temperature of 70 •C for 24 h . In addition, using grounded waste concrete as the sole precursor, Ahmari et al. re- ported 7D compressive strength of 7 MPa and 11 MPa using 5 M and 10 M with an alkali mixture ratio of 1 . Due to the lack of reported extensive studies on the utilization of finely grounded waste cement concrete as a sole precursor for geo- polymer production, the present study aims to analyse the effect of the molarity of NaOH solution and alkali mixture ratio (NaOH/Na 2SiO3) on the fresh properties and mechanical strength of geopolymer mortar at ambient temperature curing. Different molarities of NaOH solution (6–16 M) and AM ratio (1.5–3.5) were formulated. Further, the List of abbreviations and notations: AM Alkali mixture (Na 2SiO3 / NaOH solution) ANOVA Analysis of Variance C&D Construction and Demolition COD Coefficient of Determination, denoted as R2 C-S-H Calcium Silicate Hydrate D Age of casting in days (Ex.- 28D means 28 days of casting) dF Degrees of Freedom DTG Derivative Thermogravimetry EDX Energy Dispersive X-ray Edyn Dynamic Modulus of Elasticity FTIR Fourier Transform Infrared Spectroscopy GW Glass Waste IR Infrared JCPDS Joint Committee on Powder Diffraction Standards M Molarity MS Mean of Squares MSW Municipal Solid Waste NA Natural aggregate N-A-S-H Sodium Alumino Silicate Hydrate OPC Ordinary Portland Cement RA Recycled aggregate Rh Relative humidity RMSE Root Mean Square Error RS River sand Sample symbol (Ex. - 6M1.5AM) Here ‘6M’ is the molarity of NaOH solution and ‘1.5AM ’ is the AM ratio value SD Standard Deviation SEM Scanning Electron Microscope SM Silicate Modulus, the ratio of SiO2/Na 2O SS Sum of Squares TGA Thermogravimetric Analysis UPV Ultrasonic Pulse Velocity WCC Waste Cement Concrete XRD X-ray Diffraction XRF X-ray Fluorescence Spectroscopy Å Angstrom v Velocity ρ Density n…Si2O5∙Al2O2†‡2nSiO 2‡4nH 2O⎬⎬⎬⎬↗NaOHorKOHn…OH†3SiO…† Al …OH†2OSi…OH†3 (1) n…OH†3SiO…† Al …OH†2OSi…OH†3⎬⎬⎬⎬↗NaOHorKOH…NaCK†…‡†⎫ ⎬⎭† Si † OO† Al † OO† Si † OO⎩ ⎪⎨‡4nH 2O (2) S.K. Das and S. Shrivastava Construction and Building Materials 301 (2021) 124380 3mineralogical, chemical, and microstructural analysis for the identified mixtures from the mechanical test results were analysed by conducting Scanning Electron Microscopy (SEM), Energy Dispersive X-ray analysis (EDX), X-ray Diffraction (XRD), Fourier Transform Infrared Spectros - copy (FTIR), and Thermogravimetric Analysis (TGA) with Derivative Thermogravimetry (DTG). 2.Materials and Methodology 2.1. Materials used Waste cement concrete (WCC) originated from demolished plain cement concrete slabs as construction and demolition (C&D) waste was used in this study as a precursor. Table 1 shows the X-ray fluorescence spectroscopy (XRF) of WCC and river sand. The particle size distribution of WCC powder is presented in Fig. 1a. River sand was used as fine aggregate, and its gradation curve is shown in Fig. 1b. Gradation of the river sand was tested for the limit specified for the use in masonry mortar as per IS:2116 –1980 , and it fits within the limit (Fig. 1b). The scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) of WCC is shown in Fig. 2a and 2b. Table 2 presents the physical properties of the materials. XRD analysis (Fig. 3) shows quartz, albite, portlandite and calcite in the WCC. Further, the presence of quartz and albite is due to the ag- gregates ; portlandite and calcite are due to cement in the WCC . The XRF analysis shows that WCC contains 63.70 wt%, 7.13 wt% and 19.70 wt% of SiO2, Al2O3 and CaO, respectively. Whereas EDX also confirms that the vital elements in the WCC are silica (Si) and calcium (Ca) with a low amount of aluminium (Al). Microstructural analysis through SEM presents the irregular particle dimension of WCC. This varying particle size impacts the workability of the mixtures as discussed in the results section (Section 3.1). FTIR analysis (Fig. 4a) of the WCC was conducted within an infrared region of 500–4000 cm1. A medium sharp peak observed around 3725 –3850 cm1 is due to the presence of Table 1 XRF analysis of the base materials. Material Oxides (wt.%) SiO2 Al2O3 CaO TiO 2 MnO Fe2O3 MgO Na2O K2O P2O5 SO3 Cl WCC 63.70 7.13 19.70 0.07 0.05 3.49 1.03 0.59 1.02 0.15 1.23 0.13 River Sand 96.48 0 1.13 0 0.03 2.01 0.34 0 0 0 0 0 Fig. 1.Particle size distribution curve of (a) WCC and (b) Fine aggregate. Fig. 2.(a) SEM image and (b) EDX spectra of WCC. Table 2 Physical properties of the materials used. Material Bulk density (kg/m3) Water absorption (%) Fineness modulus River Sand 1599 1.80 2.74 WCC 1450 S.K. Das and S. Shrivastava Construction and Building Materials 301 (2021) 124380 4the O–H stretching bond . The band around 1650 –1700 is due to the bending O–H bonds . The highest intensity peak was observed at 1040 cm1 due to a high concentration of Si-O-Si bonds in the WCC . The presence of quartz found in the XRD analysis (Fig. 3) is confirmed by the sharp peak at 782 cm1 and 692 cm1 [34,35] . The peaks in the lower wavenumber 500–650 cm1 are assigned to the covalent bonding of Si-O-Si . The TGA analysis (Fig. 4b) shows a continuous weight loss till 650 •C of 5.5% when heated at a rate of 10 •C per minute till 900 •C in air medium. Also, the TGA graph shows three significant mass losses. The first phase of mass loss ranges from room temperature to 350 •C due to the evaporation/dehydration of different hydrates (C-S-H, ettringite, carbo-aluminates). Within this range, the initial mass loss from room temperature to 110 •C is due to the evaporation of surface to some extent of bound water; 110–170 •C temperature range decomposes the ettringite and part of carbo-aluminate hydrates [37,38] . Finally, the range between 180 and 350 •C governs the bound water mass loss by dehydration of C-S-H and total carbo-aluminate hydrates [39,40] . The second phase occurs in the temperature range of 400–550 •C, where the dihydroxylation of another hydration product, i.e., portlandite occurs. Its presence is also confirmed by the XRD analysis . The third phase of decomposition around temperature ranging from 620 to 680 •C is due to CaCO 3 (calcite) . 2.1.1. Selection procedure and preparation of precursor Though ample research has been reported utilizing WCC as fines , fine aggregates [42-44] , and coarse aggregates [45-47] for pro- ducing geopolymers but most of them used fly ash and GGBS as a primary precursor and substituted some portion of it with WCC. Very few articles utilize WCC of unknown quality as a primary precursor for geopolymer mortar preparation . Few articles also reported known laboratory-made cement concrete as C&D waste as precursors for geo- polymers . Hence, in this study, WCC, a plain cement concrete slab, was used and collected from a landfill site located in the Jaipur city of the state of Rajasthan in India. After collecting the waste, it was grounded in a D-crusher and then in a pulveriser to obtain a finely grounded particle sizeD90 µm (Fig. 1a). The C&D waste was not chemically treated before grinding. Most of the reported studies on utilizing WCC as the precursor employ heat curing regime. Hence, in the present study, controlled ambient temperature curing was conducted along with WCC as a sole precursor for geopolymerization. 2.2. Research methodology 2.2.1. Experimental process 2.2.1.1. Physical testing. In this study, different mix combinations were formulated by altering the alkali proportions only. A combination of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) was used for alkalination. Laboratory-grade (99% purity) NaOH and commercial- grade Na2SiO3 (Na2O ˆ8.40%, SiO2 ˆ27.22% and H2O ˆ64.38% as provided by manufacturer) was used. The mix ratio of Na2SiO3 to NaOH solutions was varied from 1.5 to 3.5 with an increment of 1. The molarity of NaOH was also varied from 6 M to 16 M with an increment of 2 M. A detailed mix combination is shown in Table 3. The NaOH solution was prepared 24 h before casting as the rest period will help the solution to cool down naturally. After 24 h, two different alkali solutions were mixed and allowed to rest for another day before utilizing it for exper - imental work. Other researchers have also followed a similar approach [49-51] . In the mixing process, initially, the precursor and fine aggregates were mixed in a Hobart mixer for 2 min till a homogeneous mixture was obtained by visual inspection. Then the alkali solution was poured uniformly into the dry mixture, and the mixing was continued for another 2–3 min to get a final consistent mixture. After mixing, the fresh mortar was cast into different sized moulds for compression (cube mould 50 ×50 ×50 mm), flexural (prism mould – 40 ×40 ×160 mm) and drying shrinkage (beam size – 25 ×25 ×250 mm) test. All samples were mixed, cast, and vibrated (for one minute on a table vibrator to expel the entrapped air bubbles within the mixture) at room temperature ranging from 24 •C to 26 •C and kept in the same condition for 24 h. De-moulding was performed after 24 h (except shrinkage test specimens), and the samples were placed at 30 •C with Rh of 85 ±5% in a temperature-controlled oven. The shrinkage test specimens were de- moulded after 48 h of casting. The flow of the fresh mixtures was Fig. 3.XRD analysis of WCC. Fig. 4.(a) FTIR and (b) TGA with DTG plot for WCC. S.K. Das and S. Shrivastava Construction and Building Materials 301 (2021) 124380 5measured using a flow table test as per ASTM C1437 , and the flow table used is as per the specifications mentioned by ASTM C230/C230M . Setting time test was also conducted at room temperature of 24–26 •C using Vicat needle apparatus according to Indian Standard code IS:4031 (Part-5)-1988 . The destructive and non-destructive test results reported in this study were the average of three tested specimens with the standard deviation as an error. Compressive strength tests were carried out on all specimens at a specified time using a servo-controlled universal testing machine with a load rate of 0.9 kN/s to 18 kN/s according to ASTM C109/109 M . Flexural tests were carried out at a load rate of 0.044 kN/s following ASTM C348 on the flexural prism mould using a three- point loading setup. The flexural strength was calculated using Eq (3), where Sf is the flexural strength in MPa, and P is the maximum load at failure in N. Sfˆ0B0028 P (3) By adopting the procedure defined in ASTM C1148 and ASTM C490 , the drying shrinkage test was conducted using an automated length comparator with precision to quantify the length shift up to 0.001 mm. Ultrasonic pulse velocity (UPV) tests were performed on the 28D, 56D and 90D cured beam prism specimen of size 16 ×4 ×4 cm. Transducers of frequency 55 kHz were pressed on the two ends of the specimens, and the time required by the ultrasonic wave to travel from one end to another were measured in microseconds. The Dynamic Modulus of Elasticity (Edyn) of the mortar specimens were calculated by the ultrasonic pulse velocity method according to BS EN 12504-4:2004 by using the obtained UPV values. Eq (4) is used to calculate the Edyn values from the obtained UPV values. Edynˆ…v2×ρ† (4) The velocity (km/s) of the longitudinal ultrasonic wave was obtained from the UPV test, and the density (kg/m3) was calculated by measuring the weight and the dimensions of each beam mortar specimen. 2.2.1.2. Microstructural analysis. To better comprehend the physical test, microstructural analysis (SEM, EDX, XRD, FTIR, TGA) was per- formed by obtaining samples from various portions of the 28D cured specimens after conducting the compressive strength test. All collected samples were quenched in acetone for 7D and transformed to different levels of fineness as per the requirements of each microstructural analysis. JSM-7610FPlus FESEM coupled with EDX detector was used to examine the microstructure and elemental composition changes for the change in molarity and alkali solution mixture ratio. Gold sputtering was applied on the specimens for one minute to coat the samples with a thin layer of 100 Å before testing. Rigaku Miniflex 600 was used to conduct the XRD analysis. This analysis determines the mineralogical variations. Scanning of the sam- ples was performed for Bragg ’s angle (2-theta) from 5•to 80•at a speed of 1•per minute. Cu-K α radiation and graphite monochromator was used, and a diffractometer records the diffracted beams at various an- gles. Philips X’Pert Highscore software was used to plot the data in in- tensities vs 2θ (Bragg ’s angle), and the peaks were identified by comparing the peaks with the data files available in the JCPDS database. Fourier-transform infrared spectroscopy (FTIR) works on the prin- ciple that each element either absorbs or transmits some wavelengths in the wide infrared zone, which will precisely help to identify the avail- able bonding or functional groups within the elements. Mostly the wavenumbers for the mid-infrared (IR) zone of 400–4000 cm1 was utilized to determine the vibrational or rotational / bending vibrational structures. The Bruker ’s Alpha II model was used to measure the same within a range of 500–4000 cm1 wavenumber. The background IR spectra were initially recorded, followed by the samples ’ emission s- pectra. The ratio of the sample to the background spectrum gives the absorbance spectrum of the sample. The absorbance spectra are then converted into transmittance. The resulting transmittance spectral Table 3 Description of mixture details. Symbol Waste material Quantity (g) Fine aggregate Quantity (g) NaOH solution (wt.% of WCC) Na2SiO3 solution (wt.% of WCC) Water* (wt.% of WCC) SM Na2O (%) 6 M1.5AM WCC 760 RS 2280 32 49 57 1.45 11.2 8 M1.5AM WCC 760 RS 2280 32 49 56 1.28 12.7 M1.5AM WCC 760 RS 2280 32 49 54 1.16 14 M1.5AM WCC 760 RS 2280 32 49 53 1.07 15.2 M1.5AM WCC 760 RS 2280 32 49 52 0.99 16.3 M1.5AM WCC 760 RS 2280 32 49 51 0.94 17.3 6 M2.5AM WCC 760 RS 2280 23 58 56 1.86 10.4 8 M2.5AM WCC 760 RS 2280 23 58 55 1.68 11.5 M2.5AM WCC 760 RS 2280 23 58 54 1.54 12.5 M2.5AM WCC 760 RS 2280 23 58 53 1.45 13.3 M2.5AM WCC 760 RS 2280 23 58 52 1.37 14.1 M2.5AM WCC 760 RS 2280 23 58 51 1.30 14.8 6 M3.5AM WCC 760 RS 2280 18 63 55 2.10 10 8 M3.5AM WCC 760 RS 2280 18 63 54 1.91 11 M3.5AM WCC 760 RS 2280 18 63 53 1.81 11.6 M3.5AM WCC 760 RS 2280 18 63 53 1.71 12.3 M3.5AM WCC 760 RS 2280 18 63 52 1.63 12.9 M3.5AM WCC 760 RS 2280 18 63 51 1.57 13.4 *Water – The total amount of water (from alkali solutions) present in each batch of mixture. S.K. Das and S. Shrivastava Construction and Building Materials 301 (2021) 124380 6graph shows various modes of vibration/rotation/bending in the structural bonds and functional groups. The thermogravimetric analysis (TGA) was used to observe weight loss or mass change when a sample is exposed to a uniform increase in temperature. It is represented as a percent change in mass vs tempera - ture. It also provides information on oxidation, decomposition, ab- sorption, adsorption, and change in phase. Shimadzu DTH-60H was used to analyse the samples for TGA at a rate of 10 •C per minute to 900 •C. The apparatus was initially calibrated at room temperature with an empty crucible for temperature and weight. Then approximately 12–15 mg of the sample was placed in the crucible, and the test was carried out. 2.2.2. Statistical analysis A full factorial design was conducted at a 95% confidence level for ANOVA and F-test using Minitab ® 18 to evaluate the statistical signif - icance of the identified factors influencing the response . Identified factors with their different levels have been listed in Table 5. 3.Results and discussion 3.1. Effect on flowability Fig. 5 presents the variation in flowability. It was observed that the flow or cohesiveness of the fresh mixtures depends on the molarity and AM ratio. Increasing the molarity of the NaOH solution and AM ratio reduces the flowability as well as increases the cohesiveness of the mixture. A similar kind of behaviour was also found by other researchers . With an increase in the Na2SiO3 content, the total amount of water in the mixture remains almost the same (Table 3), but the incremental presence of a highly viscous Na2SiO3 solution increases the AM ratio, and results in a reduction of the flowability . Although maintaining a total solid (precursor and fine aggregate) to alkali solution ratio at 0.2, the overall flowability remains above 105%, which is aligned with the requirements specified in ASTM C1437 . 6 M1.5AM and 16 M2.5AM mixture reported the maximum and minimum flow of 140% and 102%, respectively. The possible reason for the 102% flow for the 16 M2.5AM mixture can be attributed to the mixing of a greater quantity of finer particles in the fine aggregate. Ghosh and Ghosh reported that increasing the water content increases the flow of the mixture by reducing the viscosity and results in delayed geopolymerization and lower strength . Table 3 and Fig. 5 show that Na2O content also plays an essential role in the flow percentage. For each group of AM ratios with an increase in the Na2O content, the flow percentage decreases due to an increase in the viscosity. Further, higher Na2O and lower water content increased the rate of geopolymerization and initi- ated the rapid deterioration of the plasticity of the mixture . 3.2. Effect on the setting time Fig. 6 shows the variations in the initial and final setting time of the mixtures with the variation in the molarity of NaOH and AM ratio. Higher initial and final setting time is seen for low molarity and AM ratio mixes. A significantly small quantity of Na2O slows down the geo- polymerization process at ambient temperature and takes a longer time to set . In contrast, increased molarity as well as Na2O content in- tensifies the geopolymerization and lowers both setting times. This Table 4 Ultrasonic Pulse Velocity (UPV) and Dynamic Modulus of Elasticity (Edyn) values for different mixtures at different curing age. Symbol Average Ultrasonic Pulse Velocity (km/s) Average Dynamic Modulus of Elasticity, Edyn (GPa) 28D 56D 90D 28D 56D 90D 6 M1.5AM 2.92 3.01 3.01 20.72 21.28 21.11 8 M1.5AM 3.23 3.31 3.27 20.78 22.02 21.86 10 M1.5AM 3.29 3.39 3.46 22.35 23.82 24.85 12 M1.5AM 3.58 3.72 3.72 26.25 27.59 27.94 14 M1.5AM 3.49 3.55 3.61 25.62 25.55 26.67 16 M1.5AM 3.61 3.57 3.72 27.08 26.85 28.37 6 M2.5AM 3.29 3.28 3.26 21.29 21.62 21.35 8 M2.5AM 3.61 3.75 3.75 26.35 28.97 28.86 10 M2.5AM 4.07 4.15 4.21 34.02 34.91 36.10 12 M2.5AM 3.71 3.67 3.76 29.11 29.25 30.42 14 M2.5AM 3.47 3.55 3.56 25.16 25.72 25.54 16 M2.5AM 3.61 3.71 3.81 26.85 28.11 29.27 6 M3.5AM 3.03 3.12 3.09 18.21 19.51 19.50 8 M3.5AM 3.48 3.53 3.46 24.74 24.47 24.68 10 M3.5AM 3.45 3.47 3.61 24.36 24.76 26.25 12 M3.5AM 3.75 3.85 3.89 29.01 30.02 31.31 14 M3.5AM 3.49 3.66 3.75 24.83 27.56 28.75 16 M3.5AM 3.57 3.62 3.75 25.64 27.23 28.41 Table 5 Factors and levels for ANOVA and F-test. Factor Level 1 Level 2 Level 3 Level 4 Level 5 Level 6 M 6 8 10 12 14 16 AM 1.5 2.5 3.5 D 3 7 28 56 90 Fig. 5.Flowability of different mixtures. Fig. 6.Variation in setting time of different mixtures. S.K. Das and S. Shrivastava Construction and Building Materials 301 (2021) 124380 7behaviour of geopolymer is in good agreement with the findings of other researchers where they had reported reduced setting times when the Na2O content is increased in the mixture [64,65] . Though from the point of ease of application of the mixture, a higher initial setting time is desired but increasing the setting time with water reduces the compressive strength. Hence, it can be concluded that an increased setting time can be achieved with lower molarity of NaOH solution or by lowering the Na2O content in its solution with Na2SiO3 when the two alkalis were used for geopolymerization. However, it also affects other properties viz. compressive and flexural strengths. 3.3. Compressive strength The change in the compressive strength for different molarity (from 6 M to 16 M) with the variation in the AM (from 1.5 to 3.5) ratios is presented in Fig. 7. Observations from Fig. 7 show that both molarity of the NaOH solution and curing age are the influential factors for the generation of compressive strength when the curing temperature, pre- cursor, and fine aggregate are kept fixed. It is a proven fact that higher alkalinity (higher amount of Na‡cations) increases the dissolution of Si and Al from the aluminosilicate source [61,66] . However, excess hy- droxide (OH–) ions also lead to rapid precipitation of the aluminosili - cates at an early age and hinder the availability of Si and Al in the mixtures for geopolymerization at different curing ages . Our study shows a maximum compressive strength of 20.55, 20.65 and 20.70 MPa at 28D, 56D and 90D for the 10 M2.5AM mixture. Whereas for the same molarity with AM ˆ1.5, it was 12.6, 17.5 and 19 MPa; for AM ˆ3.5, it was 14.5, 14.65 and 15 MPa at 28D, 56D and 90D casting age, respectively. Interestingly, Fig. 7 shows no specific pattern with the variation in molarity and AM ratio. However, increasing the Na2SiO3 content and the molarity of NaOH solution leads to lower compressive strength. A considerable variation in the compressive strength between 7D and 28D was observed for mixtures with both AM 1.5 and 3.5, which shows the delayed geopolymerization effect. Whereas the mixtures having AM ˆ2.5, the variation was more diminutive, and initial strength gain was much higher than the other two AM ratio mixtures. The effect of SiO2/Na 2O (SM) was calculated and analyzed. Fig. 8 shows the variation in compressive strength with the SiO2/Na 2O ratio value in ascending order. The optimum SiO2/Na 2O value is 1.54 (10 M2.5AM), where the maximum compressive strength was observed. Moreover, the second-highest compressive strength was obtained around SiO2/Na 2O ratio of 0.94. Fig. 8 indicates a threshold value of SiO2/Na 2O ratio is required to get the optimum result. Similar obser - vations regarding the threshold limit are also reported by other re- searchers [68,69] . Cho et al. found that increasing the SiO2/Na 2O from 0.8 to 2.0 decreases the compressive strength due to an increase in the percentage of porosity, and the optimum SiO2/Na 2O value is 1.4 when fly ash of class F grade was utilized as a precursor . Our study also found the optimum SiO2/Na 2O content to be around 1.54, while increasing the Na2SiO3 content simultaneously increases the SiO2/Na 2O ratio value, decreasing the compressive strength by reducing the reac- tivity of the geopolymeric gel . Further, depending on the molarity and AM ratio, Na2O% is calcu - lated for each mixture, and the corresponding compressive strength with age is presented in Fig. 9 in ascending order of Na2O%. While it is well known that increasing the Na2O% enhances the geopolymerization by increasing the solubility of amorphous silica and alumina from the precursor but also the high rate of dissolution of silica and alumina from the precursor could not end up to the geopolymeric chain and causes a blocking effect to the synthesis of geopolymers and further strength gain [69,70] . It can be observed from Fig. 9 that 12.5% Na2O content leads to maximum compressive strength, beyond which there is a drastic fall in the compressive strength, and again it increases at 17.5%. Further variation in compressive strength with increment in the percentage of Na2O content could not be studied as the scope of this research is limited Fig. 7.Change in compressive strength for different mixtures with curing age. Fig. 8.Change in compressive strength with the variation in SiO2/ Na2O content. Fig. 9.Change in compressive strength with the variation in Na2O content. S.K. Das and S. Shrivastava Construction and Building Materials 301 (2021) 124380 8to this level. So it can be concluded that the optimum Na2O content is 12.5% for the highest compressive strength. 3.4. Flexural strength Fig. 10 shows the change in the flexural strength of each mixture. The maximum and minimum flexural strength was also achieved by 10 M2.5AM and 6 M1.5AM mixture similar to the observations for the compressive strength. It is observed from Fig. 10 that increasing the molarity can achieve higher flexural strength for all the three different Na2SiO3 content, but AM2.5 mixtures almost attain its 60% of 28D flexural strength within the first 7D of curing. In contrast with other silicate content mixtures, the initial 7D flexural strength was merely 25–35% of its 28D flexural strength. It is also observed that AM2.5 is the optimum Na2SiO3 content. Any variation from it results in delayed geopolymerization, which is also observed from the flexural strength difference between 7D and 28D, where there is no considerable surge in the flexural strength. A best-fitted correlation plot between compressive and flexural strength depicts a COD (R2) value of 0.96, proving an excellent corre - lation between the physical strength parameters computed through destructive testing. Also, the correlation can be helpful to ascertain the flexural or compressive strength from one test result without any destructive testing for the other one. 3.5. Drying shrinkage analysis Shrinkage in specimens occurs due to drying when there is a differ - ence between the atmospheric humidity and surface moisture of the specimen. Less atmospheric humidity than the surface of the specimen absorbs the water from the specimen, which further leads to a reduction of the water content within the specimen and reduces the water voids and changes the shape and size of the specimen. Every measurement for a specific specimen was conducted for a particular side and direction which was marked on the specimen at the very first length comparator test to minimize the error due to the warping effect with curing age . The drying shrinkage variation of each sample is presented in Fig. 11. It is seen that increasing the AM ratio from 1.5 to 3.5 increases the maximum shrinkage percentage with age with the variation in the molarity of NaOH solution. The minimum shrinkage value was obtained by 10 M2.5 AM and 12 M2.5AM, whereas the maximum was by 16 M3.5AM. Drying shrinkage results were obtained till 180D of casting to get the ultimate drying shrinkage value. During experimentation, it was observed that all the geopolymers took an average of 90D to stabilize the drying shrinkage. Beyond 90D, the drying shrinkage value becomes stable. As the quantity of precursor and fine aggregate were fixed so the Fig. 10.Flexural strength plot of different mixtures. Fig. 11.Change in the drying shrinkage values for different mixtures with curing age. S.K. Das and S. Shrivastava Construction and Building Materials 301 (2021) 124380 9variation in drying shrinkage was mainly governed by the alkali content and secondarily by the particle size of the fine aggregates. High Na2SiO3 content increases the cohesiveness of the mixture, which could be observed from the flowability of the mixtures (Fig. 5). From Fig. 11, the maximum drying shrinkage was observed for AM1.5 mixtures as 0.002% after 180D, whereas for AM3.5 mixtures, the minimum drying shrinkage value as 0.0022% after 180D irrespective of the molarity of NaOH. The high cohesiveness of the fresh mixture and adhesive nature of Na2SiO3 tend to create honeycombs, which with age intensifies the drying shrinkage. Further, it was observed that 10 M and 12 M mixtures resulted in the most negligible drying shrinkage value and could be taken as the optimum molarity to get a minor drying shrinkage effect. 3.6. Ultrasonic pulse velocity and Dynamic modulus of Elasticity Table 4 presents the mean of UPV (km/s) and Edyn (GPa) of three test specimens for each symbol. Where it was observed that the UPV in- creases after 28D till 56D but beyond 56D until 90D it remains almost the same. A similar phenomenon was observed for Edyn also as it had been computed using the method mentioned in BS EN 12504 –4:2004 using the UPV values. Fig. 12 shows that the UPV value increases with the curing age, though the increment is minimal for almost half of the mixtures. This phenomenon justifies that with curing age at room temperature curing conditions, the geopolymerization rate was slow but steady when WCC was used as a sole precursor. Maximum UPV value is observed for 10 M 2.5AM mixture, and the same mixture shows the highest compressive strength. Other than 6 M mixtures, almost all different mixtures reported UPV within a range of 3.5 to 3.75 km/s which depicts a good quality zone . The R2 value was found to be 0.77 when the UPV was compared with the compressive strength for the test results obtained at 28D, 56D and 90D age. Dynamic modulus of elasticity (Edyn) is also an essential factor in assessing the mortar quality and have been calculated as mentioned under section 2.2.1.1. The lowest and highest Edyn value is shown by 6 M3.5AM and 10 M2.5AM respectively. Variation in the Edyn value represents the stiffness of the mortar, where lower values indicate lower stiffness due to the presence of porosity in it and vice versa. Fig. 13 shows that Edyn value increases with the curing age, indicating increased compactness of the mixture with age. This was possible due to the delayed geopolymerization of the WCC due to the absence of heat curing. Further, analysing Fig. 13, it is observed that for AM ˆ1.5, increasing the molarity, the Edyn value increases, which indicates the increased compactness of the final product. Whereas for AM 2.5 and 3.5, the outcome was mixed with the variation in the molarity of NaOH so- lution. So, increasing the AM ratio with the molarity does not affect the Edyn value significantly, and it remains within a range of 25 to 30 GPa. However, AM2.5 mixtures show better Edyn values when compared to AM3.5 mixtures, which signifies the effect of Na2SiO3. Increasing the Na2SiO3 content leads to a highly porous structure and simultaneously decreases the Edyn value. An optimum value for Edyn was obtained for AM 2.5 mixtures among the three different Na2SiO3 content. An R2 value of 0.76 was found when the compressive strength and Edyn values were correlated. 3.7. Statistical analysis of the results For the statistical assessment of the different factors affecting the geopolymer mortar compressive and flexural strength, ANOVA and F- test were conducted. A confidence level of 95% was assigned. A higher F-value demonstrates the variation of the parameters, which signifi - cantly affects the samples ’ performance characteristics . A full factorial design with three factors and different levels of each factor was applied to analyse the influence of the factors. In Table 5, the factors and their levels are listed where M is the molarity of the NaOH solution; AM is the mixing ratio of Na2SiO3 solution to NaOH solution; and D is the age of casting in days. Tables 6 and 7 represents the ANOVA results of the geopolymers mortars concerning their compressive and flexural strength, respectively. From Table 6, it is observed that both M and D have a significant effect on the compressive strength with a p-val - ueD0.05, whereas AM is not significant. It further supports the destructive test results, where no pattern was found between M and AM Fig. 12.Change in the UPV values for different mixtures at 28D, 56D and 90D curing age. Fig. 13.Change in the Edyn values for different mixtures at 28D, 56D and 90D curing age. Table 6 Results of ANOVA for compressive strength (MPa). Factor SS dF MS F-value p-value Significance M 89.70 1 89.70 17.67 0.00 D0.05 Significant AM 0.73 1 0.73 0.15 0.71 D 2360.30 1 2360.30 464.89 0.00 D0.05 Significant M ×M 23.32 1 23.32 4.59 0.03 D0.05 Significant AM ×AM 102.86 1 102.86 20.26 0.00 D0.05 Significant D ×D 598.16 1 598.16 117.81 0.00 D0.05 Significant M ×AM 13.31 1 13.31 2.62 0.11 M ×D 8.23 1 8.23 1.62 0.21 AM ×D 8.08 1 8.08 1.59 0.21 Error 406.17 80 5.08 Total 3610.86 89 S.K. Das and S. Shrivastava Construction and Building Materials 301 (2021) 124380 10as shown in Fig. 7. For the predicted compressive strength (Fig. 14) after the ANOVA, the RMSE was found to be 2.25 MPa, and R2 was 0.87, which shows a good level of correlation. Similarly, from Table 7, M and D have a significant effect on the response of the experiment regarding flexural strength. Also, from Fig. 14, the predicted flexural strength has an R2 value of 0.90 with RMSE as 0.49 MPa. Fig. 15 shows the main and interaction effect of SM and Na2O regarding the compressive strength of the geopolymer mortar. Though the factors alone are not significant, the effect of their interaction is significant, which is observed from the Pareto chart. Also, a zone was found after the ANOVA test, which results in the achievement of the maximum compressive strength. 4.Microstructural analysis Microstructure analysis was carried out to complement the assess - ment and correlate the observations made during mechanical testing. For all the microstructural analyses, 28D cured specimens were used. The samples were collected from different parts of the crushed samples after the compression testing. Three samples, i.e., 10 M2.5AM, 12 M1.5AM and 16 M1.5AM, were analysed for microstructure analysis. 4.1. Microstructure examination by SEM and elemental analysis by EDX For a proper understanding of the microstructure, three different mix proportions (10 M2.5AM, 16 M1.5AM and 12 M1.5AM) were identified depending on the highest compressive strength and a series of SEM images were taken and EDX were conducted. The results are presented in Fig. 16 and Table 8. Fig. 16 presents two series of SEM images where the first series (a, b, and c) shows the crushed/semi-powdered specimen images, and the second series (d, e, and f) shows the saw-cut surface images of the identical specimen. Fig. 16d presents the most compact microstructure for the batch designated as 10 M2.5AM. In contrast, Fig. 16e shows multiple levels of voids with fracture lines between the sand particles and geopolymer paste which reveal an improper bonding between them and consequently result into lower mechanical strength. Fig. 16f shows a relatively compact structure. Fig. 16e shows a clear interfacial transition zone between the sand particle and geopolymer paste. From Fig. 16b and c, the samples prepared by using a 1.5AM ratio presented voids of different sizes and show a weaker bonding between the particles. Whereas the 2.5AM mixture images (Fig. 16a and d) show the most compact matrix. These voids can be directly correlated to their compressive strength, where it was found that the most compact matrix represents the highest compressive strength at different curing ages. Upon close inspection, multiple hairline cracks are observed for each mixture due to the drying shrinkage effect. Though the 10 M2.5AM mixture achieved the highest physical strength through proper bonding, drying shrinkage cracks were visible within the geopolymer paste area. Along with the sialate bonds, the high concentration of NaOH can dissolve the gypsum present in the mixture and convert it into calcium hydroxide (Eq (5)) . This also strengthens the pozzolanic reactivity Table 7 Results of ANOVA for flexural strength (MPa). Factor SS dF MS F-value p-value Significance M 3.29 1 3.29 13.48 0.00 D0.05 Significant AM 0.08 1 0.08 0.35 0.55 D 99.82 1 99.82 621.95 0.00 D0.05 Significant M ×M 12.31 1 7.31 32.02 0.04 D0.05 Significant AM ×AM 11.75 1 11.75 48.02 0.00 D0.05 Significant D ×D 41.12 1 41.12 168.04 0.00 D0.05 Significant M ×AM 0.12 1 0.12 0.48 0.49 M ×D 0.14 1 0.14 0.58 0.45 AM ×D 0.01 1 0.01 0.02 0.91 Error 19.58 80 0.24 Total 188.22 89 Fig. 14.(a) Pareto chart of the standardized effects of compressive strength depending on the factors (molarity, AM and curing age); (b) Best fitted plot for compressive strength; (c) Pareto chart of the standardized effects of flexural strength depending on the factors (molarity, AM and curing age); (d) Best fitted plot for flexural strength. S.K. Das and S. Shrivastava Construction and Building Materials 301 (2021) 124380 11between the formed calcium hydroxide and aluminosilicates and leads to calcium silicate hydrate gel . CaSO 4∙2H 2O…s†‡NaOH…aq†→4Ca…OH†2…s†‡Na2SO 4…aq† (5) From the examination of the parent WCC through EDX analysis, it is found that silica (Si), alumina (Al) and calcium (Ca) are the predominant minerals present. From Table 8 it is observed that after geo- polymerization there is a huge change in the atomic percentage of the minerals. This can be attributed to the ionic reactions that happen within the minerals due to the formation of covalent bonding of the polymers and hence, variations in the cohesiveness and strength prop- erties are observed . The increase in the quantity of sodium (Na) is due to the alkalis present in the mixtures for geopolymerization. From Table 8 it is observed that the Si/Al ratio value maintains 16 M1.5AM (1.80) D10 M2.5AM (3.55) D12 M1.5AM (5.54) DWCC (6.48). The optimum strength was obtained by Si/Al ˆ3.55, which is almost equivalent to the poly-sialate di-siloxo formation of the geopolymers, whose theoretical value stands at Si/Al ˆ3. The second highest compressive strength is obtained by Si/Al ˆ1.80, which stands close to poly-sialate siloxo, i.e., Si/Al ˆ2. The least compressive strength is observed for Si/Al ˆ5.54, which comes under poly-sialate multi-siloxo, i.e., Si/Al F3 among the three-mix proportion analysed. Ca in the geopolymer mixture also reinforces the geopolymer network by acting as a charge balancing cation. From Table 8, the optimum Ca/Si ratio is found to be 0.24 and it is aligned with the research findings reported by other researchers [76,77] . 4.2. X-ray Diffraction (XRD) analysis Fig. 17 shows the XRD pattern of the three selected samples at 28D curing age along with a comparison with the WCC. The peaks observed at the Bragg ’s angle (2θ) values of 21•, 26.5•, 36.5•, 43.5•, 60.1•and 68.3•are for the different crystal planes of quartz which also suggest that the predominant mineral in WCC is quartz [78,79] . These high- intensity peaks for all the three mixtures at the Bragg ’s angle mentioned above are due to the quartz, which remains in an inert phase and does not participate in the geopolymerization and further addition of fine aggregate to WCC for mortar preparation intensifies the peaks of quartz [79,80] . Nevertheless, it was also reported by Lecomte et al. that though quartz remains in an inert phase and high molarity could reduce its intensity due to dilution effect, which can be observed for 16 M1.5AM mixture at 21•Bragg ’s angle . Furthermore, small intensity peaks are observed in between 20•to 30•which indicate the formation of geopolymers (except the quartz peaks at 21•and 26.5•) . Also, it has been reported by researchers that halo peaks around 28•to 30•repre - sent the predictable amorphous structures of geopolymers . Fig. 17 also depicts that, after alkali activation of WCC, the peaks shifted towards the right (i.e., towards higher Bragg ’s angle value). This phenomenon indicates the formation of the amorphous sodium alumi - nosilicates which is the key binding agent in geopolymers. High- intensity peaks for the 10 M2.5AM combination at higher Bragg ’s angle values indicate optimum geopolymer production, which is also demonstrated during mechanical testing by achieving maximum strength among the various mixtures. Also, peaks observed at Bragg ’s angle 32•, 42.5•, 50.5•and 52•correspond to zeolites which get formed due to geopolymerization upon alkali activation, and it is also observed that with the increase in the molarity of the mixture, the intensity of the peaks reduces . Similar behaviour upon alkali activation was observed by Heah et al. . Fig. 15.(a) Main effects plot for compressive strength; (b) Pareto chart of the standardized effects of compressive strength depending on the factors (SM and Na2O %); (c) Interaction effects plot for compressive strength; (d) Contour plot of compressive strength vs SM, Na2O%. S.K. Das and S. Shrivastava Construction and Building Materials 301 (2021) 124380 124.3. Fourier transform infrared spectroscopy (FTIR) analysis Fig. 18 presents the FTIR analysis of WCC and geopolymers. The band assignments to different types of bonding are tabulated in Table 9. The change or shift of FTIR spectra before and after geopolymerization of WCC are observed primarily below 2000 cm1, around 2350 cm1 and within 3500 –4000 cm1 wavenumbers. Spectra below 2000 cm1 are sharper for WCC than the three geopolymers (10 M2.5AM, 12 M1.5AM and 16 M1.5AM), confirming more amorphous nature of the geopolymers in comparison to WCC. The bands at higher wavenumbers, i.e., 3500 –4000 cm1, are assigned to the stretching vibrations of the O–H bond, which has sharp and broad peaks for the geopolymers due to the presence of water molecules within the geopolymers. A flat peak occurred around 2350 cm1 due to the formation of C-O vibrational bonds in CO2 constricted in the amorphous phase of the geopolymer . This kind of behaviour is attributed to the use of WCC as a pre- cursor. The subsequent sharp peak was observed between 1500 and 1700 cm1 related to the stretching vibration of the O-C-O bonds. It is observed that with this range, the maximum and minimum intensity peak is obtained by 16 M1.5AM and WCC, respectively. A higher peak is attributed to the capacity of the material to absorb environmental CO2 due to the presence of Ca within the precursor and formed CaCO 3 [66,85] . And peaks around 1463 cm1 close to the 1500 –1700 cm1 range is assigned to the C–O stretching vibrational bond, which is assigned to the formation of CaCO 3. Further, it is also observed that the lesser the peak intensity, the higher the compressive strength. This phenomenon can also be restated as the lower the CO2 absorption ca- pacity higher will be the compressive strength for geopolymers. Samples Fig. 16.SEM images of 28D sample of 10 M2.5AM (a and d), 12 M1.5AM (b and e) and 16 M1.5AM (c and f). Table 8 Change in the elemental atomic percentage before and after geopolymerization. Symbol Minerals (Atomic, wt. %) Si Al Ca Na K Fe Si/Al Na/Al Ca/Si WCC 14.90 2.30 5.76 0 0.31 0.31 6.48 0 0.38 16 M1.5AM 0.56 0.31 0.28 2.47 0.07 0.23 1.80 7.96 0.50 12 M1.5AM 1.33 0.24 0.28 2.93 0.07 0.18 5.54 12.21 0.21 10 M2.5AM 1.21 0.34 0.29 2.67 0.11 0.22 3.55 7.85 0.24 S.K. Das and S. Shrivastava Construction and Building Materials 301 (2021) 124380 13showing a sharp peak centred around 1000 cm1 is assigned to the vibrational stretching mode of Si-O-Si of SiO4 tetrahedral structure [24,25,86] . The key observation for the wavenumbers D1000 cm1 before and after geopolymerization of WCC is the peak formation pattern of Si-O vibrational bonds. A peak broadening for the geo- polymers around 1000 cm1 and shifting of peaks of the geopolymers towards the lower wavenumbers, i.e., around 580–600 cm1, indicates the random formation of Si-Al bonds . This shifting of Si-O related bands to lower wavenumber is due to the depolymerization of silicates and the exchange of Si with the Al atoms. A similar kind of behaviour was also reported by other researchers when using WCC as a precursor for geopolymers [4,87-89] . 4.4. Thermogravimetric analysis (TGA) Fig. 19 shows the TGA graph of the specimens before and after geopolymerization of the parent material (WCC) at different molarity (10 M, 12 M and 16 M) and AM ratios (1.5 and 2.5). TGA and DTG graphs (Fig. 20) show three major areas of mass loss for the WCC which correspond to three temperature ranges: i) room temperature 200•C, ii) 300-400•C, and iii) 600–700 •C They correspond to loss of bound water, dehydration of calcium hydroxide, and decomposition of CaCO 3 [92-94] . The mass loss encountered by WCC for the above-mentioned temperature zones are 1.82%, 3.1% and 5.45%, whereas for the geo- polymers within the same temperature zone the mass loss is 3.22%, 3.36% and 4.18% for 10 M2.5AM; 3.29%, 3.38% and 4.13% for 12 M1.5AM; 3.54%, 3.61% and 4.59% for 16 M1.5AM. The weight loss was higher for the geopolymers to 600 •C than WCC due to the involvement Fig. 17.XRD pattern of 28D sample of WCC, 10 M2.5AM, 12 M1.5AM and 16 M1.5AM. Fig. 18.FTIR spectra of 28D sample of WCC, 10 M2.5AM, 12 M1.5AM and 16 M1.5AM. Table 9 Assignments of different FTIR transmittance peaks. Sl. No. Band range (cm1) Type of bonding Reference 1 525 O-Si-O (symmetric bending) Carrasco et al. 2 500–650 Si-O-Alvi and AlO 6 (Polyhedral form) Z. Zuhua et al. 3 580 Si-OH and Siloxane backbone (vibrational) H. Yoshino et al. 4 780, 1040 Si-O-Si (stretching vibration) Allahvardi and Kani , F. Rubio et al. 5 1463 C–O stretching vibrational bond may be attributed to CaCO 3 I. García Lodeiro et al. 6 1500 – 1700 O-C-O stretching vibrational bond S.K. Das and S. Shrivastava 7 2350 C-O vibrational bond Z. Li and L. Zhang 8 3600 –3850 O–H stretching vibrational bond S.K. Das and S. Shrivastava Fig. 19.TGA curve of 28D sample of WCC, 10 M2.5AM, 12 M1.5AM and 16 M1.5AM. S.K. Das and S. Shrivastava Construction and Building Materials 301 (2021) 124380 14of multiple reaction phases within the geopolymer. These reaction phases can be summarized as (a) up to 250–300 •C the weight loss is predominantly for the evaporation of molecularly bound water and zeolitic water present within the geopolymers and the de-hydroxylation phase of the N-A-S-H gel available within the geopolymers [95,96] ; (b) beyond 300 •C to 600 •C the de-carbonation governs the weight loss and de-hydroxylation of secondary carbonates and crystalline zeolitic pha- ses, respectively [97,98] . Further, above 600 •C, a sudden weight loss is observed for WCC due to the decomposition of CaCO 3 in higher quantity than the geopolymers which is attributed to the existence of small amount of CaCO 3. Similar observation is also reported by other re- searchers using slag as a precursor for geopolymer production [98-100] . However, in our study, 16 M1.5AM shows the maximum mass loss beyond 600 •C. The same phenomenon is also observed in the FTIR analysis (Fig. 18). 5.Conclusion A thorough experimental and microstructural analysis was con- ducted to understand the geopolymeric potential of waste cement con- crete used as a single precursor for geopolymer production. A series of destructive and non-destructive tests were conducted at different curing ages. The summary and critical conclusions of this study are mentioned below: ≡Increasing the amount of Na2SiO3 decreases the flowability and setting time of the mixtures by increasing their cohesiveness and rapid hardening. It impacts the workable time. However, it does not significantly affect the compressive or flexural strength. A lower quantity of Na2SiO3 would be helpful to have good workability and workable time. Also, a substantial increase in the amount of Na2SiO3 increases the drying shrinkage effect in the mortar. ≡12.5% Na2O was found to be the optimum limit for WCC based geopolymers. Further variation from it reduces the mechanical strengths. While for silicate modulus, SiO2/Na 2O ratios between 1 and 1.5 were found optimal. ≡An alkali mixture ratio of 2.5 is optimum among the three ratios as proved by experimental observations. It expedites the geo- polymerization by gaining good compressive strength within 7D of casting. In comparison, 1.5AM and 3.5AM delays the geo- polymerization. Optimum molarity is found to be within 10 M to 12 M. ≡ANOVA and F-test validates molarity and curing age as a significant factor influencing the mechanical strength. In contrast, AM is not a significant factor for achieving the same. ≡The presence of significant amount of CaO in WCC results in the formation of a hybrid geopolymer by producing both the C-S-H gel and the poly-sialate phase. At ambient temperature curing condi - tions, the former coexists with the geopolymers and enhances the particle connection. Overall, based on the results of the experiments, 100% WCC may be utilized as a single precursor for manufacturing geopolymers at ambient temperature curing, broadening its applicability from precast material to cast-in-situ applications. However, the presence of CaO and the availability of C-S-H gel phase may affect the durability of the manu - factured geopolymers, which must be extensively investigated. 6.Data statement All the data related to this article can be obtained from the corre - sponding author upon stating the reason for collecting the data through email. 7.Funding information This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Fig. 20.TGA with DTG curve of 28D sample of WCC, 10 M2.5AM, 12 M1.5AM and 16 M1.5AM. S.K. Das and S. Shrivastava Construction and Building Materials 301 (2021) 124380 15CRediT authorship contribution statement Sourav Kumar Das: Investigation, Methodology, Writing - original draft. Sandeep Shrivastava: Conceptualization, Methodology, Super - vision, Writing - review & editing. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements Authors would like to acknowledge the help provided by NCESS, Thiruvananthapuram for XRF analysis; Central Instrumentation Facility, MIT Manipal and Sophisticated Analytical Instrument Facility, Manipal University Jaipur for SEM and EDX analysis; Central Analytical Facility, Manipal University Jaipur for FTIR and TGA analysis; and Manipal University Jaipur for providing their Material Testing Laboratory resources.

Inte rnational Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 0 4 Issue: 0 5 | May -201 7 www.irjet.net p-ISSN: 2395 -0072 © 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 1306 EXPERIMENTAL STUDY OF FACTORS INFLUENCING COMPRESSIVE STRENGTH OF GEOPOLYMER CONCRETE Ajay Sharma 1, Juned Ahmad 2 1 PG Student, Structural Engineering, Integral University, Uttar Pradesh, India 2 Assistant professor, Department Of Civil Engineering, Int egral University, Uttar Pradesh, India ------------------------------------------------------------------- --***-------------------------------------- ------------------------------- Abstract - Manufacture of Portland cement produces large of volumes of carb on dioxide and other gases. Releasing these gases causes atmospheric pollution and subsequent environmental degradation. Finding a suitable alternative solution to mitigate the environmental degradation caused by using Portland cement is very important for environmental sustainability. On the other side, fly ash is the waste material of coal based thermal power plant, available abundantly but pose disposal problem. There are environmental benefits in reducing the use of Portland cement in concrete, and usin g a cementitious material, such as fly ash. Geopolymer concrete is new sustainable concrete which is manufactured by replacing cement 100% with processed fly ash which is chemically activated by alkaline solutions made from sodium silicate (Na2SiO3) and so dium hydroxide (NaOH). This thesis presents the effect of several factors like alkaline liquid to fly ash ratio, molarity of NaOH, curing hours and curing temperature on the compressive strength of fly ash based geopolymer concrete. Fly ash is taken as the basic material to develop the geopolymer concrete and it is activated by the alkaline solution of sodium silicate and sodium hydroxide. The test variables were molarities of sodium hydroxide (NaOH) 12M, 4M, 16M, and 18M, ratio of NaOH to sodium silicate (Na2SiO3) 2.5, alkaline liquid to fly ash ratio 0.35, 0.40, 0.45 and 0.50 were used in the present study. The experiment were also conducted on GPC cubes for curing temperature of 75° C, 90° C and 105° C with curing period of 12, 18 and 24 hours by adoptin g hot oven curing method. The test result indicated that the compressive strength increases with increase in molarity of NaOH but it decreases with increases in water content. It is also absorbed that compressive strength is remarkably affected by the curi ng hours and curing temperature. When curing temperature is increases, the compressive strength is also increases and it requires less curing period to gain the higher strength. 1.INTRODUCTION 1.1 General Production of cement is one of the major contr ibutors to the emission of green -house gasses like carbon dioxide. Day by day the World’s Portland cement production increases with the increasing demand of construction industry. Cement is the main ingredient for the production of concrete. But the produc tion of cement requires large amount of raw material. During the production of cement burning of lime stone take place which results in emission of carbon dioxide (CO2) gas into the atmosphere. There are two different sources of CO2 emission during cement production. Combustion of fossil fuels to operate the rotary kiln is the largest source and other one is the chemical process of burning limestone. In 1995 the production of cement was 1.5 billion tons which goes on increasing up to 2.2 billion tons in 201 0. One ton of production of cement causes one ton of emission of CO2 into the atmosphere. It is e stimated that the emission of carbon dioxide due to cement production to be nearly about 7% of the total production of carbon dioxide, which make required to g o for other greener alternative binder from Portland cement [1 ]. Fly ash is the waste residue that results from the combustion of coal in thermal power station is available at large scale all over the world. In India more than 100 million tons of fly as h is produced annually. Out of this, only 17 – 20% is utilized either in concrete or in stabilization of soil. Most of the fly ash is disposed off as a waste material that coves several hectors of valuable land. As fly ash is light in weight and easily fli es, this creates severe health problems like asthma, bronchitis, and so forth. There are environmental benefits in reducing the use of Portland cement in concrete, and using a by -product material, such as fly ash as a substitute. With silicon and aluminium as the main constituents, fly ash has great potential as a cement replacing material in concrete. For every ton of fly ash used in place of Portland cement saves about a ton of carbon dioxide emission to the atmosphere [2 ]. Davidovits proposed a new term geopolymer in 1978 to represent the mineral polymers resulting from geochemistry. Geopolymers are members of the family of inorganic polymers in which the mineral molecules ar e linked with covalent bond. Geopolymers are produced by source materials or by -product of geological origin that is rich in silica and alumina like fly -ash when react with alkaline solution at elevated temperature. The chemical reaction that takes place in this case is polymerization, so this binder is called geopolymer. Geopolymer concr ete is a new type of concrete in which cement is fully replaced by the pozzolanic materials that is rich in Silicon (Si) and Aluminium (Al) like fly ash. It is activated by highly alkaline liquids to produce the binder which binds the aggregates in concrete when subjected to elevated temperature. The Inte rnational Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 0 4 Issue: 0 5 | May -201 7 www.irjet.net p-ISSN: 2395 -0072 © 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 1307 concrete made with such industrial waste is eco -friendly and so it is called as “Green concrete”. The chemical composition of the geopolyme r material is similar to zeolitic materials, but t he microstructu re is irregular. The polymerization process involves a fast chemical reaction under alkaline condition on Si -Al minerals, those results in a three -dimensional polymeric chai n and ring structure existing of Si -O-Al-O bonds. Poly (sialates) as the resulted m aterial has the empirical formula as below: Mn [ -(SiO2)z -AlO2]n. wH2O Where: M = the alkaline element or cation such as potassium, sodium or calcium n = the degree of polycondensation or polymerisation z = 1,2,3 or higher The main concept behind this geopolymer material is the polymerization of the Si -O-Al-O bond which develops when Al-Si source materials like Fly ash is mixed with alkaline liquids . The geopolymer can be one of these basic form:  Poly (sialate), [-Si-O-Al-O-]  Poly (sialate -siloxo), [-Si-O-Al-O-Si-O-]  Poly (sialate -disiloxo), [-Si-O-Al-O-Si-O-Si-O-] The schematic formation of geopolymer mat erial can be shown by equations (1) and (2). n( Si2O5, Al2O2 ) + 2nSiO2 + 4nH2O +NaOH/KOH (Si-Al materials) | | Na+, K+ + n(OH)3 -Si-O-Al--O-Si-(OH | (OH)2 (Geopolymer precursor) ---------------------- n(OH)3 -Si-O-Al--O-Si-(OH)3 + NaOH/KOH | | (OH)2 | ( Na+, K+) -(-Si-O-Al--O-Si-O-) + 4nH2O | | | O O O ( Geopolymer Backbone) ----------------------- The exact mechanism of setting and hardening of the geopolymer material is not clear. However, most proposed mechanism consists the chemical reaction may comprise the following steps: 1. Dissolution of Si and Al atoms from the source material through the action of hydroxide ions. 2. Transportation or orientation or condensation of precurso r ions into monomers. 3. Setting or polymerisation of monome rs into polymeric structures [3 ]. Water is released during the chemical reaction that occurs in the formation of ge opolymers. This water, released from the geopolymer concrete during the rest per iod, oven curing and further drying periods, leaves behind dis continuous nano -pores in the concrete , which provide benefits t o the performance of geopolymer concrete . The water in a geopolymer mixture, plays no role in the chemical react ion that takes plac e; it provides the workability to the mixture during handling [ 4] 1.2 Constituents of Geopolymer Concrete There are two main constituents of Geopolymers, namely the source mate rials and the alkaline liquids. By -product materials such as fly ash, silica fume, slag, r ice husk ash, GGBS, red mud, etc can be used as source materials. The most common alkaline liquid used in g eopolymer concrete is a combination of sodium hydroxide or potassium hydroxide and sodium silicate or potassium silicate. It is importa nt that the alkali ne liquid is prepared by mixing both the solutions together at l east 24 hours prior to use. The mass of N aOH solids in a solution depend on the molarity of the solutio n. 1.3 Advantages of Geo -Polymer Concrete  High early compressive strengt h gain  Good abrasion resistance  Rapid controllable setting and hardening  Fire r esistance up to 1000 degree centigrade and no emission of toxic fumes when heated  High level of resistance to a range of different acids and salt solutions  Low thermal cond uctivity and low shrinkage  Impermeable like normal OPC concrete  Bleed free  High surface definition that replicates mould patterns . 1.4 Objective of the Present S tudy To study the effect of factors like Molarity, alkaline liquid to fly ash ratio, curing hour and curing temperature that affects the compressive strength of fly ash based geopolymer concrete. Inte rnational Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 0 4 Issue: 0 5 | May -201 7 www.irjet.net p-ISSN: 2395 -0072 © 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 1308 2 EXPERIMENTAL PROGRAMME 2.1 Materials Used A. Fly A sh In this study, fly ash (ASTM Class F) obtained from Rosa Thermal Power Station Shahajahanpur was used. The chemical and physical properties of fly ash shown below in table 2.1 and 2.2 respectively. Table -1: Chemical Properties of Fly Ash Characteristics Observed Value (%) Range Specified for Class - F Fly ash (as per ASTM C -618) Silicon dioxide (SiO2) 56.31 46-60 Alumina (Al2O3) 31.82 21-28 Iron oxide (Fe2O3) 4.77 5-9 Calcium oxide (CaO) 2.33 0.5-8 Magnesium Oxide (MgO) 1.09 0.2-4 Sulphur trioxide (SO3) 0.16 0-0.4 Sodium oxide (Na2O) 0.042 0-0.3 Potassium oxide (K2O) 0.013 0-0.2 Titanium (TiO2) 2.01 1-2.1 Table -2: Physical Properties of Fly A sh Characteristics Observed Value Specific Gravity 2.18 Fineness(m2/kg) 340 Lime reactivity(N/mm2) 4.8 Loss on Ignition(% by mass) 0.70 Soundness by auto -cleave method 0.12 B. Alkaline S olution The combination of sodium silicate to sodium hydroxide was used as alkaline solution in the present study and the ratio of both was maintained to 2.5 throughout the study. The solution was prepared one day prior to be used. I. Sodium H ydroxide Generally N aOH is available in market in pellets or flakes form with 96% to 98% purity where the cost of the product depends on the purity of the material. S odium hydroxide in pellet form was used in this work of 97% purity. The solution of NaOH was formed by dissolv ing it in deionised water for the molarity of 12M, 14M, 16M & 18M. The NaOH solution was prepared 24 hours before casting of specimens. II. Sodium S ilicate Sodium Silicate ( Na2SiO3 ) is also known as waterglass which is available in the market in gel form and also in the solid form. Sodium silicate in gel form was used in this study having 31% of SiO2, 14% of Na2O & 55% of H2O. The ratio of silicon dioxide ( SiO2) and sodium oxide (Na2O) in sodium silicate gel is 2.21. Fig.-1: Sodium Hydroxide Fig.-2: Sodium Silicate Liquid Pellets 2.2 Mix Proportioning Details The geopolymer concrete was made for sixteen different mix proportion of fly ash, alkaline solution, fine aggregate and coarse aggregate with variation in alkaline liquid to f ly ash ratio as 0.35, 0.40, 0.45 & 0.50 for mo larities of 12M, 14M, 16M, &18M. Table -3: Mix details of fly ash based geopolymer Concerte S.No. Alkaline sol./Fly ash ratio Fly ash (Kg/m3) Fine aggregate (Kg/m3) Mix-1 Mix-2 Mix-3 Mix-4 0.35 566 Mix-5 Mix-6 Mix-7 Mix-8 0.40 556 Inte rnational Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 0 4 Issue: 0 5 | May -201 7 www.irjet.net p-ISSN: 2395 -0072 © 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 1309 Mix-9 Mix-10 Mix-11 Mix-12 0.45 546 Mix-13 Mix-14 Mix-15 Mix-16 0.50 536 Coarse aggregate (Kg/m3) Sodium hydroxide (Kg/m3) Sodium silicate (Kg/m3) Molarity (M) 58 145 12 16 1032 165.71 12 16 1013 186.43 12 16 994 207.14 12 16 2.3 Mixing Casting and Curing of Geopolymer Concrete In the laboratory, the fly ash and the aggregates was first mixed together in dry state 2 -4 minutes to get hom ogeneou s mix. The alkaline solution was mixed with the extra water and t his liquid components were added to the mixed aggregate and the mixing continued usually for another 12 - 15 minutes so that binding paste covered all the aggregates and mixture become homogeneous and uniform in colour. The fresh concrete could be handled up to 120 minutes without any sign of setting and without any degradation in the compressive strength. After the mixing is done, the fresh geopolymer concrete was filled in the moulds in three layers with required compaction same as the usual methods used in the case of Portland cement concrete and the specimens are kept on a vibrating table so that to minimize amount of voids present in the fresh concrete . The workability of the fresh concrete was measured by means of the conventional slump test. For the polymerisation process, the high temperature curing is required in geopolymer concrete . The required temperature may be provided either by oven curing or by steam curing. In t he presen t study, oven curing was used. The GPC cubes were placed in an oven for the period of 12, 18 and 24 hours. After the curing period, the test specimens were l eft in the moulds for at least 5 -6 hours in order to avoid a major change in the environmental cond itions. After de-moulding, the concrete specimens were allowed to become air -dry in the laboratory until the day of the compressive strength testing. Fig.-4: Addition of Alkaline Solution Fig.-5: Fresh Geopolymer Concrete Fig.-6: Oven Curing of GPC Cubes Inte rnational Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 0 4 Issue: 0 5 | May -201 7 www.irjet.net p-ISSN: 2395 -0072 © 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 1310 2.4 Testing of Geopolymer Concrete C ubes The geopolymer hardened concrete cubes were tested for compressive strength. The compressive strength test was performed according to IS -5160: 1959. Cube specimens of size 150mm × 150mm× 150mm were pre pared for each mix. After one day of rest period, they were cured in oven for 12, 18 & 24 hours and were demoded and stored until the day of testing. For specimens with uneven surfaces, capping was used to minimize the effect of stress concentration. The compressive strength reported is the average of three results obtained from three identical cubes. Fig.-7: Compressive Strength Testing of GPC Cubes 3 . EXPERIMENTAL RESULTS AND DISCUSSION 3.1 Effect of Molarity and AL (Alkaline Liquid)/Fly -Ash Ratio on the Compressive Strength of GPC Table -4: Compressive Strength of Alkaline solution to fly ash ratio=0.35 Mix No. Molarity (M) Compressive Strength (MPa) @ 7 days Average comp. Strength (MPa) Mix -1 Mix-2 Mix-3 Mix-4 12 26.60 26.30 24.90 14 29.70 31.2 32.90 16 35.60 34.8 32.70 18 31.70 33.9 35.90 34.10 Chart -1: Effect of molarity on compressive strength of geopolymer concrete for AL/Fly -ash ra tio 0.35 Table -5: Compressive strength for Alkaline solution to fly ash ratio=0.40 Mix No. Molarity (M) Compressive strength (MPa) @ 7 days Average comp. Strength (MPa) Mix-5 Mix-6 Mix-7 Mix-8 12 34.8 32.1 33.2 14 36.4 36.7 34.6 16 41.8 40.3 38.4 18 37.9 40.8 42.9 Chart -2: Effect of molarity on compressive strength of geopolymer concrete for AL/Fly -Ash ratio 0.40 Inte rnational Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 0 4 Issue: 0 5 | May -201 7 www.irjet.net p-ISSN: 2395 -0072 © 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 1311 Table -6: Compressive stre ngth for Alkaline liquid to fly ash ratio=0.45 Table -7: Compressive strength for Alkaline liquid to fly - ash ratio=0.50 Mix No. Molarity (M) Compressive Strength (MPa) @ 7 days Average comp. Strength (MPa) Mix-9 Mix-10 Mix-11 Mix-12 12 36.2 36.8 39.2 14 42.5 40.4 38.2 16 44.4 43.5 43.2 18 43.4 42.9 Chart -3: Effect of molarity on compressive strength of geopolymer concrete for AL/Fly -ash ratio 0.45 Cha rt-4: Effect of molarity on compressive strength of geopolymer concrete for AL/Fly -ash ratio 0.50 The results indicated that the compressive strength increases with increase in molarity of NaOH solution upto 16M but beyond the molarity 16M, slightly var iation in compressive strength is observed for the molarity 18M. Results also show that the compressive strength is increases with increment in alkaline liquid to fly ash ratio but for ratio value beyond 0.45, slightly decrease in compressive strength is o bserved. It means w hen this ratio is increases, the water content in the solution is increases which affect the compressive strength. 3.2 Effect of Curing Hour and Curing Temperature on Compressive Strength of GPC Table -8: Compressive strength of GPC spe cimens at curing temperature of 75°C Mix No. Curing Tempe - rature (°C) Curing Period (hours ) Compressiv e Strength (MPa) Mean Compressiv e Strength (MPa Mix -11 12 26.9 27.8 27.5 18 34.6 34 35.4 24 37.2 37.4 35.1 Mix No. Molarity (M) Compressive Strength (MPa) @ 7 days Average comp. Strength (MPa) Mix-13 Mix-14 Mix-15 Mix-16 12 33.4 33.4 31.9 14 37.9 37.0 35.2 16 39.2 39.7 41.1 18 37.6 38.9 40.1 Inte rnational Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 0 4 Issue: 0 5 | May -201 7 www.irjet.net p-ISSN: 2395 -0072 © 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 1312 Chart -5: Effect of curing hours on compressive strength of GPC for temperature 75°C Table -9: Compressive strength of GPC specimens at curing temperature of 90°C Mix No. Curing Tempe - rature (°C) Curing Period (hours) Compressive Strength (MPa) Mean Compressive Strength (MPa) Mix-90 12 38.1 38.4 36.7 18 42.2 42 43.7 24 44.4 43.5 42.9 Chart -6: Effect of curing hours on compressive strength of GPC for temperature 90°C Table -10: Compressive strength of GPC specimens at curing temperature of 105°C Mix No. Curing Tempe - Raptur e (°C) Curing Period (hours ) Compressiv e Strength (MPa) Mean Compressiv e Strength (MPa) Mix -11 12 43.9 42.9 44.7 18 40.7 41.2 40.9 24 37.9 38.7 38.1 Chart -7: Effect of curing hours on compressive strengt h of GPC for temperature 105°C The compressive strength of GPC concrete is observed to increases at curing temperatures 75°C and 90°C for 12, 18 and 24 hr of curing period, but when curing is done at 105°C, compressive strength increasing up to 12 hr of curing, after that it start decreasing. Hence it is observed that when curing temperature is increa sed, it requires less curing hours to gain same compressive strength. 3. CONCLUSIONS Based on the experimental work reported in this study, the following conclusions are drawn: 1. Compressive strength of geopolymer concrete is increases with increase in al kaline solution to fly ash ratio upto 0.45, but at 0.50 the strength slightly decreases because of increase in water content present in alkaline solution. Inte rnational Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 0 4 Issue: 0 5 | May -201 7 www.irjet.net p-ISSN: 2395 -0072 © 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 1313 2. Compressive strength of GPC is also increases with increase in concentration of NaOH up to 16 M, b ut for 18 M, there is no remarkable changes in compressive strength but the cost of production is increases. 3. At 75 °C temperature , the compressive strength increases gradually with the increases in curing period up to 24 hr. 4. At 90°C temperature, the sample s gained 95 % strength at 18 hours of curing, beyond this curing period, minor increment in strength is recorded. 5. Compressive strength of GPC samples at 105°C temperature certain increases up to 12 hours of curing period but it decreases when it cured for 24 hr at 105°C. It has been observed from the above discussion that there are various parameters that affect s the compressive strength of the geopolymer concrete. Therefore, parametric study of variou s factors influncing the compressive strength of the ge opolymer concrete is strongly recommended first before conducting any further investigations related to mechanical properties and durability of the geopolymer concrete in order to get the desirable benefits from the further investigations. ACKNOWLEDGEMENT Author thanks to Asst. 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