bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Modelling of Corroded RC Columns Repaired with High Performance Fiber Reinforced Concrete Jacket
Authors: di Carlo Fabio , Meda Alberto , Rinaldi Zila
Published: September 2016

Reinforcement corrosion can lead to a severe damage in reinforced concrete columns with subsequent loss of bearing capacity. This condition can be deleterious in case of a seismic event. The possibility of repairing and strengthening damaged columns with high performance fiber reinforced concrete (HPFRC) jacketing has been experimentally investigated by some of the authors in previous papers, through full-scale tests on specimens under cyclic loads. The main aim of the intervention was not only to restore the original bearing capacity but also to increase the column durability. In the present paper, a numerical model is developed with the FEM software Diana in order to simulate the cyclic behaviour of corroded r.c. columns reinforced with HPFRC. Particular attention is devoted to the simulation of the corrosion phenomenon and to the strain localization due to the jacket presence. The chemical attack is defined in such a way to account for both the geometrical and mechanical variations of the bar properties. The numerical analyses represent a very useful tool for highlighting the main parameters that have to be considered in evaluating the behaviour of the damaged and then repaired elements. Finally, they constitute a support for the design and, as a consequence, for the reinforcement optimization.
Strengthening of a Bridge Pier with HPC: Modeling of Restrained Shrinkage Cracking
Authors: Reggia Adriano , Sgobba Sara , Macobatti Fabio , Zanotti Cristina , Minelli Fausto , Plizzari Giovanni A.
Published: September 2016

After more than fifty years from the opening of the largely discussed “Autostrada del Sole” Highway in 1964, the infrastructure system in Italy appears marked by the passing of time, similarly to what observed in several other countries worldwide. The great heterogeneity of the Italian landscape has determined a great variety of construction types, such as large span concrete bridges over the northern rivers and large arch concrete bridges over the valleys of the central region. Increment of vehicle traffic and new seismic regulations are setting new requirements to adapt the existing infrastructure, which should be otherwise replaced. Moreover, reinforced concrete (RC) aging and deterioration have led to structural and material degradation, including severe cracking and corrosion. Specialized materials such as High Performance Concrete (HPC) could represent a viable convenient solution for repairing, strengthening and retrofitting of RC structures as both structural capacity and durability can be refurbished. However, alongside high mechanical performance, HPC is characterized by a high cracking sensitivity at very early age, due to its high stiffness and shrinkage. Restrained shrinkage cracking, particularly significant in repaired structures where the existing concrete generates a considerable restraint against the free movement of the repair material, may represent a limit to the effective application of these materials. For this reason, shrinkage compatibility of HPC with the existing concrete substrate needs to be experimentally and numerically assessed. A study is herein presented where, based on experimental tests, different numerical models are developed and compared to assess and eventually minimize the risk of shrinkage cracking in bridge piers strengthened with HPC.
Assessing Viscoelastic Properties of Concrete during its Early Ages through Forced Dynamic Excitation of Test Beams
Authors: Granja José Luís , Azenha Miguel
Published: September 2016

This paper aims to demonstrate the feasibility of a recently proposed approach (termed VisCoDyn) to assess the viscoelastic behaviour of concrete from the earliest ages, by introducing a known dynamic excitation to a simply supported specimen. The method involves the continuous monitoring of the response of the tested sample in terms of amplitude (force and displacement), as well as the evaluation of the phase lag between the applied force and the response. The acquired data is then used to calculate the storage and loss moduli, according to procedures that are normally used in the context of material testing in polymer science. Indeed, the loss modulus is known to be relatable to the viscoelastic properties of materials.The paper presents the current state of development of the VisCoDyn test methodology together with several test results obtain in specimens that were tested during the first 24 hours of curing. Parallel testing with other techniques is also presented for reference.
Passive Behaviour of New Alloy Corrosion Resistant Steel Cr10Mo1 in Simulating Concrete Pore Solutions with Different Chloride Contents
Authors: Ai Zhi Yong , Jiang Jin Yang , Wei Sun , Ma Han , Zhang Jian Chun , Song Dan
Published: September 2016

This work aims at studying the passive behaviour of new alloy corrosion resistant steel Cr10Mo1 and plain carbon steel (as a reference), in simulating concrete pore solutions contaminated with different concentrations of chloride (0 M, 0.2 M, 0.6 M and 1.0 M, as NaCl). The electrochemical behaviour was evaluated by linear polarization resistance, d.c. potentiodynamic polarization and electrochemical impedance spectroscopy. The surface films composition was investigated by X-ray photoelectron spectroscopy (XPS). The results show that the passivity of the corrosion-resistant steel has no significant decline with chloride contents increasing, while carbon steel hardly passivates with chloride above 0.6 M. The primary constituents of the passive films formed on the corrosion-resistant steel and carbon steel are very different; the former contains both Cr and Fe oxides while the letter consists of only Fe species. Cr oxides, as the key components for the passive film on the corrosion-resistant steel, can still remain stable and protective under high concentration of chloride, which supports the excellent passive performances of the corrosion-resistant steel in severe conditions.
Molecular Dynamics Study of the Interaction of C-S-H and Chloride Ions
Authors: Zhou Yang , Xu Guo Dong
Published: September 2016

Molecular Dynamics was employed to investigate the interaction of calcium silicate hydrate (C-S-H), the primary hydration product of cement based materials, and chloride, causing severe durable problems of concrete. The 11Å tobermorite structure was chosen to describe the C-S-H structure and the CLAYFF force field was used. It is observed in the simulation that there are no bound chlorides at 303K, while a fraction of chlorides appear in the adsorption district of tobermorite/solution interface at 323K indicating the temperature increase can improve chloride sorption capacity of C-S-H. The formation of Ca-Cl cluster is found on the surface of tobermorite, which is assumed to promote the chloride sorption. The experimental results of sorption isotherms of C-S-H in CaCl2 and NaCl aqueous solutions with the same chloride concentration have proved this point. Other researchers have made the same conclusion by means of molecular dynamics modeling, NMR tests or zeta potential experiments.
Drying of Recycled Aggregate Concrete: Plastic Shrinkage, Cracking Sensitivity, and Durability
Authors: Bendimerad Ahmed Zakarya , Roziere Emmanuel , Loukili Ahmed
Published: September 2016

This paper presents the results of experimental research on recycled concrete at early age and long term. It consists in studying the effect of initial water saturation of recycled concrete gravel (RG). Five mixtures were investigated, one mixture with natural aggregates only (reference concrete) and the second with 100% of RG using four initial water saturations: 30%, 70%, 100% and 120% of saturated surface dried (SSD) state. A stress/strength approach was used to quantify the risk of cracking at early age. It is based on experimentally assessed parameters. At long term the effect of initial water saturation on the ultimate drying shrinkage was investigated. The drying shrinkage was correlated with drying depth and the natural carbonation was also studied. At early age the results indicate RG affected the properties of the recycled concrete. However, the concrete with oversaturated RG showed a behavior close to reference concrete in terms of cracking sensitivity. At long term, the drying shrinkage is weakly depending of initial water saturation, but the durability of concrete can be affected by the drying depth. A good correlation between compressive strength at one day and the carbonation depth at 18 months was observed
Methodology for Analysis of the Reactivity of Coal Fly Ash Using Selective Dissolution by Hydrofluoric Acid
Authors: Reis Rui , Ribeiro M.J.P. , Abrantes João Carlos de Castro , Camões Aires , Teixeira Elisabete , Malheiro Raphaele
Published: September 2016

The use of some additions as cement replacement has played an important role in the amount of clinker reduction. Due to its huge worldwide availability one of the most important and recognised replace agent is the fly ash, but is also estimated that only 30 to 40% of fly ash is used, although there are some challenges to be overcome, such as the reactive potential quantification. Chemical analysis is typically determined by the oxides content and does not take into account the vitreous and crystalline phase ratio. Therefore, this paper describes in detail one selective dissolution method, based in the hydrofluoric acid attack, to the quantification of the vitreous phase (reactive) and crystalline phases (not reactive). Fly ash from Portuguese Pego thermoelectric power plant was submitted to different attacks. To confirm the method and its effects, chemical and physical analysis were performed, such as STA, XRF, XRD with Rietveld refinement, SEM, EDS and laser diffraction granulometry. The results can be used to quantify the potential reactivity of this type of fly ash. The best results were achieved with 1% hydrofluoric acid attack during 6 hours.
A Mesoscale Three-Dimensional Moisture Transport Model in Concrete
Authors: Zhou Cheng Zong , Gu Xiang Lin , Huang Qing Hua , Jin Xian Yu
Published: September 2016

Concrete was considered as a three-component composite material consisting of mortar matrix, coarse aggregates and interfacial transition zones (ITZ) at the mesoscale level. Based on the random accumulation model of spherical aggregates, a mesoscale geometric model was developed after discretizing the mortar matrix and ITZ into mesh elements using Voronoi diagram method. Combined with the third boundary condition, a mesoscale three-dimensional model to simulate the moisture transport process in concrete exposed to atmosphere environment was then developed using finite difference numerical method, where the transport of liquid water and water vapor were considered as permeation and diffusion respectively. Moreover, the model was verified and then applied to investigate the influence of ITZ on the distribution of relative humidity in concrete. The results indicated that the moisture transport process was overall accelerated since blocking effect of coarse aggregates was partially counteracted by the existence of ITZ.
Autogenous Shrinkage in High Performance Concrete with Chemical Admixtures
Authors: Canul-Polanco Jennifer Anette , Durán-Herrera Alejandro , Valdez-Tamez Pedro
Published: September 2016

Durability in High Performance Concrete have resulted in the development of admixtures to mitigate several concrete deterioration mechanisms. Due to the low water/binder, HPC enables autogenous shrinkage that could lead to cracks at early ages. Superabsorbent polymers, shrinkage reducing admixtures and corrosion inhibitor based on calcium nitrite were used in HPC with silica fume to evaluate autogenous shrinkage. SAP was added with an amount of intenal curing water determined by the modification proposed by Jensen to the Power’s Model. Results showed that admixtures could improve or aggravate autogenous shrinkage.
High Stiffness Concrete for Tall Buildings under Severe Conditions: Mix Design and Structural Member Test
Authors: Fan Tian Yuan , Li Zongjin
Published: September 2016

A new type of concrete, which contains volcanic aggregate and well-graded river sand, having both high strength and ultra-high modulus of elasticity has been developed for tall buildings under severe conditions, and its properties were characterized. The structural deformation of high-rise buildings can be substantially reduced by using this type of concrete, thereby decreasing the cross-section area of the structural members and increasing the economic benefits, not to mention alleviating shrinkage and creep problems of concrete. Uniaxial compression test, static elastic modulus test and scanning electron microscope test were conducted to characterize the properties of concrete specimens with different mix proportions. The experimental results showed that volcanic rock as coarse aggregate, well-graded river sand as fine aggregate, sand ratio around 43%, silica fume content about 10% as well as some mineral admixtures such as metakaolin and nanosilica led to higher modulus of elasticity of concrete. A particular type of concrete with the compressive strength of 146 MPa and modulus of elasticity of 53.5 GPa was developed, which is much stiffer than normal concrete in the code of practice. Four concrete mixtures including C45, C80, high modulus and ultra-high modulus concrete were applied in producing structural members, verifying the advantages of utilization of high stiffness concrete.
Material Properties of Ultra - High Performance Concrete in Extreme Conditions
Authors: Citek David , Rydval Milan , Rehacek Stanislav , Kolisko Jiří
Published: September 2016

The Ultra High Performance Concrete (UHPC) is a very promising material suitable for application in special structures. However, the knowledge of performance of this relatively new material is rather limited. The exceptional mechanical properties of UHPC allow for a modification of the design rules, which are applicable in ordinary or high strength concrete. This paper deals in more detail with impact of thermal stress on bond properties between prestressing strands and UHPC and an influence of high temperature to final material properties of different UHPC mixtures. Specimens in the first experimental part were subjected to the cycling freeze-thaw testing. The relationship between bond behavior of both type of material (UHPC and ordinary concrete) and effect of cycling freeze-thaw tests was investigated. The second part of experimental work was focused on mechanical properties of UHPC exposure to the high temperature (Tmax = 200°C to Tmax = 1000°C). Tested mechanical properties were compressive and flexural strengths, the fracture properties will be presented in the next paper. The obtained experimental data serve as a basis for further systematic experimental verification and more accurate information about the significantly higher material properties of UHP(FR)C and its behavior in extreme conditions.
The Influence of Steel Fibers on the Dynamic Response of Self-Compacting Concrete
Authors: Pająk Małgorzata , Kühn Tino
Published: September 2016

Concrete subjected to high strain rates behaves notably differently in comparison to quasi-static conditions, which can be affected by the addition of steel fibers. The influence of steel fibers on the dynamic compressive behavior of self-compacting concrete (SCC) was studied experimentally using Split Hopkinson Pressure Bar (SHPB) tests. The investigations were performed in a range of quasi-static rates up to dynamic strain rates of 462 1/s. The effect of steel fibers on the stress-strain diagram, dynamic increase factor (DIF) and failure pattern of SCC conducted under high strain rates was analyzed. The experimental results presented in this paper and the ones from recent works of other authors indicate that application of steel fibers reduces the strain-rate sensitivity of different concretes and has a beneficial effect on the specimen failure pattern. Moreover, the conducted SHPB tests show an important role of fibers in reduction of the strain rates reached in the specimen under the same pressure level in comparison to plain concrete specimens.
Durability of Lightweight Slurries for Oilwell Cementing
Authors: Balthar Vivian Karla Castelo Branco Louback Machado , Toledo Filho Romildo Dias , de Moraes Rego Fairbairn Eduardo , de Miranda Cristiane Richard
Published: September 2016

In a deepwater environment, unconsolidated formations at seabed and naturally fractured carbonates at reservoir zones with high permeability are commonly found. In this context, the use of lightweight slurries is necessary to effectively cementing these formations, in order to mitigate slurry losses to the formations and to prevent their fracture. This work investigates the mechanical properties and durability of high performance lightweight slurries to be used in this environment. The mixtures were formulated within the framework of the Compressible Packing Model and were extended using hollow ceramic or glass microspheres. Tests were carried out to determine the slurries apparent density, rheology, free fluid, sedimentation, fluid loss, resistance to acid attack, sorptivity and total water absorption. A mechanical characterization was performed by uniaxial and triaxial compression and splitting tensile strength tests and were correlated with the durability tests. The reference slurry, extended with bentonite, presented a 1.46 g/cm3 density and compressive strength of 3 MPa (cure at 27oC/ 2.7 days). The slurries containing glass and ceramic microspheres were slightly lighter and presented a higher mechanical performance as compared to ordinary slurry. Besides, these mixtures presented a higher resistance to acid attacks and lower sorptivity, especially the lightweight slurry containing ceramic microspheres.
Bond Properties in Lightweight Self-Compacting Concrete
Authors: Muciaccia Giovanni , Rosati Gianpaolo
Published: September 2016

The original development and use of Self-Compacting Concrete (SCC) in Japan started from the problem of the durability of concrete. Indeed, the reduction in the number of skilled workers, and the consequent poor compaction of structures, was a topic of great concern in the eighties, and helped the introduction of SCC.
More recently, SCC is being commonly used in solid concrete slab in residential buildings for its excellent flowability. Additionally, to reduce structural self-weight without excessively affecting the slab thickness (which could represent a major issue in this applications), lightweight concrete represents a preferable solution. In this type of structure the development of anchorage or lap length becomes crucial, thus requiring a proper understanding of the bond mechanism.
The result of an experimental campaign to assess bond properties for Lightweight Self-Compacting Concrete (LWSCC) are presented in this paper. The main investigated parameter is the bar size (ranging from 8 to 24mm) while the cover to diameter ratio and the bonded length to diameter ratio were kept constant. The experimental results are finally compared with code predictions.
Effect of Multi-Walled Carbon Nanotubes on Mechanical Properties and Durability of Latex-Modified Cement Mortar
Authors: Meng Ling Shi , Leung Christopher K.Y. , Li Geng Ying
Published: September 2016

This paper studies the effects of multi-walled carbon nanotubes (MWCNTs) on the mechanical properties and durability of polymer latex-modified cement mortar. Latex-modified cementitious materials possess many advantages. However, reduction of mechanical properties due to the introduction of an amorphous structure within the cement composite has limited its application. In this study, multi-walled carbon nanotubes functionalised with carboxyl group (MWCNTs-COOH), ranging from 0% to 0.15% by weight, are added into mortar modified with 0.6 wt.% polyvinyl alcohol (PVA) latex. Mechanical properties including compressive strength and flexural strength are measured. Water absorption test and rapid chloride diffusion test are performed to assess durability performance. Results indicate considerable increase of compressive strength and flexural strength, as well as improvement in durability, by the addition of MWCNTs-COOH. With Scanning Electron Microscopy conducted on both the latex solution and cement composite, the microstructural changes resulted from MWCNT addition are revealed.
Influence of Nanoclay on Concrete Subjected to Freeze-Thaw Cycles and Bond Behavior between Rebar and Concrete
Authors: Fan Ying Fang , Zhang Shi Yi , Shah Surendra P.
Published: September 2016

This paper explores the effects of nanokaolinite clay (NKC) on the behavior of cement-based materials concrete. The resistance of NKC modified cement-based materials to freezing-thaw cycles and the corrosion processes of rebar embedded in the concrete were investigated. Ordinary Portland cement was partially substituted with NKC in ratios of 0%, 1%, 3%, and 5% by weight. The Rapid Freeze-Thaw Cabinet was used to measure the resistance of ordinary Portland cement concrete and concrete with clay to deterioration caused by repeated cycles of freezing and thawing, compressive strength were measured at regular intervals. The corrosion conditions of the rebar embedded in the concrete were studied by an electrochemical accelerated penetration system, pullout tests were performed to assess the bond properties including bond-slip curve, ultimate bond strength between concrete and rebar before and after corrosion. It is revealed that the introduction of NKC improves the freeze-thaw resistivity values and bond behavior in the concrete specimens compared to the control concrete; the corrosion of the rebar embedded in the concrete is impeded efficiently.
Effects of Water-Cement Ratio on Concrete Sulfate Corrosion Rate
Authors: Du Jian Min , Han Xiao Li , Li Zai Ting , Li Guo , Ji Yong Sheng
Published: September 2016

Water-cement (w/c) ratio is an important parameter in concrete mix ratio design, which also plays an important influence on concrete sulfate corrosion rate. In this paper, concrete cubic specimens with w/c of ratio as 0.4, 0.5 and 0.6 were fabricated, respectively, and put into 10% Na2SO4 solution and tap water for 240 days. During the submerging process, superficial corrosion phenomena were observed and concrete cubic strengths were measured periodically. The results showed that the lower the w/c ratio, the stronger the concrete sulfate corrosion resistance is. At the same time, concrete with lower w/c ratio always correspond smaller corrosion layer thickness. Based on the degradation of cubic compressive strength of corroded concrete specimens, the development models of corrosion thickness of each w/c ratio concrete are established as sulfate corrosion goes on
Degradation of Concrete Structures due to External Sulfate Attack
Authors: Cefis Nicola , Comi Claudia
Published: September 2016

In this paper, we focus on the numerical simulation of degradation of concrete structures subject to External Sulfate Attack (ESA). A diffusion-reaction model is used to describe the diffusion of sulfates inside the material and the reaction with the reactive constituents of the cement paste (calcium aluminates). The mechanical analysis is based on a new bi-phase chemo-elastic model with chemical and mechanical damage. The results obtained with the proposed approach are compared with experimental data on a reduced scale tunnel lining structure subject to ESA.
Real Case: Assessing Sulfate Resistance of Coastal Protection Precast Elements
Authors: Aracil Francisco , Dufour Gaetan , Wauters Peter , de Schutter Geert , Torrent Roberto
Published: September 2016

As part of a new harbor development, a new offshore breakwater will be constructed, for which the use of coastal protection plain precast concrete elements (AccropodesTM II) is required. The applicable exposure class is S1 (ACI 318). Over 4'000 elements have been produced. The owner required guarantees on the sulfate resistance of the elements before accepting them for usage in the project. For this, a revision of the documentation available was conducted, complemented by a thorough field investigation, measuring the coefficient of air-permeability kT (Swiss Standard SIA 262/1) of preselected elements (damaged during transportation) and elements representing the 28 weeks of production. The site NDTs confirmed a high quality of the majority of elements that were judged fit for the purpose. However, the NDTs confirmed the questionable quality of those cast during the initial period, requiring further evaluation before acceptance.The paper presents the results of: water aggressiveness, cement chemistry, strength quality control and air-permeability kT, and the criterion used to assess sulfate resistance of the elements.
Resistance of Concrete to Na2SO4 Freeze-Thaw Cycles and Failure Mechanism Analysis
Authors: Li Guo , Du Jian Min , Wu Xiao Suo , Yang Kun
Published: September 2016

Rapid freeze–thaw cycle experiments were carried out on concrete specimens with 0.4, 0.5, and 0.6 water–cement (w/c) ratio in 0% (tap water), 1%, and 5% Na2SO4 solutions, respectively, to study the performance of ordinary concrete resistance to sulfate freeze–thaw cycle. The specimens underwent visual inspection, and mass losses and relative dynamic elastic modulus (RDEM) were measured regularly. Scanning electron microscope observation and X-ray diffraction analysis were conducted on partial specimens after the freeze–thaw cycle experiment. Research results show that due to the coupling effects of freeze–thaw cycle and sulfate corrosion, freeze–thaw cycles of concrete in Na2SO4 solution caused more damages than in tap water. Higher Na2SO4 concentration produced severe damages. Concrete with different w/c ratios exhibit different sulfate freeze–thaw cycle resistances, and concrete with lower w/c ratio usually produces stronger resistance. RDEM loss is considered the control index to determine concrete failure. The corrosion products in Na2SO4 solution freeze–thaw cycle are mainly ettringite and gypsum. With the increase in Na2SO4 concentration, ettringite formation gradually decreases and gypsum formation gradually increases.
Influence of Frost Damage on Chloride Penetration into Concrete
Authors: Zhang Peng , Wittmann Folker H. , Wang Yan Ru , Zhao Tie Jun , Ting Guan
Published: September 2016

In most national and international codes for durability design, service life is estimated after selection of one single and dominant deteriorating process such as carbonation, chloride penetration or frost attack. Application of existing codes has shown, however, that the predicted service life is not reached in practice in most cases. Early damage occurs and as a consequence expensive repair measures become frequently necessary, long before the design service life is reached. One reason for this discrepancy is certainly the fact that in practice each dominant deteriorating process is usually accompanied by other aggravating processes. In this contribution capillary absorption of different types of concrete is studied first. The influence of an increasing number of freeze-thaw cycles on capillary absorption of water is studied first, then chloride penetration before and after exposure to a certain number of freeze-thaw cycles was determined experimentally. It was found that an increasing number of freeze-thaw cycles increases chloride penetration significantly, and hence reduces service life in aggressive environment. It can be concluded that for realistic service life prediction the interaction between frost damage and chloride penetration has to be taken into consideration in regions with low temperatures.
Chloride Distribution Feature in Surface Layer of Cement Paste under Cyclic Drying-Wetting Condition
Authors: Chang Hong Lei , Mu Song , Liu Jian Zhong
Published: September 2016

This research focuses on chloride distribution in the surface layer of cement paste and the relation between chloride distribution and pore structure under two different drying-wetting regimes. The results of chloride profiles obtained by three different methods reveal that it dose exist a feature that chloride content first gose up then down with a maximum value Cmaxappearing in the homogeneous surface layer of cement paste subjected to indoor cyclic dry-wet condition. Besides, the Cmaxincreases with the ratio of water to cement (W/C) increasing. And the regime with higher drying temperature and longer wetting time leads to higher Cmax. Moreover, Cmaxappears at the same location for both total and free chloride. In addition, Cmaxincreases with total porosity, the most probable pore size, and average radius increasing, while it decreases with tortuosity decreasing.
Chloride Proofing Performance and Rebar Corrosion Protection Performance of SHCC Having Bending Cracks
Authors: Kobayashi Koichi , Hara Yuto , Kojima Yuta , Rokugo Keitetsu
Published: September 2016

The chloride penetration depth and the corroded area on rebar were investigated for SHCC test specimens prepared with Portland cement on its own, and with 25% replacement with limestone powder. After being given bending cracks, the specimens were subjected to wetting and drying cycles of chloride solution by a ponding test. It was found that maximum chloride penetration depth was affected by the cover depth and the deformation applied to the test specimen. The corroded area on the rebar was correlated to the number of cracks in the SHCC and the total of the crack widths. For the same number of cracks and total width of the cracks, the corrosion area was greater in the mix with limestone powder.
Lessons Learned from the Treat Island Marine Exposure Site
Authors: Thomas Michael
Published: September 2016

The marine exposure site on Treat Island near Eastport, Maine, was built more than 75 years ago and during this period a wide range of concrete types have been placed on the site. Treat Island represents a very severe exposure condition with the highest tides in the world, salinity typical of the Atlantic Ocean and approximately 100 freeze-thaw cycles per annum. The various research programs that have used this facility have investigated the effects of numerous parameters including fibre-reinforcement, polymer-impregnation, supplementary cementing materials, sulfur concrete, high-alumina cement, ettringite-based rapid-set binders, w/cm and strength, ultra-high-performance concrete, corrosion-resistant reinforcement, impact of load and cracking, “mechanical air-entrainment”, and use of corrosion-inhibiting admixtures. Performance has been evaluated in a number of ways including visual assessment, pulse velocity, dynamic modulus, chloride profiling, and electro-chemical corrosion monitoring. The paper presents an overview of “lessons learned” with detailed information on factors affecting the rate of chloride ingress.
Effects of the Hygrothermal Conditions on the Fracture Energy of the Concrete
Authors: Kallel Hatem , Carré Hélène , La Borderie Christian , Masson Benoît , Tran Nhu Cuong
Published: September 2016

The scenario of a severe accident in the containment building of a nuclear plant results in an increase in pressure, temperature and relative humidity that can reach respectively 5 bars, 140 °C and the saturation of water vapour. As well as the regulatory calculations, accurate knowledge of the thermal and mechanical behaviour of materials and more specifically of concrete is required to carry out more precise numerical simulations.
Our study aims to investigate the mechanical behaviour of concrete under homogeneous conditions of moisture and temperature. An experimental apparatus was designed in order to assess the evolutions of the fracture energy of concrete. Different temperature levels up to a maximum of 110 °C and at different values of the controlled moisture content were investigated. The equipment was used to perform DCT (Disk-shape Compact Tension) tests at 30, 90 and 110 °C. Five levels of degree of liquid water saturation (Sw) were investigated for each temperature level.
Experimental Study on Temperature Response in Damaged Concrete under Atmospheric Environment
Authors: Min Hong Guang , Zhang Wei Ping , Gu Xiang Lin
Published: September 2016

The temperature field in concrete has a significant influence on durability of concrete structures. Meanwhile, there is always damage caused by loads in concrete of a real structure, which affects heat transfer and temperature field. In this paper, the tests on temperature response to heating and cooling as well as moisture transport in concrete with different damage levels were carried out. Five concrete specimens were compressed under uniaxial load to 25%, 40%, 55%, 70% or 85% of the compressive strength, corresponding to different damage levels. One concrete specimen was not subjected to any load, as a comparison specimen. The internal temperature in concrete specimens during heating or cooling process was measured by an embedded humidity and temperature sensor. Thermal conductivity of concrete is the key parameter in denoting the ability of concrete to transfer heat and decreases with the increasing damage level. When the temperature gradient exists in both sides of concrete, the moisture transport will occur in the heat transfer direction. Regardless of heating or cooling process, there is always a hysteresis effect and the temperature response rate changes quickly in the initial stage and decreases gradually with time in damaged concrete. The greater the initial temperature difference is, the greater the initial temperature response rate is. In the same initial temperature difference, the temperature response rate decreases slightly with the increasing damage level, while the moisture transport mass increases evidently.
UHPC and FRC in Severe Environmental Conditions
Authors: Rehacek Stanislav , Simunek Ivo , Citek David , Kolisko Jiří
Published: September 2016

Structure and properties of cement composite are time-varying characteristics, depending among others on environmental conditions. The key idea is a struggle for complex research of joint effect of physical, chemical and dynamic loads on the internal structure [1] of cement composite and understanding the correlation between changes in microstructure and macro-scale properties [2, 3]. During the experimental program, specimens will be exposed to combined influence of freeze-thaw cycles [4,5,6], aggressive chemical agents [7] and dynamic loading [8]. The aim is to create a theoretical basis for design of effective cement composites meant to be used in severe environmental conditions.
Experimental Study on Chloride Diffusion, Strength and Fresh Properties of Ion-Exchange Resin Mixed Grout
Authors: Sanada Osamu , Mutsuyoshi Hiroshi , Yao Luan , Sumida Atsushi
Published: September 2016

In Japan, a number of existing prestressed concrete bridges are suffering chloride attack. Especially in the cases that bridges were constructed decades ago, grouts tending to bleed or swell were often used, and the grouting was not well done. As a result, ducts were not completely filled and voids remained. For the incompletely grouted zones, tendons were vulnerable and more severely corroded. To repair those bridges, effective and economic regrouting materials and method are requisite. Recently, a new repair grout has been developed in the authors’ group by mixing ion-exchange resin, a widely used polymer in water purification, into cement paste. Since IER can absorb chloride ions, IER mixed grout is promising to remove free chloride ions in the unfilled duct. In this study, the chloride ion diffusion properties of IER mixed grout was investigated experimentally. Tendons, which were preliminarily spread at the surface with chloride, were grouted using the IER mixed grout. After curing, the chloride amount in the grout was analyzed using potentiometric titration against silver nitrate. It was confirmed that IER effectively absorbed chloride ions from the surface of tendon, and thus is promising to alleviate the corrosion. Furthermore, to promote the practical use, other properties of the grout, such as strength, flowability and bleeding ratio, were test. It is found that as IER ratio increased strength and flowability tended to decrease but bleeding did not occur. When mix proportion and addition ratio of IER were adopted properly, those properties satisfied the acceptance criterias in design code.
Development of a New Concrete Marine Exposure Site on the Arabian Gulf-East Coast of Saudi Arabia
Authors: Abd El Fattah Ahmed Mohsen
Published: September 2016

A concrete durability site in the Eastern Province of Saudi Arabia that exposes Saudi concrete to harsh marine conditions on the Arabian Gulf and salty air conditions was constructed. The site contains 32 concrete blocks formed from eight different mixtures made with Cement Type I, Cement Type V, Cement Type I with 6% silica Fumes, 25% fly Ash, 70% Ground-granulated blast-furnace slag (GGBFS), Migrate Corrosion Inhibitors (MCI), Calcium Nitrite based inhibitors (CNI) and Caltite. Each mixture formed 4 blocks; 2 were reinforced with black steel and two were plain concrete. The concrete blocks were 1200 mm high, 460 mm wide and 230 mm thick placed vertically. The concrete blocks were placed at three zones to achieve different exposure conditions which are atmospheric, splash or spray zone and tidal zone. Samples will be taken periodically to measure the rate of chloride ingress in each concrete mixture under the different exposure conditions. Embedded steel reinforcement in specimens in atmospheric zone have not recorded corrosion activities at six months of exposure. The steel bars in three zones will be monitored for corrosion activity through linear polarization test. The measured chloride profiles in the exposure site will be compared to the measured concrete transport properties from the companion laboratory specimens. Standard compressive test and bulk diffusion test were conducted for 150x300 mm and 75x150 standard cylinders, respectively. All of the cylinders’ strength exceeded the designed compressive strength of 28 MPa. Whereas for 35 days standard bulk diffusion test, mix contained 100% cement type I had the least chloride concentration, and mix 5 that had 70% GGBFS and 30% cement type I had the highest surface chloride concentration. Overall chloride profiles for all the mixes were within ranges reported in literature. Further tests of chloride binding capacity and bulk diffusion for different intervals will be undertaken.
Mechanical Behavior and Recovery of FRC after High Temperature Exposure
Authors: Akca Abdullah Huzeyfe , Özyurt Nilüfer
Published: September 2016

During fire, one or two faces of structural members experience higher temperatures than other faces and the deterioration on these faces may continue after fire. High temperature exposure above 400 °C causes deterioration in strength, modulus of elasticity and durability of concrete. Inclusion of fibers and air entraining agents in concrete mixes may reduce the destructive effects of high temperatures on concrete. Therefore, 8 groups of 0.45 w/c ratio of concrete were designed by using polypropylene fibers as low melting point fibers and hooked end steel fibers as high melting point fibers and air entraining admixture as a chemical additive. 15 cm cubic concrete specimens were produced and the five sides of the cubes were insulated with gypsum boards to maintain one face heating. An electrical furnace was used to heat concrete to 1000 °C and K-type thermocouples were placed in specimens to monitor temperature distribution in concrete. Moreover, two different re-curing methods, air and water, were applied after heating to see the change in mechanical properties and crack occurrences on the heated surface of concrete specimens. SEM and XRD investigations were conducted on the samples taken from the heated surfaces and the inner parts of the concrete in order to understand the morphological changes due to heating and re-curing. Results showed that deterioration on the surfaces due to high temperature exposure continued during air re-curing process and compressive strength and modulus of elasticity values of these specimens also diminished. On the other hand, compressive strength of water re-cured concrete stayed constant after heating and partial recovery of modulus of elasticity were obtained and the positive effect of water re-curing were observed on polypropylene fiber reinforced concrete prominently.
Fibre Cocktail to Improve Fire Resistance
Authors: Balázs György L. , Czoboly Olivér
Published: September 2016

Favourable experience with fibre reinforced concrete (FRC) resulted in its increasing use worldwide. The properties of fibre reinforced concrete are mostly influenced by the type and the amount of fibres. Our experimental study was directed to the possible improvements of the residual flexural strength and the properties of concrete exposed to high temperatures with different fibre cocktails including steel, micro polymer or cellulose fibres. The influence of type and amount of fibres on residual flexural strength in cold state were tested after 300, 500 or 800 °C temperature loading.
Mechanical Properties and Damage Evolution of Siliceous Concrete Subjected to Elevated Temperatures
Authors: Chu Hong Yan , Jiang Jin Yang , Sun Wei , Zhang Ming Zhong
Published: September 2016

Siliceous concrete (SC) is applied in European Pressurized Water Reactor that is a key component of the third generation nuclear power plant. This paper investigates the mechanical properties and damage evolution of SC (with and without polypropylene fibers) exposed to high temperatures. The mass loss, compressive strength, splitting tensile strength and spalling sensitivity of SC before and after being heated to 200, 400, 600, 800, and 1000 °C are investigated. The ultrasonic testing technique was used to assess the thermal damage, by evaluating the variations of the ultrasonic wave velocity (UWV) for different temperature levels. According to the available literature, a new relationship between damage and UWV was proposed to establish a damage evolution model of SC. The results indicated that: (a) specimens without polypropylene (PP) fibers suffered severe spalling in the range 380-400°C and 470-510°C, while no spalling took place in the specimens with PP fibers in the whole range 25-1000°C; (b) the damage evolution with and without polypropylene fibers was similar, and could adequately be described by means of a Weibull distribution model.
Concrete Fire Testing - A Review of the Thermal Boundary Conditions
Authors: Maluk Cristian
Published: September 2016

Experimental studies of concrete in fire or at elevated temperature have traditionally given relatively little scientific attention to quantifying the severity, and to some extent reproducibility, of the thermal boundary conditions imposed on specimens during testing. This paper examines the heat transfer fundamentals of fire testing when controlling the time-history of temperature inside a furnace (or oven), versus controlling the time-history of incident radiant heat flux at a specimen’s exposed surface. The thermal boundary conditions of a concrete specimen during fire testing are fundamentally based on conservation of energy, and thus typically formulated in terms of heat fluxes. While from the standpoint of concrete fire behaviour the aim is typically only to gauge the distribution of temperatures inside concrete; this is rarely explicitly acknowledged or quantified during concrete fire testing. This shows that continued unexamined use of varied heating techniques presents a serious threat to harmonization of the thermal boundary conditions imposed during concrete testing. The current work proposes adopting test control by in-depth temperature distributions or net heat fluxes for a rigorous comparison of the thermal boundary conditions imposed on test specimens when using different heating techniques.
Mechanical Properties of Oven-Dried Mortar Exposed to High Temperature Considering Different Raw Material
Authors: Rongviriyapanich Onnicha , Sato Yasuhiko , Pansuk Withit
Published: September 2016

Concrete structures can be deteriorated in extreme service conditions especially for fire incidents. For the evaluation of the post-fire performance, analytical methods are very powerful and useful. However, widely applicable mechanical models of fire-damaged material have not yet been proposed. To develop such models, the scale of control volume considering strength, stiffness and deformability is one of important factors. This paper presents an experimental study in which visual observations and mechanical properties of oven-dried mortar after exposed to the fire curves of ISO 834 and ASTM E119 for 90 minutes and to be left to cool down in air were conducted. Mortars were made from two different types of fine aggregate and cement. Experimental results indicate that the raw material made mortar is a prominent factor to introduce the different fire damage characteristics. Meanwhile, the mechanical properties of mortar in fire problem are strongly related to temperature that mortars were experienced to.
Effects of Exposure Term on the Strength and Elasticity of Concrete Subjected to Elevated Temperature up to 175°C
Authors: Matsuzawa Koichi , Kitsutaka Yoshinori , Abe Michihiko , Kasami Hideo , Tayama Takafumi , Nishi Hironobu
Published: September 2016

There are many papers on the effects of high temperature on concrete, but papers about properties of concrete subjected to lower elevated temperature such used in nuclear power plants are still limited. This paper presents the results of experiments conducted to determine the effects of term of exposure to elevated temperatures below the limit for concrete component in nuclear power plants. Sealed cured cylinders made of normal weight concrete containing ordinary portland cement were subjected to temperatures from 20 to 175°C without seal for 10, 30 and 90 days. After exposure, cylinders were tested for weight loss, compressive strength and static modulus of elasticity.
Preliminary Assessment of Durability of Sustainable RC Structures with Mixed-In Seawater and Stainless Steel Reinforcement
Authors: Lollini Federica , Carsana Maddalena , Gastaldi Matteo , Redaelli Elena , Bertolini Luca , Naani Antonio
Published: September 2016

The massive use of natural resources such as fresh water or virgin rock for aggregates in the construction industry originates the need for possible alternative solutions aimed at the environmental sustainability, as, for instance, the use of chloride-contaminated raw materials for the production of concrete. In the framework of a research project financed by the Infravation Program (Advanced systems, materials and techniques for next generation infrastructure), an experimental study is undertaken aiming at demonstrating the safe utilization of seawater and salt-contaminated aggregates (natural or recycled) for a sustainable concrete production when combined with non-corrosive reinforcement to construct durable and economical concrete infrastructures. Considering the lack of sufficient fresh water in many regions of the world, this paper focuses on a preliminary evaluation of the possibility of replacing fresh water used to mix/cure concrete with seawater, combined with different types of stainless steel reinforcement. Based on literature data and the performance-based approach of “Model Code for Service Life Design” published by the International Federation for Structural Concrete (fib), risks associated with the use of using seawater in relation to the service life a reinforced concrete element in a marine environment are investigated. During the development of the project, laboratory and field tests will allow for the collection of experimental data to better define the durability evaluation and analyse advantages of the proposed approach in terms of life cycle assessment.