Proceedings of the 7th World Congress on Mechanical, Chemical, and Material Engineering (MCM'21)
Prague, Czech Republic Virtual Conference – August, 2021
Paper No. MMME 117
DOI: 10.11159/mmme21.117

Evaluation of the Mechanical Behavior of Mortars Obtained By
Geopolymerization of Calcined Clay and Demolition Mortar
D.L. Mayta-Ponce1, V.C. Bringas-Rodríguez1, J.F. Gamarra-Delgado1, M.L. Benavides-Salinas1,C.K. Palomino-Naupa1, G.P. Rodríguez-Guillén1 and F.A. Huamán-Mamani1

Grupo de Investigación en Ciencia y Tecnología de Materiales, Departamento de Ciencias Naturales, UniversidadCatólica San Pablo, Arequipa, PerúUrb. Campiña Paisajista, Quinta Vivanco s/n, Arequipa 04001, Perúdlmayta@ucsp.edu.pe; veronicawnh@gmail.com; frank.gamarra23@gmail.com; mirandabenavides7@gmail.com;
cpalominon@unsa.edu.pe; gprodriguez@ucsp.edu.pe; fhuaman@ucsp.edu.pe

1

Abstract –Geopolymeric mortars were prepared from a mixture of calcined clay powders (from demolition bricks), demolition mortar
and a 12 molar alkaline hardening solution of sodium hydroxide. The geopolymeric mortars were compared physically, microstructurallyand mechanically with their Portland cement counterparts. The results revealed similar densities between both types of mortars(geopolymeric and ordinary Portland cement). The microstructure was also similar in both mortars, two phases can be clearly identified,the continuous binder phase and the phase of individual fine sand particles dispersed within the continuous cement phase. Regarding themechanical data, it could be verified that the mixture with 80 Vol.% of fine sand, 10 Vol.% of calcined clay and 10 Vol.% of demolitionmortar was the one that showed the best mechanical results, with an average mechanical resistance of 34.5 MPa. However, the highest
average mechanical strength value for geopolymeric mortars is below the average mechanical strength value of ordinary Portland cement
mortar (50 MPa).
Keywords: mechanical behavior, mortars, geopolymerization, calcined clay, demolition mortar, Portland cement

1. Introduction

Geopolymers are a class of inorganic synthetic materials obtained at room temperature by a chemical process called
geopolymerization, which consists of the solubilisation of amorphous phases of aluminosilicates present in industrial solidwaste, calcined clays, natural minerals, among others, by the action of a alkaline activator in aqueous solution [1,2].
Geopolymers have received extensive interest of the scientific community in recent years, mainly due to the variety ofapplications in which they can be used, this derived from their excellent fire resistance, low density, low cost, easy
manufacturing, excellent chemical/thermal stability and eco-friendly synthesis [3,4].
For some years these materials have been considered revolutionary for their potential use as an alternative material toordinary Portland cement [5,6]. Several research papers have reported that geopolymeric concretes can reach up to 70% ofmaximum compressive strength within the first 4 hours of curing at an appropriate temperature [7], unlike Portland cementconcretes, which require up to 28 days to reach maximum mechanical resistance. On the other hand, geopolymeric concrete
shows very little shrinkage due to drying, it was noticed that after one year it presents between 5 to 7 times less shrinkage
than Portland cement concrete [8,9]. On the other hand, several works have shown the negative influence of sulfates on
Portland cement concrete, which drastically reduces its mechanical resistance to compression, this reduction is explained by
the reaction of sulfates with the calcium present in Portland cement, which leads to the formation of gypsum and ettringite[10], which are phases that require a greater volume and therefore their formation generates internal stresses in the Portland
cement concrete, which then lead to nucleation and propagation of cracks. On the other hand, geopolymeric concrete does
not present similar problems because its properties depend on other types of reactions (in the absence of calcium) [11,12].
Geopolymeric concretes exhibit good mechanical response to high temperatures compared to their Portland cement
concrete counterparts; in this regard, Kong et al. [12] studied the mechanical behavior of Portland cement and geopolymer
pastes after being subjected to high temperatures, noticing that while at 800 °C the geopolymer paste improves its resistanceto compression, Portland cement paste at 400 °C lost all its residual resistance, this loss of resistance of the Portland cement
paste was attributed to the decomposition of Ca(OH)2 at approximately 400 °C. One of the most important materials in thecomposition of conventional concretes is Portland cement, which is basically a mixture of gypsum and clinker, the latter isMMME 117-1

obtained by calcining limestone and clay at temperatures from 1350 ºC to 1450 °C. Obtaining the Clinker is accompaniedby large CO2 emissions. In this regard, it has been determined that a cement kiln produces approximately 0.8 tons ofCO2 for every ton of Portland cement [13].

2. Materials and Methods

2.2. Sample Preparation
Adequate amounts of binder and fine sand were ground in an alumina mortar and then sieved separately on an
ASTM # 140 sieve (106 μm), then based on 20 g. of powder mixes and with the matrices of mixes of table 1 wereprepared. In the case of geopolymeric mortars (GM) samples, binding powders and 10 ml of Na(OH) solution weremixed for 5 minutes, then the corresponding mass of fine sand (FS) was added and mixed for another 5 minutes, theGM paste obtained was compacted for 5 minutes at 60 MPa in a 20 mm diameter hardened steel cylinder mold. In thecase Portland cement mortars (M-PC) samples, the PC powder was mixed for 5 minutes with 10 ml of drinking water,
the following preparation steps were similar to those followed for GM samples preparation. The cylindrical specimens
of GM and M-PC obtained were placed in hermetic bags for 7 days and then dried in an oven at 60 ºC for 24 hours.
Table 1. Matrix of mixtures for the preparation of geopolymeric (GM) and conventional mortars ofPortland cement (M-PC)

fine sand(FS)(Vol.%)
80
M-20CC0DM80
M-15CC5DM80
M-10CC10DM80
M-5CC15DM
80
M-0CC20DM
80
M-20PC
samplecalcined clay (CC)(Vol.%)
201510500BINDER
demolition mortar (DM)(Vol.%)
051015200

Portland cement (PC)(Vol.%)
00000202.3. Physical, Structural, Microstructural and Mechanical Characterization
All prepared mortars were physically, microstructurally and mechanically characterized. The physicalcharacterization consisted in the determination of the real density by the pycnometry technique, for this research acalibrated glass pycnometer and distilled water were used. The microstructural characterization was carried out on
polished surfaces of the manufactured mortars. The preparation of the samples for microscopy began with a fineroughing of the surfaces using SiC abrasive paper of # 600, # 800 and # 1200 grit, then surfaces were polished using
diamond paste (6, 3 and 1 micron) and lubricating liquid. The polished surfaces were cleaned with plenty of distilledwater and were air dried, no grain development technique was used. Microstructural observations were made in an
AMSCOPE brand light microscope (50X - 500X), model ME320B-PZ (USA).
The mechanical tests consisted of uniaxial compression tests at a constant compression speed of 0.05 mm / min, in
an air atmosphere and were carried out in a universal testing machine, MICROTEST brand, model EM1 / 50 / FR,(Spain). Samples for compression tests consisted of 10x5x5 mm3 parallelepipeds and were obtained from cylindricalsamples of set mortars. From the mechanical tests, force and displacement data were obtained, which were later
converted into stress vs. deformation

3. Results and Discussion

3.1. Physical and Microstructural Characterization
The average real density for all the materials studied was 1.8 g/cm3. Fig. 1 shows light microscopy micrographs ofthe six types of mortars studied, two well differentiated phases could be identified, on the one hand, a continuous phasein dark gray contrast that corresponds to the interconnected binder phase (Portland cement or mixture of calcined clay
and demolition mortar) and, on the other hand, individual polygonal particles are seen dispersed within the continuous
phase, which corresponds to the fine sand particles (light gray phase).

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(a)

(b)

100 µm(c)100 µm(d)100 µm(e)100 µm(f)100 µm

100 µmFig. 1: Light microscopy micrographs of geopolymeric (a-e) and conventional Portland cement mortars (f)3.2. Mechanical Characterization
Fig. 2 presents stress vs. strain for all the mortars studied, from these curves it could be noticed that the geopolymericmortar M-10CC10DM in fig. 2 (c) with 80 Vol.% of fine sand, 10 Vol.% of calcined clay and 10 Vol.% of demolition mortar
was the one that showed the best mechanical results, among all geopolymeric mortars, however, the data from maximumstrengths for Portland cement mortars were higher than all the values found for geopolymeric mortars.

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50
45404035σ302520σ15maximum

minimum= 26 MPa= 16 MPa

50σmaximum

45= 41 MPa

35302520σ15minimum= 20 MPa

35
30

5060
50

0

160

M-5CC15DM(d)55523STRAIN (%)

50

0

550
454040σ= 27 MPamaximumσ= 25 MPa

2520minimum

35
30
2520

1515

1010

55000132STRAIN (%)

45STRESS (MPa)454030σmaximum

σ01= 18 MPaminimum

32STRAIN (%)

1= 30 MPa

32STRAIN (%)

4σ= 54 MPa(f)554535060

M-0CC20DM(e)55

4minimum= 39 MPa

1504maximum

201023STRAIN (%)

σ

2551σ

4050

M-10CC10DM(c)

55

1010

STRESS (MPa)

STRESS (MPa)4560

M-15CC5DM(b)55

STRESS (MPa)

STRESS (MPa)5060

M-20CC0DM(a)55

STRESS (MPa)60

σmaximumminimum= 46 MPa

3530252015= 13 MPa

1054550M-20PC
0123STRAIN (%)

45Fig.2: Stress vs. strain curves for the six types of mortars studied

4. Conclusions

Geopolymeric mortars derived from calcined clay powders and demolition mortar, and conventional Portland
cement mortars were prepared and compared regarding their physical, microstructural and mechanical characteristics.
The real density of geopolymeric and conventional Portland cement mortars was similar and around 1.8 g / cm3, onaverage.
The microstructure of geopolymeric and conventional Portland cement mortars was also similar, finding for bothcases a continuous and interconnected binder phase of Portland cement or a mixture of calcined clay powders andgeopolymerized demolition mortar and, on the other hand, polygonal particles were found individual dispersed within
the continuous phase, which corresponds to the fine sand particles.
The geopolymeric mortar with 80 Vol.% of fine sand, 10 Vol.% of calcined clay and 10 Vol.% of demolition mortar
was the one that showed the best mechanical results, among all the geopolymeric mortars studied.
The maximum mechanical resistance for Portland cement mortars were higher than all the values found forgeopolymeric mortars.

Acknowledgements

This work was financed by CONCYTEC - FONDECYT within the framework of call E041-01 with contract N°
36-2018-FONDECYT-BM-IADT-AV and was executed in the laboratories of the Universidad Católica San Pablo.

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