Alkali activated clay mortars with different activators

Construction and Building Materials 212 (2019) 85–91

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Alkali activated clay mortars with different activators A. Karozou a,⇑, S. Konopisi a, E. Paulidou b, M. Stefanidou a a b

School of Civil Engineering, Dept. of Civil Engineering, Aristotle University of Thessaloniki, Greece Solid State Section, Physics Department, Aristotle University of Thessaloniki, GR-54124 Thessaloniki, Greece

h i g h l i g h t s
Develop alkali activated earthen materials with enhanced physical and mechanical properties.
The role of pH has been proven critical for the influence of the alkali activators on the properties of clay mortars.
Water-glass addition (WGS) is as unadvisable activator for clay materials.
Sodium carbonate(SC) is a promising alkali activator even at lower pH values.
Water-glass with the NaOH solution (WGN), is a promising activator in terms of mechanical characteristics and structural cohesiveness of the mortar.
Clay mortars activated with potassium metasilicate (PO) and water-glass with the NaOH solution (WGN), with pH = 12–14, presented the highest

compressive strength.

a r t i c l e

i n f o

Article history: Received 19 October 2018 Received in revised form 4 March 2019 Accepted 18 March 2019

Keywords: Physical characteristics Mechanical properties Microstructure pH

a b s t r a c t The purpose of this study was to develop alkali activated earthen materials with enhanced physical and mechanical properties. Specifically, clay mortars were produced, by using various alkaline activators of different pH (values 11–14). The specimens were cured in certain conditions. The physical and mechanical properties of the mortars manufactured were measured at the age of 28 days. Specifically, capillary absorption, shrinkage, Karsten tube penetration, porosity, as well as compressive and flexural strength tests were performed. Additionally, microscopic analysis was also conducted. The results of the experiments indicated the positive effect of potassium metasilicate and the combination of sodium metasilicate with sodium hydroxide solution on mechanical characteristics. The influence of sodium carbonate as an alkali activator was also proven beneficial on the physical properties of the specimens. In conclusion, the alkaline activators with pH > 12, lacked in enhancing physical properties, yet allowed the development of mechanical strength, while the alkaline activators with lower pH values showed reversed results. Ó 2019 Elsevier Ltd. All rights reserved.

1. Introduction Nowadays, the growing demand on housing and infrastructure results in the increase of concrete use. Since concrete is one of the primary causes of global warming, accounting for 7% of worldwide CO2 emissions, ways to reduce its use are being studied [1,2]. The development of alternative materials, such as earth, that can provide an inexpensive and sustainable solution in construction, is drawing attention as to replace conventional building materials in certain cases [3]. Yet, the high vulnerability of earthen structures to water and their low mechanical strength has limited their use in modern building designs. So, to cope with these drawbacks various

⇑ Corresponding author. E-mail address: [email protected] (A. Karozou). https://doi.org/10.1016/j.conbuildmat.2019.03.244 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.

methods have been tested until today, such as the use of Portland cement and other binders (like fly ash) to stabilize soil mass [4,5]. As a rapidly developed method of enhancing mechanical properties, alkali activation has gained popularity through the past few decades. Alkali activated materials (AAM) have been known in the scientific world for more than a hundred years. The concept of using AAM as a replacement for cement in construction, however, has remained stationary, since fundamental research has started only around the 1990s, without focusing on engineering properties [6]. Nevertheless, nowadays, an increase in literature on AAM in cement construction has grown exponentially over the last few decades [7]. As the urge to reduce carbon dioxide emissions is growing, different techniques and materials are tested as to replace ordinary Portland cement (OPC). The first attempts to use AAM in cement started with Kühl, followed by Chassevent, Feret and Purdon at the early 1940’s with research on slags [8]. Later, at the late

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1950’s Glukhovsky was the first to refer to ‘‘soil cements” by using clays and alkaline metal solutions, while Davidovits at the late 70’s, introduced geopolymers with blends of metakaolinite, limestone and dolomite [7–9]. Since clay is a greatly sensitive material when interacting with water, this study focuses on enhancing its structure through alkali activation. For centuries, different additives have been tested as to increase mechanical stability and water resistance. Traditionally, mineral and synthetic additives (sand, pozzolan, ashes, Portland cement, lime, gypsum, soap bitumen), vegetable and animal additives (fibers, oils, fats, tannins, latexes, excrements, urine, blood, casein, animal glues were some agents used for enhancement [10] while more recently polyvinyl alcohols, ethyl silicates, epoxy and acrylic resins and a variety of other polymers have been tested [11,12]. All these agents have been widely used in restoration projects of cultural heritage, presenting, however, drawbacks in terms of compatibility [13–16]. Alkali activation is the procedure in which a solid aluminosilicate precursor reacts with an alkali activator, as to form a hardened final binder [17,18]. For each precursor the correct activator is needed, thus, concerning earthen materials, solutions of Ca(OH)2, NaOH and KOH are mainly chosen as to dissolve the clay minerals and reform non-swelling binding networks [17,19]. The nanostructure of AAM is determined by the calcium content of the precursor, as the high calcium systems mainly produce hydrated calcium aluminosilicate gel (CASH). At low calcium systems the alkali aluminosilicate gel (NASH) prevails [20,21]. The treating conditions are correlated with the nature of the precursors and activators used, as to avoid efflorescence and achieve higher mechanical strength. Curing in both ambient and elevated temperatures, as well as sealing of the AAΜ mortars to avoid fast dehydration, is recommended [20,22,23]. The method of alkali activation has been applied mostly in fly ash [24] and slags, yet a few studies have focused on the creation of AAM in clayey materials that are mainly focused on kaolinite [25,26]. For instance, the study of Faheem et al. [27] introduced the use of clay geopolymers in brick construction [21] while Uddin and Saraswath [28] have used clay and red soil with alkali solutions to produce mortars for the construction industry. Moreover, a recent study of Bruno et al. investigates the stabilization of compressed earth blocks by alkaline activation and silicon-based admixture [29]. Also, alkali-activated materials show enhanced properties compared to ordinary Portland cement ones, with greater resistance to acids and heat, lower drying shrinkage and higher strength [20]. Clay as an aluminosilicate material with a high calcium content, constitutes a raw material with great interest for alkali activated mortar manufacturing. Thus, this study focuses on designing alkali activated clay mortars and examines their potential use in modern construction. For that purpose, the mechanical and physical properties of the produced mortars were recorded at the age of 28 days.

2. Materials and techniques 2.1. Design of mortars and materials used The purpose of this study is to examine the effect of various alkali activators in clay mortars, as to enhance their mechanical and physical properties. A reference composition (recorded as A) was created for comparison reasons with no alkaline activators. In all cases, the specimens prepared were of 40  40  160 mm dimensions for each series of mortars. For mortar manufacture, the clay used had a total calcium oxide content of 25% and was coming from the area of Crete. It consisted of quartz, calcite, calcium aluminum hydroxide and cancrinite, as can be indicated by

the XRD analysis in Fig. 1. To use it as a binder, the dry clay was sieved to have a grain diameter of less than 0.5 mm. Moreover, in Fig. 2, the particle size distribution (Malvern 2000, Mastersizer) is presented. The value of d(0.9) shows that 90% of the clay binder is less than 247.314 lm, while 50% of the clay is less than 34.148 lm and 10% is less than 3.377 lm. So, the particles of 2–500 lm size prevail in the mass. In Table1 the chemical composition of clay by AAS is presented. Apart from the main silicon and aluminum oxides the clay is rich in calcium oxide, CaO. The presence of sulfates, as soluble salts are also noticeable. The specific gravity of dry clay is 1.96 g/cm3 (ASTM-C188-95) while the color determination using Munsell charts is 5Y 7/1 light grey. The sand used for the mortars was washed river sand of siliceous composition with similar color with that of clay and grain size between 0 and 4 mm with no salt content. Four alkaline activators were used: potassium metasilicate, K2SiO3, provided by CAS Composite Anode Systems GmbH (PO), sodium carbonate solution, Na2CO3 (prepared from p.a. reagent provided by MERCK) recorded as SC, sodium metasilicate, Na2SiO3, also known as water-glass provided by Sika (WGS) and sodium hydroxide solution, NaOH, (prepared from micropearls provided by Lach-ner) mixed with water-glass (provided by Uzin) of ratio 1:1 (WGN). In each step the pH value level of the solutions was measured (by Knick pH-Meter 766), in order to achieve high pH values of the mixtures (pH > 11). Different alkalinity was observed, with the pH varying from 7 to 8 for the reference mortar up to 13–14 for the WGN mortar. The final pH values of the fresh mortars are presented in Table 2. The mixture proportions of the mortars were 1:2.5 (clay: aggregate ratio) by weight, with the same amount of clay in every mixture, while the liquid to solid ratios (L/S) for every mortar are recorded in Table 2. The goal was to reach workability of 15 ± 1 cm as tested by flow table (EN 1015-3:1999), as to produce an easy workable mortar (Table 2). It should also be noted that all mortars were cured at ambient conditions of 60%RH and 20 ± 2 °C, apart from WGN mortar that was sealed and matured at 65 °C, based on previous experience [30]. 2.2. Tests conducted In all cases, non-alkaline (A) and alkaline activated mortars (PO, SC, WGS and WGN) were tested after 28 days from their production for comparison reasons. As to test the behavior of the mortars against water penetration, capillary absorption (UNI EN15801:2010), Karsten tube penetration (EN 16302:2013) and porosity (RILEM CPC11.3) tests were performed. It is noted, that the porosity test was conducted using heptane instead of water, due to the inability of the specific material to withstand direct water penetration. Moreover, as to test the breathability of the materials, meaning the ability to remove water as fast as they absorb it, the drying procedure was also carried out. The drying index indicated as ID was calculated [31,32]. The procedure followed for the drying test was as a reverse capillary test, while the final value recorded for each mortar was until weight stabilization. Besides testing water absorption through capillary, water absorption through Karsten tube penetration test was examined. Karsten tubes are calibrated glass tubes with volume graduation. The tubes were applied onto the surface of the specimens using plasticine and the tubes were filled with water. The duration of the test was ten (10) min, while the drop in the water level was recorded at regular intervals of 30 s. Apart from the physical properties tested, the mechanical properties of the mortars were examined as well. Compressive and flexural strength tests (EN1015-11) were conducted after the completion of 28 days for all specimens. The dynamic modulus was also calculated indirectly by using ultrasounds. Moreover, as

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(a) (a)

(b)

Qu ar t z Calcite, sy n Calcium Aluminum Hydroxide Hydrate M u sc o v i t e 2 M 1 C an cr in i t e Ta lc 2M R u t i le, sy n

3 4.5 % 15 . 6 % 14.5% 9. 1% 12 % 8.3 % 6. 3 %

Fig. 1. XRD analysis of Cretan clay (a) Qualitative phase and (b) Quantitative phase analysis.

Fig. 2. Particle size of Cretan clay used.

Table 1 Chemical composition of clay of Crete, % w.t.

Clay

Na2O

K2O

CaO

MgO

Fe2O3

Al2O3

SiO2

LoI

Cl-

NO 3

SO2 4

0.94

2.09

25.33

7.48

6.52

13.03

30.87

13.74

0.01

0.01

0.21

Table 2 Mortars composition (in g) and properties of fresh state. Mortar

Clay [g]

Sand [g]

Activator

L/S

pH

Workability [mm]

A PO SC WGS WGN

800 800 800 800 800

2000 2000 2000 2000 2000

no activator Potassium metasilicate Sodium carbonate solution Water-glass Water-glass with sodium hydroxide solution

0.65 0.62 0.71 0.95 0.69

7–8 12–13 11 11 13–14

155 150 150 155 155

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to evaluate volume stability, the shrinkage of the mortars was also measured. The specimens were preserved at a chamber of constant conditions of temperature and humidity (20 ± 2 °C, 65 ± 5% RH) and the daily alteration of dimensions of the mortars was recorded. Moreover, stereoscopic observation through LEICA WILD M10 microscope of all mortars was conducted, as to detect cracking, roughness and surface modifications. Furthermore, microscopic examination by SEM (JEOL840A JSM) equipped with EDS device was substantial, to determine the development of inner structure and indicatively determine the molar ratios of SiO2/Al2O3, CaO/ SiO2 and M2O/Al2O3 (M = Na or K). In all cases, optical observation of color change using Munsell charts was determined. 3. Experimental results and discussion 3.1. Physical properties of mortars The capillary coefficient indicates the trend of the untreated specimens A to absorb water in a linear trend. In general, as it can be detected both in Fig. 3 and Table3, PO mortars presented greater absorption when compared with the reference, while SC mortars presented the lowest absorption rate through time. Both WGN and WGS mortars showed a characteristic high absorption due to capillary, with WGS specimens presenting material loss, after two hours in contact with water, thus making impossible the further conduction of the experiment. As presented in Table3, the high value of capillary coefficient of WGS mortars underlines their great absorption rate. After the completion of the capillary absorption test, the drying test was conducted as a reverse capillary test. The measurements lasted until the weight stabilization of the specimens. This was achieved after three successive measurements in different time intervals when the values did not differ. It is noted that the weight stabilization occurred for all specimens in a period of 28 days. As a result, the drying index ID (EN 16322:2013), which reflects the product’s resistance to drying, was determined by Eq. (1):

Z ID ¼

tf

0

M i dt Mmax  t f

ð1Þ

mi mf A

where: Mi ¼ The mi symbol indicates the mass of the specimen at time ti (kg), while mf represents the final mass of the specimen at the final time of the experiment tf (h). Therefore, Mi stands for the residual amount of water of the specimen at time ti per unit area in kg/m2, while Mmax equals with the maximum difference in the mass of the specimen at the beginning of the test at time t0 (kg/m2) [31,32]. Since drying index shows the resistance of the material to drying, it can be observed in Table3, that reference mortars A show a great resistance to drying with the second highest value of ID recorded. Moreover, in Fig. 4 the drying final times for each of

A

PO

SC

WGS

WGN

3.50

dW/A (g/cm2)

3.00 2.50

the specimens can be detected. The behavior of WGN mortars is close to the reference one presenting, however, the longest drying period. The shortest drying period was presented by SC mortars, while judging from the ID value, they were also the least resistant to drying compared with the other specimens. The highest ID value of PO mortars cannot be considered representative, since during the drying procedure material disintegration had begun. Moreover, it should be noted that efflorescence of the WGN mortars was observed during the conduction of the experiment, a fact that was considered as a negative aspect. The experiment was not conducted for the WGS mortars, since they were destroyed during the capillary absorption test. Concerning the porosity of the mortars used, the relatively low porosity values of PO and WGN mortars reported in Table 3, suggest the compact structure of the specimens. It is also noted that the high porosity value of WGS mortars, agrees with the high absorption rate through capillary, while the value of the SC mortars reveals a highly porous structure. Fact that justifies the low value of drying index. As far as the water absorption through Karsten tubes is concerned, the results indicated a high absorption of WGS and WGN mortars, with the latter presenting the greatest absorption recorded (Table 3). Significant is the fact that SC mortars showed a low water intake in both water absorption tests, as can be detected from capillary and Karsten tube test results. Mortars treated with potassium metasilicate presented a medium absorption rate during the Karsten tube test, while untreated mortar A showed a low water intake. Lastly, color alteration was insignificant in all tests conducted. Moreover, volume loss of the mortars was recorded for 42 days, with PO mortar presenting a stable structure. In general, mortars activated with sodium carbonate (SC) resulted in the greater volume loss among all mortars with 42.13% deterioration in relation to the reference. Also, a lower volume stability was observed for WGS mortar with 19.09% comparative volume loss, while WGN mortar showed a behavior close to the reference mortar with an improvement of 11.12%. 3.2. Mechanical properties of mortars The results of the mechanical tests of the mortars are presented in Table 4. The results indicate the positive effect of the potassium metasilicate (PO) and the water-glass and NaOH solution (WGN). Yet, an increase in compressive strength is detected in PO and WGN specimens by 29.21% and 151.46% respectively, compared to the reference. Impressive is the fact that WGN mortar presented a great mean value of dynamic modulus Ed, indicating the high compact structure of the mortars activated. Mechanical properties were enhanced also in the case of PO, while SC presented values comparable to the reference. The values are the average of 6 samples in each case. The standard deviation of the mortars is indicated for the values of all mechanical properties examined. In total, mechanical properties were enhanced in the case of PO and WGN mortars, while the mechanical properties for SC were comparable to the reference. 3.3. Microscopic and stereoscopic observation

2.00 1.50 1.00 0.50 0.00 0

5

10

15

20

25

Sqrt t (min0.5)

Fig. 3. Capillary absorption of mortars.

30

35

40

Through stereoscopic observation it was detected that almost all the surfaces of the mortars presented similar characteristics. Compact structure with small shrinkage cracks was present in all specimens, while a smoother surface was observed for PO mortar (Fig. 5). Furthermore, WGS mortar presented the greatest amount of surface shrinkage cracks, while granting a darker color to the samples as can be detected in Table 3 through the Munsell values. Efflorescence was spotted both optically and microscopically for

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A. Karozou et al. / Construction and Building Materials 212 (2019) 85–91 Table 3 Physical properties of mortars recorded. Mortar

Porosity [%]

Capillary coefficient [g/cm2 *min1/2]

ID

Water penetration [ml/min]

Volume loss [%]

Munsell values

A PO SC WGS WGN

16.47 14.28 20.07 23.86 15.58

0.26 0.49 0.15 2.16 1.48

0.14 0.22 0.05 – 0.12

0.21 0.42 0.04 1.13 2.69

4.82 2.00 6.85 5.74 4.28

5Y 5Y 5Y 5Y 5Y

A

PO

SC

7/1 5/1 7/1 4/1 4/1

light grey grey light grey dark grey dark grey

WGN

0.0

Dw/A (kg/m2)

-50.0

0

5

10

15

20

25

30

-100.0 -150.0 -200.0 -250.0 -300.0 -350.0 -400.0 Sqrt T (Hours0.5) Fig. 4. Drying curves of mortars.

Table 4 Mechanical properties of clay mortars at 28 days. Mortars

Compressive strength [MPa]

SDTV For compressive strength

Flexural strength [MPa]

SDTV For flexural strength

Dynamic modulus Ed [GPa]

SDTV For dynamic modulus Ed

A PO SC WGS WGN

0.82 1.06 0.85 0.76 2.06

0.058 0.083 0.192 0.021 0.199

0.32 0.27 0.29 0.29 0.80

0.232 0.043 0.070 0.055 0.241

3.32 3.24 3.19 4.36 17.12

0.47 0.19 0.260 1.845 6.539

A

WGS

PO

WGN (a)

SC

WGN (b)

Fig. 5. Stereoscopic observation of the mortars (scale 1000 lm).

WGN mortar on the surface of the samples, while inside the mass of PO mortar the development of efflorescence was recorded, as it can be detected in Fig. 5. A loose crystal structure was observed for the non-modified mortar A, while for the PO mortar a formation of rod crystals was noticed. The formation of leaf like crystals and the good cohe-

siveness between the binder and the aggregates was detected through SEM for WGN mortar. Cohesiveness of the mortar structure was favorable in this case, forming a continuous structure. Furthermore, SC mortar presented a dense structure with more porous of irregular shape explaining the high porosity values recorded. WGS mortar formed a bulky crystal network. Moreover,

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Table 5 EDS spectrum analysis of figure (1) mortar A, (2) mortar WGN (a) and (3) mortar WGN (b). (1) Spectrum A

Weight%

Na Al Si S K Ca Fe O

1.87 7.5 20.9 0.98 1.48 13.22 12.34 41.72

(2) Spectrum WGN (a)

Na

Mg

Al

Si

S

Cl

K

Ca

Fe

Spectrum 1 Spectrum 2

1.27 14.14

1.32 3.03

18.18 19.45

47.14 48.11

0.09 0.15

0.22 0.35

2.39 2.23

1.86 10.07

6.02 2.46

Table 6 Effect of different activators in physical and mechanical properties. Mortars

Porosity

Capillary

Drying

Water absorption

Compressive strength

Flexural strength

Dynamic modulus

Volume loss

Α PO SC WGS WGN

s ++   ++

s  ++  

s  + x +

s  +++  

++ s  +++

s    ++

s s s + +++

s ++   s

+: ++: +++: s:

: : : x:

positive effect very positive effect greatly positive effect neutral effect

the efflorescence of WGN mortar was clear, with sodium and calcium developments (Fig. 6), as can be also detected by the results of the EDS analysis in Table5, with the high amounts of sodium and calcium in every spectrum that was analyzed. From Table5 the indicative atomic ratios for the non-activated synthesis A and the alkaline activated WGN composition arise. Due to the higher values of mechanical properties, the atomic ratios for the WGN synthesis are reported as a comparison to those of the reference mortar A. In spectrum (1), the ratios calculated for composition A were Si/Al = 2.67, Si/Ca = 2.26 and Na/Al = 0.29, while for the WGN the ratios calculated were Si/Al = 2.47, Si/ Ca = 4.78 and Na/Al = 0.73. The Si/Ca and Na/Al ratios are higher for the alkali activated composition WGN (Spectrum 2), due to the nature of the alkaline activator and the solubilization of the precursor in high alkali conditions. This observation perhaps justi-

A

WGS

negative effect very negative effect greatly negative effect test not conducted

fies the increase in the mechanical properties for WGN mortar. In both cases, the Si/Al ratios showed similar values and seemed to be unaffected. Moreover, it is mentioned that elemental sodium is available from the alkaline solution of the activator, as well as ions of Si. In total, the effect on the properties of the various mortars are gathered in Table 6, were all mortars were rated in comparison to the values of the reference mortar A. 4. Conclusions In an effort to activate clay rich in calcium using different pH environments and different activators interesting results derived. The tests conducted indicated the low performance of the specimens cured with plain water–glass addition (WGS) in every exper-

PO

SC

WGN (a)

WGN (b)

Fig. 6. SEM images of the various mortars (scale-60 lm for A, PO, SC, WGS and WGN (a) mortars, scale-50 lm for WGN (b) mortars).

A. Karozou et al. / Construction and Building Materials 212 (2019) 85–91

iment. The inability of the mortars to withstand water penetration, as well as the poor mechanical characteristics marks it as unadvisable activator for clay materials. The activator of sodium carbonate (SC) led to relatively low values of compressive strength and high values of porosity. However, the behavior of sodium carbonate against water intake was beneficial in terms of capillary and water absorption by Karsten tubes, an aspect that grants sodium carbonate as a promising alkali activator for clay, even at lower pH values for special applications. The composition of water-glass with the NaOH solution (WGN), is another promising activator, since it indicated the best results in terms of mechanical characteristics and structural cohesiveness of the mortar. This specific composition has shown the highest oxide ratios in relation to the non-activated composition, fact that as suggested by theory, results in an increase of compressive strength and dynamic modulus, as well as in a reduction of porosity values [17–20]. One disadvantage of this mortar was the efflorescence that was forming while drying, without however, causing structural disintegration, as it was the case for the samples treated with potassium metasilicate (PO). This latter activator increased the cohesiveness of the mortars, reduced the porosity yet it didn’t affect positively the mechanical properties. Also, it caused disintegration at specific drying conditions. Considering the pH values of fresh mortars, it seems that the mortars activated with potassium metasilicate (PO) and water– glass with the NaOH solution (WGN), with pH = 12–14 presented the highest compressive strength results. It is highly probable that in this aluminosilicate rich in calcium binder, different types of gels coexist. Apart from calcium silicate hydrate gel (CASAH) which takes aluminum in its structure, calcium-aluminate-silicate hydrate gel (CAAASAH) and geopolymeric gel are expected to be formed simultaneously. The investigation of the mechanism should be carried out in order to gain deeper knowledge and understand the conditions appropriate to achieve the optimum results in each case scenario. Conflict of interest None. Acknowledgements Author Karozou A. would like to thank the General Secretariat for Research and Technology (GSRT) and the Hellenic Foundation for Research and Innovation (HFRI) for funding the research through the scholarship funding program for PhD candidates. References [1] L. Reig, M.A. Sanz, M.V. Borrachero, J. Monzó, L. Soriano, J. Payá, Compressive strength and microstructure of alkali-activated mortars with high ceramic waste content, Ceram. Int. 43 (2017) 13622–13634, https://doi.org/10.1016/j. ceramint.2017.07.072. [2] I. Garcia-Lodeiro, A. Palomo, A. Fernández-Jiménez, An overview of the chemistry of alkali-activated cement-based binders, handbook of alkaliactivated cements, Mortars Concr. (2014) 19–47, https://doi.org/10.1533/ 9781782422884.1.19. [3] S.H. Sameh, Promoting earth architecture as a sustainable construction technique in Egypt, J. Cleaner Prod. 65 (2014) 362–373, https://doi.org/ 10.1016/j.jclepro.2013.08.046. [4] C. Galán-Marín, C. Rivera-Gómez, J. Petric, Clay-based composite stabilized with natural polymer and fibre, Constr. Build. Mater. 24 (2010) 1462–1468, https://doi.org/10.1016/j.conbuildmat.2010.01.008. [5] Q.B. Bui, J.C. Morel, S. Hans, N. Meunier, Compression behaviour of nonindustrial materials in civil engineering by three scale experiments: the case of rammed earth, Mater. Struct./Materiaux et Constructions. 42 (2009) 1101– 1116, https://doi.org/10.1617/s11527-008-9446-y. [6] J. Provis John, T. van Deventer, T Committee Star, Alkali Activated Materials, State-of-the-Art Report, Springer, Netherlands, 2014. RILEM TC 224-AAM.

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