Improvement of the properties of a mortar with 5% of kaolin fillers in sand combined with metakaolin, brick waste and glass powder in cement

Construction and Building Materials 152 (2017) 632–641

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Improvement of the properties of a mortar with 5% of kaolin fillers in sand combined with metakaolin, brick waste and glass powder in cement Radhia Harbi, Riad Derabla, Zahreddine Nafa ⇑ Laboratory of Civil Engineering and Hydraulic (LGCH), University of 08 May 1945, BP 401, 24000, Guelma, Algeria

h i g h l i g h t s
Developing new composite cements from waste recycling, aimed at protecting the environment and upgrading existing local materials in large but

under-exploited quantities.
Improve the mechanical performance of the mortar as well as its durability in a sulphatic medium.
Developing new composite cements from waste recycling Improve the mechanical performance of the mortar Improve also its durability in a sulphatic

medium.

a r t i c l e

i n f o

Article history: Received 4 April 2017 Received in revised form 29 June 2017 Accepted 4 July 2017

Keywords: Filler Kaolin Glass powder Brick waste Metakaolin Cement mortar

a b s t r a c t This experimental work focused on the study of the possibility of using kaolin dust (K) as filler in sand combined with additions of glass powder (GP), brick waste (BW) and metakaolin (MK) in order to improve the mechanical performance of the mortar as well as its durability in a sulphatic medium. The properties studied are compressive strength, bending tensile strength, porosity, water absorption and sulphate resistance. The incorporation of filler into the sand and the additions in the cement made it possible to obtain mortars possessing physico-mechanical properties and durability which are at least superior to that of the reference mortar. Mixtures containing glass powder (GP) and / or metakaolin (MK) are better than those containing brick waste (BW). Ó 2017 Elsevier Ltd. All rights reserved.

1. Introduction Protecting the environment is one of the major preoccupations of researchers at present. Cement production processes, even though they have improved considerably with respect to the environment, are still polluting. The production of cement should be reduced by the use of other less polluting materials, or it may be necessary to try to substitute cement products by recycling ecoproducts or waste for the production of concrete and high mortar performance. The reuse of various wastes that constitute an environmental problem has also been the subject of much recent work. Among

⇑ Corresponding author at: Department of Civil Engineering and Hydraulic, University of 08 May 1945, BP 401, 24000, Guelma, Algeria. E-mail addresses: [email protected], [email protected] (Z. Nafa). http://dx.doi.org/10.1016/j.conbuildmat.2017.07.062 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.

these works are studies on brick waste and glass incorporated into cement matrices. Recent studies [1–4] have shown that glass powder (GP) has very interesting pozzolanic properties and can be used as an alternative cementitious addition. The results of these studies revealed that GP gives better results in concretes. Also: the mechanical properties as well as the resistance to penetration of the chloride ions and the resistance to freezing–thawing of the BAP incorporating the GP are comparable to or better than that of the control, depending on the replacement percentage. Other recent studies [5–7] have shown that the use of brick (BW), marble and tuff waste as an addition in self-propelled concrete (SPC) gives quite satisfactory results, but it is the tuff which gives the best mechanical performance. The results of other researchers have shown that the valorisation of BW in the ceramic sector is feasible, and it therefore has a dual interest, scientific and industrial.

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The chemical composition of the cement is given in Table 1 and its physical and mechanical characteristics are shown in Table 2. The mineralogical composition of the CPA cement was supplied by the laboratory of the Ain-Touta cement plant according to the NF EN 196–2 standard:

In general, mortar or brick concrete (used as a powder or aggregate) gives lower mechanical strengths than the control concrete because the brick has a high porosity and a high water absorption capacity. Kaolin (K) is an abundant clay in most parts of the world. Small quantities are used for the manufacture of high-quality ceramics, while the rest is untapped. The use of K and MK as an additive in the manufacture of mortars and concretes has been the subject of several studies [8–12]. Most researchers show that MK is a good addition that reduces pores and makes the structure waterproof. The results revealed that the inclusion of MK significantly reduced shrinkage, but increased the mechanical strengths of concretes and mortars. The researchers showed that concrete with MK gave an improvement in sulphate resistance compared to simple concrete. In this study, K was first used as filler in the sand to seal the pores between sand grains and thus improve its compactness in order to obtain a high performance mortar. It is also used after transformation into MK for its binding activity in cement to improve the compactness of the cementitious matrix. This clay was calcined in a laboratory furnace at a temperature of 750 ° C for a period of 4 h, and after cooling the calcined clay was ground. The calcination of the clay at 750 °C allows the starting water (dehydroxylation) and the formation of metakaolinite [13–16] to be an amorphous structure. This makes it more reactive than the starting clay (K). Our work consists in developing new composite cements from waste recycling, aimed at protecting the environment and upgrading existing local materials in large but under-exploited quantities. The additions involved in this study are: glass powder (GP), brick powder (BW) and metakaolin (MK), used as substitutes for cement, 5, 15 and 25%. On the other hand, kaolin (K) was used as filler in sand with an adopted content of 5%. A 10% level is found to be excessive and has led to reduced compactness and adversely affected resistance and durability. For the sake of complementarity and comparison, three combinations of additions have been adopted. These are unary, binary and ternary combinations. We investigate the effect of these additive combinations on the mechanical strength, porosity, immersion water absorption and chemical sulphate aggressions in the elaborated mortars.

C3 S ¼ 52:48%; C2 S ¼ 22:69%; C3 A ¼ 3:89% < 5% and C4 AF ¼ 16:32%:

2.1.2. Sand We used as starting sand a coarse sand from the Tebessa sand pit (sand1). A second sand is obtained by adding 5% of kaolin fillers to the first: sand2 = sand1 + 5% filler of kaolin. The sand 1 and 2 are of limestone mineralogical nature and their granulometric curves are continuous and their fineness modulus are of the order of 3.25 and 2.94 respectively. The whole physical properties of the two sands are given in Table 3. We believe that the decrease in water content is due to the decrease in the porosity of the new sand because the kaolin, which is very fine, has been able to occupy a large volume of voids which has reduced the free space to contain the water. 2.1.3. Mineral additions The kaolin used is a very fine dust from the ETER ceramic factory in Guelma (East of Algeria). Its fineness, determined using the digital Blaine apparatus, is: SSB = 12,603 cm2/g. The glass powder was obtained by crushing waste from bottles using a ball mill. Its measured fineness is: SSB = 5067cm2/g. The brick waste was micronized to powder by grinding. The powder obtained has a fineness of SSB = 7718 cm2/g. The metakaolin was obtained by calcination of the clay at 750 ° C for 4 h and then after grinding by balls, a fineness of SSB = 8781 cm2 / g was obtained. The chemical compositions of the various mineral additions used are shown in Table 1. 2.1.4. Adjuvant The adjuvant used is the ‘‘MEDAPLAST4000 produced by the company GRANITEX (Algeria). It is a super- plasticizer with a high water reducer. The MEDAPLAST SP40 makes it possible to obtain concretes and mortars of very high qualities. In addition to its main function, it reduces the water content of concrete and mortar. The recommended dosage range is 0.6–2.5% of the cement weight. 2.2. Composition of mortars In order to study the influence of the different mineral additions used, 22 mortar mixtures were composed. Unary combination mortars had a single addition, while the others were formulated from binary and ternary combinations. For each composition, 3 specimens were tested. A preliminary study allowed us to appreciate the influence of the percentage of filler in the sand. We used 10% of filler, but this percentage led to a decrease in compactness and has adverse effects on the strength and durability of the mortar. We then opted for a percentage of kaolin filler in the sand equal to 5%. The combinations adopted comprise dosages of 5 and 25% for the six binary combinations and 5, 5 and 15% for the three ternary combinations

2. Materials and methods 2.1. Raw materials 2.1.1. Cement The cement used is an artificial Portland cement CPA-CEM I 42.5 (CRS 400) from the cement plant in Ain Touta (East of Algeria).

Table 1 Chemical compositions of cement and mineral additions.

C K GP BW MK

CaO

SiO2

Fe2O3

Al2O3

MgO

K2O

Na2O

SO3

Cl-

CaO free

PAF 1000 °C

60.16 0.20 8.05 2.31 1.29

23.03 41.97 69.10 69.05 57.98

4.25 0.12 1.80 1.52 0.75

4.18 38.00 0.89 23.02 38.31

1.32 0.07 1.65 1.05 0.11

0.82 / 0.28 2.59 0.21

0.44 / 18.18 1.28 0.89

2.76 0.75 0.05 0.04 0.36

0.018 / 0.004 0.089 0.006

0.81 / / / /

2.98 16.8 / / /

Table 2 Physical and mechanical properties of cement. Specific weight (g/cm3)

Specific surface area (cm2/g)

Normal Consistency (%)

Setting time Beginning

End

3.06

3901

25.92

2 h–15 mn

3 h–20 mn

Withdrawal 28 d (um/m)

Tensile strength 28 d (MPa)

Compressive strength 28 d (MPa)

660

7.40

47.28

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Table 3 Physical properties of sands and mineral additions. Properties 3

Apparent density (g/cm ) Specific weight (g/cm3) Porosity (%) Compactness (%) Water content (%) Water Absorption (%) Equivalent of sand (%) Specific surface area (cm2/g)

Sand1

Sand2

K

GP

MK

BW

1.67 2.42 21.11 78.89 1.35 18.33 97.22 /

1.76 2.54 20.58 79.42 0.33 10.66 87.5 /

0.62 2.40 / / / / / 12603

1.07 2.55 / / / / / 5067

0.67 2.39 / / / / / 8781

1.05 2.39 / / / / / 7718

Table 4 Different mortar compositions (mass%). Compositions

Cement%

GP%

BW%

MK%

Sand%

K%

W/C

SP%

F%

D

C/S

C1 C1-SP C2 C2-SP GP5 GP15 GP25 BW5 BW15 BW25 MK5 MK15 MK25 5GP+25MK 25GP+5MK 5GP+25BW 25GP+5BW 5MK+25BW 25MK+5BW 5GP+5BW+15MK 5GP+15BW+5MK 15GP+5BW+5MK

100 100 100 100 95 85 75 95 85 75 95 85 75 70 70 70 70 70 70 75 75 75

– – – – 5 15 25 – – – – – – 5 25 5 25 –

– – – – – – – 5 15 25 – – – – – 25 5 25 5 5 15 5

– – – – – – – – – – 5 15 25 25 5 – – 5 25 15 5 5

100 100 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95

– – 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5

0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6

– 2.5 – 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5

60 80 60 80 72 75 80 77 75 70 65 62 60 65 75 70 80 65 60 60 65 70

2.07 2.04 2.05 2.04 2.12 2.11 2.08 2.12 2.08 2.05 2.09 2.08 2.07 2.08 2.10 2.10 2.09 2.10 2.07 2.09 2.10 2.10

0.33 0.33 0.35 0.35 0.33 0.30 0.26 0.33 0.30 0.26 0.33 0.30 0.26 0.24 0.24 0.24 0.24 0.24 0.24 0.26 0.26 0.26

5 5 15

For this purpose, and in order to show the possible interactions between the additions, all the combinations used are detailed in Table 4.

MSSD: Mass of the saturated test specimen, superficially dried, weighed in air (g) Mdried: Mass of the dried test piece (g). MS ’: Mass of the saturated test specimen, weighed in water (g).

Notation C1: mortar without K and without SP, C1-SP: mortar without K and with SP, C2: mortar with K and without SP, C2-SP: mortar with K with SP. 5GP + 25MK: mortar with 5% GP and 25% MK 5GP + 25BW: mortar with 5% GP and 25% BW 5MK + 25BW: mortar with 5% MK and 25% BW 5GP + 5BW + 15MK: mortar with 5% GP, 5% BW and 15% MK 15GP+5BW + 5MK: mortar with 15% GP, 5% BW and 5% MK 5GP + 15BW + 5MK: mortar with 5% GP, 15% BW and 5% MK

2.3.3. Resistance to sulphates The resistance of the various mortars to sulphates was determined on prismatic specimens 4  4  16cm3 subjected to attack in a solution of sodium sulphate (Na2SO4). After demoulding, the curing of the test pieces takes place for 28 days in water followed by immersion for 28 days, 90 days and 180 days in a 5% concentration of sodium sulphate (Na2SO4) solution. Subsequently, they are subjected to tensile tests by bending and then compression.

3. Results and discussion In this work we have chosen to work with mass percentages for two reasons. The first being the difficulty of precisely measuring the volumes and the second is that of the apparent densities which are not very different, the results would be close.

2.3. Nomenclature of tests 2.3.1. Mechanical resistance Tensile bending and compression tests were conducted in accordance with NF EN 1015–3 and NF EN 1015–11 respectively). 2.3.2. Porosity by hydrostatic weighing and absorption by immersion The test was carried out according to ASTM C 624 [17]. The test pieces were completely dried and then immersed in water until saturation. The volume porosity was determined according to the following formula:

e¼

MSSD  M dried  100% M SSD  M S0

e: Volumic porosity established experimentally by hydrostatic weighing excluding the volume of air trapped and / or entrained (%).

3.1. Compressive strength 3.1.1. Effect of the nature and dosage of the addition At 28 days of age, a drop in the strength of the mortars developed from the 5% cement substitution was observed in one of the three additions to the control mortar (Fig. 1). This decrease is logically explained by the fact that the additions have a lower actual density than cement and have not been able to fill all the pores. For the higher substitution rates (15 and 25%), the fall continues in the case of BW, whereas the resistance increases for the other two additions and even exceeds that of the control mortar because the specific surfaces of MK and GP are greater than that of the cement, which has helped to produce several modifications within the solid skeleton of the mixture. The small particle size of the substitutions fills the voids and increases the density of the material, and therefore the water caught in the pores is released,

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635

Fig. 1. Effect of addition percentage on compressive strength of mortars at 28 days.

Fig. 2. Compressive strengths of mortars with separate additions.

Fig. 3. Effect of additive combinations on the 28 days compressive strength of mortars.

which increases the compactness of the paste, improves workability and reduces water demand, as shown by the work of [18–20]. Moreover, the absorption of the two additions decreases as the level of MK and GP increases. Also, these are the two most reactive elements in the hydration of cement, which fills the pores, reduces W /C and densifies the skeleton of the paste. The resistance of the mortar to the MK is greater than the other additions thanks to its pozzolanic reactivity, which allowed the consumption of the Ca (OH)2 portlandite and the formation of new HSCs which consolidated the structure. On the other hand, the mortar’s resistance to BW decreases with the increase in the content of the addition due to the increase in the absorption of water by immersion according to the results of the absorption test carried out. As for the mortars with addition to the different maturities (Fig. 2), the comparison of the resistances of the four control mortars C1, C1-SP, C2 and C2-SP shows that the mortar resistance of C2-SP is the greatest. This finding can be explained by the exis-

tence of kaolin filler dust, which was able to fill and densify the pores, and its pozzolanic reactivity led to the consumption of the Ca(OH)2 portlandite and the formation of new SCH (silicate of calcium hydrate), which were able to consolidate the structure and also the adjuvant, which increases the resistance. In the very long term (90 and 180 days), the compressive strength increases progressively with the age of conservation in water, after the resistance at 28 days reached a level of 90% of the final strength. At 180 days the strength of the mortar prepared with 25% MK is higher than that of the mortars prepared with 25% GP or BW. BW-based mortars remain the least resistant, which leads us to conclude that the BW should be used at limited levels (at 5% in our case). 3.1.2. Effect of binary or ternary combination of additions The results of the compressive strength at 28 days of the mortars with a combination of two and three additions are shown in Fig. 3. It is noted that for all the combinations there is a drop in

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the cement, especially at high percentages (15% and 25%) and they therefore offer more pozzolanity. On the other hand, the absorption of MK is lower than that of GP because the MK is finer than GP and therefore the strength of the MK-based mortar is higher than that of the GP and BW-based mortars. The same findings can be reported for the longer terms (90 and 180 days) (Fig. 4).

resistance compared to that of the mortar sample C2-SP. However, this drop is less significant for combinations containing MK and / or GP because the water absorption is lower than that of the mortar with BW. For the latter, the greater the percentage of substitution is, the greater is the drop of resistance. This is due to the fact that the water absorption of the mortar with 25% BW is greater compared with those with 5% and 15%. The 28 days strengths of the mortars with the binary combination (5GP + 25MK) and the ternary combination (5GP + 5BW + 15MK) are superior to those of the other compositions because the GP and MK have superior surface areas and lower water absorption, which makes them more reactive in the presence of

7 Days

3.2. Tensile strength by bending Taking the additions separately, the results of the tensile strengths shown in Fig. 5 indicate that the substitution of 5% of

28 Days

90 Days

180 Days

Compressive strength (Mpa)

60 50 40 30 20 10 0

Mortars Fig. 4. Compressive strengths of mortars with combined additions.

Tensile strength by bending at 28 days (Mpa)

10

7.5

5

2.5

0 C2-SP

BW5

BW15

BW25

GP5

GP15

GP25

MK5

MK15

MK25

Fig. 5. Effect of the addition percentage on the 28 days tensile strength of the mortars.

Tensile strength by bending (Mpa)

7 Days

28 Days

90 Days

180 Days

12 10 8 6 4 2 0 C1

C1-SP

C2

C2-SP BW5 BW15 BW25 GP5

GP15 GP25 MK5 MK15 MK25

Fig. 6. Flexural tensile strengths of mortars with separate additions.

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Tensile strength by bending at 28 days (Mpa)

10 8 6 4 2 0

Fig. 7. Effect of combinations of additions on tensile strength at 28 days of mortars.

Tensile strength by bending a (Mpa)

7 Days

28 Days

90 Days

180 Days

12 10 8 6 4 2 0

Fig. 8. Flexural tensile strengths of mortars with combined additions.

21.00

Porosity (%)

20.00

19.00

18.00

17.00 C2-SP

BW5

BW15 BW25

GP5

GP15

GP25

MK5

MK15 MK25

Fig. 9. Effect of the addition percentage on the porosity of the mortars.

Absorption by immersion (%)

10.5

10

9.5

9

8.5 C2-SP

BW5

BW15

BW25

GP5

GP15

GP25

MK5

MK15

Fig. 10. Effect of percentage addition on immersion absorption of mortars.

MK25

638

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cement immediately led to a drop in resistance for the three additions with respect to the control mortar. This fall in the case of brick powder for the high percentages of substitutions (15% and 25%) is because as the content increases, the absorption increases. In the case of GP and MK, the resistance increases gradually for 15% and then for 25% of substitution, like the results for the compressive strength. In Fig. 6, the increase in resistance with increasing age can be clearly seen. In the long term, the resistance of C2-SP is large and comparable to that of MK. On the other hand, in the short term, MK is the largest. In the case of the combination of additions, Fig. 7 shows that at the age of 28 days, for all combinations, the resistance fell compared to that of the control mortar. However, these falls are less

18.50

18.00

17.50

Absorption by immersion (%)

Fig. 11. Porosity accessible to water of different mortar compositions.

9.9 9.7 9.5 9.3 9.1 8.9 8.7 8.5

Fig. 12. Water absorption by immersion of mortars.

28 Days

90 Days

180 Days

Compressive strength (Mpa)

45 40 35 30 25 20 15 10 5 0 C2-SP BW5 BW15 BW25 GP5 GP15 GP25 MK5 MK15 MK25 a 28 days Compressive strength (Mpa)

Porositéy (%)

19.00

90 days

180 days

40 35 30 25 20 15 10 5 0

b Fig. 13. Compressive strength of test specimens immersed in Na2SO4. (a): separate additions; (b): combined additions.

R. Harbi et al. / Construction and Building Materials 152 (2017) 632–641

Tensile strength by bending (Mpa)

28 Days

90 Days

180 Days

10 8 6 4 2 0

a Tensile strength by bending (Mpa)

28 days

90 days

180 days

10 8 6

639

On the other hand, the increase of 15 and 25% allowed a good filling of the pores by the substitution thanks to its greater fineness. Therefore, the decrease in pores is associated with a decrease in water absorption and leads to an increase in strength. 3.3.2. Effect of the binary or ternary combination of additions Fig. 11 clearly shows that the two compositions (5GP + 25MK and 5GP + 5BW + 15MK) give the lowest porosities. These two compositions also give the lowest absorptions (Fig. 12) and are the same most resistant mortar mixtures. These results can be explained by the fact that the MK has the greatest fineness (small particle size) and for this it fills the maximum of the pores and makes the structure less porous which gives less water absorption. These findings are also made by many researchers as in the work ([18–20]). On the other hand, it is the combinations (5GP + 25BW and 5GP + 15BW + 5MK) which give the highest values of the water absorption because, when the BW level is increased, the porosity increases and therefore the absorption of Water increases accordingly.

4

3.4. Sulphate resistance tests

2 0

b Fig. 14. Tensile strength of test specimens immersed in Na2SO4. (a): separate additions; (b): combined additions.

significant for combinations containing MK and / or GP than for the combination containing BW. Fig. 8 shows that in the long term, for all combinations of additions, there were falls of resistance compared to the control mortar. Nevertheless, these falls are greater for combinations containing 25% of BW. 3.3. Porosity by hydrostatic weighing and absorption by immersion 3.3.1. Effect of the nature and dosage of the addition The results obtained from the three additions separately substituted for the cement are shown in Fig. 9. These results show a continuous decrease in porosity in the case of MK compared to the control mortar (C2-SP). On the other hand, mortars based on BW and based on GP with the 5% substitution content showed an increase in porosity and then a decrease for contents of 15 and 25%. These results can be explained by the good filling of the pores; in fact, the MK is very fine compared to the cement, which makes it possible to fill the pores from 5%, while on the other hand BW and GP are less fine, which does not allow the filling of the maximum pores. This is overtaken by the increase in the GP and BW grades, which are characterized by a high surface area. The influence of the rate of addition on the immersion absorption of the mortar is very clear in Fig. 10. Thus, it can be seen that for brick waste, the absorption increases progressively with the addition rate because brick is a more porous material and less fine than GP and MK. However, for the case of GP and MK, the absorption certainly increases for a substitution rate of 5%, but it gradually falls again for the rates of 15 and 25% because for the rate of 5% the pores were not filled completely by the additions but were filled by water, which explains the fall of resistance.

The results of the compressive strength and flexural tensile strength of the specimens preserved in a prepared sulphated aggressive medium containing a solution of Na2SO4 are presented in Figs. 13 and 14. The results for all mortars show a gradual increase in compressive strength and flexural tensile strength and those up to 90 days of immersion in the Na2SO4 solution. Beyond this time there is a generalized drop in resistance for all mortars. Up to 90 days of curing, the increase in resistance is because the specimens are still in the process of the hydration of the anhydrous cement products, but is also due to the reaction of Na2SO4 with Ca (OH)2 to form gypsum, which clogs the micropores and gives a denser structure, positively influencing the mechanical resistance. The decrease in resistance observed at 180 days is probably due to the expansive effect of sulphate attack. The formation of swelling (expansive) sulphated hydrate leads to the creation of microcracks, indicating a destructuration of the material. This is consistent with the explanation obtained by other researchers [21,22]. With regard to the separate additions, it is clear that the increase in the percentage of substitution influences the resistance to Na2SO4 attacks positively in the case of MK and to a lesser degree for GP. On the contrary, there is the opposite effect in the case of BW, so that for a 25% substitution, a complete deterioration of test specimens is also observed at the age of 180 days immersion in the solution of Na2SO4 (Fig. 16). In the case of the combined additions, it is observed that the mortars obtained with a combination containing a high BW content, such as (5MK + 25BW and 5GP + 25BW), exhibit the lowest resistances to acid attacks. In contrast, the mortars obtained with a combination containing a high content of MK, such as (25MK + 5BW and 25MK + 5GP and 5GP + 5BW + 15MK), exhibit the strongest resistances. This is explained by the fact that the addition of BW gives a non-compact structure because of its high porosity, which leads to the high absorption of the sulphate solution, which in turn degrades the performance of the mortars, especially for the high BW content. On the other hand, the external appearance of the test pieces of Fig. 15 does not deteriorate, which is explained by the fact that the pozzolanic reaction of MK participates in the closure of the pores, especially in the mixture GP + MK, and which leads to consolidation of the structure, which is then more resistant to external aggressions and avoids the deterioration of the test piece.

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Fig. 16. Mortar specimen with 25% BW after 180 days of immersion in the Na2SO4 solution.

4. Conclusion The main aim of this study is to combine the positive effects of the use of filler in sand on the one hand and mineral substitutions in cement on the other hand to obtain mortars offering high mechanical performance and good durability with regard to sulphate attacks. The fillers used are of kaolin, while the mineral additions used are glass powder, brick powder and metakaolin. A preliminary study allowed us to fix the percentage of filler in the sand at 5%. The most favorable addition is metakaolin and the most suitable dosage is (25%). This addition helps to improve the mechanical strengths of the mortars and the durability due to its pozzolanic reactivity which decrease the porosity and also the absorption of water. These beneficial results lead to limit the expansion of the chemical aggressions and the degradation of the material. The worst addition is brick powder especially with high dosage. It decreases the strength of the mortar specimens and increases their capillary water absorption which promotes the infiltration of the external aggression and therefore leads to the deterioration of the material. The most favorable combinations (binary or ternary) are 5GP + 25MK and 5GP + 5BW + 15MK, giving a more resistant and more durable mortars than those obtained with the other combinations (5GP + 25BW, 5MK + 25BW and 5GP + 15BW + 5MK) Work is in progress and others are planned to investigate the impact of the combination of these additions in substitution of part of the cement on the mechanical properties of concrete. References

Fig. 15. Mortar specimens with 25% MK after 6 months of immersion in the Na2SO4 solution.

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