Latex influence on the mechanical behavior and

Journal of Adhesion Science and Technology

ISSN: 0169-4243 (Print) 1568-5616 (Online) Journal homepage: http://www.tandfonline.com/loi/tast20

Latex influence on the mechanical behavior and durability of cementitious materials Yacine Benali & Fouad Ghomari To cite this article: Yacine Benali & Fouad Ghomari (2017) Latex influence on the mechanical behavior and durability of cementitious materials, Journal of Adhesion Science and Technology, 31:3, 219-241, DOI: 10.1080/01694243.2016.1208378 To link to this article: http://dx.doi.org/10.1080/01694243.2016.1208378

Published online: 19 Jul 2016.

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Date: 04 November 2016, At: 07:59

Journal of Adhesion Science and Technology, 2017 VOL. 31, NO. 3, 219–241 http://dx.doi.org/10.1080/01694243.2016.1208378

Latex influence on the mechanical behavior and durability of cementitious materials Yacine Benali and Fouad Ghomari EOLE Laboratory, Faculty of Technology, Civil Engineering Department, Abou Bekr Belkaid University, Tlemcen, Algeria

ABSTRACT

The results of an experimental program conducted on latex-modified mortars are presented in this article. These mortars have become of growing interest in the field of construction. They were used as superplasticizers, or water reducers, for finishing work applications and for repairs, coatings, and waterproofing. This study is about using two polymers (latex), i.e. styrene–butadiene rubber and styrene–acrylic, in order to assess their performance in replacing cement in mortars. A series of mortar mixtures, containing 0, 2.5, 5, 10, 15, and 20% of solid polymer latex (by weight), were prepared and tested in the fresh and hardened states. The test parameters include the fluidity, compressive and flexural strengths, porosity accessible to water, adhesion to clay bricks, and cementitious substrates. The experimental results showed that substituting cement into modified mortars improves their fluidity and adhesion. In the case of clay substrates, a cohesive failure occurs within the substrate layer beyond 10% of substitution, while the rupture takes place at the interface for all formulations tested on cementitious substrates. It was also noted that the flexural tensile strength improved beyond 60 days. However, the compressive strength of polymer mortars decreased with the substitution rate of cement, for all maturities considered. However, for porosity accessible to water, the results follow a linear function, with an inflection at 5% of latex substitution.

ARTICLE HISTORY

Received 21 March 2016 Revised 8 June 2016 Accepted 27 June 2016 KEYWORDS

Modified mortar; latex; fluidity; porosity; strength; adhesion

1. Introduction The concept of mortars modified with synthetic polymers was introduced several decades ago.[1–11] Since then, a renewed interest has manifested itself, in the field of construction, for the use of these materials.[1,4,10] They continue to be very promising materials for new applications, especially for facade coatings, tile adhesives, sealing coatings, decorative coating, and external thermal insulation; they are used also for the repair of civil engineering structures in the field of public works, and in some road applications as well.[1,3,10,12–15] The latex polymers, which are manufactured by emulsion polymerization [16] (very successful process from the technical and environmental point of view, because water is

CONTACT Yacine Benali

[email protected]

© 2016 Informa UK Limited, trading as Taylor & Francis Group

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Y. Benali and F. Ghomari

used as a solvent and also the amount of volatile organic compounds (VOCs) released during their preparation and application is negligible, etc.),[17–24] prove to be the most commonly used polymers. They are commercialized as aqueous dispersions, often milky white.[25] These monomers are petrochemical products, made from crude oil.[26,27] They can be produced from coal or natural gas as well.[26,27] The literature, in this area, shows that there is a variety of types of latex, depending on the kind of monomers or polymers used in their manufacture. The main types used are the acrylic polymers (PA), styrene–acrylic copolymers (SA), styrene–butadiene copolymers (SBR), vinyl acetate copolymers, and vinyl acetate homopolymer.[8,28–33] The choice of a type of latex depends on the specific properties required for the application.[28,29] Over the last few years, SBR and acrylic latex (SA and PA) have been the main types to be used. [2,34–37] This latex represents 37% (SBR) and 30% (SA and PA) of the total synthetic waterborne latex, manufactured industrially.[24] They have long been used to modify mortars; they turned out to be effective. SBR development, for modifying the cementitious matrices, started in the middle of the last century, in the United States. The application requests were for stuccoes, vessel protective coatings and bridge decks, as well as for screeds, tile adhesives,[28], and for the repair coatings of concrete and reinforced concrete structures.[38] Their molecular formula includes flexible monomers of butadiene and rigid styrene monomers [11,35,39]; the combination of these two provides mortars with many desirable features.[11,16,35,39,40] As for the styrene–acrylic latex, they have been used for over 40 years to modify the hydraulic cement mixes.[28,36] This is an acrylic polymer modified with monomers of styrene, which enhances the cohesion and tenacity of mortars, as well as the strength and resistance of the latex film against water and the alkalis.[40,41] The resulting mortars are generally used as thin coatings for concrete restoration,[28] as well as for tile adhesives, floor coatings, exterior insulation finishing systems, and concrete repair.[29,42] Since the beginning, the formulation of modified systems has always been based on a simple association of cement, water, sand, and latex[1,3,39,43,44] combined with a polymer/cement ratio, generally ranging from 5 to 20% of dry latex extracts, depending on the weight of cement in the mixture.[1,28] The different formulations are used not only to improve the properties of conventional mortars, but also as an admixture to reduce the mixing water into the mixture.[3,4,25,28,34,37–39,43,45,46] During the setting of these modified systems, some physical, chemical, and physicochemical reactions occur between these components.[47] After the curing period and the evaporation of mix water, a network structure is obtained, where the cement hydrates and polymer interpenetrate to form a co-matrix and a polymeric film.[1,3,8,28,29,38,44,46,48] These two elements improve the cohesion between the aggregates and cement paste at the interface, and also increase the compactness of the hardened material. This will therefore ameliorate its flexural and tensile strengths, its adhesion to different substrates as well as its durability, while slowing down its permeability to water and also the diffusion of aggressive species, such as carbon dioxide, chlorides, and sulfates.[8,10,11,15,28,29,37–40,44,46,49] Moreover, latex-modified cementitious materials have better water retention,[1,4,34,38] sufficient entrainment of air [28,34], and also a better fluidity,[14,25] due to the presence of super-plasticizers in the constituents of latex.[45] The present work is a part of a research using two types of synthetic latex: styrene–butadiene (SBR) and styrene–acrylic (SA), not only as an admixture to reduce the mixing water of


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Table 1. Chemical composition of cement. SiO2 22.17

Al2O3 6.18

Fe2O3 3.62

CaO 59.45

MgO 1.05

SO3 2.63

K2O 0.49

Na2O 0.19

Cl 0.004

P2O5 0.18

TiO2 0.43

Loi 2.62

Table 2. Physical characteristics of cement. Bulk density (T/m3) Specific gravity (Le Châtelier Densitometer) (T/m3) Blaine’s specific area (cm2/g)

1.01 3.02 3597

Table 3. Identification of physical properties of sand used. Bulk density (T/m3) Absolute density (T/m3) Sand equivalent (%) Percentage of fines (%) Fineness modulus

1.43 2.50 84.5 15.7 3.01

mortars but also as a substitute of Portland cement (because its production is energy-hungry and it is responsible for several environmental damages [50])). The mortars were prepared with proportions varies from 0, 2.5, 5, 10, 15, and 20 % (by weight). The main objective is to highlight the influence of these materials on the mechanical properties, adhesion, and durability of conventional mortars, though the properties of cement mortars can be improved by the addition of latex as a water reducer plasticizer. The modification mechanism, through the replacement of cement by latex, is not clear yet; and a lot of research work needs to be performed.

2. Materials and methods 2.1. Materials used A Portland cement compound of type CPJ CEM II / A 42.5, meeting the Algerian standard NA 44, from the cement plant of Beni-Saf, in the Wilaya of Ain Temouchent, was used. Its main constituents are clinker, natural pozzolan of volcanic origin from the deposit of Bouhamidi (Beni-Saf, Algeria), and gypsum. The chemical composition of this cement is given in Table 1, and its physical characteristics are summarized in Table 2. The sand used is crushed limestone sand 0/3 mm, from the quarry of Djebel Abiod of (ENG1), Sidi Abdelli, in Tlemcen (Algeria). This choice was made because it is the main quarry that supplies the entire region. The quarry of Djebel Abiod produces clean sand 0/4 mm. This sand was passed through a 3.15-mm mesh sieve. The choice of sieving is dictated by the fact that sand 0/3 is the most frequent type used in the literature for the preparation of mortars. No washing or size correction has been performed for the formulation of various mortars. The characteristics of the sand after sieving are summarized in Table 3. Clay bricks, with horizontal perforations and grooves in the coating, of dimensions (100 × 200 × 300 mm3), were used as substrates for the adhesion tests. These substrates have a

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Table 4. Physical characteristics of latex polymers used. Name of product Nature Color and form Odor Properties of the film Density (T/m3)

According to the manufacturer at (20°C) Measured in the laboratory at 19°C Viscosity (cps, 30°C) (Brookfield RVT 20 rpm) Total bulk solids (%) According to the manufacturer Measured in the laboratory pH According to the manufacturer Measured in the laboratory at (19°C) Particle size (μm) Minimum temperature of film forming (MFFT), °C Glass transition temperature (Tg), °C Type of surfactant

SikaLatex Styrene–butadiene rubber (SBR) Viscous milky white Low Not clear, flexible 1.02 1.01 – 50 45 7.5 9.65 – – – –

D-70 Styrene–acrylics (SA) Viscous milky white Low Clear, hard 1.07 1.5 – 1.6 (50±1) 50 – 7.90 0.1–0.3 17 +16 Non ionic

Figure 1. Molecular structure of latex used. (a) SBR latex; (b) SA latex.

bulk density equal to (1.41 T /m3), and water absorption equal to (13.55%). This test was performed according to the standard ASTM C 373.[51] Two latex polymers: styrene–butadiene (SBR) and (SA) manufactured, respectively, by SIKA El DJAZAIRE and TECHNALab, were used. Their physical and chemical characteristics are reported in Table 4 and Figure 1. 2.2. Method of preparation of samples and tests performed 2.2.1. Mixes and cures Our experimental program consisted in replacing amounts of cement by latex proportions ranging from 2.5 to 20% (by weight) of dry extract. The results obtained were compared with reference mortars with similar composition, where cement is the only binder. The cement-to-sand ratio (C/S) used was 1/3 (by weight). This choice was prescribed by the fact that these are the most frequent compositions encountered in the literature. The (W/C) ratio used for the manufacture of control mortars was 0, 5. This ratio was validated after the mechanical strength test of two mortars with two different ratios (W/C) equal to 0.5–0.55.


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Table 5. Details of mixing proportions modified mortars. Designation mixtures M. Ref Styrene–butadiene rubber (SBR) M. 2,5% SBR M. 5% SBR M. 10% SBR M. 15% SBR M. 20% SBR Styrene–acrylic (SA) M. 2,5% SA M. 5% SA M. 10% SA M. 15% SA M. 20% SA

Sand(g) 1350

Cement (g) 450

P (g) 0

W/C 0.5

Fluidity (mm) 125

1350

438.75 427.5 405 382 360

25 50 100 150 200

0.498 0.48 0.425 0.35 0.25

125 130 145 160 165

1350

438.75 427.5 405 382 360

22.5 45 90 135 180

0.498 0.48 0.425 0.35 0.25

125

The polymer-modified mortars were prepared with partial substitution of cement at different weight ratios, i.e. 2.5, 5, 10, 15, and 20%. The substitution ratios were calculated using the total solid content in the latex (see Table 5). As for the (W/C) ratio, two ways to manufacture a latex-modified mortar [14,52] were found in the related literature. • The first is to maintain the (W/C) ratio constant in order to have a hydration level close to that of the cement paste (typical laboratory procedure), • The second one, more common (the mortar strength increases), is to adjust the viscosity of the modified mixture to that of ordinary mortar, usually by adjusting the (W/C) ratio. The second method was used in this study. The viscosity of the SBR-modified mortars was adjusted so as to have a fluidity between 125 and 165 mm (fluidity of usual mortars, see Table 5), whereas the (W/C) ratio was adjusted so as to have the fluidity of the SA-modified mortar similar to that of the reference mortar (125 ± 5) mm. This was done using the flow table test, according to the standard ASTM C 1437–07,[53] while using a frustoconical mold that meets the requirements of standard ASTM C230 / C 230 M-08,[54] where the spreading is the average of two perpendicular diameters. The components of these polymer-modified mortars were mixed according to the pre-wet method to reduce the amount of entrained air in the fresh mortar.[52,55] For that, cement and sand are mixed with water first, and then, the latex is added. In order to determine the mechanical parameters and the porosity accessible to water, the molds containing the polymer mortar samples were covered with plastic film and stored in the laboratory environment. The samples were unmolded after 24 h and kept in water for 6 days at 20 ± 3°C and then in the open air at 20 ± 3°C with a relative humidity (RH) equal to 55 ± 10%, until the test at 7, 14, 28, 60, 90, 180, and 360 days, because curing in humid conditions, such as immersion into water, or the moist cure, which is applicable to cement mortar and ordinary concrete, is detrimental to the modified mortar and concrete.[1,6] For this, several authors [1,4,7,11,46,56,57] stated that the optimal properties of modified systems can be achieved by a combination of wet and dry processing. • Wet in order to hydrate cement and to avoid cracking due to plastic shrinkage.[28] • Dry to evaporate the excess water off to allow for the development of the polymer film.[1,11]

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Reference mortars were immersed into water at 20 ± 3 °C until the day of the test, whereas the samples used to determine the adhesion on two different substrates, i.e. bricks and cementitious materials, were kept in the laboratory environment at 20 ± 3 °C with a RH = 55 ± 10%, up to the day of the test. This was done to simulate the application in a real environment. 2.2.2. Test procedure The evaluation of the compressive strength and bending tensile strength was performed at 7, 14, 28, 60, 90, 180, and 360 days, according to standard EN 196–1,[58] on specimens of dimensions (40 × 40 × 160 mm3). It is known from the literature that these properties are the most important, if sustainability indicators are excluded. The porosity accessible to water was investigated next. This is an important parameter when evaluating and predicting the durability of structures.[33] In this work, saturation of the samples was performed according to the recommendations of the modified standard AFREM.[59] Tests were carried out on fragments recovered from the flexural tensile test on specimens (40 × 40 × 160 mm3). The following equation was used for the calculations:

P(%) =

Mair − Mdry Mair − Mwater

× 100

where Mair, Mdry, and Mwater are the mass of saturated sample weighed in air, the mass of dry sample, and its hydrostatic mass, respectively. A drying temperature of 60 °C was selected. The reason for this choice is that at this temperature, the microstructure and cement hydrates are not changed, but this change may occur at high temperatures. The samples were maintained at that temperature until the mass stabilizes (Mdry), which is when two consecutive weightings, separated by 24 h, do not differ by more than 0.05%. For adhesion property, several researchers have stated that the fundamental purpose of using polymers in the cementitious mixture is to improve the adhesion and the durability of this latest, because the quality of repair and protection of structures depends mainly on the adhesion of mortars to the substrate to be repaired or protected.[8, 60–63] Previous works in this area have shown that the adhesion measurement tests are usually tests of rupture between two materials. They can be achieved either by pulling (traction) or flexural tensile and/or by direct or indirect shear.[8,30,64,65] In this work, the adhesion measurement was carried out using the methods (a) and (b) as shown in Figure 2. According to the literature, these two tests are easy to perform and can produce good results.[8,64,65] The peel test by direct pulling, often called ‘pull-off ’, was performed on mortars used on hollow clay bricks. The same formulations of mortars, previously defined, were applied on one of the larger faces of the brick (300 × 200 mm2). This face was wetted before applying mortar, to avoid the absorption of water of mortars in the fresh state, while meeting the recommendations of Mirza et al. [66] and Courard et al. [67], who recommended a saturation level of the substrate higher than 50% and lower than 90% for a good adhesion. The thickness of the applied layer was (20 mm). Such a choice was made because generally the thickness of repair or protection mortars exceeds (10 mm), depending on the degree of damage. These mortars were tested after 28 days of curing. The samples were prepared by drilling three circular holes of diameter (50 mm) on the mortars applied to the bricks; 24 h


225

Figure 2. Methods used for measuring adhesion.

Figure 3. Adhesion test by pull-off.

before the test. Then, cylindrical metal disks of the same diameter (50 mm) were stuck on the removed parts with an epoxy adhesive (see Figure 3). After 24 h, a male ball, fixed on the metallic disks, was received in the ball socket which is located at the base of the central axis of the adhesion tester. The peel tests consist of applying a growing traction force on the male ball, perpendicularly to the surface of the disk, until rupture. The value of adhesion (in MPa) of the coating to the brick is obtained by dividing the maximum force of the fracture (in N) by the surface of the bonded surface (mm2). This value was recorded, and the fracture interface was analyzed in each case. The adhesion test by flexural tensile was performed on so-called bicomponent specimens, to simulate a repair system.[8] The test specimens are of the same size as that of the samples used for mechanical testing (40 × 40 × 160 mm3), but they consist of two parts (see Figure 4). The substrate part is the portion to be repaired in the system. This is a half specimen of dimensions (40 × 40 × 80 mm3), with a flat surface obtained by sawing the initial sample and

226


Figure 4. Adhesion test by flexural tensile: (1) device tensile test by flexural tensile, (2) repair mortar, (3) mortar support.

made with conventional Portland cement mortar. It must be manufactured at least 28 days before use and kept in the laboratory prior to use. The water absorption of these substrates is about 6.54%, calculated using the standard ASTM C 373.[51] The other half of the sample is the repair product part which is made with the mortar to study. First, the contact face of the mold was wetted, and then, the repair product part was cast directly into the mold (40 × 40 × 160 mm3), where the substrate part was already positioned. The test was performed on the specimens at the age of 28 days (see Figure 4). The rupture observed with the two methods, used to measure the adhesion, can be cohesive in the substrate (S) or in mortar (M); it can be adhesive as well, along the interface (A), or it can be mixed, i.e. both cohesive and adhesive (AS) or (AM).

3. Results and discussion 3.1. Fluidity Considering the results in Table 5, it can be said that both SA and SBR are water reducers. Indeed, when the substitution rates went from 0 to 20%, the fluidity of fresh mixture increased significantly, from 125 to 165 mm for SBR, but remained constant at 125 mm for SA, while the (W/C) ratio dropped from 0.5 to 0.25. Many research studies have shown that the presence of polymer, especially in latex form, in Portland cement mortar and concrete improves the workability at low water–cement ratios. In their study, Folic and Radonjanin [56] mentioned that the incorporation of latex (SBR) into fresh concrete causes a typical effect of admixtures, like super-plasticizers. They found that the latex effect enables making concrete mixtures of a required consistency, with a water quantity up to 30% less than that used in traditional concrete. Muthadhi et al. [11] studied the effect of elevated temperature and duration of exposure on polymer-modified concrete. The styrene–butadiene rubber latex polymer solids were


227

added in this study in terms of 0, 5, 10, and 20% by mass of cement. The authors found that the workability of fresh concrete increased with increasing polymer content. The slump value of concrete varied between 60 and 170 mm. However, the quantity of mixing water was decreased from 148 to 109.6 l/m3. In their work, Soni and Joshi [16] showed that the addition of SBR at 5, 10, 15, and 20% latex /cement ratio in concrete, increases the slump value from 25 to 90 mm. Wang and Wang [36] focused in their paper on the effect of the styrene–acrylic ester copolymer (SAE) latex on the performance of cement mortar. These authors observed that the water-reduction rate of the SAE latex-modified mortars increases linearly with the increase of the mp/mc ratio, reaching about 40% when the mp/mc is 20%. Aliabdo and Abd_Elmoaty [68] studied the interactions between the main self-compacting concrete components (filling and high dose of chemical additives) and polymer. They found that for keeping the flow diameter constant at (70 ± 2 cm), it is necessary to decrease the level of the super-plasticizer (naphthalene and modified polycarboxylic ether), while increasing polymer content (SBR and PVA). They also found that the use of styrene–butadiene rubber is more efficient in decreasing the dose of modified polycarboxylic ether-based chemical admixture, than using polyvinyl acetate. These authors justified these observations by the coherence due to the ‘ball-bearing’ action of the polymer particles, their dispersion, the entrapped air, and the plasticizing effect of latex. Therefore, the obtained results show that the two types of latex are water reducers, but SBR is a higher range water reducer than SA latex. This may be due to the large amount of water existing in SBR (≈55%). 3.2. Compressive strength The compressive strength of reference mortars as well as those modified by SBR and SA as a function of polymer content and age is illustrated, respectively, in semi-logarithmic chart in Figures 5 and 6. These results are the average of six tests on fragments recovered from the flexural tensile strength test. A preliminary analysis of the results allows us making the following observations. The evolution curves of the compressive strength of the reference mortars and modified vs. time (7 to 360 days) show the same trend. Overall, the strength of all mortars increases steadily with the conservation period (from 7 to 60 days) of specimens. Beyond that age, the strength of all mortars remains constant, taking into account the experimental uncertainties. This may be attributed to the time required for cement hydration and its curing. Indeed, during the mixing, the tricalcium silicate (alite) and bicalcium silicate (Belite) undergo dissolution and produce calcium silicate hydrates (CSH), and calcium hydroxide ‘portlandite’, designated as ‘CH’ by cement manufacturers.[8] The CSH precipitate around the cement grains and forms bridges between them; this causes the subsequent hardening of the samples. The continuous formation of CSH gradually fills the capillary pores, and this increases the compactness of the samples and therefore improves the compressive strength.[45] Moreover, when examining more closely the values obtained at specific ages, it is found that reference mortars develop greater compressive strengths, at all ages (7 to 360 days). It is obvious that the compressive strength of mortars decreases (loss) while the cement substitution rate increases, for all examined maturities. This loss is about 21, 33, 32, 34, and

228


Figure 5. Influence of age on the compressive strength as a function of polymer SBR content mortars.

Figure 6. Influence of age on the compressive strength as a function of polymer SA content mortars.

35%, when the strength of reference mortars is compared to SBR-modified mortars at the age of 360 days and it is 23, 28, 32, 33, and 34% for the SA-modified mortars at the same age. Note that beyond 10% of polymer additions, the values of strength are generally similar.


229

Several research studies have shown that the presence of polymers has a low impact on the compressive strength, and it may even have a negative impact.[8,28,49] Wang et al. [4] found that for a constant (W/C) ratio, the strength at 28 days shows a slight increase for small amounts of SBR (≤2%); then, it starts decreasing sharply as the added quantity increases. Wang et al. [36] concluded that when the ratio (W/C) is well adjusted, such as in our case, the compressive strength of mortars modified by acrylic–styrene drops sharply as the (P/C) ratio increases, for 3, 7, and 28 days of storage. The same authors [40] noted in another study that the compressive strength increases with the conservation period of the samples in water; however, it decreases as the amount of SBR increases up to 10%. Beyond that amount, the strength slightly increases at 7 and 28 days, while it decreases for a conservation period of 3 days. Marceau et al. [48] showed that adding a ratio (P/C) ≤5% of SBR (aqueous dispersion) or SA (powder) results in a significant decrease in the mechanical properties, and more specifically in the compressive strength. However, for (P/C) ratios higher than this value, the mechanical strength falls slowly. Ngassam [8] also found that the addition of the polymer ethylene vinyl acetate (EVA) or styrene–butadiene SBR (powder) reduces the compressive strength of mortars at 28 days of dry cure (in the open air). Chew et al. [69] found that for mortars kept in the open air, with an adjusted fluidity, the compressive strength of mortars modified with styrene–acrylate emulsion (SAE) latex was reduced by approximately 52% when the (P/C) ratio rose from 0 to 44%. Barluenga and Hernandez-Olivares [52] reported that incorporating SBR in cement mortars causes a reduction in the compression strength, with a constant (W/C) ratio. However, the compressive strength does not change much for adjusted ratios, at all ages considered. Ramli and Tabassi [6] found that the compressive strength of ferrocement mortars modified by SBR, PAE (aqueous dispersion), and VAE (powder) decreased by approximately 27 and 23% for mortars kept in free air and in seawater, as compared to unmodified cement mortars. Most of these authors justified these observations by the fact that a polymer has a larger capacity of water retention, a high closed porosity due to air entrainment by the polymer [4,8,36,40,48], and also to the delay in hydration of cement, caused by the presence of surfactants in the mixture.[49,70] However, other researchers [6,52,69] justified these same observations by the low mechanical capacity of the latex and also by the change observed in the microstructure of the mixture. In the co-matrix network of modified mortars, there are two types of bonds, i.e., cement–cement and cement–polymer. The cement–polymer bonds are weaker than the cement–cement bonds. When the polymer content increases, the polymer film covers the hydrated cement and aggregates, thus forming several polymer–cement bonds. This results in a decrease in the compressive strength of the modified samples. Therefore, if one takes into account the recommendations of standards EN 1504–3 [71] and TRA 651,[72] and also the balance between performance and the amount of polymer introduced, regarding the performance relative to repair products, then a substitution percentage ranging from 10 to 15% of latex, which develops a strength (≥25 MPa) at 28 days, appears to be effective for non-structural repair mortars of type R1 (≥10 MPa), and type R2 (≥15 MPa), for structural repair of type R3 (≥25 MPa), and also for masonry mortars (≥12.5 MPa).

230


Figure 7. Influence of age on the flexural tensile strength as a function of polymer SBR content mortars.

3.3. Flexural tensile strength The results of the flexural tensile strengths of control and modified mortars as a function of age and polymer content are shown, respectively, on the semi-logarithmic chart, in Figures 7 and 8. These results represent the average of three tests on prismatic specimens of dimensions (40 × 40 × 160 mm3). Based on these experimental results, it can be stated that the flexural tensile strength of all polymer-modified and reference mortars increases steadily. Similarly, the compressive strength also rises with the conservation period of specimens, from 7 to 60 days. Beyond that age, the strength of mortars follows a constant trend, provided that the experimental uncertainties are taken into consideration. This is due, as previously said for the compressive strength, to the hydration of cement, its hardening and also to the formation of the polymer film over time. These results corroborate those found in the literature.[4,36,40,52] Figures 7 and 8 shows that the flexural tensile strength of mortars decreases when the substitution rate of polymer increases, for all maturities (7–28 days). The reduction in strength may be attributed to the amount of substituted cement, delayed cement hydration under dry conditions, the fixing of polymer particles on cement particles, and also to the co-matrix and the undeveloped polymer film. However, the loss in strength is recovered at 60 days. This strength increases by 5 and 34%, respectively, when mortars modified with 20% of SBR and 20 % SA are compared to control mortars. This can be explained by the improved cohesion between the aggregates and cement paste. This cohesion is enhanced by the formation of the polymeric film and the co-matrix which is a network structure in which the hydrated cement phase and the polymer phase interpenetrate. A model, which explains the mechanism of the microstructure of modified systems, was proposed by Ohama.[1,3] This model was subsequently developed by Gemert et al. [70] and Tian et al. [73].


231

Figure 8. Influence of age on the flexural tensile strength as a function of polymer SA content mortars.

To summarize these models, it can be said that during the mixing of modified mortars, a gel of hydrated cement forms and some polymer particles adhere to the non-hydrated cement grains and aggregates.[8,33] These polymer grains limit the hydration of cement and cause a delay in its setting.[8,30,41] The aqueous phase is saturated by calcium hydroxide formed during hydration. Calcium hydroxide reacts with the surface of silica aggregates to give a layer of calcium silicate.[1] In the case of dry curing, as water is used in cement, the hydrated structure is developed and a continuous polymeric film can be formed. The polymer particles get closer to each other, flocculate, deform progressively, and then coalesce. The polymer film binds the cement hydrates formed and adheres to the calcium silicate layer on the granules.[8,33] Some reactions also occur between the reactive functional groups of certain polymers and calcium ions Ca2+, calcium hydroxide Ca(OH)2, and the silicate layers on the surface of aggregates.[8,33] So, this increases the cohesion between the cement hydrates and aggregates, and consequently improves the strength of mortars. Comparing the two Figures 7 and 8, we are enable to note that the flexural tensile strength of SA-modified mortars shows better improvement than that of SBR-modified mortars. This is due to the nature and functioning of the polymer as well as to the amount of water that exists in mortar; the quantity of water in SBR-modified mortars is larger than that encountered in those modified by SA, for identical polymer contents. Our results confirm the conclusions of Gemert et al. [70] and Ngassam [8]. The beneficial effect of polymers is generally more noticeable in the flexural tensile strength than in the compressive strength because polymers enhance the strength of the binder–aggregate interface, which is particularly needed during the flexural tensile tests.

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Figure 9. Porosity accessible to water of modified mortars.

3.4. Porosity accessible to water Figure 9 displays the results related to the porosity accessible to water for the different mortars studied. These results are the average of six measurements done on fragments recovered from three flexural tensile tests. Porosity accessible to water is significantly influenced by the substitution rates, particularly by large values, while the flexural tensile is impacted by both the substitution rate and drying, as already reported in the literature related to modified mortars.[8,16,52] Figure 9 shows that the open porosity of SBR- and SA-modified mortar, respectively, follows a linear function with an inflection at 5% substitution rate. Furthermore, we note that the porosity decreases in modified mortars compared to the control mortar for replacement levels of cement beyond 10%. This decrease is, respectively, around 50 and 48% for 20% substitution rate of modified mortars with SBR and SA. These observations are also confirmed by Figure 10, where it can be clearly noted that the center of the samples remained dry beyond 10% substitution rate after testing the porosity accessible to water. This means that water has not reached the center of these samples. These results are certainly due to the change observed in the microstructure of mortars as a result of the introduction of the polymer in sufficient amount and also because of drying. The formation of the polymer film and the co-matrix in the matrix network of the modified systems comes bridging the open pores and cracks, and also slowing their progress. This decreases the number of pores (200 nm pore radius) and enhances the strength of the binder–aggregate interface, as previously explained.[7,8,16,28,33,46] However, because coherent polymeric films cannot form, and also the amount of cement present in mortar decreases, with 2.5 and 5% substitution rates, compared to control mortar, then a slight increase in the porosity accessible to water is observed at these levels. Afridi et al. [74] noted that at a


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Figure 10. Specimens cut after the test of the porosity accessible to water.

Figure 11. Adhesion of mortars to clay bricks.

(P/C) of 10% or more, a coherent polymer film may appear, whereas for low rates, that film is less pronounced and its beneficial effect is hardly observed. 3.5. Adhesion to bricks and cementitious substrates The results of the adhesion for reference and modified mortars to bricks and cementitious substrates as a function of the substitution rates are illustrated in Figures 11 and 12. These

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Figure 12. Adhesion of mortars to cementitious substrates.

results are the average of the values obtained from three tests on mortars applied to clay bricks and cementitious substrates. The adhesion to bricks and cementitious substrates was reported to be significantly influenced by the cement substitution rate. This influence is more noticeable beyond 5% (wt%) cement replacement by the two types of latex. SBR- and SA-modified mortars showed, respectively, an adhesion increase to bricks of 84 and 82%, for a 20% (wt%), replacement rate compared to ordinary control mortars. The adhesion increase to cementitious substrates was 52 and 49%, for the same substitution rate of 20% (wt%). Several studies, reported in the literature, have examined the effect of polymer addition on the adhesion of mortars to different substrates. Afridi et al. [75] carried out several adhesion tests on mortar substrates; they noted that the addition of EVA or SBR latex, in the form of powder or emulsion, to mortars, with rates increasing from 0 to 20%, increases adhesion. Moreover, Ohama [1,3] showed that the adhesion of mortars, modified by SBR, EVA, and PAE, to cementitious substrates, increases as the (P/C) ratio rises from 0 to 20%. In addition, Mansur et al. [9] confirmed the beneficial effect of introducing powdered polymers, such as EVA poly (ethylene-co-vinyl acetate), on the adhesion of mortars applied on ceramic substrates. Similar observations were also made by Jenni et al. [76] on the adhesion of mortars prepared with polyvinyl alcohol powder and cellulose ether. Brien and Mahboub [77] also considered four powdered polymers, the first one based on acrylic, the second one on styrene–butadiene, and the two others on vinyl acetate; they studied their effect on the behavior of adhesion of mortars prepared with calcium sulfoaluminate cement. The authors used three different substrates, i.e. ordinary concrete prepared with Portland cement, wood


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Figures 13. (a) and (b). Failure mode of the samples after the peel test (pull-off).

substrates, and metal and glass materials, with a (P/C) ration equal to 15%. As a conclusion, they found that all modified mortars displayed good adhesion characteristics, especially for concrete-based substrates. The improvement in adhesion is mainly attributed to the formation of a polymer film and hydrated cement compounds at the interface between the modified mortar and substrate.[8,9,30,78] Latex films interweave cement hydrates, forming the monolithic polymer–cement co-matrix structure at the interface (modified mortar – substrate), and come bridging the pores and cracks in this interface.[9] A small amount of carboxylic acid is chemically bound onto the polymer particle surface. This acid when ionized in the highly alkaline environment (high pH medium) of fresh mortar tends to interact with calcium ions from the cement hydrates, which generally results in improved stability of the polymer latex and higher bond strength between the latex-modified mortar and the existing substrates.[8,9,57] Furthermore, the substrates used in this study are known to be very porous materials; according to Mansur et al. [9], the adhesion of modified mortars to substrates, which have a high water absorption (>6 wt.%) (very porous), exhibits a mechanical anchoring and a general improvement in mortars properties in addition to the formation of a continuous polymer film at the interface. It can be said that the latex and cement hydrates can seep into the porous network of substrates (clay bricks and cementitious materials), and thus adhere strongly to these substrates. Our results are in good agreement with the results found by Mansur et al. [9]. The model developed by these authors, which explain the mechanisms of adhesion at the interfaces between the mortars and porous substrates, can summarize our results. A closer examination of the results allows noting that better adhesion properties were obtained with SBR-modified mortars, especially for significant substitution rates, compared with mortars modified by SA. An explanation was suggested by Ngassam [8] on the adhesion of mortars modified with EVA and SA. The best adhesion performance obtained for mortars modified with SBR is due to their rheological behavior. Indeed, these mortars have a higher fluidity than that encountered in mortars containing SA (see Table 5). Several researchers [8,60,61,79] defined fluidity in terms of the wettability of the material; they stated that the material should have good wettability and a good flow in order to increase the effective contact surface area between mortar and the substrate. This will certainly improve the adhesion strength of mortars to the different substrates. Figures 13 and 14 show the failure mode of the samples, after the peel test and flexural tensile test were performed on the bicomponent mortars.

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Figure 14. Rupture mode of samples after the bending tensile test.

In the case of bricks, it is noted that beyond 10% cement replacement by latex, the failure is purely cohesive within the substrate layer, unlike the case of low replacement levels where the failure is nearly at the interface. At the rate of 10% substitution by SA, the failure is cohesive both within the substrate and at the interface (see Figure 13(a) and (b)). By cons, for cementitious substrates, the failure is reported at the interface, for all formulations studied (see Figure 14), which means that the failure is not cohesive. This is certainly due to the state of the surface of the substrate layer (flat surfaces). We think that to better bring out the cohesive failure, it is necessary that the cement substrate has a rough surface. The increase thereof causes an increase in the contact surface which increases the adhesion.[60,62,65,66] The low values obtained for adhesion of the mortars to clay bricks can be attributed to the nature of the substrates used (very porous and perforated), and mostly to the testing method.[1,65] Clay bricks, with horizontal perforations and water absorption equal to 13.55%, do not have high mechanical properties (in tensile). For this reason, the value of adhesion must be low. This is also confirmed by the results obtained for mortars modified by substitution rate (≥10%, wt %). It is clear that even if the failure is located in the substrate (in brick), the value of adhesion remains low. Regarding the test method, many researchers conclude that the measure of bond strength between two layers of concrete is to a significant extent influenced by the choice of test method. Ohama [1], Naderi et al. [80], and Momayez et al. [65] found out that the value of adhesion, through in tension (direct tension, pull-off), is much lower than the value of adhesion obtained by other test methods (slant shear and bisurface shear). Moreover, Momayez et al. [65] have concluded that the pull-off test provides the most conservative bond measurement because it is not influenced by friction or other forces that are present in other methods.


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4. Conclusions Increasing the substitution levels of cement by the latex (SBR and SA), in the cementitious mix, leads to a reduction in the quantity of mixing water. Therefore, the latex can be successfully used as water reducers. The compressive strength increases with the increase in cement content in the mix and with age. However, increasing the amount of polymer into the mix decreases the open porosity accessible to water (beyond 10% by weight cement replacement) as well as the compressive strength. It also promotes an increase in the flexural tensile strength beyond 60 days. Furthermore, the drying of modified mortars was noted to have a significant impact on the flexural tensile strength, after 28 days. SBR- and SA-modified mortars also cause an increase in the bond strength of mortars to clay bricks and to cement substrates as well. Beyond 10% cement replacement, failure in modified mortars is purely cohesive within clay substrates, unlike the case of low substitution levels where the failure occurs at the interface. However, for flat cementitious substrates, the failure is always at the interface, for all the formulations studied. Increasing the wettability and spreading of mortars tend to raise the effective contact area between mortar and the substrate, which improves adhesion. Substitution of cement by latex, with rates ranging from 10 to 15% (by weight), seems to be efficient according to the required applications, if one takes into account the balance between mechanical performance, durability, and the amount of polymer incorporated. From the results obtained, one can say that using latex for partial replacement of Portland cement in mortars may offer better durability, improved adhesion to various substrates, and a slightly improved mechanical behavior, and this gives them a longer lifetime.

Note 1. ENG : Algerian Company of Aggregates.

Disclosure statement No potential conflict of interest was reported by the authors.

References [1] Ohama Y. Handbook of polymer-modified concrete and mortars. properties and process technology. Park Ridge (NJ): Noyes Publications; 1995. [2] Ohama Y. Recent progress in concrete-polymer composites. Adv. Cem. Bas Mat. 1997;5:31–40. [3] Ohama Y. Polymer-based admixtures. Cem. Concr. Compos. 1998;20:189–212. [4] Wang R, Wang P-M, Li X-G. Physical and mechanical properties of styrene–butadiene rubber emulsion modified cement mortars. Cem. Concr. Res. 2005;35:900–906. [5] Morin V, Moevus M, Dubois-Brugger S, et al. Effect of polymer modification of the paste–aggregate interface on the mechanical properties of concretes. Cem. Concr. Res. 2011;41:459–466. [6] Ramli M, Tabassi AA. Mechanical behaviour of polymer-modified ferrocement under different exposure conditions: an experimental study. Compos. Part B: Eng. 2012;43:447–456. [7] Ramli M, Tabassi AA. Effects of polymer modification on the permeability of cement mortars under different curing conditions: a correlational study that includes pore distributions, water absorption and compressive strength. Constr. Build. Mater. 2012;28:561–570.

238


[8] Ngassam ILT. Durabilité des réparations des ouvrages d’art en Béton [Durability of repairing concrete structures] [Phd thesis]. France: University of Paris-Est; 2013. p. 219. French. [9] Mansur AAP, Nascimento OLd, Mansur HS. Physico-chemical characterization of EVA-modified mortar and porcelain tiles interfaces. Cem. Concr. Res. 2009;39:1199–1208. [10] Khattab MM. Effect of gamma irradiation on polymer modified white sand cement mortar composites. J. Ind. Eng. Chem. 2014;20:1–8. [11] Muthadhi A, Kothandaraman S. Experimental investigations on polymermodified concrete subjected to elevated temperatures. Mater. Struct. 2013;47:977–986. [12] Amde AM, Colville J, Brown JC. Polymer modification of masonry cements in brick masonry. TMS J. 2007:69–78. [13] Shao-jie L, Hong-jie L, Pei-xin L, et al. Preparation and properties of an environment friendly polymer-modified waterproof mortar. Constr. Build. Mater. 2011;25:2635–2638. [14] Balayssac JP, Nicot P, Ruot B, et al. Influence of admixtures on the cracking sensitivity of mortar layers applied to a mineral substrate. Constr. Build. Mater. 2011;25:2828–2836. [15] Shao-jie L, Hong-jie L, Pei-xin L, et al. Preparation and properties of a core-shell styrene-acrylic copolymer modified adhesion mortar using iron tailings as the aggregate. J. Adhes. Sci. Technol. 2014;28:722–730. [16] Soni K, Joshi YP. Performance analysis of styrene butadiene rubber-latex on cement concrete mixes. J. Eng. Res. Appl. 2014;4:838–844. [17] Wang Q, Fu S, Yu T. Emulsion polymerization. Prog. Polym. Sci. 1994;19:703–753. [18] Amaral Md. Assessing the environmental cost of recent progresses in emulsion polymerization. React. Funct. Polym. 2004;58:197–202. [19] Thickett SC, Gilbert RG. Emulsion polymerization: state of the art in kinetics and mechanisms. Polym. 2007;48:6965–6991. [20] Nguyen D. Etude de la nucléation controlée de latex polymère à la surface de nanoparticules d’oxyde pour l’élaboration de colloides hybrides structurés [Study of the controlled nucleation of polymer latex to the surface of the oxide nanoparticles for the development of structured hybrid colloids] [Phd thesis]. France: University of Bordeaux 1; 2008. p. 166. French. [21] Erdmenger T, Guerrero-Sanchez C, Vitz J, et al. Recent developments in the utilization of green solvents in polymer chemistry. Chem. Soc. Rev. 2010;39:p. 182. [22] Youssef I. Polymérisation en émulsion et en miniémulsion. Influence de la combinaison de stabilisants moléculaires et macromoléculaires et suivi in situ par spectroscopie Raman [Emulsion polymerization and miniemulsion. Influence of the combination of molecular and macromolecular stabilizers and monitoring in situ by Raman spectroscopy] [Phd thesis] France: University of Lorraine; 2012. p. 182. French. [23] Pragliola S, Vita RD, Longo P. Aqueous emulsion polymerization of styrene and substituted styrenes using titanocene compounds. Polymer. 2013;54:1583–1587. [24] Ojeda T, Yamak HB, Ross KA, et al. Polymer science. In: Yılmaz F, editor. Croatia: InTech; 2013. p. 256. [25] Al-Zahrani MM, Maslehuddin M, Al-Dulaijan SU, et al. Mechanical properties and durability characteristics of polymer- and cement-based repair materials. Cem. Concr. Compos. 2003;25:527–537. [26] Gélinas L. Plastiques biosourcés : étude de leur performance environnementale comparativement aux plastiques pétrochimiques [Bio-based plastics: study of their environmental performance compared to petrochemical plastics] [Master’s thesis]. Canada: University of Sherbrooke; 2013. p. 111. French. [27] Rémy É Les plastiques biosourcés présentent-ils moins d’impacts négatifs pour l’environnement que les plastiques issus de la pétrochimie? [Biobased plastics they have fewer negative impacts on the environment as plastics derived from petrochemicals?] [Master’s thesis]. Canada: University of Sherbrooke; 2014. p. 197. French. [28] ACI Committee 548. Polymer-modified concrete. Farmington Hills (MI): American Concrete Institute; 2003. p. 40. [29] ACI Committee 548. Guide for the use of polymers in concrete. Farmington Hills (MI): American Concrete Institute; 1997. p. 29.


239

[30] Pierre N. Interactions mortier-support : éléments déterminants des performances et de [Mortarsupport interactions: determinants element of performance and adhesion of mortar] [Phd thesis]. France: University of Toulouse; 2008. p. 224. French. [31] Goto T. Influence des paramètres moléculaires du latex sur l’hydratation, la rhéologie et les propriétés mécaniques des composites ciment/latex [Influence of molecular parameters of the latex on hydration, rheology and mechanical properties of the composite cement / latex] [Phd thesis] France: University of Paris VI Pierre and Marie Curie; 2006. p. 243. French. [32] Shao-jie L, Qian-qian H, Feng-qing Z, et al. Utilization of steel slag, iron tailings and fly ash as aggregates to prepare a polymer-modified waterproof mortar with a core–shell styrene–acrylic copolymer as the modifier. Constr. Build. Mater. 2014;57:15–23. [33] Soufi A. Etude de la durabilit_e des systèmes béton armé : mortiers de réparation en milieu marin [Study of the durability of reinforced concrete systems – repair mortars in marine environment] [Phd thesis] France: University of La Rochelle; 2013. p. 235. French. [34] ACI Committee 548. Report on polymer-modified concrete. Farmington Hills (MI): American Concrete Institute; 2009. p. 39. [35] Baghini MS, Ismail A, Karim MR, et al. Effect of styrene–butadiene copolymer latex on properties and durability of road base stabilized with Portland cement additive. Constr. Build. Mater. 2014;68:740–749. [36] Wang R, Wang P. Function of styrene–acrylic ester copolymer latex in cement mortar. Mater. Struct. 2010;43:443–451. [37] Baueregger S, Perello M, Plank J. Influence of anti-caking agent kaolin on film formation of ethylene–vinylacetate and carboxylated styrene–butadiene latex polymers. Cem. Concr. Res. 2014;58:112–120. [38] Ukrainczyk N, Rogina A. Styrene–butadiene latex modified calcium aluminate cement mortar. Cem. Concr. Compo. 2013;41:16–23. [39] Diab AM, Elyamany HE, Ali AH. The participation ratios of cement matrix and latex network in latex cement co-matrix strength. Alexandria Eng. J. 2014;53:309–317. [40] Wang R, Wang P-M. Action of redispersible vinyl acetate and versatate copolymer powder in cement mortar. Constr. Build. Mater. 2011;25:4210–4214. [41] Wang R, Yao L, Wang P. Mechanism analysis and effect of styrene–acrylate copolymer powder on cement hydrates. Constr. Build. Mater. 2013;41:538–544. [42] ACI Committee 548. Guide for the use of polymers in concrete. Farmington Hills (MI): American Concrete Institute; 2009. p. 30. [43] Mehta PK, Monteiro PJM. Concrete Microstructure, Properties and materials. 3rd ed. New York (NY): McGraw-Hill Proffessional; 2006. p. 684. [44] Almesfer N, Ingham J. Effect of waste latex paint on concrete. Cem. Concr. Compos. 2014;46:19–25. [45] Diab AM, Elyamany HE, Ali AH. Experimental investigation of the effect of latex solid/water ratio on latex modified co-matrix mechanical properties. Alexandria Eng. J. 2013;52:83–98. [46] Ramli M, Tabassi AA, Hoe KW. Porosity, pore structure and water absorption of polymermodified mortars: an experimental study under different curing conditions. Comp. Part B: Eng. 2013;55:221–233. [47] Medeiros MHF, Helene P, Selmo S. Influence of EVA and acrylate polymers on some mechanical properties of cementitious repair mortars. Constr. Build. Mater. 2009;23:2527–2533. [48] Marceau S, Lespinasse F, Bellanger J, et al. Microstructure and mechanical properties of polymermodified mortars. Eur. J. Environ. Civ Eng. 2012;16:571–581. [49] Sikora P, Łukowski P, Cendrowski K, et al. The effect of nanosilica on the mechanical properties of polymercement composites (PCC). Procedia Eng. 2015;108:139–145. [50] Vargas J, Halog A. Effective carbon emission reductions from using upgraded fly ash in the cement industry. J. Cleaner Prod. 2015;103:948–959. [51] ASTM C373-88. Standard test method for water absorption, bulk density, apparent porosity, and apparent specific gravity of fired whiteware products. West Conshohocken (PA): ASTM International; 2006. p. 2

240


[52] Barluenga G, Hernandez-Olivares F. SBR latex modified mortar rheology and mechanical behaviour. Cem. Concr. Res. 2004;34:527–535. [53] ASTM C1437-07. Standard test method for flow of hydraulic cement mortar. West Conshohocken (PA): ASTM International; 2007. p. 2. [54] ASTM C230/C230 M-08. Standard specification for flow table for use in tests of hydraulic cement. West Conshohocken (PA): ASTM International; 2008. p. 6. [55] Kim J-H, Robertson RE. Prevention of air void formation in polymer-modified cement mortar by pre-wetting. Cem. Concr. Res. 1997;27:171–176. [56] Folic RJ, Radonjanin VS. Experimental research on polymer-modified concrete. ACI Mater. J. 1998;95:463–468. [57] Yang Z, Shi X, Creighton AT, et al. Effect of styrene–butadiene rubber latex on the chloride permeability and microstructure of Portland cement mortar. Constr. Build. Mater. 2009;23:2283– 2290. [58] BS EN196-1. Methods of testing cement – Part 1: determination of strength. London: Br. Stand Institution; 2005: p. 28 [59] Benfraj A Transfert dans les bétons non saturés : Influence des laitiers et de l’endommagement mécanique [Transfert in non saturated concrete : influence of slag and mechanical damage] [PhD thesis]. France: University of Nantes; 2009. p. 189. French. [60] Courard L, Piotrowski T, Garbacz A. Near-to-surface properties affecting bond strength in concrete repair. Cem. Concr. Compos. 2014;46:73–80. [61] Courard L. Contribution à l’analyse des paramètres influençant la création de l’interface entre un béton et un système de réparation [Contribution to the analysis of the parameters influencing the creation of the interface between a concrete and a repair system] [PhD thesis] Belgium: University of Liège; 1998. p. 198. French. [62] Garbacz A, Courard L, Kostana K. Characterization of concrete surface roughness and its relation to adhesion in repair systems. Mater. Charact. 2006;56:281–289. [63] Belaidi ASE, Benabed B, Soualhi aH. Physical and mechanical properties of concrete repair materials in dry and hot-dry environment. J. Adhes. Sci. Technol. 2015;29:543–554. [64] Courard L. Adaptation of the pull-off test for the evaluation of the superficial cohesion of concrete substrates in repair works: analysis of the test parameters. Mater. Struct. 2004;37:342–350. [65] Momayez A, Ehsani MR, Ramezanianpour AA, et al. Comparison of methods for evaluating bond strength between concrete substrate and repair materials. Cem. Concr. Res. 2005;35:748– 757. [66] Mirza J, Durand B, Bhutta AR, et al. Preferred test methods to select suitable surface repair materials in severe climates. Constr. Build. Mater. 2014;50:692–698. [67] Courard L, Lenaers J-F, Michel F, et al. Saturation level of the superficial zone of concrete and adhesion of repair systems. Constr. Build. Mater. 2011;25:2488–2494. [68] Aliabdo AAE, Abd_Elmoaty AEM. Experimental investigation on the properties of polymer modified SCC. Constr. Build. Mater. 2012;34:584–592. [69] Chew MYL, Tan PP, BSc YSY. Effect of styrene acrylic ester polymer on mortar render properties. Architectural Sci. Rev. 2011;47:43–52. [70] Gemert DV, Czarnecki L, Maultzsch M, et al. Cement concrete and concrete–polymer composites: two merging worlds. A report from 11th ICPIC Congress in Berlin, 2004. Cem. Concr. Compos. 2005;27:926–933. [71] BS EN1504-3. Products and systems for the protection and repair of concrete structures. Definitions, requirements, quality control and evaluation of conformity. Structural and nonstructural repair. London: Br. Stand Institution; 2006. p. 30. [72] Gregoire Y, Smits A. Choix des mortiers de maçonnerie [Choice of masonry mortars]; 2011. p. 11. French. [73] Tian Y, Jin X-y, Jin N-g. Research on the microstructure formation of polyacrylate latex modified mortars. Constr. Build. Mater. 2013;47:1381–1394. [74] Afridi MUK, Ohama Y, Demura K, et al. Development of polymer films by the coalescence of polymer particles in powdered and aqueous polymer-modified mortars. Cem. Concr. Res. 2003;33:1715–1721.


241

[75] Afridi MUK, Ohama Y, Iqbal MZ, et al. Water retention and adhesion of powdered and aqueous polymer-modified mortars. Cem. Concr. Compos. 1995;17:113–118. [76] Jenni A, Holzer L, Zurbriggen R, et al. Influence of polymers on microstructure and adhesive strength of cementitious tile adhesive mortars. Cem. Concr. Res. 2005;35:35–50. [77] Brien JV, Mahboub KC. Influence of polymer type on adhesion performance of a blended cement mortar. Int. J. Adhes. Adhes. 2013;43:7–13. [78] Do J, Soh Y. Performance of polymer-modified self-leveling mortars with high polymer–cement ratio for floor finishing. Cem. Concr. Res. 2003;33:1497–1505. [79] Courard L. Parametric study for the creation of the interface between concrete and repair products. Mater. Struct. 2000;33:65–72. [80] Naderi M, Ghodousian O. Adhesion of self-compacting overlays applied to different concrete substrates and its prediction by fuzzy logic. J. Adhes. 2012;88:848–865.