Physical and mechanical properties of styrene-butadiene rubber emulsion modified cement mortars

Polymer-modified cement mortars were prepared by varying polymer/cement mass ratio (P/C) with a constant water/cement mass ratio of 0.4. The effect of styrene-butadiene rubber (SBR) emulsion on the physical and mechanical properties of cement mortars is studied. With P/C below 10%, the toughness of the modified mortars enhances with the increase of P/C. A relationship between the physical and mechanical properties of the modified cement mortars at P/C below 10% is found; that is, the compressive strength and flexural strength of the modified mortars are directly proportional to the apparent bulk density. But when P/C is above 10%, the mechanical properties are not highly dependent on the apparent bulk density, and the flexural and compressive strength of the mortars are not improved further with more polymer. Two curing methods [wet cure: 2, 6 or 27 days immersed in 20 °C water; mixed cure: 6 days immersed in 20 °C water followed by 21 days at 20 °C and 70% relative humidity (RH)] were also evaluated in this paper. The results have shown that the mixed cure is more beneficial to the improvement of the mortar properties. A possible mechanism for polymer modification and the relationship between the physical and mechanical properties is proposed based on SEM and IR analyses. The interpenetrating structure between the polymeric phase and cement hydrates forms at a P/C of 8%, and fully develops at a P/C of 10%. The properties of the polymer-modified mortars are influenced by the polymer film, cement hydrates and the combined structure between the organic and inorganic phases.     

Preparation of a new polymer-modified adhesive mortar using fine iron tailings as aggregate

In this paper, a new polymer-modified adhesive mortar is prepared using the fine iron tailings, eco-cement, redispersible latex powder, additives, and water. In our study, the fine iron tailings are used to replace the natural river sand as the mortar aggregate and the optimal process conditions are determined by the orthogonal experiment. The obtained results are shown as follows: The ratios of cement–sand and polymer–cement are 1:2.5 and 4%, respectively, with the aggregate modulus 0.81 and water reducing agent 0.5% (cement-based). The properties of the polymer-modified adhesive mortar obtained under the optimal process conditions conform to JC/T 547-2005 (China Professional Standard: Ceramic Tile Adhesive). Moreover, the microstructure of the polymer-modified adhesive mortar is studied and discussed. The results show that the network formed by the intertwined polymer film can prevent the merger of micro-cracks and improve the adhesive mortars’ overall cohesion. Therefore, adding polymer to the adhesive mortar can improve its failure stress and enhance its bonding strength.     

Performance of polymer-modified self-leveling mortars with high polymer-cement ratio for floor finishing

Recently, polymer-modified mortar has been studied for proposed use on industrial floors as top coat with thin thickness, typically 5-15 mm. The purpose of this study is to evaluate basic properties of self-leveling materials using polymer dispersions as kinds of SBR latex, PAE and St/BA emulsions for thin coatings (under 3 mm in thickness). Superplasticizer and thickener have been included in the mixes to reduce bleeding and drying shrinkage as well as to facilitate the workability required. The self-leveling materials using four types of polymer dispersion are prepared with polymer-cement ratios of 50% and 75%, and were tested for basic characteristics such as density, flow, consistency change and adhesion in tension. The test results showed that the self-leveling mortars using PAE emulsion at a curing age of 28 days were almost equal to those of conventional floor using urethane and epoxy resins. The adhesion in tension of self-leveling mortars using SBR latex and PAE emulsion at a curing age of 3 days is over 1.67 MPa. It was noted that the consistency change is strongly dependent on the type of polymer dispersion. It is concluded that the self-leveling mortars with polymer dispersions can be used in the same manner as conventional floor-finishing materials using thermosetting resin in practical applications.     

Effect of polymer cement modifiers on mechanical and physical properties of polymer-modified mortar using recycled artificial marble waste fine aggregate

Various polymer-modified mortars using recycled artificial marble waste fine aggregate (AMWFA) were prepared and investigated for the purpose of feasibility of recycling. Styrene–butadiene rubber (SBR) latex and polyacrylic ester (PAE) emulsion were employed as polymer modifier, and compared each other. The replacement ratio of AMWFA was also changed to investigate the effect of it on physical properties. Adding polymer cement modifier into mortar reduced water–cement ratio, and PAE was the more effective polymer cement modifier to reduce water–cement ratio than SBR. PAE emulsion-modified mortar increased the air content entrained as the proportion of PAE was increased. There was little difference in water absorption between SBR latex and PAE emulsion. The compressive strength decreased in the presence of polymer cement modifiers compared to that of no polymer cement modifiers, but the compressive strength of 20% of polymer–cement ratio was higher than that of 10%. After the hot water resistance test, both compressive strength and flexural strength were decreased.     

Effect of polymer modification of the paste–aggregate interface on the mechanical properties of concretes

We investigated the effect of thin viscoelastic polymer coatings around aggregate particles on the mechanical properties of “micro-concretes” with a maximum aggregate diameter of 10 mm. Aggregate particles > 5 mm were pre-treated with a latex at dosages of up to 2% by mass and dried prior to using the treated aggregate in the micro-concrete mix. Cured prisms were tested in flexion. The results show that thin polymer coatings on aggregates have a significant effect on micro-concrete cracking behaviour at much lower polymer dosages than are commonly used in polymer-modified mortars. We observed a significant improvement in post-peak energy absorption relative to the use of the same amount of polymer dispersed in the bulk paste. But, under the conditions tested here, reductions in the strengths and moduli of the composites due to the polymer additions appear to have more than outweighed the observed positive effects of increases in fracture energy and characteristic length.     

Study of rehabilitation mortars: Construction of a knowledge correlation matrix

In old building rehabilitation practices, the gathering of full knowledge on used mortars is the most difficult task due to their complexity and variability. At the same time, this necessity of knowledge is critical, since the rehabilitation work must guarantee physical, chemical and mechanical compatibility between former and restoration mortars, not relinquishing aesthetic details. However, the characterization of old mortars can be a very complex process, since it involves different techniques and potentially controversial outcomes.In this work, several mortars were prepared and characterized, in order to improve knowledge that will facilitate the further choice of a suitable material to replace any old mortar. Analytical techniques like XRD and DTA/TGA were used in the determinations of chemical compositions, and physical properties determinations (apparent density, open porosity, compression strength, flexural strength, elastic modulus) were important to understand the mechanical behaviour and durability and to relate it with the prepared formulations composition.     

Properties of alite cements

For carrying out a comprehensive investigation on physical and mechanical properties of alite mortars and concretes, large quantities of monoclinic alite were produced at the University of California at Berkeley. Laboratory-size specimens were employed to determine strength, drying shrinkage, and sulfate resisting characteristics of mortars and concretes made with alite cements. Small amounts of gypsum (3%) addition accelerated the setting and hardening of the alite cements, however, large amounts (6%) resulted in strength deterioration. Drying shrinkage of alite concretes was significantly lower than portland cement concretes of the same fineness. Long term sulfate immersion of concrete specimens made with an alite cement caused serious spalling and strength loss.     

Mechanical and adhesion properties of polymer-modified cement mortars in relation with their microstructure

In this study, cement mortars were modified with a commercial polymer admixture. The aim of this study is to investigate the influence of the polymer content on the mechanical and adhesion properties of the mortars and to relate these properties with mortars’ microstructure. A series of mortars were produced with various polymer/cement/water/aggregate ratios. The adhesion properties of the mortars to clay bricks were tested with a simplified tensile testing measurement. The microstructure of mortars, as well as interfaces, were evaluated by Scanning Electron Microscopy (SEM). It was found that with high polymer content, large size hardened particles are formed, reducing the compressive strength of the mortars. Polymer addition enhances the adhesion between the mortar and brick. The mortar microstructure at the interface affects the adhesion properties and the mode of failure.     

Experimental study of accelerated leaching on hollow cylinders of mortar

Two mortars, differencing mainly in their initial porosity, were degraded by the use of a chemically accelerated process with ammonium nitrate solution. To specifically study the leached material, the chemical attack was undertaken on thin walled tubes. The leaching effects were evaluated by studying variations in mechanical and hydraulic properties. For both mortars tested, the kinetics of relative loss in strength, in elastic modulus and of increase in permeability were similar. For the same time of degradation, the increase in porosity and the loss in volumetric mass roughly depend on the estimated cement paste proportion of each mortar. The total process of degradation was carried out in three steps: 4, 8 and 16 days. Very sharp variations of all the studied properties were observed until 8 days of leaching followed by a plateau. These two phases are attributed to Portlandite dissolution first then to progressive C-S-H decalcification. At the end of the leaching test, a permeability increase of more than two orders of magnitude and a loss in strength and elastic modulus of more than 85% were observed for both mortars.     

Performance characteristics of subdenier monofilament polypropylene fiber reinforced mortars

An experimental investigation on the properties of fresh and hardened mortars reinforced with subdenier monofilament polypropylene fiber (MMPPF) is reported. Fiber effects on properties of mortars were assessed. Properties studied were flow, unit weight, setting time, bleeding ratio, compressive strength, impact resistance, water infiltration, and flexural load‐deflection. The results revealed that the addition of MMPPF had a positive effect on workability of fresh mortars, impact resistance, water impermeability, and flexural toughness, but had no positive effect on compressive strength. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2251–2256, 2004     

Superplasticized portland cement: production and compressive strength of mortars and concrete

This paper deals with the effect of intergrinding different percentages of a naphthalene-based superplasticizer with Portland cement clinker and gypsum on the fineness of the product, and on the water requirement and the compressive strength of the mortars made with the superplasticized cement. The properties of the fresh and hardened concrete made with the superplasticized cements were also investigated. The results showed that the intergrinding of a given amount of a naphthalene-based superplasticizer with Portland clinker and gypsum reduced the grinding time required for obtaining the same Blaine fineness as that of the control Portland cement without the superplasticizer. The water requirement of the mortars made with the superplasticized cements was similar to that of the mortars made with the control Portland cements when the same amount of the superplasticizer was added at the mortar mixer; for a given grinding time and a Blaine fineness of 4500 cm²/g, the mortars made with the superplasticized cement had higher compressive strength than those made with the control Portland cement. For a given grinding time or Blaine fineness of cement ≥5000 cm²/g, the slump loss, air content stability, bleeding, autogenous temperature rise, setting times, and compressive strength of the concrete made with the superplasticized cements were generally comparable to those of the concrete made with the control Portland cements when the superplasticizer was added at the concrete mixer.     

Assessment and prediction of drying shrinkage cracking in bonded mortar overlays

Restrained drying shrinkage cracking was investigated on composite beams consisting of substrate concrete and bonded mortar overlays, and compared to the performance of the same mortars when subjected to the ring test. Stress development and cracking in the composite specimens were analytically modeled and predicted based on the measurement of relevant time-dependent material properties such as drying shrinkage, elastic modulus, tensile relaxation and tensile strength. Overlay cracking in the composite beams could be very well predicted with the analytical model. The ring test provided a useful qualitative comparison of the cracking performance of the mortars. The duration of curing was found to only have a minor influence on crack development. This was ascribed to the fact that prolonged curing has a beneficial effect on tensile strength at the onset of stress development, but is in the same time not beneficial to the values of tensile relaxation and elastic modulus.     

Investigation of Shale Brick Interface with Cement-Lime and Polymer-Modified Mortars

Bonds between cement-lime mortar and shale brick, and between polymer-modified mortar and shale brick, were studied using a scanning electron microscope (SEM). The results showed that the bond is greatly influenced by the microstructure and chemical composition of the mortar at the interface contact area and by the microstructure of the brick surfaces. For relatively porous bricks, cement-lime mortars give a better bond, apparently due to better interpenetration of the fresh mortar into the open pores of the brick, creating a greater bond area. The presence of calcium contributes to good bonds, while large amounts of silicon were found in poorly bonded areas. Latex-modified mortars are not able to penetrate brick surfaces and are able to create strong bonds only on limited locations and allow water to enter brick masonary.     

Properties of latex blends and its modified cement mortars

In this paper, the mechanical properties of three latex blends and the mechanical properties and chloride diffusivity of the latex-modified mortars are studied. The relationships between the properties of polymer films formed from latex blends and the properties of the latex blend-modified mortars are illustrated. The test results showed that the modified mortar with the blend of styrene-acrylic ester (SAE) and styrene-butadiene rubber (SBR) showed synergistic effect; especially the flexural strength of the SAE/SBR blend-modified mortars was about 20-40% higher than that of monolatex-modified mortars. However, the vinyl chloride-vinylidene chloride copolymer (PVDC)/SBR and PVDC/SAE blends-modified mortars showed antisynergistic effect. The compressive strength of the modified mortars increased with the increasing of the tensile strength of the latex films, while the flexural strength of the modified mortars did not depend on the tensile strength of the latex films. When PVDC with the mass fraction of 0.2 or SAE copolymer emulsion with mass fraction of 0.4 was blended into SBR latex, the latex blend-modified mortars showed lower chloride diffusivity. The chloride diffusivity of the modified mortars increased approximately linear with the tensile strength of the latex blend films, and decreased with increase of the elongation at rupture of the latex blend films. When the elongation at rupture of the latex blend films increased from 200-300% to more than 800%, the chloride diffusivity of the modified mortars decreased from 10-15×10⁻¹² to 3-4×10⁻¹² m²/s.     

Effect of the monomer ratio on the properties of poly(methyl methacrylate butyl acrylate) latex‐modified mortars

This article deals with the effect of the monomer ratio on the typical properties of polymer‐modified mortars with poly(methyl methacrylate butyl acrylate) latices. Polymer‐modified mortars, with methyl methacrylate/butyl acrylate copolymer latices of various methyl methacrylate/butyl acrylate ratios, were prepared with different polymer/cement ratios and were tested for their workability, air content, compressive strength, flexural strength, and water absorption. On the basis of the test results, the effects of the monomer ratio and polymer/cement ratio on the typical properties were examined. The properties of the latex‐modified mortars were affected to a great extent by both the monomer ratio and polymer/cement ratio. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2403–2409, 2004     

Hydrophobic lime based mortars with linseed oil: Characterization and durability assessment

Linseed oil was added to lime and lime metakaolin mortars in order to impart hydrophobic properties and investigate its resistance to weathering agents involving water transport. Different properties of the mortars with 6 months of age were evaluated: open porosity, pore size distribution, water absorption by capillarity, mechanical strength, carbonation reactions, microstructure and durability assessed by testing the resistance to sodium chloride accelerated ageing test. Significant durability improvement of both lime and lime metakaolin mortars enriched with linseed oil was achieved: remarkable capillarity reduction and consequently higher resistance to NaCl cycles. Linseed oil had a different effect on the two studied mortars: mechanical strength was slightly reduced for lime and slightly raised for lime metakaolin. The mechanism for the durability improvement was found to be related to the modification of the chemical structure rather than on the alteration of the physical properties of the mortars.     

Mechanical properties of masonry repair dolomitic lime-based mortars

180 different mortars made with a dolomitic lime and different aggregates were prepared in order to be used in restoration works. This paper focuses on the effect of technological variables on pore structure and mechanical properties of magnesian lime-based mortars. Compressive and flexural strengths of the specimens were discussed according to curing time, binder : aggregate ratios, attributes of the aggregates and porosity, at long-term tests.A strong increase in the strength of mortars has been found after 365 curing days as compared to 28 curing days. The strength has been mainly attributed to the portlandite carbonation, because no significant changes have been observed in the brucite. However, higher strengths than similar aerial lime-based mortars led us to think of other mechanism which increases the strength: the calcite formation through a reaction of dedolomitization (alkali carbonate reaction, ACR) and the brucite crystallization were discussed.The pore structure has presented a significant influence on the strength. More binder amounts mean more strength due to the higher values of open porosity, which allows the carbonation process. The aggregate characteristics have been correlated with the strength and porosity. Limestone and angle-shaped aggregates, reducing large pores, cause a strength increment.     

Effect of material characteristics on the properties of blended cements containing high volumes of natural pozzolans

The effect of three different natural pozzolans from Turkish deposits on the properties of blended cements produced by intergrinding cement clinker with a high volume of natural pozzolan (55 wt.% of the cementitious material) was investigated. The particle size distribution of blended cements, setting time, heat of hydration, and compressive strength of blended cement mortars were determined. Experimental results showed that the hardness of the pozzolanic material strongly influenced the particle size distribution and the related properties of the blended cements by affecting the fineness of the components of the blended product. The early strength of the mortars was strongly affected by the particle size distribution of blended cements, whereas the strength development performance of the mortars was more related to the pozzolanic activity of the natural pozzolan present in the blended cement.     

可再分散性乳胶粉的作用机理与应用研究

可再分散性乳胶粉(SWF)是聚合物改性砂浆中的主要组分。探讨了SWF的作用机理,研究了SWF掺量对砂浆粘接强度、压缩强度、弯折强度和抗冻融能力等影响。实验结果表明,当w(SWF)≥20%时(占干聚合物改性砂浆的质量分数),其综合性能得到显著改善。     

内养护对不同细度水泥制备的砂浆性能的影响

研究了饱和轻骨料内养护对不同细度水泥配制的砂浆自收缩、强度、水化程度、显微硬度以及界面过渡区形貌等的影响。结果发现：内养护可显著降低不同细度水泥配制的砂浆的早期自收缩,但减缩效果随着水泥比表面积增大而降低;内养护的砂浆后期自收缩仍持续增加,水泥越粗,自收缩后期增长越大;内养护能够显著促进水泥早期水化,这种促进作用在细水泥中最显著。在相同条件下,轻骨料的引入对砂浆强度的影响作用与水泥细度有关;显微硬度以及界面过渡区微观形貌结果显示,轻骨料内养护能显著改善粗水泥体系微观结构,对细水泥体系微观结构的改善则无显著贡献。