Effect of epoxy resin on the intrinsic properties of masonry mortars

The paper presents an assessment on the properties of three different types of masonry mortars, namely Portland cement mortar (CM), polymer cement mortar (PCM) and polymer mortar (PM) of various compositions. The effect of binder content (cement and/or epoxy) on CM, PCM or PM has been explored in the study. An assessment was carried out on the basis of mechanical (compressive, tensile and flexural strength), physical (water uptake, chloride ion permeability), morphological (porosity) and thermal (coefficient of thermal expansion) properties of the mortars. A comparative cost analysis of the mortars is also discussed in this article. The results show that the mechanical strength of both PCM and PM improves markedly with the addition of epoxy resin, and the higher rate of incremental strength is found for PM. Consequently, the chloride ion penetration, water uptake, porosity and thermal expansion of the mortars decrease significantly with the resin content, but the rate of drop in chloride ion penetration, water uptake, porosity and thermal expansion is much higher for PM. The test results indicate that the variation of binder content (epoxy/cement) is found to be the key factor determining the mortar properties and cost.     

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.     

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.     

聚丙烯酸酯乳液在水泥砂浆中的应用

为了提高水泥砂浆的韧性,选用了能形成柔性薄膜结构的聚合物--聚丙烯酸酯乳液对水泥砂浆进行改性.研究了聚丙烯酸酯乳液对水泥砂浆体积密度、抗压强度、抗折强度、韧性、动弹模量和黏结抗拉强度的影响.结果表明:聚丙烯酸酯乳液在一定程度上降低了水泥砂浆体积密度和抗压强度,对抗折强度影响较小,改善了水泥砂浆的韧性,并且可提高黏结抗拉强度.当乳液掺量(质量分数)大于5%时,28 d混合养护聚丙烯酸酯乳液水泥砂浆的压折比降低到3以下,只有当乳液掺量大于10%时,水泥砂浆的黏结抗拉强度才明显提高.     

海水和矿物掺合料对硫铝酸盐水泥砂浆性能的影响

本文研究了不同拌和水以及海水拌和时粉煤灰和硅灰掺量对硫铝酸盐水泥(SAC)砂浆力学性能和表观孔隙率以及净浆凝结时间、化学收缩、孔溶液pH值和氯离子结合能力等的影响,并通过XRD、SEM和EDS分析水泥水化产物和微观结构。结果表明,海水能加快SAC早期水化并提高其早期强度,但后期强度和淡水拌和时无明显差别。粉煤灰和硅灰均会延长SAC凝结时间,对早期抗压强度不利,而掺加质量分数为5.0%和7.5%的硅灰能提高SAC砂浆28 d抗压强度。硅灰掺量增加时会提高用水量和表观孔隙率,降低流动性,使水泥化学收缩增大,降低净浆pH值且减少氯离子结合量;粉煤灰能够提高砂浆流动性,减少水泥化学收缩,但掺量越大对SAC砂浆抗压强度和抗折强度越不利,掺质量分数为10%的粉煤灰可小幅提高氯离子结合量且减小表观孔隙率。     

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。     

Latex influence on the mechanical behavior and durability of cementitious materials

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.     

Properties of fly ash-modified cement mortar-aggregate interfaces

This paper investigates the effect of fly ash on strength and fracture properties of the interfaces between the cement mortar and aggregates. The mortars were prepared at a water-to-binder ratio of 0.3, with fly ash replacements from 15 to 55%. Notched mortar beams were tested to determine the flexural strength, fracture toughness, and fracture energy of the plain cement and fly-ash modified cement mortars. Another set of notched beams with mortar-aggregate interface above the notch was tested to determine the flexural strength, fracture toughness, and fracture energy of the interface. Mortar-aggregate interface cubes were tested to determine the splitting strength of the interface. It was found that a 15% fly ash replacement increased the interfacial bond strength and fracture toughness. Fly ash replacements at the levels of 45 and 55% reduced the interfacial bond strength and fracture toughness at 28 days, but recovered almost all the reduction at 90 days. Fly ash replacement at all levels studied increased the interfacial fracture energy. Fly ash contributed to the interfacial properties mainly through the pozzolanic effect. For higher percentages of replacement, the development of interfacial bond strength initially fell behind the development of compressive strength. But at later ages, the former surpassed the latter. Strengthening of the interfaces leads to higher long-term strength increases and excellent durability for high-volume fly ash concrete.     

Effect of carbon fibres on the mechanical properties and corrosion levels of reinforced portland cement mortars

The changes in mechanical properties of portland cement mortars due to the addition of carbon fibres (CF) to the mix have been studied. Compression and flexural strengths have been determined in relation to the amount of fibres added to the mix, water/binder ratio, curing time and porosity. Additionally, the corrosion level of reinforcing steel bars embedded in portland cement mortars containing CF and silica fume (SF) have also been investigated and reinforcing steel corrosion rates have been determined. As a consequence of the large concentration of oxygen groups in CF surface, a good interaction between the CF and the water of the mortar paste is to be expected. A CF content of 0.5% of cement weight implies an optimum increase in flexural strength and an increase in embedded steel corrosion.     

聚苯乙烯接枝聚丙烯酸丁酯乳液改性水泥砂浆的性能及微观结构分析

合成了聚苯乙烯(PS)接枝聚丙烯酸丁酯(PBA)乳液(PS-g-PBA),并将其用于改性水泥砂浆,考察了PS-g-PBA乳液含量及PS与PBA的质量比对改性水泥砂浆的减水率、流动度、力学性能以及毛细孔吸水率的影响.结果表明,3种水泥改性剂的减水效果优异,减水率的极大值为56.7％,改性水泥砂浆的毛细孔吸水率下降明显,其...     

硅烷偶联剂对复合水泥砂浆性能的影响

通过红外光谱分析及砂浆强度测试，研究了硅烷偶联剂对不同种类复合水泥砂浆的稠度、分层度、抗折强度及抗压强度的影响。结果表明，加入硅烷偶联剂能提高普通水泥砂浆、苯丙胶乳改性水泥砂浆的抗折强度和抗压强度；当硅烷偶联剂质量分数为0．5％时，普通水泥砂浆的抗折强度和抗压强度达到极大值，提高约10％；当硅烷偶联剂质量分数为1％时，苯丙胶乳改性水泥砂浆的抗折强度和抗压强度达到极大值，提高约20％；同时，硅烷偶联剂还能增大普通水泥砂浆和苯丙胶乳改性水泥砂浆的稠度，但砂浆的分层度略有增大。加入经硅烷偶联剂处理的钢纤维，能够提高普通水泥砂浆及苯丙胶乳改性水泥砂浆的抗折强度和抗压强度；当钢纤维用硅烷偶联剂质量分数为1％的硅烷偶联剂水溶液处理时，钢纤维增强砂浆的抗折、抗压强度达到极大值，提高10％以上。     

Effects of organo-modified montmorillonite on strengths and permeability of cement mortars

Organo-modified montmorillonites (OMMT) which have been widely used in polymer/clay nano-composites are employed here as fillers and reinforcements in cement mortars. The ratio of quartz sand and cement is 2.75 while the water/cement ratios of 0.40, 0.485 and 0.55 are considered for the cement mortars we studied. Experimental results indicate that the coefficients of permeability of cement mortars could be 100 times lower if a lower dosage of OMMT micro-particles is added. At the same time, the compressive and flexural strengths of cement mortars can be even increased up to 40% and 10%, respectively. It is also found that the optimal dosage of OMMT micro-particles to give higher compressive and flexural strengths and a lower coefficient of permeability for cement mortars is less than 1%. Meanwhile, the microstructure of cement mortars is characterized by using SEM, EDS and MIP to evaluate the effects of OMMT micro-particles on the improvements of strengths and permeability of cement mortars.     

碳纳米管-水泥基复合材料的力学性能和微观结构

研究了掺碳纳米管水泥砂浆的力学性能和微观结构,并与掺碳纤维水泥砂浆的性能进行了对比。低含量的碳纳米管-水泥复合材料具有良好的抗压强度和抗折强度。用扫描电镜对碳纳米管-水泥复合材料以及碳纤维-改性水泥复合材料的微观结构进行了分析。结果表明：复合材料中碳纳米管表面被水泥水化产物包裹,同时碳纳米管水泥砂浆的结构密实。碳纤维表面光滑,在碳纤维与水泥石之间存在明显裂缝。孔隙率测试结果表明碳纳米管的掺入改善了材料的孔结构。     

Influence of the porosity gradient in cement paste matrix on the mechanical behavior of mortar

This paper is devoted to the study of the influence of the microstructure of mortar on its mechanical behavior. For this purpose, mechanical tests have been carried out on mortars and a mathematical model, the (n + 1)-phase model, has been used to take into account three variable parameters of the microstructure of mortar (the thickness of the interfacial transition zone, the porosity gradient in the cement paste matrix and the nature of the constituents of the Interfacial Transition Zone) for some given parameters (volume fraction of aggregates, porosity of the mortar and mechanical behavior of the aggregates and the cement paste). By fitting some measured moduli to the model predictions, we can estimate in a non-destructive manner, the possible distribution of porosity within the Interfacial Transition Zone. Our results provide information on the data such micromechanical models can deal with in order to predict the elastic behavior of mortars.     

新旧水泥砂浆界面粘结性能试验研究

在荷载和环境因素作用下,混凝土结构产生不同程度的劣化。为了保证结构的安全性和耐久性,需要对损伤水泥基材料进行修复。基体的含水饱和度、界面粗糙度、修补砂浆的水灰比以及试件的养护条件都会影响修补砂浆与基体间的粘结强度。选取四种含水饱和度(0%、30%、70%、100%)的旧砂浆作为基体,浇筑水灰比为0.4和0.6的新砂浆,试件密封养护28 d,剪切试验结果表明:当新砂浆水灰比为0.6,旧砂浆含水饱和度按照70%、30%、100%、0%的顺序变化时,界面的剪切强度逐渐减小;当新砂浆水灰比为0.4,旧砂浆含水饱和度按照30%、0%、70%、100%的顺序变化时,界面的剪切强度逐渐减小。同时发现,新砂浆水灰比为0.4时的界面剪切强度普遍大于水灰比为0.6的数值。通过切槽法改变旧砂浆的界面粗糙度,然后浇筑水灰比为0.6的新砂浆,试件标准养护。剪切试验结果表明:当旧砂浆界面粗糙时,界面间的剪切强度是旧砂浆光滑时的1.26倍。选取两种含水饱和度(0%、100%)的旧砂浆作为基体,浇筑水灰比为0.4和0.6的新砂浆,分别进行标准养护和密封养护,剪切试验结果表明:在旧砂浆含水饱和度和新砂浆水灰比相同的情况下,标准养护下的界面剪切强度明显大于密封养护下的界面剪切强度。     

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.     

Methods of obtaining pore solution from cement pastes and mortars for chloride analysis

Two techniques for the recovery of pore solution from cement mortars are examined: pore solution expression and miscible displacement using a high pressure permeameter. In the former, the pore solution is expressed from the mortar by crushing; in the latter, it is eluted from the mortar over 30 min by miscible displacement with water. Experimental results are presented for a range of cement pastes and mortars into which known amounts of chloride ion have been incorporated by using sodium chloride solution as the mix water. The results show that both eluted and expressed solutions exhibit a decrease in chloride ion concentration as the cement matrix ages, with the elution method showing a greater sensitivity to mix composition. Both methods show a decrease in chloride concentration as the water: cement ratio of the mix is increased. Overall, the high pressure elution method is capable of recovering a significantly higher proportion of the incorporated chloride. The application of these techniques to pore solution analysis is discussed.     

再生混凝土单轴受压下多重界面过渡区的破坏机理研究

为研究再生粗骨料混凝土在单轴受压荷载下的破坏特性,使用数字图像相关技术记录混凝土立方体在破坏过程中的应变变化规律,并结合显微硬度测试、背散射电子成像技术等观测手段对界面过渡区的宽度和孔隙率进行定量表征。试验结果表明,分别经骨料强化和砂浆强化后,再生混凝土的抗压强度较未处理试样提升了17.86%和35.55%,说明砂浆强化更有利于提升再生混凝土的抗压强度。骨料强化可以提升老砂浆显微硬度值,降低老骨料-老砂浆界面过渡区孔隙率;砂浆强化可以提升新砂浆显微硬度值,降低老骨料-新砂浆界面过渡区以及新-老砂浆界面过渡区的孔隙率。经强化处理后的特定界面产生贯通裂缝的概率降低。     

涂层对速凝3D打印水泥砂浆力学性能的影响

3D打印砂浆普遍存在层间界面粘结较弱、抗折强度较低的问题,而膨胀水泥浆涂层涂覆于砂浆表面可产生表层压应力,进而提升其抗折强度,作为界面剂涂覆于层间可同时增强其界面粘结强度。本文通过将硫铝酸盐水泥与膨胀剂混合而成的涂层涂覆于速凝3D打印砂浆的表面与层间,研究了该涂层对不掺纤维及掺0.5%(体积分数)玄武岩纤维3D打印砂浆试件力学性能的影响规律。结果表明,涂覆层间涂层对无纤维与掺纤维速凝3D打印砂浆的层间界面粘结强度提升率分别为21.4%、12.2%,同时对其抗压强度也有一定提升作用。仅涂覆表面涂层与仅涂覆层间涂层对3D打印砂浆的抗折强度提升效果相当;同时涂覆表面及层间涂层对3D打印砂浆的抗折强度提升效果最显著,与无纤维、掺纤维的无涂层试件相比,提升率最高分别可达44.2%、23.2%。涂层对于无纤维3D打印试件层间粘结强度及抗折强度的提升效果优于掺纤维试件。     

再生细骨料含水状态对砂浆性能的影响

采用再生细骨料取代质量分数30%河砂制备砂浆,通过预湿处理将再生细骨料含水率处理为其饱和面干吸水率的0%、30%、70%、100%,分别控制拌合用水量或总用水量一致,研究再生细骨料含水状态对砂浆性能及微观结构的影响规律。结果表明,拌合用水量一致时,砂浆流动度随再生细骨料含水率增大而增大,骨料含水状态对养护后期(28 d)力学性能的影响较小;总用水量一致时,砂浆流动度随再生细骨料含水率增大而减小,再生细骨料干燥状态下砂浆28 d力学性能较骨料含水状态下更好。两种用水量控制方案下,采用干燥再生细骨料配制的砂浆抗氯离子侵蚀性能均表现最优,且可达到与普通砂浆相当或更优的水平。微观结果表明,骨料的含水状态对微观结构影响显著,骨料预湿处理会对使新界面过渡区孔隙率增大、平均显微硬度下降,进而对宏观力学及耐久性能产生不利影响。在工程应用中保证流动度的前提下,应尽可能采用含水率低的再生细骨料配制砂浆。