Experimental study on properties of polymer-modified cement mortars with silica fume

This paper discussed the flexural and the compressive strengths of polyacrylic ester (PAE) emulsion and silica fume (SF)-modified mortar. The chloride ion permeability in cement mortar and the interfacial microhardness between aggregates and matrix were measured. The chemical reactions between polymer and cement-hydrated product were investigated by the infrared spectral technology. The results show that the decrease of porosity and increase of density of cement mortars can be achieved by the pozzolanic effect of SF, the water-reducing and -filling effect of polymer. Lower porosity and higher density can give cement mortars such properties as higher flexural and compressive strength, higher microhardness value in interfacial zone and lower effective diffusion coefficient of chloride ion in matrix.     

Porosity and mechanical properties of epoxy-resin modified cement mortar

The strength and fracture properties of epoxy resin modified cement mortar are studied. The amount of epoxy resin added varies from 5% to 17% by weight. Compared to the control unmodified cement samples, the experimental results show a 65% increase in flexural strength and a 85% increase in the specific fracture work at about 10% epoxy content. It is verified that void-filling is not the strengthening mechanism involved. The maximum size pores are less than the calculated size of the critical flaw so that they do not control the flexural strengths of these epoxy resin modified cement mortars. This finding is consistent with the concept of the crack growth resistance curve applied to cement mortar.     

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。     

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.     

水性环氧树脂改性水泥砂浆力学性能及微观结构

通过对水泥砂浆中掺加水性环氧树脂,制备了水性环氧树脂改性水泥砂浆,研究了不同聚灰比下,水性环氧树脂对水泥砂浆水化和强度的影响.运用XRD、TG/DSC、SEM、FTIR微观测试手段,研究了水性环氧树脂对水泥砂浆水化产物的影响.研究结果表明:水性环氧树脂可形成聚合物膜会延迟水泥水化;水性环氧树脂的加入会降低水泥砂浆的抗压强度;当聚灰比在2％范围以内,水性环氧树脂可以提高水泥砂浆的抗折强度.     

焙烧水滑石对砂浆中氯离子渗透的影响

通过3.5%NaCl溶液连续浸泡的方式,从砂浆的孔隙结构和氯离子结合能力两个方面,研究了CLDHs的掺加对水泥砂浆抗氯离子渗透的影响,结果表明:与空白砂浆相比,随CLDHs的掺量增加,砂浆强度在一定程度上有所降低,但孔隙结构密实度相应提高;CLDHs的掺加能够显著提高砂浆的抗氯离子侵蚀能力,砂浆氯离子结合能力提高了20%~36%,氯盐浸泡28 d氯离子的渗透深度减小了26%~35%,且CLDHs掺量不宜过大,以占胶凝材料的3%左右为宜.     

干湿交替氯盐环境下氧化石墨烯水泥砂浆抗侵蚀研究

抗氯离子侵蚀能力的强弱对水泥基材料服役寿命长短有着关键性的影响。本文研究了不同氧化石墨烯(GO)掺量(0%、0.02%、0.04%、0.06%、0.08%、0.10%,质量分数)在干湿交替氯盐环境下对水泥砂浆抗氯离子侵蚀性能的影响,分析了不同GO掺量下自由氯离子浓度与水泥砂浆抗氯离子侵蚀性能之间的关系,并利用扫描电子显微镜从微观角度分析水泥砂浆的抗侵蚀性能。结果表明:GO能显著提高水泥砂浆的抗氯离子侵蚀能力,最佳掺量范围为0.04%~0.06%;在同一钻孔深度处,水泥砂浆内的自由氯离子浓度随着GO掺量的增加先降低后升高;GO能有效调节水泥砂浆的微观形貌,减少内部孔隙产生,密实结构,提高水泥砂浆抗氯离子侵蚀能力。     

Masonry repair lime-based mortars: factors affecting the mechanical behavior

The increasing use of lime-based mortars for the restoration of historic buildings and structures justifies the research on these materials. The focus of this paper is the effect of technological variables on pore structure and mechanical properties of lime-based mortars. The influence of curing time, binder-aggregate (B/Ag) ratio, aggregate attributes and porosity is discussed. Mortars prepared with aerial lime, varying aggregate types and B/Ag ratios ranging from 1:1 to 1:5 by volume were tested. Compressive and flexural strength measurements, as well as X-ray diffraction (XRD) and thermal studies, were performed after 3, 7, 28, 91, 182 and 365 days. A strong increase in strength of mortar mixtures after 365 curing days (as compared to 28 curing days) is found. In spite of the fact that larger amounts of binder increase the total porosity, the strength of these mixtures is also increased. A good interlocked structure is obtained as binder contents increase. Also, higher porosities allow better portlandite carbonation. A relationship between mechanical properties and pore structure was established. However, in case of binder excess, the increase in voids leads to a strength reduction. The use of calcareous aggregates improves strength more as compared to the use of siliceous aggregates. Factors as grain size distribution and grain shape of the aggregates have also been considered.     

高沸醇木质素环氧树脂改性水泥砂浆的力学性能研究

用高沸醇竹子木质素合成了木质素环氧树脂和木质素环氧树脂亲水衍生物。用红外光谱对产物进行了表征,并研究了不同聚/灰比和养护条件对高沸醇竹子木质素环氧树脂及其亲水衍生物改性水泥砂浆的力学性能的影响。结果表明:随着聚/灰比的增加,试样的抗折强度提高,而抗压强度降低,试样的韧性增强,当聚/灰比大于0.12时,抗折强度明显提高;混合养护条件所得试样的综合性能优于水养护条件。     

Microstructural analysis of plain and reinforced mortars under chloride-induced deterioration

This paper reports the results of microstructural analysis of plain and steel-reinforced mortar specimens deteriorated by chlorides that were admixed or introduced through chloride ingress. The electrical properties of mortars were measured and their microstructural characteristics were investigated using quantitative image analysis techniques. The influence of chloride ions on mortar microstructure are discussed in terms of hydration and corrosion products. The research reveals that chlorides will induce changes in the chemical compositions and morphology of cement hydration products, and thereby exert influence on ion transport in the mortar specimens. The electrical properties of plain and reinforced mortars are not only related to the presence of chlorides in the pore system but are also influenced by the pore structure characteristics. The cementitious matrix undergoes certain alterations in conditions of the combined effects of: cement hydration, chloride ion transport and chemical binding mechanisms. To this end the pore structure characteristics appeared to be a significantly contributing factor in the process of chloride-induced corrosion in reinforced cement-based materials.     

Compatibility between ecocement produced from incinerator ash and reactive aggregates in ASR expansion of mortars

Recently, in Japan, two new-type hydraulic cements, high early strength type ecocement (HEC) and normal type ecocement (NEC), have been developed using incinerator ashes up to 50% of the raw materials. In this study, the compatibility of these ecocements with various types of reactive aggregates with respect to alkali-silica reaction (ASR) was studied. Ordinary Portland cement (OPC) and blast furnace slag cement (BFSC) were also used for a comparative study. Two types of the accelerated mortar bar expansion test, the JIS A1146 and the Danish methods, were used to clarify the expansion behavior of mortars made with the above cements. The influence of a combination of the chemical and mineralogical compositions of cement and the reactive components of aggregate on both the amount of ASR gel and the expansion rate of the mortar was also investigated. From the results, it was found that the expansion behaviors of mortars due to ASR varied significantly depending on a combination of both the mineralogical composition of cement and the reactive component of aggregate.     

含玻璃砂的高性能碱激发矿渣砂浆性能研究

采用玻璃砂代替部分细骨料制备碱激发矿渣(AAS)砂浆后,研究了玻璃砂含量(0%、10%、20%、30%,质量分数)对AAS砂浆抗压强度、抗折强度、干燥收缩、导热系数和碱-硅酸反应(ASR)膨胀率的影响,并通过扫描电子显微镜(SEM)对微观机理进行了分析。结果表明：掺10%～30%的玻璃砂能显著提高AAS砂浆的早期抗压强度,但会略微降低28 d抗压强度;AAS砂浆的抗折强度随玻璃砂掺量的增加先增大后减小,10%掺量时最有利于3 d抗折强度,20%掺量时最有利于28 d抗折强度;AAS砂浆的干燥收缩、导热系数和ASR膨胀率均随玻璃砂掺量的增加而减小,与对照组相比,掺30%玻璃砂的AAS砂浆导热系数降低14.4%,56 d干燥收缩率降低27.6%,14 d ASR膨胀率降低39.6%,28 d ASR膨胀率降低34.5%;SEM分析发现玻璃砂表面有水化产物生成,其与胶凝材料的结合比石英砂更紧密,使AAS砂浆的微观结构更加致密。     

Corrosion behavior of steel in alkali-activated fly ash mortars in the light of their microstructural,mechanical and chemical characterization

This study concerns the corrosion behavior of steel in different room temperature cured alkali-activated fly ash mortars exposed to chloride solution. The corrosion process was monitored by polarization resistance and corrosion potential measurements and the results were interpreted in the light of a complete microstructural, mechanical and chemical characterization of the mortars. The most compact alkali-activated mortars have higher porosity and lower mechanical properties than a cement-based mortar (CEM), but the protectiveness afforded to the rebars is slightly higher than that obtained in CEM. The reason for this discrepancy is connected to a lower chloride content accumulated in the former mortar type and to a specific inhibition of the rebar corrosion afforded by the pore electrolyte in alkali-activated mortars.     

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.     

Corrosion resistance and chloride diffusivity of volcanic ash blended cement mortar

This article reports the results of an investigation on the chloride diffusivity and corrosion resistance of volcanic ash (VA) blended cement mortars with varying curing times of up to 1 year. The mortars had 20% and 40% VA as cement replacement and water/binder ratio of 0.55. The accelerated chloride ion diffusion (ACID) test was used to calculate the chloride ion (Cl⁻) diffusion coefficient (D_i) of the mortars using the Nernst-Plank equation for steady state condition. In addition, electrical resistivity, mercury intrusion porosimetry and differential scanning calorimetry (DSC) tests were conducted. Electrochemical measurement such as linear polarization resistance was used to monitor the corrosive behavior of the embedded steel bars. The chloride ingress into the mortars was also studied. Good correlations were found among D_i, total pore volume (TPV) and electrical resistivity of the mortars. It was also found that blending cement with VA significantly reduced the long-term D_i and hence increased the long-term corrosion resistance of mortars. This fact was also supported by the presence of lower quantity of Ca(OH)₂ and higher quantity of Friedel's salt in the VA blended mortars as observed from the DSC tests. Mortars with 40% VA showed better performance in terms of Cl⁻ diffusivity, chloride ingress and passivation period of embedded steel compared with the control mortar with 0% VA.     

Porengrössenverteilung von Mörteln nach lagerung im wasser und in einer chloridlösung

For the purpose of the investigation of relations between the chloride diffusion into concrete and the pore structure of the hardened cement paste, the porosity of cement mortars were examined. The mortar specimens of four cements with a graded blast-furnace slag content (0 to 79 % by mass) prepared at w/c ratios 0,50 and 0,70 were stored in a concentrated NaCl solution and water respectively up to 2 years. The pore size distributions of the mortars were determined by means of mercury intrusion porosimetry and water absorption. The samples stored in water showed a relationship between the percentage of small (gel) as well as great (capillary) pores and the slag content of the cement and the w/c ratio of the mortar. After 6 and 12 months, the storing in the chloride solution effected an alteration of the pore structure reducing the total and gel pore volume and increasing the capillar pore volume. Later, the gel pore fraction was near to that of the specimens stored in water.     

Investigations on the performance of silica fume-incorporated cement pastes and mortars

Studies on the performance of cementitious products with silica fume (SF) are very important, as it is one of the inevitable additives to produce high-performance concrete (HPC). In this study, some experimental investigations on the influence of SF on various preliminary properties of cement pastes and mortars are reported. The properties included specific gravity and normal consistency (NC) of cement and air content and workability of mortar with different SF contents. Pozzolanic and chemical reactions of SF have been studied on setting times, soundness and shrinkage of cement pastes. Further, strength developments in compression and tension in cement mortars have also been studied at various SF contents. SF was varied from 0% to 30% at a constant increment 2.5/5% by weight of cement. Test results show that the SF changes the behavior of cement pastes and mortars significantly. It has been observed that the water-binder (w/b) (cement+SF) ratio seemed to play an important role for the performance of the products with higher SF contents. NC, soundness and drying shrinkage of cement pastes and the strength of mortar increase as the SF content increases, while the initial setting times of cement pastes and the air content and workability of mortar decrease as the SF content increases. However, hardly any influence has been observed on the final setting times of cement pastes. The early age hydration reactions of C₃A and C₃S increase with the addition of SF. The optimum SF content ranges between 15% and 22%.     

VAC/DMC阳离子无皂乳液改性水泥砂浆研究

利用醋酸乙烯酯／甲基丙烯酰氧乙基三甲基氯化铵（VAC／DMC）阳离子型无皂乳液对水泥砂浆进行了改性研究，并与普通VAC均聚物乳液进行了比较。研究表明，！与普通水泥砂浆相比，VAC/DMC节离子型无皂乳液改性砂浆（聚灰比为0．1时）的抗折强度较普通砂浆够提高77％，其改性效果明显好于普通VAC乳液，表明用阳离子无皂乳液改性水泥性能能够取得良好效果。探讨VAC／DMC对水泥砂浆改性的原因。     

Polymer concrete and polymer mortar using resins based on recycled poly(ethylene terephthalate)

Fundamental properties of polymer concrete (PC) and polymer mortar (PM) made from unsaturated polyester resins based on recycled poly(ethylene terephthalate), PET, are described. Mechanical properties investigated include strength, modulus of elasticity, ductility index, Poisson's ratio, coefficient of thermal expansion, shrinkage, and exotherm. Durability properties include chemical resistance, water absorption, sand-blast resistance, and thermal cycles of thin overlays on portland cement concrete slabs. Resins based on recycled PET offer the possibility of a lower source cost for forming useful PC and PM (PC/PM) based products. The recycling of PET in PC and PM would also help alleviate an environmental problem and save energy.     

掺钢渣-矿渣-粉煤灰复合微粉混凝土性能研究

研究了由钢渣-矿渣-粉煤灰制备的复合微粉对混凝土强度、收缩性能和氯离子渗透性能的影响。结果表明：在同水胶比下,复合微粉等量取代水泥后,混凝土7d强度低于普通混凝土的强度,当复合微粉掺量小于45％时,其28d及以后强度高于普通混凝土。在同水胶比下,复合微粉等量取代水泥后,可有效降低混凝土的干燥收缩,且混凝土的抗氯离子渗透性能显著提高。