Resistance to wear of fast-track Portland cement concrete

The selected fast-track Type I Portland cement concretes were studied for resistance to wear at both opening and maturity (28 days) times. The effect of four cements contents, namely: 386, 445, 505, and 564 kg/m³ (with and without an accelerating admixture) is also ascertained. The trial matrices were examined for plastic and bulk properties, and wear resistance. Depth of wear and rate of deterioration as functions of matrix proportions and constituents, opening-time categories, and testing duration were determined. The influence of variables such as cement content, curing age, and accelerating admixture on compressive strength and abrasion resistance of the selected matrices were studied. The coefficient of variation and abrasion index for the abrasion test of the trials concrete were also examined. Lastly, the relationship between the abrasion resistance (depth of wear) and compressive strength at both opening and maturity ages were investigated.     

真空脱水混凝土抗氯离子侵蚀性能研究

提出了制作真空脱水试件的试验方法;分析了真空脱水、粉煤灰和减水剂对混凝土抗氯离子侵蚀能力的影响;推断出运用真空脱水技术能改善混凝土抗氯离子侵蚀的性能,粉煤灰的掺量对混凝土抗氯离子侵蚀能力产生有利影响.     

橡胶集料混凝土研究进展综述

橡胶集料水泥混凝土具有轻质、弹性减震、降噪隔音、延性和韧性好等优点,目前是水泥混凝土领域的研究热点.本文综述了国内外在该领域已有的研究成果,全面介绍了该种混凝土的物理力学性能,指出了今后的研究方向,为该种材料的深入研究和应用提供了借鉴和指导意义.     

人工气候环境下混凝土氯离子扩散系数衰减速率

根据人工气候环境下的混凝土侵蚀试验测得的混凝土氯离子浓度,基于Fick第二定律,分别计算了侵蚀40、80、120、160、200d后的混凝土氯离子扩散系数,证实了氯离子扩散系数随侵蚀时间增大而减小;引入混凝土氯离子扩散系数衰减速率的概念,并分析计算得到了不同侵蚀时间的氯离子扩散系数衰减速率及其与时间的关系模型.计算结果表明:在人工气候环境下,随侵蚀时间的延长,混凝土氯离子扩散系数衰减速率相应减小.     

混凝土氯离子扩散性评价的交流阻抗法

如何延长氯盐环境中钢筋混凝土结构的使用寿命已经成为混凝土耐久性设计的主要目标。通过交流阻抗法评价配合比、掺合料和表面涂层对混凝土氯离子扩散性的影响,基于试验结果,定量分析了混凝土交流电阻随水灰比、最大骨料直径、骨料级配、粉煤灰掺量、耐蚀剂和表面涂层的变化特性,并给出了相应的解释,发现水灰比、骨料级配、粉煤灰和表面涂层对交流电阻的影响较大,这些结论可为钢筋混凝土结构的耐久性设计提供理论依据。     

Organic acid transport through a partially saturated liner system beneath a landfill

A one-dimensional model was developed to investigate the transport of organic acids (commonly found in landfill leachate) through a partially saturated composite liner system beneath a landfill. Specific attention was paid to the influence of water content distribution on aqueous-phase diffusion process. Composite liner system was investigated, which was consisted of a geomembrane and a compacted clay liner underlain by three kinds of attenuation layer: sand layer, sandy clay loam layer, and clay layer. Volumetric water content profile in soil layers was obtained by Van Genuchten model, and the Millington and Quirk model was employed to describe the non-linear relationship between volumetric water content and diffusion coefficient. Three cases were analyzed and compared, i.e., totally saturated condition, unsaturated condition without considering unsaturated diffusion model, and unsaturated condition considering unsaturated diffusion model. The numerical results show that the unsaturated sand attenuation layer could serve as excellent diffusion barrier to organic contaminant due to its low water retention capacity. When the dependence of diffusion coefficient on volumetric water content is sufficiently considered, the contaminant flux decreases significantly in all the three kinds of attenuation layer. Unsaturated diffusion model capturing the relationship between water content and diffusion coefficient enables a more reasonable prediction of contaminant transport and distribution in soils.     

Ag/AgCl电极测量水泥浆体中氯离子扩散系数

研究了Ag/AgCl-Pt电极型传感器的电位与氯离子浓度关系;并将传感器其埋入净浆在线监测氯离子扩散过程;同时计算分析了传感器的误差。结果表明:传感器电位值随氯离子浓度的增大而降低,与氯离子浓度的对数成现良好的线性关系,传感器线性响应范围宽,稳定性好,对氯离子具有较高的选择性;埋入水泥基材料中能监测孔隙液中氯离子浓度;传感器测量氯离子扩散系数相对误差约为30%,有望实现混凝土氯离子扩散系数的原位测定。     

长龄期粉煤灰混凝土氯离子扩散系数的试验研究

通过电导率法研究了水胶比、骨料含量、粉煤灰掺量和龄期对混凝土氯离子扩散系数的影响。测试结果表明,混凝土氯离子扩散系数随着水胶比的减小或骨料含量的增大而减小。粉煤灰的掺入显著增大了混凝土的抗氯离子渗透能力,最佳掺量为30%。从龄期的影响看,540 d内的混凝土氯离子扩散系数表现出显著减小的趋势,当龄期从540 d增加到1800 d时,混凝土氯离子扩散系数几乎维持不变。     

Experimental characterization of Portland cement-calcined soldier-ant mound clay cement mortar and concrete

Experimental studies on soldier-ant mound clay as cement replacement material is an on-going research in the Civil Engineering Programme, Abubakar Tafawa Balewa University, Bauchi, Nigeria. In this study, soldier-ant mound clay was calcined to 800 °C to produce calcined soldier-ant mound clay (CSAMC) and used in the proportions of 0%, 10%, 20%, 30% and 40% by mass of cement to study its effect on cement mortar and concrete properties. The study showed that CSAMC is pozzolanic, can reduce the heat of hydration by about 17% percent when cement was replaced with 40% CSAMC and accelerated the setting time of concrete. The mortar compressive strength of mix containing 10% CSAMC superceded the reference mix when cured above 60 days and the ratio of the splitting tensile strength to the flexural strength is approximately 0.33.     

Coupled diffusion of chloride and other ions in saturated concrete

Corrosion of reinforcing steel due to chloride ions is one of the severe deterioration problems in longterm performance of reinforced concrete structures. The deterioration process is frequently found in marine concrete structures, highway pavements, and bridges exposed to deicing salts. The diffusion of chloride ions is associated and strongly affected by other ions in the pore solution in concrete. In this paper, chloride penetration into concrete structures was mathematically characterized by the Nernst-Planck equation which considered not only diffusion mechanism of the chloride ions but also ionic interaction among other ions coming from externally applied deicers and within the Portland cement paste. Electroneutrality was used to determine the electrostatic potential induced by the ionic interaction. The material models of chloride binding capacity and chloride diffusion coefficient were incorporated in the governing equations. The governing equations were solved by using finite element method. A numerical example was used to illustrate the coupling effect of multi-ionic interactions and the effect of influential parameters. The numerical results obtained from the present model agreed very well with available test data.     

水泥混凝土路面施工程序和质量控制

介绍了混凝土路面板的施工程序和施工工艺以及各程序中的质量控制,包括模板安装、混凝土的拌运、摊铺、振捣、接缝和表面修整等,最后说明了工程完工后的检查项目和应达到的质量要求.     

Strength and corrosion properties of Portland cement mortar and concrete with mineral admixtures

This work aims to validate the design assumptions by the California Department of Transportation in order to better define the strategies used to design concrete structures with adequate corrosion mitigation and thus a “maintenance-free” service life. To this end, various laboratory tests were conducted to investigate the compressive strength of and chloride diffusivity in mortar and concrete samples with cement partially replaced by various minerals (class F and class N fly ash, ultra-fine fly ash, silica fume, metakaolin, and ground granulated blast-furnace slag), the porosity of mineral concretes, the freeze–thaw resistance of mineral mortars in the presence of deicers, and the effect of supplementary cementitious materials on the chloride binding and chemistry of the pore solution in mortar.     

Laboratory evaluation of incorporating waste ceramic materials into Portland cement and asphaltic concrete

Laboratory tests were conducted to evaluate the feasibility of incorporating fired ware scrap, a waste ceramic material from automobile manufacturing, into pavement material. In this study, crushed fired ware scraps were added into Portland cement concrete (PCC) and hot-mix asphalt (HMA) to replace fine aggregates.The results of this study indicated that the fired ware scraps can be potentially used in the Portland cement concrete and HMA mixture. The compressive strength of PCC was improved by adding crushed scrap. However, due to the high water absorption of the crushed scrap, crushed scrap content is recommended to be less than 10% and a water reduction additive is recommended to provide adequate workability. For HMA, the test results indicated that adding a certain amount (up to 15% by weight) of ground scrap improved the binder’s total resistance to deformation. The dynamic modulus, flow number and indirect tensile strength of the HMA mixture were all improved by adding “filler” made of ground scrap. 2.5% “filler” content was recommended for a dense-graded HMA surface mixture.     

橡胶集料水泥砂浆和混凝土的性能研究

废轮胎颗粒掺加到水泥砂浆和混凝土中会明显降低材料强度,大大限制其应用。针对该问题,应用多种方法来改进橡胶混凝土的力学性能,例如降低W/C、掺加硅灰、偶联剂预处理橡胶颗粒等。研究结果表明，降低W/C能够明显提高橡胶混凝土的强度,橡胶颗粒表面用PVA和硅烷偶联剂处理能够显著增加抗压强度，如果多种方法联合使用效果更好。此外，橡胶改性混凝土的强度虽然有所降低，但其韧性和抗疲劳特性却显著增加。应用SEM分析了橡胶混凝土的微观结构,结果同样证实偶联剂处理橡胶颗粒表面能够提高水泥基体与橡胶颗粒的界面粘结强度。     

低热硅酸盐水泥在三峡工程大体积混凝土中的研究及应用

低热硅酸盐水泥具有早期水化热低的特性,因此在水工大体积混凝土温控防裂方面体现出了较大的优越性.介绍了低热硅酸盐水泥大体积混凝土在三峡工程的试验研究及现场的应用情况,为低热硅酸盐水泥在水利水电工程大体积混凝土中推广应用积累了经验.     

硬化混凝土中水泥用量的测定方法概述

水泥用量是混凝土配合比的重要参数,测定混凝土中的水泥用量对耐久性判断及配合比检查具有重要意义。硬化混凝土中的水泥用量可用化学分析方法及光学显微镜法测得。化学分析法又分为水泥溶解法与可溶性SiO2和CaO分析法,光学显微镜法包括荧光显微镜和扫描电镜。重点对化学分析方法的测定原理、试验方法及结果计算做了介绍,评价了各种方法的精密度与准确性,并总结了可能对测定造成影响的因素。     

混凝土孔体积分形维数及其与氯离子渗透性和强度的关系

采用压汞法对含不同掺合料混凝土的孔分形结构进行了试验研究,测定了其孔体积分形维数,探讨了含不同掺合料混凝土的孔体积分形维数与氯离子渗透性能及强度的关系。结果表明:混凝土孔体积分形维数越大氯离子渗透系数越大;含不同掺合料混凝土的孔体积分形维数与氯离子渗透系数相关性由高到低依次为:粉煤灰矿渣石灰石水泥;含不同掺合料的混凝土的孔体积分形维数与强度相关性由高到低依次为:粉煤灰矿渣水泥石灰石。     

疲劳荷载作用下混凝土中氯离子扩散性研究现状

目前,针对静力荷载作用下的混凝土中氯离子扩散现象的研究较为广泛,但很少对疲劳荷载作用下氯离子在混凝土中的扩散进行研究。基于疲劳荷载作用下混凝土中氯离子扩散重要性,在从不同研究角度总结了现有的研究成果的基础上,提出了考虑混凝土内部损伤累积及环境等多因素耦合作用下混凝土中氯离子的扩散性;最后阐述了使用超声波波速作为损伤指标研究氯离子扩散性的可行性及优越性。     

Effect of cement type on the resistance of concrete against chloride penetration

In chloride containing environment, chloride permeability of concrete is an important parameter affecting the service life of concrete structures. The primary objective of this experimental study was to study the effect of cement types on the resistance of concrete against chloride penetration for given compressive strength classes. These cements included two different types of granulated blast-furnace slag cement (CEM III/A 32.5N and CEM III/A 42.5N), a sulfate resisting cement (SRC 32.5), and a Portland cement blended with fly ash; all of which compared to an ordinary Portland cement (CEM I 42.5R). For each binder type, four concretes at different strength classes were produced and as a result 20 mixtures were obtained. Rapid chloride ion penetration tests according to ASTM C 1202 were conducted. In addition, electrical resistivity and capillary water absorption tests were carried out. In order to characterize the concrete quality, compressive strength of the specimens were also obtained. The test results clearly demonstrated that the blast-furnace slag cements have the highest resistance against chloride penetration, while the pure Portland cement and sulfate resisting cement have the lowest resistance. Concretes produced with the sulfate resisting cement had substantially higher capillary sorption compared to other mixtures. Test results confirmed the strong relationship between the chloride permeability and electrical resistivity.     

Effect of styrene–butadiene rubber latex on the chloride permeability and microstructure of Portland cement mortar

We evaluated the chloride permeability and microstructure of Portland cement mortar modified by styrene–butadiene rubber (SBR) latex, using mortar samples with various polymer/cement (P/C) mass ratios. The incorporation of SBR improved the chloride penetration resistance along with the general ionic permeability of the mortar, while increasing its ionic transport resistance and decreasing its electric capacitance. These data suggest that admixing SBR led to denser and more refined microstructure of the cured cement mortar. Field-emission scanning electron microscopy images confirmed such improvements in the pore structure and the formation of an interpenetrating network structure of SBR and cement hydrate phases at relatively higher P/C ratios. Besides slightly reducing Portlandite content and mitigating carbonation with the increasing P/C ratio in mortar, SBR was also found to promote the formation of calcium aluminate trisulfate hydrate phases and facilitated chloride binding.