Structural shear behaviour of recycled concrete with silica fume

This paper is the outcome of the second stage of studies carried out on the structural behaviour of recycled concrete. The first stage determined, using beams specimens, the shear behaviour of recycled concrete with which 50% of the coarse aggregate was replaced by recycled coarse aggregate (obtained from concrete demolition waste). This stage revealed minor differences (recycled concrete – conventional concrete) in ultimate loads and these differences were found to increase when cracking was taken into account. In this study, it was determined that the addition of 8% silica fume to recycled concrete (recycled concrete with silica fume) improved this behaviour. Moreover, the use of this material in recycled concrete produced changes in its structural behaviour similar to those induced in conventional concrete (conventional concrete with silica fume). Finally, experimental results were compared using current codes and it had been seen that all of them were conservative so t can be used for the shear design of recycled concrete beams with silica fume.     

Carbonation-induced reinforcement corrosion in silica fume concrete

This study presents the results of carbonation depth and carbonation-induced reinforcement corrosion in concrete samples with silica fume additions of up to 20% and water/binder ratios ranging from 0.30 to 0.80. The behavior of the additions is determined by the w/b ratios. For w/b ratios lower or equal to 0.45–0.50, carbonation processes in these materials are controlled by the porosity of the material and the consumption of Ca(OH)₂ has a negligible effect on carbonation. For higher w/b ratios, the consumption of Ca(OH)₂ plays a significant role. At the same time, the results of reinforcement corrosion indicate that the effect of silica fume additions depends on their concentration. In concentrations equal to or lower than 10%, silica fume will not reduce corrosion resistance and it may actually increase it when used in concentrations below this level. When used in concentrations greater than 10%, silica fume increases the potential for carbonation-induced reinforcement corrosion.     

关于使用硅粉混凝土进行桥面铺装的探讨

叙述了在混凝土中掺加硅粉,结合应用高效复合减水剂,不仅能减少单位水泥用量,而且可赋予混凝土较高的抗渗性能,掺加硅粉还可使混凝土强度对生产过程中变异因素敏感性降低,强度波动范围受到有效控制,结合工地实际情况,探讨了在桥面铺装混凝土中添加硅粉的可行性,并通过具体实验数据证明其合理性。     

Performance of lightweight concrete with silica fume after high temperature

In this study, the effect of silica fume on compressive and splitting tensile strength of lightweight concrete after high temperature was investigated experimentally and statistically. The mixes incorporating 0%, 10%, 20% and 30% silica fumes were prepared. After being heated to temperatures of 200, 400 and 800 °C, respectively, the compressive and splitting tensile strength of lightweight concrete was tested. This article adopts Taguchi approach with an L₁₆ (4⁵) to reduce the numbers of experiment. Two control factors (percentage of silica fume and heating degree) for this study were used. The level of importance of these parameters on compressive and splitting tensile strength was determined by using analysis of variance (ANOVA) method.     

关于硅灰和高性能混凝土的一些思考

硅灰的商业化应用在美国已有25年的历史。在此期间,硅灰从一种处于研究阶段的材料演变成一种在混凝土中被广泛规定使用的组分。硅粉在被市场所接纳的时间,恰好是“高性能混凝土”一词产生的前夕,有充分的理由说明：最初的硅灰混凝土项目正是高性能混凝土的起源。本文简述了在美国市场中硅灰使用的发展历史;回顾了硅灰混凝土如何发展成为高性能混凝土;并总结了使用硅灰的适用场合、配合比、抹面和施工性能等方面的经验。     

大体积混凝土的水化热分析

阐述了水化热分析的必要性以及分析原理,结合实例,通过大型结构计算有限元程序Midas/Civil对水化热分析的方法进行了说明,指出温度应力的分析和控制是防止裂缝的主要措施,是大体积混凝土设计和施工的前提.     

硅灰在混凝土中的应用进展

硅灰组成的90%为SiO2,且多数为无定型SiO2,它在提高混凝土工作性能和耐久性等方面发挥了重要作用。对硅灰在混凝土中的应用发展进行总结,并对硅灰在高性能混凝土中的应用进行展望。     

Estimation of the permeability of silica fume cement concrete

Deterioration and durability of concrete structures mainly depend on permeability of concrete. Silica fume (SF) as a mineral admixture for high performance concrete produces more discontinues and impermeable pore structure in concrete. The higher permeability reductions with silica fume are due to pore size refinement and matrix densification, reduction in content of Ca(OH)₂ and cement paste-aggregate interfacial refinement. During the hydration process the transition interfacial zone is gradually densified due to pozzolanic reaction between silica fume and calcium hydroxide. Based on a microstructure model, a procedure for predicting the permeability of high strength silica fume cement concrete is developed by considering water-to-binder ratio, silica fume replacement ratio and degree of hydration as major influencing factors. Results of the permeability calculated using the procedure is verified with the available literature. Subsequently, effects of silica fume on the permeability of concrete are evaluated. Finally, optimum silica fume replacement ratios that reduce the permeability of concrete reasonably are proposed for durable concrete.     

硅粉在混凝土中的应用探讨

作者分析了硅粉在混凝土中的作用机理，以及硅粉对混凝土物理、力学性能的影响，从而指出在混凝土中掺入适量的硅粉，是一种所需投资较少且有明显效果的方法，并可带来良好的环境效益和社会效益。     

硅粉粉煤灰混凝土的室内试验研究

结合具体的工程实例,通过试验对硅粉混凝土和硅粉粉煤灰混凝土的制备进行了研究,并对二者的经济性作了分析比较,得出硅粉粉煤灰混凝土较硅粉混凝土的坍落度高,且工程经济性与适用性强的结论。     

Properties of polypropylene fiber reinforced silica fume expansive-cement concrete

This paper reports on a comprehensive study on the mechanical properties of expansive-cement concrete containing silica fume and polypropylene fibers. Properties studied include those of the fresh mix properties, length change, rapid chloride permeability, compressive strength, flexural behavior, and bond of hardened concrete. Silica fume content used was 5 and 10% and fiber volume fraction was 0.10, 0.30, and 0.50%. Results show that the use of 5% silica fume combined with 0.30% fiber volume fraction results in optimum mixture design for repair applications from the standpoints of workability, bond, strength, length change and permeability.     

Properties of fly ash concrete modified with hydrated lime and silica fume

This paper presents the results of an experimental investigation on the properties of fly ash concrete incorporating either hydrated lime or silica fume to improve the early strength of concrete. Test results indicated that the addition of lime and silica fume improved the early age compressive strength of fly ash concrete. The inclusion of silica fume was also found to increase the 28 days strength significantly. The air permeability of concrete containing lime and silica fume either decreased or remained almost the same when compared to the concrete without these. The addition of lime and silica fume also improved the sorptivity of concrete.Through the use of differential scanning calorimetry and thermogravimetric analysis (DSC/TG), it was demonstrated that the addition of hydrated lime increased the Ca(OH)₂ content; whereas the addition of silica fume decreased the Ca(OH)₂ content in the cement paste. The mercury intrusion porosimetry (MIP) data confirmed the beneficial action of hydrated lime and silica fume, towards decreasing the total pore volume of fly ash cement paste.     

硅灰裹砂法对混凝土性能的影响研究

硅灰裹砂法是一种新的搅拌工艺,本研究简单介绍了硅灰裹砂法在混凝土中的作用机理,着重研究硅灰裹砂法对混凝土性能的影响.研究结果表明:在不改变机械设备,不增加人力、物力的前提下,硅灰裹砂法较常规方法对掺硅灰混凝土力学性能提高10%～20%,并显著地提高了混凝土抗氯离子渗透性能.     

硅粉混凝土的基本性能与工程应用

硅粉混凝土具有良好物理力学性能和耐久性能,为了进一步提高硅粉混凝土的应用效率,分析总结了硅粉混凝土的试验研究和工程应用成果,指出了硅粉在混凝土中的作用机理以及硅粉混凝土的应用技术要点.     

A combined ultrasound method applied to high performance concrete with silica fume

The use of ultrasonic relative amplitude ratio (RAR) and ultrasonic pulse velocity (UPV) to evaluate the strength of high performance concrete (HPC) with 10%, 20% and 30% silica fume content at water/binder ratios from 0.22 to 0.40 with different curing conditions is presented in this paper. As the composition, maturity, free water content and curing conditions are factors that influence the strength of concrete, their effect on the measured UPV and the RAR are determined. Results show that UPV measurement is less sensitive at high level of strength but has good correlation with the compressive strength of HPC with silica fume, whereas RAR maintain good sensitivity at all level of strength (irrespective of the factors that influence the strength) with reduced correlation coefficient. The suggested combined UPV and RAR-strength correlation can be used to estimate the compressive strength of HPC with silica fume and can be combined with other nondestructive testing methods for better estimation of strength.     

钢渣粉硅灰混凝土的力学性能及耐久性研究

通过试验测试分析了钢渣粉单掺以及与硅灰二元复掺混凝土在不同配合比下的和易性、力学性能和耐久性能,并基于改性前后混凝土微观结构特征的测试分析揭示了钢渣粉单掺以及与硅灰二元复掺对混凝土材料的改性机理。试验研究结果表明:钢渣粉取代混凝土中水泥最适宜的比例是10%,此时混凝土的力学性能和耐久性能都得到有效的提高,掺量20%的钢渣混凝土与普通硅酸盐混凝土各项性能相近。钢渣粉与硅灰的二元复掺可以使混凝土的力学性能和耐久性得到显著提高。钢渣粉在混凝土中的作用有两个:一是作为活性胶凝材料发生水化反应,但其活性比水泥低;二是微集料效应,分散水泥颗粒填充混凝土的孔隙,提高混凝土的密实度。     

硅灰配制海工自密实高性能混凝土的研究

开展了复掺硅灰与矿渣粉海工自密实高性能混凝土的试验研究.试验结果表明,矿渣粉较大的海工自密实混凝土工作性较差,采用硅灰替代矿渣粉可改善海工自密实混凝土的工作性,在复掺硅灰和矿渣粉总掺量为70％,硅灰掺量5％的条件下,掺入55％～65％矿渣粉自密实混凝土具有较高的流动性、填充性、间隙通过性和抗离析性等工作性;28 d抗压强度大于50 MPa,56d的电通量小于1 000C,90d扩散系数小于1.5×10-12 m2/s,具有较高的抗压强度和抗氯盐侵蚀性能,满足海洋环境下抗氯盐侵蚀的质量要求.     

不掺硅灰C80级泵送混凝土的配制与工程应用

在不掺硅灰的情况下,通过双掺或三掺技术.充分发挥活性掺合料的超叠加效应,采取普通材料能配制C80高性能混凝土,用于泵送施工,直接浇筑墙、柱结构,即高强混凝土结构直接暴露于大气之中.     

复掺粉煤灰和硅灰在自密实混凝土中的应用

复掺粉煤灰和硅灰应用到自密实混凝土中,可以增大新拌混凝土的流动性,改善离析泌水,增加混凝土硬化后的强度,提高其耐久性能。试验研究了粉煤灰的最佳掺量,以及几种矿物质掺合料复掺的复合效应。     

Hydration characteristics of hydrothermal treated cement kiln dust–sludge–silica fume pastes

Cement kiln dust (CKD)–sludge–silica fume pastes were hydrothermally hardened at a pressure of 8 atm of saturated steam for different autoclaving ages. Hydration characteristics of the autoclaved CKD–sludge–silica fume pastes were studied by the determination of compressive strength and chemically combined water contents at different autoclaving ages. The phase composition and morphology of the formed hydrates were studied using X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The replacement of silica fume in CKD–sludge mixtures results in a marked increase in strength values of the autoclaved specimens at all stages of the hydrothermal process. The results of X-ray diffraction analysis and SEM-micrographs of autoclaved specimens for various mixtures indicates that the main hydration products identified are calcium silicate hydrates and minor amounts of CaCO₃.