Effect of dust in coarse aggregates on reinforcement corrosion in concrete

This paper reports results of a study conducted to investigate the effect of dust, contributed by the coarse aggregates, on the corrosion of reinforcing steel in concrete. The concrete specimens were prepared with up to 10% dust in the coarse aggregates. Two other batches of reinforced concrete specimens were also prepared. In one batch of specimens the aggregates were washed with raw water (total dissolved solids: 3338 ppm) while the dust in the second batch was removed by vacuum suction. Reinforcement corrosion was monitored by measuring corrosion potentials and corrosion current density. The results indicated that up to 10% dust in the coarse aggregates did not cause any corrosion of the reinforcing steel. Similarly, reinforcement corrosion was not noted in the concrete specimens prepared with coarse aggregates washed with raw water or cleaned with vacuum suction.     

粗集料性能对路面混凝土抗折强度的影响

本文研究了粗集料的最大粒径、级配和压碎指标值等对路面混凝土抗折强度的影响，结果表明，合适的最大粒径和连续级配有助于提高混凝土的抗折强度，粗集料的压碎指标值与混凝土的抗折强度没有明显的相关关系。     

大粒径再生粗骨料自密实混凝土强度试验研究

为充分消解老旧建筑拆解的废弃黏土砖,并应用于村镇低层建筑建设中,将废弃黏土砖制备成大粒径再生粗骨料,采用骨架密实堆积法,寻求5～100mm粒径范围再生粗骨料的最大密度,降低再生粗骨料的空隙率,通过曲线拟合合理级配再生粗骨料,从而制备出具有良好工作性、满足普通混凝土使用要求的再生粗骨料自密实混凝土.通过本试验研究可以有效减少再生粗骨料的制备成本,简化再生粗骨料的制备过程,并拓展再生粗骨料混凝土的应用范围,具有良好的经济效益.     

粗集料级配对混凝土强度发展历程的影响

在粗集料掺量相同的前提下,变动混凝土的粗集料级配和水胶比,以考察粗集料级配对混凝土强度发展历程的影响.试验结果表明:从提高混凝土强度的角度,随着混凝土水胶比的降低,其胶凝材料用量增大,同时,宜采用最大粒径较小的粗集料,反之亦然.     

粗骨料颗粒级配对混凝土抗压强度的影响

本文阐述了不同颗粒级配的粗骨料对不同水胶比的混凝土抗压强度的影响。     

小粒径再生粗骨料对预制混凝土力学性能影响的研究

研究5~10 mm小粒径再生粗骨料对预制混凝土抗压强度、劈裂抗拉强度和弹性模量的影响。结果表明,抗压强度随龄期延长而提高,且主要发生在前7 d,7 d抗压强度达到其28 d抗压强度的77%;劈裂抗拉强度随龄期的延长而提高,3 d劈裂抗拉强度达到其28 d强度的64%;弹性模量也随龄期的延长而提高,龄期为1、3、7和14 d时,弹性模量分别为其28 d弹性模量的32%、46%、62%和91%。通过与欧洲规范对比,基于试验结果,建议了劈裂抗拉强度和弹性模量的计算模型。研究结果更好的实现再生混凝土在小截面预制混凝土构件上的工程应用。     

Influence of recycled concrete aggregates on strength properties of concrete

Many structures in the middle-east’s Gulf region are now either reaching the end of their design life or were not constructed according to the specifications. Demolition or maintenance work on such structures results in large amount of concrete rubbles. Recycling concrete wastes will lead to reduction in valuable landfill space and savings in natural resources. The objective of this study is to investigate the strength of concrete made with recycled concrete coarse aggregate. The variables that are considered in the study include the source of the recycled concrete and target concrete strength. The toughness and soundness test results on the recycled coarse aggregate showed higher percentage loss than natural aggregate, but remained within the acceptable limits. The compressive and splitting tensile strengths of concrete made with recycled coarse aggregate depend on the mix proportions. In general, the strength of recycled concrete can be 10–25% lower than that of conventional concrete made with natural coarse aggregate.     

粗集料级配对道路混凝土抗折强度的影响

分析了影响道路混凝土抗折强度的因素，研究了粗集料级配对道路混凝土抗折强度的影响，通过三种不同级配粗集料的对比试验表明：合理的级配能大幅度提高道路混凝土的抗折强度。     

粗骨料种类对高强混凝土高温爆裂性能的影响

从构成混凝土的基本材料人手,研究改善高强混凝土高温爆裂性能,可降低混凝土的材料成本,简化生产工艺.试验证明粗骨料的品种成为影响高强混凝土高温性能最主要的因素之一,如果粗骨料内含铁元素或其他金属矿物含量高,将加快爆裂出现.以石灰石为骨料可明显提高裂缝出现的温度并推迟裂缝出现的时间,使得采用降温防爆措施成为可能.     

Effect of coarse aggregate quality on the mechanical properties of high strength concrete

This paper reports results of a study conducted to evaluate the effect of four types of coarse aggregates, namely calcareous, dolomitic, quartzitic limestone, and steel slag, on the compressive and tensile strength, and elastic modulus of high strength concrete. The highest and lowest compressive strength was obtained in the concrete specimens prepared with steel slag and calcareous limestone aggregates, respectively. Similarly, the split tensile strength of steel slag aggregate concrete was the highest, followed by that of dolomitic and quartzitic limestone aggregate concretes. The lowest split tensile strength was noted in the calcareous limestone aggregate concrete. The type of coarse aggregate also influences the modulus of elasticity of concrete. Weaker aggregates tend to produce a more ductile concrete than stronger aggregates do.     

不同粗细骨料组合下的混凝土性能研究

选取了10种不同性质的粗细骨料组合,在相同的配合比条件下进行了混凝土强度、变形及热学性能试验,并对试验结果进行了比较分析。研究结果表明,不同骨料组合下混凝土的性能有一定差异,这种差异既和骨料的特性有关,也和骨料与砂浆间的界面特性有关。混凝土的弹性模量、线膨胀系数和导温系数主要决定于粗骨料的性质,而粗、细骨料的强度对混凝土强度影响不大。     

Enhancing mechanical properties of concrete prepared with coarse recycled aggregates

The recycling of concrete is an important means to a sustainable material flow. The limited reuse of recycled aggregates is due to the lower quality of concrete production. Various methods have been attempted to minimise the negative effect. In this paper, the effect of adding fly ash as well as incorporating polyethylene terephthalate (PET) fibres in a concrete mix to mitigate the lower quality of recycled aggregates in concrete is presented. The study consists of two stages: in stage 1 the effects on some of the fresh and hardened concrete properties were studied and the percentage replacement of the natural coarse aggregate (NCA) by the recycled coarse aggregate (RCA) was established. From a chosen percentage of 10%, 20%, 30%, 50% and 100%, we found that the 20% replacement (RCA20) did not seem to jeopardise the compressive strength and water absorption of RCA concrete. Experimental studies were further carried out in stage 2 on the improvement on the mechanical properties of RCA20 concrete by incorporating 25% fly ash and 0.5% and 1.0% PET fibre. Beneficial effects of appropriated fly ash and PET fibre content applied on the RCA were obtained.     

混凝土粗骨料堆积的定量体视学研究

将预拌混凝土用粗骨料筛分为各单粒级颗粒,分别测定孔隙率和定量体视学参数后,进行骨料级配试验及其体视学参数计算,分析粗骨料堆积孔隙率与体视学参数之间的相关性,探讨运用定量体视学方法进行骨料最紧密堆积设计的可能性.结果表明:单粒级粗骨料孔隙率与球形率、圆度之间具有良好的相关性;级配粗骨料孔隙率与球形率、填充度之间具有良好的相关性;基于定量体视学参数的多元回归公式能够较精确预测粗骨料的孔隙率,为实现粗骨料的级配优化设计提供了可能.     

粗集料强度对混凝土抗压强度影响的试验研究

试验研究了碎石、钢、砂浆、页岩陶粒和加气混凝土集料强度对高强、中强和低强基体混凝土抗压强度的影响，研究结果表明粗集料强度对混凝土抗压强度影响较大，用于配制混凝土的粗集料必须具备一定的强厦。只有集料强度与基体强度相互协调时，才能更好地发挥集料和基体的作用；当集料与基体两相强度差异较大时，高强相的强度不能充分利用。     

再生粗骨料混凝土早期强度试验研究

通过试验研究水灰比、再生粗骨料取代率和用水量对再生混凝土早期抗压强度和抗折强度的影响。研究结果表明,再生混凝土各龄期的强度系数随水灰比、骨料取代率、单位用水量等因素变化不大。再生混凝土的各个龄期的抗压和抗折强度均随水灰比和再生骨料取代率的增大而降低。根据试验结果建立了再生粗骨料取代率为100%的再生混凝土早期抗压强度和抗折强度计算模型,该模型计算结果与他人试验结果吻合较好。     

不同母体的再生粗骨料对混凝土强度影响

回收再利用废弃混凝土会大大减少建筑垃圾填埋空间,同时能节省宝贵的自然资源.主要研究了不同母体的再生粗骨料对再生混凝土的强度影响,考虑了再生混凝土的不同母体来源及配制的目标强度.对再生粗骨料的磨耗性及坚固性测试表明:虽然再生骨料的质量损失率比天然粗骨料大,但仍然在规范规定的限值之内;不同母体的再生粗骨料对混凝土的强度影响...     

Characteristics of self-consolidating concrete using two types of lightweight coarse aggregates

This paper presents the development of lightweight aggregate self-consolidating concrete (SCC) using two types of lightweight aggregates having different densities. Lightweight aggregate SCC properties have been evaluated in terms of flowability, segregation resistance and filling capacity of fresh concrete as per the standards of the Japanese Society of Civil Engineering (JSCE). The measurement of the mechanical properties of hardened lightweight aggregate SCC, including compressive strength, splitting tensile strength, elastic moduli and density, as well as its specific strength were also carried out. The characteristics of lightweight aggregate SCC at the fresh state showed that as the density of the lightweight coarse aggregate decreases, the flowability improves but the segregation resistance tends to decrease. The 28-days compressive strength of the lightweight SCC was found to be 32 MPa or higher. The relationship between the compressive strength and the splitting tensile strength was found to be similar to the expression presented by CEB-FIP, and the relationship between the compressive strength and the elastic moduli was found to be similar to the expression suggested by ACI 318-05 which takes into consideration the density of concrete. The density of the lightweight aggregate SCC decreased by up to 14% compared to that of the control SCC, and the specific strength decreased by up to 20%.     

不同取代率再生粗骨料混凝土的和易性

系统研究了不同再生粗骨料取代率对混凝土和易性的影响,试验中再生粗骨料的掺入量分别为0,30%,50%和100%,试验结果表明粗骨料取代率对混凝土的流动性、粘聚性与保水性有不同的影响。     

石轻页岩陶粒混凝土的强度试验研究

为了探讨水胶比和碎石体积取代率对次轻页岩陶粒混凝土的物理力学性能影响,通过正交试验得到了LC20最佳配合比,然后再通过不同水胶比(0.30、0.35、0.40)和不同碎石体积取代率rg(0、10%、20%、30%、40%、50%)进行试验,并通过干表观密度、抗压强度、抗折强度、劈拉强度、比强度和折压比,以及断截面破坏形态,探讨其变化规律。结果表明,当碎石取代率为30%,水胶比为0.30时,次轻页岩陶粒混凝土的上述各项指标除折压比外均为最优,并能同步提高强度和韧性,而且还可以有效弥补页岩陶粒产量有限、价格较高和施工性能较差的缺陷。     

再生粗骨料钢筋混凝土梁短期刚度研究

对27根再生混凝土梁和3根普通混凝土梁进行正截面弯曲性能试验,研究再生混凝土梁短期刚度及其计算方法。试验结果表明,相同条件下再生混凝土梁跨中挠度比普通混凝土梁跨中挠度大11%左右。参考普通混凝土梁,根据试验结果回归出再生混凝土梁内力臂系数、截面弹塑性抵抗矩系数以及不均匀系数表达式,从而得出再生混凝土梁短期刚度的计算式。通过收集国内外再生混凝土梁试验结果对本文刚度公式进行验证,两者吻合较好。