SCC mixes with poorly graded aggregate and high volume of limestone filler

Nonpozzolanic fillers are frequently used to optimise the particle packing and flow behaviour of cementitious paste in self-compacting concrete (SCC) mixes. This paper deals with the influence of finely ground limestone and crushed limestone dust on the properties of SCC mixes in the fresh and hardened state. Mixes were prepared using poorly graded crushed limestone aggregate. To compensate the lack of fine material in the crushed sand, a viscosity agent (VA) was added to the mixtures. The results obtained indicate that finer and better-graded limestone dust significantly increases the deformability of the paste. When a high volume of this filler was added to the SCC mix, the required self-compacting properties were achieved at a lower water/(cement+filler) ratio, and it also appeared that the addition of filler improves the 28-day compressive strength of concrete mixes due to the filler effect and improved fine-particle packing.     

Combined effects of mineral admixtures and curing conditions on the sorptivity coefficient of concrete

The effect of mineral admixture and curing condition on the sorptivity of concrete are investigated. In the present work, the maximum particle size and the grading of coarse aggregate, the cement content and water/cement ratio of the concrete are kept constant. Then, in the ordinary Portland cement (OPC) 42.5 concrete, a portion of the sand is replaced by a mineral admixture such as fly ash (FA), limestone filler, sandstone filler or silica fume (SF). This paper presents the results of both the sorptivity coefficient and the compressive strength of OPC 42.5 concretes with these mineral admixtures, and concretes with OPC 32.5, blended cement (BC) or trass cement (TC). The results obtained indicate that the sorptivity coefficient of concrete decreases as the compressive strength of concrete increases. It is also shown that the sorptivity coefficient of concrete is very sensitive to the curing condition. The effect of curing condition on the sorptivity coefficient of concrete seems to be higher in low-strength concretes.     

The effects of different fine and coarse pumice aggregate/cement ratios on the structural concrete properties without using any admixtures

Structural lightweight concrete solves weight and durability problems in buildings and structures. In order to produce the high strength concrete in the civil engineering applications, lightweight concrete mixtures containing the fine pumice aggregate (FPA) from Nev°ehir region in Turkey and coarse pumice aggregate (CPA) from Yali Island in the Eastern Mediterranean were tested and the research findings were discussed in this paper. To analyse the effects of FPA and CPA/cement ratios on the structural concrete engineering properties, the range of different pumice aggregate/cement (A/C) ratios of 2:1, 2 1/2:1, 3:1, 3 1/2:1 and 4:1 by weight and cement contents of 440, 375, 320, 280 and 245 kg/m³, respectively, were used to make pumice aggregate lightweight concrete (PALC) mixture testing samples with a slump of from 35 to 45 mm.The experimental research findings showed that PALC has strengths comparable to normal weight concrete, yet is typically 30-40% lighter. PALC showed the design flexibility and substantial cost savings by providing less dead load due to its lower density values. The properties, which increase in value and indicate the increasing quality with lower A/C ratios (high cement contents), are compressive strength, modulus of elasticity and density. Properties, which decrease in value and indicate the increasing quality, with lower A/C ratios are water absorption and carbonation depth. In all cases, lowering the A/C ratio (higher cement content) increases quality. The research showed that structural lightweight concrete can be produced by the use of fine and coarse pumice aggregates mixes without using any additions or admixtures.     

Properties of concrete incorporating fine recycled aggregate

The properties of concrete containing fine recycled aggregate are investigated. Recycled aggregate consisted of crushed concrete (CC) or crushed brick (CB) with particles less than 5 mm in diameter. The free water/cement ratio was kept constant for all mixes. The fine aggregate in concrete was replaced with 0%, 25%, 50% and 100% CC or CB. Generally, there is strength reduction of 15-30% for concrete containing CC. However, concrete incorporating up to 50% CB exhibits similar long-term strength to that of the control. Even at 100% replacement of fine aggregate with CB, the reduction in strength is only 10%. Beyond 28 days of curing, the rate of strength development in concrete containing either CC or CB is higher than that of the control indicating further cementing action in the presence of fine recycled aggregate. More shrinkage and expansion occur in concrete containing CC or CB.     

Optimization of concrete mix water volume in press concretes

The press — method of concrete compaction with simultaneous vacuumizing makes it possible to add an increased volume of mix water to concrete mix. In this way workability of concrete mix is improved, which is a particularly important factor in the technology of concretes with fine, waste crushed aggregates of the fraction 0 to 2 mm. The effect of the water volume in concrete mix on some properties of pressed concrete with fine, waste carbonate aggregate is selectively estimated in the paper. Adequate mathematical models of the investigated properties of concrete, obtained experimentally, are analyzed.     

添加剂对中间包干式料性能的影响

本研究以电熔镁砂为主要原料,采用连续颗粒三级级配,即骨料部分的颗粒尺寸为：5-3mm、3-1mm、1～0mm,基质料包括粒径≤0．044mm和≤0．088mm两种细粉。骨料与基质料的质量比为65：35。以烧结镁砂为主要原料,B1和B2分别为自制改性硅酸盐结合剂JA和JB,再添加GA和GB作为改性剂,SA、SB和SC为烧结剂。通过选择结合剂、烧结剂和改性剂的种类和加入量,研制出性能优异的碱性中间包干式振动料。实验结果表明：所研制的碱性干式料性能优良,可有效降低膨胀、收缩,同时还能促进氧化镁质干式料的烧结。     

不同类型再生细骨料对保温混凝土力学性能的影响

为了研究不同类型再生细骨料对玻化微珠保温混凝土力学性能的影响,将废弃混凝土再生细骨料和废弃黏土砖再生细骨料分别以25%、50%、75%和100%(体积分数)取代率取代保温混凝土中的天然河砂,并测试了再生保温混凝土的抗压强度、劈裂抗拉强度和弹性模量。结果表明: 25%是废弃混凝土再生细骨料在保温混凝土中的最优取代率;75%是废弃黏土砖再生细骨料在保温混凝土中的最优取代率。再生细骨料的压碎值和再生胶砂强度比在实际工程中可以有效区分不同类型再生细骨料的品质。废弃黏土砖再生细骨料中的火山灰材料可以有效提高再生保温混凝土的密实度,而废弃混凝土再生细骨料中残余的氢氧化钙却降低了再生保温混凝土的力学性能,因而废弃黏土砖再生细骨料具有更高的回收利用价值。     

The effect of aggregate variation on the compressive strength of laterite concrete

Laboratory testing of 96 (150×150 mm) concrete cube specimens were performed to study the effect of aggregate variation on the strength of laterite concrete. The different investigations were carried out using granite gravel as coarse aggregate and lateritic sand as fine aggregate. The best proportions between laterite and 20 mm gravel were determined and concrete mixes with specific strengths were designed. Strengths at 7, 14, 28 days were found and the effect of aggregate variation studied. Finally it was concluded that laterite can be used with good result as a fine component of concrete mixes.     

骨料种类与级配对路面混凝土耐磨性能的影响

提高路面混凝土耐磨性能对行车安全和道路服役寿命具有重要意义。本文通过优化普通砂石骨料架构提高道路混凝土的耐磨性能,研究了机制粗骨料级配、细骨料种类与用量、胶凝材料用量及水胶比对路面混凝土力学性能与耐磨性能的影响。结果表明,16~31.5 mm碎石由质量分数25%增加到70%时,混凝土磨损量降低了29%。与河砂混凝土相比,机制砂混凝土磨损量降低58.3%,同时适当增加砂率可提高耐磨性能。降低胶凝材料用量和水胶比可在保证混凝土强度的同时进一步提高耐磨性(磨损量仅为(0.320±0.070) kg/m²)。机制骨料表面粗糙,棱角较多,与水泥浆体机械咬合力增强,有利于骨料嵌锁架构的形成,路面混凝土耐磨性能改善机制的提出为优化设计高耐磨路面混凝土提供了理论依据与技术支撑。     

Effect of fine aggregate replacement with Class F fly ash on the abrasion resistance of concrete

This paper presents the abrasion resistance of concrete proportioned to have four levels of fine aggregate replacement (10%, 20%, 30%, and 40%) with Class F fly ash. A control mixture with ordinary Portland cement was designed to have 28 days compressive strength of 26 MPa. Specimens were subjected to abrasion testing in accordance with Indian Standard Specifications (IS: 1237). Tests were also performed for fresh concrete properties and compressive strength. Tests on compressive strength and abrasion were performed up to 365 days.Test results indicated that abrasion resistance and compressive strength of concrete mixtures increased with the increase in percentage of fine aggregate replacement with fly ash. Abrasion resistance of concrete was improved approximately by 40% over control mixture with 40% replacement of fine aggregate with fly ash, and concrete with fine aggregate replacement could be suitably used.     

再生骨料特征参数对混凝土强度的影响

再生骨料(RCA)对混凝土的性能影响极大,了解RCA对混凝土性能的影响,对提高RCA的利用效率,降低建筑行业碳排放并响应国家“双碳”政策至关重要。本文借助CT扫描技术获取了四组不同RCA替代率下掺锂渣再生混凝土的骨料特征图像,运用数字图像处理方法获得了RCA的形状系数(SF)、棱角度(AN)、棱角与表面纹理(AT)指数及三维球体度(SP),分析了它们的分布规律及特点,并通过灰色关联分析方法建立了骨料特征参数与抗压强度的联系。结果表明:RCA具有较高的不规则性,由于骨料残留的砂浆量不同,其表面呈现粗糙且多棱角的特点;四个骨料特征参数均表现出较高的灰色关联度,其中SP关联性最大,达到0.942;在合理的骨料混合比例下,试验样品可以满足C30混凝土强度的要求,且在30%(质量分数)RCA替代率下力学性能最优。     

粉煤灰渣替代细骨料对砂浆混凝土强度及抗冻性影响

通过筛分和破碎两种方式分别获得粒径区间为0.6~1.18 mm、0.3~0.6 mm的粉煤灰渣,并用其等体积替代对应粒径区间的细骨料,分析粉煤灰渣对砂浆工作性和强度的影响,探究粉煤灰渣的最优替代粒径区间。结合扫描电镜(SEM)、能谱分析(EDS)等方法分析了粉煤灰渣替代细骨料后砂浆试件的强度变化机理。基于砂浆最优替代粒径区间结果,验证了砂浆混凝土试件的强度和抗冻性。研究结果表明:分别以筛分方式和破碎方式得到的0.3~0.6 mm粒径区间粉煤灰渣替代对应区间细骨料后,其砂浆试件强度均与基准组(未替代)基本一致;而以筛分方式得到的0.3~0.6 mm粒径区间粉煤灰渣替代对应区间细骨料后,其混凝土试件强度和抗冻性与基准组基本一致。在水泥提供的氢氧化钙环境下粉煤灰渣表面生成水化硅酸钙,从而增加了水泥和粉煤灰渣界面胶结强度,强化水泥与粉煤灰渣界面区域,凹凸不平的粉煤灰渣表面与水泥浆咬合嵌锁,保证了试件的强度。     

Properties of lightweight expanded polystyrene concrete reinforced with steel fiber

Expanded polystyrene (EPS) concrete is a lightweight, low strength material with good energy-absorbing characteristics. However, due to the light weight of EPS beads and their hydrophobic surface, EPS concrete is prone to segregation during casting, which results in poor workability and lower strength. In this study, a premix method similar to the ‘sand-wrapping’ technique was utilized to make EPS concrete. Its mechanical properties were investigated as well. The research showed that EPS concrete with a density of 800-1800 kg/m³ and a compressive strength of 10-25 MPa can be made by partially replacing coarse and fine aggregate by EPS beads. Fine silica fume greatly improved the bond between the EPS beads and cement paste and increased the compressive strength of EPS concrete. In addition, adding steel fiber significantly improved the drying shrinkage.     

结构加固用干混自密实混凝土的制备与强度试验

本文选取不同的水料比和粗骨料含量,制定了8种制备干混自密实混凝土的配比方案。根据不同方案制备的干混自密实混凝土拌合物的坍落扩展度、T500扩展时间,选取满足自密实混凝土工作性能的配比进行抗压强度、抗折强度、劈裂抗拉强度和钢筋握裹强度试验。试验结果表明,当水料比取1.3,粗骨料含量取30%和35%时,制备的干混自密实混凝土同时具备良好的工作性能和力学性能,可应用于结构加固。     

Effect of fine aggregate replacement with Class F fly ash on the mechanical properties of concrete

This paper presents the results of an experimental investigation carried out to evaluate the mechanical properties of concrete mixtures in which fine aggregate (sand) was partially replaced with Class F fly ash. Fine aggregate (sand) was replaced with five percentages (10%, 20%, 30%, 40%, and 50%) of Class F fly ash by weight. Tests were performed for properties of fresh concrete. Compressive strength, splitting tensile strength, flexural strength, and modulus of elasticity were determined at 7, 14, 28, 56, 91, and 365 days. Test results indicate significant improvement in the strength properties of plain concrete by the inclusion of fly ash as partial replacement of fine aggregate (sand), and can be effectively used in structural concrete.     

硅灰对超轻水泥基复合保温材料性能的影响

超轻水泥基复合保温材料(UCIM)是以水泥为胶凝材料,膨胀聚苯乙烯泡沫塑料(EPS)颗粒、掺合料、泡沫剂、改性剂和水等为主要原料,采用物理发泡工艺制备而成。UCIM由EPS颗粒与泡沫混凝土基体互穿构成,不同品种的掺合料等效替代水泥后,能不同程度影响水泥浆体对EPS颗粒的包裹性,从而影响UCIM结构的均匀性与制品性能。通过设计不同掺量的掺合料,对比硅灰、偏高岭土及矿粉所制备的UCIM的均匀性及强度,结果表明,当采用硅灰时,UCIM未产生分层离析现象且制品强度试验结果较好;通过微孔拍摄及强度、热工性能测试,系统研究了硅灰掺量对UCIM的泡沫混凝土基体的孔结构、强度和导热系数的影响,结果表明,适宜掺量的硅灰能提高UCIM的力学性能,使UCIM的泡沫混凝土基体的平均孔径减小,进而有利于降低UCIM导热系数。     

The influence of aggregate type on the physical and mechanical properties of high‐performance concrete subjected to high temperature

This paper presents the results of an experimental study on the behaviour of high‐performance concretes after high temperature exposure. The high temperature exposure is related to the potential risk of fire, and mechanical properties analysis is needed afterwards to assess the residual strength of the material. The results presented in the paper show the properties evolution of four concretes made with four different aggregate types: basalt, granite, dolomite and riverbed gravel. The mix compositions allow comparisons, because the cement paste and mortar compositions and their volumes remain the same for all the four concretes. Moreover, the aggregate particle size distribution was chosen to be quasi identical so that this factor does not affect the concrete behaviour. The decrease of tensile strength value with the increase of temperature is more pronounced than compressive strength reduction thus, the exponential and power function equations were proposed to describe f_tT–f_cT relationship. The change of modulus of elasticity in relative values is similar, although the initial values of modulus are different and correspond to the aggregate type. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of aggregate on the performance of confined concrete

This paper presents an experimental investigation for the mechanical behavior of confined concrete specimens made with different types of coarse aggregates and subjected to concentric loads. The response of the specimens varies with the variation in the properties of the aggregates. The effect of different levels of transverse reinforcement ratio on the behavior of the studied types of concrete is investigated and the results are analyzed and presented in the study. The study included forty-eight cylindrical specimens of 100 mm diameter and 650 mm height. The results of the study show considerable effect for the type of the used aggregate on the mechanical behavior of the specimens. The effect of changing the spacing of the stirrups and the configuration of the stirrup closure are also investigated and analyzed in the paper.     

Single-drop agglomeration of fine mineral admixtures for concrete and water requirement of pastes

This paper deals with water requirement determination of fine mineral admixtures for concrete by a simple and rapid test based on “single-drop” agglomeration. Eighteen fine and very fine mineral admixtures for concrete, different in origin and characteristics are tested. The influence of cement and high-range water-reducing admixtures are also studied. The “single-drop” test results are compared with standard tests proposed in concrete technology. The water–fine mineral admixture ratio of the formed agglomerate is proportional to the water requirement of the mineral admixture determined by the standard tests for concrete mixtures. However, the frictional forces between particles are not taken into account by the “single-drop” test and consequently the dispersing effect of high-range water-reducing admixtures. Round- and angular-shaped particles present a linear function between the water–fine mineral ratio and fineness, which is determined by the BET specific surface area or the average particle size of the minerals. Irregular-shaped particles present two to three times higher water–fine mineral ratio than that of round-shaped particles with equivalent fineness. In this case, the very low granular packing of mixtures exclude any use in concrete. When there is low cement content, the water–fine mineral-plus-cement ratio and consequently the porosity of binary blended mixtures increase significantly because of interaction phenomena between cement particles and water.     

Investigation of the mix ratio design of lightweight aggregate concrete

According to the analysis of the domestic and overseas researches and achievements of lightweight aggregate concrete, a new strength formula on account of tube compressive strength of lightweight aggregate and glue-capacity ratio is put forward on the mix ratio design of lightweight aggregate concrete. The conception of concrete filler coefficient is also proposed, the theoretical formula of sand-aggregate ratio is deduced and the quasi-principle of stationary water consumption by considering the working character of concrete is summarized. Therefore, the designing equation of mix ratio of lightweight aggregate concrete which is tested by some further experiments is defined.