Influence of filler type on the properties of foam concrete

Most of the investigations on foam concrete in the past have been confined to neat cement paste, cement paste with partial replacement with admixtures and to cement–sand mixes. This paper reports the results of a systematic study to ascertain the influence of filler type (i.e., sand and fly ash) and the particle size of sand on the properties of moist cured foam concrete. This study shows that the consistency of mixture, for achieving pre-formed foam concrete of design density, mainly depends on the filler type. The flow behaviour of foam concrete is mainly influenced by the foam volume. A reduction in particle size of sand caused an improvement in strength of foam concrete. For a given density, replacement of sand with fly ash resulted in higher strength. Finer filler resulted in a higher ratio of strength to density.     

粉煤灰对泡沫混凝土物理力学性能的影响

研究了粉煤灰掺量和水灰比对粉煤灰掺量较大的泡沫混凝土的干密度和抗压强度的影响,利用经验公式计算泡沫混凝土的孔隙率,重点研究泡沫混凝土的孔隙率和干密度、抗压强度的关系。研究结果表明随着粉煤灰掺量的增加泡沫混凝土的干密度和抗压强度均呈下降的趋势。当粉煤灰掺量由25%上升到30%时,不同水胶比的泡沫混凝土干密度下降均超过了60 kg/m3;粉煤灰掺量由30%提高到40%时,不同水胶比的泡沫混凝土抗压强度下降的趋势都明显减小。以粉煤灰取代水泥后,孔隙率和干密度的拟合公式为 Y =27126.8-64295.9X +38334.4X 2,相关系数为0.9097;孔隙率和抗压强度的拟合公式为Y =58.7-142.2X +86.3X 2,相关系数为0.9802。     

Shrinkage behavior of structural foam lightweight concrete containing glycol compounds and fly ash

Shrinkage behavior of the structural foam lightweight concrete with density of 1600 kg/m³ was investigated. Owing to high drying shrinkage of the lightweight concrete, glycol compounds were used in the concrete mixture to study their effect on shrinkage behavior. Propylene glycol (PG), triethylene glycol (TEG) and dipropylene glycol tert-butyl ether (DPTE) were selected for testing of drying shrinkage of the lightweight concrete. Partial replacement of cement and sand with fly ash was also used to reduce the shrinkage. Results indicated that PG, TEG and DPTE were effective in reducing the shrinkage of lightweight concrete through reduction of surface tension of water. However, DPTE significantly reduced the surface tension and caused the foam instability and early stiffening of mixture. The partial replacement of cement and sand with fly ash could also reduce the shrinkage of the lightweight concrete. In this case, the compressive strength was also enhanced owing to the additional pozzolanic reaction.     

Effect of fly ash and slag on concrete: Properties and emission analyses

Recycled concrete is a material with the potential to create a sustainable construction industry. However, recycled concrete presents heterogeneous properties, thereby reducing its applications for some structural purposes and enhancing its application in pavements. This paper provides an insight into a solution in the deformation control for recycled concrete by adding supplementary cementitious materials fly ash and blast furnace slag. Results of this study indicated that the 50% fly ash replacement of Portland cement increased the rupture modulus of the recycled concrete. Conversely, a mixture with over 50% cement replacement by either fly ash or slag or a combination of both exhibited detrimental effect on the compressive strength, rupture modulus, and drying shrinkage. The combined analysis of environmental impacts and mechanical properties of recycled concrete demonstrated the possibility of optimizing the selection of recycled concrete because the best scenario in this study was obtained with the concrete mixture M8 (50% of fly ash+ 100% recycled coarse aggregate).     

Fly ash concrete-potential without misuse

This paper presents a comprehensive review of the engineering properties of fly ash concrete in its fresh and hardened form. It is shown that two major factors influence the properties of fly ash concrete—its intrinsic variation in composition, and the philosophy of mix proportioning adopted to produce the concrete. The effects of ash variability can be covered by three basic criteria of mix proportioning—namely, low water-cementitious ratio, inclusion of a water-reducing plasticizer, and an early and long curing period. It is then shown that these criteria can be utilized to produce concrete containing 50% ash replacement and having 40 to 60 MPa 28-day strength, with high workability, low water/cementitious ratios of 0.30 to 0.45, and one-day strengths of 10 to 20 MPa. Properties of strength, elasticity, shrinkage and creep are reported, and durability aspects briefly discussed. The paper unfolds the secret of utilizing the full pozzolanic potential of fly ash in practice.     

Workability and strength behaviour of concrete with cold-bonded fly ash aggregate

This paper discusses the development of empirical models for workability and compressive strength of cold-bonded fly ash aggregate concrete in terms of mixture proportioning variables such as cement content, water content and volume fraction of cold-bonded aggregate through statistically designed experiments based on Response Surface Methodology. Factor level of cement is taken from 250 to 450 kg/m³ to introduce weak as well as strong matrix phase in the concrete. Apart from water content, workability of concrete is highly influenced by main and interaction effect of volume fraction of cold-bonded aggregate in the composition. Response surface indicate that increase in cement content causes to change the predominant failure mode from mortar failure to aggregate fracture and concrete strength decreases with increase in volume fraction of aggregate at higher cement contents. The models developed have been found useful in arriving typical relationship to establish a mixture proportioning methodology for cold-bonded fly ash aggregate concrete.     

Models for strength prediction of foam concrete

There are several strength prediction relations developed for plain cement paste, mortar and concrete. In concrete where air voids contribute significantly to volume of voids (like aerated and foam concrete), more general expressions including the volume of air voids is to be developed as the better alternative. The objective of this paper is to propose prediction relations for the compressive strength of foam concrete by extending two of the well-known relations available for cement paste, mortar and normal concrete, viz., Balshin’s strength-porosity model and Power’s gel-space ratio equation. For this, theoretical equations were derived for porosity and gel-space ratio relating it to the density, proportion of ingredients in the mix and material characteristics like specific gravity. Foam concrete with fly ash showed lesser dependency on pore parameters than cement-sand mixes. As both the prediction relations developed in this study consider the effect of composition on the strength, it can serve as a simple tool for predicting the strength of foam concrete. But strength-porosity model stands out compared to gel-space model as it correlates well with the measured strength and also because of its ease in application since it employs the composition of constituents and easily measurable parameters.     

原料配比对泡沫膏体充填材料性能的影响

以水泥、粉煤灰、煤矸石、膨润土等为原料制备了泡沫膏体充填材料,采用单因素试验研究了不同水料比条件下,原料配比对泡沫膏体充填材料流动度、凝结时间、干密度及后期抗压强度的影响规律。结果表明:流动度随水料比和煤矸石掺量的增加而增加,随发泡剂和膨润土掺量的增加而减小,但在高、低水料比条件下流动度随粉煤灰掺量的增加其变化趋势略有不同;凝结时间随水料比、粉煤灰、煤矸石及发泡剂掺量的增加而延长,而膨润土掺量则对其影响不大;干密度随水料比、粉煤灰、煤矸石及发泡剂掺量的增加而减小,随膨润土掺量的增加先减后增;后期抗压强度随煤矸石、发泡剂掺量的增加而减小,随膨润土掺量的增加先增后减,在高、低水料比条件下粉煤灰对其影响规律相反,此外高水料比有助于原料之间配合成型,对强度有益,但随原料掺量的增加其强度急剧下降。     

Influence of binders on properties of sintered fly ash aggregate

Sustained research and development work on the utilization of fly ash for various productive uses have been carried out in the past. In the construction industry, major attention has been devoted to the use of fly ash in concrete as a cement replacement. The production of artificial lightweight coarse aggregate using fly ash has potential for its large-scale utilization in the construction industry and this is an area that merits attention in many parts of the world, bearing in mind the rapid dwindling of sources of natural aggregates. As only limited details on manufacture and parameters influencing properties of sintered fly ash aggregates have been reported in the literature, a systematic study was undertaken. In this paper, the relative performance of three binders, viz., cement, lime and bentonite, on the properties of sintered fly ash aggregate is reported. The salient observations are (i) the characterization studies on sintered fly ash aggregates show that the properties of aggregates depend on the type of binder and its dosage, (ii) the significant improvement in strength and reduction in water absorption of sintered fly ash aggregate is observed when bentonite is added with fly ash, (iii) the binders used did not alter the chemical composition, while they influence the microstructure of the aggregate, which results in enhancement in the properties of aggregates.     

Freeze–thaw resistance and transport properties of high-volume fly ash roller compacted concrete designed by maximum density method

The aim of this study is to evaluate the effect of high-volume fly ash on some durability characteristics of roller compacted concrete (RCC). In addition to a control mixture without fly ash, two different series of mixtures were prepared by partial replacement of either cement or aggregate with fly ash. The mixtures were designed by a maximum density method. A total of 28 mixtures having four different water/binder ratios (0.30, 0.35, 0.40 and 0.45 by mass) were prepared to determine the optimum water/binder ratio. Among these, seven mixtures containing the optimum water content were selected for further experimental study. It was observed that in the mixtures where cement was substituted with fly ash, increasing the fly ash content adversely affected the durability performance up to 90 days. However, fly ash substitution for a part of the aggregate improved the durability characteristics of the mixture as the amount of fly ash increased.     

Effect of specimen size and shape on compressive strength of concrete containing fly ash: Application of genetic programming for design

The use of fly ash as a mineral admixture in the manufacture of concrete has received considerable attention in recent years. For this reason, several experimental studies are carried out by using fly ash at different proportions replacement of cement in concrete. In the present study, the models are developed in genetic programming for predicting the compressive strength values of cube (100 and 150 mm) and cylinder (100 × 200 and 150 × 300 mm) concrete containing fly ash at different proportions. The experimental data of different mixtures are obtained by searching 36 different literatures to predict these models. In the set of the models, the age of specimen, cement, water, sand, aggregate, superplasticizers, fly ash and CaO are entered as input parameters, while the compressive strength values of concrete containing fly ash are used as output parameter. The training, testing and validation set results of the explicit formulations obtained by the genetic programming models show that artificial intelligent methods have strong potential and can be applied for the prediction of the compressive strength of concrete containing fly ash with different specimen size and shape.     

漂珠聚氨酯复合泡沫力学特性及本构模型研究

以粉煤灰漂珠为主要组分的复合泡沫具有较高的比强度和比吸能,在轻质抗冲击结构设计和缓冲防护领域极具应用潜力。然而,漂珠尺寸和增强相等因素对材料力学性能和行为的影响机制尚不清楚,且当前研究尚未构建该类复合泡沫的力学模型,不利于开展结构设计中材料选型和数值仿真等工作。为此,该研究针对漂珠尺寸和蜂窝铝增强相对复合泡沫的力学性能和变形行为的影响规律进行系列准静态压缩实验研究,在此基础上采用Avalle理论构建该复合泡沫的力学模型。结果表明:①当相对密度小于0.29时,漂珠尺寸对复合泡沫的力学性能几乎没有影响;当相对密度大于0.29时,漂珠尺寸对复合泡沫力学性能的影响随密度的增大而增大;②对于含增强相的复合泡沫,含小尺寸漂珠的复合泡沫力学性能有明显提高,铝蜂窝的额外增强效果对包含小尺寸漂珠的复合泡沫更为明显,该增强机制主要是将材料的初始失效模式由剪切转变为轴向压溃;③使用Avalle理论构建的本构模型,其应力平台阶段和能量耗散特性的拟合与实验结果一致,可较为准确地预测该材料的基本力学性能。该研究可为粉煤灰的综合利用及其复合泡沫在轻质抗冲击结构设计中的应用提供理论参考和基本预测模型。     

Abrasion resistance and mechanical properties of high-volume fly ash concrete

The abrasion resistance and mechanical properties of concrete containing high-volume fly ash (HVFA) were investigated. Sand (fine aggregate) was replaced with 35, 45, and 55% of Class F fly ash by mass. The water to cement ratio and the workability of mixtures were maintained constant at 0.46 and 55 ± 5 mm respectively. Properties examined were compressive strength, splitting tensile strength, flexural strength, modulus of elasticity and abrasion resistance expressed as depth of wear. Test results indicated that replacement of sand with fly ash enhanced the 28-day compressive strength by 25–41%, splitting tensile strength by 12–21%, flexural strength by 14–17%, and modulus of elasticity by 18–23% depending upon the fly ash content, and showed continuous improvement in mechanical properties up to the ages of 365 days. Replacing fly ash with sand significantly improved the abrasion resistance of concrete at all ages. Strong correlation exists between the abrasion resistance and each of the mechanical properties investigated.     

Concrete durability presented by acceptable chloride level and chloride diffusion coefficient in concrete: 10-year results in marine site

Generally, concrete with high resistance to the marine environment should have high compressive strength, a low chloride diffusion coefficient (D _C), and a high acceptable chloride level (Ac). Considering all parameters simultaneously, this study evaluated the degree of fly ash concrete durability based on 10-year results in a marine site. Based on the concrete durability (Ac/D _C, as compared to cement concrete with a W/B ratio of 0.45) and compressive strength, the degree of concrete durability proposed in this study indicates that fly ash concretes with a W/B ratio of 0.45 and 15–35 wt % fly ash replacement exhibit high-quality performance in a marine site.     

Strength development of fly ash concretes

Compressive strength developed by concretes containing fly ash up to 80% of the cementitious fraction is presented. The effects of mix design technique, quantity of cement in the mix and the curing period on the strength development of fly ash concrete are also included. A comparison of the rate of strength development of the control and fly ash concretes is also provided. It is concluded that the optimum level of replacement of cement by fly ash depends on the actual amount of cement in the mix.     

Experimental design to optimize high-volume of fly ash grout in the presence of welan gum and superplasticizer

Applications such as soil, rock and oil-well grouting all require enormous amounts of cement and are good examples of areas where a high volume of fly ash could partially replace cement to produce low-cost, environmentally safe and durable concrete. There is an increasing need to identify the rheological properties of cement grout using a simple test to determine the fluidity, and other properties of underwater grouts such as washout resistance and compressive strength. This paper presents statistical models developed using a factorial design which was carried out to model the influence of key parameters on properties affecting the performance of underwater grout. Such responses of fluidity included mini-slump and flow time measured by Marsh cone, washout resistance, unit weight and compressive strength. The models are valid for mixes with 0.40 to 0.60 water-to-cementitious materials ratio, 0.02 to 0.08% of anti-washout admixture, by mass of binder, and 0.6 to 1.8% of superplasticizer, by mass of cementitious materials. The grout was made with 50% of pulverized-fuel ash replacement, by mass of cementitious materials. Also presented are the derived models that enable the identification of underlying primary factors and their interactions that influence the modelled responses of underwater cement grout. Such parameters can be useful to reduce the test protocol needed for proportioning of underwater cement grout. This paper highlighted the influence of W/CM and dosage of antiwashout admixture and superplasticizer on fluidity, washout resistance and compressive strength and attempted also to demonstrate the usefulness of the models to improve understanding of trade-offs between parameters.     

Compressive strength and chloride resistance of self-compacting concrete containing high level fly ash and silica fume

The influence of high-calcium fly ash and silica fume as a binary and ternary blended cement on compressive strength and chloride resistance of self-compacting concrete (SCC) were investigated in this study. High-calcium fly ash (40–70%) and silica fume (0–10%) were used to replace part of cement at 50, 60 and 70 wt.%. Compressive strength, density, volume of permeable pore space (voids) and water absorption of SCC were investigated. The total charge passed in coulombs was assessed in order to determine chloride resistance of SCC. The results show that binary blended cement with high level fly ash generally reduced the compressive strength of SCC at all test ages (3, 7, 28 and 90 days). However, ternary blended cement with fly ash and silica fume gained higher compressive strength after 7 days when compared to binary blended fly ash cement at the same replacement level. The compressive strength more than 60 MPa (high strength concrete) can be obtained when using high-calcium fly ash and silica fume as ternary blended cement. Fly ash decreased the charge passed of SCC and tends to decrease with increasing fly ash content, although the volume of permeable pore space (voids) and water absorption of SCC were increased. In addition when compared to binary blended cement at the same replacement level, the charge passed of SCC that containing ternary blended cement was lower than binary blended cement with fly ash only. This indicated that fly ash and silica fume can improve chloride resistance of SCC at high volume content of Portland cement replacement.     

Behaviour of concrete-filled steel tubular columns incorporating fly ash

The subject of this work is to investigate the effect of fly ash on the strength of concrete filled steel tubular columns from 28 to 365 days. A contrast study was carried out on concrete filled steel tubular columns incorporating 10–40 wt% fly ash, and for control Portland cement concrete filled steel tubular columns. The effect of pre-coating the inner surface of steel tubes with a thin layer of fly ash was also studied. Assessments of the concrete mixes were based on the compressive strength and the bond strength. The results show that a lower replacement with fly ash can improve both bond strength and compressive strength, while a higher replacement with fly ash requires a relatively longer time to achieve similar beneficial effects. Pre-coating the inner surface of steel tubes with a thin layer of fly ash can notably improve the bond strength. The microstructure of the interface between concrete and steel tube was also studied by using scanning electron microscopy analyzer.     

Heat deformations of fly ash concrete

When dealing with concrete resistance to high temperatures it is important for design purposes to know the elastic parameters, such as the temperature–strain curves and the modulus of elasticity.Concretes containing a high volume of fly ash differ from conventional mixes in the cementitious phase. This results in a different behaviour under heating compared to plain Portland cement concretes. To find the elastic response of fly ash concrete four series of concrete mixtures were manufactured: one with cement only, another with 30% by mass partial replacement of cement by fly ash, and two with 30% and 40% by mass replacement of cement by ground fly ash. Tests were carried out on cylinders (150 × 300 mm). A high-calcium fly ash was used.The conditions were selected so that the applied level of stress corresponded to 25% or to 40% of the ultimate compressive strength of concrete, and a transient type of temperature regime was followed. Based on the experiments the critical temperature, the residual deformation and the modulus of elasticity were determined.The results indicate that concretes containing a high volume of fly ash are more sensitive to high temperatures, since they developed greater deformations. The fineness of the fly ash used also seems to influence the degree of deformation in an adverse way.     

Optimization of concrete mixture with hybrid blends of metakaolin and fly ash using response surface method

This paper presents the experimental results of a research carried out on the strength and permeability related properties of high performance concretes made with binary and ternary cementitious blends of fly ash (FA) and metakaolin (MK). The replacement ratios for FA were 10% and 20% by weight of Portland cement and those for MK were 5% and 10%. Compressive strength, chloride permeability, water sorptivity, and water absorption properties of concretes were obtained in this study for different testing ages up to 90 days. The influences of fly ash, metakaolin, and testing age on the properties of concretes have been identified using the analysis of variance. The statistical based regression models and the response surface method with the backward stepwise techniques were employed in the multi-objective optimization analysis. That is carried out by maximizing compressive strength while minimizing chloride permeability, water sorptivity, and water absorption. It was observed that fly ash and especially metakaolin were very effective on the aforementioned properties of the concretes, depending mainly on replacement levels and duration of curing. The results indicated that the ternary use of fly ash and metakaolin with the approximate cement replacement values of 13.3% and 10% respectively has provided the best results for the testing age of 90 days, when the optimized strength and permeability based durability properties of the concretes are concerned.