Effect of fly ash and slag on the fracture characteristics of high performance concrete

The premature deterioration of concrete structures in aggressive environments has necessitated the development of high performance concrete (HPC). The major difference between conventional concrete and HPC is essentially the use of chemical and mineral admixtures. The improved pore structure of HPC achieved by the use of chemical and mineral admixtures causes densification of paste-aggregate transition zone, which in turn affects the fracture characteristics. Hence, studies were taken up to investigate the effect of fly ash and slag on the fracture characteristics of HPC. Beam specimens (geometrically similar and single size variable notch) with locally available fly ash (25%) and slag (50%) as cement replacement materials were prepared and tested in a servo-controlled Universal Testing Machine (UTM) under displacement control. From the value of the peak load for each beam, various fracture parameters were calculated. The results show that there is a reduction in the fracture energy due to addition of fly ash or slag, which can be attributed to the presence of unhydrated particles of size larger than that of normal flaws in concrete. Also due to densification, the post peak behaviour is steeper for the fly ash or slag based HPC mixes. The results of the investigation are presented in this paper.     

Copper slag as sand replacement for high performance concrete

This paper reports on an experimental program to investigate the effect of using copper slag as a replacement of sand on the properties of high performance concrete (HPC). Eight concrete mixtures were prepared with different proportions of copper slag ranging from 0% (for the control mix) to 100%. Concrete mixes were evaluated for workability, density, compressive strength, tensile strength, flexural strength and durability. The results indicate that there is a slight increase in the HPC density of nearly 5% with the increase of copper slag content, whereas the workability increased rapidly with increases in copper slag percentage. Addition of up to 50% of copper slag as sand replacement yielded comparable strength with that of the control mix. However, further additions of copper slag caused reduction in the strength due to an increase of the free water content in the mix. Mixes with 80% and 100% copper slag replacement gave the lowest compressive strength value of approximately 80 MPa, which is almost 16% lower than the strength of the control mix. The results also demonstrated that the surface water absorption decreased as copper slag quantity increases up to 40% replacement; beyond that level of replacement, the absorption rate increases rapidly. Therefore, it is recommended that 40 wt% of copper slag can used as replacement of sand in order to obtain HPC with good strength and durability properties.     

Benefits of internal curing on service life and life-cycle cost of high-performance concrete bridge decks – A case study

This paper investigates the impact of internal curing on the service life of high-performance concrete (HPC) bridge decks by using analytical models to predict the times to onset of corrosion, onset of corrosion-induced damage, and failure of decks. Three bridge deck design options were compared: (i) normal concrete deck; (ii) HPC deck with supplementary cementing materials (SCM); and (iii) HPC deck with SCM and internal curing. It was found that the use of internal curing can extend the service life of high-performance concrete bridge decks by more than 20 years, which is mainly due to a significant reduction in the rate of penetration of chlorides in concrete as a result of reduced early-age shrinkage cracking and reduced chloride diffusion. Compared to normal concrete, HPC with SCM and internal curing was predicted to add more than 40 years to the service life of bridge decks in severe environmental conditions. Life-cycle cost reductions of 40% and 63% were estimated when conventional HPC and internally-cured HPC were used in bridge decks instead of normal concrete, respectively, despite the fact that the in-place unit cost of internally-cured HPC can be 4% higher than that of conventionally-cured HPC, which in turn can be up to 33% higher than that of normal concrete. This is due to a longer service life and less frequent maintenance activities offered by low-permeability HPC bridge decks.     

Copper slag waste as a supplementary cementing material to concrete

Summary The use of industrial solid waste to concrete production is environmentally friendly because it contributes to reducing the consumption of natural resources, the pollution concrete production generates and the power it consumes. This paper presents the results of a study on the use of copper slag as pozzolanic supplementary cementing material for use in concrete. Initially, the chemical and mineralogical characteristics of the copper slag were determined. After this, concrete batches were made with copper slag additions of 20% (relative to the cement weight) and a set properties were investigated, i.e., specific gravity, compressive strength, splitting-tensile, absorption, absorption rate by capillary suction and carbonation. The results pointed out that there is a potential for the use of copper slag as a supplementary cementing material to concrete production. The concrete batches with copper slag addition presented greater mechanical and durability performance.     

高性能混凝土抗裂性能研究

该文对高性能混凝土的抗裂性能进行了系统的研究,主要包括:高性能混凝土收缩与抗裂性能的试验方法,研制出一种测试混凝土抗裂性能的诱导开裂试验方法,该方法避免了混凝土裂缝出现位置的随机性以及混凝土塑性沉降引起的材料不均匀等带来的测试结果不准确,同时研制出一种多点、实时、自动监测混凝土试件开裂时间的系统,可应用于测试混凝土早期的裂缝出现时间;进行了大量自生收缩试验和干燥收缩试验,对影响高性能混凝土自生收缩和干燥收缩的因素进行了深入的研究,提出了减少收缩变形的混凝土原材料选用和粉煤灰及矿渣单掺与多掺的最佳掺量,提出了高性能混凝土自生收缩和干燥收缩计算模型;采用平板诱导开裂法和圆环测试系统进行了大量的抗裂性能试验,深入研究了混凝土原材料特别是粉煤灰及矿渣影响高性能混凝土抗裂性能的规律,提出了实现高抗裂性能的混凝土原材料选用和粉煤灰及矿渣单掺与多掺的最佳掺量;研究成果成功地应用于实际工程中,取得了显著的技术和经济效益。     

Characteristics of Crack Growth in High Performance Concrete Subjected to Fire

An experimental investigation was conducted to identify the characteristics of crack growth in high performance concrete (HPC) subjected to fire, including two parts of work, i.e. crack growth resistance determinations and cracking observations, using concrete of three strength grades 40 MPa, 70 MPa, and 110 MPa. The crack growth resistance curves (R-curves ) of HPC subjected to high temperatures were determined using notched three-point bend beam specimens of 100 mm×100 mm×300mm. The R-curve (crack growth resistance curve) flattening shows that the crack growth resistance has been significantly reduced by elevated temperature. Concrete with a higher strength grade has a steeper R-curve, with a higher fracture toughness but a shorter critical crack growth. The shorter critical crack growth means that concrete of a higher strength grade has a more brittle behavior. The concrete cracking observations reveal that the consequences of rapid heating are quite different from those of slow heating. For slow he     

Stress curves and mechanical properties of high performance concrete

Abstract

In this research, high performance concrete (HPC) was designed by the minimum void ratio method, and slag and silica fumes partially replaced cement, as well as fly ash replacing about 15% of sand. Stress curves for compressive, splitting and flexure strengths of HPC specimens were measured and indicated the experimental concretes had better pastes to void ratios than control batches ratio N=V_p /V_v =1.3. The result indicates that pozzolanic materials provide not only a chemical strength effect, but also a physical packing effect. The compressive stress curves may keep growing as the concrete ages.     

The influence of silica fume on the corrosion resistance of steel in high performance concrete exposed to simulated sea water

This investigation examined the influence of silica fume on the corrosion behaviour of steel in high performance concrete (HPC) by comparing the behaviour of HPC concretes with and without a 10% by mass of cement addition of silica fume. Reinforced concrete prisms (500 × 100 × 100 mm) with embedded corrosion probes were loaded in three-point bending to achieve a 0.3 mm crack and exposed to simulated sea water for up to four years. Corresponding prisms without induced cracks were also studied as controls. For the HPC with silica fume, pore size distribution measurements showed that after exposure to the simulated sea water, the hydration and pozzolanic reactions near the induced crack blocked almost all continuous pores in the 0.01 to 10 m range. This affected the type and distribution of corrosion products that formed by restricting the access of chlorides and oxygen to the surface of the steel. Thus, only magnetite (Fe₃O₄) formed and was confined the space provided by the induced crack, effectively plugging the crack. In HPC without silica fume, oxygenated corrosion products such as goethite (-FeOOH) and akaganeite (-FeOOH) formed in the induced crack region. The implications of these observations on the service life of high performance concrete structures are discussed.     

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).     

锰渣掺合料对砂浆收缩性能的影响

锰铁高炉废渣研磨后,勃氏法测得比表面积为5400cm2/g.磨细锰渣掺合料以15%和30%替代水泥,制作砂浆试件并测试干燥收缩值,同时试验了激发剂对锰渣水泥试件收缩值的影响.结果表明,锰渣掺合料会使砂浆试件的收缩增大,锰渣掺量愈多收缩值愈大.S激发剂促使锰渣水泥砂浆试件早期收缩增大.试验结果对锰渣掺合料用于混凝土结构中的收缩与抗裂性能具有参考意义.     

聚乙烯醇纤维增强钢渣粉-水泥复合材料基本力学性能及微观结构

通过掺加钢渣粉来制备聚乙烯醇（PVA）纤维增强钢渣粉-水泥基复合材料,从宏微观两个方面研究了这种复合材料的性能。考虑了基体材料的水胶比（0.25和0.35）、不同钢渣粉质量分数（0、30wt%、60wt%、80wt%）,采用抗压强度试验、薄板四点弯曲试验研究了PVA纤维增强钢渣粉-水泥基复合材料的基本力学性能变化规律及其在弯曲荷载作用下的裂缝控制能力,采用扫描电镜观测了破坏后试样的微观结构。结果表明,水胶比和钢渣粉掺量均可明显影响PVA纤维增强钢渣粉-水泥基复合材料的基本力学性能,在低水胶比条件下（水胶比为0.25）,钢渣粉掺量达到80wt%时,试样表现出较高的韧性指数和良好的裂缝控制能力,基本满足工程所需强度要求,水胶比为0.35时钢渣掺量不宜超过60wt%;同时,从节能减排的角度考虑,利用钢渣粉制备PVA纤维增强钢渣粉-水泥基复合材料是可行的。      

Effects of granulated blast furnace slag and superplasticizer type on the fresh properties and compressive strength of self-compacting concrete

This paper presents the results of an experimental investigation carried out to study the effect of granulated blast furnace slag and two types of superplasticizers on the properties of self-compacting concrete (SCC). In control SCC, cement was replaced with 10%, 15%, 20%, and 25% of blast furnace slag. Two types of superplasticizers: polycarboxylate based superplasticizer and naphthalene sulphonate based superplasticizers were used. Tests were conducted for slump flow, the modified slump test, V-Funnel, J-Ring, U-Box, and compressive strength. The results showed that polycarboxylate based superplasticizer concrete mixes give more workability and higher compressive strength, at all ages, than those with naphthalene sulphonate based superplasticizer. Inclusion of blast furnace slag by substitution to cement was found to be very beneficial to fresh self-compacting concrete. An improvement of workability was observed up to 20% of slag content with an optimum content of 15%. Workability retention of about 45 min with 15% and 20% of slag content was obtained using a polycarboxylate based superplasticizer; compressive strength decreased with the increase in slag content, as occurs for vibrated concrete, although at later ages the differences were small.     

Accelerated carbonation and performance of concrete made with steel slag as binding materials and aggregates

Steel slag has been used as supplementary cementitious materials or aggregates in concrete. However, the substitution levels of steel slag for Portland cement or natural aggregates were limited due to its low hydraulic property or latent volume instability. In this study, 60% of steel slag powders containing high free-CaO content, 20% of Portland cement and up to 20% of reactive magnesia and lime were mixed to prepare the binding blends. The binding blends were then used to cast concrete, in which up to 100% of natural aggregates (limestone and river sands) were replaced with steel slag aggregates. The concrete was exposed to carbonation curing with a concentration of 99.9% CO₂ and a pressure of 0.10 MPa for different durations (1d, 3d, and 14d). The carbonation front, carbonate products, compressive strength, microstructure, and volume stability of the concrete were investigated. Results show that the compressive strength of the steel slag concrete after CO₂ curing was significantly increased. The compressive strengths of concrete subjected to CO₂ curing for 14d were up to five-fold greater than that of the corresponding concrete under conventional moist curing for 28d. This is attributed to the formation of calcium carbonates, leading to a microstructure densification of the concrete. Replacement of limestone and sand aggregates with steel slag aggregates also increased the compressive strengths of the concrete subjected to CO₂ curing. In addition, the concrete pre-exposed to CO₂ curing produced less expansion than the concrete pre-exposed to moist curing during the subsequent accelerated curing in 60 °C water. This study provides a potential approach to prepare concrete with low-carbon emissions via the accelerated carbonation of steel slag.     

Optimum content of copper slag as a fine aggregate in high strength concrete

This study investigated the mechanical properties of high strength concrete incorporating copper slag as a fine aggregate and concluded that less than 40% copper slag as sand substitution can achieve a high strength concrete that comparable or better to the control mix, beyond which however its behaviors decreased significantly. The workability and strength characteristics were assessed through a series of tests on six different mixing proportions at 20% incremental copper slag by weight replacement of sand from 0% to 100%. The results indicated that the strength of the concrete with less than 40% copper slag replacement was higher than or equal to that of the control specimen and the workability even had a dramatic growth. The microscopic view demonstrated that there were limited differences between the control concrete and the concrete with less than 40% copper slag content. It also suggested that the determination of the copper slag replacement level should consider with the desired compressive strength of concrete.     

Design of self-compacting concrete with ground granulated blast furnace slag

Ground granulated blast furnace slag (GGBS), due to its pozzolanic nature, could be a great asset for the modern construction needs, because slag concretes can be of high performance, if appropriately designed. The use of GGBS as a cementitious material as well as fine filler is being increasingly advocated for the production of High Performance Concrete (HPC), Roller Compacted Concrete (RCC) and self compacting concrete (SCC), etc. However, for obtaining the required high performance in any of these concrete composites, slag should be properly proportioned so that the resulting concrete would satisfy both the strength and performance criteria requirements of the structure. The present paper is an effort towards presenting a new mix design methodology for the design of self compacting GGBS concretes based on the efficiency concept. The methodology has already been successfully verified through a proper experimental investigation and the self compacting slag concretes were evaluated for their self compactability and strength characteristics. The results indicate that the proposed method can be capable of producing high quality SCC.     

Experimental investigation of basic oxygen furnace slag used as aggregate in asphalt mixture

Chinese researchers have commenced a great deal of researches on the development of application fields of basic oxygen steel making furnace slag (BOF slag) for many years. Lots of new applications and properties have been found, but few of them in asphalt mixture of road construction engineering. This paper discussed the feasibility of BOF steel slag used as aggregate in asphalt pavement by two points of view including BOF steel slag's physical and micro-properties as well as steel slag asphalt materials and pavement performances. For the former part, this paper mainly concerned the mechanochemistry and physical changes of the steel slag and studied it by performing XRD, SEM, TG and mercury porosimeter analysis and testing method. In the second part, this paper intended to use BOF steel slag as raw material, and design steel slag SMA mixture. By using traditional rutting test, soak wheel track and modified Lottman test, the high temperature stability and water resistance ability were tested. Single axes compression test and indirect tensile test were performed to evaluate the low temperature crack resistance performance and fatigue characteristic. Simultaneously, by observing steel slag SMA pavement which was paved successfully. A follow-up study to evaluate the performance of the experimental pavement confirmed that the experimental pavement was comparable with conventional asphalt pavement, even superior to the later in some aspects. All of above test results and analysis had only one main purpose that this paper validated the opinion that using BOF slag in asphalt concrete is feasible. So this paper suggested that treated and tested steel slag should be used in a more extensive range, especially in asphalt mixture paving projects in such an abundant steel slag resource region.     

Influence of recycled aggregates and high contents of fly ash on concrete fresh properties

This study presents the fresh properties of concrete with supplementary cementitious materials (SCM) and recycled concrete aggregates (RCA), with emphasis on the feasibility of using high volumes of fly ash (FA) in RCA concrete. For this purpose, two mix families (0% coarse RCA and 100% coarse RCA) were produced, both with and without superplasticizers (SP). The coarse natural aggregates (NA) were replaced with coarse RCA at 0% and 100%, respectively. For each of the mentioned families, three incorporation levels (0%, 50% and 100%) of fine RCA were used with 0%, 30% and 60% of FA, resulting in 28 compositions. Each mix was tested in the fresh state by means of slump, density and air content. The results of this study show that RCA decreased the slump of concrete mixes, but the required water content can be minimized by incorporation FA. Regardless of the water absorption of the aggregates, for a given fine RCA incorporation ratio and the same ratio of FA, no increase in water content is required to obtain the same target slump as in the reference concrete. On the other hand, for a given coarse RCA incorporation ratio, a five times lower FA ratio is enough to obtain the same target slump as in the reference concrete. Air voids in concrete mixes were more affected by the shape of the aggregates than by their water absorption. The air content of concrete mixes increased as the incorporation levels of FA and RCA increased. However, in comparison with the individual effects, the air content decreased by combining the incorporation of both FA and RCA. Moreover, the rate of reduction in fresh density by increasing the incorporation of RCA and FA was similar in concrete mixes with and without SP.     

The effects of supplementary cementing materials in modifying the heat of hydration of concrete

This paper is intended to provide guidance on the form and extent to which supplementary cementing materials, in combination with Portland cement, modifies the rate of heat evolution during the early stages of hydration in concrete. In this investigation, concretes were prepared with fly ash, condensed silica fume and ground granulated blastfurnace slag, blended with Portland cement in proportions ranging from 5% to 80%. These concretes were subjected to heat of hydration tests under adiabatic conditions and the results were used to assess and quantify the effects of the supplementary cementing materials in altering the heat rate profiles of concrete. The paper also proposes a simplified mathematical form of the heat rate curve for blended cement binders in concrete to allow a design stage assessment of the likely early-age time–temperature profiles in large concrete structures. Such an assessment would be essential in the case of concrete structures where the potential for thermally induced cracking is of concern.     

玄武岩-碳纤维/矿渣混凝土力学性能正交试验

应用正交试验法开展了16组玄武岩-碳纤维(BF-CF)/矿渣混凝土和1组C40级基准混凝土的塌落度、立方体抗压强度和劈裂抗拉强度试验,研究了BF、CF和矿渣三种因素对BF-CF/矿渣混凝土力学性能的影响。结果表明:BF-CF/矿渣混凝土立方体抗压强度和劈裂抗拉强度均高于C40基准混凝土,立方体抗压强度最大提高了21.0%,劈裂抗拉强度最大提高了35.3%。BF和CF的掺入均会减小混凝土的塌落度,BF对于塌落度的减小更加明显,BF对塌落度的最大降幅为67.1%;矿渣代砂率是影响BF-CF/矿渣混凝土立方体抗压强度的显著因素,随着矿渣代砂率的增大,立方体抗压强度先增大后减小,矿渣对立方体抗压强度的最大提高幅度为7.6%;BF是影响BF-CF/矿渣混凝土劈裂抗拉强度的显著因素,劈裂抗拉强度随BF体积率的增加而增大,BF对劈裂抗拉强度的最大增幅为12.0%,CF对劈裂抗拉强度的提升不明显。对正交试验的结果进行回归分析得出BF-CF/矿渣混凝土立方体抗压强度和劈裂抗拉强度预测模型,模型精度较高。      

KHM170型卧辊磨制备钢渣超细粉工业试验研究

基于KHM170型卧辊磨的钢渣超细粉制备终粉磨工业试验系统,在给定钢渣粉、矿渣粉、水泥熟料粉的质量和粒度范围内,进行用钢渣粉部分代替矿渣粉制作水泥混凝土的强度试验。结果表明,KHM卧辊磨终粉磨系统可以实现钢渣超细粉终粉磨,可用于以热焖渣、滚筒渣为原料制备钢渣微粉的工业化生产;矿渣粉中掺加质量分数不超过30%的钢渣粉,且在满足钢渣粉比表面积大于矿渣粉比表面积和水泥熟料粉比表面积时,可以作为优选的混合材料大量用于混凝土。