Effect of Granulated Blast Furnace Slag and fly ash addition on the strength properties of lightweight mortars containing waste PET aggregates

In this work, the effect of Granulated Blast Furnace Slag (GBFS) and fly ash (FA) addition on the strength properties of lightweight mortars containing waste Poly-ethylene Terephthalate (PET) bottle aggregates was investigated. Investigation was carried out on three groups of mortar specimens. One made with only Normal Portland cement (NPC) as binder, second made with NPC and GBFS together and, third made with NPC and FA together. The industrial wastes mentioned above were used as the replacement of cement on mass basis at the replacement ratio of 50%. The size of shredded PET granules used as aggregate for the preparation of mortar mixtures were between 0 and 4 mm. The waste lightweight PET aggregate (WPLA)–binder ratio (WPLA/b) was 0.60; the water–binder (w/b) ratios were determined as 0.45 and 0.50. The dry unit weight, compressive and flexural–tensile strengths, carbonation depths and drying shrinkage values were measured and presented. The results have shown that modifying GBFS had positive effects on the compressive strength and drying shrinkage values (after 90 days) of the WPLA mortars. However, FA substitution decreased compressive and flexural–tensile strengths and increased carbonation depths. Nevertheless a visible reduction occurred on the drying shrinkage values of FA modifying specimens more than cement specimens and GBFS modified specimens. The test results indicated that, GBFS has a potential of using as the replacement of cement on the WPLA mortars by taking into consideration the characteristics. But using FA as a binder at the replacement ratio of 50% did not improve the overall strength properties. Although it was thought that, using FA as binder at the replacement ratio of 50% for the aim of production WPLA concrete which has a specific strength, would provide advantages of economical and ecological aspects.     

高性能混凝土约束收缩对氯离子扩散的影响

对粉煤灰和矿渣粉双掺总量占胶凝材料总质量的百分比分别为30%,40%和50%及掺合比例分别为1∶2,2∶3和1∶1的高性能混凝土进行了平板收缩试验和快速氯离子扩散系数测定（RCM法）试验,分析了高性能混凝土有约束和无约束收缩开裂性能及对氯离子扩散系数的影响规律。研究结果表明:无约束的混凝土平板均未发生开裂,有约束的混凝土平板基本开裂,双掺矿物掺合料显著改善了混凝土的抗裂性能,当粉煤灰和矿渣粉的掺合比例为1∶1时,其抗裂性能最好,且随着掺量的增加,混凝土的抗裂性越好;矿物掺合料双掺总量和掺合比例一定时,各配比约束收缩混凝土的等效氯离子扩散系数均高于无约束收缩混凝土的氯离子扩散系数,即约束收缩增大了混凝土的氯离子扩散系数,收缩应变越大,混凝土的抗氯离子性能越差;当粉煤灰和矿渣粉掺合比例为1∶1时,约束收缩对混凝土内氯离子扩散的影响最小。     

Wet and dry cured compressive strength of concrete containing ground granulated blast-furnace slag

This paper reports a part of an ongoing laboratory investigation in which the compressive strength of ground granulated blast-furnace slag (GGBFS) concrete studied under dry and wet curing conditions. In the study, a total of 45 concretes, including control normal Portland cement (NPC) concrete and GGBFS concrete, were produced with three different water-cement ratios (0.3, 0.4, 0.5), three different cement dosages (350, 400, 450 kg/m³) and four partial GGBFS replacement ratios (20%, 40%, 60%, 80%). A hyperplasticizer was used in concrete at various quantities to provide and keep a constant workability. Twelve cubic samples produced from fresh concrete were de-moulded after a day, then, six cubic samples were cured at 22±2 °C with 65% relative humidity (RH), and the remaining six cubic samples were cured at 22±2 °C with 100%RH until the samples were used for compressive strength measurement at 28 days and three months. Three cubic samples were used for each age and curing conditions. The comparison was made on the basis of compressive strength between GGBFS concrete and NPC concrete. GGBFS concretes were also compared within themselves. The comparisons showed that compressive strength of GGBFS concrete cured at 65%RH was influenced more than that of NPC concrete. It was found that the compressive strength of GGBFS concrete cured at 65%RH was, at average, 15% lower than that of GGBFS concrete cured at 100%RH. The increase in the water-cementitious materials ratios makes the concrete more sensitive to dry curing condition. The influence of dry curing conditions on GGBFS concrete was marked as the replacement ratio of GGBFS increased.     

Strength and drying shrinkage properties of self-compacting concretes incorporating multi-system blended mineral admixtures

Drying shrinkage can be a major reason for the deterioration of concrete structures. The contraction of the material is normally hindered by either internal or external restraints so that tensile stresses are induced. These stresses may exceed the tensile strength and cause concrete to crack. The present study investigated compressive strength and particularly drying shrinkage properties of self-compacting concretes containing binary, ternary, and quaternary blends of Portland cement, fly ash (FA), ground granulated blast furnace slag (GGBFS), silica fume (SF), and metakaolin (MK). For this purpose, a total of 65 self-compacting concrete (SCC) mixtures were prepared at two different water to binder ratios. It was observed that drying shrinkage lessened with the use of FA, GGBFS, and MK while incorporation of SF increased the drying shrinkage.     

Stiffness and strength development of the soft clay stabilized by the one-part geopolymer under one-dimensional compressive loading

In this paper, the one-part alkali-activated geopolymer was adopted as the soil binder to stabilize the soft clay under the one-dimensional compressive loading. Factors influencing the stiffness and strength of the one-part geopolymer stabilized soil such as the proportion of silicon-aluminum raw materials, the mass ratio of solid NaOH (NH) to raw materials and the water-binder ratio were taken into account. The stiffness development of the one-part geopolymer stabilized soft clay under one-dimensional compressive loading was investigated by an improved transducer system equipped with a pair of bender extender elements and the tactile pressure sensor, from which the time history of earth pressure coefficient (i.e., K₀) and elastic wave velocity (i.e., the compression wave velocity V_P and the shear wave velocity V_S) of the stabilized soil sample could be measured, respectively. Furthermore, the unconfined compressive strength (UCS) of the stabilized soil sample cured under varied one-dimensional compressive loadings was tested to reveal the strength development of the geopolymer stabilized soil sample. Among different mixing proportions, the alkali-activated binary precursor [90% ground granulated blast furnace slag (GGBFS) and 10% fly ash (FA)] exhibits the highest performance in terms of the V_S, V_P and UCS of the geopolymer stabilized soil sample when the activator/precursor and water/solid ratio are 0.15 and 0.7 (i.e., the 4.67 mol/L of NH solution), respectively. The prediction of UCS for the one-part geopolymer stabilized soft clay was proposed and established based on the elastic wave velocity (i.e., V_S and V_P). The outcome of the current study sheds light on the practical use of the one-part alkali-activated geopolymer as a soil binder in ground improvement.     

Mechanical properties of reactive powder concrete containing mineral admixtures under different curing regimes

Mechanical properties (compressive strength, flexural strength, and toughness) of reactive powder concrete (RPC) produced with class-C fly ash (FA) and ground granulated blast furnace slag (GGBFS) were investigated under different curing conditions (standard, autoclave and steam curing) in this study. Test results indicate that, compressive strength of RPC increased considerably after steam and autoclaving compared to the standard curing. On the other hand, it was observed that steam and autoclave curing decreased the flexural strength and toughness. Increasing the GGBFS and/or FA content improved the toughness of RPC under all curing regimes considerably. Furthermore, SEM micrographs revealed dense microstructure of RPC.     

矿渣超量取代水泥高性能混凝土性能研究

研究了矿渣超量取代对水泥混凝土抗压强度、氯离子渗透性、气体渗透性和干燥收缩的影响。研究发现．矿渣等量取代30％水泥配制高性能混凝土．混凝土强度和渗透性最优;等量取代混凝土早期强度低,并且随矿渣掺量增加而下降。矿渣超量取代技术能有效提高矿渣大掺量混凝土早期强度。超量取代技术不仅能提高矿渣等量取代水泥混凝土强度,而且更能改善混凝土氯离子渗透性能和气体渗透性．最佳超代系数为1．3。矿渣超量取代水泥混凝土虽然增大了矿渣掺量．但并不会增大混凝土干燥收缩。     

The effect of conditioning to a predetermined weight loss on the permeability of concrete

The durability properties of concrete can be assessed via gas permeability tests. The moisture content of the concrete plays a major role in its permeability to gas, and the conditioning stage of any gas permeability test aims to minimise and standardise the amount of moisture present in the concrete via oven drying, usually at a temperature of 105 °C. However, this is known in some circumstances to take a considerably longer period of time in comparison to the permeability testing itself. This study examines whether a relationship exists between the moisture content of a specimen and its permeability by investigating the permeability of concrete specimens dried by varying amounts. It was found that a simple relationship of the form y = ax^b could be established for both normal and high strength concrete subjected to pressure decay-time permeability testing.     

高温后纤维矿渣微粉混凝土的弯曲性能

通过纤维矿渣微粉混凝土在高温后的弯曲试验,探讨了温度、矿渣掺量、纤维类型与掺量、混凝土强度等级对高温后纤维矿渣微粉混凝土抗折强度和荷载-挠度曲线的影响.结合扫描电镜照片,研究了高温后纤维矿渣微粉混凝土的劣化机理.结果表明,高温后纤维矿渣微粉混凝土弯曲性能随受热温度的升高而不断劣化;钢纤维、矿渣微粉和聚丙烯纤维均会在一定程度上提高高温后混凝土的弯曲性能.通过对试验结果的统计分析,提出了在考虑温度、矿渣微粉掺量和钢纤维掺量影响下的纤维矿渣微粉混凝土抗折强度计算公式.     

粉煤灰对高性能混凝土强度的影响

探讨了粉煤灰在高性能混凝土中的活性效应及作用机理。通过试验研究得出,当水胶比为０．３５以下时,在水泥砂浆中掺入３０％粉煤灰,其强度比可达到０．９５以上;在混凝土中掺入５０％粉煤灰,其抗压强度可达到６０ＭＰａ以上,可见粉煤灰在高性能混凝土中能发挥较好的活性效应。     

按耐久性设计高性能混凝土的原则和方法

高性能混凝土不是一个混凝土的品种,而是表明混凝土的“性能（performance）或者 质量、状态、水平的一种称谓,是按照具体工程要求和所处环境条件,满足特殊组合的性能而均匀、致密的高质量混凝土。高性能混凝土的耐久性设计步及原材料选择与控制、配合比设计、制备工艺和施工质量控制的全过程。按工程要求的耐久性选定原材料后,从“NEL法的氯离了扩散系数－渗透性关系”中初选水胶比,用绝对体积法计算配合比,进行试配和强度样核。     

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.     

Effects of stabilizers on CO2 fixation capacity in neutralization of alkali construction sludge

Construction sludge, generated from tunneling and piling, is typically in a liquid state. It can be improved via physical treatments, such as dehydration, and/or chemical treatments, using stabilizers, in order to to be recycled as construction material. To adjust the strength of sludge, chemical treatments are often preferred. However, chemical treatments frequently result in alkali leaching. Methods to reduce alkalinity by curing the alkaline sludge under CO₂ gas at a certain concentration have been proposed in Japan. In recent years, technologies that utilize CO₂ to improve the quality of cementitious material have received considerable attention in terms of carbon capture. Therefore, the effects of stabilizers on the CO₂ fixation capacity of alkaline sludge during pH neutralization were investigated in this study. Accelerated carbonation and carbonate content measurement tests were conducted to detect the CO₂ content fixed in alkaline sludge specimens treated with various stabilizers. The test results showed that the fixed maximum CO₂ content per gram of dry mass of sludge, (m_CO2)^max, increased with the calcium oxide (CaO) content of the stabilizer(s) per gram of dry sludge, C_CaO. However, the rate of increase in (m_CO2)^max with C_CaO was significantly affected by the type of stabilizer used. In the case of quicklime (QL), the ratio of (m_CO2)^max to C_CaO was approximately 0.5, whereas, in the cases of fly ash (FA) and steel slag (SS), the ratio was approximately 0.25. The ratios for biomass ash and paper sludge ash were between that for QL and that for FA and SS. Detailed analyses of the test results suggest that the CaO content per gram of stabilizer(s) in the sludge, C*_CaO, can provide an estimate of the fixed maximum amount of CO₂ per gram of stabilizer(s) in the sludge, (m*_CO2)^max. However, other factors, including the amount of water-soluble Ca, should be considered for a precise evaluation. Additionally, the experimental results showed that the decrease in pH owing to neutralization increases with the increasing C_CaO. However, the type of stabilizer did not significantly affect the relationship between the degree of CO₂ fixation and the degree of neutralization.     

粒化高炉矿渣和CaSO4对高强混凝土收缩特性影响试验研究

基于正交设计方法,在水胶比为0.3的条件下,研究了0、20%、40%的粒化高炉矿渣(GGBFS)和0、1.5%、3.0%、4.5%的CaSO4对高强混凝土凝结时间、收缩性能的影响,并采用XRD分析了水化过程。结果表明,掺入GGBFS和CaSO4能缩短凝结时间;复掺20%GGBFS和CaSO4的高强混凝土抑制自收缩效果优于复掺40%GGBFS和CaSO4的高强混凝土;复掺40%GGBFS和4.5%CaSO4能有效降低高强混凝土的干燥收缩性能。XRD结果表明,掺入GGBFS和CaSO4有利于水泥的水化反应,促进水化产物的生成。     

高强高性能混凝土在沈阳除冰盐环境下的氯离子扩散行为

采用化学分析，测定了高强混凝土（HSC）和高性能混凝土（HPC）在3种氯盐暴露环境中的自由氧离子分布规律。结果表明：HSC-HPC的抗氨离子扩散行为并不取决干其抗压强度的大小．而与活性掺合料的种类和掺量密切相关，掺加粉煤灰（FA）能够降低其氯离子扩散速度，掺加硅灰（SF）将使其氟离子扩散速度提高。分析指出，HSC尤其是掺加FA的HPC，非常适合干东北地区恶劣的露天除冰盐环境。     

Effect of mineral admixtures and curing periods on shrinkage and cracking age under restrained condition

This paper presents the test results on cracking behavior at medium age of uniaxially restrained specimens containing different types of mineral admixture, namely fly ash and limestone powder. In this study, the uniaxially restrained shrinkage, free shrinkage and strength tests were conducted to study the potential of cracking of concrete under restrained shrinkage condition. The influences of water to binder ratio, mineral admixtures and curing period of concrete on cracking behavior were investigated in this study. The investigation showed that cracking age and cracking strain of restrained specimens vary with mix proportion, mineral admixture and curing period. The potential of shrinkage cracking is not influenced only by cracking strain and amount of shrinkage but also on shrinkage rate and tensile creep. Mixture with lower water to binder ratio (w/b = 0.35) shows shorter cracking age than the mixture with higher water to binder ratio (w/b = 0.55). Fly ash and limestone powder significantly increase cracking age of concrete. The cracking age increases with the increase of the replacement ratio of fly ash. The higher shrinkage rate, when exposed to drying, of mixture with longer curing period leads to shorter cracking age.     

Structural behavior of concrete filled steel tubular sections (CFT/CFSt) under axial compression

In this study, compressive strength, modulus of elasticity and steel tensile coupon tests are performed to determine material properties. Sixteen hollow cold formed steel tubes and 48 concrete filled steel tube specimens are used for axial compression tests. The effects of width/thickness ratio (b/t), the compressive strength of concrete and geometrical shape of cross section parameters on ultimate loads, axial stress, ductility and buckling behavior are investigated. Circular, hexagonal, rectangular and square sections, 18.75, 30.00, 50.00, 100.00 b/t ratio values and 13, 26, 35 MPa concrete compressive strength values are chosen for the experimental procedure. Analytical models of specimens are developed using a finite element program (ABAQUS) and the results are compared. Circular specimens are the most effective samples according to both axial stress and ductility values. The concrete in tubes has experienced considerable amount of deformations which is not expected from such a brittle material in certain cases. The results provide an innovative perspective on using cold formed steel and concrete together as a composite material.     

Effect of aspect ratio and volume fraction of steel fiber on the mechanical properties of SFRC

In this study, effects of aspect ratio (l/d) and volume fraction (V_f) of steel fiber on the compressive strength, split tensile strength, flexural strength and ultrasonic pulse velocity of steel fiber reinforced concrete (SFRC) were investigated. For this purpose, hooked-end bundled steel fibers with three different l/d ratios of 45, 65 and 80 were used. Three different fiber volumes were added to concrete mixes at 0.5%, 1.0% and 1.5% by volume of concrete. Ten different concrete mixes were prepared. After 28 days of curing, compressive, split and flexural strength as well as ultrasonic pulse velocity were determined. It was found that, inclusion of steel fibers significantly affect the split tensile and flexural strength of concrete accordance with l/d ratio and V_f. Besides, mathematical expressions were developed to estimate the compressive, flexural and split tensile strength of SFRCs regarding l/d ratio and V_f of steel fibers.     

Effect of GGBFS on time dependent compressive strength of concrete

This paper addresses the compressive strength properties when GGBFS is used to make concrete and discuss in detail the compressive strength development of concrete cubes and cylinders. The uniaxial compression tests have been conducted on these concrete specimens with and without GGBFS at the ages of 3, 7, 28, 56, 90, 150 and 180 days. Experimental values show increasing concrete strength with GGBFS up to 40% but at a higher period of maturity (56 days and more). Sixty percent GGBFS blending, however, shows reduced strength when compared to 40% blending. A comparative study has also been carried out between the experimentally obtained compressive strength and strength predicted by the models given in SP-24 (Indian Standard), ACI-209, CEB-FIP and GL-2000. Based on the experimentally obtained results a strength predicting models has also been proposed for GGBFS based concrete.     

Determination of relevant parameters influencing gas permeability of mortars

This paper is devoted to the study of the influence of the microstructure of cementitious materials on their gas permeability. For that purpose, cement pastes with four water to cement ratios W/C and mortar specimens with two aggregate volume contents have been cast. On the one hand gas permeability tests with a low pressure device have been carried out on desaturated materials and on the other hand porosity features have been determined by mercury porosimetry measurements. Gas permeability depends upon the mixture parameters (W/C, aggregate volume content, aggregate size) and the moisture content. Correlation between gas permeability and pore size distribution has been discussed from Katz–Thompson equation too. Our results showed that permeability predicted from the threshold radius of the capillary porosity for cement pastes and mortars whatever the aggregate volume content corresponds to permeability measured after drying at relative humidity, RH equal to 90%. For preconditioning with lower RH, the measured permeability is influenced by microcracking generated by drying shrinkage.