Effect of electric arc furnace dust on the properties of OPC and blended cement concretes

This paper presents results of a study conducted to evaluate the mechanical properties and durability characteristics of ordinary Portland cement (OPC) and blended cement (silica fume and fly ash) concrete specimens prepared with electric arc furnace dust (EAFD). Concrete specimens were prepared with and without EAFD. In the silica fume cement concrete, silica fume constituted 8% of the total cementitious material while fly ash cement concrete contained 30% fly ash. EAFD was added as 2% replacement of cement in the OPC concrete and 2% replacement of the total cementitious content in the blended cement concretes. Mechanical properties, such as compressive strength, drying shrinkage, initial and final setting time, and slump retention were determined. The durability characteristics were evaluated by measuring water absorption, chloride permeability, and reinforcement corrosion. The initial and final setting time and slump retention increased due to the incorporation of EAFD in both OPC and blended cement concretes. The drying shrinkage of EAFD cement concrete specimens was more than that of concrete specimens without EAFD. The incorporation of EAFD was beneficial to OPC concrete in terms of strength gain while such a gain was not noted in the blended cement concretes. However, the strength differential between the blended cement concretes with EAFD and the corresponding concretes without EAFD was not that significant. The water absorption and chloride permeability, however, decreased due to the incorporation of EAFD in both the OPC and blended cement concretes. The corrosion resistance of OPC and blended cement concrete specimens increased due to the addition of EAFD.     

基于不同掺和料的透水混凝土性能试验研究

透水混凝土是一种利于促进水循环,改善城市生态环境的环保型建筑材料,本文通过分析目标孔隙率、粉煤灰的量、硅粉的量和纳米SiO₂的量等因素对透水混凝土正交试验影响。结果表明:透水混凝土抗压强度的最优配合比为目标孔隙率取16%、硅灰掺量取8%、粉煤灰掺量取10%、纳米SiO₂掺量取0.5%;透水混凝土孔隙率的最优配合比为目标孔隙率取24%、粉煤灰掺量取10%、硅灰掺量取2%、纳米SiO₂掺量取1%;透水混凝土透水系数的最佳配合比为目标孔隙率取24%、硅灰掺量取8%、粉煤灰掺量取20%、纳米SiO₂掺量取1%。     

矿物掺和料对玄武岩纤维水泥砂浆强度发展的影响

研究了粉煤灰和硅灰对玄武岩纤维增强水泥基材料强度发展规律的影响,分析了粉煤灰和硅灰复掺对水泥砂浆中玄武岩纤维耐腐蚀性的影响.结果表明：玄武岩纤维对水泥基材料的早期抗折强度具有增强作用,后期增强效果下降,甚至会降低基体强度;粉煤灰和硅灰可显著延长玄武岩纤维对水泥砂浆抗折强度增强效果的时效.XRD图谱和显微结构分析表明,粉煤灰和硅灰复掺后降低了水泥基体中Ca(OH)2晶体的含量和玄武岩纤维的腐蚀程度,改善了玄武岩纤维和水泥基体之间的界面性质.     

Performance assessment of Alccofine with silica fume,fly ash and slag for development of high strength mortar

Previous studies on concrete have identified silica fume (SF) as the most effective supplementary material, whereas fly ash (FA) and slag have been identified as economical materials with long term strength potential. Development of blended cement mortar referred to as blended mortar (BM) requires similar assessment. The present study explores the application of Alccofine (AL) as supplementary material and compares its performance with conventional materials namely SF, FA and ground granulated blast furnace slag (GGBS). The mortar specimens with binder to fine-aggregates (b/f ) ratio of 1:2 are prepared at water to binder (w/b) ratios of 0.4 and 0.35. The strength values and stress-strain curve for control and BM specimens are obtained at 7, 28, 56, and 90 d curing periods. The assessment based on strength activity index, k-value method and strength estimation model confirms that AL, despite lower pozzolanic activity, contributes to strength gain, due to reduced dilution effect. Assessment of stress-strain curves suggests that the effect of w/b ratio is more dominant on the elastic modulus of BM specimens than on control specimens. The observations from the study identify enhanced strength gain, improved elastic modulus and higher energy absorption as key contributions of AL making it a potential supplementary material.     

沸石与其他矿物质粉体的复合对碱-硅酸反应的影响

采用天然碱活性石灰质骨料,按照快速砂浆棒法(ASTM C1260),研究了天然沸石分别与粉煤灰、矿渣和硅灰的复合对碱-硅酸反应(ASR)的影响。结果显示,沸石与其他矿物质掺合料的复合对ASR的抑制效果与沸石的品质及其他矿物质掺合料的品质有关。     

矿物掺合料对水泥砂浆强度和早期开裂的影响

综合评价了粉煤灰、硅粉对水泥砂浆早期收缩开裂和强度的影响,进一步研究了粉煤灰、硅粉对砂浆自由收缩、初始开裂时间以及初始开裂时抗折强度的影响,在本试验材料体系内,优化出开裂敏感性相对较优的水泥基材料组成。     

河道疏浚底泥制备泡沫混凝土试验研究

利用河道疏浚底泥制备泡沫混凝土,研究了石灰、粉煤灰和微硅粉部分代替水泥,以及外掺偏硅酸钠、水玻璃和生物炭对所制备的底泥基泡沫混凝土抗压强度、导热系数和吸水耐水性能的影响。结果表明,微硅粉的加入优化了孔隙分布,可诱发火山灰反应,改善底泥基泡沫混凝土的综合性能;外掺2%的大麦草生物炭(500℃)可使底泥基泡沫混凝土的抗压强度提高14.2%,导热系数降低4.78%;添加石灰、粉煤灰和偏硅酸钠降低了泡沫混凝土的综合性能;水玻璃对泡沫混凝土的性能影响不大。     

Characteristics of lightweight concrete containing mineral admixtures

This research investigates the properties of fresh and hardened concretes containing locally available natural lightweight aggregates, and mineral admixtures. Test results indicated that replacing cement in the structural lightweight concrete developed, with 5–15% silica fume on weight basis, caused up to 57% and 14% increase in compressive strength and modulus of elasticity, respectively, compared to mixes without silica fume. But, adding up to 10% fly ash, as partial cement replacement by weight, to the same mixes, caused about 18% decrease in compressive strength, with no change in modulus of elasticity, compared to mixes without fly ash. Adding 10% or more of silica fume, and 5% or more fly ash to lightweight concrete mixes perform better, in terms of strength and stiffness, compared to individual mixes prepared using same contents of either silica fume or fly ash.     

Sulfate resistance of plain and blended cements exposed to magnesium sulfate solutions

This study was conducted to evaluate the performance of plain and blended cements exposed to magnesium sulfate solutions with varying sulfate concentrations for up to 24 months. Four types of cements, namely Type I, Type V, Type I plus silica fume, and Type I plus fly ash, were exposed to five magnesium sulfate solutions with sulfate concentration of 1%, 1.5%, 2.0%, 2.5%, and 4.0%. The sulfate-resistance was evaluated by visual examination, and measuring reduction in compressive strength. Maximum deterioration, due to sulfate attack, was noted in Type I cement. The performance of Type V, Type I plus silica fume and Type I plus fly ash cements was not significantly different from each other. The enhanced sulfate-resistance noted in the Type I cement blended with either silica fume or fly ash indicates the usefulness of these cements both in sulfate and sulfate plus chloride environments.     

Mineralogical study of polymer modified mortar with silica fume

Experimental investigation on the effects of styrene acrylic polymer and silica fume on the mineralogical composition of pastes of high-early-strength portland cement after 28 days of casting are presented in this paper. Thermogravimetry and derivative thermogravimetry were used to study the interaction between polymers and cements, and the extent of pozzolanic reaction of mortars with silica fume. Differential scanning calorimetry and X-ray diffraction were also used to investigate the cement hydration according to the additions. The results showed that the addition of silica fume and polymer reduces the portlandite formation due to delaying of portland cement hydration and pozzolanic reaction.     

硅灰对硫铝酸盐水泥水化行为的影响机理

通过抗压强度、凝结时间、电阻率测定以及X射线衍射(XRD)、扫描电镜(SEM)和孔溶液分析,研究了掺硅灰硫铝酸盐水泥浆体的水化行为.结果表明:5%掺量(质量分数,下同)的硅灰可以很好地改善水泥浆体的抗压强度,10%硅灰掺量的试样抗压强度只在1,28d时稍高于空白试样;掺入硅灰明显缩短了硫铝酸盐水泥的凝结时间;硫铝酸盐水泥的主要晶体水化产物是钙矾石,28d时的钙矾石量稍高于3d时,掺硅灰试样的钙矾石量要高于空白试样;掺硅灰试样的电阻率变化曲线高于空白试样,表明硅灰的掺入能够加快水泥的水化速率;硬化水泥浆体的孔溶液碱度随着硅灰掺量的增加而降低,掺硅灰试样的Ca2+浓度高于空白试样,表明硅灰促进了熟料的溶解,5%硅灰掺量试样的Al 3+浓度最低,表明其促进水化的效果更明显.     

矿物掺合料对C100～C120超高强混凝土基本性能的影响

通过正交试验考察了胶凝材料总量、水泥用量及超细粉煤灰用量对超高强混凝土抗压强度的影响,研究了硅灰、超细粉煤灰与复合硅材等矿物掺合料对C100~C120超高强混凝土基本性能的影响。结果表明,对超高强混凝土强度影响最主要的因素是水泥在胶凝材料中所占的比例;超细粉煤灰与硅灰复掺对超高强混凝土工作性能与强度改善效果较好;复合硅材对超高强混凝土的工作性能与强度均有一定的提高。     

纳米SiO2超高强高流态混凝土及改性机理

通过正交试验提出纳米超高强高流态混凝土的胶凝材料配合比设计参数,并研究了纳米SiO_2的掺入对传统掺硅灰、粉煤灰超高强水泥基胶凝材料强度及工作性能的影响。在保证水胶比不变的条件下,开展了混凝土配合比试验,并研究了纳米SiO_2对混凝土抗压强度的影响及其微观机理。结果表明:超高强高流态混凝土中胶凝材料最优比例为:纳米SiO_2:硅灰:粉煤灰:水泥=1:8:20:71;在胶凝材料用量为600～1 000kg/m~3范围内,随着其掺量的增加,混凝土流动度不断增加,抗压强度先增大后减小,当其掺量为800kg/m~3时,抗压强度最大。分析认为,纳米SiO_2、硅灰与粉煤灰形成的三元多尺度堆积体系能优化粉体材料在混凝土中的微集料密实填充效应,纳米SiO_2的二次水化反应也有效改善了硬化水泥石的微观结构,并优化其形态分布,进一步增大其强度。     

粉煤灰和硅灰对白云石基碱式硫酸镁水泥影响的研究

在白云石基碱式硫酸镁水泥(DBMSC)中掺加不同掺量的粉煤灰、硅灰,并通过研究其凝结时间、力学性能、流动度、水泥放热速率、孔径分布等,结合XRD观察其水化产物组成,分析粉煤灰、硅灰对DBMSC的影响。试验结果表明,在DBMSC中掺加适量粉煤灰有助于提高其后期强度,改善胶砂流动度;适量硅灰有助于提高其早期强度,但对改善其胶砂流动度的效果不明显;粉煤灰和硅灰均对DBMSC具有缓凝作用,降低水泥水化热。     

Effect of silica fume on cement hydration and temperature rise of concrete in tropical environment

Investigated herein is the effect of temperature on heat development in cement pastes and concretes with and without silica fume cured at relatively high temperatures often encountered in tropical environment. With an initial temperature of 30°C, adiabatic temperature rise of the concrete with 8% silica fume as cement replacement was similar to that of the control Portland cement concrete up to about 18 h. After 24 h, however, the temperature of the silica fume concrete was lower than that of the control concrete. Since the concrete with 8% silica fume had a higher 28-day compressive strength (72.5 MPa) than the control concrete without silica fume (59.2 MPa), the concrete with silica fume is likely to have a lower temperature rise as compared with the control concrete of equivalent 28-day strength by reducing cementitious materials content with the same water content. The extent of heat evolution in the silica fume pastes was generally greater at lower temperatures of 20-50°C, but less at 65°C than in the control paste. At the relatively high curing temperatures, the degree of cement hydration in the paste with silica fume was lower than that in the control cement paste at early ages. However, the pozzolanic reaction started even before 24 h after water was added.     

Effect of silica fume on cement hydration and temperature rise of concrete in tropical environment

Investigated herein is the effect of temperature on heat development in cement pastes and concretes with and without silica fume cured at relatively high temperatures often encountered in tropical environment. With an initial temperature of 30°C, adiabatic temperature rise of the concrete with 8% silica fume as cement replacement was similar to that of the control Portland cement concrete up to about 18 h. After 24 h, however, the temperature of the silica fume concrete was lower than that of the control concrete. Since the concrete with 8% silica fume had a higher 28-day compressive strength (72.5 MPa) than the control concrete without silica fume (59.2 MPa), the concrete with silica fume is likely to have a lower temperature rise as compared with the control concrete of equivalent 28-day strength by reducing cementitious materials content with the same water content. The extent of heat evolution in the silica fume pastes was generally greater at lower temperatures of 20–50°C, but less at 65°C than in the control paste. At the relatively high curing temperatures, the degree of cement hydration in the paste with silica fume was lower than that in the control cement paste at early ages. However, the pozzolanic reaction started even before 24 h after water was added.     

Properties of blended sulfoaluminate belite cement

The subject of the study was the possibility of the blending of sulfoaluminate belite (SAB) cement by means of various pozzolanas. The results obtained show that it was possible effectively to modify the properties of SAB cement by means of granulated blast furnace slag, fly ash, and silica fume, and the properties of materials based on these blends. Interesting properties from practical viewpoints of these materials was their compressive strength. As it is very well known, this is by the blending used to decrease. From a viewpoint of the acceptable compressive strength decrease, for SAB cement blends well-found portions of pozzolana with the values of approximately 5–15% seem to be optimal. This range was significantly lower than well-found portions of pozzolanas with values of approximately 20–40% for Ordinary Portland Cement (OPC) blends. The main cause was the fact that unique sources of calcium hydroxide needed for pozzolanic reaction in SAB was only β–C₂S compared to OPC having two sources of calcium hydroxide — the hydration of C₃S and β–C₂S. Therefore, the amount of calcium hydroxide for the pozzolanic reaction in the SAB cement blends was significantly lower. That was why the lower portions of pozzolanas in SAB cement blends were suitable.     

Potential use of spent mushroom compost ash as an activator for pulverised fuel ash

The utilization of pulverised fuel ash (PFA) as a replacement material for Portland cement has resulted in improved concrete properties. However, the pozzolanic activity of PFA is slow, resulting in poor strength development of PFA concrete at early ages. To overcome this problem many researchers have investigated methods of activating (mechanically, thermally and chemically) the pozzolanic reactivity of PFA. This paper assesses the potential use of spent mushroom compost ash (SMCA) as a chemical activator for PFA blended cement systems.When added to the PFA/OPC paste mix SMCA had the effect of improving early strength development. X-ray diffraction results showed that, in the mix which contained 20% SMCA, ettringite formation was improved at both 7 and 28 days, whereas thermogravimetric analysis identified depletion of calcium hydroxide levels at both 3 and 7 days for the same sample pastes. It is therefore considered that the increased strength development in SMCA mixes is a result of the presence of large quantities of sulfates in SMCA, which, when hydrated, has activated the glassy phases present in PFA to form ettringite, as well as possibly accelerating the pozzolanic activity.     

Assessing the effectiveness of pozzolans in massive high-strength concrete

This paper investigates the effects of supplementary cementitious materials on the temperature rising profile, heat evolution and early-age strength development of medium- and high-strength concrete. A total of 13 different mixtures were prepared, with two water–cement ratios (0.3 and 0.46). Natural pozzolan, fly ash, and silica fume were included in the specimens. The results showed that natural pozzolan, particularly fly ash served to decrease the amplitude of peak temperature, delay the occurrence of the peak, and decrease the sharpness of the temperature rising profiles. In contrast, the temperature profile of silica fume specimens was similar to those without silica fume. It was found that the best mixture, the highest early-age strength and the lowest heat liberation, corresponded to the specimen containing fly ash at 15% (be cement weight). This result justifies the advantage effect of fly ash which is able to develop sufficient tensile strength to resist thermal cracking potential in massive high-strength concrete.     

双掺粉煤灰和硅粉混凝土抗冻性能试验研究

在深入分析混凝土冻融破坏机理及其影响因素的基础上,提出在混凝土中双掺硅粉和粉煤灰的方法,并按有关规范要求进行普通混凝土与双掺混凝土抗冻性能的对比试验。试验结果表明:双掺混凝土因基于"等量替换法"用硅粉和粉煤灰替换了一部分水泥,减小了水泥用量和增大了水灰比,故双掺混凝土的强度和弹性模量均明显低于普通混凝土,但减水剂的使用降低了水胶比,使双掺混凝土的抗冻性能优于普通混凝土。