Effects of copper sludge on cemented clay using ultrasonic pulse velocity

To evaluate the behavior of cemented clay treated reinforced with copper sludge, 63 ultrasonic pulse velocity tests were conducted. The copper sludge content, curing period and moisture content were all varied so that the behavior of the sample could be examined. The cement content was 11% by weight clay. The copper sludge contents were 0, 5, 10, 15, 25, 30 and 35% by weight of the cement and samples were cured for 7, 28, and 60 days. The results of this study can be used for estimating of the impacts of these variables on mechanical properties of cemented clay soil treated with copper sludge. The results of this study indicates that at early age of curing time inclusion of copper sludge decreases the ultrasonic pulse velocity. The ultrasonic pulse velocity of samples at 7 and 28 days decreases by increasing copper sludge content. The ultrasonic pulse velocity of sample on the wet side is higher than wet side of the dry unit weight-moisture content curve. Moreover an optimum percentage for the copper sludge (%15) in which the behavior of cemented clay improves significantly.     

粉煤灰/硅灰复合掺合料对水泥净浆性能的影响

研究了水泥标准稠度用水量、粉煤灰掺量、硅灰掺量、粉煤灰与硅灰双掺对水泥净浆性能的影响.结果表明,硅灰使水泥净浆需水量明显增加,粉煤灰、硅灰双掺可克服单掺粉煤灰早期强度低的缺点,短期内能提高水泥净浆的抗压强度.     

Effect of fiber reinforcement on deformability properties of cemented sand

In this study, a series of unconfined compression tests have been performed to determine the effect of polyvinyl alcohol (PVA) fiber inclusion on deformation characteristics of cemented sand. The cement contents were 2, 4, and 6% by weight of the dry sand and samples were cured for 7 days. PVA fibers with a length of 12 mm and a diameter of 0.1 mm were added to sand-cement mixtures at a weight ratio of 0.0%, 0.3%, 0.6% and 1% (dry wt.). The compression stress-axial strain, secant modulus of elasticity (E₅₀), tangent modulus of elasticity (E_tan), failure mode, energy absorption capacity (EA), energy base index, strain base index, deformability index and axial strain at peak strength of the samples were described. Tests results show that addition of cement to sand increased stiffness and unconfined compression strength (UCS), and leading to a brittle behavior. Moreover, addition of PVA fibers to cemented sand increased the UCS and axial strain at peak strength and increased softening stress after the maximum strength. In addition, the fiber inclusion increases the energy absorption capacity and decreases the secant modulus of elasticity.     

Modeling of compressive strength of cemented sandy soil

This paper attempted to show the application of particle swarm optimization in the prediction of the compressive strength of cement sandy soil from the curing period, porosity of sample and percentage of cement. The results of the study show that the unconfined compressive strength of the cement stabilized sandy soil increases with an increasing cement content curing time period. Moreover the compressive strength decreases with an increasing porosity. The compressive strength improvement due to cement treatment has a larger increase in samples with less porosity. In addition, particle swarm optimization algorithm is and accurate technique in estimation of compressive strength of cement stabilized sandy soil. In order to compare of existing correlations, a total number of 100 unconfined compressive tests and 15 scanning electron microscope tests have been conducted on cemented Babolsar sand. It can be concluded that compared to existing correlations models, particle swarm optimization algorithm models give more reliable prediction about compressive strength of cement satblized sandy soil. Moreover, the sensitivity analysis of the polynomial model shows that cement content and porosity have significant impact on predicting unconfined compressive strength.     

Investigations on the compressive strength of silica fume concrete using statistical methods

The present paper deals with a mathematical model developed using statistical methods to predict the 28-day compressive strength of silica fume concrete with water-to-cementitious material (w/cm) ratios ranging from 0.3 to 0.42 and silica fume replacement percentages from 5 to 30. Strength results of 26 concrete mixes, on more than 300 test specimens, have been analyzed for statistical modeling. The ratios of compressive strengths between silica fume and control concrete have been related to silica fume replacement percentage. The expression, being derived with strength ratios and not with absolute values of strength, is independent of the specimen parameters and is applicable to all types of specimens. On examining the validity of the model with the results of previous researchers, it was observed that for results on both cubes and cylinders, predictions were obtained within 7.5% of the experimentally obtained values.     

用SiO2微粉制备碳化硅粉体的研究

为回收利用SiO2微粉,探究了以SiO2微粉为原料通过碳热还原法制备碳化硅粉体的最佳工艺条件;研究了分别以石油焦、活性炭和石墨粉为还原剂对冶炼效果的影响。在最佳碳质还原剂的基础上,研究了不同配碳比(还原剂与SiO2微粉的质量比为1∶3.5、1∶3、1∶2.5、1∶2、1∶1.5)和不同冶炼时间(15、30、45、60 min)对冶炼效果的影响。结果表明:石油焦、活性炭、石墨粉3种碳质还原剂中,石油焦的冶炼效果最佳;将石油焦与原料SiO2微粉以质量比1∶2进行混合,在中频感应炉中以1650℃冶炼45 min为最佳冶炼工艺条件;以此能够得到晶粒生长较好、品质较高的碳化硅粉体,碳化硅含量高达93.50%(w)。     

Effects of densified silica fume on microstructure and compressive strength of blended cement pastes

Some experimental investigations on the microstructure and compressive strength development of silica fume blended cement pastes are presented in this paper. The silica fume replacement varies from 0% to 20% by weight and the water/binder ratio (w/b) is 0.4. The pore structure by mercury intrusion porosimetry (MIP), the micromorphology by scanning electron microscopy (SEM) and the compressive strength at 3, 7, 14, 28, 56 and 90 days have been studied. The test results indicate that the improvements on both microstructure and mechanical properties of hardened cement pastes by silica fume replacement are not effective due to the agglomeration of silica fume particles. The unreacted silica fume remained in cement pastes, the threshold diameter was not reduced and the increase in compressive strength was insignificant up to 28 days. It is suggested that the proper measures should be taken to disperse silica fume agglomeration to make it more effective on improving the properties of materials.     

气相法白炭黑的生产、应用及市场分析

叙述了国内外气相法白炭黑的生产技术现状、用途 ,对我国气相法白炭黑的市场进行了分析及前景预测。鉴于国外先进的生产企业不向中国转让其先进的生产技术 ,而国内企业的生产技术落后、生产规模小 ,建议有实力的企业除可以与高校合作研究开发新的生产工艺外 ,还可以与乌克兰表面化学研究所联系购买其较先进的生产技术     

以硅灰、白炭黑、硅溶胶为硅源合成碳化硅晶须的研究

以硅灰、白炭黑、硅溶胶为硅源,炭黑为碳源,采用碳热还原法合成碳化硅晶须,通过XRD及SEM对合成产物的物相及形貌进行分析,探讨了合成温度(分别为1 400、1 450、1 500、1 550℃)、硅源、n(C)∶n(SiO2)对合成碳化硅晶须的影响.结果表明:n(C)∶n(SiO2)为2.4～3.6,合成温度为1 500 ℃,保温3 h时,硅溶胶与炭黑反应没有生成碳化硅晶须,硅灰、白炭黑与炭黑反应均生成碳化硅晶须;以硅灰为硅源合成碳化硅晶须的质量及数量明显优于以白发黑为硅源合成碳化硅晶须;合成碳化硅晶须的最佳n(C)∶n(SiO2)为3.3.     

Influence of silica fume on the tensile strength of concrete

The present paper is directed towards developing a better understanding on the isolated contribution of silica fume on the tensile strengths of high-performance concrete (HPC). Extensive experimentation was carried out over water-binder ratios ranging from 0.26 to 0.42 and silica fume-binder ratios from 0.0 to 0.3. For all the mixes, compressive, flexural and split tensile strengths were determined at 28 days. The compressive, as well as the tensile, strengths increased with silica fume incorporation, and the results indicate that the optimum replacement percentage is not a constant one but depends on the water-cementitious material (w/cm) ratio of the mix. Compared with split tensile strengths, flexural strengths have exhibited greater improvements. Based on the test results, relationships between the 28-day flexural and split tensile strengths with the compressive strength of silica fume concrete have been developed using statistical methods.     

粉煤灰/硅灰对低标号混凝土性能的影响

研究了单掺粉煤灰、硅灰和双掺粉煤灰/硅灰对低标号混凝土的工作性、强度和干缩性的影响。结果表明,粉煤灰和硅灰能改善新拌低标号混凝土的工作性,硅灰使得低标号混凝土在短期内的干缩变化加大,造成早期裂缝,短期内双掺粉煤灰/硅灰能有效提高低标号混凝土的抗压强度。     

Utilization of fly ash with silica fume and properties of Portland cement-fly ash-silica fume concrete

This paper reports the normal consistency, setting time, workability and compressive strength results of Portland cement-fly ash-silica fume systems. The results show that water requirement for normal consistency was found to increase with increasing SF content while a decrease in initial setting time was found. Workability, measured in term of slump, was found to decrease with silica fume content (compared to blends without silica fume). However, it must be noted that despite the reduction in the slump values, the workability of Portland cement-fly ash-silica fume concrete in most cases remained higher than that of the Portland cement control concrete. Furthermore, the utilization of silica fume with fly ash was found to increase the compressive strength of concrete at early ages (pre 28 days) up to 145% with the highest strength obtained when silica fume was used at 10 wt%. Moreover, scanning electron micrographs show that utilization of fly ash with silica fume resulted in a much denser microstructure, thereby leading to an increase in compressive strength.     

Rheology of cementitious paste with silica fume or limestone

The rheological behaviour of cementitious pastes where cement has increasingly been replaced by densified silica fume (SF), untreated SF or limestone has been studied. The effect of SF on the flow resistance, taken as the area under the flow curve, was found to depend on the dispersing ability of the plasticizer as illustrated by pastes with naphtalene sulphonate-formaldehyde condensate (SNF) and polyether grafted polyacrylate (PA).The gel strengths increased with increasing SF replacement of cement independently of plasticizer type. The cementitious gel strength was, however, depending on the type of SF since pastes with densified SF developed lower gel strengths than pastes with untreated SF. This phenomenon was attributed to agglomerates in the densified SF which remained unbroken by the mixing and measurement sequence.Both flow resistance and gel strength decreased with increasing limestone replacement. Thus, silica fume may have an advantage over limestone filler as stabilizing agent for self-compacting concrete preventing segregation upon standing and reduced form pressure due to a more rapid gel formation.     

Effect of silica fume and fly ash on heat of hydration of Portland cement

Results of calorimeter tests on Portland cement-silica fume-fly ash mixtures are presented. Data indicate that silica fume accelerates cement hydration at high water/cementitious ratios and retards hydration at low water/cementitious ratios. On the other hand, fly ash retards cement hydration more significantly at high water/cementitious ratios. When silica fume and fly ash are added together with cement, the reactivity of the silica fume is hampered and the hydration of the cementitious system is significantly retarded.     

添加切割废料对硅灰制备碳化硅的影响

为回收利用硅灰,将硅灰通过碳热还原法制备了SiC粉体.研究不添加切割废料时温度(1550、1650、1750、1850℃)对冶炼效果的影响.在较优冶炼温度基础上,研究了切割废料添加质量(分别为硅灰添加质量的5％、15％、25％、35％、50％)对制备碳化硅粉体的影响.结果表明:最佳冶炼温度为1750℃,此时产物中SiC...     

Experimental study on properties of polymer-modified cement mortars with silica fume

This paper discussed the flexural and the compressive strengths of polyacrylic ester (PAE) emulsion and silica fume (SF)-modified mortar. The chloride ion permeability in cement mortar and the interfacial microhardness between aggregates and matrix were measured. The chemical reactions between polymer and cement-hydrated product were investigated by the infrared spectral technology. The results show that the decrease of porosity and increase of density of cement mortars can be achieved by the pozzolanic effect of SF, the water-reducing and -filling effect of polymer. Lower porosity and higher density can give cement mortars such properties as higher flexural and compressive strength, higher microhardness value in interfacial zone and lower effective diffusion coefficient of chloride ion in matrix.     

硅灰和减水剂对硅酸三钙水化调控机理的研究

采用XRD、精密水化微量热、ESEM、EDS和NMR等测试技术,研究了硅灰和聚羧酸减水剂对C3S水化的影响。结果表明：聚羧酸减水剂的掺入抑制了C3S的早期水化放热,而硅灰消耗了C3S水化产生的CH,促进了C3S的水化.两者都使C3S水化产物C-S-H凝胶的形貌由针棒状发生了转变,且其硅氧四面体的聚合状态有较大不同,尤其是硅灰显著影响了C-S-H凝胶硅氧四面体聚合状态中Q1、Q2的含量。     

Effect of silica fume on steel fiber bond characteristics in reactive powder concrete

In this paper, the effect of silica fume on the bond characteristics of steel fiber in matrix of reactive powder concrete (RPC), including bond strength, pullout energy, etc., are presented. The experimental results on steel fiber pullout test of different conditions are reported. Various silica fume contents ranging from 0% to 40% are used in the mix proportions. Fiber pullout tests are conducted to measure the bond characteristics of steel fiber from RPC matrix. It is found that the incorporation of silica fume can effectively enhance the fiber-matrix interfacial properties, especially in fiber pullout energy. It is also concluded that in terms of the bond characteristics, the optimal silica fume content is between 20% and 30%, given the conditions of the experimental program. The microstructural observation confirms the findings on the interfacial-toughening mechanism drawn from the fiber pullout test results.     

利用硅灰制备免蒸压PHC管桩

本文主要通过在管桩混凝土中使用硅灰和矿粉双掺,实现PHC管桩混凝土免蒸压工艺。结果表明：双掺硅灰和矿粉后,PHC管桩经蒸养4 h（常压,95 ℃）,蒸养后1 d强度可达到80 MPa以上,蒸养后自然养护3 d强度达到85 MPa以上,满足免蒸压要求。     

Effect of nano silica and fine silica sand on compressive strength of sodium and potassium activators synthesised fly ash geopolymer at elevated temperatures

Environment friendly geopolymer is a new binder which gained increased popularity due to its better mechanical properties, durability, chemical resistance, and fire resistance. This paper presents the effect of nano silica and fine silica sand on residual compressive strength of sodium and potassium based activators synthesised fly ash geopolymer at elevated temperatures. Six different series of both sodium and potassium activators synthesised geopolymer were cast using partial replacement of fly ash with 1%, 2%, and 4% nano silica and 5%, 10%, and 20% fine silica sand. The samples were heated at 200°C, 400°C, 600°C, and 800°C at a heating rate 5°C per minute, and the residual compressive strength, volumetric shrinkage, mass loss, and cracking behaviour of each series of samples are also measured in this paper. Results show that, among 3 different NS contents, the 2% nano silica by wt. exhibited the highest residual compressive strength at all temperatures in both sodium and potassium‐based activators synthetised geopolymer. The measured mass loss and volumetric shrinkage are also lowest in both geopolymers containing 2% nano silica among all nano silica contents. Results also show that although the unexposed compressive strength of potassium‐based geopolymer containing nano silica is lower than its sodium‐based counterpart, the rate of increase of residual compressive strength exposed to elevated temperatures up to 400°C of potassium‐based geopolymer containing nano silica is much higher. It is also observed that the measured residual compressive strengths of potassium based geopolymer containing nano silica exposed at all temperatures up to 800°C are higher than unexposed compressive strength, which was not the case in its sodium‐based counterpart. However, in the case of geopolymer containing fine silica sand, an opposite phenomenon is observed, and 10% fine silica sand is found to be the optimum content with some deviations. Quantitative X‐ray diffraction analysis also shows higher amorphous content in both geopolymers containing nano silica at elevated temperatures than those containing fine silica sand.