Reaction Degree of Silica Fume and Its Effect on Compressive Strength of Cement-silica Fume Blends

The compressive strength of the cement-silica fume blends with 5mass%, 10mass%, 20mass% and 30mass% of silica fume and water to binder ratio of 0.28, 0.32 and 0.36 from three days to ninety days were investigated. The reaction degree of silica fume was calculated from the Q4 silica tetrahedron, which was used as a probe obtained from 29 Si solid state nuclear magnetic resonance analysis. The fl at of compressive strength after 28 days disappeared for blended cement with inereasing reaction degree of silica fume. The compressive strength of the blended cement pastes approached that of P.I. cement pastes after 56 days and exceeded that after 90 days. The addition of silica fume and the w/b ratio of blends are both critical to the reaction degree of silica fume. The appropriate addition of silica fume, high silica fume reaction degree and low w/b ratio are benefi cial to the compressive strength of the cement-silica fume blends.

Effect of Silica Fume on Compressive Strength of Oil-Polluted Concrete in Different Marine Environments

In the present research, effect of silica fume as an additive and oil polluted sands as aggregates on compressive strength of concrete were investigated experimentally. The amount ofoil in the designed mixtures was assumed to be constant and equal to 2% of the sand weight. Silica fume accounting for 10%, 15% and 20% of the weight is added to the designed mixture. After preparation and curing, concrete specimens were placed into the three different conditions： fresh, brackish and saltwater environments （submerged in fresh water, alternation of exposed in air ＆ submerged in sea water and submerged in sea water）. The result of compressive strength tests shows that the compressive strength of the specimens consisting of silica fume increases significantly in comparison with the control specimens in all three environments. The compressive strength of the concrete with 15% silica fume content was about 30% to 50% higher than that of control specimens in all tested environments under the condition of using polluted aggregates in the designed mixture.

Effect of Fly Ash and Silica Fume on Hydration Rate of Cement Pastes and Strength of Mortars

The effect of fly ash and silica fume on hydration rate and strength of cement in the early stage was studied. Contrast test was applied to the complex cementitious system to investigate the hydration rate. Combined with mechanical strength, the influence of fly ash and silica fume during the hydration process of complex binder was researched. The peak of the rate of hydration heat evolution and the mechanical strength decreased as the ratio of fly ash increased, however, as the ratio of silica fume increased, the peak of the rate of hydration heat evolution and the mechanical strength increased obviously. When the ratios of fly ash and silica fume are 10% and 5%, the peak of the rate of hydration heat evolution is the highest. At the same time 7 days of flexural and compressive strength are the highest as 8.89 MPa and 46.52 MPa, respectively. Fly ash and silica fume are the main factors affecting the hydration rate and the mechanical property.

Replacement of alkali silicate solution with silica fume in metakaolin-based geopolymers

A metakaolin(Mk)-based geopolymer cement from Tunisian Mk mixed with different amounts of silica fume(SiO_2/Al_2O_3 molar ratio varying between 3.61 and 4.09) and sodium hydroxide(10M) and without any alkali silicate solution, is developed in this work. After the samples were cured at room temperature under air for 28 d, they were analyzed by X-ray diffraction(XRD), Fourier transform infrared(FTIR) spectroscopy, environmental scanning electron microscopy, mercury intrusion porosimetry, ^(27)Al and ^(29)Si nuclear magnetic resonance(NMR) spectroscopy, and compression testing to establish the relationship between microstructure and compressive strength. The XRD, FTIR, and ^(27)Al and ^(29)Si NMR analyses showed that the use of silica fume instead of alkali silicate solutions was feasible for manufacturing geopolymer cement. The Mk-based geopolymer with a silica fume content of 6 wt%(compared with those with 2% and 10%), corresponding to an SiO_2/Al_2O_3 molar ratio of 3.84, resulted in the highest compressive strength, which was explained on the basis of its high compactness with the smallest porosity. Silica fume improved the compressive strength by filling interstitial voids of the microstructure because of its fine particle size. In addition, an increase in the SiO_2/Al_2O_3 molar ratio, which is controlled by the addition of silica fume, to 4.09 led to a geopolymer with low compressive strength, accompanied by microstructures with high porosity. This high porosity, which is responsible for weaknesses in the specimen, is related to the amount of unreacted silica fume.

THE PROPERTIES OF SILICA FUME-MAGNESIUM OXYCHLORIDE CEMENT MATERIALS

The properties of a new magnesium Oxychloride cement (MOC) material formed by silica fume uniformly mix in MOC paste was presents. The influence of silica fume on the water resistance and compressive strength of MOC paste was invesigated in this study. It is shown that when 30 weight percent of silica fume is added to the MOC paste, a high strength and water resisting new material with 112MPa compressive strength and 1 00 water resisting coefficient could by obtained.

Enhancing Concrete Properties Using Silica Fume:Optimized Mix Design

In the current work concrete mixes containing(7.0-33.11)weight%silica fume as fractional substitution of cement with water/cement ratio(0.42-0.48)were formulated conferring to an implemented two factorial central composite design.The samples were water cured for 7,28,56,and 90 days.The samples were tested for compressive strength and density.The experimental results approved that compressive strength and density increase with age and with rising silica fume content up to 11.9 wt.%.Response surface analysis results for samples cured for 28 days confirmed that silica fume concrete with developed compressive strength(53.42 MPa)could be prepared by incorporation of 11.9 wt.%silica fume as a substituent for cement using a 0.42 water/cement ratio.An intensification in compressive strength and density(up to 39.3%and 2.6%)respectively was recorded for silica fume concrete mixes in contrast to Portland cement concrete.Overall,the research findings revealed that silica fume concretes prepared with appropriate silica fume content and water/cement ratio exhibited superior strength and density features candidate them to be used effectively in civil engineering structural applications.

Utilization of Cement Kiln Dust (CKD) with Silica Fume (SF) as a Partial Replacement of Cement in Concrete Production

This research aimed to clarify the role of by-product materials, such as CKD with SF as partial replacement by weight of cement in concrete manufacturing and inclusion on different characteristics of concrete. Concrete test specimens were mixed with 0%, 5%, 10%, 15%, 20% and 25% (CKD) with 15% (SF) as partial replacement by weight of Cement (CEM I-52.5N). Fresh concrete properties have been evaluated by workability measurement slump test. While hardened concrete properties have been evaluated by compressive, split tensile and flexural strengths tests at ages 7, 28 and 56 days, but evaluated for bond strength, modulus of elasticity and chemical composition measurement with X-Ray Fluorescence at age of 28 days. The test results have revealed that the increase of CKD amount with fixed amount of SF in concrete mixtures as partial replacement by weight of cement leads to gradual decrease of fresh concrete workability. In concrete mixtures, 20% CKD in the presence of 15% SF as partial replacement by the weight of cement are the optimum ratios which can be used without any negative effect on mechanical properties compressive, indirect tensile, flexural and bond strength at all the ages of concrete. Also modulus of elasticity and bond strength increased by 8.81% and 0.69% respectively at the age 28 days compared with control mixture.

Effect of silica fume on the fresh and hardened properties of fly ash-based self-compacting geopolymer concrete

The effect of silica fume on the fresh and hardened properties of fly ash-based self-compacting geopolymer concrete （SCGC） was investigated in this paper. The work focused on the concrete mixes with a fixed water-to-geopolymer solid （W/Gs） ratio of 0.33 by mass and a constant total binder content of 400 kg/m3. The mass fractions of silica fume that replaced fly ash in this research were 0wt%, 5wt%, 10wt%, and 15wt%. The workability-related fresh properties of SCGC were assessed through slump flow, V-funnel, and L-box test methods. Hardened concrete tests were limited to compressive, splitting tensile and flexural strengths, all of which were measured at the age of 1, 7, and 28 d after 48-h oven curing. The results indicate that the addition of silica fume as a partial replacement of fly ash results in the loss of workability; nevertheless, the mechanical properties of hardened SCGC are significantly improved by incorporating silica fume, especially up to 10wt%. Applying this percentage of silica fume results in 4.3% reduction in the slump flow; however, it increases the compressive strength by 6.9%, tensile strength by 12.8% and flexural strength by 11.5%.

Comparison of High Performance Fly Ash Concrete Using Nano Silica Fume on Different Mixes

This paper investigates the experimental results on the effect of nano silica fume on compressive strength development of concretes containing high volume fly ash (HVFA). The effect of various silica fumes contents such as 1%, 2% & 3% (wt. %) as partial replacement of cement on the compressive strength of cements is evaluated in the first part. The nano silica fume content which exhibits the highest compressive strength above is used in high volume fly ash concretes containing 30% and 50% class F fly ash. The results show that among three different silica fumes contents, the addition of 1% increases the compressive strength of concretes. The addition of 1% silica fume also increases the early age and 28 days compressive strengths of HVFA concretes.

硅灰及矿渣粉对大掺量粉煤灰砂浆力学性能的影响及机理研究

以硅灰和矿渣粉(GGBS)为辅助胶凝材料,使用聚羧酸高性能减水剂,分别研究了硅灰和GGBS对大掺量粉煤灰砂浆抗压强度的影响。通过压汞测试(MIP)、扫描电子显微镜(SEM)以及X射线衍射(XRD)等方法对制备试件的孔结构、微观产物、物相组成进行分析,得到了硅灰和GGBS影响大掺量粉煤灰砂浆强度的机理。结果表明:单掺硅灰的大掺量粉煤灰砂浆的抗压强度随着硅灰含量增加先增大后减小,单掺GGBS的规律与硅灰类似;复掺硅灰和矿渣时,砂浆的强度较其他同龄期组均有一定的提高,二者表现出良好的协同作用;无论是单掺还是复掺,硅灰和GGBS都对大掺量粉煤灰砂浆强度有良好的提升作用。砂浆试件总孔隙率和大孔占比与抗压强度总体呈负相关,强度越高的砂浆试件微观结构越致密,但相比于总孔隙率,毛细孔和大孔占比表现出与抗压强度更好的相关性。当硅灰和GGBS质量分数分别为8%和6%时,砂浆28 d强度最大,为88.05 MPa。

硅灰热焊接改性塑料颗粒对砂浆抗压强度与微结构的影响

为解决塑料憎水表面所导致的塑料砂浆抗压强度较低的问题,本文利用废弃聚丙烯(PP)塑料的热塑性,通过热焊接工艺将硅灰焊接于PP表面,制备硅灰@塑料颗粒复合颗粒(SF@PP),并对复合颗粒的亲水性和火山灰活性进行测试。结果表明,硅灰热焊接改性显著改善了PP的亲水性并提高了其火山灰活性,促进了水化产物的界面沉积,界面密实度提升。相应地,塑料砂浆的孔隙率明显降低,抗压强度显著提升,提升幅度为26.07%~31.04%。研究结果有利于高效利用废弃塑料,并为高性能塑料砂浆的制备提供依据。

硅灰对磷酸镁水泥基注浆材料早期力学性能及微观结构的影响

利用硅灰作为矿物掺合料,研究硅灰对磷酸镁水泥基注浆材料(MPCG)早期力学性能及微观结构的影响。结果表明,MPCG的主要水化产物为K型鸟粪石(KMgPO4·6H2O),掺6%硅灰能减少基体内微裂纹的产生,使MPCG基体更致密,从而提高MPCG的早期抗压强度和耐水性,此时,在空气中养护7 d的抗压强度达到11.7 MPa。

基于正交试验的矿物掺合料透水混凝土性能研究

在透水混凝土中掺入硅灰和矿粉,设计了四因素四水平正交试验,采用极差法分析了目标孔隙率、水胶比、硅灰掺量、矿粉掺量对透水混凝土抗压强度和透水性能的影响,并对其微观形貌进行了分析。结果表明:各因素对透水混凝土抗压强度和透水性能影响的大小顺序为目标孔隙率>水胶比>硅灰掺量>矿粉掺量;透水混凝土的抗压强度和透水系数之间呈负相关关系;微观分析发现,未掺硅灰、矿粉的透水混凝土微观结构存在明显孔洞,硅灰或矿粉的掺入可以对孔洞进行有效填充,在一定程度上减少了孔隙数量,可改善透水混凝土的综合性能。

硅灰对高炉镍铁渣粉水泥土性能影响机制研究

高炉镍铁渣粉是一种前期火山灰活性较低的绿色可持续新型建筑材料。本文探讨了外掺硅灰对高炉镍铁渣粉水泥土无侧限抗压强度的影响规律,分析高炉镍铁渣粉和硅灰替代率对其无侧限抗压强度和破坏模式的影响。结合扫描电子显微镜(Scanning Electron Microscope, SEM)和X-射线衍射仪(X-ray Diffractometer, XRD)揭示硅灰对高炉镍铁渣粉水泥土性能影响机制。研究结果表明:在一定范围内,高炉镍铁渣粉水泥土的强度随硅灰掺量的增加而提升,归因于硅灰促进水泥水化反应以及硅灰发生二次火山灰反应生成C-S-H凝胶包裹土颗粒表面,未发生水化反应的颗粒减少,凝胶将土壤颗粒、高炉镍铁渣粉颗粒和小硅球等共同构建“网络状”空间骨架填充在大土壤颗粒之间,进一步提升了水泥土的密实性与强度,硅灰的最佳掺量为10%。硅灰掺量高会消耗大量Ca(OH)_(2),影响硅灰发生二次火山灰反应,特别是掺量增加至30%时,水泥土强度降低3.6%。

Probing the hydration of composite cement pastes containing fly ash and silica fume by proton NMR spin-lattice relaxation

Proton NMR spin-lattice relaxation (T1) was used as a prober for observing the hydration process of composite cement pastes blending fly ash and silica fume during the early age.The distribution at initial time,evolution curves and signals intensity of T1 were shown in this paper.Results demonstrate that the T1 distribution curves at initial time exhibit two peaks,which are regarded as two different water phases in the pastes.The evolution curves of T1 are in good agreement with the hydration process of composite pastes and could be roughly divided into four stages:initial period,dormant period,acceleration period and steady period.The hydration mechanism for each stage was discussed.The hydration of the composite cement pastes was retarded by the addition of fly ash and silica fume when compared to that of pure cement.However,the hydration degree of the cement in the blends was promoted.

硅灰对再生混凝土界面过渡区的影响

为改善再生混凝土的力学和耐久性能,以硅灰为增强材料对再生混凝土进行改良。研究了硅灰对再生混凝土3 d、28 d、90 d抗压强度和28 d、90 d抗氯离子渗透性能的影响。结合扫描电镜、显微硬度等微观观测手段,分析了28 d再生混凝土试样微观结构和性能变化。采用压汞法测试了再生混凝土的孔结构参数,探究硅灰对再生混凝土孔隙性能的影响。结果表明:硅灰可以提升再生混凝土的抗氯离子渗透性能,随掺量的增加提升效果先增后减;掺入硅灰可以改善再生混凝土多重界面过渡区结构,增加界面过渡区(ITZ)显微硬度,降低孔隙率。再生混凝土内部存在较多有害孔隙,硅灰可以细化孔隙结构,降低孔隙率,掺量为6%时效果最佳。

高温下赤泥与硅粉协同强化固井水泥石力学性能

为了抑制水泥石高温下强度衰退现象,研究硅粉加量,以及赤泥与硅粉在高温下的协同作用对G级油井水泥石抗压强度的影响,并借助X射线衍射、热重分析高温下水泥水化产物的变化,通过扫描电镜观察水泥石的微观形貌。结果表明:225℃高温养护7 d后,35%硅粉(质量分数)可以提高水泥石高温力学性能,5%赤泥(质量分数)可以协助硅粉进一步提高水泥石高温下的强度,同对照组相比抗压强度提高11.3%。赤泥掺入促进水泥石内部生成纤维状硬硅钙石(Ca_(6)Si_(6)O_(17)(OH)_(2), C_(6)S_(6)H)物相,水泥石内部孔结构减少,水泥石内部结构致密。

硅灰掺量对纤维混凝土力学性能影响试验研究

为了探究硅灰替换水泥掺入纤维混凝土后,纤维混凝土抗压、抗折、抗初裂冲击和抗破坏冲击等性能的优劣,在掺加硅灰的质量分数为0、5%、7.5%、10%时,对纤维素纤维与聚乙烯纤维体积质量均为0.9 kg/m 3的纤维混凝土试件进行破坏分析与力学性能分析。结果表明:当硅灰质量分数为5.0%时,纤维混凝土的抗压强度、抗破坏冲击耗能达到最佳,分别为53.5 MPa、9417.6 kJ;当硅灰质量分数为7.5%时,纤维混凝土的抗初裂冲击耗能为6621.8 kJ,达到最佳;硅灰的掺加使纤维混凝土的抗折强度减小,掺量过大会导致纤维混凝土力学性能劣化。

硅粉掺量对水泥石抗压强度的影响实验分析

塔里木油田超深井井底温度普遍超过150℃,随之而来的是高温条件下固井水泥石强度衰退严重影响到井筒的完整性及油气开采效率。文章通过开展固井水泥中硅粉掺量和细度的分析实验,系统研究了在150~190℃高温条件下固井水泥石在28 d中的抗压强度发展规律。结果表明,温度在150~190℃时,通过调整硅粉的加量和细度可以使水泥石在28 d中抗压强度保持稳定。其中,温度在150~160℃及160~170℃条件下,300目硅粉就可以满足要求,掺量分别为35%和45%;温度在170~180℃之间,需要采用500目的硅粉,掺量为60%;温度在180~190℃时,需要添加200目和500目的硅粉混合物,以1∶2的比例搭配,总掺量为70%。同时,运用X射线衍射(XRD)和扫描电镜(SEM)技术对水泥石水化产物进行分析,发现水泥中掺入一定比例的细硅粉有利于雪硅钙石的生成,使水泥石基体在高温环境下保持稳定,解决强度衰退问题。

硅灰和稻壳灰对竹浆纤维水泥基复合材料抗劣化性能的影响

以硅灰和稻壳灰作为掺合料(固定总掺量为40%)、竹浆纤维作为增强材,采用抄取法制备了纤维增强水泥基复合材料,并研究了干湿循环和热水浸泡老化试验下,不同硅灰和稻壳灰掺入比例对竹浆纤维水泥基复合材料力学性能的影响。结果表明:不同掺入比例的硅灰和稻壳灰均有效提高了竹浆纤维水泥基复合材料在干湿循环和热水浸泡老化下的抗弯强度和断裂韧性,其中,单掺40%硅灰的提高效果最好。