硅粉粉煤灰混凝土的室内试验研究

结合具体的工程实例,通过试验对硅粉混凝土和硅粉粉煤灰混凝土的制备进行了研究,并对二者的经济性作了分析比较,得出硅粉粉煤灰混凝土较硅粉混凝土的坍落度高,且工程经济性与适用性强的结论。     

复掺粉煤灰和硅灰在自密实混凝土中的应用

复掺粉煤灰和硅灰应用到自密实混凝土中,可以增大新拌混凝土的流动性,改善离析泌水,增加混凝土硬化后的强度,提高其耐久性能。试验研究了粉煤灰的最佳掺量,以及几种矿物质掺合料复掺的复合效应。     

不同比例粉煤灰与硅灰对再生混凝土强度影响

将再生粗骨料以15%,25%,35%,45%的比例和再生细骨料以20%的比例按等量取代的方法加入混凝土中,探究了其对再生混凝土强度的影响,再将粉煤灰、硅灰以6∶4,7∶3,8∶2,9∶1的比例,等量取代25%和35%,加入混凝土中,研究其对混凝土和易性及抗压强度的影响,并分析了不同龄期的再生混凝土的抗压强度,筛选出了最优的配合比,为提高工业废料及建筑废物的利用率提供了理论依据。     

Properties of fly ash concrete modified with hydrated lime and silica fume

This paper presents the results of an experimental investigation on the properties of fly ash concrete incorporating either hydrated lime or silica fume to improve the early strength of concrete. Test results indicated that the addition of lime and silica fume improved the early age compressive strength of fly ash concrete. The inclusion of silica fume was also found to increase the 28 days strength significantly. The air permeability of concrete containing lime and silica fume either decreased or remained almost the same when compared to the concrete without these. The addition of lime and silica fume also improved the sorptivity of concrete.Through the use of differential scanning calorimetry and thermogravimetric analysis (DSC/TG), it was demonstrated that the addition of hydrated lime increased the Ca(OH)₂ content; whereas the addition of silica fume decreased the Ca(OH)₂ content in the cement paste. The mercury intrusion porosimetry (MIP) data confirmed the beneficial action of hydrated lime and silica fume, towards decreasing the total pore volume of fly ash cement paste.     

Properties of sustainable concrete containing fly ash,slag and recycled concrete aggregate

The suitability of using more “sustainable” concrete for wind turbine foundations and other applications involving large quantities of concrete was investigated. The approach taken was to make material substitutions so that the environmental, energy and CO₂-impact of concrete could be reduced. This was accomplished by partial replacement of cement with large volumes of fly ash or blast furnace slag and by using recycled concrete aggregate.Five basic concrete mixes were considered. These were: (1) conventional mix with no material substitutions, (2) 50% replacement of cement with fly ash, (3) 50% replacement of cement with blast furnace slag, (4) 70% replacement of cement with blast furnace slag and (5) 25% replacement of cement with fly ash and 25% replacement with blast furnace slag. Recycled concrete aggregate was investigated in conventional and slag-modified concretes. Properties investigated included compressive and tensile strengths, elastic modulus, coefficient of permeability and durability in chloride and sulphate solutions. It was determined that the mixes containing 50% slag gave the best overall performance. Slag was particularly beneficial for concrete with recycled aggregate and could reduce strength losses. Durability tests indicated slight increases in coefficient of permeability and chloride diffusion coefficient when using recycled concrete aggregate. However, values remained acceptable for durable concrete and the chloride diffusion coefficient was improved by incorporation of slag in the mix. Concrete with 50% fly ash had relatively poor performance for the materials and mix proportions used in this study and it is recommended that such mixes be thoroughly tested before use in construction projects.     

Appraisal of long-term effects of fly ash and silica fume on compressive strength of concrete by neural networks

This study focuses on studying the effects of fly ash and silica fume replacement content on the strength of concrete cured for a long-term period of time by neural networks (NNs). Applicability of NNs to evaluate the effects of FA and SF for a long period of time is investigated. The investigations covered concrete mixes at different water cementitious materials ratio, which contained low and high volumes of FA, and with or without the additional small amount of SF. 24 different mixes with 144 different samples were gathered form the literature for this purpose. These samples consist concretes that were cured for 3, 7, 28, 56 and 180 days. A NN model is constructed trained and tested using these data. The data used in the NN model are arranged in a format of eight input parameters that cover the fly ash replacement ratio (FA), silica fume replacement ratio (SF), total cementitious material (TCM), fine aggregate (ssa), coarse aggregate (ca), water content (W), high rate water reducing agent (HRWRA) and age of samples (AS) and an output parameter which is compressive strength of concrete (f_c). A NN program was devised in MATLAB and the NN model was constructed in this program. The results showed that NNs have strong potential as a feasible tool for evaluation of the effect of cementitious material on the compressive strength of concrete. It was found that FA content contributed little at early ages but much at later ages to the strength of concrete. It can also be concluded that the enhancement effect of low content of SF on compressive strength was not significant.     

Optimization of early flexural strength of pavement concrete with silica fume and fly ash by the Taguchi method

In this study, an attempt has been made to optimize the early flexural strength of concrete pavement (CP) by using the Taguchi Method. The experiments were designed using an orthogonal array technique in L₁₆ array with four factors, namely, the water/cementitious ratio of 0.30, 0.35, 0.40 and 0.45, four different types of gradations with maximum aggregate size of 32?mm, fly ash (FA) 0%, 5%, 10%, 15% and silica fume (SF) 0%, 10%, 20% and 30% by weight of cement. The response data were analyzed using an analysis of variance (ANOVA) technique by the Taguchi method. According to the ANOVA table, water/cementitious ratio and SF content play significant roles for early flexural strength of CP. Moreover, the optimum conditions were found to be 0.35 water/cementitious ratio, gradation with minimum content of fine aggregates, 5% FA content and 0% SF content at 7 days curing. Maximum flexural strength of 5.31?MPa was achieved at the optimum conditions.     

硅灰和粉煤灰在200 MPa活性粉末混凝土中的应用机理

活性粉末混凝土(RPC)由于具有超高强度、韧性及耐久性而得到快速推广应用。采用0.14的极低水胶比制备200 MPa的RPC,并测试硅灰和粉煤灰对RPC强度和微结构的影响。研究结果表明:RPC的强度随着硅灰掺量的增加呈现先增大后减小的趋势,随着粉煤灰掺量的增加而减小,适量的硅灰掺量和较小的粉煤灰掺量有助于RPC获得较高的强度。硅灰和粉煤灰均具有较高的填充效应和火山灰活性,其活性二氧化硅可与氢氧化钙水化生成水化硅酸钙,尤其是颗粒极细的硅灰,可大幅改善浆体微结构,提高RPC的强度。     

双掺硅灰、粉煤灰轻骨料混凝土试验研究

基于松散体积法配制同时加入硅灰和粉煤灰两种矿物掺合料的轻骨料混凝土,采用正交试验设计,通过改变净水灰比、粉煤灰掺量、砂率、硅灰掺量四个影响因素,浇筑不同配合比的轻骨料混凝土试块,测定其干表观密度、28 d抗压强度和比强度,分析各影响因素对轻骨料混凝土性能的影响.研究结果表明:硅灰能显著提高轻骨料混凝土抗压强度,且硅灰掺量在3％～6％之间较为合理.并配制出了结构用强度等级为LC30～LC45的双掺硅灰、粉煤灰轻骨料混凝土,为双掺硅灰、粉煤灰轻骨料混凝土的应用提供依据.     

粉煤灰、矿渣及硅灰对水泥胶砂流动性及早期强度的影响

本文在试验的基础上研究了矿物掺合料单掺和复掺时对水泥胶砂流动性及1d早期强度的影响。试验结果表明,与不掺掺合料的基准胶砂相比,矿物掺合料的使用可以提高胶砂的流动度,但同时极大地降低了胶砂的早期强度。与单掺粉燥灰的胶砂相比,多种矿物掺合料复掺可以提高胶砂的1d强度,但会降低胶砂的流动性。     

Compressive strength, chloride diffusivity and pore structure of high performance metakaolin and silica fume concrete

This study is to relate the mechanical and durability properties of high performance metakaolin (MK) and silica fume concretes to their microstructure characteristics. The compressive strength and chloride penetrability of the control and the concretes incorporated with MK or silica fume (SF) at water-to-binder (w/b) ratios of 0.3 and 0.5 are determined. The pore size distribution and porosity of the concretes are also measured. The effect of MK and SF on the interfacial porosity is discussed based on test results. It is found that MK concrete has superior strength development and similar chloride resistance to SF concrete, and the MK concrete at a w/b of 0.3 has a lower porosity and smaller pore sizes than the control (plain) concrete. The resistance of the concretes to chloride ion penetration correlates better with the measured concrete porosity than with the paste porosity. The differences between the measured and calculated concrete porosity is smaller for MK and SF incorporated concrete than for the control concrete, indicating an improvement in the interfacial microstructure with the incorporation of the pozzolanas. This difference is found to be related to the strength and chloride penetrability of concrete to some degree.     

Influence of fly ash and silica fume on the consistency retention and compressive strength of concrete subjected to prolonged agitating

Good workability at construction site is essential for high quality concrete since concretes of bad workability are prone to yield low strength and poor durability properties since placement and consolidation procedures cannot be performed properly. Nevertheless, this is what usually encountered in practice because slump loss is indispensable particularly when long delivery times are the case. This would be more pronounced when mineral additives are incorporated into the concretes. In this study, concretes of C25/30 class with fly ash and silica fume were produced and slumps were measured with time elapsed. At the end of each agitating period, the slumps of the mixtures were restored to the initial slumps using a superplasticizer and specimens were thereafter prepared for strength measurement. The effectiveness of using fly ash and silica fume in concrete in relation with slump loss was sought by determining the amount of superplasticizer used. Regardless of the mixture recipe, it can be concluded that as the total amount of cementitious materials increases in the concrete mix of the same initial slump, the slump loss with the elapsed time decreases.     

粉煤灰和硅粉对混凝土强度影响的试验研究

针对于提高混凝土强度和耐久性的问题,可以在混凝土中加入矿物外加剂以替代部分水泥,最常用的矿物外加剂是粉煤灰和硅粉.通过一系列试验,研究了在其他因素不变的情况下,不同掺量粉煤灰和硅粉对混凝土的工作性、抗压强度、劈拉强度、抗弯拉强度等的影响,并分析探讨其规律,为配制高强高性能混凝土提供参考.研究结果表明:粉煤灰和硅粉都可不同程度的改善混凝土和易性.粉煤灰对混凝土各种强度的增长主要表现在后期,具有很好的"强度潜力";而硅粉由于活性高,其对混凝土强度增长的贡献主要在前期,后期相对较缓慢,但对于需要配制抗折强度高、抗冲击耐磨性好的混凝土,硅粉作为矿物外加剂则是首选.     

硅粉、脱水高岭土及低钙粉煤灰对混凝土耐化学性的影响

本文评价了侵蚀性化学环境对采用不同替换水平值的普通硅酸盐水泥(OPC)、硅粉(SF)、脱水高岭土(MK)及低钙粉煤灰配制而成的水泥浆体的影响。使用硫酸、盐酸、硝酸、乙酸、磷酸及硫酸钠和硫酸镁的混合物可以模拟出自然的逆化学性环境。同时利用抗压强度测量值及耐化学性信息资料提出了现实的普通硅酸盐水泥／矿物外掺料的比重。     

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.     

同水胶比下混凝土中水泥-矿渣-粉煤灰-硅灰的混料效应

为探索同一水胶比下混凝土中水泥-矿渣-粉煤灰-硅灰多元掺合料对强度和渗透性的混料效应,通过混料设计,研究了同一水胶比下混凝土水泥、矿渣、粉煤灰和硅灰混料因子对7、28 d抗压强度和28 d电通量的影响.按多元混料回归设计的方法分析评价了各因素影响的内在规律,探讨了显著因素之间的交互作用.研究表明:建立的同一水胶比下水泥...     

蒸养制度对粉煤灰混凝土强度的影响

以不同龄期的抗压强度为控制指标,研究了蒸养制度对粉煤灰混凝土强度的影响.试验结果表明对粉煤灰混凝土而言,蒸养制度预养时间2h、升温时间2h、恒温温度60℃左右、恒温时间8h以及降温时间1h是比较合理的.     

双掺硅灰、粉煤灰对青藏铁路用高性能混凝土性能的影响

本文采用在混凝土中双掺硅灰和粉煤灰及添加引气剂的方法，向青藏铁路建设用混凝土浇筑施工提供配合比，确保混凝土性能满足施工与使用要求。试验研究表明，对于水胶比为0．41左右的混凝土，该方法能明显改善混凝土的抗硫酸盐腐蚀能力，有效提高混凝土抗冻融循环达300次。根据抗氯离子渗透试验结果推测，这主要是由于混凝土中矿物掺合料与氢氧化钙发生进一步水化，增强了混凝土的密实性，改善了混凝土耐久性。     

粉煤灰高性能混凝土抗剪性能试验研究

本文采用正交试验方法，研究了水胶比，超细粉煤灰（ultra fine fly ash,简称UFA）掺量以及胶凝材料总用量对粉煤灰高性能混凝土抗剪强度的影响，并通过优选的配合比，考虑粉灯灰高性能混凝土与普通混凝土抗剪强度之间的差异，试验结果表明，水胶比对粉煤灰高性能混凝土的28d抗剪强度影响显著；粉煤灰高性能混凝土的抗剪强度7d时较不掺UFA的基准混凝土低，在28d时可赶上甚至超基准混凝土。     

粉煤灰、硅灰对机敏水泥砂浆抗压强度及压敏性影响

粉煤灰、硅灰可以改善机敏水泥砂浆巾纤维分散性.以15%、20%、25%的超细粉煤灰,16%、25%的硅灰掺入到机敏水泥砂浆中,通过对其抗乐强度的研究,以及它在小应力循环作用下压敏性变化规律的研究,指出机敏水泥砂浆抗压强度和压敏性并不取决于单一的粉煤灰或硅灰掺量,而是取决于硅灰和粉煤灰两种超细粉的合理搭配;机敏水泥基材料阻抗能够反应所受外力作用情况,在受力的最初阶段,材料内部结构变化不大,其阻抗几乎保持不变,但随外力作用的加剧,材料内部原有孔隙被压实,阻抗也呈下降趋势.