Effect of partial replacement of geopolymer binder materials on the fresh and mechanical properties: A review

The growth of demand for concrete raises concerns about the consumption of natural resources and ordinary Portland cement. Geopolymer composites show promise as a sustainable alternative for conventional cement concrete. Considering the wide range of potential geopolymer composites applications (including suitability for transportation infrastructure, underwater applications, repair and rehabilitation of structures as well as recent developments in 3D printing), the desired fresh and mechanical properties of the geopolymer composite may vary between applications: for example, rapid setting can be a merit for certain applications and a demerit for others. Therefore, the desired fresh and mechanical properties (e.g., workability, setting time, compressive strength, etc.) can be controlled for a given geopolymer source material through its partial substitution by natural or by-product materials. Recognizing the critical role of various replacement materials in enhancing the potential applications of geopolymer composites, the present review was undertaken to quantify and understand the effect of partial replacement by fly ash, metakaolin, kaolin, red mud, slag, ordinary Portland cement, and silica fume on the setting time, workability, compressive strength and flexural strength of various source materials addressed in the literature. The review also provides insights into research gaps in the field to promote future research.     

Activation of Pozzolanic Reaction of Hydrated Portland Cement Fly Ash Pastes in Sulfate Solution

The activation of the pozzolanic reaction of fly ash in portland cement paste immersed in sulfate solution has been studied. Mixtures of two Spanish fly ashes (ASTM class F) with 0%, 15%, and 35% replacement of portland cement by fly ash were immersed in Na₂SO₄ solution, of 2880 ppm SO₄²⁻ concentration, for a period of 90 days. The resistance of the different mixtures to the sulfate attack was evaluated using the Koch-Steinegger test. The results showed that all of the mixtures were sulfate resistant, despite the high Al₂O₃ content of the fly ash. The diffusion of SO₄²⁻ and Na⁺ ions through the pore solution activated the pozzolanic reactivity of the fly ashes, causing microstructural changes, which were characterized by X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM). As a result, the flexural strength of the mixtures increased, principally for the fly ash of a lower particle size and 35% of addition.     

一种天然活性混合材料的研究开发

研究了多孔硅质岩矿粉掺入到普通硅酸盐水泥中对水泥性能的影响．认为多孔硅质岩矿粉是一种良好的天然活性混合材料，可用于制作掺混合材料的硅酸盐水泥或复合硅酸盐水泥．     

掺粉煤灰对不同水泥品种钢渣混凝土基本力学性能试验研究

通过粉煤灰替代部分普通硅酸盐水泥和高抗硫水泥的试验,结果得出两种水泥配制钢渣混凝土抗压、抗折强度均随着粉煤灰掺量的增加呈递减趋势;但是当粉煤灰掺量一定时,两种水泥品种配制钢渣混凝土都表现出抗折、抗压强度随着龄期的增长而提高。在粉煤灰掺量相同情况下,两种水泥品种钢渣混凝土相同龄期的抗压强度均表现普通硅酸盐水泥钢渣混凝土高于高抗硫水泥钢渣混凝土;其抗折强度则大多表现出高抗硫水泥钢渣混凝土比普通硅酸盐水泥钢渣混凝土的高。     

纳米C—S—H/PCE对硅酸盐-硫铝酸盐复合水泥凝结硬化的影响

研究了纳米C-S—H/PCE对硅酸盐-硫铝酸盐复合水泥凝结时间、早期水化历程及抗压强度的影响,采用XRD、TG、pH计和SEM等分析测试手段对早龄期水化产物和液相碱度等进行表征,探讨了纳米C-S—H/PCE对硅酸盐-硫铝酸盐复合水泥的增强机理.结果表明:掺加纳米C—S—H/PCE能有效缩短硅酸盐-硫铝酸盐复合水泥浆体初...     

低温条件施工对水泥混凝土路面质量的影响

水泥混凝土路面是典型的板状结构,浇筑时混凝土的温度、基层温度、模板温度、环境温度、相对湿度以及风速等对混凝土的浇筑、压实、饰面以及长期路用性能影响较大.低温条件对早期混凝土质量如工作性、凝结时间和早期强度以及体积稳定性和耐久性的影响不可忽视.在总结低温条件对混凝土质量影响的基础上,认为控制混凝土的浇筑温度和浇筑后数日的养护温度对路面的长期性能至关重要.对目前通常采用的控制混凝土浇筑时温度的措施如改善配合比、提高混凝土组分温度、掺加特种外加剂和采取合理的养护措施等作了详细介绍.     

硅酸盐水泥-矿渣复合浆体的水化反应进程研究

为考察矿渣对水泥水化进程的影响,系统研究了在不同的养护龄期、水胶比、矿渣掺量条件下,水泥-矿渣复合浆体的矿渣反应程度、非蒸发水含量、Ca(OH)2含量、孔隙率和力学性能.根据实验结果,研究了复合浆体中矿渣反应程度和非蒸发水含量的变化规律,探讨了矿渣的掺入对Ca(OH)2含量的影响,提出了水化反应进程中水泥与矿渣对Ca(OH)2的供求模式,分析了矿渣与水泥的叠加与互补效应,确定了矿渣的最佳掺量范围和最大掺量范围.上述结果可为矿渣在水泥基材料中合理有效地利用提供一定的科学依据.     

硅酸盐熟料-煤矸石/粉煤灰混合水泥水化模型研究

对两种不同3CaO·SiO_2(C_3S)含量的硅酸盐水泥和分别掺有30%(质量分数,下同)煤矸石和30%粉煤灰的混合水泥中水化产物含量变化和形态进行了研究,建立了水化产物量变模型和水化产物形态模型,分析了模型的主要特征和意义。相同龄期,高C_3S硅酸盐水泥比低C_3S硅酸盐水泥生成更多的水化硅酸钙(calcium silicate hydrate,CSH)凝胶和氢氧化钙。含混合材的水泥水化时,CSH凝胶在水化早期和后期有两个增长幅度较大的阶段,并且1年后形成的CSH凝胶量与纯硅酸盐水泥的相当。水泥水化产物与混合材的二次水化反应较慢,研究掺有混合材水泥更长龄期的水化产物含量及结构变化,将有助于理解混合材对水泥性能的作用机理。     

纳米二氧化硅对硅酸盐水泥水化硬化的影响

利用微量热分析、X射线衍射、差热分析、扫描电镜和氮气吸附等手段研究了纳米SiO2对硅酸盐水泥水化硬化的影响.结果表明:纳米SiO2掺量为5%(质量分数)时,其高火山灰反应能大量吸收Ca(OH)2,进而促进水泥水化,提高水化开始时的放热速率,并改善水泥浆体的微观结构,使得水泥石更加均一密实.同时,纳米SiO2的掺入使得标准稠度需水量急剧上升,凝结时间缩短,促进水泥石的中后期强度增长.     

硅酸盐水泥-粉煤灰-脱硫石膏复合材料的性能研究

在脱硫石膏中掺入不同质量分数的硅酸盐水泥和粉煤灰,组成硅酸盐水泥-粉煤灰-脱硫石膏复合材料,研究了其力学性能和耐水性能.结果表明:当硅酸盐水泥和粉煤灰的掺量分别为16％和8％的时,其7d的抗折强度达5.85 MPa、抗压强度达21.33 MPa,吸水率下降18.19％.在硅酸盐水泥、粉煤灰和脱硫石膏的共同作用下,硅酸盐水泥和粉煤灰水化生成的主要产物水化硅酸钙、钙矾石填充于脱硫石膏晶体之间和硬化体的空隙当中,有效增强了脱硫石膏的强度,降低了吸水率.