粉煤灰和矿渣粒度分布对混凝土微观结构和抗氯离子渗透性的影响

针对胶凝材料比表面积和粒度分布等物理性质存在的差异,将P·Ⅱ水泥,Ⅰ级、Ⅱ级粉煤灰和S95级、S105级矿渣进行互掺,固定水泥用量,设计了4种粉煤灰和矿渣的组合方式,通过流动度试验分析了组合方式对净浆流动性的影响,并将粒度分布曲线与Fuller分布曲线进行了比较。在净浆配合比的基础上,对不同组合方式的混凝土进行了工作性、力学性能及自由氯离子浓度测试,探讨了粉煤灰和矿渣的粒度分布对混凝土强度和抗氯离子渗透性的影响,并对硬化浆体水化产物的微观形貌和化学组成进行了分析,揭示了影响机理。研究结果表明,矿物掺合料的粒度分布是决定颗粒级配优劣的重要因素。Ⅰ级粉煤灰具有更强的滚珠效应,在提高流动性方面起了关键性作用。粉煤灰和矿渣的水化及火山灰反应程度影响着混凝土的力学性能和耐久性能,由于Ⅰ级粉煤灰有更大的比表面积,火山灰活性也较高,因此Ⅰ级粉煤灰和S95/S105级矿渣组合的净浆流动度,混凝土的工作性、抗压强度和抗氯离子渗透性均明显高于Ⅱ级粉煤灰和S95/S105级矿渣组合。其中Ⅰ级粉煤灰和S95级矿渣组合的胶凝材料粒度分布曲线与Fuller曲线最为接近,粒度分布最优,水化浆体中Ca(OH)₂含量最低,火山灰反应最为充分,对应的混凝土微观结构致密,抗氯离子渗透性最好。

Effects of Fly ash and Slag Particle Size Distributions on Microstructure and Chloride Ion Penetration Resistance of Concrete

This study is aimed at the differences of physical properties such as specific surface area and particle size distribution of cementitious materials. The P·Ⅱ cement, grade Ⅰ and grade Ⅱ fly ash, grade S95 and grade S105 slag were intermixed. Four combinations of fly ash and slag were designed on the premise of fixed cement dosage. The effect of the combination method on the fluidity of the pure slurry was analyzed through the fluidity experiment, and the particle size curve was compared with the Fuller distribution curve. Tests on workability, mechanical properties and free chloride ion concentration of concrete with different combinations were carried out on the basis of the pure slurry mix proportion. The microscopic morphology and chemical composition of hydration product of hardened slurry were analyzed. The effects of particle size distribution of fly ash and slag on the strength and chloride ion penetration resistance of concrete were discussed, and the influence mechanism was revealed. The research results show that the particle size distribution of mineral admixtures is an important factor in determining the quality of particle gradation. The ball effect of grade Ⅰ fly ash is stronger, which makes it play a key role in improving fluidity. The mechanical properties and durability of concrete are affected by the hydration of fly ash and slag, and the degree of pozzolanic reaction. The grade Ⅰ fly ash has larger specific surface area and higher pozzolanic activity. Therefore, the fluidity, workability, compressive strength and chloride ion penetration resistance of grade Ⅰ fly ash and S95/S105 slag combination group are significantly higher than the combination of grade Ⅱ fly ash and S95/S105 slag combination group. Among all the combinations in this experiment, the particle size distribution curve of cementitious material of the combination of grade Ⅰ fly ash and grade S95 slag is the closest to the Fuller curve. The particle size distribution of this combination is the best, the content of Ca(OH)₂ in the hydrated slurry is the lowest, and the pozzolanic reaction is the most sufficient. The corresponding concrete has a dense internal structure, and the chloride ion penetration resistance of concrete is good.