Study on relationship of microstructure, phases percolation and macro-performance of cement-based materials - Part III: Analysis of admixture effect of mineral admixtures

Due to the distinction of physical and chemical properties, different mineral admixtures brings on many changes in cement paste microstructure, which made different mineral admixtures representing different admixture effect. Based on porosity-strength model constructed in anterior paper, the errors between the porosity-strength data regression curve of pure cement paste and porosity-strength data regression curve of paste with mineral admixtures were discussed. The paper indicated the errors reflected the influence of mineral admixture on properties of cement-based materials. Positive error shows that mineral admixture has positive effect on cement-based materials strength, and negative error shows that mineral admixture has negative effect. The paper analyzed in detail positive and negative action of admixture effect of steel-making slag, slag and fly ash at different hydration stage in 180 days. The results indicated that all mineral admixtures can increase paste strength sigma(0) to various degrees at the critical point of pore percolation in three dimensions, which embody micro-aggregate effect of mineral admixture. At the same time, different mineral admixture displayed different negative effect in different length hydration early age due to the distinction in the power of the second hydration, and they displayed different degree positive effect at hydration later age.