Study on the characteristics of alkali-activated fly ash-slag improved by cenosphere: Hydration and drying shrinkage

Cenosphere is coal-based solid waste material, which has similar chemical compositions to fly ash. In this paper, the effect of the cenosphere on hydration kinetics and drying shrinkage characteristics of AAFS pastes were explored, and the action mechanism of the cenosphere was deeply revealed. The results showed that the hy-dration induction period was prolonged, the hydration exothermic rate was reduced or the peak value was delayed during the acceleration period, and the 72 h hydration degree of the sample was increased when mixed with the cenosphere. The incorporation of more than 20% cenosphere significantly reduced the drying shrinkage of AAFS pastes. Comparing the results of compressive strength, drying shrinkage, and pore structure, the most suitable content of the cenosphere is 20%. To significantly improve the drying shrinkage of alkali-activated materials, the content can also be increased. The action mechanisms of the cenosphere are shown as the filling effect, pozzolanic activity, and surface effect. The addition of cenosphere reduces the amount of C-S-H, C-A-S-H and N-A-S-H gel phases, but increases the formation of silicates (calcium hydrosilitates and calcium hydroaluminates).

Automated summary

This paper explores the effect of cenosphere, a coal-based solid waste material with similar chemical compositions to fly ash, on the hydration kinetics and drying shrinkage characteristics of AAFS pastes, and reveals its action mechanism. The results show that the presence of cenosphere prolongs the hydration induction period, reduces the hydration exothermic rate or delays its peak value during the acceleration period, and increases the 72-hour hydration degree of the sample. Incorporating more than 20% cenosphere significantly reduces the drying shrinkage of AAFS pastes. The most suitable content of cenosphere is found to be 20% based on the comparison of compressive strength, drying shrinkage, and pore structure results. The action mechanisms of cenosphere include filling effect, pozzolanic activity, and surface effect. The addition of cenosphere decreases the amount of C-S-H, C-A-S-H, and N-A-S-H gel phases, but increases the formation of silicates (calcium hydrosilicates and calcium hydroaluminates).