Fly ash-based artificial aggregates synthesized through alkali-activated cold-bonded pelletization technology

Abstract

The shortage of natural aggregates caused by massive infrastructure construction has promoted the development of alternative aggregates. In this study, artificial aggregates based on alkali-activated technology were designed and manufactured, where fly ash (FA) and a blended sodium silicate/hydroxide solution were used as the precursor and activator, respectively. The mechanical properties, densities, water absorption, reaction products, internal pore distribution, and carbonation resistance of the produced artificial aggregates with different alkali content and activator modulus were investigated to ensure their usability in concrete. The experimental results showed that the artificial aggregate with an alkali content of 5.5% and an activator modulus of 1.5 was found to be the optimal formulation in this study, considering the varied properties and the dosage of activator. The strength of long-term cured aggregates increased slightly when the modulus was increased from 1.2 to 1.5, but decreased significantly when the modulus was further increased to 2.0. The qualitative and quantitative analysis results of X-ray computed tomography images further revealed that the bulk pores inside the aggregate were mainly concentrated in the center, while the capillary pores were primarily distributed near the surface. This study provided the understanding of the internal pore distribution of artificial aggregates synthesized by disc granulation for possible application in concrete.