Effects of NaOH solution concentration and aging on fracture properties and ductility of ambient-cured heavyweight geopolymer concrete

Abstract

In this paper, effects of NaOH solution concentration (i.e. 2, 4, and 6 M) and aging (i.e. 3, 7, and 28 days) on fracture properties and ductility behaviour of ambient-cured heavyweight geopolymer concrete (ACHWGC) have been investigated. Fracture parameters of the ACHWGC including total fracture energy (GF), initial fracture energy (Gf), fracture toughness (KIC), characteristic length (Lch), effective size of the process zone (Cf), critical effective crack-tip-opening displacement (δc) and the brittleness number (β) were determined using work of fracture method (WFM) and size effect method (SIZEM) and the results obtained were analysed. The results indicate that: (a) maximum fracture energy and the highest brittleness are achieved for samples with 4 M NaOH concentration. (b) as the age increases, fracture energy and brittleness of the samples increase. (c) the mixes gain approximately 82.47% and 86.26% of their 28-day initial and total fracture energies in the first 3 days, respectively. (d) increase in the rate of fracture energy, and decrease in the rate of characteristic length with respect to the mix age for 4 M NaOH concentration are more than those for the 6 M one. (e) as both the total fracture energy (GF) and the initial fracture energy (Gf) increase by the age, the GF/Gf ratio decreases. (f) at the age of 28 days, the GF/Gf ratios for the specimens with 4 M and 6 M NaOH concentrations are equal to 3.16 and 3.32, respectively and (g) as the compressive strength increases, the fracture energy, the fracture toughness, and the brittleness of the ACHWGC are enhanced.