Long-term durability of iron-rich geopolymer concrete in sulphate, acidic and peat environments

Abstract

This study assesses the behaviour of iron-rich type F fly ash geopolymer concretes (GC) exposed to simulated sulphate, acidic, and peat environments, typical of those encountered in tropical peatlands. GC and Portland cement (PC) concrete of comparable strengths were exposed to a range of simulated solutions for 18 months, including 5 % magnesium sulphate (MgSO 4 ), 5 % sodium sulphate (Na 2 SO 4 ), 1 % and 3 % sulfuric acid (H 2 SO 4 ) and peat. The GC generally outperformed PC in all conditions. The GC showed a significant increase in strength in the first year, along with enhanced durability properties. Microstructural analysis indicated a decrease in total porosity and pore size. This was attributed to continuing geopolymerization leading to the foration of additional N-A-S-H gel, which filled the pores and solidified the concrete matrix. However, compressive strength decreased at 18 months due to crack propagation caused by drying shrinkage. In Na 2 SO 4 , GC attained an 8.9 % and 6.3 % increase in compressive strength at 12 and 18 months, respectively, again attributed to ongoing geopolymerization. GC exposed to MgSO 4 exhibited a significant decrease in compressive strength of approximately 11 % at 12 months and 19.8 % at 18 months, attributed to the formation of lower-strength M-A-S-H from reaction between MgSO 4 and N-A-S-H gel. After 12 months GC exposed to 1 % and 3 % H 2 SO 4 demonstrated a decrease in compressive strength of approximately 1.2 % and 4.5 %, respectively, together with 2 % and 3 % mass loss. Chemical and microstructural data confirmed this strength reduction due to the vulnerability of N-A-S-H to when exposed to H 2 SO 4 . GC exposed to peat solution exhibited a 1.25 % increase in compressive strength at 12-month, but a decrease of 11.3 % at 18-month. Microstructural analysis observed a reduction in Na + within GC matrix, and the presence of gypsum. The reduction in pore sizes and total porosity suggested generation of zeolite crystalline material was contributing to the pore filling. • Geopolymer concrete is suitable for construction in a native peat environment. • Geopolymer concrete outperforms portland cement in long-term peat exposure. • Gopolymer concrete withstands long-term exposure to sulfuric acid and sulphate. • Geopolymer has superior durability in sodium sulphate to magnesium sulphate. • The long term performance of the geopolymer was influenced by microcracking.

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