The degradation mechanisms of alkali-activated fly ash/slag blend cements exposed to sulphuric acid

Abstract

In the present work alkali-activated fly ash/slag cements (AACs) are synthesized and exposed to sulphuric acid (pH = 1.0) to investigate their anti-corrosion properties. The mineralogical compositions, pore structure and microstructure of different layers of the corroded samples are examined, along with the compressive strength change. The results show that with fly ash/slag ratio varying from 100/0 to 0/100, the compressive strengths of all of the samples decrease during acid attack; the most anti-corrosion mixture is found in the pure fly ash binder, which retains 83.5% strength after 28 days of exposure. Gypsum is only observed in the surface layer (0–5 mm) of samples. In terms of pore structure, the acid attack results in higher porosities in the corroded layers than their corresponding uncorroded layers. The samples with slag addition show a notably pore structure change. The sulphuric acid attack on the AACs binders has certainly led to the increase of porosity, regardless of the compact level of AACs (slag addition leads to compacter microstructure). The Al/Si atomic ratios in the corroded layer decrease after acid attack, and the reduction ratios become smaller as slag content increases, suggesting a dense matrix is advantage to impede the loss of aluminum from gel structures.