THE ROLE OF SODIUM NITRATE IN COUNTERACTING THE CARBONATION OF PLASTICIZED ALKALI-ACTIVATED SLAG CEMENT CONCRETE UNDER CYCLIC INFLUENCE OF SEA WATER

Abstract

Carbonation of alkali-activated slag cement concrete in marine structures under cyclic influence of sea water in actual operating conditions causes by increased risk connected with deterioration due to increased content of gel phase. Aggressive environment in case of drying under the influence of atmospheric CO2 and wetting in sea water can be classified as combination of exposure classes XC4 and XS3. These risks increase in case of fresh concretes with high consistency due to the modern requirements. The aim of this research was to determine the effectiveness of resistance to carbonation of plasticized alkali-activated slag cement concrete, exploited under cyclic influence of sea water, due to application of additive NaNO3. The advanced crystallization of hydrates in alkali-activated slag cement based both on soda ash and sodium metasilicate was shown. The state of plasticized alkali-activated slag cement concrete, which exposes to carbonation under cyclic influence of sea water in actual operating conditions, was estimated according proposed author’s methodology. The performances properties were determined after 90 cycles of wetting in sea water and drying (t= 105 ± 3 °С) under the influence of atmospheric concentration of CO2 (K≈0.04 %). The deterioration of concrete was determined by falling of flexural strength. The major falling of flexural strength in case of sodium metasilicate (by 11.8 %) compared to soda ash (by 10.3 %), used as alkaline components, is due to higher volume of gel-like phases. The effectiveness of additive NaNO3 in plasticized alkali-activated slag cement concrete after 90 cycles of drying-wetting in sea water was confirmed by positive effect on one’s properties. Advanced crystallization of gel-like phases caused the higher effectiveness of resistance to aggressive environment in the presence of sodium metasilicate compared to soda ash. The change of anion in alkaline component from carbonate to silicate ensured the lower open capillary porosity from 26.2 down to 11.9 % and the higher conditionally closed porosity from 22.9 up to 34.8 % in alkali-activated slag cement concrete while application of mentioned salt. Specified perfection of pore structure, caused by nature of alkali component, was accompanied by the higher density from 2.1 up to 2.7 %, the major compressive strength from 11.5 up to 15.0 % as well as flexural strength from 7.9 up to 11.2 % and the lower rate of carbonation from 25.0 down to 50.0 %.