ENHANCEMENT OF STEEL REINFORCEMENT PROPECTION IN ALKALI-ACTIVATED SLAG CEMENT CONCRETE MIXED WITH SEAWATER

Abstract

Modern trends in construction industry in terms of efficient use of raw materials and energy, implying a responsible attitude to environment, predetermine application of alkali-activated slag cement concrete (further, AASC concrete). It’s well-known the increased risk of steel reinforcement corrosion is caused by mixing concretes with seawater, presented by chlorides and sulfates. One of the benefits of AASC concrete is possibility to be mixed with seawater. The aim of this research was the enhancement of AASC concrete’s protective properties, mixed with seawater, to steel reinforcement due to modification by complex of additives (further, CA), including portland cement, calcium aluminate cement and clinoptilolite. Kuzel’s salt (3CaO∙Al2O3∙0,5CaCl2∙0,5SO4∙10H2O) was fixed in hydration products of AASC, modified by proposed CA, after 180 d of hydration. Formation of mentioned salt is due to chemical binding of Cl- and SO42- ions by calcium hydroaluminate 3CaO∙Al2O3∙10H2O, formed by co-acting of Portland cement and calcium aluminate cement during hydration process. Clinoptilolite enhances occlusion function of hydrates presented by alkaline hydro-alumina-silicates. State of steel reinforcement, evaluated according to DSTU B V.2.6-181:2011, confirms the effectiveness of CA in plasticized AASC concrete, mixed with seawater. Mass loss of steel rebars, which were reached from AASC concrete, modified by high-plasticizing additive of sodium lignosulphonate, was in compliance with mandatory requirements (no more than 10 g/m2). This fact is evidence of corrosion absence. Obtained results confirm mitigation of steel reinforcement corrosion risk in plasticized AASC concrete, modified by CA and mixed with seawater. This phenomenon is caused by binding of Cl- and SO42- ions due to chemical adsorption by gel-like phases, chemical binding in Kuzel`s salt as well as their occluding by zeolite-containing admixture and alkaline hydro-alumina-silicates. In addition, increased strength of AASC concrete, while mixing with seawater, is caused by both water-reducing effect of salts of strong acids and densification of artificial stone microstructure under their influence.