Enhancing the hydration activity of steel slag-Portland cement composite by BES sodium activator

Abstract

The low hydration activity of steel slag (SS) limits its use in cement-based materials. The aim of this work was to explore the feasibility of N, N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid (BES) sodium as a novel activator in enhancing the hydration of SS-Portland cement (PC) (mass ratio of 3:7) composite. The compressive strength and hydration process of SS-PC composite and the working mechanism of BES sodium were systematically investigated. The results showed that at low dose (0.1 %), BES sodium significantly enhanced the 3–28 d compressive strengths by 2.1–4.6 MPa. This enhancement stemmed from the simultaneous acceleration of aluminates (C₃A and C₁₂A₇), ferrites (C₄AF and C₂F), and silicates (C₃S and β-C₂S) hydration, and which facilitated the formation of ettringite (AFt), hemicarboaluminate (Hc), and C–S–H gels. At high dose (0.5 %), BES sodium did not affect the 3 d compressive strength and significantly increased the 7 and 28 d compressive strengths by 4.7 and 4.2 MPa. This was because the excessive acceleration of aluminates inhibited early silicates hydration. This inhibition gradually disappeared from 7 to 28 d. The activation mechanism involved BES sodium accelerated the dissolution and hydration of minerals via complexing to Ca²⁺, Al³⁺ and Fe³⁺, and its stronger complexation for Al³⁺ and Fe³⁺ explained the preferential acceleration for aluminates/ferrites. Crucially, using 0.1 % BES sodium can effectively reduce 0.221–0.234 tons of CO₂/ton SS-PC under the premise of 28 d compressive strength more than 42.5 MPa. This highlighted the potential of BES sodium as an effective activator in improving SS utilization by enhancing SS hydration activity.