Regulating the flowability of sodium carbonate-activated low-carbon cementitious binder using 1-hydroxyethylidene bis-phosphonic acid tetrasodium (HEDP-4Na) and phosphorus-free polyepoxysuccinic acid (PESA(Na))

As a low-carbon inorganic binder, sodium carbonate (Na₂CO₃)-calcium carbide slag (CCS)-activated granulated blast furnace slag (GGBS) paste exhibits poor time-dependent flowability before setting. This paper used two organic scale inhibitors, 1-hydroxyethylidene bisphosphonic acid tetrasodium (HEDP-4Na-H4N) and phosphorus-free polyepoxysuccinic acid (PESA(Na), PN), to enhance its flowability over 80 min. New findings were discussed under different mass ratios of PN and H4N, specifically 1:0, 2:1, 1:1, 1:2, and 0:1. The results showed that dosages of 0.15 % PN-H4N (1:1) effectively improved the time-dependent flow diameters and reduced the yield stress of the binder paste within 80 min. The co-additions of PN and H4N improved the Zeta potentials of the particles and sustained high CO₃^2- concentrations while low OH^- concentrations in the pore solution. The formation of calcite was suppressed, and the precipitation and crystal size of gaylussite were limited. Increasing the addition dosage and adopting the delayed addition method of PN and H4N both helped enhance the effect of PN and H4N. The high dispersibility of GGBS, CCS, and pre-formed calcite (using the time-delayed addition method), as well as the lasting inhibition effect on gaylussite formation and growth, are two key factors in maintaining the high flowability of the paste. The co-addition of PN and H4N did not compromise the compressive strength, with values exceeding 30 MPa and 40 MPa achieved at 3 d and 28 d, respectively.