Effects of C-S-Hs-PCE and Na2SO4 on hydration behavior of cement-lithium slag binder

Abstract

Application of C-S-Hs-PCE and sodium sulfate into Portland cement containing 20 wt% lithium slag (LS) powder was investigated, in order to strengthen early mechanical properties. Synergistic effects of C-S-Hs-PCE and sodium sulfate on hydration properties and microstructure of cement-LS system were analyzed. Results showed that C-S-Hs-PCE was advantageous for modifying fluidity of fresh LS-cement binder, while increased dosage of sodium sulfate decreased dispersibility of fresh paste. C-S-Hs-PCE and sodium sulfate exhibited a synergistic effect on strength enhancement, hydration acceleration as well as setting behavior of LS-cement binder. Sodium sulfate increased alkalinity of interstitial solution and promoted dissolution of LS. Dissolved Al and Si from LS powder reacted with dissolved sulfate ions from sodium sulfate to produce extra hydrates, and C-S-Hs-PCE accelerated pozzolanic reaction as well as hydration reaction via nucleation effect collaborated with dispersing effect. C-S-Hs-PCE accelerated reaction process of sodium sulfate via nucleation effect, and activation effect of sodium sulfate provided more newly-formed hydrates to act as nucleation seeds or crystal skeleton for induce hydration of new phases. The accelerated hydration generated more AFt and C-S-H gel in the matrix. Newly formed hydrates promoted exceedingly the appearance of network, leading to a refinement of pore structure as well as enhancement in mechanical strength. Application of LS into cement as a greener binder could be obtained by synergistic adoption of C-S-Hs-PCE and sodium sulfate.