Hydration and structure formation of chloride-activated cement paste

The result of the research is the formulation of chloride-activated high-strength cement paste with accelerated hardening, increased strength, and without heat treatment. The cement paste was activated by introducing a chloride-containing additive into the cement-water system. The additive was synthesized by keeping the cement in a 3 % hydrochloric acid solution, i.e. under conditions of acid corrosion of the binder. The additive is the solid part of the cement-HCl suspension, aged for 24 hours at a ratio of solid and liquid phases of 1:10. The optimized amount of additive is 5 % by weight of dry cement. The effect of the additive on the hardening kinetics, structure, and strength of the activated cement paste was studied. It was established that acid corrosion products of cement have structure-forming activity. A significant increase of the compressive strength of the activated cement paste relative to the control sample was found over the entire hardening interval (1–3–7–28 days). At the daily age of normal hardening, the strength of activated cement paste increased by 165 %. At 28 days of age, the strength increased by 42 %. The X-ray phase and infrared spectral analysis results suggest the following. The acceleration of setting and the increase in the strength of the cement composite is realized due to the intensification of hydration processes and the binding of portlandite, the early formation of structure-forming phases as ettringite and Kuzel salt Са₄Al₂(ОН)₁₂Cl(SO₄)_0.5∙6H₂O (analog of Friedel’s salt), as well as weakly crystallized calcium hydrosilicates with a tobermorite-like structure.