MECHANICAL ACTIVATION OF PORTLAND CEMENT WITH THE ADDITION OF GROUND LIMESTONE AND ITS EFFECT ON THE EXOTHERMIC AND STRENGTH OF CEMENT STONE

Abstract

The article presents the results of experimental studies aimed at establishing the regularities of the influence of mechanochemical activation of Portland cement with the addition of ground limestone (up to 40 %) on the thermo-mechanical properties of cement stone during hardening and after setting.

It has been determined that an effective approach to improving the properties of blended binders (Portland cement + ground limestone) is their activation in the presence of a superplasticizing admixture of the “Relaxol-Super PC” type in an amount of up to 1 % by weight of the binder. The use of a high-speed activator (n = 1800 rpm) ensures the intensification of cement hydration processes, stabilization of the required workability of the cement-limestone mixture at a lower water demand (compared to non-activated compositions), and enhances the exothermic heat release during hardening.

The experimental data made it possible to quantitatively assess the influence of the mechanochemical activation duration and the amount of superplasticizer on the water content of the cement-limestone system. A dominant effect of the superplasticizer and activation for 180 seconds on the reduction of the water-to-solid ratio was identified, resulting in improved physical and mechanical properties of the composite.

It was established that the introduction of ground limestone into the cement–water system leads to an increase in the water-to-solid ratio while maintaining the required workability. In particular, replacing 20 % of Portland cement with ground limestone increases the W/S ratio from 0,38 to 0,41 (approximately by 8 %), while a 40% limestone replacement raises this ratio to 0,42 (by about        11 %).

Mechanochemical activation of the cement–limestone composition was found to intensify heat release processes, increasing both the rate of temperature rise and the maximum temperature of the exothermic reaction. For non-activated Portland cement compositions, the induction period of heat release lasts about 3–3,5 hours from the moment of mixing, whereas for mechanochemically activated cement it does not exceed 2 hours.

It was determined that mechanochemical activation of cement–limestone systems increases the compressive strength of cement stone at the age of 3 days by 30…35 %, and in the presence of a superplasticizer — by up to 70 %. The obtained results confirm the efficiency of the combined effect of mechanical activation and chemical modification in forming a cement stone structure with enhanced performance characteristics.