MECHANICAL ACTIVATION OF PORTLAND CEMENT WITH GROUND LIMESTONE ADDITION AND ITS INFLUENCE ON EXOTHERM AND STRENGTH OF CEMENT STONE

The results of experiments discussed in the article are related to the influence of mechanochemical activation of Portland cement with the addition of ground limestone (up to 40 %) on the thermo-mechanical characteristics of hardening cement stone. The activation of a mixed binder (portland cement + mechanical activation) using the superplasticizing additive Relaxol-Super PC in the amount of up to 1 % of its mass is relevant for this study. The use of a high-speed activator (n=1500 rpm) ensures the acceleration of cement hydration processes, the maintenance of the necessary level of mobility of cement-limestonecompositionswith a lower consumption of mixing water, (compared to a mechano-activated composition of intensification of exothermic heating. The given experimental data made it possible to evaluate the influence of the activation period and superplasticizer consumption on the water content of the cement mixing composition. The priority role in reducing the water-hardening ratio of the mechano-activation of the binder within 180 seconds was revealed, and as well as the content of the superplasticizer. The analysis of experimental data shows that the introduction of ground limestone into the composition of the cement-water composition leads to an increase in the water-solid ratio (under the condition of maintaining the given mobility of the composition). Thus, replacing 20 % of Portland cement with ground limestone causes an increase in W/T from 0.38 to 0.41, that is, by almost 8 %. An increase in the content of ground limestone to 40 % causes an increase in W/T to 0.42 (almost 11 %). Activation of the cement-water composition with the addition of ground limestone helps to increase the intensity of its heating, as well as to increase its temperature. Experimental data indicate the presence of an induction period of exothermic heating of the cement-water composition both on Portland cement that was not subject to mechanical activation (this period was approximately 3...3.5 hours from the moment the binder was mixed with water) and on Portland cement that was not subject to mechanical activation - the induction period in this case did not exceed 2 hours. The mechanochemical activation of the cement-limestone composition helps to increase the strength of the cement stone at the age of 3 days by 25...30 %, and taking into account the superplasticizer - by 35...45 %.