INFLUENCE OF MECHANICAL ACTIVATION OF PORTLAND CEMENT WITH GROUND QUARTZ SAND ADDITIVE ON THE COMPRESSIVE STRENGTH OF CONCRETE

Abstract

In contemporary practice of manufacturing concrete and reinforced concrete products and structures, cements containing mineral additives, in particular ground quartz sand, have gained wide application. Such cements are produced either by simultaneous grinding of Portland cement clinker, gypsum dihydrate, and quartz sand, or by thorough mixing of Portland cement with ground quartz sand. A promising approach to improving the physico-mechanical properties of concrete based on such blended cements is the application of intensive mechanical activation in a high-speed turbulent mixer.

This study presents experimental results concerning the influence of mechanical activation of blended Portland cement in the presence of the superplasticizer SP-5 on the compressive strength of concrete at the ages of 3, 7, and 28 days. The blended Portland cement was obtained by combining Portland cement CEM I 52.5 (PC-I 500) with ground quartz sand in proportions ranging from 30 % to 60 % by mass of the blended binder.

The experimental program was designed using a D-optimal mathematical approach, with variation of the following factors:

• X₁ – content of blended cement (370 ± 50 kg/m³);
• X₂ – proportion of ground quartz sand (45 ± 15 % of the blended binder mass);
• X₃ – dosage of the superplasticizer SP-5 (0,5 ± 0,5 % of the blended binder mass).

The developed mathematical models demonstrate that the most significant factors influencing the compressive strength of concrete at different curing ages are the proportion of ground quartz sand (X₂) and the dosage of superplasticizer (X₃). An increase in the proportion of ground quartz sand in the binder from 30 % to 60 % results in a reduction in compressive strength, whereas increasing the dosage of SP-5 from  0 % to 1 % leads to a comparable percentage increase in compressive strength. The combined application of mechanical activation of the blended binder and the superplasticizer SP-5 provides an improvement in compressive strength, compared to the control specimens, by an average of 25–30 %.