CONSTRUCTION MORTAR BASED ON MECHANOACTIVATED PORTLAND CEMENT WITH THE ADDITION OF GROUND LIMESTONE

Abstract

In the practice of production of building solutions, cements with the use of mineral additives and, in particular, ground limestone are widely used. Technologically, such mixed cements can be obtained both by compatible grinding of Portland cement clinker, dihydrate gypsum and limestone additive, and by thorough mixing of Portland cement with ground limestone. A promising method for improving the mechanical characteristics of building solutions is intensive mechanic-chemical activation of mixed cements in high-speed turbulent mixers. The issues considered in the article related to determining the influence of recipe and technological factors on the strength of building mortar at the age of 3, 7 and 28 days were investigated. The compressive strength of samples made from a mixture solution on both a mechanically activated binder and a binder of similar composition, but which was not subject to mechanical activation, was studied. The experimental studies were carried out using the D-optimal mathematical plan with variation of the following factors: X₁ – the ratio of the mass of the mixed binder to the mass of unground quartz sand in the construction mortar (from 1:3 to 1:1); X₂ – ground limestone content in the mixed binder (20 ± 20 %); X₃ – consumption of the superplasticizing additive Relaxol-Super PC (0.5 ± 0.5 % of the binder weight). The obtained mathematical models indicate that the maximum effect (of the listed factors) on the strength of the mortar is exerted by the content of the mechanically activated binder in it. An increase in its consumption in the composition of the mortar mix causes an increase in the strength of the mortar at the age of 3 days from 24 to 40.5 MPa, i.e. by almost 70 %. At the age of 28 days, the effect of the consumption of the activated mixed binder on the strength of the mortar is somewhat reduced and does not exceed 60 %. The next factors influencing the strength of the mortar are the consumption of superplasticizer and the percentage of ground limestone. The combined effect of mechanochemical activation in the presence of 1 % Relaxol-Super PC allows the introduction of up to 40 % ground limestone into Portland cement, while providing the same compressive strength of the mortar as when using non-mechanically activated Portland cement, but without the addition of ground limestone.