Use of Metakaolin and Additives from Waste for the Production of High-Strength Lightweight Concrete

Abstract

Understanding the effects of various superplasticizer (SP) types on the rheological characteristics of foamed cement pastes, as well as on the physical and mechanical characteristics of environmentally friendly porous lightweight aggregate concretes, is crucial. Differently extending the setting time of Portland cement (PC) pastes are three tested superplasticizers, lignosulfonates (LS), polycarboxylates (PCX), polyacrylates (PA), air-entraining additive (AM), and their mixtures. The findings reveal that PA, either used alone or in conjunction with AM, only slightly delays the setting time of PC paste. The metakaolin additive (MKA) to PC ratio, as well as AM, determine the dynamic viscosity of PC pastes. In pastes containing AM and PA, raising the MKA to PC ratio enables more air to be entrapped, which leads to uniform pore distribution and an increase in apparent porosity of 2.2 times. After 7 days of hardening, an LWAC sample series with an increased MKA to PC ratio showed a drop in compressive strength of up to 14 times; however, after 56 days of hardening, a rise in compressive strength was shown as a trend. The results obtained can be used for the production of high-quality lightweight concretes with the use of different additives.