The synergetic interaction of chemical admixtures on the properties of eco-friendly lightweight concrete from industrial technogenic waste

Abstract It is important to know how different superplasticisers (SP) types affect the rheological properties of foamed cement pastes and influence the physical and mechanical properties of eco-friendly porous lightweight aggregate concretes based on industrial technogenic waste. Three tested superplasticisers—lignosulfonates SP(S), polycarboxylates SP(C), polyacrylates SP(A), air-entraining admixture (AEA) and their combinations—differently prolong the setting time of Portland cement (OPC) pastes. The results show that SP(A) retards the setting time of OPC paste to the minimum extent both in individual use or in combination with AEA. The dynamic viscosity of OPC pastes depends on the metakaolin additive (MA) to OPC ratio and AEA. In pastes with the highest MA to OPC ratio, the dynamic viscosity is 2.46 times higher than in a paste without MA. The effect of AEA in the pastes expresses itself in increased dynamic viscosity, up to 50.8% compared to the same samples without AEA. Increasing the MA to OPC ratio in pastes with AEA and SP(A) allows entraining a higher volume of air, which results in uniform pore distribution and increasing apparent porosity by 2.2 times. Increasing the MA to OPC ratio in a eco-friendly lightweight aggregate concrete (LAC) sample creates a highly porous macrostructure, resulting in decreased density, up to 40.1%, and thermal conductivity coefficient, up to 2.1 times (from 0.152 to 0.073 W/(m·K) and increased water absorption, up to 44.8% (from 5.73% to 8.3%). With an increased MA to OPC ratio in a LAC sample series, the compressive strength decreased up to 14 times after 7 days of hardening, however, after 56 days of hardening, the tendency of increase for compressive strength is observed.