Thermal insulating coating mortars with mining and steel residues and the proposition of a "thermal insulating admixture"

The present work developed a thermal insulating coating/plastering mortar from the complete replacement of the natural aggregate by friable quartzite (QTZ), with the addition of steelmaking slag powder (SSP). Despite having promising characteristics, no studies so far have taken advantage of the thermal insulating properties of the SSP. Initially, the QTZ and PEA were characterized according to physical, chemical, mineralogical, and morphological analyses. The mortars were prepared with Portland cement, hydrated lime, air-entraining admixtures (AEA), fine aggregates, and SSP. Four mixes were produced: (1) reference (REF) (with natural sand); (2) QTZ + AEA (NO SSP); (3) QTZ + AEA + 5%SSP, and (4) QTZ + AEA + 10%SSP. The following tests were carried out: flow, water retention, specific gravity (density), water absorption by immersion and by capillarity, flexural strength, compressive strength, adhesive strength, UPV, morphology, shrinkage, thermal conductivity, specific heat, and potential of environmental contamination. As result, the QTZ presented physical characteristics similar to those of the natural aggregate, except for the high content of powdery material. The mortar with 5% SSP had the lowest thermal conductivity (56% lower than REF) and the highest specific heat (37% higher than REF). The SSP's mineralogical composition and resulting pore system were the most influential factors for these properties. Therefore, the SSP can be considered a "thermal insulating admixture" and the use of these residues is technically feasible to improve the thermal performance of buildings.