Impact of alkaline-activated SiMn slag and recycled expanded polystyrene on the thermal performance of lightweight masonry mortars

This research presents the use of industrial waste as an alternative to Portland cement and natural raw materials, promoting an alternative binder with a lower carbon footprint and more sustainable, and with properties focused in building field. The results are presented regarding the performance offered by lightweight and thermally insulating mortars manufactured by combining a binder based on the alkaline activation of a SiMn slag, in which the activation is carried out thanks to an alkaline attack of NaOH on a glass powder residue, and a variable amount (from 0 % to 100 % of the aggregate volume) of expanded polystyrene residue (EPS R). In addition, non-recycled EPS (EPS N) has been tested to compare its behaviour with the recycled polymer. The manufactured mortars have been completely characterized, covering the main properties of their application as a coating for masonry applications: behaviour in the fresh state, mechanical performance, dimensional stability, adherence to bricks and their insulating properties. The results show that the type of EPS, mainly its density, shape and particle size distribution, has made a difference in properties such as density, mechanical strength, shrinkage, thermal insulation and capillarity. EPS R has an irregular shape, is smaller in size and has a higher density than EPS N, generating more points of union with the paste. Thus, EPS R, compared to EPS N, has lower values of workability, shrinkage and adhesion; and higher values of density, flexural and compressive strength, thermal conductivity and capillarity. The increase in the percentage of replacement of mineral aggregate by EPS has allowed the manufacture of mortars with reduced capillarity but has also meant significant decreases in workability, density, mechanical resistance to bending, compression and adhesion. Despite the above, mortars with 100 % EPS meet more than enough the requirements necessary to be used as masonry and coating mortars. Mortars made with 100 % EPS for both types of EPS studied can be classified as lightweight masonry mortars and lightweight coating mortars. Although the 100 % EPS mortars studied cannot be classified as thermal insulation mortars, it has been demonstrated that they make a significant contribution to thermal insulation. For both types of EPS, in addition, the coating mortars meet the requirements necessary to be used outdoors, contributing to the average resistance to filtration of the coating. • The temperature of the activator is decisive in the density and mechanical strength. • The key properties of the EPS are: density, shape and particle size distribution. • Mortars with 100 % EPS meet the requirements as masonry and coating mortars. • EPS has been shown to be useful in the design of lightweight and insulating masonry mortars. • Incorporation of EPS waste in mortars can improve the sustainability and energy efficiency of buildings.