Production of evaporation suppression floating covers using ultra-lightweight alkali-activated slag concrete

Evaporative losses from reservoirs exacerbate water shortage during dry spells. Notwithstanding the extensive application of self-assembling floating covers for suppressing evaporation, the cover material is often overlooked and limited to available choices such as plastics. The present study is aimed at the production of floating covers using ultra-lightweight alkali-activated slag concrete that offers a range of mechanical and chemical features. Concrete specimens were made with different percentages of ground granulated blast-furnace slag as the binder, sodium metasilicate as the alkaline activator and lightweight perlite aggregates with a density of 100–150 kg/m³. To solve the problem of fracture in the preliminary specimens, slag was partially replaced with 15, 20 and 30% lime. In addition, microsilica (10, 12 and 15%) was introduced to improve the mechanical properties of the samples. In designs without microsilica, 30% replacement of slag with lime resulted in the desirable density, strength and permeability of samples. Results showed that microsilica generally increased the density, resistance and thermal conductivity of samples by 7, 74 and 14%, respectively, while water absorption and permeability decreased by 15% and 14%, respectively. The dry density of samples was obtained between 340 and 516 kg/m³ with a compressive strength of 0.2–0.9 MPa and a conductive heat transfer coefficient of 0.067–0.093 W/mK.