Production of ultra-lightweight alkali-activated slag concrete as a evaporation suppression floating element Motahareh Pourmand m.pourmand@cv.iut.ac.ir Date of submission: 2020/ / Department of Civil Engineering Degree: M.Sc. Language: Farsi Isfahan University of Technology, Isfahan 84156-83111, Iran Supervisors: Mohammadreza Eftekhar, eft@cc.iut.ac.ir The global freshwater demand has been intensified with population growth, climate change, global warming and change in rainfall patterns in recent decades. Storing water in local reservoirs during rainy seasons is a way to mitigate water scarcity problems in dry spells. The increasing number of water reservoirs highlights the need for efficient measures to suppress evaporative losses. Among different techniques, modular floating elements have shown a reliable performance in mitigating evaporation from water reservoirs. Notwithstanding the high efficiency of these often plastic fabricated floating elements, their effects on water quality parameters and associated environmental issues during production cast doubt on their application. Milad Aminzadeh, m.aminzadeh@cc.iut.ac.ir Lightweight concrete as a unique material with desirable economic and technical properties is an alternative for production of floating elements. However, the use of Portland cement as the key binder of lightweight concrete is often linked with consumption of considerable energy and raw material causing certain environmental issues. Replacing Portland cement in the normal concrete with alkali-activated binders can be considered as an appropriate solution. In the present study, slag and sodium metasilicate pentahydrate as the one-part alkaline binder were invoked to produce modular floating elements using lightweight perlite aggregates. After performing various experiments with variable percentages of lightweight aggregates and slag, the two main values of 130 and 150 kg/m3 were determined for slag. Lime was further used to solve the problem of fracture and fading of the samples. For this purpose, 15, 20 and 30% of lime were replaced with slag. In addition, microsilica with variable percentages of 10, 12 and 15% was introduced to improve mechanical properties of the samples including density, compressive strength, water absorption, permeability, and thermal conductivity. Considering the porous nature and inherent water absorption characteristics of concrete specimens that eventually supply water to the surface of floating elements, glaze coating was used to waterproof the surface of samples. The results showed that lime and microsilica may effectively change mechanical properties of samples. In designs without microsilica, 30 % replacement of lime with slag resulted in desirable density, strength, water absorption, and permeability of samples. In designs with microsilica admixture, increasing the percentage of microsilica generally increased the density, resistance, and thermal conductivity of samples by 26%, 57%, and 12%, respectively. Moreover, the filling properties of microsilica particles caused 10% and 25% reduction in water absorption and permeability, respectively. The density of dry samples was obtained between 340 to 516 kg/m3 with compressive strength of 0.2-0.9 MPa and conductive heat transfer coefficient of 0.067- 0.093 W/mK. The minimum permeability was 3.97× 10-10 m2 and the minimum 48-hour water absorption was 52%. Keywords Evaporation suppression floating element; One-part alkali-activated slag; Microsilica; Ultra-lightweight concrete; Perlite aggregate