Effect of nanomaterials additives on performance of concrete resistance against magnesium sulfate and acids

This paper is dedicated to study the effect of nanomaterials, represented by Nano-SiO2 (NS) and Nano-Metakaolin (NMK), on the absorption, total porosity, magnesium sulfate resistance and acid resistance of High Strength Concrete (HSC) and High-Performance Concrete (HPC). An experimental study was carried out on three grades of concrete (55 MPa, 80 MPa and 90 MPa) with cement content of 350, 450 and 600 kg/m(3) and water/binder ratio of 0.45, 0.29 and 0.24 respectively. The considered dosages of NS is 0.5%, 1%, 1.5% and 2% by weight of cement as an addition, whereas these dosages were 1%, 3%, 6% and 9% in case of NMK. Some of concrete specimens were immersed in 10% magnesium sulfate solution and the other specimens were immersed in nitric acid and sulfuric acid after 7 days of water curing, where the pH value for each used acid was 1.0. The magnesium sulfate and acids resistance were evaluated in terms of compressive strength loss, expansion strain, weight loss, and Ultrasonic Pulse Velocity (UPV) loss. The relation between compressive strength loss and each of expansion strain, weight loss and UPV loss were also studied. In addition, to judge the cost effectiveness of concrete with and without NS subjected to magnesium sulfate attack, the cost of compressive strength for each one MPa was determined for different concrete grade levels. The tests results have shown a pronounced increase in compressive strength as a result of using nanomaterials at different ages. Moreover, adding NS and NMK has revealed a remarkable reduction in water absorption and porosity of HSC and HPC. Furthermore, the use of NS and NMK enhances the magnesium sulfate resistance and both nitric and sulfuric acid resistance (1.0 pH value) with different concrete grade levels. (C) 2019 Elsevier Ltd. All rights reserved.