Effect of nanomaterials additives on performance of concrete resistance against magnesium sulfate and acids Ahmed M. Diab a , Hafez E. Elyamany a , Abd Elmoaty M. Abd Elmoaty a , Muftah M. Sreh a,b a Structural Engineering Department, Faculty of Engineering, Alexandria University, Egypt b Faculty of Engineering, Elmergib University, Libya highlights  Mechanical properties were improved due to using NS and NMK.  Adding of NS and NMK improves magnesium sulfate and acids resistance.  In general, NS durability performance is better than NMK. article info Article history: Received 3 December 2018 Received in revised form 25 February 2019 Accepted 11 March 2019 Keywords: Nanomaterials Magnesium sulfate Nitric acid Sulfuric acid Compressive strength loss Expansion strain abstract This paper is dedicated to study the effect of nanomaterials, represented by Nano-SiO 2 (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 car- ried 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 evalu- ated 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 deter- mined for different concrete grade levels. The tests results have shown a pronounced increase in com- pressive 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 resis- tance (1.0 pH value) with different concrete grade levels. Ó 2019 Elsevier Ltd. All rights reserved. 1. Introduction Civil constructions usually consume a great part of the natural resources extracted from the planet, in which concrete represents the greatest cause of this consumption. Therefore, a great interest was oriented to replace the traditionally ingredients of concrete structure by a new material in order to increase its durability. It is well documented in chemistry, physics and mechanics that con- crete production with nanomaterials results in much harder and cheaper concrete that can improve the mechanical and physical properties of concrete. Recently, mixing concrete with nanomateri- als, as additives, can improve the concrete performance, due to their properties at the ultra-fine level, since they have two main advantages; (i) filling the voids between the cement grains, acting as a filler effect, producing a denser microstructure. In addition, nanomaterials have the property of pozzolanic activity, and (ii) improving the bond between aggregate and cement paste [1]. Both formations of Nano-SiO 2 , either in powder form or col- loidal dispersion, were used as a concrete additive in some previ- ous studies [2–10]. The colloidal form, when compared with the powder form, has the advantage of a better dispersion within the cement paste. Thus, the probability of forming agglomerates decreases [6]. The previous studies have revealed the fact that Nano-SiO 2 is a better choice than any other nanomaterials, since https://doi.org/10.1016/j.conbuildmat.2019.03.099 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved. Construction and Building Materials 210 (2019) 210–231 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat