International Journal of Advanced Structures and Geotechnical Engineering ISSN 2319-5347, Vol. 02, No. 01, January 2013 IJASGE 020103 Copyright © 2012 BASHA RESEARCH CENTRE. All rights reserved. Mitigating Sulphate Attack in High Performance Concrete BASHIR ALAM 1 , SALMAN AFZAL 2 , JUNAID AKBAR 1 , MUHAMMAD ASHRAF 3 , KHAN SHAHZADA 1, MUHAMMAD EJAZ SHABAB 4 1 Department of Civil Engineering, UET Peshawar, Pakistan 2 Department of Civil Engineering, IQRA National University, Peshawar, Pakistan 3 Department of Civil Engineering, CIIT, Abbottabad, Pakistan 4 Sarhad University of Science and Information Technology, Peshawar, Pakistan Email: salmanafzalkhan@gmail.com Abstract: The research addresses the mitigation of Sulphate attack on concrete as it is considered one of the major degradation-causing phenomenons in the durability of concrete. The primary variable in the research was the introduction of Silica Fume as a 12% replacement by weight of cement. Super-plasticizer was also used in order to attain high strength and make the concrete more workable in the presence of silica fume. A concrete batch, with a proper mix design was prepared, aiming at a high strength of 6000psi. Part of the batch was tested for 28 days Strength and part of it was subjected to cyclic wetting and drying exposure to Sulphate-rich environment, the solution being 50 g/l of Na 2 SO 4 . The quality of concrete was measured by Non-Destructive Testing which showed an appreciable improvement in the resistance of concrete to Sulphate attack due to addition of Silica fume whereas the Normal concrete cylinders were affected severely in the Sulphate environment. The same concrete cylinders were tested afterwards for compressive strength under the Universal Testing Machine and the results showed an alarming reduction in strength of the normal concrete cylinders whereas the Silica fume made concrete cylinders showed small reduction in strength. The main conclusions derived from this study are that the use of Silica fume leads to a better performance of concrete in Sulphate rich environments although the strength may not be altered as desirable. Keywords: Sulphate attack, Silica fume, Non-Destructive Testing, Universal Testing Machine 1. Introduction Many concrete structures require costly repair works as they deteriorate under the influence of aggressive environmental agents. The most common among these agents are alkali-aggregate reactivity, freeze- thaw deterioration and attack by sulphates [1]. It is for this reason that High-Performance Concrete has been a choice of concrete mix designers for achieving a long-lasting and economical structure [2]. According to the Texas Department of Transportation, sulphate attack is defined as a series of reactions that may occur in hardened concrete members as a result of presence of sulphate ions in the matrix [3]. The products obtained from this reaction hold a larger volume as compared to the reactants in the cement matrix which causes an internal stress generation propagated by the expansion of the product. Ultimately, the concrete will crack, spall and loss of mass occurs, endangering the overall integrity of the design life of the structure [4]. The United States Bureau of Reclamations (USBR) was the pioneer of identifying the sulphate attack in early 1908 and the only means of mitigating this expansive reaction was controlling the permeability of concrete [5]. The nature of the manifestation of degradation due to sulphate attack depends largely on several factors which include the exposure conditions [6]. [7] has proposed a three- kind exposure scenario for sulphate attack generation i.e. continuous Immersion in sulphate environments, cyclic exposure to wetting/ drying exposure in sulphate environment and partial immersion in sulphate environment. [8] determined that the cyclic exposure to wetting/ drying in sulphate environment leads to a strong scenario for degradation due to sulphate attack and the time span is greatly reduced for detecting the phenomenon. One of the greatly debated agenda among researchers remains as how to detect and quantify the sulphate attack occurring in concrete members. American Society for Testing and Materials has developed a few tests for detecting deterioration due to sulphate attack. [9] involves accelerating the expansion of mortar which are cast in the form of bars by the addition of gypsum to the Portland cement. [10] is an immersion test of ASTM in which mortar bars are immersed in 50 g/l sodium sulphate solution and their expansion in monitored for a period of six months. [11] has proposed an experimental methodology for determining the deterioration of concrete members due to sulphate attack instead of cement mortar bars. 2. Materials and Methods Materials: Cement: ASTM Type-I cement (Normal cement) was used during the study and by [12] the fineness of cement was ensured. Aggregates: The fine and coarse aggregate used in the study was obtained from local quarries. Tests were conducted on the aggregate specimen to collect