Influence of activated fly ash on corrosion-resistance and strength of concrete V. Saraswathy * , S. Muralidharan, K. Thangavel, S. Srinivasan Concrete Structures and Failure Analysis Group, Corrosion Science and Engineering Division, Central Electrochemical Research Institute, Karaikudi 630 006, Tamilnadu, India Received 22 May 2001; accepted 22 May 2002 Abstract Various activation techniques, such as physical, thermal and chemical were adopted. By adopting these methods of activation, hydration of fly ash blended cement was accelerated and thereby improved the corrosion-resistance and strength of concrete. Concrete specimens prepared with 10%, 20%, 30% and 40% of activated fly ash replacement levels were evaluated for their com- pressive strength at 7, 14, 28 and 90 days and the results were compared with ordinary Portland cement concrete (without fly ash). Corrosion-resistance of fly ash cement concrete was studied by using anodic polarization technique. Electrical resistivity and ul- trasonic pulse velocity measurements were also carried out to understand the quality of concrete. The final evaluation was done by qualitative and quantitative estimation of corrosion for different systems. All the studies confirmed that upto a critical level of 20– 30% replacement; activated fly ash cement improved both the corrosion-resistance and strength of concrete. Chemical activation of fly ash yielded better results than the other methods of activation investigated in this study. Ó 2002 Elsevier Ltd. All rights reserved. Keywords: Reinforcement corrosion; Fly ash cements; Activated fly ash; Electrical resistivity; Ultrasonic pulse velocity 1. Introduction The development and use of blended cement is growing rapidly in the construction industry mainly due to considerations of cost saving, energy saving, envi- ronmental protection and conservation of resources. Fly ash, a siliceous material obtained from different thermal power stations is now being considered as a cementitious ingredient for concrete. The use of fly ash in mortar and concrete, as a partial replacement of Portland cement, appears to constitute a very satisfactory outlet for this industrial by-product. The use of fly ash to replace a portion of the cement has resulted in significant savings in the cost of production of concrete. It was found that, in order to get resemblance in properties with ordinary Portland cement (OPC), fly ash needs special treatments like mechanical grinding, thermal activation, alkali ac- tivation etc. [1,2]. A new method of fly ash activation with addition of Ca(OH) 2 and a small quantity of Na 2 SiO 3 was reported [1]. Alkali activation showed improved accelerated set- ting and hardening [3]. Studies conducted on mortars containing 15–60% fly ash as a replacement of Portland cement showed good correlation between strength and particle mean diameters when fly ash substitution was 60% [4–6]. Addition of fly ash caused a decrease in chloride permeability of concrete upto 50% cement re- placement [7]. Moreover, the threshold chloride level decreased with increasing fly ash content [8]. Values obtained were 0.70%, 0.65%, 0.50% and 0.20% (acid soluble chloride) by mass of cementitious material for concrete with 0%, 15%, 30% and 50% fly ash, respec- tively. Despite the lower threshold values, fly ash con- crete was found to provide better corrosion protection to the steel due to its increased resistance to chloride ion penetration and increased electrical resistance. Earlier work reported [9,10] that fly ashes accelerate reinforcement corrosion due to the presence of unburnt carbon and sulphur. In order to produce fly ashes with stable properties and adequate quality, many power * Corresponding author. Tel.: +91-04565-27550; fax: +91-04565- 27779. E-mail address: corrmurali@yahoo.com (V. Saraswathy). 0958-9465/$ - see front matter Ó 2002 Elsevier Ltd. All rights reserved. doi:10.1016/S0958-9465(02)00068-9 Cement & Concrete Composites 25 (2003) 673–680 www.elsevier.com/locate/cemconcomp