Influence of metakaolin as supplementary cementing material on strength and durability of concretes A.A. Ramezanianpour a , H. Bahrami Jovein b,⇑ a Concrete Technology and Durability Research Center, Amirkabir University of Technology, Tehran, Iran b Department of Civil Engineering, Amirkabir University of Technology, Tehran, Iran article info Article history: Received 8 May 2011 Received in revised form 8 November 2011 Accepted 2 December 2011 Available online 3 January 2012 Keywords: Metakaolin Compressive strength Water penetration Electrical resistivity RCPT Salt ponding Sorptivity abstract Durability of concrete is an important issue for predicting the service life of concrete structures. Recently, the properties of metakaolin as high-quality pozzolanic materials are investigated by several researchers. It is not widely produced and used due to the lack of adequate experiments on this material in the Middle East. Local kaolin with high kaolinite content was thermally treated by a special furnace at 800 °C and 60 min burning time to produce metakaolin. This study investigates the performance of concrete mixtures containing local metakaolin in terms of compressive strength, water penetration, sorptivity, salt ponding, Rapid Chloride Permeability Test (RCPT) and electrical resistivity at 7, 28, 90 and 180 days. In addition, microstructure of the cement pastes incorporating metakaolin was studied by XRD and SEM tests. The percentages of metakaolin that replace PC in this research are 0%, 10%, 12.5% and 15% by mass. The water/binder (w/b) ratios are 0.35, 0.4 and 0.5 having a constant total binder content of 400 kg/m 3 . Results show that concrete incorporating metakaolin had higher compressive strength and metakaolin enhanced the durability of concretes and reduced the chloride diffusion. An exponential relationship between chloride permeability and compressive strength of concrete is exhibited. A significant linear relationship was found between Rapid Chloride Permeability Test and salt ponding test results. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Concrete is probably the most extensively used construction material in the world. It is only second to water as the most heavily consumed substance [1]. The majority of the cementitious binders used in concrete are based on Portland cement clinker, the manufacture of which is an energy-intensive process. In addition, it produces a large amount of greenhouse gas emissions, mostly CO 2 , resulting from release of CO 2 from limestone in the pyro-processing of clinker. On the other hand, the concrete industry is one of the major consumers of natural resources. In order to reduce energy consumption, CO 2 emission and increase production, cement plants produce blended cements, comprised of supplementary cementitious materials such as metakaolin, silica fume, natural pozzolan, fly ash and limestone. In recent years, metakaolin (MK) has been studied because of its high pozzolanic properties [2–5]. Unlike other pozzolans, it is a pri- mary product, not a secondary product or by-product, which is formed by the dehydroxylation of kaolin precursor upon heating in the temperature range of 700–800 °C [6,7]. The raw material in- put in the manufacture of metakaolin (Al 2 Si 2 O 7 ) is kaolin. Metaka- olin on reaction with Ca(OH) 2 , produces C–S–H gel at ambient temperature and reacts with CH to produce alumina containing phases, including C 4 AH 13 ,C 2 ASH 8 , and C 3 AH 6 [8,9]. Larbi [10] showed that calcium hydroxide can be virtually eliminated from the cement matrix by using sufficient adapted metakaolin concen- trations. Metakaolin is increasingly being used to produce high- strength, high-performance concrete with improved durability. Extensive research is reported in the literature concerning different properties of MK paste and concrete such as porosity, pore size dis- tribution, pozzolanic reaction, compressive and durability of MK concrete [1,11–13]. Brooks and Johari reported that compressive strength increased with the increase in the metakaolin content [14]. Similar results were also reported by Li and Ding where concrete achieved the highest compressive strength with 10% MK content [15]. Metakao- lin concrete, compared to PC concrete, exhibits significantly lower sorptivity [16]. The incorporation of metakaolin in concrete led to significant in- crease of resistance to chloride penetration. Gruber et al. reported that the use of 8% and 12% high-reactivity metakaolin (HRM) signif- icantly lowered the chloride ion diffusion coefficient of concrete [17]. Parande et al. was deduced that up to 15% replacement of 0950-0618/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2011.12.050 ⇑ Corresponding author. Tel.: +98 21 64543074/915 1110160; fax: +98 21 64543074. E-mail addresses: hamed.bahrami.j@gmail.com, h_bahrami@aut.ac.ir (H. Bahrami Jovein). Construction and Building Materials 30 (2012) 470–479 Contents lists available at SciVerse ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat