Effectiveness of surface coatings in improving concrete durability A.A. Almusallam * , F.M. Khan, S.U. Dulaijan, O.S.B. Al-Amoudi Department of Civil Engineering, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia Abstract This paper reports results of a study conducted to evaluate the durability of concrete coated with concrete surface coatings representing five generic types. The durability of the uncoated and coated concrete specimens was evaluated by assessing water absorption, chloride permeability and chloride diffusion. The chemical resistance was evaluated by immersing the uncoated and coated mortar specimens in 2.5% sulfuric acid. The results indicated that epoxy and polyurethane coatings performed better than acrylic, polymer and chlorinated rubber coatings. However, noticeable variation in the performance of the same generic type procured from different manufacturers was noted. Therefore, the selection of coatings should be done after conducting trial tests rather than basing it solely on the generic type. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Surface coatings; Concrete durability; Chemical resistance 1. Introduction Thenecessityforprovidingsupplementaryprotection toconcreteinsituationswherethestructuresareexposed to aggressive environments is now well appreciated. Several researchers [1–3] have attributed premature de- terioration of concrete exposed to severe environments totheunrealisticevaluationoftheseverityoftheservice- environment. As a consequence, the requirement for a holistic approach to the design of a durable concrete structure has been advocated [4]. It is now realized that the economic superiority of Portland cement concrete can only be utilized by formulating materials specifica- tionsandconstructionpracticescommensuratewiththe severityoftheserviceconditions. The protection methods that are presently adopted include: (i) use of protective concrete surface coatings; (ii)useofmetallic,epoxyandpolymericcoatingsonthe steel and (iii) use of corrosion inhibitors. Some of these measures are suitable for the new concrete structures while others can be adopted for old structures as well. Whilecoatedreinforcingsteelbarshavebeenutilizedin construction during the past decade there have been conflicting opinion on their usefulness, vis- a-vis, the localized corrosion at locations of coating damage. Similarly, the usefulness of concrete inhibitors in re- ducing reinforcement corrosion is yet to be established. Coatings, particularly coal tar, chlorinated rubber, epoxy,etc.havebeenappliedonthefootingsandpiers, to avoid concrete deterioration due to sulfate attack. However, concrete coatings of several generic types are now marketted for protecting concrete at both above and below ground levels. Studies [5–8] to date have shownencouragingresultsontheperformanceofvapor barriers, vapor permeable coatings, surface penetrating sealers and protective coatings. Ibrahim et al. [9] eval- uated the performance of silanes, silanes/siloxanes and acryliccoatings.Inthatstudy,thebestperformancewas indicated by silanes/siloxanes with a top coat. Dulaijan et al. [10,11] evaluated the performance of cement- and epoxy-based coatings in protecting concrete. Results of that study [10] indicated that epoxy modified cement- basedcoatingsprovideadequateprotectiontoconcrete. However, the crack bridging capacity of the polymer modifiedcementitiouscoatingwasreportedtobebetter thanthatofothercement-basedcoatings.Theadhesion of all the epoxy resin-based coatings, to the concrete substrate,wasnotedtobebetterthanthatoftheacrylic resin-basedsurfacecoatings[11].Thewaterpermeability intheconcretespecimenscoatedwiththeselectedresin- based surface coatings was reported to be very low and * Corresponding author. Tel.: +966-3-860-4440; fax: +966-3-860- 2879. E-mail address: musallam@kfupm.edu.sa (A.A. Almusallam). 0958-9465/03/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0958-9465(02)00087-2 Cement & Concrete Composites 25 (2003) 473–481 www.elsevier.com/locate/cemconcomp