Bond strength of epoxy-coated bars in underwater concrete Joseph J. Assaad a,b,⇑ , Camille A. Issa a a Lebanese American University (LAU), Byblos, Lebanon b Holderchem Building Chemicals, Baabda, Lebanon article info Article history: Received 9 September 2011 Received in revised form 5 November 2011 Accepted 2 December 2011 Keywords: Bond strength Epoxy-coated bars Underwater concrete Washout loss abstract A comprehensive research project was carried out to assess the effect of washout loss on bond between underwater concrete (UWC) and epoxy-coated reinforcing steel. Washout loss of investigated mixtures was evaluated using the CRD C61 test method. The compressive and bond strengths of UWC were deter- mined using the same concrete samples that were used for washout loss measurement. Test results showed that the ultimate bond strengths of epoxy-coated bars embedded in UWC are affected by the level of washout loss. Compared to reference concrete sampled in dry condition, a decrease in bond varying from 15% to 25% was measured for UWC possessing washout loss in the range of 8% ± 3%. The bond stress vs. slip behavior of epoxy-coated bars is remarkably different than the one obtained using reference concrete. Mixtures subjected to some washout exhibited less stiffness together with a decrease in the ultimate bond strength and shifting of the slip towards lower values. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Epoxy-coated steel bars are frequently used to reinforce marine and offshore concrete structures at the tidal zone where high cor- rosion resistance is required [1–3]. Concrete within such zone undergoes cyclic wetting and drying processes, thus resulting in significant localized chloride accumulations that penetrate the capillary voids and precipitate corrosion. In warm climates, the high temperatures accelerate the corrosion process, and in cold cli- mates, the combined action of freezing and corrosion can be quite detrimental to concrete durability. For elements located at deep layers inside the water (i.e., piles or foundations), uncoated steel bars can be used because oxygen is virtually excluded which makes the steel much less susceptible to corrosion attack [4]. Investigations carried out in the past on the bond behavior be- tween concrete and epoxy-coated bars have reached to the conclu- sion that bond capacity decreases when epoxy coatings are applied on the reinforcement [5]. Compared with uncoated bars, the de- crease in bond strength was found to range from 15% to 50% depending on several factors such as the coating thickness, bar size and location, deformation patterns, concrete properties, and cast- ing conditions [5–7]. Therefore, to compensate such loss, design codes stipulated an increase in the development (or embedment) length of the bars. For example, in ACI 318, the development length is multiplied by a factor of 1.5 for epoxy-coated bars with a cover of less than 3 d b or clear spacing between bars less than 6 d b (where d b is the bar diameter), and a factor of 1.2 for other cases [8]. In the AASHTO bridge specification, these factors are 1.5 and 1.15, respec- tively [9]. Concrete used for casting marine and offshore structures is gen- erally refereed to as underwater concrete (UWC). The UWC devel- ops lower in situ performance than other concrete cast and consolidated above water. Typical in situ residual compressive strengths reported in the literature were in the order of 80–90% for UWC cast using the tremie/hydrovalve technique [10], 50– 70% for self-consolidated UWC depending on turbulence of water and location of extracted cores for strength testing [11], and as low as 40% for concrete having a slump of 230 mm made without anti-washout admixture (AWA) [12]. The drop in UWC strength can be attributed to a combination of factors such as washing out of fine cementitious particles and exceeding the specified water-to-cementitious materials ratio (w/cm), agitation of wet concrete by the action of surrounding water, segregation of aggre- gates during placement, hydrostatic water pressure, erosion of concrete surfaces, and improper consolidation. Normally, the bond between epoxy-coated steel and UWC can- not be the same as that experienced for concrete cast above water. This is due to the fact that performance of materials and applica- tion procedures that perform well in dry conditions are often inad- equate for underwater applications [4]. For instance, the pullout strength of anchors embedded in polyester resin under submerged conditions were found to be as much as 50% less than the strength of similar anchors installed under dry conditions [13]. Also, for UWC characterized by lower in situ performance, it becomes diffi- cult the establishment of a realistic estimation of the contribution 0950-0618/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2011.12.047 ⇑ Corresponding author at: Lebanese American University (LAU), Byblos, Lebanon. Tel.: +961 3437 786; fax: +961 5921 118. E-mail addresses: joseph.assaad@lau.edu.lb (J.J. Assaad), cissa@lau.edu.lb (C.A. Issa). Construction and Building Materials 30 (2012) 667–674 Contents lists available at SciVerse ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat