Low-cost glass fiber composites with enhanced alkali resistance tailored towards concrete reinforcement

Glass fiber reinforced polymer (GFRP) composites were modified through introduction of ion-exchangers in order to enhance their longevity in the alkaline environment of concrete. Glass fiber composites offer a desired balance of performance and cost for replacement of corrosion-prone steel reinforcement in concrete; their rapid deterioration in the alkaline environment of concrete is, however, a major drawback. Ion exchangers are insoluble solids carrying cations (or anions) which can be exchanged with ions of the same sign. Cation exchangers of hydrogen form replace alkali metal cations (e.g., K+ in alkaline solutions diffusing into the polymer matrix) with H. This exchange of cations neutralizes aggressive alkaline solutions by converting K+ OH- (and Na+ OH-, etc.) into H2O. Fine weak-acid cation exchangers, when introduced as coating on glass fiber composite bars (applied immediately after pultrusion and before curing of polymer matrix) proved to be compatible with the industrial-scale pultrusion process of composite bars without any need to modify the curing process. Thorough laboratory investigations and industrial-scale pultrusion efforts, were undertaken, which successfully demonstrated that introduction of selected ion exchangers into the polymer matrix (or a surface layer of matrix) does not interfere with the pultrusion process, and yields significant gains in the alkali resistance of glass fiber composites. The durability characteristics of glass fiber composite bars modified with weak-acid cation exchanger coating were investigated under two different accelerated aging conditions. The modified composite bars provided desirable durability attributes under these two different accelerated aging effects, including exposure to the alkaline pore solution of concrete and salt solution. The mechanical characteristics of modified glass fiber composite bars (with weak-acid cation exchanger coating) were investigated by conducting compression, flexure, and shear tests. The results indicated that the modification of pultruded bars did not alter their mechanical performance. (C) 2013 Elsevier Ltd. All rights reserved.