Viscoelastic response of an epoxy adhesive for construction since its early ages: Experiments and modelling

Epoxy adhesives have been extensively used in strengthening of reinforced concrete structures. In spite of that, research on the viscoelastic behaviour of these adhesives and its influence on the mechanical behaviour of strengthened concrete structures is scarce, particularly at the early ages of curing. The main goal of present work is to better understand the tensile creep behaviour of a specific commercial epoxy adhesive both at early ages and at long term. For this purpose, an experimental program comprising tensile creep tests was performed, in which epoxy specimens were subjected to: (i) equal stress levels but loaded at different ages, and; (ii) two different stress levels for a specific loading age. The results obtained have confirmed the viability of the principles of homogeneity and superposition, thus allowing the classification of this epoxy as linear viscoelastic. In addition, analytical simulations with Burgers model were carried out, and its predictive performance was considered insufficient at early ages, particularly upon unloading. In order to surpass some disadvantages of this model, a new framework is proposed to analytically evaluate the creep curing behaviour of this type of viscoelastic epoxy adhesives. The obtained results evidenced the capability of the proposed framework to predict the creep behaviour of an epoxy adhesive since its early ages.This work is supported by FEDER funds through the Operational Program for Competitiveness Factors - COMPETE and National Funds through FCT - Portuguese Foundation for Science and Technology under the project FPReDur FCOMP-01-0124-FEDER-028865 (FCT reference PTDC/ECM-EST/2424/2012) and the project VisCoDyn FCOMP-01-0124-FEDER-041751 (FCT reference EXPL/ECM-EST/1323/2013), as well as the project POCI-01-0145-FEDER-007633. The authors also like to thank the S&P Clever Reinforcement Ibérica Lda. company for providing the material tested in ambit of the present work. The first author wishes also to acknowledge the grant SFRH/BD/89768/2012 provided by FCT. The second author wishes also to acknowledge the grant SFRH/BDE/96381/2013 co-funded by CiviTest-Pesquisa de Novos Materiais para a Engenharia Civil, Lda and by FCT.