Long-term creep behavior of resin-based polymers in the construction industry

Abstract

For lifetime assessment of resin-based injection mortar systems in structural applications, a fundamental knowledge of the long-term deformation and failure behavior of such materials is required. This research work addresses the long-term deformation behavior by experimental determination of creep modulus curves for two commercially available epoxy resin (EP) and vinyl ester (VE) resin applied in the construction industry, e.g. for post-installed fastenings, retrofitting and strengthening (FRPCs). The experimental approach involves an accelerated procedure for providing creep modulus data for these complex material systems, considering various material states of practical engineering relevance. Three reference material states were defined as upper and lower bound states, respectively, for the expected creep behavior. They were experimentally accomplished by appropriate temperature and moisture preconditioning. The upper bound reference state I represents and is referred to as the “(fully) cured & dry” state. Conversely, two lower bound reference states representing (a) reference state II “standard-cure – as received” and (b) reference state III “(fully) cured & wet” were defined. For reference state I (upper bound), a stress level of 10 MPa was chosen for the creep experiments at different temperatures, and creep modulus master curves for a temperature of 23 °C and up to 50 years were deduced making use of the time-temperature equivalency principle. The creep modulus curves for the lower bound material reference states II and III were assessed based on modulus reduction factor deduced from short-term tensile experiments together with the functional creep characteristics of the upper bound reference state I. In addition, a hypothetical quasi-worst-case material state as a third “conservative” lower bound state was defined by simply superimposing and hence multiplying the reduction factors for reference states II and III. In this manner, a creep modulus function scatter band for the defined upper and lower bound conditions was achieved, which can be used for deformation modeling and simulation of injection mortar systems. While for the EP resin based resin the effect of curing state was found to be negligible (at least over the range investigated) with the effect of moisture content being more apparent, for the VE resin based resin, both material conditions profoundly affect the creep modulus properties.