Early age prediction of adhesive anchor strength through curing kinetics and pry out behaviour models

The accurate prediction of early-age bond and shear capacity of adhesive anchors remains a critical challenge for engineers aiming to establish reliable performance metrics for bolt applications. Established models such as Arrhenius, Bilinear, and Pry-out have been employed as standards within the field. However, these models display limitations in predicting bond shear capacity and accurately determining curing times across various resin chemistries and environmental conditions. This study addresses these shortcomings by employing both experimental and mathematical models to analyse the tensile, shear, and stiffness development of epoxy and vinyl-ester bonded anchors cured for 5, 10, and 15 days at temperatures ranging from 12 to 18 °C. Additionally, it focuses on creating new predictive models for early-age bond and shear capacities. A comprehensive series of 54 pull-out tests was conducted on three different anchor types, enabling an assessment of strength progression, load-slip behaviour, and pry-out mechanisms. Under the tested conditions (C 25/30 concrete; ambient curing at 12-18 °C; three Fischer resin systems), vinyl-ester anchors exhibited a faster early-age strength gain, reaching more than 90% of their measured 15-day capacity by day 10. Epoxy anchors reached approximately 80% within the same period. These findings apply strictly to the tested temperature window, substrate type, and adhesive systems, and should not be generalised beyond this scope without further validation. To estimate early-age shear capacity, pry-out multipliers were calibrated against tension data, yielding values of 1.48 for epoxy anchors, 1.34 for standard vinyl-ester anchors, and 1.31 for high-bond vinyl-ester anchors. These findings present a contrast to the conventional application of the universal shear-to-tension factor of 1.50 recommended in EN 1992-4. Furthermore, the study offers an interpretation of bond-slip mechanisms, drawing from existing models and introducing a unified growth formulation that accounts for the effects of curing duration and resin chemistry. In doing so, the research identifies critical design gaps in early-age applications and suggests resin-specific models tailored for cold-weather conditions.