Cure cycle optimisation of structural epoxies used in composite civil infrastructure through the use of TTT diagrams

Adhesive bonding is becoming increasingly common in civil infrastructure construction due to the increased use of advanced composites. Due to the large scale of the structures and their application in outdoor settings, the conditions during adhesive curing are substantially different from those in other industries. However, little information exists on curing conditions of commonly used adhesives in civil infrastructure applications making the design of such adhesive-bonded joints difficult. This paper presents a study investigating different phase transitions involved in the curing process of Sikadur® −30, a commonly used adhesive in civil infrastructure applications. A time–temperature-transformation cure diagram was developed for this epoxy system. Oscillatory rheological data were used to determine the gel times. Differential scanning calorimetry tests were used to estimate the time taken for vitrification. Unreacted system and fully reacted system glass transition temperatures were determined to be −48 °C and 70 °C, respectively. Reaction kinetic simulations were carried out for the Sikadur® −30 epoxy system based on the obtained experimental data. The numerical predictions were validated against a comprehensive experimental program. Predictions were shown to be in excellent agreement with the experimental results. This research provides the pathway for structural composite designers to determine important information such as pot life and curing times under different environmental exposure conditions for better design of advanced composite bonded joints.