Effect of coarse aggregate grading optimization on temperature, thermal stress and compressive strength of carbon fiber-reinforced concrete by ohmic heating curing

The ohmic heating (OH) method is demonstrated to be promising for the curing of carbon fiberreinforced mortar under ultra-low temperature condition. For the large-scale application in engineering and the reduction of carbon emission, the addition of coarse aggregates is necessary. However, coarse aggregates also influence on the temperature distribution and mechanical strength of OH cured concrete. This study proposed an optimization process of coarse aggregate gradation by combining particle packing theory with thermal simulation. The gradation was firstly decided by modified Andreasen & Andersen curve, and then optimized by the numerical simulation of temperature and thermal stress, in order to relieve the high thermal stress gradient in cold condition. The experimental results showed that the compressive strength of the samples with coarse aggregates of both 5-10 mm and 10-16 mm cured by 2 days OH curing at -20 degrees C reached 51.94 MPa, which was higher than samples including single aggregate diameter level, presenting a comparable strength value with 7 days room temperature (RT) curing. In addition, the microstructure and hydration products of concrete with OH and RT curing were compared and analyzed. This work will provide better guidance on the optimization design of mix proportion of carbon fiber-reinforced concrete for promoting the development of OH curing of concrete in large-scale practical applications.