Early-Age Cracking Analysis of a HVFA Concrete Structure Based on Thermo-Hygro-Mechanical Modeling Combined with XFEM

Due to the low hydration rate of high-volume fly ash (HVFA) concrete at early age, the temperature gradient between the concrete core and surfaces could be effectively reduced. However, the low hydration rate results in a lack of hydration degree for early-age HVFA concrete. Thus, during curing, compared to the strength of ordinary Portland cement (OPC), a subsequent lower one of HVFA concrete leads to a more sensitive response to inner stresses induced by thermal and moisture loads. Based on ABAQUS, in this paper, user subroutines in the temperature and moisture fields were developed, with regard to the hydration degree, for simulation of the temperature and moisture influences on concrete. Additionally, the Double Power Law (DPL) model was used to depict early-age deformations of concrete in the mechanical field. Combined with the extended finite element method (XFEM), another subroutine for early-age cracking analysis in the mechanical field was then developed. Together with aforementioned subroutines, a thermo-hygro-mechanical model is derived. For evaluation of early-age cracking initiation and propagation of a pier composed of HVFA concrete, the model was implemented with XFEM. The obtained results show that (1) temperature and restraints are the main causes of cracking; (2) moisture loss affects surface cracks on structures at early age; and (3) although the temperature difference between the core and surfaces is not much obvious due to the reduced rate of heat dissipation from hydration, cracking of early-age HVFA concrete is still likely to happen for its low early strength. Thus, timely curing is critical to prevent early cracking