Durability of Highly Flowable Self-Healing Concrete under Freeze-Thaw Actions

Presented By: Jialuo He, Washington State University Description: This laboratory study used the UF (Urea-formaldehyde) microcapsules and PVA (polyvinyl alcohol) microfibers as a self-healing system to improve the durability of concrete in cold climates. The resistance of this self-healing concrete to freeze-thaw cycles were evaluated by measuring the change of relative dynamic modulus of elasticity (RDM) with respect to the number of freeze-thaw cycles. The control specimens (either with or without PVA microfibers) approached the state of failure and the corresponding RDM dropped 38% after being subjected to 54 freeze-thaw cycles. However, the UF microcapsules alone could increase the number of freeze-thaw cycles that concrete can withstand from 54 to about 600 and the associated RDM drop was reduced to 10%. With the aid of PVA microfibers, this self-healing system exhibited an even better performance that the associated RDM drop was almost 0% by the end of 600 freeze-thaw cycles. The 3-D X-Ray micro-computed tomography (CT) was employed to investigate the microstructure of the concrete specimens after being subjected to 300 freeze-thaw cycles. Based on the reconstructed 3-D images of internal void system, the empty microcapsules after the healing agent being consumed played an important role in providing extra space for the volume expansion of the internal liquid due to freezing. The voids size distribution and fraction of each type of voids revealed that part of the microcracks with a size smaller than 100 µm were healed. The authors established a nonlinear polynomial relationship between the RDM and the number of freeze-thaw cycles (N). In addition, we employed the Weibull distribution model to conduct the probabilistic damage analysis and characterize the relationship between N and damage level (D) with different reliabilities.