During their service life, concrete structures are subjected to combined fluctuations of temperature and relative humidity, which can influence their durability and service life performance. Self-healing has in recent years attracted great interest to mitigate the effects of such environmental exposure on concrete structures. Several studies have explored the autogenous crack self-healing in concrete incorporating superabsorbent polymers (SAPs) and exposed to different environments. However, none of the published studies to date has investigated the self-healing in concrete incorporating SAPs under a combined change in temperature and relative humidity. In the present study, the crack width changes due to self-healing of cement mortars incorporating SAPs under a combined change of temperature and relative humidity were investigated and quantified using micro-computed tomography and three-dimensional image analysis. A varying dosage of SAPs expressed as a percentage (0.5%, 1%, and 2%) of the cement mass was incorporated in the mortar mixtures. In addition, the influence of other environments such as continuous water submersion and cyclic wetting and drying was studied and quantified. The results of segmentation and quantification analysis of X-ray µCT scans showed that mortar specimens incorporating 1% SAPs and exposed to environments with a combined change in temperature and relative humidity exhibited less self-healing (around 6.58% of healing efficiency). Conversely, when specimens were subjected to cyclic wetting and drying or water submersion, the healing efficiency increased to 19.11% and 26.32%, respectively. It appears that to achieve sustained self-healing of cracks, novel engineered systems that can assure an internal supply of moisture are needed.
Acrylic polymer is a superabsorbent for water and widely used in diapers, in which its swelling behavior can be significantly affected by several factors, i.e., the time, temperature, pH, and salt concentration, and thus the product performance in the applications. In this work, the water absorption behavior of acrylic superabsorbent polymers by each of these individual factors was investigated. The results showed that the water absorbency increases with the pH in the range of 2 to ~7 and decreases when the pH continues to increase. However, it decreases with the increases in NaCl concentration in the solution. Moreover, more water can be absorbed by the acrylic polymers at the higher temperature. Based on a previously developed kinetic swelling model and the information from the above investigations, a semiempirical model for predicting the swelling behavior of superabsorbent polymers (SAPs) under different conditions has been developed. Data showed that the model can predict (with a relative error of <4.5%) the amount of water absorbed by acrylic SAPs under different swelling conditions. The model would be very helpful to the practical application in both product design and its performance evaluation.