Natural Polymer-based Hydrogel Incorporating Self Healing Mortar

Abstract

In this study, the self healing capacity of mortars incorporating a natural polymer-based hydrogel (chitosan) as a healing agent is compared to control mortars without the healing agent. The hydrogels are placed into mortars after two different methods of encapsulation. The aim of encapsulating the healing agents is to provide water proofness during the fresh state of mortars. The chitosan macrospheres (diameter≈1 mm) were stabilized by lyophilizing and encapsulated by a synthetic polymer and cement based insulation material provided from the market. Pre-trials have shown that the encapsulated hydrogel macrospheres have shown a considerable expansion after the capsules were torn. The method for observing the self healing mechanism is as follows: control and test series were cast and cured for 7 days in water at standard conditions, and then, a controlled pre-load is applied at three-point bending. The pre-loading causes controlled cracking at the lower mid points of the mortar specimens. Just after the pre-loading, the microphotographs of the cracks were taken by stereomicroscope and their ultrasonic pulse velocity (UPV) values were determined. The specimens were then placed into air-tight containers and cured over water for a further 21 days. The UPV measurements were taken after curing and the microphotographs of the cured samples were taken. The difference between the UPV measurements compared to control samples before and after curing and leaking of hydrogels into the cracks are the confirmations of the healing mechanism. The findings obtained from this study reveal promising results for incorporation of the chitosan hydrogel as a self healing agent for cementitious mixtures.

Report from 13^th ICPIC and 7^th ASPIC: New Trends on Concrete-Polymer Composites

“…By using similar system, Lucowski and Adamezewski [47] studied the self repairing degree as a function of polymer/cement and binder/aggregate ratios. On the other hand, Ertug et al [48] tested a natural polymer-based hydrogel (chitosan) as a self healing material in cement mortars. Encapsulated hydrogel spheres in mortar were torn after cracking and showed considerable expansion, hence the cracks are sealed as seen in Figure 6.…”

“…(a) (b) Fig. 6 The microphotograph of a crack on a sample from B series, x25 magnification, a) 7-day old sample, b) 28-day old sample (sealed) [48].…”