REINFORCING CEMENTITIOUS STRUCTURES BY PH ACTIVATED IN-SITU SHRINKING MICROFIBER

This paper describes an innovational fiber reinforcement technology for cementitious composite structures by using shrinking microfibers. Unlike incumbent passive reinforcing microfiber technology, in-situ shrinking microfibers that respond to an external stimulus such as heat, pH, or moisture variations can induce pre-compression to matrix and create additional resistance from external loads. In this paper, pH-activated shrinking (pHAS) microfibers and pH passive (pHP) microfibers made from chitosan powder were used to investigate the reinforcing effect of shrinking mechanism. The specimens reinforced by the range of 0 to 2 wt% of pHAS microfibers, pHP microfibers as well as control samples were prepared, and mechanical properties were compared with three-point bending tests and compression tests. For the three-point bending tests, the reinforcing effect from pHAS microfibers were shown in the specimens with 0.5 wt%, 133 % increase in maximum bending strength compared to the control specimens. However, in compression tests, significant strength increases were not shown, for several possible reasons: (i) weak bonding between fibers and matrix, (ii) small % elongation to break of chitosan microfibers, (iii) abrupt moisture content change in cementitious matrix due to chitosan microfibers, and (iv) micro-cracks due to shrinking related de-bonding which caused more damaging in compression tests than in three-point bending tests. To solve the problems, application of microfibers made from blending Poly(ethylene oxide) (PEO) and chitosan has been also studied.