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.