EARLY AGE BOND STRENGTH DEVELOPMENT OF FIBERS IN FRC COMPOSITES

摘要

The main objective of the study described in this paper was to investigate the early age bond characteristics between a cement matrix and different fibers. During the first 24 hours after mixing, the matrix properties, particularly strength and modulus, change by orders of magnitude due to the high rate of hydration; this influences bond or the pull-out behavior of a given fiber and leads, with time, to different pull-out characteristics for the same fiber. The mechanisms involved include adhesion, friction, and mechanical anchorage; each can have a predominant effect at a particular time. Pull-out tests of PVA and nylon fibers, as well as of smooth, hooked, and twisted (Torex) steel fibers were carried out at 4, 6, 8, and 24 hours after matrix has been placed. A special apparatus was developed to perform the testing with consistency and minimize the variability. The effect of matrix age on pull-out behavior is presented and compared for different fibers and results analyzed in terms of the various mechanisms observed.