INFLUENCE OF HIGH-REACTIVITY METAKAOLIN AND SILICA FUME ON THE FLEXURAL TOUGHNESS OF HIGH-PERFORMANCE STEEL FIBER-REINFORCED CONCRETE

For steel fiber-reinforced concrete with practical fiber volume fracti ons, the major post-peak energy dissipation mechanism is the pull-out of fibers across a crack. With undeformed, smooth fibers, post-peak en ergy dissipation or ''toughness'' is mainly a function of fiber-matrix adhesional bond whereas for the highly stressed deformed fibers, prop erties of the bulk matrix also become important. High-performance matr ices tend to be brittle, and addition of pozzolanic admixtures, partic ularly silica fume, further increases the brittleness. An increased ma trix brittleness can cause crushing and splitting of the matrix and ir t turn, curtail the ability of fibers to transfer stresses during pull -out, thus reducing the overall toughness. This paper examines the inf luence of two pozzolanic materials-high-reactivity metakaolin (HRM) an d silica fume-on the toughness characteristics of high-performance fib er-reinforced concrete. It is concluded that HRM is particularly effec tive in improving the post-peak energy absorption capacity of concrete with fibers, and unlike silica firme, no particular post-peak brittle ness is seen to occur.