Methi Wecharatana

A model for predicting fracture resistance of fiber reinforced concrete

Abstract A theoretical model is presented to predict the crack propagation resistance of fiber reinforced cement based composites. A crack in the matrix is divided into a traction free zone, fiber bridging zone and the matrix process zone. The crack closing pressure due to fibers depends on the (Mode I) crack opening displacement (COD). A method is suggested to estimate this relationship from the pull-out tests. Although calculations of COD are based on linear elastic fracture mechanics concepts, the energy absorbed in the fiber bridging zone is included in the analysis. Theoretical results are compared with the experimental data of notched beam and double cantilever beam specimens.

Properties of High-Performance Fly Ash Concrete

In this study, two types of fly ash, dry and wet bottom ashes of different particle size distributions, were used. Physical and chemical properties of these fly ashes were tested and compared with the original feed fly ashes received directly from the utility. The effects of these fly ashes on the strength of concrete were studied when used as 15, 25, 35, and 50 percent cement replacement by weight of cement. The results show that fly ash, when proportioned properly, can enhance the properties of concrete. The chemical composition of fly ash of different particle size distributions varies slightly. For fly ash with large particle size distribution, the fly ash concrete reaches only 85 percent of the control concrete strength at the age of 180 days.