Tensile behavior of fiber-reinforced DSP cement.

The mechanisms responsible for the improvement in tensile strain capacity of fiber reinforced densified small particles (FR-DSP) cement containing high volume fraction of discontinuous steel fibers, randomly distributed throughout the matrix were investigated. Existing micromechanical models based on energy principles were further improved for predicting the tensile strain capacity of the composite, which is highly dependent on the properties of the fiber matrix interface. The debonding and pullout behavior of a single steel fiber from cement based matrices was examined using a specially designed apparatus which provides simultaneous results on total fiber displacement versus load in addition to monitoring the fiber displacement at the free end. In this apparatus the fiber goes through the entire specimen, which made it possible to determine the point of complete debonding. To control the embedment length, a plastic tube was inserted around the fiber. The described method coupled with an appropriate analyses provides a quantitative determination of interfacial properties which are relevant to toughening of brittle materials through fiber-reinforcement. The technique was used on a high strength cement-based matrix (DSP), and on an ordinary strength cement matrix. Other parameters investigated included fiber embedment length, fiber volume fraction in the cement matrix, and matrix surface effect. A model was proposed for analyzing the debonding process in single fiber pullout tests. The model provides a simple and direct way of estimating the debonding energy and the frictional bond strength of the fiber/matrix interface, by evaluating the part of the area under the pullout curve corresponding to pure debonding. The results indicate that: (1) the dense DSP matrix has significantly improved interfacial properties as compared to the ordinary strength matrix; (2) the major energy of pullout in both systems is due to sliding; and (3) both the debonding energy and sliding energy increase with fiber embedment length. These results are important for understanding the role of steel fibers in improving the tensile properties of high performance fiber reinforced composites. The results obtained from uniaxial tension tests on FR-DSP containing small amount of main reinforcement confirmed an increase in the elastic and inelastic strains of the composite as predicted from previous models.Ph.D.Civil EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/104424/1/9527578.pdfDescription of 9527578.pdf : Restricted to UM users only