Effects of formwork dimensions on the mechanical performance of fiber-reinforced cement based materials

Abstract

The aim of this work was to study the relationship between formwork/sample variables and fiber properties to help define design principles of structures, generally when fiber reinforced materials are considered. For this purpose parameters such as formwork dimensions and fiber aspect ratio were varied and related to resulting fiber dispersion state and mechanical performance. Two parameters were defined to understand the effects of varying formwork dimensions on the fiber alignment and resulting mechanical performance. Two different length of the same steel fibers were used. One of the parameters was selected to be the ratio of formwork or flow width to the fiber length (w/fL) and the other one was the ratio of formwork thickness to the fiber length (t/fL). Two concrete mixtures with two different length of the same fiber were cast into formworks with varying thicknesses and widths to obtain various flow behaviors from the materials. Six different w/fL and 4 different t/fL values were obtained and results evaluated by using optical image analysis and mechanical tests. A series of experiments were performed to correlate the fresh and hardened state properties of FRCs by means of fiber dispersion and orientation. Specimens were cast using same mix designs, only fiber length and specimen depth parameters were varied. Two different mixes were prepared by varying fiber length and two different specimen thickness values were set. Therefore, 4 different groups of specimen were obtained. These FRC’s are cast into different size of moulds, having same length and depth, but various widths. Before exposing to flexural test, each specimen having various widths were cut in order to make all the specimens have the same width. After that, in order to determine the hardened state properties, specimens were exposed to four-point bending test. Finally, image analysis were conducted in order to better understand fiber orientation. To do fiber orientation analyses, specimens were cut into 2 pieces, near the major crack, after four-point bending tests. Microscopic images were taken from the cross sections of these cut specimens by using an optical microscope. Then these microscopic images were analyzed by using a tensor description method and fiber orientations in each of the x, y and z directions were obtained. Results showed the importance of the formwork dimensions, hence effect of mould dimensions on the flow behavior, fiber orientation and resulting mechanical performance of the fiber-reinforced cement-based materials.