Influence of compressive strength and curing time of fiber reinforced concrete on its residual flexural tensile strength

Abstract

Compressive strength is the basic parameter determining the quality of concrete. The addition of fibers to concrete allows us to create a composite with unique properties. The resulting fiber concrete can be tested in many ways, and one of the most interesting and still developing parameter is the residual flexural tensile strength. The current market situation in the construction industry in Central and Western Europe related to the problem of obtaining qualified manual workers and the prices of building materials encourage the design and thorough testing of increasingly complex products, including modern concrete. The relationship between compressive strength and residual strength is an unexplored area that is worth developing in scientific studies. The article presents the relationship between the compressive strength of designed fibre reinforced concrete and its residual flexural tensile strength. The test program included the analysis of concrete in compressive strength classes: C16/20, C25/30, C30/37 and C70/85 made of cement CEM II/B-V 42.5 R-HSR/NA and CEM I 42.5 N-MSR/NA. In each of the designed concrete classes, two types of hook-shaped steel fibres with variable slenderness (l/d ratio) of 50 and 67 were used. Fibre dosage was also diversified and set at 20, 30, 40 and 45 kg/m3 of the concrete mixture. Residual strength tests were performed in accordance with PN-EN 14651 using the ARAMIS device for digital image correlation. The experimental findings showing the relationship between the compressive strength of concrete and its residual flexural tensile strength are included. The experimental data obtained show that increasing the compressive strength class of concrete does not result in an evident increase in the residual flexural tensile strength. The research also analyzed the influence of curing time of concrete on its residual strength, including tests after 28, 180 and 360 days after concreting. The obtained results confirm the significant influence of steel fibres in transferring bending loads. The influence of sample maturation time on the compressive strength of the designed fibre concrete was also confirmed.