Simplified DEWS test for steel fibre-reinforced concrete characterisation

Ensaio DEWS simplificado para caracterização do concreto reforçado com fibras de aço

Abstract

Fibre Reinforced Concrete (FRC) is internationally recognised as a structural material in the fib Model Code 2010 and at a national level in the recently published ABNT standard NBR 16935, which establishes the structural design procedure based on post-cracking parameters. This publication should foster an increase in the number of applications of FRC in Brazil in the next years. In this context, many researchers have investigated the use of the DEWS test for the FRC characterisation as an alternative to the three-point bending test (3PBT) usually recommended by standards. The DEWS test is conducted by applying a compressive load on specimens with triangular grooves that induce a pure mode‑I tensile fracture. Despite the advantages of the test, such as a smaller specimen and simpler testing procedure to obtain the anisotropic/orthotropic material properties, it still requires transducers to measure crack opening and generate the triangular grooves in the specimen, which is more complex, and labour demanding. This study addresses these issues by proposing a simplified test method and preparation consisting of removing the transducers (correlating the machine stroke and the crack opening) and generating the triangular groves during the casting instead of sawing afterwards. These modifications made the testing procedure much easier to perform. The experimental program assesses the modifications in the DEWS test setup and their influence on the post-cracking characterisation of FRC. Additionally, the effective fibre content and orientation were assessed by performing the inductive test. The results show that FRC characterisation can be successfully conducted using a simpler configuration of the DEWS test. This alternative test presents some advantages in comparison with the 3PBT test for FRC quality control, especially the lower volume of material and the test control by machine displacement.

Keywords:
fibre reinforced concrete; mechanical characterisation; indirect tensile test; DEWS