Study on methods of testing tensile strength of concrete

Abstract

The tensile strength of concrete is a critical parameter in structural engineering, influencing crack resistance, durability, and overall performance. The brittle nature of concrete causes low tensile strength; hence, indirect methods for testing the tensile strength of concrete, such as the Direct Tension Test, Brazilian Splitting Test (BST), Flexural test, and other novel methods, present limitations related to stress distribution and real-world applicability. This research attempts to further investigate the applicability of a novel method by making certain improvements to past studies of a similar setup for determining the tensile strength of concrete using direct axial force and compares its performance with BST and Cube Compression Test (CCT) across different concrete ages and grades. The experimental procedure involved testing concrete grades C25 and C35 at 3, 7, 14, 28, and 56 days. Specimens were cast in separate batches and subjected to three testing methods: the novel method of Modified Direct Tension Test (MDTT), the Brazilian Splitting Test (BST), and a Cube Compression Test (CCT). The unstandardized MDTT specimen details, dimensions, and method of testing have been described, enabling further research on the proposed method. The novel method aims to provide a more representative measure of direct tensile behaviour while addressing limitations observed in BST. Tensile strength values obtained from both methods are analysed and compared, alongside cube compression test results, to establish correlations between tensile and compressive strengths. Preliminary findings suggest that the newly introduced method may offer improved reliability in capturing tensile failure mechanisms. The results also suggest that the tensile strength vs compressive strength gain patterns vary with time for both tensile strength testing methods. It was also found out that the novel method provides consistent results, and the specimen modification made to direct the tensile crack at the centre is successful in more than 80% of the cases. This research further attempts to discuss the practical applications for the MDTT in cases such as Precast concrete evaluation, bridge and tunnel structural performance, and FRC & UHPC strength and quality assessments. Modifications to be made to the testing apparatus to make it a more reliable method of testing the tensile strength of concrete are also discussed. Further recommendations have been provided to increase the number of test cases and investigate the influence of strain rate on the MDTT setup, which would contribute to the development of concrete testing methodologies as an alternative approach that would enhance accuracy and practical implementation in structural assessments.