Comparative torsional behaviour of concrete made from stone, brick and recycled brick concrete as coarse aggregate

Abstract

Concrete's torsion properties are important because different parts of a structural elements made of concrete are subjected to equilibrium or compatibility torsion. Like many mechanical properties, torsional capacity also depends on the type of coarse aggregate utilized to make concrete. There is currently no research available in existing literature that describes the precise torsional behavior of concrete produced with coarse aggregate such as crushed clay brick and recycled brick concrete. Hence, an experimental scheme was conducted where concrete having equivalent target strength was made with four different types of coarse aggregate, such as natural stone aggregate concrete, crushed virgin clay brick aggregate concrete, crushed recycled brick concrete aggregate concrete and recycled stone aggregate concrete. Concrete with four different target compressive strength i.e., 2750 psi (18.9 MPa), 3000 psi (20.7 MPa), 3250 psi (22.4 MPa) and 3500 psi (24.1 MPa) were casted. Beam samples prepared from these four types of concrete were subjected to pure torsion using appropriate frames and loading arrangement up to failure. From this, different aspects of torsional behavior, i.e., ultimate torque and twisting angle and their relationship up to failure, torsional stiffness, and torsional toughness, were observed and compared meticulously. It was observed that the cracking angle due to torque remained close to 45° for concrete prepared from natural stone and recycled stone, but for concrete prepared from virgin brick and recycled brick concrete, the crack angle varied between a wide range of 39° to 56°. For a specific target strength, beam samples from virgin brick and recycled brick concrete had ultimate torque that was roughly 95% and at best 90% of that of natural stone aggregate concrete, respectively.The initial slope of torque vs. angle of the twist curve of beam samples prepared from virgin brick and recycled brick concrete was only 47–52% of that of beam samples prepared from natural stone aggregate. The torsional toughness of virgin brick concrete was found to be 68%–72% of that of natural stone aggregate concrete. On the other hand, the torsional toughness of recycled brick concrete was only about 58% to 61% of that of natural stone aggregate concrete. In addition, ultimate experimental torques were compared with predictions of torsional strength made by five commonly used models, including the elastic theory, plastic theory, the ACI CodeSpace Truss Analogy Method, the Turkish Standard TS500 and Space Truss Analogy. Average deviation of predicted torsional capacity from experimental results calculated along with standard deviation to elaborate effectiveness of these five models in predicting torsional capacity of concrete prepared from brick and recycled brick aggregate concrete.