Comparative analysis of the effects of aggregates and fibres on the fracture performance of lightweight aggregate concrete based on types I and II fracture test methods

Abstract

This study aims to evaluate different influencing factors, such as the types of coarse aggregates with different elastic moduli, different mixing methods for aggregates and fibres (steel fibre, basalt fibre and polypropylene fibre) and two fracture test methods, on the fracture performance of concrete. LC30 all-lightweight shale ceramsite (SC) concrete was regarded as the benchmark. SC was replaced with limestone gravel at a volume ratio of 30% and changed into gravel lightweight concrete. Forty-two three-point bending notched beams and 42 single-side double-notched beams were firstly fabricated, then type I tensile test and type II shear test were conducted. The load (P, kN)–deflection (δ, mm) curves and load (P, kN)–crack mouth opening displacement (CMOD, mm) curves were obtained via type I test, and P–δ curves were obtained via type II test. The effects of aggregates and fibres on type I and II failure modes were analysed, and the influence on the initial fracture toughness, unstability fracture toughness and fracture energy was evaluated. The linear relationships between fracture energy and unstability fracture toughness were determined by type I test, and the relations amongst the initial and unstability fracture toughness and shear force were identified by type II test. Comparative analysis shows that the influence of high-modulus aggregates and fibres on the fracture performance is considerable. The peak load of type II test is an order of magnitude larger than that of type I test, and the peak displacement is also much larger. The failure characteristics of type II test have the composite features of type I and II fracture tests. Some kind of ratios exist between the initial and unstability fracture toughness of types II and I. However, the extent of type I impact on type II is difficult to quantify.