Influence of micro polypropylene fibres on the fracture energy and mechanical characteristics of recycled coarse brick aggregate concrete

Abstract This study intends to measure the influence of micro polypropylene fibres (MPPF) on the fracture characteristics and mechanical properties of recycled coarse brick aggregates (RCBA) concrete. A total of 25 concrete mixes were produced, and slump, compressive, splitting tensile and flexural strengths, fracture energy, load-crack mouth opening displacement (CMOD) relationship, microstructure, residual flexural strength, toughness were measured. RCBA were sorted from an old building devastation and substituted by natural coarse aggregates (NCA) at five contents in terms of mass: 0%, 25%, 50%, 75% and 100%. In addition, MPPF were added at five contents: 0%, 0.5%, 1%, 1.5%, 2% in terms of volume. Moreover, fracture surface analysis was also carried out and a new model was developed between the MPPF numbers and fracture energy. New formulas were also developed to predict the mechanical properties of concrete produced by various MPPF and RCBA contents. Results showed that 100% RCBA could be used as a substitute for NCA without a drop in mechanical properties of concrete when 2% MPPF were also added. In addition, the presented models with high accuracy could be utilized as useful tools to forecast the mechanical and fracture energy of concrete containing different RCBA and MPPF contents.