Compressive mechanical behaviors of recycled lump concrete containing multi-source crushed concrete lumps: Experiment and discrete element modeling

Utilizing large pieces of crushed concrete lumps (CCLs) in combination with freshly poured concrete to fabricate recycled lump concrete (RLC) has emerged as an eco-friendly and cost-effective method for advancing sustainable development in construction industry. Nevertheless, existing research predominantly focuses on RLC using CCLs from a single origin, while the mechanical properties of RLC containing multi-source CCLs have been largely overlooked. This neglect impedes the broader application of CCLs in engineering practices owing to uncertainties in design and safety implications. To address this gap, the current study undertakes two key tasks. First, seventy-two prisms incorporating two types of CCLs with varying mix ratios were produced and tested to evaluate the impact of CCL property discrepancies on the uniaxial mechanical behavior of RLC. Subsequently, discrete element simulations were conducted to explore the effects of the new concrete's water-to-binder ratio, CCL source number, replacement ratio, mix ratio and spatial distribution on RLC's strength and deformation characteristics. Furthermore, the simulations analyzed the internal damage evolution and final crack patterns of RLC prisms under compression. The study yielded the following key findings: (a) The inclusion of multi-source CCLs in RLC has a negligible impact on the compressive mechanical properties of the concrete. Two modified empirical models were formulated to estimate the elastic modulus and compressive strength of the composite. (b) The compressive failure pattern of RLC prisms with multi-source CCLs, marked by segmentation into smaller columns via primary cracks, mirrors that of conventional concrete and single-source RLC, though internal damage progression is strongly influenced by the strength ratio between new and old concrete. (c) RLC prisms with vertically stratified CCLs demonstrate elastic moduli comparable to those with uniformly distributed or horizontally stratified CCLs, albeit with a noticeable reduction in compressive strength. (d) The mechanical variability of RLC containing multi-source CCLs exceeds that of RLC with single-source CCLs, with compressive strength and elastic modulus reductions ranging from 2 % to 8 %.