Mesomechanical properties of concrete with different shapes and replacement ratios of recycled aggregate based on base force element method

Abstract

In order to study the mesomechanical properties of recycled aggregate concrete (RAC) under uniaxial tension, a numerical model of RAC with two different aggregate shapes (circular and convex) and five different replacement ratios of recycled aggregate (0, 30, 50, 70, and 100%) was established. A new finite element method-base force element method (BFEM) was used to derive the element strain and the element stiffness matrix with an explicit expression without Gauss integral. The two-dimensional numerical model of the RAC was simulated to study the effect of aggregate shape, replacement ratio of recycled aggregate, aggregate distribution and interfacial transition zone (ITZ) properties on mesomechanical properties of RAC. Simulation results demonstrated that once the first crack appeared, the peak stress and peak strain were reached. The first crack appeared in old ITZ, which was located in whether the upper part or the lower part of the large-size recycled aggregate. The continuous cracks were mainly around the recycled aggregate and the aggregate concentrated area. Comparing with natural concrete, when the replacement ratio of recycled aggregate was 100%, the elastic modulus decreased by 16~25%, the peak stress decreased by 12~15%, and the peak strain changed slightly. The ITZ had a significant influence on the mechanical properties of RAC and must be considered in the analysis.

Base force element method based on the complementary energy principle for the damage analysis of recycled aggregate concrete

“…According to Wang et al, Xiao et al, and Belén et al, it has been described that the shape of the stress‐strain relationship of RAC is similar to that of NAC. As shown in Figure A, the numerical relative stress‐strain relationships are in good agreement with experimental results …”

“…One should note that (17), the arbitrary vectors = [ 1 , 2 ] and are Lagrange multipliers in Equation (17). Therefore, the node displacement can be expressed as:…”

“…It is commonly found that the structure and characteristics of RAC are different from natural aggregate concrete (NAC) . Compared with NAC at the mesoscale, the structure of RAC is much more sophisticated, and the primary ingredients of an RAC model are regarded as a five‐phase system . In addition to aggregates, new cement mortars, and new interfacial transition zones (New ITZs) between them, the RAC has two more mesophases compared with that of NAC: one is the old adhered mortar intrinsically clinging to the surfaces of recycled aggregates, and the second is the old ITZs between the old adhered mortars and the recycled aggregates.…”

“…3,42,48,49 Compared with NAC at the mesoscale, the structure of RAC is much more sophisticated, and the primary ingredients of an RAC model are regarded as a five-phase system. 17,48 In addition to aggregates, new cement mortars, and new interfacial transition zones (New ITZs) between them, the RAC has two more mesophases compared with that of NAC: one is the old adhered mortar intrinsically clinging to the surfaces of recycled aggregates, and the second is the old ITZs between the old adhered mortars and the recycled aggregates. According to the macroscopic experimental and numerical simulation investigations, it is now accepted that under the same situations the mechanical properties of RAC are worse when compared with the NAC.…”

Impact resistance of RC beams under different combinations of mass and velocity: mesoscale numerical analysis

“…characteristics between the ITZ and the mortar, an equivalent method was thus adopted here, i.e., regarding the actual ITZ and part of the mortar as the equivalent ITZ, where the thickness is set as 5 mm. This treatment was also used by other researchers during the process of modeling [40,41].…”