Abstract
The old mortar attached to recycled aggregate (RA) is the main reason for the difference in water movement between recycled aggregate concrete (RAC) and natural aggregate concrete (NAC). In this study, considering the old and new interfacial transition zones (ITZs), a five-phase composite model for describing the water transport and distribution in RAC is established at the mesoscale. The key parameters describing water unsaturated transport in two types of mortar, saturated hydraulic conductivity (Ks) and van Genuchten model parameters (α, n), are obtained through the constant-head permeability test and isothermal adsorption test. By using the finite element method, the numerical simulations of unsaturated moisture movement in the homogeneous mortar, NAC, and five-phase RAC are systematically carried out. The proposed moisture transport model in the matrix is validated by comparison with the available experimental findings from the literature. The results show that the model can well predict unsaturated water transport in cement-based materials, including RAC. A parameter sensitivity analysis is undertaken to ascertain the main influencing factors of water transport in RAC. It is concluded that the RA replacement rate (Rra), the thickness of the old mortar (dm), and the aggregate volume fraction (Fa) are the primary parameters affecting moisture movement in RAC.
Highlights
With the rapid progress of infrastructure construction, two contradictions have gradually emerged
Equation 16 was implemented in the commercial finite element software, COMSOL Multiphysics, the multi-field coupled finite element method (FEM) simulation program, and the cloud map of water distribution of NA concrete (NAC) and recycled aggregate (RA) concrete (RAC) at different times were obtained to describe the 2D water distribution in RAC and NAC at different times (Figures 7A,B)
This phenomenon can be explained that water only moves in the matrix and single ITZ on condition that natural aggregates (NAs) is assumed as impermeable, whereby the real water transport area is equivalent to narrowing
Summary
With the rapid progress of infrastructure construction, two contradictions have gradually emerged. One is the imbalance between excessive and unsustainable exploitation of natural resources and the ever-growing requirements of building materials. Another is that the increasing wastes from construction and demolition conflicts with inadequate waste disposal methods. This phenomenon poses a severe threat to the economic development and ecological equilibrium in many countries and regions all over the world (Oikonomou, 2005; Xiao et al, 2012; Fraj and Idir, 2017; Tam et al, 2018; Lam et al, 2019; Song et al, 2020). Compared with NA concrete (NAC), RA concrete (RAC) whose applications are limited to low-level civil construction works are rarely used in modern infrastructure construction due to the inferior performance of RA caused by its complicated composition
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