Abstract: To further improve the rationality of design and management of low alkali recycled aggregate planting concrete in various scenarios of sponge cities, the pore size distribution of natural aggregate, recycled concrete aggregate and recycled red brick aggregate were first measured by mercury intrusion porosimetry, then the water absorption rate-time curves and water content-time curves of planting concrete with different aggregates were measured separately in both water absorption and water reversion states. Characterization model of water absorption and reversion characteristic of low alkali recycled aggregate planting concrete established and Pearson correlation coefficients were applied to reveal the microscopic mechanism of water absorption and reversion characteristics of planting concrete. The results show that the water absorption rate-time curves (goodness of fit R² no less than 0.95) and water content-time curves (goodness of fit R² no less than 0.99) are fitted accurately by power function and double exponential function. The water absorption model includes two parameters, which are initial water absorption coefficient and incremental water absorption coefficient. The water reversion model includes three parameters, which are initial water content coefficient, initial water reversion coefficient and residual water content coefficient. Aggregate type significantly affects the water absorption and reversion characteristic of low alkali planting concrete, and this difference mainly comes from the pore structure of aggregate. A higher porosity of pores above 100 nm in aggregate provides planting concrete with a higher initial water absorption rate, stronger sustained water absorption capacity, a higher saturated water absorption rate, but reduce the residual water absorption rate after water reversion. Pores lower than 100 nm of aggregate increase the residual water content of planting concrete. In addition, the pores below 100 nm continuously absorb water through capillary action, and some pore structures have small pores (below 100 nm) in series with large pores (above 100 nm), forming a siphon structure with capillary pores absorbing water and large pores storing water, thus the continuous water absorption capacity of planting concrete is significantly related to both the pores above 100 nm and below 100 nm.

Key words: planting concrete, recycled aggregate, low alkali cement, pore structure, water absorption and reversion characteristic, microscopic mechanism