Simulation of moisture transport in hydrating cement-based overlay systems
Hua Dong 1, 2, Peng Gao 2, 3, Guang Ye 2
1 School of Materials Science and Engineering, Southeast University, Nanjing 211189, China
2 Microlab, Faculty of Civil Engineering and Geosciences, Delft university of Technology, Stevinweg 1, 2628 CN Delft, the Netherlands
3 School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, People's Republic of China
Drying of cement-based overlay system is a critical issue, because it causes differential shrinkage between the overlay material and the concrete substrate, and may induce cracking/debonding of the overlay material. In this paper the mechanisms of moisture transport in hydrating cement-based overlay systems are studied. A model is proposed for simulating the moisture transport. Parameter study is conducted to quantitatively investigate the influence of the thickness of overlay material and the curing conditions on hydration of the overlay materials. The evolution of moisture profile in the overlay system and the development of degree of hydration of the overlay material are calculated. The change of water in the overlay material is investigated, in terms of water absorbed by the substrate, water consumed by hydration of the overlay material and water evaporated to the environment. The simulation results show that water evaporation is a dominating factor that causes water loss of the overlay material, while the water absorption by the substrate plays only a minor role. Moist curing is much more effective than sealed curing (e.g. by using sealing agent) for the hydration of the overlay material. The degree of hydration of the overlay material is significantly increased with longer moist curing. Under the same curing condition (e.g. moist curing + drying), thinner overlay materials are more vulnerable to the water loss and exhibit lower degree of hydration. It suggests that for a proper hydration of cement-based overlay material, moist curing is recommended rather than applying a sealing agent.
Key words: Moisture transport, cement-based overlay material, hydration, thickness, curing condition