Study on water absorption of cement-based materials containing water repellent by using low-field nuclear magnetic resonance

Abstract Water absorption and aggressive ions play a fundamental role in estimating the chemical and physical degradation of cement-based materials’ structure, leading to a decline in durability and lifespan. Water absorption by cement-based structures is accompanied by a subsequent reconfiguration of nano-scale porosity, resulting in water entrapment. Therefore, limiting water absorption by using water-repellent admixtures as an integral hydrophobic modifier during the mixing process of fresh cement paste is needed. Additionally, the low-field nuclear magnetic resonance (LF-NMR) technique was employed to characterize the water absorption of cement paste containing water-repellent admixtures and integral hydrophobicity. Cement pastes with 0-3% dosages of Isobutyltriethoxysilane (IS) were prepared. The effect of IS on transverse relaxation time (T 2 ), pore size distribution variations, pore structure development, and total peak area by LF-NMR of cement paste during the water absorption process from 0 to 72 hours were measured. The results indicate that the intensity signal of T 2 distribution and the amount of water in capillary pores of control cement paste (CP) sharply increased during the absorption process. Furthermore, the CP exhibited the highest absorption rate during the immersion process. The cement paste incorporated with IS signals the intensity of T 2 distribution and the water in capillary pores is significantly reduced. The IS specimens showed the lowest absorption rate and the amount of water in capillary pores was reduced. The addition of IS admixtures exhibited high efficiency in resisting capillary water absorption, which could have numerous applications in protecting concrete structures in coastal areas, including coastal architecture, sea bridges, flood control dams, and ports.