The improvement of freezing–thawing resistance of concrete by cellulose/polyvinyl alcohol hydrogel

• Cellulose/PVA hydrogel retain compressive strength of concrete after frost action effectively. • Hydrogel optimizes the microstructure of paste during freezing and thawing cycle. • Hydrogel can prevent the crack propagation and reduce coarse pores after frost action. • Freezing-thawing enhances the molecular binding. Reducing the free water and releasing the expansion stress is the crucial to improve the freeze–thaw resistance ability of concrete especially in cold region. This paper presented an innovative approach to fix the free water of concrete in an eco-friendly polymer during its cross-linking process under freeze and thaw cycling. The modification mechanism was evaluated by determining the morphology of polymer and the three-dimensional pore structure of hardened cement paste. Results show that the incorporation of cellulose/PVA hydrogel is able to retain the compressive strength after 20 cycles of freeze–thaw attack. Cellulose/PVA solution could promote the early hydration of cement, but exerts limit effect on the composition of hydration products. The network of cellulose/PVA hydrogel after cycling of freeze–thaw presented a multiscale pore structure, which could eliminate the osmotic and expansion pressure. The addition of hydrogel is able to prevent fracture propagation in hardened cement paste caused by freeze–thaw attack.