Study on frost resistance of shotcrete by micro-nano bubble water and admixture

Shotcrete was prepared by using micro-nano bubble water as mixing concrete water in cooperation with air-entraining agent (AOS-R) and superabsorbent polymer (SAP), and its frost resistance performance was experimentally studied. The results show that the incorporation of AOS-R and SAP will reduce the 28-day strength of concrete, but MNBW can compensate for the strength loss to a certain extent. The frost resistance of concrete mixed with alkali accelerators is inferior to that of concrete mixed with the alkali-free accelerator. The incorporation of AOS-R or SAP into shotcrete can improve its frost resistance to in some degree as well. Given the frost resistance of concrete mixed with SAP is not as effective as AOS-R, MNBW can play a synergistic effect to improve the frost resistance of concrete. The main reason why the AOS-R improves the frost resistance of concrete is that it generates a large number of small bubbles to isolate the water transmission channel which manage to relieve the crystallization pressure of water. MNBW improves the frost resistance of concrete, because it refines the pore structure and increases the density of concrete.