Effect of Micronano Bubble Water as Mixing Water on the Application Performance and Impermeability of Shotcrete

Abstract

Sprayed concrete (shotcrete) is extensively employed in underground spaces, tunnels, structural repairs, and foundation support. Micronano bubble water (MW), a form of activated water with diverse applications, to our best knowledge has received limited scholarly attention regarding its impact on sprayed concrete. This study investigates the performance of sprayed concrete mixed with either sodium metaaluminate alkali accelerator (AR) or aluminum sulfate alkali-free accelerator (AS), using MW as the mixing water. Results demonstrate that MW accelerates the setting of sprayed concrete and reduces rebound (shotcrete falling off). At low accelerator dosages, ASN-5 (5% AS, MW) shortened initial and final setting times by 12 and 16 s, respectively, compared to ASP-5 (5% AS, tap water). Similarly, ARN-3 (3% AR, MW) reduced initial and final setting times by 18 and 65 s, respectively, relative to ARP-3 (3% AR, tap water). Further, MW enhances early-age and long-term strength, with a particularly significant improvement in early strength. Compared to ARP-4, ARN-4 exhibited a 19.6% increase in one-day compressive strength and a 9.1% increase in flexural strength. Similarly, ASN-7 showed an 18.6% increase in one-day compressive strength and a 14.3% increase in flexural strength compared to ASP-7. MW also reduces water absorption and permeability while improving chloride ion ( Cl − ) resistance (ASN-7 decreased 14.9% at 90 days). Ultrasonic pulse velocity measurements increased consistently with test age and correlated well with strength development. Analysis indicates that MW refines the pore structure and improves the microstructure of sprayed concrete, contributing to enhanced durability. Specifically, MW yields a denser 28 day concrete structure, increases the quantity and volume of calcium silicate hydrate, and reduces structural defects. In summary, utilizing MW in sprayed concrete construction reduces rebound, enhances early strength, and improves long-term durability. This study offers a practical reference for the combined application of MW with AS and AR accelerators and makes up for the shortcomings and existing problems of the application of MW in sprayed concrete based on accelerator level, particularly for AR that exhibits low long-term strength.