Comparative Study of the Performance of Underwater Concrete between Anionic and Nonionic Anti-Washout Admixtures

An investigation was carried out to study the influence of two types of anti-washout admixtures (AWAs) on the performance of underwater concrete, specifically, workability and washout resistance. The tested AWAs were hydroxypropyl methylcellulose (HPMC) and polyacrylamide (PAM) as nonionic AWAs and carboxymethyl starch (CMS) and polyanionic cellulose (PAC) as anionic AWAs. Rheological properties (slump and slump flow), washout resistance, and compressive strength were measured to evaluate the properties of the fresh and hardened concrete. The results indicate that anionic AWAs are more effective at improving workability and strength than nonionic AWAs in anti-washout underwater concrete. When the nonionic AWA dosage exceeded 0.3% (W/C = 0.45), the fluidity and air content were negatively impacted. Additionally, nonionic AWAs more readily alter the morphological structure of cement paste, affecting cement particle hydration and underwater concrete properties. Regarding the mechanical properties, compared with those of concrete without AWAs and with nonionic AWAs, the 28-day compressive strength of concrete with anionic AWAs reached 37 MPa, an increase of 151% and 131%, respectively. Compared with nonionic AWAs, concrete with anionic AWAs is more stable.