Self-flowing underwater concrete mixtures

The placement of conventional concrete mixtures in underwater construction results in a high percentage of material loss owing to washout of cement paste. The current paper presents the influence of antiwashout admixture (AWA) on various properties of concrete. Eleven self-flowing concrete (SFC) mixtures using type II cement were proportioned. A combination of low water–cement (w/c), high cement contents, AWAs, fly ash and silica fume were used to enhance the resistance of fresh concrete to washout. The concrete mixtures were proportioned to be highly flowable, self-levelling and cohesive. The w/c materials ratios ranged between 0·35 and 0·39, which corresponds to a typical underwater concrete mixture. The concrete mixtures were tested for slump, slump flow, washout resistance and compressive strength. The compressive strength of each concrete mixture cast under water was determined at 3, 7 and 28 days and compared with the compressive strength of the same concrete mixture cast under normal conditions (in air). Test results indicated that the use of an AWA facilitates the production of flowable concrete mixtures with the added benefit of lower washout loss. Concrete mixture proportioned using type II cement and fly ash at a 15% level of replacement was found to develop SFC that had better fresh and hardened properties and was more resistant to washout. The self-flowing underwater concretes developed 28-day compressive strengths ranging from 20 to 28 MPa.