Design Methodology and Properties of Concrete Mixes Developed for an Underwater Repair Application

Designing a concrete mix which can be easily placed for underwater construction and repair of marine structures, while meeting strength and durability requirements can be an engineering challenge. This paper presents the design methodology and properties of a concrete mix used for an underwater repair project at a hydropower dam spillway repair located in Western Canada. Small-scale lab trials of different design mixes were initially batched to screen potential mix designs, according to properties including compressive strength, visual index, flow characteristics, and washout resistance. Based on the results, these trials were followed by larger scale mockup trials. These served not only to verify properties determined during the initial lab trials, but also to determine additional properties like abrasion resistance and capacity to bond to the substrate. Thereafter, a design was finalized to be used for on-site repairs. As per lab and mockup test results and observations, it was found that well-graded aggregates, higher paste contents, and optimal use of supplementary cementitious materials, such as silica fume and fly ash lead to high flow and ease of placement. Optimum amounts of high-range superplasticizing admixtures can also enhance the flowability, but excessive amount of superplasticizer can significantly increase bleeding. To enhance the washout resistance, use of an anti-washout admixture (water-soluble polymers with strong absorption capacity) and silica fume is also generally recommended. The type of aggregates used can also affect bleeding and flowability.