High-performance cement grout for underwater crack injection

Abstract

An investigation was carried out to compare the performance of cement and epoxy resin grouts used for the underwater crack injection of four damaged concrete bridge pier shafts and footings. A blended silica fume cement and microfine cement and a welan gum and a cellulose-based antiwashout admixtures were considered in the grout optimization study. The mixtures were tested for fluidity, viscosity, stability, penetrability, rate of setting, and strength. This paper presents the results of the laboratory evaluation and field repair, including provisions adopted for surface preparation, crack sealing and injection, and quality control. Test results showed that the use of a microfine cement grout with water-to-cement ratio of 0.6 and a high-range water reducer dosage of 2% can produce a balance between critical rheological and mechanical properties. Such grout was found to be tolerant to changes in water-to-cement ratio, high-range water reducer content, and temperature. The grout developed bond strength to submerged concrete similar to that of a high-quality epoxy resin. Despite the lower injection pressure used for the less viscous cement-based grout, the grout intake was 2.8 times greater per linear meter of surface crack than that observed for the epoxy resin grout. The use of sonic tomography to reconstitute the spatial distribution of stress wave velocities within the massive pier footings indicated that the quality of concrete was significantly improved following injection with cement-based grout. This was attributed to the high penetrability of the microfine cement grout. Such quality improvement was less pronounced in the case of injection grouting with epoxy resin. Resume : Une Otude a OtO entreprise afin de comparer la performance des coulis ‡ base de ciment et ‡ base de rOsine-Opoxie utilisOs pour liinjection sous lieau des fissures dans le fst et liempattement de quatre piliers de pont. Un ciment avec fumOe de silice, un ciment microfin, une gomme welan et un autre agent anti-lessivage ‡ base de cellulose ont OtO considOrOs dans lioptimisation du coulis. Les mOlanges ont OtO testOs pour leur fluiditO, viscositO, stabilitO, pOnOtrabilitO, taux de prise, et