HIGH-PERFORMANCE CEMENT GROUT FOR UNDERWATER CRACK INJECTION

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 fu me cement and microfine cement and a welan gum and a cellulose-based a ntiwashout admixtures were considered in the grout optimization study. The mixtures were tested for fluidity, viscosity, stability, penetrab ility, rate of setting, and strength. This paper presents the results of the laboratory evaluation and field repair, including provisions ad opted for surface preparation, crack sealing and injection, and qualit y control. Test results showed that the use of a microfine cement grou t with water-to-cement ratio of 0.6 and a high-range water reducer dos age of 2% can produce a balance between critical theological and mecha nical properties. Such grout was found to be tolerant to changes in wa ter-to-cement ratio, high-range water reducer content, and temperature . The grout developed bond strength to submerged concrete similar to t hat of a high-quality epoxy resin. Despite the lower injection pressur e 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 significantl y improved following injection with cement-based grout. This was attri buted to the high penetrability of the microfine cement grout. Such qu ality improvement was less pronounced in the case of injection groutin g with epoxy resin.