Cementitious grouts with adapted rheological properties for injection by vacuum techniques

The injection of cementitious-based grouts by vacuum pressure techniques is expected to extract part of the mixing water with direct consequences on the fresh and hardened properties. A research program was undertaken to evaluate the effect of vacuuming on the amount of water extracted along with resulting changes in grout properties including flowability, static yield stress, viscosity, unit weight, Wick-induced bleeding, and compressive strength. Tests were conducted using specimens sampled right after mixing as well as after being subjected to vacuum. Test results have shown that the extraction of water decreases fluidity (i.e., flow time and mini-slump cone) and increases the magnitude of yield stress and viscosity, mostly due to increased internal friction and cohesion within the solid particles. Grouts prepared with low water-to-cementitious materials ratio and containing moderate to high concentrations of viscosity-modifying admixtures yielded adequate water retentivity, with minor variations in rheological and hardened properties.