Compressive Strength Variability Limits of High-Strength Cementitious Grouts

The quality of grout becomes more important as many projects utilize precast concrete elements and systems to accelerate the delivery of a project. Also, the use of high-strength grout materials increases to properly connect high-strength concrete members. In the present study, two high-strength, cementitious grout materials were tested for their compressive strength to estimate a coefficient of variation (cv), to investigate effects due to curing condition and initial curing time, and to evaluate the strength ratio between cube and cylinder specimens. The 28-day strength of tested grouts reached more than 62.1 MPa (9,000 psi). The estimated cv was 2.3 %, which was slightly higher than the value of 2.1 % used in ASTM C109, Standard Test Method for Compressive Strength of Hydraulic Cement Mortars (Using 2-in. or [50 mm] Cube Specimens). Based on the estimated cv, the variability limits of compressive strength in ASTM C109 can be 9.5 % (from 8.7 %) for three cubes and 8.4 % (from 7.6 %) for two cubes. There was not a substantial difference in compressive strength between water-cured and moist-cured cubes. Also, the difference of compressive strength is minimal between cubes initially cured for 24 hours and 48 hours before demolding. The compressive strength ratio of ϕ100 mm × 200 mm cylinder specimens to 50 mm cube specimens was between 0.78 and 0.90 for different test ages. The mean ratio was 0.83. These observations can help engineers and practitioners to use ASTM C109 and ASTM C1107, Standard Specification for Packaged Dry, Hydraulic-Cement Grout (Nonshrink), with more confidence when they test high-strength, cementitious grout materials.