Pullout Resistance of Reinforcement of Lightweight Cellular Concrete Fill

Abstract

C2169Lightweight Cellular Concrete (LCC) (also called foam or gas concrete) is a special construction material, which is typically composed of portland cement, water, and air voids created by a foaming agent. This material has been increasingly used as a backfill material for geotechnical applications. This report presents a series of laboratory tests conducted to evaluate the material properties of LCC including density, permeability, compressive strength, shear strength, compressibility, elastic modulus, and Poisson\u2019s ratio with different cement to fly ash ratios and at different ages. LCC specimens used in this research project were cast in the field, and the cement to fly ash ratios used for the production of the specimens ranged from 50:50 to 100:0. Large direct shear box tests were conducted on prismatic specimens with a size of 12 inches long, 12 inches wide, and 8 inches high, while small direct shear box tests were conducted on cylindrical specimens with a size of 2.5 inches in diameter and 1 inch high. This report also presents a series of pullout tests conducted in the laboratory to investigate pullout resistance of extensible reinforcement (geogrid) and inextensible reinforcement (steel strip) embedded in LCC. Pullout displacements and pullout forces were monitored using linear variable displacement transducers (LVDT) and a load cell during the pullout process. This research project investigated the effects of age, normal stress, LCC type, cold joint, and re-pullout on pullout resistance and calculated the pullout resistance factors F* for geogrid and steel strip embedded in LCC. The laboratory material test results show that the average wet densities of LCC ranged from 30 to 36 pcf at the age of 28 days and the average dry densities ranged from 21 to 24 pcf at the same age. The permeability values of LCC ranged from 2.1 710-5 to 3.0 710-4 in./s and they increased as the cement to fly ash ratio increased. The measured cohesion values of LCC in large direct shear box tests ranged from 33 to 50 psi, while the measured cohesion values in small direct shear box tests ranged from 19 to 37 psi. This report also compares the material properties of LCC measured in this research project with those reported in the literature and shows overall good agreement. The laboratory pullout test results show that for the geogrid embedded in LCC, the maximum pullout force increased as the normal stress increased. For the steel strip embedded in LCC, the maximum pullout force was independent of the normal stress and increased as the age and the cement to fly ash ratio increased. Pullout test results also show that the presence of a cold joint did not reduce the pullout resistance, while the re-pullout test had lower pullout resistance as compared with the original pullout test for the same specimen. The pullout resistance factors F* for steel strips were greater than those for geogrids and these factors decreased as the normal stress increased