Cracking Behavior of Posttensioning Grout with Various Strand-to-Duct Area Ratios

This study investigates the effect of the strand-to-duct area ratio on the shrinkage cracking behavior of posttensioning grout. The free shrinkage behavior of grout was evaluated using various duct diameters. Test results indicated that the expansion and shrinkage strains of grout increased with the duct diameter. The strain of a restrained strand was barely affected by the number of strands but was significantly affected by the strand-to-duct area ratio. The specimen with a strand-to-duct area ratio greater than 0.3 showed shrinkage cracks in fewer than 30 days. Increasing the strand-to-duct area ratio shortened the cracking time. All the test specimens showed bleeding immediately after pumping, along with air void pockets in the grout.