Bonded tendons, installed in ducts or voids within the concrete, must be grouted for protection after tensioning. The grouting of tendons tensioned to 80,000 psi or more is a demanding job that requires special skills and materials. Grouts to be pumped into tendon ducts must have special characteristics to match the particular needs of this application. Each of these characteristics is important to the successful performance of the grout.
The grout should be capable of being mixed to a highly fluid consistency so that it can be pumped as much as several hundred feet, vertically or horizontally, penetrating the cable strands and filling all voids as it progressively moves through the duct. The ideal consistency can be described as that of thin, hot tomato soup. A more precise definition is that the grout passes through a flow cone (holding about 1.8 quarts of grout) in approximately 20 seconds (U.S. Army Corps of Engineers Specification CRD-C 611).
Other characteristics include uniformity of manufactured product, bond and density (grout, once in place, must expand), and freedom from segregation or bleeding at any point within the duct. Bleeding is to be avoided because it results in loss of bond to tendon strands; causes voids, or bleeding lenses; results in inadequate protective coverage of the tendons; and offers a possible entry point for aggressive agents later. Some grouts that may not bleed at atmospheric pressure may well bleed when pumped under pressure. Anyone involved in the work of grouting tendons should know the procedures and precautions and should be familiar with the recommended practice of the Post-Tensioning Institute.