We suspect that some of the ducts in a posttensioned floor did not get completely filled with grout. Is this a serious matter?
It could become serious. The purpose of the grout is twofold. One is to provide efficient bond between the prestressing steel and the floor and thus control the spacing of cracks in case of overload. The other is to prevent corrosion of the reinforcing steel. To satisfy either purpose the void space within the duct must be completely filled. Ducts should be provided with grout injection points in both end anchorages and there should be no sudden changes in alignment of the ducts. Vents should be provided no more than 50 feet apart to allow escape of air for free flow of grout. If there is reason to think that the ducts are not completely full the floor should be checked by qualified consultants to determine how serious the problem is and what remedial treatment may be needed.