704— Prestressed Concrete

700-76 Section 704 — Prestressed Concrete

704.1 Description 1 Furnish and place materials for pretensioning or post -tensioning concrete members. 704.2 Materials 704.2.1 Concrete 1 Provide concrete for prestressed members using the specified concrete strength. If a 28- day compressive strength of 5000 psi is specified, use a mix meeting Class 5000 as specified in Subsection 701.2.12.2. Ensure that prestressed concrete conforms to Section 701, except for the following modifications: • Use Aggregate No. 56, No. 57, No. 67, No. 78, or No. 789 as coarse aggregate. • The coarse/fine aggregate percentage ratio must be between 55%/45% and 65%/35%. • Use marine limestone coarse aggregate and/or fine aggregate in prestressed concrete only if the total water soluble content of the combined coarse and fine aggregate, when tested according to ASTM C1524, is below 100 ppm. • Do not use slag material as a coarse aggregate. • The maximum water -cementitious material ratio for prestressed concrete with 28- day compressive strength greater than 5000 psi is 0.38. • Submit concrete mix designs to the SME for review. The mix design must designate the design 28- day strength of the mix. Any mix showing a pattern of failure to meet the design 28- day strength will require a re-design of the mix. 704.2.2 Prestressing Strands 1 Provide prestressing strands of either high- tensile -strength steel wire, high-tensile- strength seven -wire strand, or high tensile- strength alloy bars , as specified. Assign a LOT number to all wire, strand, or bars and tag for identification purposes before shipment. Similarly, identify all anchorage assemblies. Store prestressing tendon material off the ground and protect from the weather using a building or other accepted cover. Do not use any prestressing strands with loose scaling rust or pitting.