3348Seven-wire Strand for Prestressed Concrete

3348.1SCOPE

Provide the MnDOT Grade 300 seven-wire, uncoated, low-relaxation steel strand for prestressed concrete beam construction.

3348.2REQUIREMENTS

Provide MnDOT Grade 300 steel strands meeting the requirements of ASTM A416, Standard Specification for Low-Relaxation, Seven-Wire Steel Strand for Prestressed Concrete with an ultimate tensile strength of 300,000 psi, based on the nominal area of the strand, except as detailed below:

A Mechanical Requirements Conduct tests for mechanical properties in accordance with the test methods of ASTM A1061, Standard Test Methods for Testing Multi-Wire Steel Prestressing Strand. Ensure the breaking strength of the finished strand conforms to the requirements prescribed in Table 3348.2-1. Table 3348.2-1 Breaking Strength Requirements Nominal Diameter of Strand, inches Minimum Breaking Strength of Strand, lbf Steel Area of Strand, sq. inches Weight of Strand pounds/1000 ft 0.600 65100 0.217 740 Measure yield strength in pounds at 1.0 percent extension under load. Ensure the minimum yield strength is at least 90 percent of the breaking strength listed in Table 3348.2-1. Initial loads for the test and minimum yield strengths are listed in Table 3348.2-2. Table 3348.2-2 Yield Strength Requirements Nominal Diameter of Strand, inches Initial Load, lbf Minimum Load at 1.0 Percent Extension, lbf 0.600 6510 58590 B Dimensions and Permissible Variations Express the size of the finished strand as the nominal diameter of the strand in inches. Ensure the diameter of the center wire of any strand is larger than the diameter of any outer wire, in accordance with Table 3348.2-3. Table 3348.2-3 Diameter Relation Between Center and Outer Wires Nominal Diameter of Strand, inches Minimum Difference Between Center Wire Diameter and Diameter of Any Outer Wire, inches 0.600 0.004 Ensure the MnDOT Grade 300 strand conforms to a size tolerance of +0.026, - 0.006 inches from the nominal diameter measured across the crowns of the wires

3348.3SAMPLING AND TESTING

Submit two copies of the mill certificate, two copies of the stress -strain curve representing the lot, and steel strand samples to the Engineer. Provide mill certifications with bond strength test results representative of the current year’s production, showing that the manufacturing process produces strand with a bond strength of at least 36,000 psi at a measured free end slip no greater than 3/32 inch. Ensure a qualified independent testing laboratory performs or certifies bond strength tests. Perform bond strength tests on an embedment length of 18 inches in accordance with standard test procedures on file in the Department’s Office of Materials.