Some prestressed concrete girders will have an architectural sandblasted finish. For this reason they will be made from a gap-graded mix. What will this mix design do to the prestress loss from creep and shrinkage of the prestressed girders?
For the same cement content and the same maximum size of coarse aggregate, gap-graded concrete is always stronger in compressive strength and higher in modulus of elasticity and rigidity than continuously graded concrete. Thus, it suffers much less creep under sustained loading and has better creep recovery following removal of load. For these reasons and because of its low drying shrinkage, prestress losses are reduced to a minimum. Gap-graded concrete is a much better material in both pretensioned and post-tensioned concrete construction than continuously graded concrete.