Abstract
The objective of the mixture design described herein was to achieve a concrete with very high compressive strength, toughness, and excellent durability (resistant to freezing and thawing), but with minimum heat-treating temperature, presetting pressure, and carbon fiber content. The concrete was required to create a non-metallic prestressing anchorage of a size and weight similar to a standard steel anchorage for use with carbon fiber reinforced polymer (CFRP) tendons. Variations in mixture design were implemented to reach optimal values for the following parameters: • High modulus and strength carbon fibers; • Carbon fiber content; • Presetting pressure; • Heat-treating temperature; and • Curing process. Tests were performed on cylindrical specimens (50 mm [2 in.] diameter by 100 mm [4 in.] long) cast in a specially designed steel mold. A mixture design and post-casting treatment process was developed that gave compressive strengths in the order of 500 MPa (73 ksi) in 7 days. Different mixtures of reactive powder concrete (RPC) were prepared (plain and fiber reinforced) with a water-cement ratio (w/c) of 0.13. Durability was assessed through freezing-and-thawing tests. Precracked specimens were used to investigate how RPC performs if water enters a crack and freezes, because in the past, freezing-and-thawing durability tests have been performed on uncracked RPC specimens. Specimens for these tests were 279 x 279 mm (11 x 11 in.) in cross section and 406 mm (16 in.) long. Durability proved excellent with no sign of damage up to 600 ASTM C 666 cycles for some specimens. Cylinders were also cast and cured for 14 days to determine compressive strength. Finally, fracture parameters of RPC were investigated for plain and carbon fiber-reinforced RPC (CFRRPC), notched and unnotched specimens, using a four-point bending test. Notched specimen tests included measurement of the crack mouth opening displacement (CMOD).