The Study of Bond Strength and Bond Durability of Reactive Powder Concrete

Abstract

This research project aims to use reactive powder concrete, RPC. as a new repair material and evaluate its bond strength and bond durability to existing concrete. One accelerated aging environment, namely a freeze-thaw cycle acceleration deterioration test, was selected for the evaluation of bond durability of the repair materials. Before and after aging, the samples were evaluated by the compressive strength, bond strength (slant shear test), steel pull out strength, and relative dynamic modulus NDT tests. The test results show that the RPC possesses high bond strength, dynamic modulus, and bond durability as compared with other concretes. The adhesion between the RPC and the steel is also much greater than that for the other concretes. It would be interesting to verify the consequences of this improved adhesion in reinforced concrete structures. Test results revealed that RPC was still in good condition after 1000 cycles of freezing and thawing in accordance with ASTM C 666-97. After 1000 cycles, the nonshrinkage high strength mortar showed a reduction in compressive strength, slant shear strength, steel pull out strength, and dynamic modulus by 17, 21, 24, and 25 %, compared with the corresponding values of 6, 7, 5, and 10 %, respectively, for RPC. Specimens of normal strength concrete were used as reference specimens. The 5 cm × 10 cm slant shear cylinders made of normal strength concrete had deteriorated severely after 600–700 freeze-thaw cycles. For the normal strength concrete, the average values of relative dynamic modulus of elasticity based on resonant frequencies after 300 and 600 freeze-thaw cycles were 75 and 55 %, compared with the corresponding values of 96 and 92 %, respectively, for RPC.

A preliminary study of RPC for repair and retrofitting materials

“…The mix design of the regular concrete (RC) with a compressive strength of 30 MPa contains no admixture and yields a slump of 150 mm. The non-shrinkage high strength mortar (HSM), with a ready-mix formula, contains 10% silica fume (Lee et al, 2005).…”

“…Freeze-thaw cycles were applied to the blocks at a rate of one cycle per 185 minutes, in accordance with ASTM C666 (1997), with 1.5 hours of freezing in cold air at -18°C followed by 1.5 hours of thawing in cool air at +4.4°C. The specimens were divided into groups of three, with groups subjected to 0, 300, 600, or 1000 freeze-thaw cycles (Lee et al, 2005).…”

“…The changes of slant shear strength for the different combinations of concretes after freeze-thaw cycling up to 1000 cycles are given in (Lee et al, 2005).…”

Design and field testing of tapered H-shaped Ultra High Performance Concrete piles

“…Also, UHPC samples at the Natural Weathering Exposure Station at Treat Island, Maine, show no significant degradation after over 500 freeze-thaw cycles and 4500 wet-dry cycles in saturated seawater (Vernet 2004). After subjecting UHPC samples to 1000 freeze-thaw cycles, Lee et al (2005) noted that their the relative dynamic modulus reduces to 90 percent. By comparison, typical relative dynamic moduli after 1000 freezethaw cycles for HPC and normal concrete are 78 percent and 39 percent of their initial values, respectively.…”

“…*Superplasticizer is expressed as the weight of the solid fraction; the liquid fraction is included in the water weight. (Compiled based on data provided by Dugat et al 1996, Castellote et al 2003, Droll 2004, de Larrard and Sedran 1994, Lee et al 2005, Blais and Couture 1999, Huh and Byun 2005, Xing et al 2006, Voo et al 2001 The selection of the components of UHPC uses the packing density optimization principle. The mix is also proportioned in such a way that the fine aggregates will be a set of movable inclusions in the matrix, rather than a rigid skeleton.…”