Form pressure characteristics of self-consolidating concrete used in repair

Author(s):  
Joseph J. Assaad ◽  
Kamal H. Khayat
Author(s):  
H. Celik Ozyildirim ◽  
Stephen R. Sharp

Historically, the Virginia Department of Transportation (VDOT) has repaired chloride-contaminated reinforced concrete bridge substructure elements that contain vertical and overhead sections with either shotcrete or a conventional A3 (3,000 psi) or A4 (4,000 psi) concrete. This study investigated using self-consolidating concrete (SCC), which has a high flow rate, bonds well, has low permeability, and provides smooth surfaces, as another option. The study also explored the use of galvanic anodes to control corrosion activity in SCC repairs. In VDOT’s Lynchburg and Staunton Districts, SCC repairs were made with and without the use of galvanic anodes. This provided a means for determining the benefit of using the anodes. The needed repair areas were determined by visual observation and sounding. After 7 years of service, SCC repair areas with and without anodes did not exhibit corrosion activity; small vertical cracks were evident in the SCC but did not affect performance. The anodes can provide protection to the steel immediately adjacent to the repair areas. However, unrepaired concrete areas away from the patched area with anodes now require additional repairs. SCC can be successfully placed; however, attention should be paid to form pressure and slump loss. Selection of repair areas should be based on corrosion-related measurements such as half-cell or chloride content, rather than sounding. Progression of corrosion demonstrates the necessity of removing all chloride-contaminated concrete not just adjacent to, but also away from the reinforcement, as anodes in the repair area will provide protection only in a narrow area around the patch.


2010 ◽  
Vol 168-170 ◽  
pp. 1991-1998
Author(s):  
Wu Jian Long ◽  
Guillaume Lemieux ◽  
Kamal Henri Khayat ◽  
Feng Xing

Some precast, prestressed beams can reach heights of 2.4 m or more necessitating special considerations for lateral pressure to ensure formwork tightness. In order to investigate the initial form pressure of the precast, prestressed self-consolidating concrete (SCC), an experimental program was undertaken. Sixteen non air-entrained and four air-entrained SCC mixtures with a slump flow of 680 ± 20 mm were evaluated. These mixtures were made with 440 to 500 kg/m3 of binder, Type MS cement or HE cement and 20% Class F fly ash, 0.34 to 0.40 water-cementitious material ratio (w/cm), viscosity modifying admixture (VMA) content of 0 to 100 mL/100 kg of binder, and 0.46 to 0.54 sand-to-total aggregate (S/A) volume ratio. Two high-performance concrete (HPC) mixtures with 0.34 and 0.38 w/cm and slump of 150 mm were also investigated. Moreover, decay in lateral pressure with time was also determined in order to evaluate the rate of pressure drop and the time required for pressure cancellation. Test results indicated that SCC proportioned with higher binder content developed higher relative initial pressure for the 2.0-m deep section. For a given binder content, the more viscous mixtures made with 0.34 w/cm exhibited lower relative initial pressure and longer duration before pressure cancellation. It is worthy to note that air-entrained SCC exhibited higher initial pressure. Finally, a good correlation was established between the final setting time and pressure cancellation time.


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