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longer-lasting repairs, especially considering the extreme freezing-and-thawing environment. For a number of reasons, Béton projeté MAH Inc. elected to use the dry-mix process over wet- mix shotcrete. The dry-mix process allowed them the ability to start and stop without having to clean out hoses. The challenges associated with the placement of shotcrete on the water (primarily lighter-weight hoses and longer conveying dis- tances) were also better addressed using the dry-mix process. Easier access to the shotcrete material, through the use of 2200 lb (1000 kg) bulk tote bags, was another key benefit of the dry process. And in addition to the logistical benefits such as easier material handling, prepackaged materials provided much improved consistency, which resulted in higher levels of quality control. Materials engineers from King Shotcrete Solu- tions (the material supplier) designed a mixture Fig. 2: Mobile hydrodemolition rig that would provide reduced shrinkage and long- term durability. Silica fume provided a denser matrix and improved adhesion and cohesion during placement. The use of powdered air- entraining admixtures provided optimal spacing factor and air void system to improve durability. The use of micro-synthetic fibers helped reduce the potential for shrinkage cracking, which also added to the long-term durability of the repairs. Béton projeté MAH Inc. was awarded the subcontract to complete the shotcrete placement and finishing. They have over 120 years of com- bined shotcrete experience in all aspects of shot- crete placement (repair, new construction, and Fig. 3: Surface preparation, hydrodemolition rig artistic work). BBMarine retained the responsi- bility for all other logistics, concrete removal, surface preparation, and so on. Repair Process For the shotcrete process to work, BBMarine worked closely with the shotcrete subcontractor to develop a planned procedure for surface prepara- tion, shotcrete placement, and shotcrete finishing. The key challenge was access to the repair areas located below the waterline. BBMarine relied on their extensive experience working in marine envi- ronments to design a special mobile cofferdam system that would allow them to move the unit Fig. 4: Area ready for shotcrete along the 0.6 mile (1 km) reservoir (basin wall). All surface areas to receive the shotcrete were prepared x 4 ft high x 4 ft deep (5.2 x 1.2 x 1.2 m) and were using the hydrodemolition method (Fig. 2 and 3). temporarily anchored to the concrete wall of the A special hydro rig was set up on a floatable barge, reservoir basin (Fig. 4 to 6). The area of contact which allowed the crew to complete the concrete between the mobile cofferdam and the surface of removals using a 20,000 psi (140 MPa) water blast. the concrete was sealed to prevent water from The barge that hosted the hydrodemolition rig was reentering the cofferdam. Gas-powered dewa- set up ahead of the shotcrete barge and moved along tering pumps were then used to remove the water the reservoir basin wall so that the repair area was from inside the cofferdam system and allow prepared before the arrival of the shotcrete barge. access for the removal crew and the shotcrete Both mobile cofferdam systems were set up crew. The shotcrete crew was provided with a to allow a work area of approximately 17 ft long wooden platform system, set up behind the cof- Shotcrete • Winter 2015 37


2015WinterShotcreteEMag
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