Precast Solutions - September/October 2008 - (Page 21) equipment, the average precast plant could dramatically reduce both operating costs and mitigate negative environmental effects associated with production. Robert Niven, President and CEO of Carbon Sense Solutions, Inc. has developed a bolt-on retrofit system to existing or new precast concrete equipment that uses combustion exhaust gases and mixes them with concrete during the concrete curing process to trigger a chemical reaction within the mixture. The reverse limestone calcination reaction in this mineral carbonization system uses captured carbon dioxide, the GHG (CO2) emission from on-site combustion equipment, to create limestone within the concrete during curing. To use the analogy of a sponge (for curing concrete), the calcium carbonate (limestone) produced in the reaction is deposited throughout the empty voids of the sponge (concrete), thereby reducing permeability and increasing strength by way of the Apollonian packing principle. • Bolt-on technology works with existing or new equipment • Exclusive licensing creates a "green" product distinction in a commodity market SCRUBBING WITH CONCRETE “Our process provides long-term concrete strength by accelerating early strength development," Niven explained. "It usually takes up to 28 days to reach the same strength rating that the carbonation process can provide in just a day. In the spirit of industrial symbiosis, we consume an industrial waste product (CO2-rich CARBON CAPTURE CAN REPLACE The process promises to offer the precast concrete industry a new and valuable greenhouse gas mitigation tool with added material property and production improvements. – Bill Dooley combustion gases) to provide a value-added product that is simple enough to deploy across the world." The process makes the concrete act as a scrubber. The process does require minor changes to the concrete mix design and manufacturing process. The retrofit developed by Carbon Sense Solutions can cost about $100,000, depending on the facility and a precast plant would likely realize a return on investment within six months, according to Niven. The retrofit is straightforward, made of components easily found anywhere. "We wanted the process to be flexible and inexpensive – applicable globally – so it could be used widely," said Niven. STEAM CURING Not only might precast production facilities reduce their GHG emissions and thereby their carbon footprint, producers might also realize significant energy savings. Furthermore, in addition to the green advantage of reducing GHGs, the CCS process shortens concrete cure time, improves efflorescence and results in a more impermeable product with a longer service life. Essentially, this process may eliminate the need for heat or steam-accelerated curing at some facilities altogether, substituting instead a chemical reaction between carbon dioxide and calcium-containing elements found in concrete [where calcium oxide or CaO = C, and silica dioxide or SiO2 = S, C2S (alite) and C3S (belite)]. Essentially, this process permanently locks the CO2 from plant-generated CO2 into the concrete matrix. Briefly, potential benefits to precast operations from the CCS process include: • Energy savings of 44 percent • Water savings of 39 percent • Superior products: 28-day concrete compressive strength in one hour; improved concrete impermeability and negligible shrinkage cracking • "Green" process enhanced with steel slag aggregate (water and heat the only by-products) CCS PILOT PROJECT RECEIVES SUPPORT A multi-phase pilot study will begin in eastern Canada this winter. Some opportunities still exist for new project partners to contribute to the project. Most of Niven's testing to date has been on precast concrete pavers. The first industrial pilot will involve a small-scale demonstration on a variety of dry- and wet-cast products. The second phase of testing will include a mock-up for large precast concrete product elements during full SEPTEMBER/OCTOBER 2008 | PRECAST SOLUTIONS 21
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