There are a number of reasons for the exceptional “green” characteristics of Rapid Set® cement and concrete. In the case of cement production practice, the emissions of carbon dioxide gas result from two aspects of the high-temperature manufacturing process.
First, in the cement kiln, the raw materials (limestone, clay, etc.) decompose, releasing large amounts of CO2.
Second, the combustion of fuel (generally coal) with air in a cement kiln, also releases carbon dioxide, much the same as carbon dioxide gas is emitted from the exhaust pipe of a vehicle that is burning gasoline or diesel fuel.
In the case of portland cement, approximately 40% of emitted CO2 results from the burning of the fuel in a kiln, and 60% comes from the decarbonation of the limestone.[ii] A recent estimate for carbon dioxide emissions for portland cement production is 0.9 pounds of CO2 per pound of ground portland cement.[iii]
An analysis of Rapid Set® manufacturing raw materials composition, pyroprocessing techniques, and cement grinding has established a baseline emission rate of 0.61 pounds of CO2 per pound of Rapid Set® cement produced, broken down as follows:[iv]
Only 0.21 pounds of CO2 per pound of cement from fuel (coal) combustion because its burning temperature is approximately 220°C lower than that of portland processes.
Only 0.40 pounds of CO2 per pound of cement from thermal decarbonation of calcium carbonate (limestone).
Rapid Set® also reduces the impact of cement production on the environment:
- The reduced burning zone temperature needed to form Rapid Set® clinker has the additional advantage of producing lesser amounts of smog-producing oxides of nitrogen.
- The softer and more friable nature of Rapid Set® clinker also lends itself to much easier grinding and a lower grinding mill energy consumption.
- Hardened Rapid Set® concrete is much more durable than portland cement concrete, and has a particularly greater resistance to sulfate or other types of chemical attack. Due to its very rapid strength producing ettringite formation, lower porosity, and subsequent internal self-desiccation, Rapid Set® is extremely impervious to carbonation, freeze-thaw susceptibility, and acid rain leaching. Thus, it has a proven record of field performance that exceeds the normal useful life span of portland cement concrete.
- A number of recycled products, such as waste calcium sulfate from chemical plants and recycled aluminum products (up to 20% by weight of the raw materials) enter into its composition. This improves the sustainability of the cement.
- Rapid Set® cement and concrete provides lower emission of green house gases, lower emissions of smog-producing nitrogen oxides, increased lifespan leading to lower frequency of repairs or replacement, and improved sustainability through the use of recycled raw materials.
[i] Klemm Report 2008
[ii] Green in Practice: Technical Brief 102, 2008 PCA Publication, http://www.concretethinker.com/papers.aspx?DocID=312
[iii] Manufacturing Fact Sheet, 2008 PCA Briefing Kit Publication, http://www.cement.org/Briefingkit/manu_facts.asp