Low carbon concrete has attracted significant attention due to the amount of CO2 that traditional concrete emits. It is demonstrated that, cement have biggest contribution in CO2 emission by 75% of total CO2 emits by concrete, and aggregate is the next great contributor by less than 20%. CO2 emitted by aggregate is mainly due to electricity and to less extend because of excavation, hauling, blasting, and transportation.
Researchers have made numerous attempts so as to produce concrete with lowest possible CO2 emissions. Not only does this make concrete more environmentally friendly but also make structures to meet requirements with regard to environmental specifications.
Production of low carbon concrete starts from quarry of raw materials to produce cement and production of concrete. There are certain techniques by which certain quantity of carbon emissions can be reduced for example the use of cement replacement materials like fly ash, silica fume, and ground granulated blast furnace slag.
Use of Supplementary Cementitious Materials
It is reported that, CO2 emitted by typical normal strength concrete mixes using Portland cement as the only binder ranges between 0.29 and 0.32 t CO2-e/m3.
Quantity of Emitted CO2 is declined substantially when certain percentage of cement is replaced by cementitious materials such as ground granulated blast furnace slag (GGBFS), fly ash (FA), and silica fume (SF).
It is demonstrated that, the influence of cement replacement materials soars up to approximately 15–20%, beyond which the rate of decrease gradually slowed.
GGBFS is found to be capable of decreasing concrete CO2 emissions by 22% in typical concrete mixes. Fly ash is found to be capable of reducing concrete CO2 emissions by 13–15% in typical concrete mixes.
Concrete Curing with Carbon Dioxide
Carbon dioxide can be used to decline detrimental environmental impact of concrete. Carbon dioxide used to activate early strength, at the same time sequester CO2 in concrete.The carbonation reaction between carbon dioxide and appropriate calcium Compounds results in permanent fixation of the carbon dioxide in a thermodynamically stable calcium carbonate.
It is claimed that, recycling construction wastes and rubbles could decline CO2 emission by nearly 6%. Added to that, reusing resources and importing regional materials decline CO2 emissions by around 3%.
Use of Highly Reactive Cement and superplasticizers
It is proven that, significant quantity of CO2 is released during cement production. So, it is highly significant to reduce CO2 emission at this stage. The use of superplasticizers and highly reactive cements as well as an optimization of particle-size distribution and reduction in water content permits a considerable reduction in Portland cement clinker in the cement and concrete.
Moreover, it is important to add suitable quantity of mineral fillers such as limestone power to provide an optimal paste volume. Additionally, the already practicable substitution of secondary raw materials like fly ash or furnace slag for cement clinker is suitable choice.
Finally, it is reported that, the use of highly reactive cement and superplasticizers can reduce CO2 release by up to 35%. This reduction rises to 60% when granulated blast furnace slag is used in combination with highly reactive cement and superplasticizer.
Advantages of Low Carbon Concrete
- Carbon emission reduction up to 75% in comparison to conventional products Accelerated early strength.
- Improved durability due to the formation of nano-CaCO3 crystals.
- Low cement and low embodied energy.
- Steam can be replaced by carbon dioxide.