Up-scaling and mainstreaming sustainable building practices in western China
Up-scaling and mainstreaming sustainable building practices in western China 

Eco-Cement

The cement industry is one of the largest emitters of CO2 emissions, with up to 5% of the world’s total, and requires high amounts of energy in its production. It is also the largest used manufactured material by mass and the second most used substance after water in the world. In addressing this more sustainable cements, which are comparable to the typical used standard, with lower CO2-emissions, have been developed. Further on-going research is also focused on the development of cement that has comparable properties to Portland cement but with lower CO2-emissions and energy consumption.

Eco-Cements for example can be a more sustainable alternative to “normal” cement. These have lower CO2 emissions. Eco-cements also have the benefit that it hardens by sequestering CO2 from the air.

 

 

 

 

 

 

 

 

 

 

 

Net emissions (sequestration) per kg cement

Source: www.tececo.com

Sustainable methods of substituting Portland cement are those of using limestone, granulated blast slags and coal ash fly. Other methods include the use of industrial waste materials like slag and natural hydraulic-setting minerals such as pozzolan as clinker substitutes. These clinker substitutes represent a potential of replacing up to 50% of Portland cement clinker while maintaining similar performance. In some applications, filler contents higher than 50% in the cement can still offer satisfactory performance. The substitution of conventional clinker by up to 40% with more sustainable alternatives could reduce CO2 emissions by up to 400 million tonnes of annually. Eco-Cements although they do have the advantage that they do not need to be calcinated they do need to be activated either by adding Portland cement or so-called geopolymers or alumino silicate-cements.

One drawback at present it that although the sustainable cements do have a comparable strength to Portland cement, there is only limited information concerning other relevant properties, such as the long-term protection of steel against corrosion, porosity and frost resistance. A sustainable use of cement can however be the use of the highest strength concrete grades only where need and lower strength but more economically viable and sustainable cement in other areas.

Optimizing the mix of coarse and fine fractions of particle packing, through for example industrialised prefabrication in a controlled environment, can also reduce the use of Portland cement without the loss of performance. If this is not possible concrete should in any case not be mixed on-site but in its very worst be industrially mixed and delivered on site as needed.

Eco-cements are to date for the most still slightly more expensive than conventional cements. There has even been the case where on the higher end of the scale a CO2-neutral cement developed in Belgium with a 5% per cent higher price has not sold one tonne. Although in many areas the use of eco-cement is not taken up to due to current pricing there is still a huge potential for this. A careful life-cycle analysis in the planning phase is however recommended. It is expected as with all innovative materials and technologies that this price will come down drastically with market uptake.

In comparison to conventional cement such as Portland cement Eco-cement has the benefit that it is fully recyclable.

For more good practice examples download our Training Handbook: Sustainable Construction.