Introduction

As far as can be seen concrete is likely to continue to be the primary volume construction material for most structural applications and its use is likely to grow in future. Portland cement (PC) and blended Portland cements are currently the only economic binders for concrete that match the performance and durability requirements under the range of conditions to which it is exposed⁽¹⁾.

However, Portland cement (and other cements such as high alumina cement) is based on calcium compounds. It is generally manufactured from a limestone and a clay or shale. In order for the compounds responsible for strength development to be formed the raw materials need to be heated to about 1450oC. It consequently requires a large amount of energy on manufacture and produces large amounts of CO₂ due to energy use and the calcination of CaCO₃ (about 1.2 tonnes of CaCO₃ are required to produce a tonne of Portland cement). Cement manufacture currently accounts for about 5% of totala global CO₂ emissions and 2% of emissions in the UK(2)). Cement manufacture is the third highest source of CO₂ emissions after fossil fuel combustion (which accounts for about 80% of total emissions) and deforestation⁽³⁾. There are also strong economic drivers for reducing energy consumption as fuel and electricity represent about 65-70% of variable costs in Portland cement manufacture⁽⁴⁾.

There have therefore been considerable moves towards reducing the energy requirement and the CO₂ emissions from cement manufacture⁽⁴⁾. There are a number of ways in which this can be done for Portland cement manufacture and use including:

• Increasing the efficiency of the manufacturing process

• Using waste materials and by-products as cement replacements

• Changing the composition of the cement.

These issues are briefly discussed in Section 2.3. Fuel consumption in clinker manufacture in Europe has fallen by about 50% in the last 40 years through process improvements and the European industry as a whole is considered to be extremely energy efficient⁽⁵⁾.

However, the pressure to reduce energy consumption and CO₂ emissions during cement manufacture has also led to the development of novel cements with intrinsically lower energy requirements and CO₂ emissions on manufacture than Portland cements. Such cements are currently attracting a great deal of interest worldwide. A number of different types have been suggested and are at varying stages of development. Of these perhaps the greatest level of interest is being shown in cements which contain a high proportion of the mineral belite, C₂S (an important component of Portland cement, see Box 1), often with an additional reactive component such as calcium sulfoaluminate, C₄A₃ s , included to improve strength development at early agesb.

Although belite cements have attracted a lot of interest they have only been manufactured and used on a large scale in China⁽⁶⁾. About 1 million tonnes per annum are produced (in total) at 15 factories in China. Additional plants are being commissioned and production is expanding. Concretes made with these cements have been used in a wide range of structural and non-structural applications in China including office blocks and fly-overs⁽⁶⁾ and have been reported to perform well. Their use is likely to spread to other countries and they have been manufactured on a significant, but non-commercial scale in Eastern Europe^(7).