ABSTRACT
However now we need to know if blended cements can be used in conditions of sulfate exposure and it becomes clear that the test methods established for Portland cement cannot be easily generalised to determine criteria for sulfate resistance of blended cements. Worse, when sulfate resisting cements with an excellent track record of performance in the face of exposure to sulfates are tested according to common tests, they often fail the acceptance criteria. Some other questions which arise are:
• High levels of slag addition are known to give good sulfate resisting blends, but what is the threshold
1 INTRODUCTION
Cementitious materials are the most used materials in the world, with more than one cubic metre of concrete being produced per person per year. It is a material of low environmental impact; the raw materials for fabrication are widely available; it is very flexible for fabrication on site and provides a strong durable material contributing to lower energy consumption of buildings in use. However, due to the huge volumes produced every year, sustainability is a big and growing issue. Since the turn of the century the production of cement has increased by about 50%, driven mainly by the growth in China. Forecasts indicate that the demand for cement will double or treble by 2050. It is estimated that cement production currently accounts for about 5% of man-made CO
even to maintain current levels of GHG emissions it would be necessary to reduce the CO
tonne by half to two thirds. About half the CO
tion are due to the decomposition of CaCO 3 to CaO
as the first step in formation of the clinker phases. Therefore improving sustainability will almost certainly lead to changes in chemistry, for which the implications on durability are unknown.
