SCIENTIFIC AND SOCIETAL ISSUES INVOLVED IN DEVELOPING SUSTAINABLE CEMENTS

This paper discusses the practicality of replacing Portland cements with alternative hydraulic cements that could result in lower total CO₂ emissions per unit volume of concrete of equivalent performance. Currently, the cement industry is responding rapidly to the perceived societal need for reduced CO₂ emissions by increasing the production of blended Portland cements, using supplementary cementitious materials that are principally derived from industrial by-products such as blast-furnace slags and coal-combustion fly ashes. However, the supplies of such by-products of suitable quality are limited, so more radical solutions to the CO₂ emissions problem may ultimately be needed. In this paper, we show that the most promising alternative systems currently appear to be those based at least in part on calcium sulfates, the availability of which is increasing due to the widespread implementation of sulfur dioxide emission controls. These include calcium sulfoaluminate-based cements, especially those that can be made from relatively common raw materials. They also include cementing systems that make better use of the potential synergies between calcium sulfate, calcium silicate and calcium aluminate hydrates. However, a great deal more R&D, mainly oriented towards establishing the usage properties and durability of concretes made from such cements, will be needed to provide the data necessary to modernise our construction codes and standards if we are to effectively use these potentially more “CO₂ efficient” technologies on a large enough scale to have a significant global impact.

• INTRODUCTION

• AN HISTORICAL PERSPECTIVE

• RAW MATERIALS CO2 VS. FUEL-DERIVED CO2

• NATURAL RESOURCES SUITABLE FOR MAKING HYDRAULIC CEMENTS

• POZZOLAN-BASED CEMENTS

• CALCIUM SULFOALUMINATE-BASED CEMENTS

• CALCIUM SULFATE-BASED CEMENTS

• CONCLUDING REMARKS

• REFERENCES