The possibility of alternative cements reducing carbon emission

Most economic growth in this century is projected to be in developing countries and statistics already show that these are the same places that are now consuming 93% of the cement produced globally. Consequently, global demand for cement is presently growing at a rate of about 4 % per annum. It is in these places of high growth and need for new infrastructure where aggressive changes in construction practices may also initiate fundamental change in the chemistry of infrastructure cement.

While the composition of OPC has remained largely the same since last century, and the mechanisms of OPC hydration and structure of C-S-H remain difficult to interpret. However, major advances in the use and performance of cement have come from three fundamental areas: (1) construction technology; (2) the science and engineering of composite materials; and (3) admixture chemistry, both organic and inorganic.

Alternative cements could be defined as inorganic cementitious materials that can be used for construction, but whose properties and composition are not yet specified by existing standards, codal practices and regulations.

The evolution of new cement types will need to overcome both technical and non-technical barriers. Requirements for mechanical performance and long-term durability are critical, but standards and specifications, whether prescriptive or performance-based, will also require robust evolution. In addition, confidence in new materials must be acquired by the end user (e.g., contractors) in the field-based application of new cements. In each case, some application flexibility will be needed, because new cements may need to be processed and placed in a manner somewhat different from OPC-based concrete.

Substantial progress should be made scientifically, before these cements can be manufactured at industrial scales. On the other hand, Calcium Sulpho Aluminate cements (CSA) appear to be emerging as a leading alternative cement over the next decade. Indeed, in near future commercial production of CSA cements appears to be implemented in the Western world.

In broader terms, the stimulus and time scale to innovation and evolution of alternative cements depends on public policy. Scientific developments and technology can inform debates, but if the cement industry is to remain competitive in the face of possible policy-driven mandates, it needs to present realistic, viable and impactful alternatives to traditional OPC.

A shift away from OPC will tend to compromise the calcium buffer, and hence the extent of passivity afforded, but simultaneous changes in reinforcing materials away from ferrous metals (e.g. fiber-reinforced polymers) may reduce the need for corrosion resistance. Nevertheless, because of the driving force to reduce CO2 emissions, some alternative cements that may emerge in the next 100 years appear promising.

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