Abstract
Special issue on cement and concrete science
As we move into the second decade of the new millennium, the needs and priorities of mankind are changing. New major economic powers are emerging in the form of the BRIC (Brazil, Russia, India and China), countries resulting in increased demand for natural resources and a significant increase in global consumption. The need for technological development to meet the changing needs of the world population is particularly apparent in the world of cement science, where efforts are constantly being made to design new materials and optimise processes to reduce the carbon footprint of cement manufacturing and in utilising existing cement technology towards the regeneration of diseased and damaged tissues. These new trends in the cement science community were particularly apparent at the 29th Cement and Concrete Science meeting at the University of Leeds in September 2009. This special issue of Advances in Applied Ceramics focuses on a selection of papers presented at the conference and relevant associated papers, which have been incorporated into this edition. In addition to these relatively new areas, the conference featured excellent work investigating the fundamentals of cement hydration1 and the corrosion of steel reinforcement.2
Although its manufacture is more energy efficient than other construction materials like steel and glass, the vast bulk of cement that is used world-wide (2800 million tonnes per year) means that it contributes significantly to atmospheric CO2 levels. As a consequence, many of the papers presented at the conference had a strong environmental emphasis, both in terms of reducing the energy demand of cement synthesis and utilising cement for the encapsulation of radioactive waste. Photiadis et al.,3 presented a paper that described the synthesis of the principle components of Portland cement in molten sodium chloride. The molten sodium chloride significantly reduced the temperature required for cement synthesis probably by increasing the efficiency of heat transfer. A simpler approach, reported by Senff et al.4 used diatomaceous earth to replace the calcium silicate components of Portland cement. Clearly, the complementary use of such technologies has the potential to reduce our global energy consumption significantly. Cementitious materials may also play an important role in energy generation in the future. Cements can be used to encapsulate metallic radioactive waste prior to storage. Ordinary Portland cements, however, cause corrosion of the encapsulated radioactive metals which generates hydrogen and causes dimensional changes to occur. Covill et al. reported the use of a magnesium phosphate cement system for the encapsulation of radioactive materials. The authors showed that, due to its lower pH value, the magnesium phosphate cements did not cause corrosion of the radioactive metals.5
Despite popular perceptions, cement is used not just for large-scale construction applications, but has also found important applications in both medicine and dentistry. Inorganic biocements provide a significant advantage over sintered bioceramics as they harden in ambient conditions enabling the addition of heat sensitive therapeutic ingredients such as growth factors and can also be moulded into the irregular contours that are routinely found in medicine and dentistry. Interestingly, although much existing cement science is used in the design of both dental and medical cement materials, often their desired properties are entirely different than most civil engineering cements. It is desirable, for example, for medical cements to degrade with time and be replaced with new tissue to enable a perfect repair. Since this is an undesirable property in many civil engineering materials, there remains relatively little in the literature on controlling the degradation of such materials. The work by O'Beirne et al. presented at the conference reported degradation data for dental Portland cements in vitro.6 Similarly, although ‘flash-setting’ is undesirable in the majority of civil engineering applications, one paper presented at the conference reported how the rapid setting of brushite cement could be exploited to enable the 3D printing of complex structures for the replacement of musculoskeletal interfaces.7 As the mean age of the population of the developed world gets older, it is inevitable that cement based technologies will begin to play an increasingly important role in the replacement and regeneration of both hard and soft tissues.
In summary, cement science has evolved in-line with changes in the political and economic landscape of the world. The readjustment of our priorities has highlighted new and relatively un-investigated areas of research and has presented a whole new set of research challenges. We believe that this special edition shows the amazing breadth of this exciting field.
Senior Lecturer in Chemical Engineering, University of Birmingham, UK