| Popis: |
There is currently an increasing pressure for the cement industry to reduce both the energy and embodied CO2 (eCO2) emissions associated with the manufacture of Portland cement. Among other technologies, the substitution of Portland cement with alternative low carbon cements is one of the reduction 'levers' of established roadmaps. The research undertaken in this study aimed to explore the potentiality of calcium sulfoaluminate (CSAC) and supersulfated cements (SSC) for use in current standardized procedures related to structural concrete in the UK. The research involved the development of chemically and dimensionally stable CSAC-based and SSC-based combinations. Their hydration mechanisms were studied and the mechanical, permeation and durability properties of concretes based on these systems were compared to those of Portland cement concretes. The hydration products of both cements -mainly ettringite- were found to be responsible for the properties of concretes. When optimally proportioned, both CSAC and SSC based concretes exhibited comparable or better performance to that of Portland cement reference concretes but poorer resistance to carbonation. Following a critical assessment of the results, a series of enhancement approaches for improvement of physio-chemical properties of CSAC- and SSC-based cements were adopted. These involved the use of additions and the variation of gypsum type in CSAC whereas in SSC, casting techniques, incorporation of alkaline admixtures and synthetic products were adopted. The study resulted in the development of a beneficial CSAC-based combination consisting of CSAC, anhydrite and fly ash. In SSC, the use of fabric formwork substantially improved the durability of the concrete. Optimum balance between associated eCO2 emissions, cost and equivalent performance of concretes to meet exemplary designation requirements was determined. Enhanced CSAC-anhydrite-fly ash combinations showed a considerable potential for use within the current design procedures. The same would imply for SSC concretes given that cost would not be a prerequisite. |
