Lime-cement stabilisation of Trondheim clays and its impact on carbon dioxide emissions

Dry deep mixing is used throughout Norway to improve soft and sensitive clays. Traditionally, binders such as lime and cement have been used in combination with relatively high binder contents. The production of lime and cement causes large emissions of carbon dioxide, and it is therefore desirable to reduce the binder contents in engineering practice. This paper presents results from a comprehensive study of various lime-based binders, with the aim to improve the understanding of the engineering properties of such stabilised clays when using reduced binder contents. Results from analyses on pH, plasticity and mineralogy are presented, and it is concluded that fine-grained quartz particles exhibit relatively high pozzolanic properties giving a considerable strength development over time, also with low binder contents. A novel correction of the binder content has been used, based on the active CaO of the binders. This correction gives remarkably consistent results between the water-binder ratio and the strength development. These results have also enabled estimations of carbon dioxide emissions as a function of binder type and strength development. It is concluded that the type of lime-based binder has little influence on the carbon dioxide emissions per unit strength for binder contents higher than 30–40 kg/m3. For lower binder contents, there is a tendency that binders with low active CaO-content give lower carbon dioxide emissions per unit strength, however, these low binder contents are difficult to obtain in field applications.