Shrinkage And The Mechanism Of The Cement-Based Material At Low Water To Binder Ratio Incorporating High Volume Mineral Admixtures

Shrinkage deformation is always one of the key properties in the research field of cement materials. The crack phenomenon due to shrinkage has become amazingly common nowadays in the concrete engineering. With the development of high performance cement materials at low water to binder ratio (W/B) and the requirement of deep-level exploitation of the mineral admixtures for the sustainable development society, the traditional theory frame system in this field confronts many new obfuscations and challenges. Those existing problems, such as the distinguishing of different shrinkage types, testing methods, mechanisms, numerical modeling and controlling measure greatly restrict the research effort in this field. The influence of the mineral admixtures on the shrinkage of the cement-based material and the behind mechanism is still controversial.The study in this thesis focused on the cement-based material at low water to binder ratio incorporating high volume mineral admixtures (HMLWBM). Specialized research was carried out on the above-mentioned problems of such materials by means of modern computer numerical technology and the combinations of macrocosmic and microcosmic measures. The modern testing techniques and research methods of intersection of different subjects were employed to reference. The thermodynamic changes of various shrinkages were investigated.First of all, the definitions of the several types of shrinkage were explicated, which demonstrated the distinction and relation of autogenous shrinkage vs. self-desiccation shrinkage as well as autogenous shrinkage (reduction in apparent volume) vs. chemical shrinkage (reduction in absolute volume). The full course of the autogenous shrinkage was investigated by stages with the development of a new automatic measuring system. The initial time of the testing for autogenous shrinkage could be advanced from the casting owing to the incorporation of perpendicular testing and non-contact sensor. The new system took effective measures to avoid the restraining of the mould and the turbulence of the outer trembling. There was no need of demoulding and moving of the specimen in the experiment. The testing course realized the automatic data input and processing. The testing results accorded with the definition very well and exhibited good long-term reliability and repetitiveness.The newly-developed testing methods and system were adopted to study the whole-course of shrinkage of HMLWBM by stages and investigate the effects of the ground blast furnace slag (Sl) and type I fly ash (Fa) on the autogenous shrinkage and drying shrinkage. The addition of high volume Fa reduced the autogenous shrinkage effectively. This reducing effect increased with the content of the Fa. The high-ratio replacement of the Sl with 439m2/kg specific area for cement increased the self-desiccation shrinkage of hardened concrete obviously. While for the drying shrinkage, high volume fly ash enhanced the shrinkage under drying condition, especially at the initial stages of drying. However, the drying shrinkage lowered when the Fa content increased from 30% to 50%. The drying shrinkage decreased with the Sl content up to 50% replacing ratio and began to increase a little with further increasing of Sl content to 70%. The composition of Fa and Sl could restrain the autogenous shrinkage and drying shrinkage synthetically in a relatively high level of replacing ratio, which should be an important technical approach to improve the shrinkage volume stability of HMLWBM. The shrinkage evolution of HMLWBM agreed well with the function ofε( t )=ε∞(1?Aeat +Bebt).