Shrinkage of concretes made of limestone-rich cements

• Applicant: Dr.-Ing. Tilo Proske
• Subject Area: Construction Material Sciences, Chemistry, Building Physics
• Term: from 2017 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 355027212

The application of grounded limestone as a main component of clinker reduced cements and concretes enables a significant reduction of construction related environmental impacts, especially CO2 emissions. Additionally, these concretes have a lower risk to cracking, induced by the heat of hydration. The advantage of limestone is the sufficient availability worldwide. However, to achieve an equivalent performance a reduction of water content in the concrete mixture is necessary. Due to the lower water and Portland cement clinker contents, such concretes have generally lower amount of hydration products and evaporable water. This leads basically to a lower shrinking potential. On the other hand, addition of grounded limestone results in a change in microstructure of the hardened cement paste. Depending to the chemical composition of limestone, also an increase of shrinkage deformation can be expected. A great concern regarding to shrinkage behavior of such concretes will be the variation of chemical and mineralogical composition of the available limestone. Thus, the questions regarding to the shrinkage behavior of cements and concrete with very high limestone contents should be answered. Within the current applied research project, the shrinkage mechanisms (autogenous shrinkage and drying shrinkage) of water reduced concretes made of limestone-rich cements will be studied fundamentally to reach a precise prediction of shrinkage deformation of construction elements made of such concretes. The shrinkage behavior will be firstly methodically investigated on hardened cement pastes with different combination of Portland cement clinker and limestone. Furthermore, the influence of quality of limestone (chemical and mineralogical composition), degree of hydration, curing duration, w/c-ratio as well as relative humidity of surrounding environment will be analyzed. In order to describe and model the shrinkage deformation of hardened cement pastes, various mechanical properties will be determined. The pore structure will be precisely studied by means of gas and vapor adsorption-desorption isotherms, mercury intrusion porosimetry and the environmental scanning electron microscopy. The moisture transport as well as residual moisture content of hardened cement paste and concrete will be analyzed. In further test series, the shrinkage deformation will be determined directly on the concrete samples. In these tests the influence of cement composition, ITZ, geometry of specimens and moisture transport and the paste content will be assessed.Based on the performed experiments it is planned to develop a new model or modify the existing prediction models for shrinkage deformation of hardened cement paste and concretes made of limestone-rich cements. Finally, concepts for shrinkage deformation of concretes composed of limestone-rich cements to be used in design and application of structural elements under practical boundary conditions will be presented.

• DFG Programme: Research Grants