Experimentell investigations and microstructure-based modeling of the elastic and visco-elastic behavior of PCC depending on temperature

• Applicant: Professorin Dr.-Ing. Andrea Osburg
• Subject Area: Construction Material Sciences, Chemistry, Building Physics ; Structural Engineering, Building Informatics and Construction Operation
• Term: from 2019 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 429470033

Due to increasing economic and ecological requirements regarding engineering structures, there is a growing need to optimize the resistance of the building material concrete against a wide variety of loads. The modification of the binder with thermoplastic polymers has been an established method for improving the durability, chemical resistance, and adhesive properties of cementitious materials for many years. The fields of application for polymer-modified cement mortars and concretes (PCC) have therefore been steadily extended in recent years. In order to establish PCC also in construction, a comprehensive understanding of the effects of polymer modifications on the mechanical behavior is fundamental. Particularly with regard to the elastic and viscous deformations properties, the PCC differ significantly from conventional mortars and concretes. However, due to the pronounced temperature dependence of the polymers, it is necessary to describe the mechanical behavior of PCC as a function of the temperature. The objective of the proposed project is to characterize the temperature dependence of the elastic and viscoelastic properties of PCC. For this purpose, cross-scale experimental and analytical approaches that complement each other are used. The temperature-dependent influence of the polymers on the load-deformation behavior of cement pastes, mortars, and concretes is characterized both by standard measurements and by novel experimental campaigns. The latter include short-term creep tests according to which the sample is subjected to a compressive force once every hour for three minutes during the first week after production. This procedure enables the quasi-continuous determination of the elastic properties and the creep strains of the samples. The results are complemented by long-term creep tests so that the creep behavior of PCC can be comprehensively described. The respective investigations are carried out at different temperatures between -20 and +60 °C. Microstructural investigations before and after the temperature influence also provide information on changes in the morphology of single phases.The results of the study are bundled in a semi-analytical multiscale model based on the methods of continuum micromechanics. By means of a bottom-up approach, homogenized properties at the macroscale are determined using the specific microstructural behavior. The microstructure changing as a result of the temperature influence can thus be directly correlated with the macroscopic material behavior. After extending an existing multiscale model by considering principles of thermo-poro-elasticity, the temperature dependence of the mechanical properties of PCC will be predictable.

• DFG Programme: Research Grants