Assesment risk of fracture in thin-walled fiber reinforced and regular High Performance Concretes sandwich elements

High Performance Concrete Sandwich Elements (HPCSE) are an interesting option for future low or plus energy building construction. Recent research and development work, however,
indicate that such elements are prone to structural cracking due to the combined effect of shrinkage and high temperature load. Due to structural restraints, autogenous shrinkage may lead to high self-induced stresses. Therefore autogenous shrinkage plays important role in design of HPCSE. The present paper assesses risk of fracture due to autogenous shrinkage-induced stresses in three fiber reinforced and regular High Performance Concretes (HPC). The research work described in this paper contains a description of experimental setup that allows measurement of effective shrinkage in HPC, which develops on an elastic inhomogeneity embedded in HPC matrix undergoing shrinkage during hydration (autogenous shrinkage). The test setup is based on direct measurement of the hydrostatic pressure developed in a simple pressure sensor embedded in the same matrix and a subsequent analysis based on Eshelby's solution for an ellipsoidal inhomogeneity embedded in an infinite matrix. The paper also presents the analysis necessary to perform an interpretation of the experimental
results and to determine effective shrinkage in the HPC matrix. Furthermore, the mechanical properties of all the mixes – static elastic modulus, compression strength, tensile strength as well as fracture energy were investigated in detail as function of time. Finally the paper describes the modeling work with HPCSE predicting structural cracking provoked by autogenous shrinkage. It was observed that risk of cracking due to autogenous shrinkage rapidly rises after 3 days in case of regular HPC and after 7 days in case of fiber reinforced HPC.