Quantifying the cracking behaviour of strain hardening cement-based composites

[摘要] ENGLISH ABSTRACT: Strain Hardening Cement Based Composite (SHCC) is a type of High Performance FibreReinforced Cement-based Composite (HPFRCC). SHCC contains randomly distributed shortfibres which improve the ductility of the material and can resist the full tensile load at strainsup to 5 %. When SHCC is subjected to tensile loading, fine multiple cracking occurs thatportrays a pseudo strain hardening effect as a result. The multiple cracking is what sets SHCCaside from conventional Reinforced Concrete (RC). Conventional RC forms one large crackthat results in durability problems. The multiple cracks of SHCC typically have an averagecrack width of less than 80 μm (Adendorff, 2009), resulting in an improved durabilitycompared to conventional RC.The aim of this research project is to quantify the cracking behaviour of SHCC which can beused to quantify the durability of SHCC. The cracking behaviour is described using astatistical distribution model, which represents the crack widths distribution and amathematical expression that describes the crack pattern. The cracking behaviour wasdetermined by measuring the cracks during quasi-static uni-axial tensile tests. The crackingdata was collected with the aid of a non-contact surface strain measuring system, namely theARAMIS system.An investigation was performed on the crack measuring setup (ARAMIS) to define a crackdefinition that was used during the determination of the cracking behaviour of SHCC. Severaldifferent statistical distributions were considered to describe the distribution of the crackwidths of SHCC. A mathematical expression named the Crack Proximity Index (CPI) whichrepresents the distances of the cracks to each other was used to describe the crack pattern ofSHCC.The Gamma distribution was found to best represent the crack widths of SHCC. It wasobserved that different crack patterns can be found at the same tensile strain and that the CPIwould differ even though the same crack width distribution was found. A statisticaldistribution model was therefore found to describe the CPI distribution of SHCC at differenttensile strains and it was established that the Log-normal distribution best describes the CPIdistribution of SHCC.After the cracking behaviour of SHCC was determined for quasi-static tensile loading, aninvestigation was performed to compare it to the cracking behaviour under flexural loading.A difference in the crack widths, number of cracks and crack pattern was found betweenbending and tension. Therefore it was concluded that the cracking behaviour for SHCC isdifferent under flexural loading than in tension.

[发布机构] Stellenbosch University