The time-dependent cracking behaviour of strain hardening cement-based composite

[摘要] ENGLISH ABSTRACT: Strain Hardening Cement-based Composite (SHCC) is part of the High Performance FibreReinforced Cement-based Composite (HPFRCC) family and is a relative new concretecomposite. This Fibre Reinforced Cement-based Composite (FRCC) contains randomlydistributed short fibres and when subjected to a uni-axial tensile load multiple crackingoccurs. The multiple cracking generates fine cracks which are normally smaller than 100μm and achieve a strain capacity of more than 5 %. There are limited publicationsregarding the research of sustained tensile tests on SHCC and especially the crackingbehaviour of SHCC under quasi-static uni-axial as well as sustained tensile loads.The cracking behaviour is described as the average crack width, number of cracks anddescriptive statistical properties which could be used to represent the distribution of themultiple fine cracks under uni-axial tension. There are two types of tests that were underconsideration to determine the cracking behaviour of SHCC. The first is quasi-static uniaxialtensile tests and the second is sustained tensile tests. The latter was dependant on theuni-axial tensile tests in terms of the sustained load applied. The sustained loads rangedfrom 40 % to 80 % of the ultimate tensile resistance recorded from the uni-axial tensiletests that correspond with a strain rate of 0.001 /s. Different strain rates were used for theuni-axial tensile tests to determine the effect on the cracking behaviour. The crackingbehaviour was determined with the aid of a non-contact optical 3D digital deformationmeasuring device called ARAMIS.The content of this thesis gives a background study of the cracking behaviour and relevantresearch performed on SHCC under certain loads as well as some literature about the timedependanteffects of a cement-based composite.The functioning of the device called ARAMIS is explained as well as the resulting effectsof this device on the preparation of the test specimens. The experimental framework for theuni-axial and sustained tensile tests is discussed. Thereafter, the experimental results of the tests are depicted and discussed. The results shedsome light on the basic material properties such as the average ultimate stress and averageultimate strain, Young's modulus, etc. for the quasi-static tensile tests as well as shrinkageand creep of SHCC. The cracking behaviour such as the average crack width, number ofcracks, the variance and skewness of the distribution of the crack widths in the testspecimens for the quasi-static uni-axial and sustained tensile tests are depicted anddiscussed.The cracking behaviour when subjected to uni-axial tensile tests with different strain ratesis significantly governed by the formation of new cracks and the average crack widthremains small with increase in strain. There is no significant difference for the crackingbehaviour found when subjected to different strain rates. However, when SHCC issubjected to a sustained load then the average crack width is dependant on the number ofcracks that form over time as well as the load level. The formation of fewer and widercracks was observed for specimens loaded at average 40 % of the ultimate tensile resistancestress, however at loading percentages of higher than 65 % more cracks developed whichresulted in a smaller average crack width.

[发布机构] Stellenbosch University