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2 Archives of Civil and Mechanical Engineering

2 2022

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Experimental and analytical study of steel–PVA hybrid fiber-reinforced mortar containing CaCO3 whiskers subjected to freeze–thaw cycles

Liu Zixing, Cao Mingli, Xie Chaopeng

Archives of Civil and Mechanical Engineering

2022

Vol. 22, no. 4

art. no. e190, 2022

In high latitude and altitude areas, cement-based composite is subject to freeze–thaw cycles. The uniaxial compressive properties and microstructure of steel–PVA fiber reinforced cement mortar incorporating CaCO3 whiskers (SPFRC-CW) before and after freeze–thaw cycles were studied in this paper. The relative mass loss (RML), relative ultrasonic pulse velocity (RUPV), and the stress–strain relationship of frost–damaged SPFRC-CW was measured for a study of the durability and mechanical property degradation rules. A damage model was established considering the freeze–thaw cycles and CW volume fraction for SPFRC-CW, which demonstrated decent consistency between theoretical and experimental curves. The microstructure was analyzed using an optical microscope (OM), scanning electron microscope (SEM), vacuum epoxy impregnation (VEI), and mercury intrusion porosimetry (MIP). The results suggest that the physical and mechanical properties of SPFRC-CW decreased with prolonged freeze–thaw cycles. The better frost resistance of SPFRC was related to the improved pore structure because of the presence of CW, as per the results of VEI and MIP.

Damage deterioration mechanism and damage constitutive modelling of red sandstone under cyclic thermal-cooling treatments

Cao Ri-hong, Fang Lei, Qiu Xianyang, Lin Hang, Li Xilong, Li Wenxin

Archives of Civil and Mechanical Engineering

2022

Vol. 22, no. 4

art. no. e188, 2022

In the process of exploiting mineral and geothermal energy resources, the influence of the cyclic heat effect on the mechanical properties of the surrounding rock becomes increasingly prominent. To further study the damage deterioration mechanism, deformation and failure characteristics of cyclic heating–cooling (H–C) of the rock, cyclic H–C treatment tests and uniaxial compression tests were conducted, acoustic emission (AE) events were monitored, and the mesoscale characteristics of the fracture surface were imaged and analysed. The results show that the number of H–C cycles played an important role in the evolutions of the strength, cumulative damage variables and deformation modulus of the red sandstone. The peak strength of the specimens decreased with the increase in the number of H–C cycles, and the damage variables increased with the number of H–C cycles. The cyclic H–C treatments promoted the development of microcracks and the growth of the stress–strain curve crack closure stage. Both the crack closure stress and crack closure strain increased with the number of H–C cycles. Furthermore, both the number of transgranular microcracks and the microcrack spacing increased during cyclic H–C treatment, which also led to the failure mode of the specimens gradually changing from shear failure to splitting failure. In addition, based on the principle of strain equivalence, a damage constitutive model under the coupling action of cyclic H–C treatment and loading was deduced. The crack closure deformation of specimens treated with different numbers of H–C cycles was well reflected by the proposed model, and the prediction of other mechanical parameters, such as the peak stress, peak strain and tangent modulus of the theoretical curves, was also verified by test data.