Mechanical properties and constitutive model of sisal fiber coral seawater concrete under uniaxial cyclic compression

To investigate the mechanical properties of sisal fiber coral seawater concrete (SiF-CSC) under cyclic compression, 20 standard cylinder specimens in total were designed to carry out uniaxial monotonic compression and uniaxial cyclic compression tests with the volume content of sisal fiber (SiF) and loading mode as variables. Through experimental research, the failure mode was observed, and the whole failure process of SiF-CSC was recorded. The whole curves of monotonic compression and cyclic compression, important mechanical performance indexes such as peak stress and peak strain, plastic strain, stiffness degradation and energy dissipation were obtained. The stress-strain mechanical properties and damage evolution of SiF-CSC under uniaxial cyclic compression were analyzed. The results show that the strength of SiF-CSC under cyclic compression was weakened by 1.87 %similar to 6.22 % compared with that under monotonic compression, and the addition of sisal fiber was beneficial to delay the degradation of its strength. When the volume content of sisal fiber in coral seawater concrete (CSC) was 0.10 %, the peak stress and peak strain enhancement were the largest, which were 2.34 % and 10.11 % respectively. Under this volume content, the sisal fiber-reinforced CSC had the best effect. Increasing sisal fiber volume content could effectively reduce the accumulation of plastic strain under cyclic compression, improve the elastic stiffness and delay stiffness reduction. Besides, the addition of sisal fiber could effectively delay energy dissipation during cyclic compression, and the maximum increase in total energy dissipation capacity was 51.36 %. In this paper, according to the characteristics of the cyclic compression curve, the four characteristic points, i.e., unloading point, common point, residual point and end point were defined. Based on this, the relationship equations of unloading point strain, common point strain, residual point strain and end point strain were established. Finally, the stress-strain constitutive equation model and damage constitutive model of SiF-CSC under cyclic compression were proposed, which can better predict the mechanical behavior of SiF-CSC under cyclic compression.