Compressive Test Characteristics and Constitutive Relationship of Wet Polypropylene Macrofiber-Reinforced Shotcrete

Fenghui Li,Chang Su,Yunhai Cheng,Fei Wu,Gangwei Li,Junfei Zhang

doi:10.1155/2021/6649283

Abstract

Shotcrete is often subject to poor ductility and cracking problems, particularly under high stresses. In order to deal with these issues, the feasibility of adding polypropylene macrofibers to shotcrete was verified. To ascertain the supporting effect, dry shotcrete, wet shotcrete, and wet polypropylene macrofiber-reinforced shotcrete (WPMS) were used as samples. Furthermore, the mechanical response characteristics thereof in uniaxial compression tests were compared and analyzed by acoustic emission (AE) monitoring. The results showed that the three materials were brittle, but the ductility, residual strength, and bearing capacity of polypropylene macrofiber-reinforced shotcrete were significantly enhanced. The energy absorption value of plain shotcrete was higher in the cracking stage, while that of polypropylene macrofiber-reinforced shotcrete was greater in the postpeak stage, which showed that the polypropylene macrofiber-reinforced shotcrete had the characteristics of a high crack-initiation strength and toughness. Besides, the energy release from fiber shotcrete occurred after the peak stress rather than near the peak stress. The average energy absorbed by polypropylene macrofiber-reinforced shotcrete was significantly higher than that in dry shotcrete and wet shotcrete, which implied that polypropylene macrofiber-reinforced shotcrete could mitigate the brittle instability of a shotcrete layer. A constitutive model of damage statistics was established based on the test data. The comparison between the experimental data and the fitting results can reflect the characteristics of the total stress-strain curve of such shotcrete. The results provide a basis for the optimization of polypropylene macrofiber-reinforced shotcrete layers.

Highlights

Shotcrete is a commonly used support and sealing method in geotechnical engineering works such as highway lanes and tunnels
Wet shotcrete can overcome the shortcomings of dry shotcrete, but there remain problems such as poor toughness and poor crack resistance [2,3,4]
Water-reducing admixture was added for the wet spray method, to 0.8% of the mass of cement, which was conducive to enhancing the strength of the shotcrete; the water-cement ratio was 0.5, and polypropylene macrofibers (1 kg/m3) were added to the wet-sprayed concrete to make wet polypropylene macrofiber-reinforced shotcrete (WPMS) (Figure 1 and Table 1) [25]

Summary

Introduction

Shotcrete is a commonly used support and sealing method in geotechnical engineering works such as highway lanes and tunnels. An effective way to enhance the mechanical properties of concrete is to add steel fibers as an additional basic material; such fibers are easy to corrode in steel-fiber shotcrete. Shock and Vibration underground geotechnical engineering works under complex, wet conditions. To tackle these problems, polypropylene macrofibers (polypropylene fiber) can be used as a substitute. Compared with the plain concrete, the wet polypropylene macrofiber-reinforced shotcrete (WPMS) has better mechanical properties and better deformation ability [9]. Wang et al [21] analyzed the wavelet energy spectra of AE signals during full stress-strain testing of polypropylene macrofiber-reinforced concrete under different strain rates. AE position detection and other indoor testing methods were adopted to investigate the mechanical response characteristics and constitutive relationship governing the uniaxial compression testing of WPMS, providing reference for the optimization of such support schemes

Experimental Program

Test Results and Characteristics

Shotcrete Damage Analysis

Conclusion