Preparation and Performance of a New-Type Alkali-Free Liquid Accelerator for Shotcrete

Yanping Sheng,Haibin Li,Bin Xue,Jianhong Fang,Anhua Xu,Yunyan Qiao,Huaxin Chen

doi:10.1155/2017/1264590

Abstract

A new type of alkali-free liquid accelerator for shotcrete was prepared. Specifically, the setting time and strength and shrinkage performance of two kinds of Portland cement with the accelerator were fully investigated. Moreover, the accelerating mechanism of alkali-free liquid accelerator and the hydration process of the shotcrete with accelerator were explored. Results show that alkali-free liquid accelerator significantly shortened the setting time of cement paste, where the initial setting time of cement paste with 8 wt% of the accelerator was about 3 min and the final setting time was about 7 min. Compressive strength at 1 day of cement mortar with the accelerator could reach 23.4 MPa, which increased by 36.2% compared to the strength of cement mortar without the accelerator, and the retention rate of 28-day compressive strength reached 110%. In addition, the accelerator still shows a good accelerating effect under low temperature conditions. However, the shrinkage rate of the concrete increased with the amount of the accelerator. 5~8% content of accelerator is recommended for shotcrete in practice. XRD and SEM test results showed that the alkali-free liquid accelerator promoted the formation of ettringite crystals due to the increase of Al3+ and SO42- concentration.

Highlights

Shotcrete has been widely used in tunnel, underground, and marine works for providing early support and preventing water seepage [1, 2]
Sommer et al [10] synthetized a type of alkali-free liquid accelerator containing 12% aluminum hydroxide, 0.5% complexing agent, 25% hydrofluoric acid, 7.5% amine, and 55% water, which offered the advantages of rapid increase in compressive strength compared with alkaline accelerators and reduced concrete crack due to the formation of ettringite
We conclude the following: (a) A new type of alkali-free liquid accelerator prepared by aluminum sulfate, sodium fluoride, triethanolamine, polyacrylamide, and formic acid in this paper has shown good accelerating effects

Summary

Introduction

Shotcrete has been widely used in tunnel, underground, and marine works for providing early support and preventing water seepage [1, 2]. Sommer et al [10] synthetized a type of alkali-free liquid accelerator containing 12% aluminum hydroxide, 0.5% complexing agent, 25% hydrofluoric acid, 7.5% amine, and 55% water, which offered the advantages of rapid increase in compressive strength compared with alkaline accelerators and reduced concrete crack due to the formation of ettringite. This accelerator can reduce the initial setting time and the final setting time of the cement paste to 6 minutes and 20 minutes, respectively; it still has its limitation in the compatibility for different types of cement. The compatibility of accelerator for different types of cement and water reducing agent, the sensibility under conditions of different temperatures, and the accelerating mechanism were investigated

Materials

Results and Discussions

Conclusion