The Performance and Mechanism Analysis of Cement Pastes Added to Aluminum Sulfate-Based Low-Alkali Setting Accelerator

Xingdong Lv,Yun Dong,Yan Shi,Beixing Li,Zhiyang Gao

doi:10.1155/2017/8906708

Abstract

We proposed a type of low-alkali liquid state setting accelerator, named HLSA; it was environmentally friendly product. To investigate the temperature adaptation and cement flexibilities of HLSA, the setting time and strength development properties of cement with HLSA were discussed in this paper. The effects of HLSA on hydration process, hydration products, and microstructure were studied by means of X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscope (SEM), and mercury intrusion porosimetry (MIP). The results show that four typical 42.5-grade ordinary Portland cement types with 6–8% HLSA could satisfy the first-grade requirements according to JC477-2005 even at a lower temperature (e.g., 10°C). Further, the percentage ratio of 28 d compressive strength of cement with 6–8% HLSA was over 90%; the XRD diffraction peak of AFt integrated area of cement with 7% HLSA was 3818 at 5 min of hydration; SEM observation revealed that AFt crystals were filled in the pore of cement at 28 d of hydration; the temperature adaptation and cement flexibilities of HLSA were excellent; the cement with HLSA coagulating in a short time attributed to promoting the formation of abundant AFt and the hydration of C3S.

Highlights

Shotcrete is a kind of concrete which is conveyed under pressure through a pneumatic hose or pipe and projected into place at high velocity, with simultaneous compaction, condensation, and hardening [1, 2]
The liquid setting accelerators can avoid the problems of dust pollution and uneven dispersing caused by powder accelerators in dry spray process
The effects of HLSA on hydration process, hydration products, and microstructure were investigated by means of X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscope (SEM), and mercury intrusion porosimetry (MIP)

Summary

Introduction

Shotcrete is a kind of concrete which is conveyed under pressure through a pneumatic hose or pipe and projected into place at high velocity, with simultaneous compaction, condensation, and hardening [1, 2]. The powder accelerators lead to problems of dust pollution, dispersing unevenly and high energy consumption in construction process. The liquid setting accelerators can avoid the problems of dust pollution and uneven dispersing caused by powder accelerators in dry spray process. The common problems that existed was that the alkali content of the liquid and powder setting accelerators were very high at the early research stage of setting accelerators. The AFt crystals are connecting reticular structure in cement pastes; the formation of cement hydration products especially calcium aluminate hydrate needs to combine free water leading to cement condensation in a short time [11] and (2) the formation of abundant hydrated calcium aluminate of the setting accelerators based on carbonate and sodium silicates. The effects of HLSA on hydration process, hydration products, and microstructure were investigated by means of X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscope (SEM), and mercury intrusion porosimetry (MIP)

Experimental

Experimental Methods

Results and Discussion

Conclusions