Open Access

ARTICLE

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

by Jianbing Zhang¹, Rongjin Liu^1,2,3,*, Siyuan Fu¹, Tianyu Gao¹, Zhongfei Zhang¹

1 College of Material Science and Engineering, Guilin University of Technology, Guilin, 541004, China
2 Guangxi Engineering and Technology Center for Utilization of Industrial Waste Residue in Building Materials, Guilin, 541004, China
3 Guangxi Beibu Gulf Engineering Research Center for Green Marine Materials, Guilin, 541004, China

* Corresponding Author: Rongjin Liu. Email:

Journal of Renewable Materials 2021, 9(11), 2001-2013. https://doi.org/10.32604/jrm.2021.015812

Received 16 January 2021; Accepted 25 February 2021; Issue published 04 June 2021

Abstract

Based on aluminum sulfate, a fluorine-free and alkali-free liquid accelerator (FF-AF-A) was prepared in this study. The setting time and compressive strength of three cement types with different FF-AF-A dosages were fully investigated. The compatibility of the FF-AF-A with the superplasticizers were also investigated, and the early hydration behavior and morphology of the hydration products of reference cement paste with the FF-AF-A were explored by hydration heat, X-ray diffractometry (XRD), and scanning electron microscopy (SEM). Test results indicated that adding the FF-AF-A at 8 wt% of the cement weight resulted in 2 min 35 s initial setting time and 6 min 30 s final setting time. The 1-day compressive strength of the cement mortar with 8 wt% of FF-AF-A reached 13.5 MPa, which represents an increase of 35% as compared to the strength of cement mortar without the FF-AF-A, and the 28-day compressive strength ratio was 119%. In addition, the FF-AF-A also showed good compatibility with different superplasticizer dosages. The results show that, when the FF-AF-A was added to the cement paste, it promoted the formation of ettringite crystals due to the aluminum ions (Al³⁺) and sulfate ions (SO₄ ^2-) reacted with gypsum in the cement, as well as promoted the hydration of tricalcium aluminate (C₃A) and tricalcium silicate (C₃S) leading to the overall structure becomes more compact. As a consequence, the hydration heat rate of the cement sharply increased, the cement paste setting time is shortened, and the compressive strength of cement mortar is improved.

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