The Effect of Red Mud Content on the Compressive Strength of Geopolymers under Different Curing Systems

Tao Ai,Danni Zhong,Yanhui Niu,Xin Yan,Yao Zhang,Jingshan Zong

doi:10.3390/buildings11070298

Abstract

To maximize the utilization of red mud in geopolymers, a red mud–metakaolin (RM-MK) geopolymer and red mud–fly ash (RM-FA) geopolymer were prepared, respectively. The effects of red mud content on the compressive strength and microstructure of the geopolymers were investigated under three different curing conditions. The results showed that the strength of the geopolymer decreased linearly with an increase in the red mud content, whether curing at room temperature or 80 °C. Surprisingly, curing in an autoclave, the appropriate amount of red mud had a favorable impact on the mechanical properties of the geopolymers. When the amount of red mud was 50%, the strength of the RM-MK geopolymer reached its highest compressive strength, 36.3 MPa, and the strength of the RM-FA geopolymer reached its highest at 31.7 MPa. Compared with curing at low temperature, curing the red mud-based geopolymers under a higher temperature and higher pressure can maximize the use of red mud. XRD analysis indicated that zeolite minerals formed. The SEM results showed that the geopolymers cured in an autoclave had a dense structure.

Highlights

Red mud is an alkaline solid waste residue generated from the alumina-refining process of bauxite
The currently reported methods for treating red mud include [4,5,6,7,8] (1) recovery of valuable elements in red mud, such as Fe, Al, Ca, Ti, etc.; (2) modified red mud is used as an adsorbent to absorb pollutants in air and water and improve the soil; and (3) red mud is rich in silicate components, such as Si, Al, Fe, and Ca, which can be used to prepare building materials, including cement, glass-ceramics, concrete, and brick
The results showed that the strength of the geopolymers improved with the addition of red mud but the improvement in strength was only for 5–20% of the red mud content

Summary

Introduction

Red mud is an alkaline solid waste residue generated from the alumina-refining process of bauxite. Much research on the application of red mud in building materials have been conducted at home and abroad. Red mud contains a large amount of iron, which has the potential to prepare high-iron aluminum cement. Zhao et al [9] prepared sulfur aluminate cement with Bayer red mud and fly ash. Some researchers have used red mud and solid wastes to prepare non-fired bricks and sintered bricks that met the standards [12,13,14]. The above research has good application prospects, the existence of alkaline substances and heavy metal elements in red mud limit the large-scale utilization of red mud in traditional buildings, compared to cement [7,15]. The current dealkalization technology is not mature and the economic cost is too high [16]

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