A dual-component strategy for ambiently-cured high-toughness red mud-based geopolymer: Modified nano-TiO2 and sodium polyacrylate

Abstract

In response to the growing demand for sustainable construction materials, this study overcomes the inherent brittleness and poor fracture resistance of red mud-based geopolymer (RBG) through the strategic combination of surface-modified nano-TiO2 (NT) and sodium polyacrylate (SPA). The NT was functionalized with silane coupling agent to improve dispersibility and interfacial bonding, while SPA was added to enhance fracture toughness. Under the condition of ambient curing, the optimum mixture containing 3 wt% (glycidoxypropyltriethoxysilane) -modified NT (GNT) and 0.5 wt% SPA achieved a 28 d compressive strength of 43.40 MPa and a flexural strength of 8.16 MPa. The performance index meets the Portland cement (PC 42.5) standards. Microstructural analyses (XRD, FT-IR and SEM-EDS) revealed that the formation of geopolymer gel was increased, the crystallinity was reduced, and the degree of polymerization was improved, which confirmed the effectiveness of this method in producing high-toughness and environmentally friendly geopolymer.

1. Introduction

With the rapid acceleration of global industrialization, the emission of substantial amounts of industrial waste has emerged as a significant threat to the environment and ecosystem [1, 2]. Industrial solid wastes (e.g., red mud (RM), slag, ceramic wastes and cinder), when mixed with aluminosilicate materials, including fly ash (FA), metakaolin, and rice husk ash, can be activated by an alkaline solution to synthesize inorganic cementitious materials [3 −5]. This material serves as a sustainable alternative to traditional cement-based materials, exhibiting excellent mechanical properties and distinct advantages [6 −8]. RM is a solid waste discharged from the alumina smelting process, which is difficult to treat because of its high alkalinity (pH=11 −12) [4]. At present, the global accumulation has exceeded 4 billion tons, and is growing at a rate of 175 million tons per year [2]. However, it is the high alkali property of RM that makes it have certain advantages in the preparation of alkali-activated cementitious materials [6, 9].

However, in the presence of ionic bonds, covalent bonds and van der Waals forces in geopolymers, it is easy to crack under low tensile strain (10−4 −10−3) [10, 11]. As building structures become increasingly complex, the demand for high-toughness cementitious materials is steadily rising. Although fiber reinforcement is a common means to improve the toughness of geopolymers (e.g., basalt fiber, and PVA fiber, which have been proved to increase the flexural strength of geopolymers by 20% −56% [12 −14]), fibers without surface modification or adaptive design often have problems (e.g., insufficient compatibility with geopolymer matrix and uneven dispersion in inorganic systems) [15, 16]. In addition, some fibers have problems such as high cost and insufficient environmental durability (e.g., steel fiber is easy to corrode and natural fiber is easy to degrade), which further limit their large-scale engineering applications [3, 17, 18]. To address these challenges and facilitate the sustainable advancement of geopolymers, researchers have suggested a range of enhancement strategies, including the incorporation of nanomaterials and polymeric modifiers [19].

Nanomaterials exhibit exceptional mechanical properties, chemical stability and surface characteristics. Consequently, they are extensively employed to modify cementitious materials, thereby enhancing their material properties [17]. For instance, DEB et al [20] added nano-SiO2 (NS) into the geopolymer, where it primarily functioned as a filling agent to reduce porosity and enhance the structural integrity of the geopolymer. Similarly, XU et al [21] observed that a smaller particle size of NS (20 nm) resulted in a more effective filling action. GOPALA KRISHNA SASTRY et al [22] investigated the impact of nano-TiO2 (NT) on FA-based geopolymer concrete (GPC) through experimental analysis. When the dosage of NT was 5 wt%, not only did the GPC exhibit the greatest strength enhancement, but its resistance to mag...