Study on rheological properties and regulation of Bayer red mud-based foamed lightweight soil

Foamed lightweight soil has become an effective material to solve subgrade problems such as uneven settlement in the traffic field because of its advantages of light weight, high strength, good fluidity, and high construction efficiency. The traditionally foamed lightweight soil is mainly made of cement prepared by foaming. With a strong transportation network, carbon peaking, and carbon neutrality, foamed lightweight soil prepared using industrial solid wastes instead of cement has gradually become a research hotspot. Bayer red mud is one of the industrial solid wastes that are most difficult to reuse. Guided by the resource utilization of industrial wastes and the demand for green construction of traffic engineering, this study proposes to use Bayer red mud instead of cement to prepare foamed lightweight soil, and its application in traffic engineering construction has huge engineering value and ecological benefits. Aiming at the problems in the engineering application of red mud-based foamed lightweight soil, this study examined the regulation methods of the rheological properties of red mud-based foamed lightweight soil and revealed the effects of the water–binder ratio and superplasticizers on rheological properties and compressive strength of red mud-based foamed lightweight soil. The optimal water–binder ratio and optimal type and dosage of superplasticizers were determined, and the dynamic control of the performance of red mud-based foamed lightweight soil was realized. In this study, naphthalene superplasticizers significantly improved the fluidity of fresh slurry. The fluidity of the slurry increased with the increase in the water–binder ratio; when the water–binder ratio is <0.5 or >0.6, the fluidity of the slurry is too thick or watery. When the water–binder ratio is 0.5–0.6, the fluidity is between 165 and 212 mm, which is beneficial for construction. Both polycarboxylate and naphthalene superplasticizers can increase the fluidity of slurry. Naphthalene superplasticizers can increase the fluidity of slurry more remarkably, and the fluidity of 0.3% naphthalene superplasticizers increased from 165 to 176 mm when the water–binder ratio was 0.5. If the water–binder ratio is increased, the compressive strength first increases and then decreases. Polycarboxylate superplasticizers can weaken the compressive strength, whereas naphthalene superplasticizers can improve the compressive strength. An infrared spectrogram analysis showed that geopolymer gel is the main hydration product of red mud-based foamed lightweight soil, naphthalene superplasticizers can promote geopolymerization and increase the amounts of hydration products, and the optimum design values of the water–binder ratio and superplasticizers are determined.