Preparation and acceleration mechanism of a ternary hardening accelerator for high-performance concrete with full aeolian sand

The application of aeolian sand to produce concrete for the engineering construction of desert areas has important significance. Preliminary studies have suggested that producing high-performance concrete with full aeolian sand (FA-HPC) is feasible. However, construction in desert areas is often the most vulnerable to harsh climatic conditions. Hence, there is a need to investigate how to accelerate the strength formation of aeolian sand concrete to reduce the negative impact of the environment on its early performance development. In this paper, the applicability of a combination of aluminum sulfate (Al2(SO4)3), sodium nitrate (NaNO3), and triethanolamine (TEA) as a ternary hardening accelerator for FA-HPC was investigated. The response surface methodology (RSM) was employed to optimize the combination of the ternary hardening accelerator. The microscopic morphology and chemical composition before and after the addition of the accelerator were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Then, the accelerated hydration mechanism was analyzed and a hydration model was established. The results showed that the addition of the ternary hardening accelerator significantly improved the early strength of aeolian sand concrete. The optimal dose combination of the accelerator is 0.93% for Al2(SO4)3, 1.29% for NaNO3, and 0.03% for TEA based on the response surface methodology (RSM). The incorporation of the accelerator increases the 12-hour and 1-day flexural strength of FA-HPC by 48.6% and 25.8%, respectively. In the ternary hardening accelerator system, NaNO3 and TEA enhance the dissolution of the mineral phase and provide a better environment for the hydration reaction. Meanwhile, the accelerator modifies the morphology of the hydration products and contributes to the strength skeleton formation. In addition, more ettringites (AFt) were formed in the effect of the ternary hardening accelerator, which improved the early mechanical properties of FA-HPC. The research results could promote the engineering application of FA-HPC in desert areas and provide theoretical guidance for the rapid construction and repair of the project.