Sulfoaluminate cement-based grouting materials (SAGMs) have emerged as a high-performance solution in modern civil engineering, prized for their rapid setting, high early strength, and volumetric stability in applications ranging from rock reinforcement and concrete crack remediation to mine tunneling support. However, the intrinsic drawback of sulfoaluminate cement-its exceedingly rapid hydration kinetics and short setting times-severely restricts the operational window for grouting operations, challenging the feasibility of large-scale field applications. While chemical admixtures are conventionally employed to disperse cement particles, retard setting, and enhance fluidity to safeguard early-age workability, the distinct mineralogical composition of sulfoaluminate cement (characterized by ye'elimite and anhydrite) compared to ordinary Portland cement creates profound compatibility challenges. Conventional superplasticizers often fail to perform optimally, leading to issues such as flash setting or uncontrolled fluidity loss. Therefore, the rational design of molecularly tailored admixtures specifically compatible with the unique chemistry of SAGMs is of paramount importance. In this study, 3-mercaptopropionic acid (MPA) was utilized as a chain transfer agent to regulate molecular weight during the free radical polymerization of acrylic acid (AA), 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), and acrylamide (AM), yielding a series of AA-AMPS-AM. The influence of MPA dosage on polymer architecture was systematically investigated, and the effects of molecular weight variation on the rheological properties, workability retention, and hydration mechanisms of SAGMs were evaluated, with a specific focus on dissolution-precipitation dynamics.

A suite of AA-AMPS-AM with tailored molecular weights was synthesized by modulating the MPA dosage during aqueous free radical polymerization. The successful synthesis and structural confirmation of these polymers were rigorously verified using Fourier-transform infrared spectroscopy (FT-IR), gel permeation chromatography (GPC), and proton nuclear magnetic resonance (¹H NMR). The performance of these polymers in SAGMs was quantitatively assessed according to Chinese National Standards: fluidity (GB/T 8077-2012), setting time (GB/T 1346-2011), and mechanical properties of hardened paste (GB/T 7897-2008). To elucidate the interaction mechanisms at the solid-liquid interface, adsorption behavior was probed using zeta potential measurements and total organic carbon (TOC) analysis. The modulation of the hydration process was investigated through the framework of dissolution-precipitation equilibrium, utilizing conductivity measurements and inductively coupled plasma (ICP) spectroscopy to track ionic concentration variations during mineral dissolution. The evolution of key hydration products was analyzed based on these ionic profiles and subsequent solid-phase characterization. Final hydration products were comprehensively identified using X-ray diffraction (XRD), thermogravimetric analysis (TG), laser particle size analysis, and scanning electron microscopy (SEM) for morphological assessment.

By maintaining a fixed monomer molar ratio of AA: AMPS: AM = 1:99:30 and adjusting the MPA dosage, water-reducing agents with systematically varied molecular weights were synthesized. Experimental results indicated that reducing the MPA dosage from 0.6% to 0.2% led to a controlled decrease in the molecular weight of AA-AMPS-AM. This molecular tuning significantly enhanced the fluidity of SAGMs; specifically, the incorporation of polymer-2, polymer-4, and polymer-6 increased the initial fluidity to 370, 365 mm, and 345 mm, respectively. Notably, the formulation containing polymer-2 exhibited exceptional fluidity retention, maintaining 100 mm of flowability even after 60 min. Adsorption analysis revealed that lower MPA dosages reduced the polymer's affinity for mineral surfaces, allowing a greater proportion to remain in the liquid phase to act as a steric dispersant. AA-AMPS-AM influenced the hydration process of the SAGMs, a lower MPA dosage strengthened the polymer's inhibitory effect on the dissolution of anhydrous calcium sulfate and calcium sulfoaluminate. This is attributed to AA-AMPS-AM effectively coating the mineral surfaces, creating a physical barrier that limits direct contact with the aqueous solution. Furthermore, AA-AMPS-AM reduced both the rate and total heat release of hydration, with the retarding effect becoming more pronounced at lower MPA contents. The polymers suppressed AFt formation and refined the particle size from 1600 nm to 200 nm, altering AFt morphology from long, slender rods to short, stubby rods. Conversely, lower molecular weight polymers (higher MPA dosage) promoted the formation of an aluminum-rich gel phase, facilitating particle aggregation on the external surface.

This study establishes a clear structure-performance relationship for polymer in SAGMs, demonstrating that molecular architecture-governed by MPA dosage-dictates their efficacy as water reducers and hydration modifiers. Reducing the MPA dosage yields polymers with lower molecular weights and narrower distributions, which optimizes slurry fluidity and effectively retards setting. Crucially, this reduction diminishes polymer adsorption onto cement grains, the resultant increase in free polymer concentration in the pore solution is pivotal for sustaining fluidity. Furthermore, the adsorbed polymer layer acts as a steric barrier that inhibits the dissolution of reactive minerals (anhydrite and ye'elimite), disrupting the dissolution-precipitation equilibrium. This leads to a delayed and modified crystallization of AFt, shifting its morphology from acicular to stubby prismatic crystals. Finally, polymerization conditions favoring lower MPA content promote the co-precipitation of Al(OH)₃ gel alongside the polymer, which encapsulates fine particles and creates a distinctly rough surface topography on the final product.