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Article

Zeolite-Modified Acrylate Grouts: Synergistic Water-Sealing Performance with Cement Slurry Combined Grouting for Water-Rich Sandy Cobble Tunnels

by
Qiusheng Wang
1,*,
Mengchao Cui
1 and
Pei Li
2,*
1
The Key Laboratory of Urban Security and Disaster Engineering of Ministry of Education, Beijing University of Technology, Beijing 100124, China
2
School of Civil Engineering, Tangshan University, Tangshan 063000, China
*
Authors to whom correspondence should be addressed.
Polymers 2026, 18(5), 600; https://doi.org/10.3390/polym18050600
Submission received: 5 February 2026 / Revised: 23 February 2026 / Accepted: 26 February 2026 / Published: 28 February 2026
(This article belongs to the Special Issue Applications of Polymers in Civil Engineering)
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Abstract

Water seepage in shield tunnels in water-rich sandy cobble strata threatens construction safety and long-term durability. Grouting, a widely used remedial technique, depends on material performance. Among common grouts, conventional acrylate (AC) grouts have inherent limitations in strata. This study develops an enhanced zeolite-acrylate composite grouting material by incorporating zeolite powder into the AC matrix. Systematic experiments assessed the impacts of zeolite dosage, slurry ratio, and water use ratio on gel time, water absorption expansion rate, and bond strength, with interfacial characteristics analyzed via SEM. Results indicate zeolite addition shortens gel time by up to 23% (excessive content retards solidification); 24-h expansion rate ranges 63–111%; bond strength shows a non-monotonic trend with zeolite dosage (initial decline then rise), and higher water content weakens adhesion. Scanning electron microscopy (SEM) confirms robust interfacial bonding. Proposed reference field parameters (water use ratio 5:1–6:1, slurry ratio 5:1–6:1, zeolite dosage 0.5–1.0%) require flexible adjustment according to on–site conditions. Notably, gel time is not inherently better when shorter in practice, but tailored to specific construction scenarios. Rigorous tests verify the composite’s superior seepage control capacity with ultrafine cement grout, providing theoretical and practical guidance for grouting design in complex hydrogeological environments.

1. Introduction

Seepage represents a common and critical challenge during shield tunnel construction in water-rich sand and gravel strata, posing significant risks to both construction safety and long-term structural integrity. Water infiltration increases internal humidity within the tunnel structure and accelerates the corrosion of embedded facilities. Moreover, seepage-induced particle migration in sandy gravel layers weakens the surrounding soil matrix, leading to ground settlement and potential tunnel deformation [1,2,3]. These deformations can further enlarge seepage pathways, establishing a detrimental cycle that compromises structural durability. Grouting has been widely adopted as the primary method for seepage control in tunnel engineering [4,5]. The effectiveness of grouting operations is largely governed by the performance characteristics of the grouting materials used [6]. Consequently, the development and selection of high-performance grouting materials are essential for achieving effective and durable sealing.
With ongoing technological progress, the variety of available grouting materials has continued to expand. These materials are generally classified as either inorganic or organic. Organic grouts–such as polyurethane and epoxy resins [7,8,9,10] typically exhibit superior injectability, permeability, controllable gel time, and bonding strength compared to conventional cement-based grouts. These properties render them particularly suitable for seepage control in water-saturated sand and gravel formations. However, concerns regarding environmental impact and safety have been associated with many organic grouts [11,12], highlighting the need for more environmentally acceptable alternatives. Among organic materials, acrylate (AC) grouts have attracted growing interest due to their low viscosity, tunable gel time, high penetration capacity, water-absorbing expansion behavior, and favorable environmental profile [13,14,15]. These materials have been successfully applied in various seepage prevention projects, including dam foundation grouting and mine water plugging [16,17]. Their adaptability to a wide range of pore and fracture geometries has been well documented [18,19,20]. International practices, such as the extensive use of chemical grouts in Japanese shield tunnels and the application of low-viscosity acrylate resins in the American underground construction [21], demonstrate the growing acceptance of polymer-based solutions for challenging hydrogeological conditions. As reported by Chen et al. [22], the application of AC grouts effectively sealed microcracks in the foundation of the Liang Hekou Hydropower Station dam. This was achieved through the implementation of an AC anti-seepage curtain, which significantly enhanced water sealing performance and ensured long-term structural stability.
Despite these advantages of AC materials, the extensive utilization of pure AC grouting materials is frequently constrained by their comparatively low mechanical strength, which can impede the long-term sealing efficacy of the grout within cracks [23,24]. To address this limitation, composite grouting techniques combining AC with cement-based slurries have been developed. In this approach, AC is initially injected to form a preliminary seal, which is subsequently reinforced by cement grout. This strategy integrates the rapid sealing capability of AC with the high mechanical strength of cement, while mitigating the key weaknesses of both materials. Pure acrylic gel exhibits an inherent weakness in its mechanical strength, and cement slurry demonstrates a vulnerability to erosion when subjected to flowing water conditions. Nevertheless, this combined approach is still confronted with numerous challenges. Under water-rich conditions, the gel time of AC grouts may be prolonged, and excessive water absorption and swelling can occupy the pore space required for subsequent cement grouting. The modification of AC grout properties through inorganic additives has emerged as a promising solution. Tang et al. [25] improved the salt resistance, water absorption, and water retention properties of AC grouts by incorporating expanded vermiculite.
The use of environmentally friendly auxiliary materials is increasingly recognized as a crucial strategy for enhancing grouting performance while minimizing ecological impact. Zeolite powder has garnered significant attention as a pollution-free additive due to its unique physicochemical properties and broad application potential. In the realm of inorganic cement systems, zeolite functions as an effective admixture that enhances material performance through multiple mechanisms: it improves cement particle hydration [26], reduces chloride ion penetration and corrosion [27], and mitigates alkali-silica reaction-induced expansion through its high cation exchange capacity and microporous structure [28]. Additionally, the SiO2 and Al2O3 components in zeolite react with Ca(OH)2 formed during cement hydration, promoting the formation of hydration products and increasing C–S–H gel content, thereby enhancing mechanical properties [29,30,31,32,33,34]. Zeolite also refines pore structure by filling capillaries and microcracks when partially replacing cement [35,36].
In the domain of organic chemical materials, zeolite boasts excellent compatibility, reinforcement, and functional regulation capacities, mainly due to its unique structural and surface properties. Its intrinsic microporous structure and large specific surface area endow strong physical adsorption and dispersion, effectively inhibiting agglomeration of organic monomers or polymer chains, improving composite system uniformity, and enhancing interphase bonding. Additionally, surface active groups (e.g., hydroxyls) of zeolite form hydrogen bonds or weak chemical bonds with polar groups (e.g., carbonyl, amino) in organics, regulating interface compatibility and mechanical stability. The validity of these effects is substantiated by extant studies: Zhang et al. [37] developed an acrylate-zeolite-agar superabsorbent resin, where zeolite powder acted as a dispersion and cross-linking regulator. The microporous structure of zeolite powder was able to adsorb water molecules and anchor the acrylate matrix, significantly improving the resin’s dispersion uniformity and water retention capacity. In the study by Bao et al. [38], a polyacrylamide-zeolite composite gel was fabricated. The gel’s cross-linking reaction, which was promoted by zeolite’s surface active sites, was found to enhance the gel’s thermal stability and mechanical strength. This is an advancement on the poor toughness of pure organic gels. Despite these advancements in concrete and polymer applications, zeolite-modified AC grouting materials remain largely unexplored.
In view of the aforementioned background, the selection of zeolite as a modifying additive for AC grouting materials is based on multiple comprehensive considerations, which further rationalize its application in the composite system. Firstly, zeolite is a non-toxic material, and its mining and processing processes have relatively minor environmental impacts, conforming to the current requirements of green and environmentally friendly engineering materials [29]. Secondly, zeolite powder is commercially available at a cost of approximately $200–400 per ton, which is significantly lower than that of synthetic polymers, endowing the composite grouting material with obvious economic advantages. Thirdly, the microporous structure and cation exchange capacity of zeolite have been demonstrated to complement the swelling and adhesive properties of acrylate polymers, thereby establishing a structural foundation for enhancing the overall performance of AC grouting materials. In light of the distinctive modification effects of zeolite in concrete and polymer systems, along with its environmental, economic, and structural benefits, the incorporation of zeolite powder as an admixture into acrylic grout not only fulfils the progressively stringent environmental protection requirements in engineering applications but also seeks to enhance the overall performance of the acrylic grout.
Acrylic materials are recognized to have a marked deficiency in strength when compared with cement-based materials. In order to achieve long-term leakage control in tunnels, it is first necessary to form an acrylic layer that can act as a water-stop curtain. This can then be reinforced by the addition of ultra-fine cement-based materials. The present study proposes a dual grouting strategy, utilizing AC material and cement grout, to control water seepage in tunnels crossing water-bearing gravel layers. In order to enhance the performance of acrylic grouting materials, zeolite powder was incorporated as a reinforcing additive. A controlled experimental approach was employed to investigate key material properties, including gel time, water absorption, expansion, and bond strength. The zeolite-AC ratio was systematically optimized. Physical model tests simulating water-rich stratum conditions demonstrated that the coordinated injection of both materials effectively blocked seepage paths.

2. Materials and Methods

2.1. Materials

The test utilized freeze-dried AC material in solid form for convenient transportation and storage. It was purchased from Henan Yixiuke Company (Henan, China). The AC material is composed of four constituent elements: magnesium acrylate as the primary agent, N,N′-methylenebis (MBA) as the cross-linking agent, ammonium persulfate (APS) as the initiator, and triethanolamine (TEA) as the accelerator. The chemical formulas of these substances are presented in Table 1. The components are divided into three parts: Aa (main agent and cross-linking agent), Ab (accelerator), and B (initiator). The usage method and composition of freeze-dried acrylic materials are demonstrated in Table 2.
In addition, 200-mesh synthetic zeolite powder was used. Zeolite powder was purchased from Tianjin Zhonglian Chemical Reagent Co., Ltd. (Tianjin, China). In comparison with natural zeolite, this synthetic version is distinguished by a purer composition, consisting primarily of SiO2 and Al2O3, and boasting a molecular formula of Na2O·Al2O3·xSiO2·yH2O. The manufacturing process of zeolite powder involves the melting of clay, silica sand, and sodium carbonate. The substance is soluble in acid but insoluble in water.

2.2. Test Methods

The sealing effectiveness of grouting materials is directly influenced by their performance. In the context of practical engineering applications, the gel time of grout plays a pivotal role in determining its permeability during injection. An insufficiently short gel time can impede the desired level of permeability, whereas an excessively long gelation time can lead to a heightened risk of loss due to water erosion. Water absorption expansion must remain within an optimal range: insufficient expansion reduces sealing efficacy, whereas excessive expansion may damage surrounding rock and weaken material strength. Furthermore, inadequate bond strength hinders the formation of a durable interface. Therefore, gel time, water absorption, expansion, and bond strength were selected as the key evaluation indicators for the zeolite-AC composite. The specific testing methodology is outlined in Figure 1.

2.2.1. Test Proportioning

In order to address the critical indicator of gel time in water leakage remediation, preliminary experiments were first conducted. An investigation was conducted into the influence of grout mix proportions on gel time, with material composition ratios being adjusted as a factor in the experiment. As demonstrated in Table 3, the slurry ratio exerts a substantial influence on the gel time. It is evident that as the water content is reduced, there is a corresponding decrease in gel time. The slurry ratios (Aa: Ab: B: water) presented in Table 3 were determined based on manufacturer recommendations and standard practice in acrylate grouting applications, following preliminary scoping tests. The selected ratios represent the typical range of water contents encountered in field conditions, ranging from highly dilute mixes for deep penetration to more concentrated formulations for rapid gelation. In order to circumvent the impact of ambient temperature on the polymerization reaction of acrylate [39], it was imperative that all tests were conducted under controlled laboratory conditions (temperature 23 ± 2 °C, relative humidity 50 ± 5%) with a view to minimizing environmental influences.
Preliminary tests were conducted to determine the material formulation. The experimental compositions are listed in Table 4, using pure AC material as the control group. This study investigates the influence of three variables on the zeolite-AC composite grouts: zeolite powder percentage, A/B component ratio, and water content. The quantity of zeolite powder was meticulously regulated within the range of 0.25% to 1.50%, a range that was ascertained through preliminary tests. The A/B component ratio was varied from 4:1 to 8:1, corresponding to the typical operational range adopted in tunnel grouting engineering. The water content, defined as the water use ratio, was set between 4:1 and 7:1 to simulate low-to-high dilution conditions encountered in practical applications. Key performance indicators are gel time, water absorption, expansion rate, and bond strength. The water ratio is defined as the total water mass divided by the total mass of AC components. The slurry ratio was designed based on established methods [40]. The zeolite powder percentage in this formulation is 1.00%, equating to 1 g of zeolite per 100 g of water.

2.2.2. Gel Time Test

Gel time, a critical parameter, directly governs the injectability, diffusion radius, and in situ sealing effectiveness of grouting operations. This test strictly followed the inverted cup method specified in the Chinese building materials industry standard JC/T 2037–2010 [41]. It involved thoroughly mixing components A and B at the specified ratio, immediately transferring them into a standard specimen container, and starting the timer. The mixture’s fluid state was monitored regularly by tilting the container. As demonstrated in Figure 2, gel time was recorded as the moment when the mixture lost all fluidity and ceased flowing under its own weight. Each formulation was tested in triplicate for reliability.

2.2.3. Water Absorption Expansion Test

Water absorption expansion capacity is a pivotal performance indicator for acrylate grouting materials as it determines their ability to self-seal micro-cracks and accommodate structural movement under hydrostatic pressure. As demonstrated in Figure 3, the test used the water displacement method to accurately measure the volume of the cured grout composite when fully saturated with water. Specimens cured under standard conditions were fully immersed in water for 24 h. The change in volume was then carefully measured by recording the volume of displaced water in a graduated cylinder. To ensure statistical significance and minimize experimental error, three specimens were prepared and tested for each mix ratio, and the final expansion rate was reported as the arithmetic mean of the triplicate measurements.

2.2.4. Bond Strength Test

The interfacial bond strength between the developed grouting material and the cementitious substrate was quantitatively tested. The test was conducted in accordance with the protocols stipulated in the Chinese National Standard GB/T 16777–2008 [42]. The schematic diagram of the customized experimental setup for this bond strength test is demonstrated in Figure 4, which illustrates the key components and assembly mode adopted in the measurement process. For the purpose of sample preparation, the zeolite-AC composite grouting material was cast into a prefabricated mold. The material was thoroughly cured under standard conditions. This process ensured a tight, integral interfacial bond with the precast cement board substrate. Prior to the initiation of formal testing, a high-strength structural adhesive (SikaAnchorFix-3001, manufactured by Sika Corporation, Lyndhurst, NJ, USA; tensile strength > 20 MPa, complying with EN 1504-6 [43]) was applied in a uniform manner to bond the metal loading head to the cement board. The board was in direct contact with the zeolite-AC composite sample. Subsequently, the metal loading head was firmly affixed to the tester’s load cell through the utilization of threaded anchor rods, thereby ensuring a secure and stable connection. This configuration ensured the coaxial transmission of the tensile load and prevented eccentric loading during the test. The tensile test was conducted at a constant displacement rate of 5 mm/min, applying a uniaxial tensile load to the loading head continuously until the occurrence of interfacial delamination or material failure. As demonstrated in Equation (1), the maximum tensile load at failure is designated as (F), whereas the effective bonding area is denoted as (S). As demonstrated in Figure 5, this specimen has undergone tensile failure, with zeolite-AC material adhering to the cement board attached to the pull-off head.
σ = F S

2.2.5. Interfaces SEM Test

Samples of minimal size, with a maximum diameter of 5 mm and a thickness of 3 mm, were extracted from the interface between the zeolite-AC composite and the cement block. The specimens were then subjected to a drying process in an oven for a period of 24 h, with the objective of eliminating moisture. This procedure is a prerequisite for the successful execution of scanning electron microscopy (SEM) imaging, as moisture has been observed to interfere with the quality of the resulting images. Following the drying process, the samples were sputter-coated with a thin layer of gold and then examined using a scanning electron microscope (SEM, Hitachi S-4800, Tokyo, Japan) operated at an accelerating voltage of 15 kV and a working distance of 10 mm.

3. Results and Discussion

3.1. Reaction Mechanism of the Acrylate with Zeolite

In the acrylate gelation process, the composite formation process is initiated by adding the initiator ammonium persulfate (APS) to the AC solution. APS decomposition generates sulfate radicals, which cleave the carbon-carbon double bonds in magnesium acrylate monomers, triggering polymerization and the formation of linear acrylate chains. Subsequently, the crosslinking agent N,N′-methylenebis(acrylamide) (MBA) is introduced; its functional groups react with active sites on linear polymer chains, forming cross-linked nodes and constructing a three-dimensional AC gel network [44,45]. As demonstrated in Figure 6a, this network features high water absorption capacity and excellent structural stability.
The inorganic component, zeolite powder, possesses a unique microporous crystalline framework [46], as demonstrated in Figure 6b. When incorporated into the AC system, a series of synergistic interactions occurs between the organic polymer and inorganic filler, resulting in the integrated structure illustrated in Figure 6c. In this composite, the three-dimensional AC network serves as a continuous matrix, with zeolite particles uniformly dispersed and firmly anchored within it [47]. The formation of this stable organic-inorganic hybrid structure is attributed to the following key mechanisms:
(1) Physical Encapsulation and Interpenetration: During in situ polymerization, zeolite particles are gradually encapsulated and mechanically interlocked by growing and crosslinking acrylate chains. Zeolite’s large specific surface area and strong adsorption capabilities enable the effective capture of acrylate monomers on its surface and pores, resulting in the formation of a uniform layer. This is followed by chain growth, which tightly wraps the particles, leading to the formation of a stable and uniform layer. This results in the formation of a robust mechanical interlock, thereby inhibiting zeolite particle agglomeration. The particles act as multifunctional physical crosslinking points, thereby enhancing the composite’s mechanical strength, dimensional stability, and gel network integrity under external forces [48].
(2) Ion Exchange and Interfacial Bonding: The zeolite framework contains abundant exchangeable cations (e.g., Na+, K+, Ca2+) [49], which are highly active and prone to exchange reactions with anionic groups. These cations undergo ion exchange with carboxylate groups (–COO−) generated after acrylate polymerization, establishing direct ionic bonds at the interface to firmly anchor polymer chains to the zeolite surface and pore openings. This ion exchange not only reduces interfacial energy and eliminates the phase boundary barrier but also improves compatibility between the hydrophobic polymer and hydrophilic zeolite. Additionally, aluminum sites in the zeolite structure can form coordination bonds with oxygen atoms in the polymer chains, further reinforcing interfacial adhesion and preventing interfacial separation under wet conditions.
(3) Nanoconfinement within Molecular Sieve Channels: Short-chain polymer segments or monomer molecules can penetrate the uniform nanochannels of the zeolite. Within these confined spaces, intensified van der Waals interactions occur between the polymer and the channel walls, leading to the formation of a confined polymer phase. This nanoconfinement effect significantly increases the effective interfacial contact area and binding energy, thereby efficiently preventing phase separation between the organic and inorganic components. This significantly improves the composite’s long-term durability in wet-dry cycling environments, critical for effective seepage control.
In summary, the zeolite-AC composite is not a simple physical mixture but forms through synergistic physicochemical interactions, including ionic bonding, physical encapsulation, and nanoscale confinement. These combined mechanisms construct a stable organic-inorganic interpenetrating polymer network (IPN). This structure retains the inherent high-water absorbency of acrylate polymers while integrating zeolite’s superior adsorption capacity, ion-exchange functionality, and mechanical reinforcement effects. As a result, the composite grouting material exhibits markedly enhanced comprehensive performance, particularly in swelling stability, bond strength, and durability, making it well-suited for tunnel seepage remediation applications.
It should be noted that while these mechanisms are inferred from the observed material behavior and supported by analogous systems in the literature [47,48,49], direct molecular-level confirmation would require further specialized investigation. The SEM observations presented herein provide microstructural evidence consistent with the proposed interfacial interactions.

3.2. Gel Time Test Results and Analysis

The present study investigates the effect of varying percentages of zeolite powder on the gel time of AC material, with controlled water use ratio and slurry ratio employed as a means of experimental manipulation. As demonstrated in Figure 7, the gel time is contingent on the slurry ratio and the quantity of zeolite incorporated.
As demonstrated in Figure 7a, the trend at a water use ratio of 4:1 illustrates the variation in the effect of different zeolite dosages under various slurry mix designs. Following the incorporation of zeolite powder, the gel time of the acrylic resin paste was found to be reduced to a certain extent, with a maximum reduction of 23% being observed. As demonstrated in Figure 7d, when the water use ratio increases to 7:1, the degree of variation in the slurry mix ratio curves diminishes. This finding suggests that an excess of water content impedes the effectiveness of zeolite in reducing gelation time. As the proportion of zeolite in the slurry was increased from 0% to 1.00%, the gel time exhibited a gradual shortening trend, reaching a minimum value as the zeolite content approached 1.00%. However, with further increases in zeolite powder content, gelation time showed a progressive increase. This result indicates that the addition of excessive amounts of zeolite powder to the material leads to stable or prolonged gelation time.
Zeolite powder, with its porous structure and high specific surface area, provides abundant active sites that promote the cross-linking reaction among AC monomers, thereby reducing the gel time. These active sites function as efficient reaction nuclei, accelerating the formation of a stable polymer network within the grout matrix. As the zeolite content increases from 1.00% to 1.50%, the gel time stabilizes or even increases slightly, indicating that the accelerating effect approaches saturation and that further additions have a limited impact on the reaction rate. Furthermore, the presence of excessive zeolite content has been demonstrated to inhibit cross-linking reactions within the slurry, thereby reducing molecular interactions between AC components and consequently prolonging gel time. In conclusion, zeolite powder has been demonstrated to effectively regulate the gel time of AC grouts, a property attributable to its structural and surface characteristics.
The gel time measurements demonstrated satisfactory reproducibility, with coefficients of variation (CV = standard deviation/mean) ranging from 0.8% to 8.2% across all formulations (n = 3 per formulation), indicating acceptable experimental precision. The observed trends demonstrated consistency across replicate tests, thereby providing support for the reliability of the reported effects.
On the basis of clarifying the single-factor regulatory effect of zeolite powder dosage on AC grout gel time, we further explore the coupled regulatory effects of zeolite powder dosage and key formulation parameters (slurry ratio and water use ratio) on gel time through a systematic analytical investigation. As demonstrated in Figure 7, three-dimensional surface plots were constructed to intuitively characterize the interactive variation law of gel time with the three factors. It should be noted that all data in the plots were the average values of multiple replicate tests, which ensured the reliability of the experimental results.
As demonstrated in Figure 8a, the slurry ratio exhibits a monotonically positive correlation with gel time. However, zeolite powder content exerts a non-monotonic regulatory effect on the relationship between slurry ratio and gel time, whereby gel time initially decreases and subsequently increases with increasing zeolite powder dosage. The 0.50–1.00% zeolite powder dosage range is the critical interval for the most significant regulatory effect, where zeolite powder exerts the strongest mitigation effect on the prolonged gel time caused by the increase of slurry ratio.
As illustrated in Figure 8b, the interactive influence of water use ratio and zeolite powder content on gel time is presented. It is evident that gel time undergoes a substantial increase in conjunction with an escalation in the water use ratio. The rise in gel time is indicative of discernible stage characteristics, which are governed by the zeolite powder content. The rate initially decelerates before accelerating in response to an augmentation in zeolite dosage.
Consistent with the above results, the 0.50–1.00% zeolite powder dosage still represents the optimal interval for the efficient regulation of the water use ratio and gel time relationship. When the zeolite powder content exceeds this range, its moderating effect on the adverse impact of excessive slurry ratio and high water use ratio on gel time is significantly attenuated, and the regulatory sensitivity of zeolite powder to the two key formulation parameters is reduced.

3.3. Water Absorption Expansion Test Results and Analysis

A systematic test was conducted to assess the short-term water absorption expansion behavior of the zeolite-AC composite grouting material. The test measured the 24-h water absorption expansion rate and plotted the corresponding variation curves. The selection of this evaluation index was motivated by its capacity to accurately reflect the early-stage volume stability of the composite gel following water absorption. This stability is a pivotal performance parameter for grouting materials in engineering applications.
As demonstrated in Figure 9, the 24-h expansion rate of the composite gel body is jointly influenced by two critical formulation parameters: the slurry mix ratio and zeolite powder dosage. The interactive effects of these two factors result in significant differences in the water absorption expansion characteristics of the gel, thereby establishing a foundation for subsequent analysis of the regulatory mechanism of zeolite powder.
The water absorption expansion of the composites demonstrated a non-linear dependence on zeolite powder content, exhibiting an initial decrease followed by a subsequent increase. The minimum expansion rate was observed at a zeolite dosage of 0.75%. The 24-h water absorption expansion rate of the gel in the absence of zeolite powder ranged from 74% to 115% across four distinct water use ratios. In contrast, the composite material incorporating zeolite powder exhibited a range from 63% to 111%. A comparison between the zeolite-free system and the zeolite-incorporated system revealed that the expansion rate could be reduced by up to 24%, indicating that zeolite powder has a certain capacity to inhibit water absorption expansion of the composite gel.
As demonstrated in Figure 9a,b, under conditions of reduced water content, the incorporation of zeolite powder into the gel substantially retards its water absorption expansion rate. It was established that, at a slurry ratio of 4:1, the expansion rate was higher. As the proportion of water in the mixture increased, the rate of expansion at this mixing ratio decreased from 115% to 72%, gradually converging with values observed under other ratios. This finding suggests that an increase in water content may diminish the enhancing effect of the slurry mix ratio on water absorption expansion. Furthermore, it was observed that when the zeolite content exceeded a certain threshold, the expansion rate increased once more, indicating a weakened inhibitory effect at high zeolite dosages.
The findings of water absorption expansion rate testing demonstrated a coefficient of variation ranging from 1.1% to 9.6% (with three samples extracted from each formulation), thereby substantiating the reliability of the test. It was evident that, irrespective of the water-to-binder ratio, the non-monotonic variation trend in zeolite dosage remained consistent. At a zeolite powder content of approximately 0.75%, the water absorption expansion rate remained at a comparatively low level. At zeolite dosages exceeding 1.00%, the expansion rate’s sensitivity to variations in slurry ratio and water use ratio diminished significantly. This attenuation of sensitivity, while not inherently beneficial, has practical implications: it indicates that the material becomes more tolerant to fluctuations in mixing proportions during field application, potentially improving construction quality control. In practice, perfect adherence to target mix ratios is challenging due to equipment limitations and human factors; a formulation with reduced sensitivity to these variations offers more consistent field performance. This characteristic is particularly valuable in tunnel grouting operations where on-site adjustments are common and precise proportioning may be compromised by site conditions.
In order to analyze the interaction between slurry ratio and zeolite powder dosage on the water absorption expansion rate, as well as the combined effect of water use ratio and zeolite content, averaged data from multiple experimental sets were used to generate three-dimensional surface plots. As demonstrated in Figure 10, the generation of these plots enables intuitive characterization of the multi-factor interactive law.
As demonstrated in Figure 10a, the water absorption expansion rate of the material decreases linearly with the increase of slurry ratio, while it presents a non-monotonic trend (initial decrease followed by increase) with the elevation of zeolite powder dosage. The combined effect of these two factors results in the expansion rate reaching its lowest and most stable values when the slurry ratio exceeds 6:1, and the zeolite powder dosage is in the range of 0.50–1.00%. As demonstrated in Figure 10b, under conditions of a low water use ratio, the water absorption expansion rate shows a distinct quadratic trend with the increase of zeolite powder dosage, decreasing initially and then increasing. Conversely, at elevated water usage levels, the regulatory impact of zeolite powder on the water absorption expansion rate is significantly reduced. Consequently, the variation of the expansion rate with zeolite dosage becomes negligible.

3.4. Bond Strength Test Results and Analysis

The bond strength of the zeolite-AC composite material changes in two distinct stages during the curing process. In the initial stage, the bond strength is low due to the composite’s incomplete polymerization. As the reaction progresses, the slurry gradually transforms into a solidified gel that exhibits stable mechanical properties.
As demonstrated in Figure 11, the variation in bond strength between the zeolite-AC composite and the cement substrate is dependent on the zeolite powder dosage, the slurry ratio, and a constant water use ratio. It is important to note that zeolite powder has no significant positive effect on bond strength; on the contrary, it slightly weakens the bond strength in most cases. This phenomenon is mainly attributed to two aspects: first, zeolite powder acts as an inert inorganic filler, and its porous structure may reduce the direct contact area between the AC polymer gel and the cement substrate, weakening the interfacial adhesion; second, the active sites on the zeolite surface may adsorb partial monomers or initiators, slightly inhibiting the complete polymerization of the AC system and resulting in a less dense gel structure at the interface, which is not conducive to the improvement of bond strength. Instead, bond strength peaks at 0% zeolite dosage, after which it exhibits a non-monotonic trend of first decreasing and then increasing with an increase in zeolite powder content. When the water use ratio reaches 7:1, the bond strength is too low to be measured directly.
It is evident that a water use ratio of 4:1 and slurry mix ratios ranging from 4:1 to 5:1 result in a particularly pronounced non-monotonic variation trend. The maximum bond strength of 17.6 kPa is achieved in the zeolite-free system, and subsequent addition of zeolite powder leads to a decrease in bond strength. This is followed by a slight rebound at a zeolite dosage of 1.50%. As demonstrated in Figure 11a, a direct correlation is evident between the decrease in bond strength and the increase in slurry ratio. The most substantial reduction, from 17.6 kPa to 9.33 kPa, is observed in this instance.
Bond strength measurements showed higher variability compared to gel time and expansion tests, with coefficients of variation ranging from 3.2% to 35.1% (n = 3 per formulation), reflecting the inherent complexity of interfacial adhesion testing. Despite this variability, the non-monotonic trend (initial decrease followed by partial recovery with increasing zeolite dosage) was statistically significant (ANOVA, p < 0.05) for water use ratios < 6:1. The observation that zeolite powder attenuates the sensitivity of bond strength to other formulation parameters (slurry ratio, water use ratio) when dosage exceeds 0.5% warrants explanation. This effect, while representing a reduction in the material’s responsiveness to compositional adjustments, offers practical advantages: it implies that once a minimum zeolite content is incorporated, the bond strength becomes more robust against unintended variations in mix proportions during field application. For tunnel grouting operations, where precise control of water content and component ratios may be challenging due to site conditions, this reduced sensitivity translates to more predictable and consistent bonding performance. The trade-off, which involves accepting a modest reduction in the maximum achievable bond strength in exchange for enhanced robustness against mixing errors, is frequently substantiated within the context of practical engineering.
In order to further elucidate the intrinsic interactive mechanism between zeolite powder dosage and key formulation parameters (i.e., slurry ratio and water use ratio) on the bond strength of the composite grout, averaged data from multiple replicate experiments were used to generate three-dimensional surface plots. The plots thus obtained facilitate a clear and intuitive characterization of the combined variation law of bond strength under the synergistic action of multiple factors. As demonstrated in Figure 12, the bond strength of the zeolite-AC composite exhibits a distinct linear decreasing trend with the increase in slurry ratio, and the declining trend tends to stabilize when the slurry ratio exceeds 6:1. It is noteworthy that the incorporation of zeolite powder further exacerbates this linear decreasing trend of bond strength with the increase in slurry ratio.
The dosage of zeolite powder has been demonstrated to exert a notable regulatory effect on the combined synergistic action of the aforementioned formulation factors on bond strength. It has been demonstrated that when the zeolite powder content exceeds 0.5% by mass, the synergistic regulatory effect of zeolite dosage and slurry ratio on the composite’s bond strength is significantly weakened. Beyond this critical threshold, both the water use ratio and zeolite powder content exert a negligible influence on the bond strength of the zeolite-AC composite. The variation in bond strength thereafter is predominantly governed by the slurry ratio alone. This experimental outcome lends further credence to the preliminary inference that zeolite powder exerts no positive enhancement effect on the composite’s bond strength; on the contrary, when its dosage exceeds 0.5% by mass, it attenuates the sensitivity of the composite’s bond strength to other key formulation parameters, which further elucidates the unique regulatory characteristics of zeolite powder within the multi-factor composite grouting system.

3.5. SEM Characterization on Interface Microstructure of Composite Grout

The zeolite-AC composite grout was prepared and then injected into the prefabricated cracks of cement specimens using professional grouting equipment. After the slurry was completely gelled, the specimens were allowed to stand for 12 h to ensure the stability of the interfacial combination, followed by manual cutting and vacuum drying to obtain SEM test samples. The research focus was the interface between the cured zeolite-AC composite and the inner crack surface of the cement substrate, and the interface microscopic morphology, adhesion state and bonding mechanism were systematically characterized by scanning electron microscopy (SEM).
As demonstrated in Figure 13, the zeolite-AC composite exhibits a denser internal microstructure compared with the cement matrix. As demonstrated in Figure 13a,b, although the sample preparation processes (drying and cutting) introduced minor initial fractures in the zeolite-AC composite itself, the composite still exhibited excellent adhesion to the cement substrate with no obvious interfacial separation or gap observed. As demonstrated in Figure 13c, the AC polymer gel exhibits excellent compatibility with the rough surface morphology of the cement substrate. Under grouting pressure, the gel can fully penetrate the micro-pores and grooves on the inner surface of the cement crack, thereby forming a robust mechanical interlocking effect and significantly expanding the effective interfacial contact area.
The recommended proportion of zeolite-AC material should be mixed and subsequently injected into the cracks of the specimen using grouting equipment. Following the complete gelation of the slurry, the test blocks were manually cut and dried after a period of 12 h of rest. The interface is defined as the contact surface between the cured zeolite-AC material and the inner crack surface of the cement substrate. The interface morphology was characterized by means of scanning electron microscopy. Further SEM observations confirm that the interfacial bond strength between the zeolite-AC composite and the cement substrate exceeds the intrinsic fracture strength of the composite itself. This explains why the initial fractures in the samples are generated inside the composite rather than at the interface. The findings fully corroborate the enhanced interfacial adhesion of the zeolite-AC composite grout, which is ascribed to the dual effects of the AC gel’s pore-filling property and the mechanical interlocking formed by interface fitting.

3.6. Determination of Optimal Proportioning

Based on the single-factor and multi-factor interaction experimental results of gel time, water absorption expansion rate, and bond strength of the zeolite-AC composite grouting material, the influences of zeolite powder dosage, slurry ratio, and water use ratio on the material’s key performances are analyzed in combination with the actual process requirements of tunnel seepage control grouting. A balanced optimization approach was employed to derive the optimal mix ratio range, rather than a single “optimum” point, recognizing that field applications require flexibility to accommodate varying site conditions. The selection basis for each parameter range is anchored in experimental findings, practical construction applicability, and the identification of trade-offs among competing performance objectives.
Optimization criteria definition: The optimization targets were defined based on practical engineering requirements for tunnel grouting in water-rich sandy cobble strata:
(1) Gel time: 50–80 s—sufficiently short to resist washout by flowing groundwater (typical flow velocities 0.05–0.2 m/s in such strata), yet long enough to ensure adequate penetration into cracks and pores (injectability requirement). Extremely short gel times (<30 s) risk premature gelation before complete filling, while excessively long times (>120 s) lead to material loss and dilution.
(2) Water absorption expansion rate: 65–80%—sufficient to seal micro-cracks and accommodate minor structural movements, but not so excessive (>100%) as to risk fracturing the surrounding rock mass or creating preferential flow paths. Lower expansion (<50%) may inadequately seal voids.
(3) Bond strength: >6 kPa—adequate to resist long-term groundwater scouring and maintain interfacial integrity. While higher bond strength is desirable, the modest reduction observed with zeolite addition (from 17.6 kPa to 8 kPa) remains within acceptable limits for this application, where the primary sealing mechanism involves mechanical interlocking and confinement rather than pure adhesion.
Parameter influence analysis and selection: For gel time, experimental results show that zeolite powder dosage is the primary influencing factor, followed by the slurry ratio; the gel time reaches the minimum when the zeolite powder content is 1.00% and the slurry ratio is not more than 6:1, and presents a positive correlation with the water use ratio, with the prolongation effect becoming more obvious as the water use ratio increases. In tunnel grouting construction, the gel time needs to balance two core process requirements: on the one hand, sufficient operability is required to ensure that the slurry can fully penetrate and fill the seepage cracks under grouting pressure without premature gelation; on the other hand, rapid gelation is needed to avoid slurry loss caused by flowing groundwater in cracks. Therefore, the zeolite powder dosage is controlled at 0.50–1.00% to avoid insufficient acceleration of cross-linking reaction at low dosage and reaction inhibition at excessive dosage; the slurry ratio is limited to no more than 6:1 to maintain the fluidity required for crack filling while ensuring the curing rate; the water use ratio is set at 5:1, under which the gel time is about 50 s, matching the on-site construction demand for controllable and rapid gelation.
For the water absorption expansion rate, the water use ratio is the most significant factor, followed by the slurry ratio. The 1.00% zeolite powder achieves the best swelling inhibition effect, which weakens with the increase of water use ratio; the expansion rate declines abnormally when the water use ratio exceeds 6:1, and the expansion performance stabilizes when the slurry ratio exceeds 5:1. On-site seepage control requires stable and moderate expansion (to avoid secondary cracking of surrounding rock or gap formation). Thus, the zeolite powder dosage is selected as 0.75–1.00% to retain the effective inhibitory effect on excessive swelling; the slurry ratio is controlled at more than 5:1 to ensure the stability of the expansion performance; the water use ratio is not more than 6:1 to avoid the loss of zeolite’s swelling inhibition effect caused by excessive water.
For bond strength, the water use ratio is the dominant factor, followed by the slurry ratio. The bond strength shows little difference at the water use ratios of 5:1 and 6:1, while the slurry has excessive fluidity and unmeasurable bond strength at 7:1. Tunnel grouting needs reliable interfacial adhesion to resist long-term groundwater scouring. Hence, the water use ratio is determined at 5:1–6:1 and the zeolite powder dosage at 0.50–1.00%, which minimizes the slight weakening effect of zeolite powder and ensures the bond strength is stably above 8 kPa.
By integrating the reasonable parameter ranges for the three key performances and their on-site construction adaptability, the comprehensive optimal mix ratio range of the zeolite-AC composite grouting material is determined as follows: zeolite powder dosage 0.50–1.00%, water use ratio 5:1–6:1, and slurry ratio 5:1–6:1. This range realizes balanced optimization of the material’s gel time, water absorption expansion rate, and bond strength, acknowledging the inherent trade-offs among these properties. Within this range, the material can fully meet the actual construction requirements of tunnel seepage remediation while accommodating site-specific adjustments based on prevailing groundwater conditions, injection pressures, and target penetration depths. It is important to emphasize that this recommended range represents a design space rather than a single fixed formulation. Field engineers may adjust parameters within this range to prioritize specific performance attributes: for example, a lower water use ratio (approaching 5:1) for faster gelation in high-flow conditions, higher zeolite dosage (toward 1.00%) for maximum expansion control, or intermediate values for balanced performance. The key performance indicators of the material within this range are summarized in Table 5.

4. Indoor Performance Test of Grouting Materials

4.1. Indoor Model Test Design

4.1.1. Background and Purpose of the Model Test

Water seepage presents a frequent and challenging issue during tunnel construction in water-rich sand and gravel strata. These formations are characterized by high permeability, low cohesion, and complex seepage paths under dynamic groundwater conditions. Conventional cement-based grouts often demonstrate inadequate performance, including non-uniform dispersion, low consolidation strength, and poor durability, which collectively undermine sealing effectiveness. Furthermore, grouting involves multiple complex procedures that cannot be fully evaluated through theoretical analysis or laboratory tests alone.
As demonstrated in Figure 14, a schematic diagram of grouting for seepage control in sand and gravel tunnels is provided. To improve the reliability and adaptability of grouting systems, this study proposes a dual-injection strategy combining the zeolite-AC material with cement slurry, validated through physical model tests. The AC material offers low viscosity, high penetrability, and controllable gelation. Zeolite addition enhances adsorption capacity and gel stability. The composite material demonstrates improved diffusion behavior and erosion resistance in dynamic water environments. Cement grout provides complementary long-term strength and structural stability. Utilizing experimental models and established grouting techniques, this research validates the effectiveness of the proposed composite for seepage control under dynamic water conditions.

4.1.2. Grouting Construction Process

As demonstrated in Figure 15, this illustrates the overall process flow for grouting construction. Grouting operations should follow the principle of investigation first, parameter setting, dynamic adjustment, and precise execution. The general construction sequence proceeds from the periphery inward, from bottom to top, and uses a staggered layout [50]. Grouting holes are typically arranged in plum blossom or rectangular patterns. Hole spacing and row spacing should be determined according to the diffusion radius obtained from field tests, usually set between 0.8 and 1.2 times the diffusion radius to ensure adequate overlap. For borehole formation, core drilling or mud-supported drilling techniques are recommended to prevent hole collapse.

4.1.3. Stratum Simulation Design

This study uses sand and gravel strata in the Beijing region as the simulated subject. In nature, sand and gravel particles exhibit grain size self-similarity, enabling fractal theory to determine their particle size distribution parameters. Based on the fractal dimension, a complete particle size distribution curve can be reconstructed; missing some particle groups does not affect the overall distribution continuity or plotting results. For a specific grouting area, establishing a continuous cumulative particle size distribution curve only requires determining the maximum particle size via field sampling.
Zhou Yao [51] proposed a general particle size distribution model for sandy gravel soils in the Beijing region, further derived based on fractal theory. As demonstrated in Equation (2), where represents the mass of particles smaller than R, MT denotes the total mass of the sand and gravel soil, R indicates a specific particle size, RL represents the maximum particle size, and D is the fractal dimension of the sand and gravel.
M ( r < R ) M T = R R L 3   −   D
Based on fractal theory, the particle size distribution of the sandy cobble stratum was characterized and showed clear fractal properties. The gradation parameters were determined by adjusting the fractal dimension D. According to Du, X.L. et al. [52], the fractal dimension of sandy gravel soils in Beijing Group 34 ranges from 2.4 to 2.6. Referring to Zhou Yao [51], the maximum particle size was set as 60 mm, and a fractal dimension D = 2.50 was used, resulting in the gradation function: y = (x/60) × 0.50. The simulated grain-size distribution curve is presented in Figure 16. The test samples were prepared using locally sourced sand and gravel from Beijing. The sand and gravel materials collected on-site were screened and mixed according to the gradation corresponding to D = 2.50. To ensure reproducibility between test batches, layered compaction (10 cm per layer, 30 compactions per layer) and density control (target dry density 1.85 g/cm3, measured range 1.83–1.87 g/cm3) were employed. Density was sampled at three points per layer after each packing to verify consistency.

4.1.4. Indoor Model Test Equipment

As demonstrated in Figure 17, the dynamic water grouting test setup consists of a dual-fluid grouting machine, a cement grouting machine, flow meters, filters, a simulated sand-cobble stratum, and an acrylic model tank. The dimensions of the model tank were designed based on previous research [51]. The model tank is structurally divided into an inlet section equipped with a flow-stabilizing zone and an outlet section with a similar flow-stabilizing arrangement. The configuration under consideration is designed to guarantee the uniform laminar flow across the simulated stratum during the testing phase. Water was continuously circulated through the system using a variable-speed pump to simulate in situ groundwater flow conditions, with flow rates controlled by a combination of pump speed adjustment and valve regulation. Inlet flow velocity was monitored using an electromagnetic flow meter (accuracy ± 0.001 m/s) and maintained at target values (0.04, 0.08, 0.12, 0.16, 0.20 m/s) with variation of <5%. Corresponding water pressures at the inlet ranged from approximately 0.1 kPa (at 0.04 m/s) to 0.5 kPa (at 0.20 m/s), simulating shallow groundwater conditions typical of urban tunnel environments. Outlet flow velocity was measured using a second flow meter, and the difference between inlet and outlet flows was attributed to water blocking by grout injection.

4.1.5. Grouting Materials

The slurry dosage employed in the test was determined through preliminary trials. The dosage data that was obtained includes the following:
(1) Zeolite-AC composite slurry: The composite slurry is constituted of acrylate solution A, solution B, and zeolite powder. The mixture composition is as follows: solution A (253 g A dry material + 25 g Ab liquid per 1000 mL water), solution B (55 g B dry material per 1000 mL water), and zeolite powder (20 g). The resulting composite has a water ratio of 6:1, a slurry ratio of 5:1, and a zeolite powder dosage of 1.00% by weight.
(2) Cement slurry: In the course of the experiment, Portland cement paste with a water-cement ratio of 1:1 was utilized as the subsequent reinforcement material. The fresh properties of the material are characterized by a fluidity of 35 cm, a viscosity of 20.1 s (Marsh funnel), and an initial setting time of 12 h. The bleeding rate was 26%, and the 7-day compressive strength reached 6.4 MPa.

4.2. Grouting Effects and Analysis

The water-blocking performance of grouting materials was subjected to rigorous testing under dynamic water conditions via a series of controlled experiments. The inflow velocity was meticulously regulated, while alterations in the outflow velocity were methodically monitored and documented to ascertain the progression of water-blocking efficacy. As indicated in Equation (3), the outflow velocity prior to grouting is designated as V0, whereas the outflow velocity following grouting is denoted as V. Utilizing these parameters, the water-blocking rate Ds was derived in accordance with the established methodology.
D s = V 0 − V V × 100 %
The effectiveness of different grouting systems under dynamic water conditions is compared in Figure 18, which presents the morphology of slurry retention and the resulting sealing structures. As demonstrated in Figure 18a, subsequent injection of cement slurry following the pure AC grout resulted in the formation of discontinuous patches, devoid of any coherent sealing structure. This observation is indicative of suboptimal compatibility and inadequate interfacial bonding. In contrast, Figure 18b demonstrates a significant synergistic effect between the zeolite-AC composite and the cement slurry, with the composite forming a continuous scaffold that facilitates the dense packing of cement grains within the gravel voids. The visual observation of continuous versus discontinuous sealing structures directly correlates with the quantitative performance difference, which has been confirmed as statistically significant by both the t-test (p < 0.00001) and two-way ANOVA (p < 0.001 for all factors). As demonstrated in Table 6, the cement slurry composite system combined with zeolite-AC attained an average water plugging rate of 44.6%.
As demonstrated in Table 6 and Figure 19, the cement slurry + zeolite-AC composite system attained an average water plugging rate of 44.6% (standard deviation 6.6%, n = 10) in simulated gravel-rich formations. This performance significantly exceeded that of the pure AC slurry + cement system, which registered only 20.2% (standard deviation 5.0%, n = 10). A two-sample t-test confirmed that the difference between the two systems is statistically significant (t = 9.24, df ≈ 17, p < 0.00001). Furthermore, while the sealing efficiency of the pure AC slurry gradually declined with increasing initial flow velocity (from 23.4% at 0.08 m/s to 12.3% at 0.20 m/s), the composite system not only maintained higher efficacy across all velocities but also showed a less pronounced decline (from 48.1% at 0.08–0.12 m/s to 40.3–43.8% at 0.16–0.20 m/s).
A two-way analysis of variance (ANOVA) with replication was conducted to examine the effects of grout type and flow velocity on water plugging rate (Table 7). The results revealed significant main effects for both grout type (F = 244.9, p < 0.001) and flow velocity (F = 15.2, p < 0.001). Importantly, a significant interaction between grout type and flow velocity was also observed (F = 8.5, p < 0.001), indicating that the effectiveness of zeolite modification varies with groundwater flow conditions. The interaction demonstrates that the benefit of zeolite modification is most pronounced at higher flow velocities, where pure AC grout shows marked performance degradation.
It should be noted that the experimental design did not include a “zeolite-AC only” control group without subsequent cement grouting, as the proposed dual-injection strategy inherently requires both components. However, to isolate the contribution of zeolite modification, comparison between pure AC + cement and zeolite-AC + cement directly assesses the effect of zeolite addition within the complete system. The statistically significant improvement confirms that zeolite modification enhances the composite system’s performance.

4.3. Limitations and Challenges of Model Testing

As demonstrated in Section 4.1, the model tests provide a reference for the relative performance of different grouting systems under controlled conditions. However, it should be noted that there are several limitations when attempting to extrapolate these results to actual tunnel construction scenarios:
(1) Scale effects: The model tank dimensions (1.5 m × 0.5 m × 0.6 m) represent a small fraction of a typical tunnel cross-section (typically 5–10 m diameter). The flow patterns, pressure distributions, and grout penetration behavior in the model may not fully capture the complexity of field-scale conditions, where heterogeneity, anisotropy, and three-dimensional flow paths play more significant roles.
(2) Idealized stratigraphy: The simulated sand-gravel stratum, while designed based on fractal theory to represent Beijing-region soils, is inherently more uniform and reproducible than natural strata. Real geological formations exhibit spatial variability in particle size distribution, packing density, and permeability that cannot be fully replicated in laboratory models. This variability may affect grout propagation paths and sealing effectiveness in ways not captured by controlled experiments.
(3) Boundary conditions: The acrylic tank walls introduce artificial boundaries that may influence flow patterns and grout distribution, particularly near the edges. In field conditions, the stratum extends infinitely (relative to grout penetration distances), allowing more natural development of grout bulbs and seepage paths.
(4) Simplified hydrogeology: The constant flow velocity and pressure conditions maintained in the model represent steady-state scenarios, whereas actual tunnel construction often encounters fluctuating groundwater levels, tidal influences (in coastal areas), and transient pumping effects. The dynamic water conditions simulated herein (0.04–0.20 m/s) cover a range of typical velocities but cannot encompass all possible field scenarios.
(5) Time scale: Model tests were conducted over hours to days, whereas tunnel service life extends decades. Long-term performance issues such as material degradation, cyclic wet-dry effects, and aging cannot be assessed from short-term laboratory tests.
Indicators of performance differences between grouting systems, rather than as absolute predictors of field behavior. The statistically significant superiority of the zeolite-AC composite over pure AC under controlled conditions provides confidence that the modification offers real benefits, but the magnitude of improvement observed in the laboratory (44.6% vs. 20.2%) may not translate directly to field performance. In order to validate the composite system’s effectiveness under actual construction conditions and to refine the recommended proportioning ranges based on site-specific geology and hydrogeology, field trials with careful monitoring of injection parameters, grout take, and post-grouting permeability are necessary.

5. Conclusions

In this study, the key properties of the zeolite-AC composite grout were evaluated by systematically varying the zeolite powder percentage, AC slurry ratio, and water use ratio. The gel time, water absorption, expansion, and bond strength were analyzed based on experimental measurements. The interfacial bonding behavior between the AC composite and cement substrate was characterized using scanning electron microscopy (SEM). Additionally, model tests were conducted to design a synergistic grouting approach using acrylic grout materials and cement slurry materials. The water-blocking effectiveness was verified through these model tests. The main conclusions are summarized as follows:
(1) Zeolite powder reduces the gel time of AC slurry by up to 23%. The gel time decreases with increasing zeolite content up to 1.00%. Beyond this dosage, the gel time stabilizes or increases slightly, indicating that the accelerating effect of zeolite reaches a limit. Excessive zeolite powder may occupy space within the mixture and hinder the cross-linking reaction, resulting in longer gel times. The gel time measurements showed good reproducibility, with coefficients of variation ranging from 0.8% to 8.2% across all formulations.
(2) The 24-h water absorption expansion of the zeolite-AC material ranged from 63% to 111%, which is 24% lower than that of the pure AC material (74% to 115%). However, when the slurry ratio was 6:1 or 7:1, and the zeolite content reached 1.50%, the expansion slightly exceeded that of the pure system. Overall, zeolite powder generally inhibits the water absorption expansion of the AC material. Coefficients of variation for expansion measurements ranged from 1.1% to 9.6%, confirming test repeatability.
(3) The bond strength of the zeolite-AC material first decreases and then increases with higher zeolite content. Bond strength is generally low under high water ratios, as excess water dilutes the material composition and hinders polymerization and cross-linking. The mix proportions should be adjusted according to specific project conditions to meet bonding requirements. Variability in bond strength measurements (CV range 3.2–35.1%) reflects the inherent complexity of interfacial adhesion testing, yet the observed trends were statistically significant (p < 0.05).
(4) The combined analysis showed that the percentage of zeolite powder was the main factor affecting the gel time, followed by the slurry ratio. The water use ratio is a key factor in water absorption, expansion and bond strength. The slurry ratio and zeolite powder percentage had less effect on these two properties. Recommended ratios are 0.50–1.00% zeolite powder, 5:1–6:1 water–use ratio, 5:1–6:1 slurry ratio to ensure comprehensive performance.
(5) Under simulated dynamic water conditions (0.04–0.20 m/s flow velocity), the zeolite-AC composite combined with subsequent cement slurry reinforcement achieved a mean water plugging rate of 44.56% (SD = 6.61%, n = 10), significantly exceeding the 20.20% (SD = 4.98%, n = 10) achieved by pure AC + cement (t-test: p < 0.00001). Two-way ANOVA confirmed significant effects of grout type (p < 0.001), flow velocity (p < 0.001), and their interaction (p < 0.001), indicating that zeolite modification substantially improves the material’s resistance to dynamic water scouring, particularly at high flow velocities. The material exhibited high retention in the model tank, effectively reducing loss caused by dynamic water flow. This system integrates three key functions: rapid gel, effective filling, and synergistic reinforcement. It offers a novel technical approach for tunnel grouting management and shows considerable potential for engineering applications.

Author Contributions

Methodology, Q.W.; data curation, M.C., P.L.; writing–original draft, M.C.; writing–review and editing, Q.W., M.C.; supervision, Q.W., P.L. All authors have read and agreed to the published version of the manuscript.

Funding

This study received no external funding.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Schematic diagram of the test process.
Figure 1. Schematic diagram of the test process.
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Figure 2. The acrylate gel time test.
Figure 2. The acrylate gel time test.
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Figure 3. Water absorption expansion rate test: (a) initial cutting of materials, (b) water-absorbing materials; (c) measure material volume; (d) material after 24 h water absorption.
Figure 3. Water absorption expansion rate test: (a) initial cutting of materials, (b) water-absorbing materials; (c) measure material volume; (d) material after 24 h water absorption.
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Figure 4. Diagram of bonding strength test equipment.
Figure 4. Diagram of bonding strength test equipment.
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Figure 5. The bond strength tensile failure specimen.
Figure 5. The bond strength tensile failure specimen.
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Figure 6. Mechanism of the zeolite-AC interaction: (a) acrylic crosslinking, (b) microstructure within zeolites, (c) cooperative mechanism.
Figure 6. Mechanism of the zeolite-AC interaction: (a) acrylic crosslinking, (b) microstructure within zeolites, (c) cooperative mechanism.
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Figure 7. Effect of water ratio on gel time: (a) water use ratio 4:1, (b) water use ratio 5:1, (c) water use ratio 6:1, (d) water use ratio 7:1.
Figure 7. Effect of water ratio on gel time: (a) water use ratio 4:1, (b) water use ratio 5:1, (c) water use ratio 6:1, (d) water use ratio 7:1.
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Figure 8. The proportion of zeolite powder and other factors on gel time: (a) slurry ratio and percentage of zeolite powder, (b) water use ratio and percentage of zeolite powder.
Figure 8. The proportion of zeolite powder and other factors on gel time: (a) slurry ratio and percentage of zeolite powder, (b) water use ratio and percentage of zeolite powder.
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Figure 9. Effect of the proportion of zeolite powder on water absorption and expansion rate: (a) water use ratio 4:1, (b) water use ratio5:1, (c) water use ratio 6:1, (d) water use ratio 7:1.
Figure 9. Effect of the proportion of zeolite powder on water absorption and expansion rate: (a) water use ratio 4:1, (b) water use ratio5:1, (c) water use ratio 6:1, (d) water use ratio 7:1.
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Figure 10. The proportion of zeolite powder and other factors on the water expansion rate: (a) slurry ratio and percentage of zeolite powder, (b) water use ratio and Percentage of zeolite powder.
Figure 10. The proportion of zeolite powder and other factors on the water expansion rate: (a) slurry ratio and percentage of zeolite powder, (b) water use ratio and Percentage of zeolite powder.
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Figure 11. Effect of zeolite powder on initial bond strength: (a) water use ratio 4:1, (b) water use ratio5:1, (c) water use ratio 6:1.
Figure 11. Effect of zeolite powder on initial bond strength: (a) water use ratio 4:1, (b) water use ratio5:1, (c) water use ratio 6:1.
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Figure 12. The proportion of zeolite powder and other factors on the bond strength: (a) slurry ratio and percentage of zeolite powder, (b) water use ratio and percentage of zeolite powder.
Figure 12. The proportion of zeolite powder and other factors on the bond strength: (a) slurry ratio and percentage of zeolite powder, (b) water use ratio and percentage of zeolite powder.
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Figure 13. SEM of the zeolite-AC material interface with cement: (a) zoom to 50 μm, (b) zoom to 10 μm, (c) zoom to 5 μm, (d) zoom to 3 μm.
Figure 13. SEM of the zeolite-AC material interface with cement: (a) zoom to 50 μm, (b) zoom to 10 μm, (c) zoom to 5 μm, (d) zoom to 3 μm.
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Figure 14. Schematic diagram of water seepage grouting sealing.
Figure 14. Schematic diagram of water seepage grouting sealing.
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Figure 15. Grouting construction process flow.
Figure 15. Grouting construction process flow.
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Figure 16. Gradation curve for trial gravel.
Figure 16. Gradation curve for trial gravel.
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Figure 17. Model test equipment: (a) the zeolite-AC material grouting, (b) cement slurry grouting.
Figure 17. Model test equipment: (a) the zeolite-AC material grouting, (b) cement slurry grouting.
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Figure 18. Grouting efficacy in model test: (a) pure acrylic grout and cement slurry injection, (b) the zeolite-AC composite material cement slurry injection.
Figure 18. Grouting efficacy in model test: (a) pure acrylic grout and cement slurry injection, (b) the zeolite-AC composite material cement slurry injection.
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Figure 19. Comparison of grouting effects in model test.
Figure 19. Comparison of grouting effects in model test.
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Table 1. Chemical table of the main components of lyophilized acrylate.
Table 1. Chemical table of the main components of lyophilized acrylate.
TypeIngredientChemical Formula
Main agentACC6H6MgO4
Cross-linking agentMBAC7H10N2O2
InitiatorAPS(NH4)2S2O8
AcceleratorTEAC6H15NO3
Table 2. Main components and form of freeze-dried acrylate materials.
Table 2. Main components and form of freeze-dried acrylate materials.
Main ComponentsMode
Acrylate APowder AaAa: White powder
Liquid AbAb: Clear liquid
Acrylate BPowder BB: White powder
Table 3. Confirmatory test results for acrylic materials.
Table 3. Confirmatory test results for acrylic materials.
MaterialSlurry Ratio:
Aa:Ab:B:Water		Gel Time/sTest Results
Acrylate7:0.7:1:80286Reaction exothermic, after gel formation of white gel, with a certain degree of elasticity and viscosity
7:0.7:1:60121
7:0.7:1:4060
Table 4. The zeolite-AC composite material test proportioning design.
Table 4. The zeolite-AC composite material test proportioning design.
Adjustment FactorsMass Proportionality and Addition
Slurry ratio4:1; 5:1; 6:1; 7:1; 8:1
Water use ratio4:1; 5:1; 6:1; 7:1
Zeolite powder percentage0.25%; 0.5%; 0.75%; 1.0%; 1.25%; 1.5%
Table 5. Optimal ratio performance index parameter.
Table 5. Optimal ratio performance index parameter.
Optimal Ratio RangePhysical PropertiesTest Values
Percentage of zeolite powder: 0.50–1.00%gel time50 s–77.5 s
Water use ratio: 5:1–6:1Water expansion rate65–77%
Slurry ratio: 5:1–6:1bond strength6 kPa–8 kPa
Table 6. Double grouting water plugging effect table.
Table 6. Double grouting water plugging effect table.
NumberGrouting MaterialInlet Flow Rate m/sOutlet Flow Rate m/sWater Plugging Rate (%)Mean ± SD (%)
1The AC + cement slurry0.0400.03321.220.20 ± 4.98
2The AC + cement slurry0.0800.06523.4
3The AC + cement slurry0.1200.09723.7
4The AC + cement slurry0.1600.13518.5
5The AC + cement slurry0.2000.17812.3
6The AC + cement slurry0.0400.03225
7The AC + cement slurry0.0800.06425
8The AC + cement slurry0.1200.09822.4
9The AC + cement slurry0.1600.13617.6
10The AC + cement slurry0.2000.17712.9
11The zeolite-AC + cement slurry0.0400.02937.944.56 ± 6.61
12The zeolite-AC + cement slurry0.0800.05448.1
13The zeolite-AC + cement slurry0.1200.08148.1
14The zeolite-AC + cement slurry0.1600.11440.3
15The zeolite-AC + cement slurry0.2000.13943.8
16The zeolite-AC + cement slurry0.0400.030 33.3
17The zeolite-AC + cement slurry0.0800.05156.8
18The zeolite-AC + cement slurry0.1200.08246.3
19The zeolite-AC + cement slurry0.1600.11242.9
20The zeolite-AC + cement slurry0.2000.13548.1
Note: Statistical comparison between groups: t = 9.24, df ≈ 17, p < 0.00001.
Table 7. Two-way ANOVA results for water plugging rate.
Table 7. Two-way ANOVA results for water plugging rate.
Source of VariationDegrees of Freedom (df)Mean Square (MS)F-Valuep-Value
Grouting material type12969.0244.91.1 × 10−12
Flow velocity4184.615.21.3 × 10−5
Type × Velocity4102.98.54.0 × 10−4
Error1012.1
Note: All p-values < 0.001 indicate statistical significance at the 0.1% level.
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Wang, Q.; Cui, M.; Li, P. Zeolite-Modified Acrylate Grouts: Synergistic Water-Sealing Performance with Cement Slurry Combined Grouting for Water-Rich Sandy Cobble Tunnels. Polymers 2026, 18, 600. https://doi.org/10.3390/polym18050600

AMA Style

Wang Q, Cui M, Li P. Zeolite-Modified Acrylate Grouts: Synergistic Water-Sealing Performance with Cement Slurry Combined Grouting for Water-Rich Sandy Cobble Tunnels. Polymers. 2026; 18(5):600. https://doi.org/10.3390/polym18050600

Chicago/Turabian Style

Wang, Qiusheng, Mengchao Cui, and Pei Li. 2026. "Zeolite-Modified Acrylate Grouts: Synergistic Water-Sealing Performance with Cement Slurry Combined Grouting for Water-Rich Sandy Cobble Tunnels" Polymers 18, no. 5: 600. https://doi.org/10.3390/polym18050600

APA Style

Wang, Q., Cui, M., & Li, P. (2026). Zeolite-Modified Acrylate Grouts: Synergistic Water-Sealing Performance with Cement Slurry Combined Grouting for Water-Rich Sandy Cobble Tunnels. Polymers, 18(5), 600. https://doi.org/10.3390/polym18050600

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