Next Article in Journal
Enhancing Sustainable Mobility Through Gamified Challenges: Evidence from a School-Based Intervention
Previous Article in Journal
An Experimental and Modelling Study on the Effect of Vegetation-Influenced Water Velocity on Cadmium Accumulation in Corbicula fluminea
Previous Article in Special Issue
Study on the Sustainability of Carbon Emission Reduction in China’s Cement Industry
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Sustainability
Volume 17
Issue 14
10.3390/su17146587
sustainability-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Correlation Between Packing Voids and Fatigue Performance in Sludge Gasification Slag-Cement-Stabilized Macadam

by
Yunfei Tan
1,
Xiaoqi Wang
2,
Hao Zheng
2,
Yingxu Liu
1,
Juntao Ma
2,3,* and
Shunbo Zhao
2
1
Zhengzhou Sewage Purification Co., Ltd., Zhengzhou 450045, China
2
International Joint Research Lab for Eco-Building Materials and Engineering of Henan, North China University of Water Resources and Electric Power, Zhengzhou 450045, China
3
Department of Civil and Environmental Engineering, University of Strathclyde, Glasgow G1 1XJ, UK
*
Author to whom correspondence should be addressed.
Sustainability 2025, 17(14), 6587; https://doi.org/10.3390/su17146587
Submission received: 6 June 2025 / Revised: 1 July 2025 / Accepted: 11 July 2025 / Published: 18 July 2025
(This article belongs to the Special Issue Recent Advances in Sustainable Construction Materials and Structural Systems)
Browse Figures
Versions Notes

Abstract

The fatigue resistance of cement-stabilized macadam (CSM) plays a vital role in ensuring the long-term durability of pavement structures. However, limited cementitious material (CM) content often leads to high packing voids, which significantly compromise fatigue performance. Existing studies have rarely explored the coupled mechanism between pore structure and fatigue behavior, especially in the context of solid-waste-based CMs. In this study, a cost-effective alkali-activated sludge gasification slag (ASS) was proposed as a sustainable CM substitute for ordinary Portland cement (OPC) in CSM. A dual evaluation approach combining cross-sectional image analysis and fatigue loading tests was employed to reveal the effect pathway of void structure optimization on fatigue resistance. The results showed that ASS exhibited excellent cementitious reactivity, forming highly polymerized C-A-S-H/C-S-H gels that contributed to a denser microstructure and superior mechanical performance. At a 6% binder dosage, the void ratio of ASS–CSM was reduced to 30%, 3% lower than that of OPC–CSM. The 28-day unconfined compressive strength and compressive resilient modulus reached 5.7 MPa and 1183 MPa, representing improvements of 35.7% and 4.1% compared to those of OPC. Under cyclic loading, the ASS system achieved higher energy absorption and more uniform stress distribution, effectively suppressing fatigue crack initiation and propagation. Moreover, the production cost and carbon emissions of ASS were 249.52 CNY/t and 174.51 kg CO2e/t—reductions of 10.9% and 76.2% relative to those of OPC, respectively. These findings demonstrate that ASS not only improves fatigue performance through pore structure refinement but also offers significant economic and environmental advantages, providing a theoretical foundation for the large-scale application of solid-waste-based binders in pavement engineering.

1. Introduction

Cement-stabilized macadam (CSM) is a typical semi-rigid base material [1,2] exhibiting both “rigid” and “flexible” characteristics [3,4]. Since its introduction, CSM has been extensively researched and widely implemented in pavement structures [5]. In China, CSM is a prevalent base material in modern road engineering, particularly for expressways, major municipal roads, and heavy-traffic highways [6,7,8,9,10]. Typically, CSM consists of a low cement content (generally 6%), aggregates, and additional components, providing high strength and enhancing load-bearing capacity without increasing pavement thickness [6,11]. As the primary load-bearing layer, CSM is prone to crack development during long-term service, which may ultimately lead to irreversible structural instability. It is widely acknowledged that cyclic loading from external sources is the principal cause of cracking in CSM [7]. Notably, a higher fatigue performance under a given stress level directly translates into an extended pavement service life [12]. Therefore, the fatigue resistance of CSM is a critical factor governing the long-term durability of pavements.
The fatigue performance of CSM is governed by multiple factors, among which mechanical properties serve as a key intrinsic determinant. The mechanical properties of CSM primarily arise from the cementitious effect of cement. However, owing to the high cost and significant shrinkage associated with cement, the dosage of cementitious materials (CMs) is typically limited, resulting in a relatively high proportion of internal voids within the CSM matrix. Numerous studies have investigated these relationships. Deng et al. reported that the compressive strength of CSM initially increases and then decreases with higher cement content, and exhibits a nonlinear increase with extended curing time [1]. Similarly, Zhao et al. observed that, within the 2–5% cement content range, the compressive strength of CSM increases by approximately 30% for each 1% increment in cement dosage [13]. Wang et al. examined the strength and fatigue performance of CSM under three-dimensional stress conditions at different ages and cement dosages, and noted that increased cement content leads to a greater disparity between tensile and compressive equivalent stresses. Both the tensile and compressive moduli of CSM improve with curing age [14]. Zhang et al. found that, under identical loading conditions, the fatigue life of CSM after long-term curing can reach several thousand cycles, which is substantially higher than that observed at early ages (only tens of cycles) [15]. Collectively, these findings indicate that excessive matrix voids resulting from low-CM content have a pronounced negative impact on the fatigue performance of CSM.
Sludge gasification slag is a solid residue generated from the pyrolysis and gasification of sewage sludge and is currently stockpiled in large quantities, posing significant challenges to both the environment and land resources. As a type of solid waste, the rational disposal of sludge gasification slag represents an effective approach to resource utilization. Alkali activation is a widely adopted technology for developing cementitious materials (CMs) worldwide [16]. Alkali-activated CMs are prepared using aluminosilicate-rich precursors, which may be sourced from metallurgical slag [17,18], sludge [19,20], red mud [21,22,23], incineration residues/fly ash [24,25,26,27], and other solid waste substitutes. Compared with conventional cement, alkali-activated materials exhibit broad applicability and considerable economic and environmental advantages, making them a superior alternative in many applications. Sludge gasification slag produced at high temperatures (800–1200 °C) is rich in silicon and aluminum, imparting it with latent reactivity. Drawing upon the alkali activation strategies employed for other aluminosilicate solid wastes, substituting cement with alkali-activated sludge gasification slag in CSM preparation is anticipated to reduce costs and address fatigue issues associated with low-CM content and high packing voids.
However, to date, few studies have systematically investigated the use of alkali-activated sludge gasification slag (ASS) in CSM under low binder dosage conditions, particularly in relation to its fatigue behavior and microstructural mechanisms. Most existing work has focused on improving static mechanical performance or environmental safety, with limited attention paid to the complex interaction between pore structure and fatigue life. Traditional experimental methods also struggle to quantify the internal structure of CSM accurately or reveal the fatigue failure mechanism from a micro–macro perspective. Therefore, there is an urgent need to develop an integrated methodology to link the internal void characteristics with fatigue resistance in ASS-based CSM, which would help optimize both cost and long-term performance.
While mercury intrusion porosimetry (MIP) is commonly employed to evaluate pore size distribution due to its high precision, it suffers from several limitations when applied to heterogeneous materials such as CSM. The high-pressure intrusion process can irreversibly alter the internal pore structure, potentially leading to inaccurate measurements. Moreover, in aggregate-based systems, where capillary pores, interfacial gaps, and intergranular voids coexist, MIP may misidentify connected pores or introduce ‘false’ pores, thereby underestimating the structural continuity of the matrix. In contrast, this study employed a digital image recognition method to quantify pore structures based on high-resolution cross-sectional images of polished specimens. This non-destructive approach provides a more intuitive and objective representation of the actual distribution of aggregates and voids within the material. Furthermore, it is particularly well-suited for analyzing materials with pronounced gradation and non-uniform textures, facilitating a clearer understanding of the relationship between microstructural features and macroscopic fatigue performance.
In response to these challenges, this study introduces three key innovations: (1) it applies alkali-activated sludge gasification slag as a novel cementitious binder in CSM, expanding the resource utilization pathway for this solid waste; (2) it incorporates image recognition techniques to quantitatively analyze internal pore structure and explores its coupling relationship with fatigue behavior; and (3) it bridges the microstructural features and macroscopic fatigue responses by analyzing mechanical and energy dissipation characteristics.
In this study, two types of CMs—ASS (alkali-activated sludge gasification slag) and cement—were used at three different dosages (4%, 5%, and 6%) to fabricate CSM. Cross-sectional image analysis was utilized to quantitatively evaluate the packing void ratio of specimens with varying mix proportions. The unconfined compressive strength, compressive resilient modulus, void distribution, and fatigue performance of the specimens were assessed. The correlations among these properties were analyzed, aiming to enhance the fatigue performance of CSM through cost control and the utilization of sludge gasification slag as a sustainable alternative material.

2. Materials and Methods

The research process is depicted in Figure 1. Initially, ASS was synthesized, and its cementitious properties were characterized by compressive strength testing, X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). Subsequently, ASS was employed as the CM for preparing CSM, and its influence on the unconfined compressive strength, compressive resilient modulus, void ratio distribution, and fatigue performance of CSM was systematically evaluated.

2.1. Preparation of ASS

The sludge gasification slag (SGS) used in this study was obtained from a sewage treatment plant in Zhengzhou, China, and was ground in a ball mill for 30 min prior to use, yielding ground sludge gasification slag (GSGS). Ground granulated blast furnace slag (GGBS) was supplied by Wuhan Wuxin New Building Materials Co., Ltd. (Wuhan, China). The cement used was P.O 42.5-grade ordinary Portland cement (OPC), provided by Henan Tianrui Cement Plant (Zhengzhou, China). The alkali activator consisted of a mixture of water glass solution and sodium hydroxide pellets. The water glass solution, a colorless and transparent viscous liquid, was manufactured by Jiashan Yourui Refractory Materials Co., Ltd. (Jiashan, China). Sodium hydroxide pellets (purity ≥96%, analytical grade) were purchased from Tianjin Hengxing Chemical Reagent Manufacturing Co., Ltd. (Tianjin, China). The physical properties of OPC and the chemical compositions of the raw materials are summarized in Table 1 and Table 2, respectively. The principal chemical constituents of GSGS are SiO2 and Al2O3, indicating its suitability for alkali activation.
To characterize the particle-level properties of the cementitious materials, the specific surface area of GGBS, GSGS, and OPC was measured using the Brunauer–Emmett–Teller (BET) nitrogen adsorption method. Prior to testing, all samples were oven-dried at 105 °C for 24 h. The analysis was performed using a Micromeritics ASAP 2460 surface area analyzer (Norcross, GA, USA) under liquid nitrogen conditions. The measured BET surface areas were 14.2 m2/g for GSGS, 12.6 m2/g for GGBS, and 2.1 m2/g for OPC, confirming the significantly finer particle characteristics of the solid-waste-based materials.
In order to further assess the environmental safety of the sewage sludge gasification slag (ASS), representative samples were randomly collected and analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES). The leaching behavior was evaluated in accordance with the concentration thresholds stipulated in the GB 5085.3-2007 Identification Standards for Hazardous Wastes—Leaching Toxicity Identification [28]. A detailed comparison between the measured results and the regulatory limits is provided in Table 3.
CGSG, GGBS, and the alkali activator were mixed using an NJ-160A paste mixer (Wuxi, China) and then cast into triple molds. After demolding, the specimens were cured under standard conditions until 3 and 28 days, with OPC specimens serving as the control group. The mix proportions are shown in Table 4. The 3-day and 28-day compressive strengths of ASS and OPC were tested according to the relevant standard, and their hydration mechanisms were analyzed using X-ray diffraction (XRD, Bruker D8 Advance, Karlsruhe, Germany) and Fourier-transform infrared spectroscopy (FTIR, Thermo Nicolet iS50, Waltham, MA, USA).

2.2. Preparation and Performance Analysis of CSM

The coarse and fine aggregates used for CSM preparation were crushed stone (5–10 mm) and river sand (0–5 mm), respectively, with their physical properties shown in Table 5. Both OPC-CSM and ASS-CSM were prepared using a fixed coarse-to-fine aggregate ratio of 6:4, and the detailed mix proportions are listed in Table 6. To determine the optimal binder content for ASS-based CSM, preliminary tests were conducted with ASS dosages of 3%, 4%, 5%, 6%, and 7%. The results showed that 6% achieved the best balance among mechanical strength, porosity reduction, and fatigue performance. At 7%, excessive paste coverage led to early-age shrinkage cracks, reduced workability, and an increased cost. Higher dosages (e.g., 9% or 12%) were not considered further due to expected diminishing returns and economic inefficiency. Meanwhile, 3% dosage exhibited poor structural integrity with high porosity and low fatigue life. Based on these observations, 6% was selected as the optimal dosage, balancing performance, cost, and structural reliability. All mixtures were then subjected to compaction, specimen molding, and curing procedures, followed by mechanical performance testing in accordance with the standard methods specified in JTG 3441-2024 [29].
The compaction test for CSM was performed according to Method A of T0804-1994, as specified in JTG 3441-2024, to determine the optimum moisture content and maximum dry density for both OPC and ASS systems. Cylindrical specimens (φ100 × 100 mm) were fabricated by static compaction in molds and subsequently cured under standard conditions in accordance with T0843-2009 and T0845-2009 for 7 and 28 days. The unconfined compressive strength and resilient modulus tests were conducted in accordance with T0805-2024 and T0808-1994, respectively, with three replicate specimens per group.
The internal aggregate and void distributions of the CSM were characterized using digital image analysis to preliminarily assess fatigue resistance. For both OPC and ASS specimens at 28 days, high-resolution cross-sectional images were obtained after wire cutting, polishing with fine sandpaper, and ink coating. A square region from the lower 70–80 mm section of each 100 mm high specimen was selected for analysis. For each group, three representative images (1500 × 1500 pixels) were selected from three independent specimens to ensure consistency and statistical validity.
All image processing was performed using ImageJ software (National Institutes of Health, v1.53). Images were first converted to grayscale and then binarized using Otsu’s automatic thresholding method, with contrast enhancement set to 500% to achieve a clear black-and-white separation. Void areas (white pixels) were marked in red, while aggregates and matrix (black pixels) were retained. The void ratio was calculated as the percentage of red pixels in the total image area. Figure 2 illustrates the overall processing workflow.
To ensure repeatability, each image was independently processed by three trained researchers following an identical procedure. The resulting porosity values showed a maximum discrepancy within ±1.2%, indicating strong methodological consistency and high operational reliability under standardized conditions.
The fatigue performance was tested using an MTS testing machine (MTS Systems Corporation, Eden Prairie, MN, USA). The cyclic loading–unloading stress amplitudes were set at 60% and 20% of the peak value, with a loading rate of 0.25 MPa/s. The testing procedure is illustrated in Figure 3.

3. Results and Analyses

3.1. Cementitious Properties of ASS

Figure 4 displays the 3-day and 28-day compressive strengths of both the OPC and ASS systems. The results indicate that both systems exhibited substantial strength gains with prolonged curing, albeit with distinct strength development patterns. At 3 days, the compressive strength of the ASS system reached 71.4 MPa, which was 27.6 MPa higher than that of OPC (43.8 MPa). This suggests that the water glass activator in the ASS system can rapidly activate the reactive components in the raw materials, promote gel phase formation, and effectively fill pores [30], thereby conferring excellent early strength. At 28 days, the compressive strength of ASS increased to 99.8 MPa, representing an increment of 28.4 MPa, while OPC increased from 43.8 MPa to 68.4 MPa, with an increment of 24.6 MPa. The strength increment of ASS was 15.45% higher than that of OPC, highlighting its greater potential for mechanical performance development. This continuous improvement is attributed to the sustained hydration reactions in the ASS system; in an alkaline environment, reactive silicon and aluminum components undergo depolymerization–repolymerization reactions to form a dense gel network [31], thereby further enhancing the matrix structure.
Figure 5 compares the mineralogical compositions of OPC and ASS systems at 3 and 28 days. In the ASS system, the main phases include SiO2, and hydration-generated C-A-S-H and C-S-H gels. With an increasing curing time, the diffraction peak intensities of SiO2 and C-A-S-H decrease significantly, while the intensity of C-S-H increases, indicating the transformation of C-A-S-H into C-S-H. This is attributed to the continuous hydration of GSGS and GGBS under alkaline conditions, where the SiO2 crystal structure is disrupted and releases reactive SiO44− ions that participate in polycondensation reactions [32]. This process provides new nucleation sites for the formation of amorphous gels and promotes the densification of the gel network, which significantly enhances the long-term strength of ASS [33]. The superior early strength of ASS results from the synergistic effect of C-A-S-H and C-S-H in the hydration products. In contrast, the OPC system shows a strong Ca(OH)2 peak at 3 days, reflecting that the early hydration mainly involves the reaction of CaO with water, which contributes little to early strength improvement [34]. As curing time increases, C-A-S-H in the ASS system continues to convert into highly polymerized C-S-H, greatly improving structural compactness. However, in OPC, the CaCO3 and C2S peaks increase, suggesting that later hydration is limited by carbonation reactions, thus hindering the hydration process and resulting in lower strength growth compared to ASS [35].
Figure 6 presents the FTIR spectra of 28-day hydration products for both the ASS and OPC systems. Characteristic absorption peaks were observed at 3440 cm−1, 1640 cm−1, 1420 cm−1, 981 cm−1, and 455 cm−1 for both systems, yet notable spectral differences were apparent. The OPC sample exhibits a pronounced absorption peak at 3640 cm−1, corresponding to the stretching vibration of –OH in Ca(OH)2, indicating the presence of residual unreacted calcium hydroxide in its hydration products. The peaks at 3440 cm−1 and 1640 cm−1 are assigned to the O–H stretching vibration of free and bound water in OPC, as well as to the hydroxyl stretching and H–O–H bending vibrations of non-bonded water in C-A-S-H gel for ASS. The peak at 1420 cm−1 corresponds to the symmetric stretching vibration of C–O bonds; its higher intensity in OPC compared to ASS reflects the formation of CaCO3 via the carbonation of hydration products [36]. This observation also confirms the extremely low carbonate content in ASS, in agreement with the XRD results. The absorption peaks at 981 cm−1 and 455 cm−1 are attributed to the asymmetric stretching of Si–O–T bonds. Notably, the ASS sample exhibits much stronger peak intensities at these positions compared to OPC, indicating a higher degree of silicate anion polymerization and a more complete formation of C-S-H and C-A-S-H gels in its hydrates [37]. Taken together, the FTIR and XRD results demonstrate that the synergistic activation of GGBS and GSGS in the ASS system promotes the efficient utilization of aluminosilicate resources and results in a denser microstructure.

3.2. Packing State of CSM

Figure 7 compares the proportions of voids and aggregates in OPC-CSM and ASS-CSM at different CM dosages. With increasing CM dosage, the void content in both systems decreases markedly, while the aggregate content correspondingly increases. Nevertheless, notable differences in the packing states are observed between the two systems. In the OPC system, increasing the CM dosage from 4% to 5% leads to a sharp reduction in void ratio from 43.67% to 34.80%, and a concomitant increase in aggregate content from 46.87% to 65.20%. These changes are more pronounced than those in the ASS system, where the void ratio decreases from 36.22% to 33.08% and the aggregate content rises from 63.78% to 66.92%. This suggests that at lower dosages, the OPC system rapidly generates a large quantity of gel products, which efficiently fill inter-aggregate voids and substantially densify the packing structure. However, when the CM dosage is further increased to 6%, the void ratio in the OPC system decreases only slightly to 33.20%, with the aggregate proportion reaching 66.80%, indicating that the densification effect has reached saturation. In contrast, the ASS system demonstrates a greater improvement in the packing state at a 6% dosage: the void ratio further drops from 33.08% to 30%, and the aggregate content increases to 70.30%. This enhancement is primarily attributed to the relatively slower formation rate and limited continuity of the gel network during the early hydration stage in the ASS system. However, at higher dosages, ongoing hydration reactions facilitate the development of a more complete cementitious network, effectively filling the remaining inter-aggregate voids and enhancing the overall integrity of the packing structure [30].

3.3. Mechanical Properties of CSM

Standard compaction tests were conducted using a static compaction method. Figure 8 illustrates the optimum moisture content and maximum dry density for both ASS and OPC samples. The results indicate that increasing CM dosage leads to higher maximum dry density and optimum moisture content in both systems. When the OPC dosage increases from 4% to 6%, the optimum moisture content rises from 4.43% to 4.70%, and the maximum dry density increases from 1.97 g/cm3 to 2.03 g/cm3, with respective increments of 0.27% and 0.06 g/cm3. For ASS, the optimum moisture content increases from 4.24% to 4.41%, and the maximum dry density increases from 2.09 g/cm3 to 2.14 g/cm3, with increments of 0.17% and 0.05 g/cm3, respectively. These results demonstrate that changes in OPC dosage exert a more pronounced effect on maximum dry density and optimum moisture content, primarily due to its hydration reaction characteristics and particle gradation. OPC requires more water as a result of the extensive consumption of free water during hydration; in contrast, the high viscosity of the water glass activator in ASS and the rapid formation of C-A-S-H gel reduce the demand for free water [38]. Moreover, the fine particles of GGBS and GSGS fill the skeleton, enhancing the maximum dry density, while the porous structure of GSGS improves inter-particle friction and bonding, further densifying the mixture.
Unconfined compressive strength and compressive resilient modulus are key indicators for evaluating the load-bearing capacity and deformation resistance of CSM [39]. As shown in Figure 9, both strength and the resilient modulus increase substantially with a higher CM dosage and a longer curing time in both the OPC and ASS systems. At an early age (7 days), the OPC system exhibits a higher unconfined compressive strength and resilient modulus. When the dosage increases from 4% to 6%, the OPC-CSM strength increases from 1.5 MPa to 2.5 MPa, and the resilient modulus rises from 992 MPa to 1230 MPa. This is attributed to the rapid hydration rate of OPC, where large quantities of hydration products quickly fill the voids between aggregates, forming an initially dense skeleton. However, after 28 days, the strength development trends of the two systems diverge. The strength of OPC-CSM increases from 3.1 MPa to 4.5 MPa (an increment of 1.4 MPa), whereas ASS-CSM increases from 3.3 MPa to 5.7 MPa (an increment of 2.4 MPa). At this stage, ASS exhibits significantly higher late-age strength than does OPC, mainly due to the sustained formation and cross-linking of C-A-S-H gel under alkaline activation, which continuously fills the voids between aggregates, reduces porosity, and enhances inter-aggregate bonding [40,41]. This results in more pronounced late-stage densification and structural stability in the ASS system.
A similar trend is observed for the resilient modulus. While the OPC system shows a higher early modulus, reflecting a tighter initial structure, the modulus of the ASS system increases more rapidly with longer curing and a higher dosage, indicating greater late-stage densification and stability.
To simulate the stress conditions of CSM in real applications, cyclic loading–unloading tests were performed to assess fatigue resistance. Figure 10 presents the stress–strain curves of CSM under cyclic loading. The OPC-5 curve is steep with narrow hysteresis loops and low ultimate strain, indicating higher rigidity, elastic-dominated behavior, limited plastic deformation, and a tendency towards brittle failure with poor energy dissipation. In contrast, the ASS-5 and ASS-6 curves display more pronounced plastic deformation, wider hysteresis loops, and significantly greater maximum strain, reflecting the ability of the ASS system to accommodate larger deformations and maintain a high load capacity, with enhanced energy dissipation and stress release capabilities. Comparing ASS-5 and ASS-6, a higher binder content further improves ductility and the width of the hysteresis loops, indicating greater toughness, plastic energy storage, better structural integrity under cyclic loading, and more stable residual deformation, thus demonstrating excellent fatigue resistance. Therefore, optimizing the ASS content markedly enhances the plastic deformation capacity and fatigue life of CSM [42], whereas the limited plastic deformation in the OPC system leads to stress concentration and structural damage under cyclic loading.
Figure 11 shows the energy response of OPC-CSM and ASS-CSM under cyclic loading. During the initial cycles, both the total absorbed energy and dissipated energy reach their peak values, as the original voids and larger cracks between aggregates undergo irreversible compaction, consuming substantial energy for structural densification [43]. Over subsequent cycles, ASS-6 consistently exhibits higher total absorbed, elastic, and dissipated energy than ASS-5 and OPC-5, with values stabilizing after the initial cycles. This indicates that increased ASS binder content significantly enhances the energy absorption, storage, and dissipation capacities of CSM, resulting in more rational energy distribution, improved toughness, and superior fatigue resistance under cyclic loading. In contrast, OPC-5 and ASS-5 show lower energy responses and more pronounced initial attenuation, with steady-state values much lower than those of ASS-6, indicating weaker energy dissipation and damage resistance and a tendency towards microcrack accumulation and performance degradation under cyclic loading.

3.4. Cost and Carbon Emissions of ASS

To evaluate the economic and environmental benefits of ASS, both the cost and carbon emissions were calculated based on raw material prices and production-related energy consumption, and were compared with those of OPC. The composition of the ASS binder includes ground sludge gasification slag (GSGS, 29.80%), ground granulated blast furnace slag (GGBS, 44.69%), water glass (22.24%), and sodium hydroxide (3.27%). Market prices and energy consumption parameters were used in all calculations.
GSGS itself was assumed to have no direct market value due to its waste origin, but the electricity required for ball milling (1.5 kW mill, 30 min per ton) was included in both the cost and emission estimations, using a standard electricity price of 1 CNY/kWh and an emission factor of 1 kg CO2 e/kWh. The unit prices of GGBS, sodium hydroxide, and water glass were set at 100, 800, and 800 CNY/t, respectively. The carbon emissions for producing OPC, NaOH, and water glass were assumed to be 735, 1150, and 850 kg CO2 e/t, respectively, based on published life cycle inventory data.
Figure 12 compares the cost and carbon emissions of ASS and OPC. The calculated cost of ASS is 249.52 CNY/t, representing a 10.9% reduction compared to that of OPC. Its carbon emissions are 174.51 kg CO2 e/t, which is only 23.8% of that of OPC—a 76.2% decrease. These results demonstrate that ASS offers significant economic and environmental advantages over OPC. Although sodium hydroxide and water glass are relatively carbon-intensive to produce, their combined content in the ASS system is only 25.5%. Therefore, the overall environmental footprint of ASS remains substantially lower than that of OPC. Furthermore, the use of high-pH activators may present occupational safety concerns in practical applications. To mitigate these risks, it is recommended that future field applications adopt improved handling measures such as pre-dissolved activator solutions, the use of low-alkali formulations, and enhanced safety protocols during mixing and transport. These suggestions have been included in the conclusions as guidance for safer and more sustainable implementation.

4. Discussion

In this study, the fatigue performance of ASS-based CSM was evaluated at a curing age of 28 days, which aligns with the mechanical performance benchmarks defined in JTG 3441-2024. At this age, the ASS system exhibited sufficient compressive strength, reduced porosity, and enhanced fatigue resistance, indicating a well-developed internal structure and binder–aggregate interaction.
However, given the continuous hydration characteristics of alkali-activated systems, particularly the prolonged formation of C-A-S-H gels, the mechanical and fatigue performance of ASS-CSM is expected to further improve beyond 28 days. Previous research has shown that such systems maintain gel development and microstructural refinement up to and beyond 90 days. Therefore, it is anticipated that the long-term fatigue behavior of ASS-CSM may exceed current performance levels. In future work, systematic fatigue testing at extended curing ages (e.g., 90 and 180 days) will be conducted, complemented by microstructural analysis, to verify the long-term stability and durability of the system. This has been explicitly identified as a direction for future research in the conclusions.

5. Conclusions

In this study, GSGS and GGBS were used as raw materials to prepare a cementitious material (CM) through alkali activation, which was then used to partially replace OPC in CSM. The gelation properties of ASS were investigated through strength testing and mechanism analyses. The fatigue performance of CSM was quantitatively evaluated by image analysis and mechanical testing. The main conclusions are as follows:
1.
ASS demonstrates excellent cementitious reactivity and long-term strength development, making it a viable alternative to ordinary Portland cement (OPC). The compressive strengths of ASS at 3 and 28 days reached 71.4 MPa and 99.8 MPa, respectively, which were 63% and 15.45% higher than those of OPC. This improvement is attributed to the continued formation of highly polymerized C-A-S-H and C-S-H gels and the sustained activation of silico-aluminate components, resulting in a denser microstructure and superior mechanical performance.
2.
The use of image-based analysis revealed a clear correlation between reduced porosity and improved fatigue resistance, confirming the effectiveness of pore structure optimization. At 6% binder content, the void ratio of the ASS system was 3% lower than that of OPC. This improvement is attributed to the formation of dense C-A-S-H/C-S-H gels that fill inter-aggregate voids, reducing stress concentration zones and enhancing energy dissipation capacity. As a result, crack initiation and propagation under cyclic loading are effectively delayed—demonstrating a clear pore structure–energy dissipation–fatigue life linkage consistent with both image and energy response data.
3.
The ASS system offers significant sustainability benefits, with a lower cost and carbon emissions than OPC. The material cost of ASS was 249.52 CNY/t, 10.9% lower than OPC, and the carbon emission was only 174.51 kg CO2 e/t—representing a 76.2% reduction. In addition to its enhanced mechanical and fatigue performance, the ASS-based CSM satisfies technical requirements for heavy-duty pavements while demonstrating considerable environmental and economic advantages, indicating strong potential for practical application.

Author Contributions

Writing—review and editing, Y.T.; writing—original draft, X.W.; methodology, J.M.; data curation, Y.T., X.W. and H.Z.; formal analysis, X.W. and Y.L.; supervision, J.M. and S.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This study was funded by the National Natural Science Foundation of China (51508191), the Science and Technology Project of Henan Province (242102321058), the key scientific research project of Henan University (24A560027), and the Colleges Young Teacher Training Project of Henan Province (2023GGJS074).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data is contained within the article.

Acknowledgments

This research has benefited from the experts and laboratory manager of International Joint Research Lab for Eco-building Materials and Engineering of Henan.

Conflicts of Interest

Author Yunfei Tan was employed by the company Sewage Purification Co., Ltd., Zhengzhou 450045, China. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

References

  1. Deng, C.; Jiang, Y.; Lin, H.; Ji, X. Mechanical-strength-growth law and predictive model for cement-stabilized macadam. Constr. Build. Mater. 2019, 215, 582–594. [Google Scholar] [CrossRef]
  2. Lv, S.; Yuan, J.; Liu, C.; Wang, J.; Li, J.; Zheng, J. Investigation of the fatigue modulus decay in cement stabilized base material by considering the difference between compressive and tensile modulus. Constr. Build. Mater. 2019, 223, 491–502. [Google Scholar] [CrossRef]
  3. Ji, X.; Zheng, N.; Niu, S.; Meng, S.; Xu, Q. Development of a rutting prediction model for asphalt pavements with the use of an accelerated loading facility. Road Mater. Pavement Des. 2016, 17, 15–31. [Google Scholar] [CrossRef]
  4. Ji, X.; Zheng, N.; Hou, Y.; Niu, S. Application of asphalt mixture shear strength to evaluate pavement rutting with accelerated loading facility (ALF). Constr. Build. Mater. 2013, 41, 1–8. [Google Scholar] [CrossRef]
  5. Xuan, D.X.; Houben, L.J.M.; Molenaar, A.A.A.; Shui, Z.H. Mechanical properties of cement-treated aggregate material–a review. Mater. Des. 2012, 33, 496–502. [Google Scholar] [CrossRef]
  6. Song, L.; Song, Z.; Wang, C.; Wang, X.; Yu, G. Arch expansion characteristics of highway cement-stabilized macadam base in Anjiang, China. Constr. Build. Mater. 2019, 215, 264–274. [Google Scholar] [CrossRef]
  7. Dong, Q.; Yan, S.; Chen, X.; Dong, S.; Zhao, X.; Polaczyk, P. Review on the mesoscale characterization of cement-stabilized macadam materials. J. Road Eng. 2023, 3, 71–86. [Google Scholar] [CrossRef]
  8. Fu, T.; Liang, J.; Rong, H.; Li, Y.; Lin, Y. Modelling of physical and mechanical properties and adiabatic temperature rise of cement-stabilized macadam. Innov. Infrastruct. Solut. 2023, 8, 332. [Google Scholar] [CrossRef]
  9. Yuan, Y.; Hu, X.; Wang, K.; Liu, Z.; Zhong, M.; Meng, K. Study on Mechanical Properties of Road Cement-Stabilized Macadam Base Material Prepared with Construction Waste Recycled Aggregate. Buildings 2024, 14, 2605. [Google Scholar] [CrossRef]
  10. Tao, R.; Cheng, X.; Jin, Y.; Qiao, J.; Zhang, X.; Kim, D.; Liu, J. Mechanical properties of double-solid waste cement stabilized Macadam. Sci. Rep. 2025, 15, 4425. [Google Scholar] [CrossRef]
  11. Ismail, A.; Baghini, M.S.; Karim, M.R.; Shokri, F.; Al-Mansob, R.A.; Firoozi, A.A.; Firoozi, A. A Laboratory investigation on the strength characteristics of cement-treated base. Appl. Mech. Mater. 2014, 507, 353–360. [Google Scholar] [CrossRef]
  12. Hernando, D.; Del Val, M.A. Guidelines for the design of semi-rigid long-life pavements. Int. J. Pavement Res. Technol. 2016, 9, 121–127. [Google Scholar] [CrossRef]
  13. Zhao, K.; Zhao, L.; Hou, J.; Feng, Z.; Jiang, W. Impact of mixing methods and cement dosage on unconfined compressive strength of cement-stabilized macadam. Int. J. Concr. Struct. Mater. 2022, 16, 16. [Google Scholar] [CrossRef]
  14. Wang, S.; Lv, S.; Pan, Q.; Wang, P.; Deng, W.; Zhang, B.; Lei, D. Investigation on strength and fatigue performance of cement-stabilized macadam under three-dimensional stress state at different ages and cement dosages. Constr. Build. Mater. 2024, 435, 136686. [Google Scholar] [CrossRef]
  15. Zhang, J.; Bai, J.; Wang, S. Fatigue damage evolution rule of cement stabilized macadam used in pavement’s base course at different curing time. Constr. Build. Mater. 2022, 325, 126827. [Google Scholar] [CrossRef]
  16. Provis, J.L. Alkali-activated materials. Cem. Concr. Res. 2018, 114, 40–48. [Google Scholar] [CrossRef]
  17. Sun, J.; Hou, S.; Guo, Y.; He, W.; Cui, Y.; Zhang, P. Effects of high-temperature curing on hydration and microstructure of alkali-activated typical steel slag cementitious material. Dev. Built Environ. 2024, 17, 100314. [Google Scholar] [CrossRef]
  18. Wang, M.; Xu, J.; Zhang, X.; Tan, L.; Mei, Y. Mechanical Performance Optimization and Microstructural Mechanism Study of Alkali-Activated Steel Slag–Slag Cementitious Materials. Buildings 2024, 14, 1204. [Google Scholar] [CrossRef]
  19. Lv, T.; Zhang, J.; Tao, R.; Hou, D.; Long, W.J.; Dong, B. Performance of acid-alkali activated dredged sludge as a supplementary cementitious material. Constr. Build. Mater. 2025, 458, 139569. [Google Scholar] [CrossRef]
  20. He, S.; Huang, X.; Yu, P.; Zhou, Y.; Luo, Y. Mechanical properties and durability of alkali-activated fly ash-municipal sludge concrete. Constr. Build. Mater. 2024, 419, 135515. [Google Scholar] [CrossRef]
  21. Yan, F.; Luo, K.; Ye, J.; Zhang, W.; Chen, J.; Ren, X.; Li, J. Effect of pore structure characteristics on the properties of red mud-based alkali-activated cementitious materials. J. Sustain. Cem. Based Mater. 2024, 13, 1753–1769. [Google Scholar] [CrossRef]
  22. Dai, Z.; Li, J.; Yi, W.; Chen, H.; Liang, X. Preparation and performance assessment of calcium carbide slag alkali-activated red mud-based cementitious material. Mater. Today Commun. 2024, 41, 110848. [Google Scholar] [CrossRef]
  23. Li, Y.; Luo, Y.; Zhou, H.; Zhong, X.; Zhou, Z.; Li, J.; Hou, H. Preparation of environmental-friendly cementitious material from red mud and waste glass sludge by mechanical activation. Constr. Build. Mater. 2024, 423, 135861. [Google Scholar] [CrossRef]
  24. Xie, G.; Zhang, W.; Liu, J.; Liang, Z.; Xing, F. Recovery potential of municipal solid waste incineration bottom ash graded by particle size in an alkali-activated cementitious material system: Curing properties and environmental leaching risk. Constr. Build. Mater. 2024, 448, 138237. [Google Scholar] [CrossRef]
  25. Jamalimoghadam, M.; Vakili, A.H.; Keskin, I.; Totonchi, A.; Bahmyari, H. Solidification and utilization of municipal solid waste incineration ashes: Advancements in alkali-activated materials and stabilization techniques: A review. J. Environ. Manag. 2024, 367, 122014. [Google Scholar] [CrossRef] [PubMed]
  26. Lan, J.; Dong, Y.; Kai, M.F.; Hou, H.; Dai, J.G. Investigation of waste alkali-activated cementing material using municipal solid waste incineration fly ash and dravite as precursors: Mechanisms, performance, and on-site application. J. Hazard. Mater. 2024, 465, 133416. [Google Scholar] [CrossRef] [PubMed]
  27. Yu, Z.; Wang, B.; Li, T.; Wang, W. Toughness study of polyacrylamide-modified slag/fly ash-based alkali-activated cementitious materials. Constr. Build. Mater. 2024, 450, 138622. [Google Scholar] [CrossRef]
  28. ISO 14001:2015; Environmental Management Systems—Requirements with Guidance for Use. International Organization for Standardization: Geneva, Switzerland, 2015.
  29. JTG 3441-2024; Test Code for Inorganic Binder Stabilized Materials in Highway Engineering. Ministry of Transport of the People’s Republic of China: Beijing, China, 2024.
  30. Zhang, X.; Li, H.; Wang, H.; Yan, P.; Shan, L.; Hua, S. Properties of RCA stabilized with alkali-activated steel slag based materials in pavement base: Laboratory tests, field application and carbon emissions. Constr. Build. Mater. 2024, 411, 134547. [Google Scholar] [CrossRef]
  31. Fort, J.; Mildner, M.; Keppert, M.; Cerny, R. Recycling of Aluminosilicate-Based Solid Wastes through Alkali-Activation: Preparation Characterization Challenges. J. Build. Eng. 2022, 54, 15. [Google Scholar] [CrossRef]
  32. Weng, L.; Sagoe-Crentsil, K. Dissolution processes, hydrolysis and condensation reactions during geopolymer synthesis: Part I-Low Si/Al ratio systems. J. Mater. Sci. 2007, 42, 2997–3006. [Google Scholar] [CrossRef]
  33. Van Deventer, J.S.; Provis, J.L.; Duxson, P.; Lukey, G.C. Reaction mechanisms in the geopolymeric conversion of inorganic waste to useful products. J. Hazard. Mater. 2006, 139, 506–513. [Google Scholar] [CrossRef] [PubMed]
  34. Jiang, H.; Ke, G.; Li, Z. Synergistic activation mechanism and long-term properties of a solid waste cementitious materials based on red mud and calcium carbide slag. Constr. Build. Mater. 2024, 438, 137313. [Google Scholar] [CrossRef]
  35. Gong, P.; Mei, K.; Zhang, L.; Xue, Q.; Wang, X.; Wei, T.; Zhang, C.; Cheng, X. Hydration and carbonation reaction dynamics in CO2-rich environment for tricalcium silicate (C3S) and dicalcium silicate (C2S). Powder Technol. 2025, 452, 120535. [Google Scholar] [CrossRef]
  36. Rafeet, A.; Vinai, R.; Soutsos, M.; Sha, W. Effects of slag substitution on physical and mechanical properties of fly ash-based alkali activated binders (AABs). Cem. Concr. Res. 2019, 122, 118–135. [Google Scholar] [CrossRef]
  37. Guo, W.; Wang, S.; Xu, Z.; Zhang, Z.; Zhang, C.; Bai, Y.; Zhao, Q. Mechanical performance and microstructure improvement of soda residue-carbide slag-ground granulated blast furnace slag binder by optimizing its preparation process and curing method. Constr. Build. Mater. 2021, 302, 124403. [Google Scholar] [CrossRef]
  38. Liu, W.; Du, R.; Zhang, R.; Zhao, Z.; Zhang, L.; Li, H. Optimal design performance of eco-friendly materials stabilized with inorganic binder based on fluidized bed coal combustion fly ash regenerated brick powder. J. Build. Eng. 2023, 65, 105800. [Google Scholar] [CrossRef]
  39. Yan, K.; Gao, F.; Sun, H.; Ge, D.; Yang, S. Effects of municipal solid waste incineration fly ash on the characterization of cement-stabilized macadam. Constr. Build. Mater. 2019, 207, 181–189. [Google Scholar] [CrossRef]
  40. Hou, D.S.; Li, Z.J.; Zhao, T.J. Reactive force field simulation on polymerization and hydrolytic reactions in calcium aluminate silicate hydrate (C-A-S-H) gel: Structure, dynamics and mechanical properties. RSC Adv. 2015, 5, 448–461. [Google Scholar] [CrossRef]
  41. Tu, W.L.; Zhang, M.Z. Multiscale microstructure and micromechanical properties of alkali-activated concrete: A critical review. Cem. Concr. Compos. 2024, 152, 105664. [Google Scholar] [CrossRef]
  42. Liu, M.Y.; Lu, J.; Jiang, W.H.; Ming, P. Study on fatigue damage and fatigue crack propagation of rubber concrete. J. Build. Eng. 2023, 65, 105718. [Google Scholar] [CrossRef]
  43. Xu, Y.; Yang, R.; Chen, P.; Ge, J.; Liu, J.; Xie, H. Experimental study on energy and failure characteristics of rubber-cement composite short-column under cyclic loading. Case Stud. Constr. Mater. 2022, 16, e00885. [Google Scholar] [CrossRef]
Sustainability 17 06587 g001
Figure 1. Sample preparation and detection process.
Figure 1. Sample preparation and detection process.
Sustainability 17 06587 g001
Sustainability 17 06587 g002
Figure 2. Image processing process.
Figure 2. Image processing process.
Sustainability 17 06587 g002
Sustainability 17 06587 g003
Figure 3. Schematic diagram of the fatigue cyclic loading and unloading protocol.
Figure 3. Schematic diagram of the fatigue cyclic loading and unloading protocol.
Sustainability 17 06587 g003
Sustainability 17 06587 g004
Figure 4. Compressive strength of two types of cementitious materials at different ages.
Figure 4. Compressive strength of two types of cementitious materials at different ages.
Sustainability 17 06587 g004
Sustainability 17 06587 g005
Figure 5. XRD patterns of two types of cementitious materials at different ages.
Figure 5. XRD patterns of two types of cementitious materials at different ages.
Sustainability 17 06587 g005
Sustainability 17 06587 g006
Figure 6. FTIR patterns of two types of cementitious materials at 28 d.
Figure 6. FTIR patterns of two types of cementitious materials at 28 d.
Sustainability 17 06587 g006
Sustainability 17 06587 g007
Figure 7. Distribution of voids and aggregates at different CM dosages.
Figure 7. Distribution of voids and aggregates at different CM dosages.
Sustainability 17 06587 g007
Sustainability 17 06587 g008
Figure 8. Maximum dry density and optimum moisture content of CSM with different CM dosages.
Figure 8. Maximum dry density and optimum moisture content of CSM with different CM dosages.
Sustainability 17 06587 g008
Sustainability 17 06587 g009
Figure 9. Mechanical properties of CSM with different CM dosages.
Figure 9. Mechanical properties of CSM with different CM dosages.
Sustainability 17 06587 g009
Sustainability 17 06587 g010
Figure 10. Stress–strain curves of CSM under cyclic loading and unloading with different CM dosages.
Figure 10. Stress–strain curves of CSM under cyclic loading and unloading with different CM dosages.
Sustainability 17 06587 g010
Sustainability 17 06587 g011
Figure 11. Relationship between energy and cycle number of CSM with different CM dosages.
Figure 11. Relationship between energy and cycle number of CSM with different CM dosages.
Sustainability 17 06587 g011
Sustainability 17 06587 g012
Figure 12. Cost and carbon emissions of ASS and OPC.
Figure 12. Cost and carbon emissions of ASS and OPC.
Sustainability 17 06587 g012
Table 1. Physical properties of OPC.
Table 1. Physical properties of OPC.
ProjectApparent Density (g/cm3) Specific Surface Area (m2/kg)Loss on Ignition (%) Setting Time (min) Compressive Strength (MPa)Flexural Strength (MPa)
InitialFinal3 Days28 Days3 Days28 Days
Standard Value2.8–3.1≥300≤5.0≥45≤600≥17≥42.5≥3.5≥6.5
Measured Value3.053732.5819125230.358.25.99.5
Table 2. Chemical composition of raw materials (wt.%).
Table 2. Chemical composition of raw materials (wt.%).
MaterialsSiO2Al2O3Fe2O3CaOMgOTiO2Na2OK2OSO3P2O5Loss
GSGS47.9918.027.646.802.590.621.662.100.2411.860.48
GGBS29.8312.380.4746.396.250.930.370.601.86-0.92
OPC23.494.062.3660.133.34-0.20-3.14-3.28
Table 3. Comparison of heavy metal content in GSGS with leaching limit in the specification.
Table 3. Comparison of heavy metal content in GSGS with leaching limit in the specification.
Heavy MetalRegulatory Limit (mg/L)Content in sGSGS (mg/L)Assessment
Chromium (Cr)150.00326014Compliant
Arsenic (As)50.080414883Compliant
Cadmium (Cd)10.00008819Compliant
Lead (Pb)50.00182935Compliant
Table 4. Mix proportions.
Table 4. Mix proportions.
CMsOPC (%)GSGS (%)BBGS (%)Water Glass ModulusWater Glass Dosage (%)Water-to-Binder Ratio
OPC100----0.36
ASS-40601.4140.36
Table 5. Performance index of aggregates.
Table 5. Performance index of aggregates.
AggregatesGrain Size (mm)Apparent Density (kg/m3)Bulk Density (kg/m3)Water Content (%)
River sand0–5258315120.04
Gravel5–10271315210.14
Table 6. Mix proportions of CSMs.
Table 6. Mix proportions of CSMs.
CMsSampleCM (%)Gravel (%)River Sand (%)
OPCOPC-446040
OPC-556040
OPC-666040
ASSASS-446040
ASS-556040
S AS-666040
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Tan, Y.; Wang, X.; Zheng, H.; Liu, Y.; Ma, J.; Zhao, S. Correlation Between Packing Voids and Fatigue Performance in Sludge Gasification Slag-Cement-Stabilized Macadam. Sustainability 2025, 17, 6587. https://doi.org/10.3390/su17146587

AMA Style

Tan Y, Wang X, Zheng H, Liu Y, Ma J, Zhao S. Correlation Between Packing Voids and Fatigue Performance in Sludge Gasification Slag-Cement-Stabilized Macadam. Sustainability. 2025; 17(14):6587. https://doi.org/10.3390/su17146587

Chicago/Turabian Style

Tan, Yunfei, Xiaoqi Wang, Hao Zheng, Yingxu Liu, Juntao Ma, and Shunbo Zhao. 2025. "Correlation Between Packing Voids and Fatigue Performance in Sludge Gasification Slag-Cement-Stabilized Macadam" Sustainability 17, no. 14: 6587. https://doi.org/10.3390/su17146587

APA Style

Tan, Y., Wang, X., Zheng, H., Liu, Y., Ma, J., & Zhao, S. (2025). Correlation Between Packing Voids and Fatigue Performance in Sludge Gasification Slag-Cement-Stabilized Macadam. Sustainability, 17(14), 6587. https://doi.org/10.3390/su17146587

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop