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Article

The Performance of Sulfoaluminate Cement Mortar with Secondary Aluminum Dross

by
Qian Wang
1,
Linchun Zhang
1,* and
Ailian Zhang
1,2
1
School of Civil Engineering, Sichuan College of Architectural Technology, Deyang 618000, China
2
School of Civil Engineering, Harbin Institute of Technology, Harbin 150090, China
*
Author to whom correspondence should be addressed.
Coatings 2025, 15(4), 459; https://doi.org/10.3390/coatings15040459
Submission received: 22 March 2025 / Revised: 5 April 2025 / Accepted: 10 April 2025 / Published: 12 April 2025
(This article belongs to the Special Issue Surface Treatment and Mechanical Properties of Sustainable Pavement Materials)
Browse Figures
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Abstract

:
This paper endeavors to explore the impact of secondary aluminum dross (SAD) on the characteristics of sulfoaluminate cement mortar. Measurements were taken for the mortar’s slump flow, plastic viscosity, initial setting time, and drying shrinkage rate (DR). Additionally, the flexural, compressive, and bonding strengths were evaluated. The leached concentrations of chromium (Cr) and zinc (Zn) in the specimens were determined. Furthermore, the carbonation depth (Dc) and chloride ion migration coefficient (CMC) were calculated. Lastly, scanning electron microscope energy spectrum analysis (SEM-EDS) and X-ray diffraction (XRD) spectrum analysis were conducted to analyze the mortar’s performance. The findings revealed that the slump flow and plastic viscosity of fresh mortar exhibited negative and positive quadratic relationships, respectively, with the mass ratio of SAD. Specifically, SAD could reduce the slump flow by 1.57% to 2.72% and augment the plastic viscosity by 5.21% to 36.89%. The placement time contributed to a decrease in the slump flow of fresh mortar by up to 20.4% and an increase in plastic viscosity by up to 11.2%. The initial setting time, mechanical strength, and DR of the mortar demonstrated quadratic variations with the mass ratio of SAD. At a 15% SAD mass ratio, the mortar exhibited the highest initial setting time, mechanical strength, and DR. The inclusion of SAD could elevate the initial setting time, flexural strength, compressive strength, bonding strength, and DR of the mortar by 14.33% to 65.07%, −14.75% to 22.58%, −8.94% to 9.96%, −13.33% to 66.67%, and −13.33% to 26.67%, respectively.

1. Introduction

Cement concrete structures inevitably sustain damage over a certain period of service [1,2]. Consequently, the repair of these damaged structures becomes imperative [3]. This necessitates the development of suitable repair materials tailored for concrete structures that have undergone degradation.
Asphalt and cement-based materials are commonly employed in the preparation of repair materials [4,5]. Asphalt is known for its rapid repair capabilities in damaged load-bearing areas. However, it is ill-suited for repairing building structures, due to its inadequate structural integrity. Furthermore, the application of asphalt releases toxic gases at certain concentrations, and its cost is relatively high [6,7]. Therefore, there is a pressing need to develop cement-based repair materials that are suitable for engineering applications.
Cement-based materials offer an alternative solution for the repair of concrete structures [8]. Portland cement is frequently used in the preparation of repair materials. Nonetheless, its slow setting speed renders it unsuitable for rapid repairs of concrete structures [9]. In contrast, sulfate aluminate cement is a fast-setting cement-based material that can be effectively applied to damaged concrete structures [10]. Extensive research has been conducted on the rheological, mechanical, and durability properties of sulfoaluminate cement concrete materials [11]. Studies have shown that sulfate aluminate cement paste exhibits lower fluidity and higher plastic viscosity compared to Portland cement paste [12,13,14]. Additionally, the mechanical strength of sulfate aluminate cement concrete cured for less than three days is higher than that of Portland cement concrete [15]. However, at later curing ages (exceeding three days), sulfate aluminate cement concrete demonstrates lower mechanical strength than Portland cement concrete [16,17]. This makes sulfoaluminate cement concrete suitable for construction projects with tight deadlines [18]. The incorporation of basalt, steel, and polypropylene fibers has been proven to enhance the flexural strength by 11.3%–21.1%, 16.7%–31.8%, and 8.6%–18.3%, respectively [19,20], while the corresponding compressive strengths increase by 5.1%–17.6%, 15.1%–28.7%, and 4.3%–14.1%, respectively [21,22]. Despite the potential of fiber-reinforced sulfoaluminate cement concrete as a repair material, there is a need to reduce its preparation cost.
Secondary aluminum dross is an industrial waste product generated during aluminum production [23]. If not properly treated, toxic elements can leach out and contaminate the environment [24]. Previous research has demonstrated that secondary aluminum dross can increase the flexural and compressive strengths by 2.1%–11.5% and 3.7%–14.3%, respectively, when specimens are cured for less than seven days [25,26]. However, when the curing age exceeds seven days, the flexural and compressive strengths decline by 1.3%–9.1% and 2.6%–19.4%, respectively. Additionally, secondary aluminum dross can reduce the drying shrinkage rate, chloride ion migration coefficient, and carbonation depth of cement concrete [27]. It has been shown to enhance the strengths of ordinary Portland cement concrete. As a fast-hardening repair cement material, sulfoaluminate cement is derived from aluminum oxide [28]. Secondary aluminum dross may provide hydraulic aluminum substances, thus potentially replacing some sulfoaluminate cement while ensuring safe disposal. However, this aspect has received limited attention.
This study investigated the slump flow and initial setting time of fresh sulfoaluminate cement mortar. It also examined the drying shrinkage rate, flexural strength, compressive strength, and bonding strength of hardened sulfoaluminate cement mortar cured for 0.25 to 28 days. The leached Zn and Cr, carbonation depth, and chloride ion migration coefficient of the sulfoaluminate cement mortar were tested. Finally, scanning electron microscope energy spectrum analysis (SEM-EDS), X-ray diffraction (XRD) spectrum analysis, and thermogravimetric curves were employed to elucidate the mechanisms underlying the performance changes in hardened sulfoaluminate cement mortar. This research provides additional raw materials and novel ideas for the preparation of sulfoaluminate cement and the treatment of secondary aluminum dross. The primary innovation of this study lies in its utilization of secondary aluminum ash to replace sulfoaluminate cement, a direction that has been scarcely explored in previous research.

2. Experimental

2.1. Raw Materials

In this study, sulfoaluminate cement (SAC) manufactured by Tangshan Polar Bear Building Materials Co., Ltd., located in Tangshan, China, was employed. The SAC exhibited a strength grade of 42.5 MPa, with an initial setting time of 21.3 minutes and a final setting time of 204.5 minutes. Quartz sand, comprising particle sizes of 0.71 mm to 1 mm, 0.35 mm to 0.59 mm, and 0.15 mm to 0.297 mm in a mass ratio of 1:1.5:1, was utilized as the aggregate for the mortar. This mass ratio of quartz sand represented the optimal grading value derived from the theory of maximum density, as per Cai’s research [2]. A polycarboxylate-based water-reducer was adopted as a high-range water-reducing agent, demonstrating a water-reduction efficiency of 39.2%. Li2SO4 and tartaric acid were employed as the early strength agent and retarder, respectively. The purity levels of Li2SO4 and tartaric acid were 99.9% and 99.6%, respectively. These three additives were supplied by Yingshan New Material Technology Co., Ltd., based in Shanghai, China. Li2SO4, at a mass ratio of 0.15% relative to the mass of SAC, served as the early strength agent. Meanwhile, tartaric acid, at a mass ratio of 0.035%, was utilized as the retarder in this investigation. Secondary aluminum dross (SAD), provided by Dongguan Yuehui Renewable Resources Co., Ltd., located in Dongguan, China, was also incorporated in this study. The particle sizes and chemical compositions of the raw materials are detailed in Table 1 and Table 2. The morphology of SAD is shown in Figure 1.

2.2. The Preparation of Mortar

The sulfoaluminate cement mortar was prepared by adhering to the following steps. Initially, the sulfoaluminate cement, standard sand, and SAD were introduced into a JJ-5 planetary cement mortar mixer provided by Shandong Huakuang High tech Development Co., Ltd., Jining, China and agitated at a mixing speed of 140 r/min for a duration of 2 minutes. Subsequently, the water-reducing agent, defoamer, and other additives were incorporated into the mixer, with the mixing speed adjusted to 285 r/min for an additional 2 minutes. Following the mixing process, a portion of the fresh mortar was poured into molds measuring 40 × 40 × 160 mm³, 100 × 100 × 100 mm³, and Φ100 × 50 mm³, and cured in a room-temperature environment (47.6% relative humidity and 21.3 °C) for 4 hours until it hardened. Thereafter, the molds were removed, and the specimens were transferred to a standard curing room (96.7% relative humidity and 20.1 °C) for curing periods of 0.25 day, 1 day, 3 days, 7 days, 14 days, and 28 days. The residual sulfoaluminate cement mortar was utilized in the measurement of slump flow and plastic viscosity. The mixing proportions of the SAD sulfoaluminate cement mortar are detailed in Table 3.

2.3. The Measuring Process

2.3.1. The Measurement of Rheological Parameters

The flowability of the cement mortar composites was assessed according to the Chinese standard GB/T 50080-2016 [29]. For each set of mixtures, the material was placed in a truncated conical circular mold and compacted. Excess mixture was carefully removed using a spatula. The mold was then gently lifted vertically, and the jumping table was activated 25 times at a rate of one activation per second. Upon completion of this process, the maximum diameter of the fresh cement mortar and the corresponding vertical section diameter were measured. The average of these diameters was recorded as the slump flow of the fresh mortar.
The plastic viscosity measurement was conducted at a temperature of 20 °C, utilizing a Brookfield RST-SST rheometer equipped with a four-blade rotor. The fresh mortar mixtures were immediately injected into the rheometer’s container after preparation. The plastic viscosity was determined by fitting the shear stress and shear rate data from the ascending stage using the Bingham model.

2.3.2. The Drying Shrinkage Rate

A shrinkage rod was utilized for measuring the drying shrinkage of specimens. The length change value was recorded using a TD511-300 dial indicator, supplied by Cangzhou Tai Ding Hengye Test Instrument Co., LTD., located in Cangzhou, China, during the curing period. The drying shrinkage rate (DSR) was calculated using Equation (1). All specimens were securely fastened to a steel frame throughout the testing procedure.
D S R = L 0 − L L 0
where L0 and L denote the specimen’s initial length and the length during curing, respectively.

2.3.3. The Initial Setting Time

The initial setting time of the specimens was measured using a ZKS-100A mortar setting time tester, supplied by Zhejiang Luda Mechanical Instrument Co., LTD., located in Shaoxing, China. The measurement process adhered to the Chinese standard JGJ 70-2009 [30]. All samples were placed in containers, ensuring that the surface of the mortar was 10 mm below the rim of the container. Subsequently, the tip of the penetration test needle, with a cross-sectional area of 30 mm², was brought into contact with the surface of the mortar, and the reading was set to zero. Finally, the mortar was vertically pressed to a depth of 25 mm within 10 seconds, and the reading was recorded. The penetration resistance value was calculated according to Equation (2). The setting time was defined as the moment when fp reaches 0.7 MPa.
f p = N p A p
where fp represents the penetration resistance (MPa), Np denotes the static pressure exerted at a penetration depth of up to 25 mm (N), and Ap signifies the cross-sectional area of the penetration test needle (30 mm²).

2.3.4. The Mechanical Strength

The flexural and compressive strengths of specimens cured for 0.25 day, 1 day, 3 days, 7 days, 14 days, and 28 days were tested, using specimens with a size of 40 × 40 × 160 mm3. Firstly, the specimens were moved to the flexural strength fixture, and then a flexural load was exerted on the specimens at a 0.05 kN/s loading rate, until the specimens were destroyed. After that, the specimens were moved to the compressive strength fixture, then loading was applied with a compressive loading rate of 2.4 kN/s until the specimens were destroyed. The bonding strength was determined with the following steps. Each specimen with a size of 40 × 40 × 160 mm3 comprised two halves. One half was made of ordinary Portland cement mortar, and the other half was made of sulfoaluminate cement mortar. The specimens were moved to the flexural strength fixture and were measured according to the same method used for determining the cement mortar’s flexural strength. The Chinese standard GBT17671-2021 was used for the measurement of the mechanical strength [31].

2.3.5. Chloride Ion Permeability Coefficient of Concrete

Specimens with dimensions of Φ100 × 50 mm³ were saturated in a vacuum saturator for 2 days. Thereafter, they were subjected to the chloride ion permeability coefficient (CMC) test using the NELD-CCM550 concrete chloride ion diffusion coefficient tester, supplied by Beijing Neerde Intelligent Technology Co., Ltd., Beijing, China. The experimental details are outlined in the Chinese standard GB/T 50082-2024 [32].

2.3.6. Carbonation Depth of Concrete

For the carbonation experiment, specimens with dimensions of 100 × 100 × 100 mm³ were utilized. Each specimen was cured for 28 days and then placed in the CCB-70F automatic concrete carbonation test box, purchased from Zhucheng Kerun Machinery Co., Ltd. (Weifang, China). The specimens were cured under a 10% CO₂ and 90% air environment. Following carbonation, the carbonation depth was measured according to the Chinese standard GB/T 50082-2024.

2.3.7. Micro-Analysis

The SU3800 scanning electron microscope (SEM), purchased from Hitachi Scientific Instruments (Beijing) Co., Ltd., Beijing, China, was employed to obtain SEM images and energy-dispersive spectroscopy (EDS) results. Initially, samples were extracted from the core of the specimens. They were then dried in an oven at 105 °C for 2 days and coated with gold by vacuum spraying. Finally, the sprayed samples were transferred to the SU3800 for SEM and EDS measurements. The XRD experiment was conducted as follows: The powdered sample was placed in a D8 Discover X-ray diffractometer (XRD), supplied by Bruker, Berlin, Germany. The XRD experiment was performed using a working voltage of 40 kV, a current of 40 mA, a scanning speed of 0.6°/min, and a scanning range of 5° to 90°. The overall experimental process is illustrated in Figure 2.

3. Results and Discussion

3.1. The Rheological Parameters

The slump flow of fresh sulfoaluminate cement (SAC) mortar incorporating SAD (a specific additive) is depicted in Figure 3. As illustrated in this figure, the slump flow of fresh SAC mortar increases with an increase in the mass ratio of SAD. Previous studies [33] have highlighted that SAD exhibits a superior ball-bearing effect compared to ordinary Portland cement, thereby enhancing the fluidity of fresh SAC mortar upon its addition [34]. However, the placing time exerts a detrimental influence on the flowability of fresh SAC mortar. Free water within the fresh SAC mortar evaporates during the placing period, consequently reducing its fluidity [35]. The incremental rate of slump flow due to SAD addition and the decremental rate due to placing time are 0%–20.4% and 0%–11.2%, respectively. The error bars associated with the slump flow measurements of fresh SAD-SAC mortar are less than 10% of the slump flow values. The correlation between slump flow and the mass ratio of SAD adheres to a quadratic function.
The plastic viscosity of fresh sulfoaluminate cement (SAC) mortar with SAD (a specific additive) is illustrated in Figure 4. As depicted in this figure, the plastic viscosity of fresh SAD-SAC mortar decreases with an increase in the SAD mass ratio. Conversely, the placing time exhibits an augmenting effect on the plastic viscosity of fresh SAC mortar. Research substantiates the inverse correlation between the slump flow and the corresponding plastic viscosity of fresh SAC mortar [36]. Consequently, as the SAD content in the SAC mortar increases, its plastic viscosity decreases; conversely, when the SAD content decreases, the plastic viscosity increases. Therefore, with an increase in placing time, the slump flow decreases, while the plastic viscosity rises.
The initial setting time of SAD sulfoaluminate cement mortar is illustrated in Figure 5. As shown in the figure, the initial setting time varies as a quadratic function in accordance with the SAD mass ratio. This is due to the fact that the hydration heat generated in SAD cement-based materials is a quadratic function of the SAD mass ratio [37]. The hydration heat is closely related to the condensation time, thus explaining the quadratic function relationship between the initial setting time and the SAD mass ratio. The initial setting time of the SAD sulfoaluminate cement mortar reaches its maximum when the SAD mass ratio is 15%. The addition of SAD can increase the initial setting time of the sulfoaluminate cement mortar by 14.33% to 65.07%. The error bars for the initial setting time are less than 10% of the actual values. The SAD mass ratio of 0% to 15% has the effect of increasing the setting time of fresh SAD mortar. This can be attributed to the fact that the added SAD reduces the pozzolanic reaction of sulfoaluminate cement, thereby extending the setting time [38]. However, when the SAD mass ratio exceeds 15%, the setting time decreases with the addition of SAD. This is because SAD increases the content of hydraulic aluminum oxide, which accelerates the hydration rate of sulfoaluminate cement and shortens the setting time of the sulfoaluminate cement mortar.

3.2. The Mechanical Strength and Drying Shrinkage Rate

The flexural strength of SAD sulfoaluminate cement mortar is presented in Figure 6. As depicted in the figure, the flexural strength of SAD sulfoaluminate cement mortar exhibits a quadratic function-based variation in relation to the SAD mass ratio. The flexural strength reaches its peak when the SAD mass ratio is 15%, with an increase of 33.6% at this ratio. When the SAD mass ratio increases from 0% to 15%, the hydration degree of sulfoaluminate cement is enhanced by the added SAD. This is because SAD promotes secondary hydration in sulfoaluminate cement, thereby increasing the mechanical strength of SAD sulfoaluminate cement mortar [39]. However, when the SAD mass ratio exceeds 15%, the mechanical strength of SAD sulfoaluminate cement mortar decreases, due to bubbles induced by SAD. The flexural strength increases with curing age, as the hydration degree is enhanced by curing time [40]. Consequently, mechanical strength improves with increased curing time. As shown in Figure 6, the flexural strength at a curing age of 0.25 days can reach 23.7% to 26.2% of the flexural strength of SAD sulfoaluminate cement mortar cured for 28 days. The error bars are less than 10% of the average flexural strength, confirming low data dispersion.
Figure 7 illustrates the compressive strength of SAD sulfoaluminate cement mortar. As shown in the figure, the compressive strength initially increases and subsequently decreases with an increase in the SAD mass ratio. The relationship between the compressive strength of SAD sulfoaluminate cement mortar and the SAD mass ratio follows a quadratic function. The SAD sulfoaluminate cement mortar with 15% SAD exhibits the highest compressive strength. At this SAD mass ratio, the compressive strength increases by 11.3% to 17.1% with the addition of SAD. Furthermore, the compressive strength increases with an increase in curing age. The compressive strength of SAD sulfoaluminate cement mortar cured for 0.25 days is 9.8% to 12.7% of the compressive strength of SAD sulfoaluminate cement mortar cured for 28 days. The error bars are less than 10% of the average compressive strength, ensuring low data dispersion. The addition of SAD at a mass ratio of 0% to 15% can enhance the compressive strength of SAD sulfoaluminate cement mortar, due to the increased secondary hydration of sulfoaluminate cement [41,42,43,44]. However, when the added SAD increases from 15% to 30%, the pores induced by SAD have a negative impact on the compressive strength of SAD sulfoaluminate cement mortar [45]. The hydration degree increases with curing time; therefore, the compressive strength of SAD sulfoaluminate cement mortar increases with increased curing time.
The bonding strength of SAD sulfoaluminate cement mortar is depicted in Figure 8. As can be seen from the figure, the bonding strength exhibits a quadratic function relationship with the SAD mass ratio. The SAD sulfoaluminate cement mortar with 15% SAD demonstrates the highest bonding strength. At this dosage, the bonding strength of the SAD sulfoaluminate cement mortar experiences an increase in the range of −13.33% to 66.67%. The bonding strength of SAD sulfoaluminate cement mortar cured for 0.25 days is 9.8% to 12.7% of that cured for 28 days. The bonding strength accounts for 15.9% to 41.2% of the flexural strength. The error bars are less than 10% of the average compressive strength, indicating low data dispersion. The reasons for the variation in bonding strength are consistent with those for flexural and compressive strengths.
The drying shrinkage rate of SAD sulfoaluminate cement mortar is presented in Figure 9. As observed in the figure, the drying shrinkage rate increases when the SAD mass ratio rises from 0% to 15%. The addition of SAD enhances the hydration degree of the SAD sulfoaluminate cement mortar, consequently increasing the drying shrinkage rate [46]. However, the drying shrinkage rate decreases when the mass ratio increases from 15% to 30%. The SAD contributes to an increase in the drying shrinkage rate of the SAD sulfoaluminate cement mortar, reaching a maximum of 10.1% to 17.2%. This phenomenon is attributed to the pores induced by the SAD, which restrict sulfoaluminate cement hydration [47]. The drying shrinkage rate of SAD sulfoaluminate cement mortar cured for 0.25 days is 18.8% to 26.9% of that cured for 28 days. The hydration degree of sulfoaluminate cement increases with curing age, leading to an increase in the drying shrinkage rate of the SAD sulfoaluminate cement mortar over time.

3.3. The Chloride Ion Migration Coefficient and Carbonation Depth

Figure 10 illustrates the chloride ion migration coefficient (CMC) of sulfoaluminate cement mortar with SAD. As evident from the figure, the CMC follows a quadratic function pattern. The incorporation of SAD can reduce the CMC by 1.96% to 15.69%. This can be attributed to the fact that the added SAD enhances the hydration degree of the sulfoaluminate cement mortar, thereby increasing its compactness. Consequently, the CMC decreases with the addition of SAD. When the mass ratio of SAD is 15%, the CMC reaches its lowest value. The SAD increases the hydration degree, which improves the compactness of the sulfoaluminate cement mortar. However, it should be noted that SAD can also introduce gas into the sulfoaluminate cement mortar, thereby reducing its compactness. As a result, the sulfoaluminate cement mortar with 15% SAD exhibits the lowest CMC.
The Dc of the SAD sulfoaluminate cement mortar is depicted in Figure 11. As observed in the figure, the Dc of the SAD sulfoaluminate cement mortar follows a quadratic function pattern. Notably, the SAD sulfoaluminate cement mortar with 15% SAD exhibits the lowest Dc. The addition of SAD can reduce the Dc by 2.1% to 18.3%. While SAD with a mass ratio below 15% negatively impacts the Dc of the SAD sulfoaluminate cement mortar, SAD with a mass ratio above 15% has a positive effect on the corresponding Dc. The SAD enhances sulfoaluminate cement hydration, thereby increasing the density of the SAD sulfoaluminate cement mortar. Consequently, the Dc decreases with the addition of SAD. However, when the mass ratio of SAD exceeds 15%, the added SAD introduces bubbles into the SAD sulfoaluminate cement mortar, leading to a decrease in its density. This, in turn, increases the migration depth of CO2, resulting in an increase in the Dc.

3.4. The Leached Cr and Zn

The leached concentrations of Cr and Zn from the SAD sulfoaluminate cement mortar are illustrated in Figure 12. As is evident from the figure, the leached amounts of Cr and Zn vary in a quadratic function pattern with the SAD’s mass ratio. At an SAD mass ratio of 15%, the leached Cr and Zn are at their lowest levels. At this specific dosage, the leached Cr and Zn decrease by 21.6% to 32.7% and 19.3% to 31.2%, respectively. The increasing immersion time has a pronounced effect on the mass fraction of leached Cr and Zn, causing them to increase accordingly. As the immersion time extends from 3 months to 9 months, the leached Cr and Zn increase by 161.9% to 210.3% and 130.5% to 186.3%, respectively. The error bars for the leached Cr and Zn are less than 10% of the average values, ensuring the accuracy of the experimental results.

3.5. Micro-Analysis Results

3.5.1. The Scanning Electron Microscope

Figure 13 presents scanning electron microscopy (SEM) images of SAD sulfoaluminate cement mortar, with SAD mass ratios of 5%, 15%, and 25%. As depicted in Figure 13, needle-shaped and flocculent hydration products are evident. When the SAD content increases from 5% to 15%, the quantity of needle-shaped hydration products and cracks diminishes, while the amount of compact hydration products rises. This phenomenon can be explained by the fact that SAD enhances the degree of hydration, thereby augmenting the production and density of hydration products. This observation corroborates that SAD sulfoaluminate cement mortar with 15% SAD exhibits superior mechanical strength. However, when the SAD mass ratio exceeds 15%, an increased number of cracks is observable (as shown in Figure 11), indicating that SAD at dosages above 15% negatively impacts the mechanical strength of SAD sulfoaluminate cement mortar.

3.5.2. Scanning Electron Microscopy–Energy-Dispersive Spectroscopy

The SEM-EDS images are displayed in Figure 14. As illustrated in Figure 14, the elements C, O, Al, Si, S, K, and Ca are present in the SAD sulfoaluminate cement mortar. The addition of SAD can increase the content of the Al element in the SAD sulfoaluminate cement mortar. This is because the mass ratio of Al₂O₃ in SAD is higher than that in SAC. Consequently, the incorporation of SAD elevates the Al content in the SAD sulfoaluminate cement mortar.

3.5.3. The X-Ray Diffraction Spectrum

Figure 15 illustrates the X-ray diffraction (XRD) spectrum of the SAD sulfoaluminate cement mortar. As shown in Figure 15, the crystals of ettringite (Aft), tetracalcium aluminoferrite (C₄A₃S ), CaSO₄·2H₂O, CaSO₄, CaCO₃, Ca(OH)₂, and Al(OH)₃ are present. With an increase in the amount of SAD added, the crystals of Aft, C₄A₃S, and Al(OH)₃ also increase. This can be attributed to the fact that SAD contains a significant amount of nano-shaped alumina, which promotes the secondary hydration of sulfoaluminate cement, leading to the formation of more Al(OH)₃ [48]. This confirms that SAD can enhance the hydration degree of the sulfoaluminate cement mortar.

4. Conclusions

The influence of secondary aluminum dross (SAD) on the properties of sulfoaluminate cement mortar has been thoroughly investigated. The findings are summarized as follows.
The slump flow and plastic viscosity of fresh sulfoaluminate cement mortar exhibit negative and positive quadratic relationships, respectively, with the mass ratio of added SAD. Specifically, the addition of SAD results in a decrease in slump flow at rates ranging from 1.57% to 2.72%, and an increase in plastic viscosity at rates ranging from 5.21% to 36.89%. Additionally, the placing time contributes to a decrease in slump flow by up to 20.4% and an increase in plastic viscosity by up to 11.2%.
The relationships between the initial setting time, mechanical strength, and DR of the mortar, and the mass ratio of SAD, are cubic functions. When the SAD mass ratio is 15%, the sulfoaluminate cement mortar demonstrates the highest initial setting time, flexural strength, compressive strength, bonding strength, and DR. The incorporation of SAD leads to an increase in the initial setting time, flexural strength, compressive strength, bonding strength, and DR of the sulfoaluminate cement mortar at rates ranging from 14.33% to 65.07%, −14.75% to 22.58%, −8.94% to 9.96%, −13.33% to 66.67%, and −13.33% to 26.67%, respectively.
The CMC and Dc of sulfoaluminate cement mortar vary quadratically with the SAD mass ratio. The addition of SAD reduces the CMC and Dc by rates ranging from 1.96% to 15.69% and 2.1% to 18.3%, respectively. When the SAD mass ratio is 15%, the CMC and Dc of the sulfoaluminate cement mortar are at their lowest.
The leached Cr and Zn from the sulfoaluminate cement mortar show a cubic function-based relationship with the mass ratio of the SAD. When the added SAD’s mass ratio is 15%, the leached Cr and Zn from the sulfoaluminate cement mortar are the highest. The SAD can decrease the leached Cr and Zn by 21.6%~32.7% and 19.3%~31.2%, respectively. Meanwhile, when the immersion time increases from 3 months to 9 months, the rates of increase in the leached Cr and Zn are 161.9%~210.3% and 130.5%~186.3%.
SAD can improve the compactness of hydration products and decrease the number and width of cracks in sulfoaluminate cement mortar. When the mass ratio of SAD is 15%, the hydration products of the sulfoaluminate cement mortar are the most compact. The element of Al in the sulfoaluminate cement mortar is increased by the added SAD. The SAD can increase the aluminum hydration products. Based on the results of SEM-EDS and XRD, the hydration degree of the sulfoaluminate cement mortar is increased by SAD.

Author Contributions

Conceptualization, Q.W.; methodology, L.Z.; validation, Q.W. and L.Z.; investigation, A.Z.; resources, Q.W.; data curation, L.Z. and A.Z.; writing—original draft, Q.W. and L.Z.; visualization, A.Z.; project administration, Q.W. All authors have read and agreed to the published version of the manuscript.

Funding

Project approved by Sichuan Higher Vocational Education Research Center (GZY23B13).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

The authors declare that there are no conflicts of interest regarding the publication of this paper.

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Figure 1. The morphology of SAD.
Figure 1. The morphology of SAD.
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Figure 2. The overall experimental process.
Figure 2. The overall experimental process.
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Figure 3. The slump flow of fresh SAD sulfoaluminate cement mortar.
Figure 3. The slump flow of fresh SAD sulfoaluminate cement mortar.
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Figure 4. The plastic viscosity of fresh SAD sulfoaluminate cement mortar.
Figure 4. The plastic viscosity of fresh SAD sulfoaluminate cement mortar.
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Figure 5. The setting time of fresh SAD sulfoaluminate cement mortar.
Figure 5. The setting time of fresh SAD sulfoaluminate cement mortar.
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Figure 6. The flexural strength of SAD sulfoaluminate cement mortar.
Figure 6. The flexural strength of SAD sulfoaluminate cement mortar.
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Figure 7. The compressive strength of SAD sulfoaluminate cement mortar.
Figure 7. The compressive strength of SAD sulfoaluminate cement mortar.
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Figure 8. The bonding strength of SAD sulfoaluminate cement mortar.
Figure 8. The bonding strength of SAD sulfoaluminate cement mortar.
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Figure 9. The drying shrinkage rate of SAD sulfoaluminate cement mortar.
Figure 9. The drying shrinkage rate of SAD sulfoaluminate cement mortar.
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Figure 10. The CMC of SAD sulfoaluminate cement mortar.
Figure 10. The CMC of SAD sulfoaluminate cement mortar.
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Figure 11. The Dc of SAD sulfoaluminate cement mortar.
Figure 11. The Dc of SAD sulfoaluminate cement mortar.
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Figure 12. The leached Cr and Zn of SAD sulfoaluminate cement mortar. (a) The leached Cr. (b) The leached Zn.
Figure 12. The leached Cr and Zn of SAD sulfoaluminate cement mortar. (a) The leached Cr. (b) The leached Zn.
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Figure 13. The SEM photos of the SAD sulfoaluminate cement mortar. (a) 5% SAD. (b) 15% SAD. (c) 25% SAD.
Figure 13. The SEM photos of the SAD sulfoaluminate cement mortar. (a) 5% SAD. (b) 15% SAD. (c) 25% SAD.
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Figure 14. The SEM-EDS photos of the SAD sulfoaluminate cement mortar. (a) 5% SAD. (b) 15% SAD. (c) 25% SAD.
Figure 14. The SEM-EDS photos of the SAD sulfoaluminate cement mortar. (a) 5% SAD. (b) 15% SAD. (c) 25% SAD.
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Figure 15. The XRD curves of the SAD sulfoaluminate cement mortar.
Figure 15. The XRD curves of the SAD sulfoaluminate cement mortar.
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Table 1. The raw materials’ particle size (%).
Table 1. The raw materials’ particle size (%).
TypesParticle Size/μm
0.30.614864360
Quartz sand00000.05920.89100
SAC00.341.9116.2429.8594.86100
SAD0.070.250.571.163.9325.9187.25
Table 2. The raw materials’ chemical compositions (%).
Table 2. The raw materials’ chemical compositions (%).
TypesSiO2Al2O3FexOyMgOCaOSO3
Quartz sand99.3-0.7---
SAC13.9415.063.2-49.913.85
SAD4.779.23.85.91.4-
Table 3. The SAD sulfoaluminate cement mortar’s mixing proportions (kg/m3).
Table 3. The SAD sulfoaluminate cement mortar’s mixing proportions (kg/m3).
WaterSACSADQuartz SandWater-ReducerLi2SO4Tartaric Acid
236.33716.260945.6315.761.070.25
236.33626.7289.54945.6315.760.940.22
236.33537.18179.08945.6315.760.810.19
236.33447.73268.53945.6315.760.670.16
236.33358.18358.08945.6315.760.540.13
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Wang, Q.; Zhang, L.; Zhang, A. The Performance of Sulfoaluminate Cement Mortar with Secondary Aluminum Dross. Coatings 2025, 15, 459. https://doi.org/10.3390/coatings15040459

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Wang Q, Zhang L, Zhang A. The Performance of Sulfoaluminate Cement Mortar with Secondary Aluminum Dross. Coatings. 2025; 15(4):459. https://doi.org/10.3390/coatings15040459

Chicago/Turabian Style

Wang, Qian, Linchun Zhang, and Ailian Zhang. 2025. "The Performance of Sulfoaluminate Cement Mortar with Secondary Aluminum Dross" Coatings 15, no. 4: 459. https://doi.org/10.3390/coatings15040459

APA Style

Wang, Q., Zhang, L., & Zhang, A. (2025). The Performance of Sulfoaluminate Cement Mortar with Secondary Aluminum Dross. Coatings, 15(4), 459. https://doi.org/10.3390/coatings15040459

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