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Article

Study on Mechanical Strength and Chloride Corrosion Resistance of Composite Mortars Mixed with Steel Slag, Bayer Red Mud, and Phosphogypsum

by
Cheng Hu
1,2,
Qijie Wang
2,
Weiheng Xiang
1,2,*,
Tao Zhang
3,
Yanguang Li
4 and
Ruhua Chen
5
1
Guangxi Key Laboratory of Green Building Materials and Construction Industrialization, Guilin University of Technology, Guilin 541004, China
2
School of Civil Engineering, Guilin University of Technology, Guilin 541004, China
3
Wengfu Group Limited Liability Company, Guiyang 550500, China
4
Changzhou Longcheng Powder Equipment Co., Ltd., Changzhou 213000, China
5
Guangxi Yunying New Material Technology Co., Ltd., Nanning 532703, China
*
Author to whom correspondence should be addressed.
Buildings 2025, 15(9), 1510; https://doi.org/10.3390/buildings15091510
Submission received: 22 March 2025 / Revised: 11 April 2025 / Accepted: 18 April 2025 / Published: 30 April 2025
(This article belongs to the Section Building Materials, and Repair & Renovation)
Browse Figures
Versions Notes

Abstract

Utilizing supplementary cementitious materials is an effective way to fabricate low-carbon cement-based materials. In this paper, the composite mortars with good properties were prepared by mixing them with basic oxygen furnace slag (BOFS), Bayer red mud (BRM), and phosphogypsum (PG). The influences of the replacement amounts of BRM and PG on the mechanical properties, hydration characteristic, chloride corrosion resistance, and microstructure of the materials were investigated. The results showed that simply adding 10 wt% BRM slightly modified the properties of the composite mortars. With the increase in PG, the mechanical strength and corrosion resistance coefficient KC of the mortars first increased and then decreased, in contrast to the chloride migration coefficient DRCM and electric flux Q. Among the samples, sample S3, with 6 wt% BRM and 4 wt% PG, had the best properties, a flexural strength of 6.6 MPa, and a compressive strength of 43.5 MPa at a curing age of 28 d. And the values of DRCM and Q of the sample, respectively, decreased by 44.06% and 22.83% compared with the control sample, along with the value of KC corroded after 120 d increasing by 16.33%. The microstructure analysis indicated that the alkali activation of BRM promoted the generation of lamellar portlandite and reticular and granular C-S-H gel. The free aluminum in BRM could dissolve into C-S-H gel to induce the generation of C-A-S-H gel. Furthermore, the generated amount of ettringite increased by adding PG. The aforementioned improvement in mechanical properties is primarily attributed to BRM promoting the hydration of the composite mortars and inducing the transformation of the C-S-H gel into C-A-S-H gel, and PG promoting the generation of ettringite. Moreover, the filling effects of BRM and PG decreased the porosity and number of harmful pores. It increased the compactness of the microstructure to endow the composite mortars with excellent chloride corrosion resistance.

1. Introduction

Excess carbon dioxide (CO2) in the atmosphere leads to global warming and climatic anomalies. In the past decade, global CO2 emissions have gradually increased annually, and exceeded 34.9 billion tons in 2021 [1]. Cement production is one of the primary sources of CO2 emissions, accounting for 8% of global CO2 emissions [2]. In general, the production of 1 ton of Portland cement clinker emits 0.69 tons of CO2 [3]. The worldwide production of cement is more than 4 billion tons every year, and about 55% of it comes from China [4,5]. Substituting fossil fuels, reducing cement consumption, extending service life, etc., are proposed feasible measures for reducing CO2 emissions of cement-based materials [6,7]. At present, the low-carbon cement technology has become a hot research field across the world.
The use of supplementary cementitious materials is an economical and effective method of reducing CO2 emissions of cement-based materials. The supplementary cementitious materials are mostly composed of industrial wastes containing potential active components [8]. Steel slag is the by-product of steel manufacturing, and 1 ton of steel production releases 0.15–0.20 tons of steel slag [9]. In China, more than 100 million tons of steel slag is discharged every year, and its cumulative storage amount exceeds 1.2 billion tons [10]. This causes a series of problems, such as environmental pollution, land occupation, and resource waste. Among the materials produced, basic oxygen furnace slag (BOFS) accounts for about 70% of the steel slag production [11]. The main minerals comprising BOFS are alite, belite, celite, and other silicate phases, similar to Portland cement [12,13]. Therefore, steel slag is considered a potential supplementary cementitious material in the building materials industry.
In recent years, some researchers have studied the effect of steel slag on the physicochemical properties of cement-based materials [14,15,16]. For example, steel slag–cement binding materials with a compressive strength of 41.83 MPa and a flexural strength of 7.24 MPa at 28 d were prepared by Hou, J.W. [17]. Kourounis, S. [18] found that steel slag with a lower amount of calcium silicates slowed down the hydration of blended cement. Owing to the low hydration activity of steel slag, the strength and durability of cement-based composite materials gradually decrease with the increase in steel slag, especially at the replacement level, exceeding 30 wt% [19]. This limits the application of steel slag use as a supplementary cementitious material.
Chemical activation is considered an effective measure with which to improve the hydration activity of auxiliary cementitious materials. At present, Liu, Z. [20], Zhang, S. [21], and Qi, L. [22] pointed out that the alkaline activators (NaOH, Na2CO3, water, glass, and so on) and sulfate activators (Na2SO4, CaSO4·2H2O) could optimize the hydrological environment to accelerate the hydration of steel slag. Further, some studies have pointed out that alkaline red mud and gypsum by-product can improve the hydration characteristics of steel slag-based cementitious materials [23,24]. For instance, Hao, X.S. [25] found that the alkali activation of Bayer red mud (BRM) promoted the generation of C-S-H gel in steel slag-based mortars. In the study of Shen, W.G. [26], the 7 d and 28 d unconfined compressive strengths of steel slag-based solidified materials had, respectively, increased by 90.58% and 60.87% after the addition of 5 wt% phosphogypsum (PG). Compared with the chemical reagents, using BRM and PG as activators has the advantage of low cost and promotes the utilization of waste residues. Moreover, the micro-aggregate filling effects of BRM and PG powders are beneficial to improve the compactness of the steel slag–cement composite cementitious material [27,28]. However, the synergistic effect of BRM and PG on the physicochemical properties and microstructure of the composite mortars has rarely been reported.
In this paper, composite mortars with high strength and excellent chloride corrosion resistance were prepared by mixing BOFS, BRM, and PG. BRM and PG were used as activators to replace steel slag with equal mass. The effects of the amount of BRM and PG added on the mechanical properties, hydration heat, chloride migration coefficient, electric flux, corrosion resistance coefficient, mineral composition, morphology, and pore structure of the composite mortars were studied. The synergistic improvement mechanism of BRM and PG in the composite mortars was investigated. The purposes of this study are to increase the utilization rate of steel slag and to reduce the carbon emissions of cement-based materials.

2. Materials and Methods

2.1. Raw Materials

P·O 42.5 cement, basic oxygen furnace slag (BOFS), Bayer red mud (BRM), and phosphogypsum (PG) were used as the raw materials. The chemical compositions and particle size distribution of the raw materials are listed in Table 1 and Figure 1, respectively. The specific surface area of BOFS, BRM, and PG were 704.85 m2/kg, 880.40 m2/kg and 816.25 m2/kg, respectively. As seen in the XRD result (Figure 2), the main mineral compositions of BOFS were alite and belite, and there was an abundance of cancrinite in BRM and plenty of gypsum in PG. The sodium and hydroxide ions in BRM could accelerate the hydration of active minerals in BOFS, and gypsum in PG was added to promote the generation of ettringite. Standard sand with a particle size of 0.08–2.00 mm and an apparent density of 2660 kg/m3 was used as a fine aggregate. The mixing water used in this study was tap water.

2.2. Mix Proportion and Sample Preparation

In this paper, BRM and PG were used to replace BOFS with equal mass to prepare the steel slag–cement composite mortars. The mix proportion of samples S0–S6 are shown in Table 2. The control sample S0 was a composite cement containing 30 wt% BOFS. In samples S1–S6, the replacement amounts of BRM were, respectively, 10 wt%, 8 wt%, 6 wt%, 4 wt%, 2 wt%, and 0 wt%, and for PG, these were, respectively, 0 wt%, 2 wt%, 4 wt%, 6 wt%, 8 wt%, and 10%. And the water–binder ratio and sand–binder ratio were kept at 0.5 and 3, respectively. Firstly, the raw materials were dosed and mixed evenly according to the sample proportion using the mortar mixer. Subsequently, the fresh mixtures were immediately poured into the prismatic mold with a dimension of 40 × 40 × 160 mm and a cube mold with a dimension of 40 × 40 × 40 mm, and then were covered with plastic film. After curing for 24 h, the sample was demolded and finally placed in the standard curing box until the correct testing age was reached.

2.3. Test Methods

According to the Chinese Standards GB/T 17671-2021, the compressive and flexural strengths at different curing ages were tested. The chloride migration coefficient DRCM and electric flux Q were tested according to the Chinese Standards GB/T 50082-2009. The corrosion resistance coefficient was used to evaluate the strength change in the mortars before and after chloride corrosion testing, and the process was described as follows: the demolded samples were placed in water heated to 50 °C for 7 d, and then were, respectively, soaked in tap water and 3 wt% NaCl solution at 25 °C. The soaking solution was overtopped to exceed the surface of the samples by at least 10 mm, and the pH value of the solution was fixed to 7.0 ± 0.2. The corrosion resistance coefficient of the samples was calculated according to Equation (1).
K C = R W R S
Further, KC is the corrosion resistance coefficient of the samples at a certain age. RW is the compressive strength of the samples soaked in tap water at their corresponding ages (MPa). RS is the compressive strength of the samples soaked in 3% NaCl solution at their corresponding ages (MPa).
The particle size distribution was measured using an automatic particle size and shape analyzer (Morphologi 4–ID, Malvern Panalytical, Malvern, UK). The hydration heat was measured using a TAM Air isothermal calorimeter (I–Cal 8000 HPC, Calmetrix, Waltham, MA, USA) under a temperature condition of 25 °C. The phase composition was performed using an X-ray diffractometer (XRD, Xpert Pro, PANalytical B.V., Almelo, Netherlands) in the 2θ range of 5–70° at 10 °/min. The TG–DSC was obtained using a thermal gravimetric analyzer (TG209F3 Tarsus, Netzsch, Selb, Germany) in an air atmosphere with a heating rate of 10 °C/min. The morphology and elemental distribution analysis (EDS) was observed using a scanning electron microscope (SEM, JSM–7900F, JEOL, Akishima, Japan). The pore structure was measured by mercury intrusion porosimetry (MIP) test using an automatic mercury injection apparatus (AutoPore 9510, Micromeritics, Norcross, GA, USA).

3. Results and Discussion

3.1. Mechanical Properties

The flexural and compressive strengths of the series S samples are shown in Figure 3. With the increase in PG, the compressive strength of the samples first increased and then decreased. The 3 d compressive strength of control sample S0 was 19.1 MPa, while the compressive strength values of samples S1–S6, respectively, were 19.8 MPa, 20.6 MPa, 22.1 MPa, 20.5 MPa, 18.6 MPa, and 17.8 MPa, which increased by 3.66%, 7.85%, 15.71%, 7.33%, −2.62%, and −6.81% in comparison to the control sample. Meanwhile, the 28 d compressive strengths of samples S0–S6 were 38.8 MPa, 40.2 MPa, 41.7 MPa, 43.5 MPa, 41.1 MPa, 38.2 MPa, and 35.4 MPa. Compared with the control sample, the 28 d compressive strengths of samples S1–S6 increased by 3.60%, 7.46%, 12.08%, 5.91%, −1.54%, and −8.74%, respectively.
Similarly, the change in flexural strength of series S samples was inconsistent with the compressive strength. Further, sample S3 mixed with 6 wt% BRM and 4 wt% PG additives possessed the highest strength, and it had a flexural strength of 6.6 MPa and a compressive strength of 43.5 MPa after curing for 28 d. That was mainly because the alkali activation of BRM and the sulfate activation of PG were conducive to an optimal microstructure of the hydration products [29,30]. Moreover, the BRM and PG with finer particle sizes could fill parts of pores to increase the compactness of the materials [31]. Adding the BRM and PG allowed the flexural and compressive strengths of the composite mortars to be enhanced. However, the excess of PG distinctly increased the gypsum content in the mortars. The dilation effect of gypsum reduced the generated content of C-S-H gel, resulting in a decrease in the mechanical strength [32].

3.2. Hydration Heat

Compared with the pure cement, the hydration exothermic process for steel slag-based composite cement can also be divided into five stages, which have a lower heat release [33]. In order to ensure the effect of BRM and PG additives on the early hydration behavior of steel slag–cement composite materials, the heat flow and cumulative hydration heat of the composite pastes are exhibited in Figure 4. In the initial hydration period, the alkali activation of BRM and the sulfate activation of PG accelerated the hydration rate to increase the heat flow and cumulative hydration heat of samples S1–S4. Nevertheless, the dissolution of excessive sulfate inhibited leaching of Ca2+ ions of the cementitious particles, resulting in a decrease in the heat flow and cumulative hydration heat of samples S5 and S6 [34]. Furthermore, PG promoted the generation of ettringite in the composite mortars [35]. The generation of ettringite slowed the hydration of alite to delay and weaken the second exothermic peak, which led to the emergence of the third exothermic peak [36].

3.3. Chloride Corrosion Resistance

3.3.1. Chloride Migration Coefficient and Electric Flux

The chloride migration coefficient and electric flux of the composite mortars at 28 d are exhibited in Figure 5. With the addition of 10 wt% BRM, the value of DRCM and the Q of sample S1 experienced a slight decrease. Moreover, the DRCM and Q values of the composite mortars decreased first and then increased with the increase in PG. In particular, sample S3 had the lowest values of DRCM and Q, which, respectively, decreased by 44.06% and 22.83% compared with the control sample, S0. It was indicated that the appropriate amount of BRM and PG increased the chloride penetration resistance of the steel slag–cement composite mortars. That was attributed to the compactness of the mortars, which was improved by the chemical activation and filling effect of BRM and PG additives. However, the hydration-inhibiting behavior of excessive PG caused a negative effect on the chloride penetration resistance.

3.3.2. Corrosion Resistance Coefficient

The corrosion resistance coefficient of series S samples soaked in 3 wt% NaCl solution for different periods is shown in Figure 6. With the increase in corrosion time, the KC value of the samples increased first and then decreased. This was due to sodium chloride, portlandite, and calcium aluminate hydrates reacting to generate Friedel’s salt, and its quantity gradually increased with the increase in corrosion time [37]. The Friedel’s salt could fill part of the micropores to make the mortars more compact, which increased the compressive strength of the samples after chloride corrosion. But an excess of Friedel’s salt generated overly consumed portlandite in the mortars, which had an adverse impact. Moreover, the KC value of the samples increased first and then decreased with the increase in PG. Compared with the control sample S0, the KC value of samples S1–S6 corroded for 120 d increased by 9.18%, 13.27%, 16.33%, 11.22%, 1.02%, and −7.14%, respectively. The change in KC value was inversely correlated with the values of DRCM and Q in the composite mortars.

3.4. Microstructure

3.4.1. XRD

The XRD patterns of the composite pastes at 3 d and 28 d are illustrated in Figure 7. When cured for 3 d and 28 d, the main mineral compositions of the samples were alite, belite, quartz, portlandite, and ettringite. The alite and belite were the unhydrated cementitious components. The characteristic peak of the C-S-H gel was not observed in the XRD patterns, and it should have been nanocrystalline. Portlandite and ettringite were the primary hydration products, and their peak intensity changes were observed. The alkali activation of BRM promoted hydration to enhance the characteristic peaks of portlandite at 18.09° and 34.09° in sample S1. With the increase in PG, the characteristic peaks of portlandite enhanced first and then weakened, and the characteristic peaks of ettringite at 9.09° and 15.78° gradually enhanced. It was suggested that an appropriate amount of PG promoted the generation of portlandite, C-S-H gel, and ettringite. And excess PG reduced the generation content of portlandite and C-S-H gel.

3.4.2. TG–DSC

The TG–DSC results of the composite pastes are displayed in Figure 8. The mass of the pastes gradually decreased with the increase in temperature. From 25 °C to 750 °C, the mass loss of samples S0, S1, S3, and S6 were 19.74%, 20.07%, 20.72%, and 20.19%, respectively. Among them, sample S3 has the greatest loss in weight mass. The temperature range of mass change in the composite pastes was mainly divided into three stages. From 25 °C to 330 °C, the first stage of mass loss corresponded to the dehydration decomposition of C-S-H gel, ettringite, and monosulphate [38,39]. The next stage of mass loss at 400–500 °C was represented to the dehydration of portlandite. The mass loss at 600–750 °C was associated with the dehydroxylation of Si-OH in the C-S-H gel and the decomposition of calcite [40].
Furthermore, the endothermic peak at 80–110 °C was due to the dehydration of C-S-H gel and ettringite, and the area of this peak obviously increased with the increase in PG. That was attributed to the addition of PG, which promoted the generation of ettringite in accordance with the results in Figure 7. The endothermic peak at 110–220 °C was due to the dehydration of monosulphate [41]. The peak area slightly increased with the single addition of BRM and obviously decreased with the increase in PG. It was implied that BRM facilitated the transformation of ettringite into monosulphate, and PG had the opposite effect.

3.4.3. SEM-EDS

The SEM images of samples S0, S1, S3, and S6 at 28 d curing age are shown in Figure 9. Reticular and granular C-S-H gel, lamellar portlandite, needle rod-like ettringite, unhydrated particles, and aggregates were observed in the samples. It was found that some pores had a size of 2–8 μm, and little microcracks existed in control sample S0. Due to the chemical activation effect of BRM and PG, the hydration products of the composite mortars grew more complete. This led to an increase in the compactness of the microstructure of samples S1 and S3, which had a higher mechanical strength and chloride corrosion resistance. However, the porosity increased and more microcracks appeared in sample S6 with the addition of 10 wt% PG, and this caused an adverse effect on the material’s properties.
In order to further determine the morphology and distribution of the hydration products, the main elements, such as O, Ca, Si, Al, S, and Fe, in the composite mortars were selected to analyze the elemental distribution. The element distribution on the fracture surface of sample S3 at 28 d is exhibited in Figure 10. The elements O, Ca, and Si were enriched in sample S3, and the sample also contained Al, S, and Fe. The region with enriched Ca and low Si and Al was assumed to be portlandite. The needle rod-like products with low Si and enriched Ca, Al, and S were assumed to be ettringite. The reticulate and granular products with enriched Ca and Si widely distributed in the sample were identified as C-S-H gels. Increased portlandite, ettringite, and C-S-H gel generation was beneficial for increasing the compactness of the microstructure, which endowed the sample with good mechanical strength and corrosion resistance. Meanwhile, some Al was detected in the C-S-H gel formation through the elemental analysis shown in Figure 11. It was demonstrated that the free aluminum in BRM could dissolve into C-S-H gel during the hydration process, which was beneficial for inducing the transformation of C-S-H gel into C-A-S-H gel to improve the strength and corrosion resistance of the mortars [42].

3.4.4. Pore Structure

Pore structure is one of the dominating characteristics in evaluating the microstructure of cement-based materials. The cumulative and incremental pore volumes of series S samples at 28 d of curing are revealed in Figure 12. According to previous studies [43,44], the pore types of the hardened samples were divided into harmless pores (<20 nm), less harmful pores (20–50 nm), harmful pores (50–200 nm), and more-harmful pores (>200 nm). The physicochemical properties of the samples were mainly determined by the size and amount of pores.
The porosities and pore volume fractions of series S samples are shown in Figure 13. The porosities of samples S0, S1, S2, S3, and S6 approximately were 19.15%, 18.19%, 15.90%, 14.98%, and 21.13%, respectively. Compared with the control sample S0, the porosities of samples S1, S2, S3, and S6 decreased by 5.01%, 16.97%, 21.78%, and −10.34%, respectively. The porosity of the composite mortars decreased first and then increased with the increase in PG. In addition, the high number of pores in the mortars was obviously decreased by an appropriate amount of BRM and PG additives. In particular, the volume fraction of harmless pores and less harmful pores in sample S3, respectively, increased to 26.65% and 29.77%. This was mainly due to the morphological effect of BRM and PG with fine particle sizes.

4. Conclusions

In this paper, BRM and PG were used to replace part of BOFS to prepare composite mortars. The mechanical properties, hydration heat, chloride corrosion resistance, and microstructure of the composite mortars were investigated. The main results are summarized as follows.
  • Using single BRM to replace BOFS, the mechanical strength and chloride corrosion resistance of the composite mortars slightly increased. Further, the 28 d compressive strength and 120 d corrosion resistance coefficient KC of the composite mortars, respectively, increased by 3.60% and 9.18% after the addition of 10 wt% BRM.
  • With the increase in PG, the compressive strength, flexural strength, chloride migration coefficient DRCM, and electric flux Q of the composite mortars increased first and then gradually decreased, in contrast to the corrosion resistance coefficient KC. Further, sample S3, with 6 wt% BRM and 4 wt% PG, achieved the highest strength and chloride corrosion resistance.
  • The alkali activation of BRM promoted the hydration of active minerals in BOFS, resulting in an increase in the amount of portlandite and C-S-H gel generated. Moreover, the free aluminum in BRM dissolved into C-S-H gel to induce the generation C-A-S-H gel during the hydration process. The increase in hydration products and the generation of C-A-S-H gel were the primary factors in improving the properties of the composite mortars.
  • The PG additive promoted the generation of needle rod-like ettringite, and inhibited the transformation of ettringite into monosulphate. The generation of ettringite and the filling effect of PG was benefited for decreasing the porosity and amount of harmful pores, resulting in the enhancement of the mechanical strength and chloride corrosion resistance. But excess PG reduced the generation content of portlandite and C-S-H gel, which caused adverse effects on the properties of the composite mortars.

Author Contributions

Conceptualization, C.H.; methodology, W.X.; formal analysis, W.X. and R.C.; investigation, Q.W. and T.Z.; resources, C.H.; writing—original draft preparation, C.H. and Y.L.; writing—review and editing, C.H., Q.W. and W.X.; funding acquisition, C.H. and W.X. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Guangxi Science and Technology Program (Project No. GuikeAD22035126 and GuikeAD25069101), the National Natural Science Foundation of China (Project No. 52368029 and 52468032), and the Basic Ability Enhancement Program for Young and Middle-aged Teachers of Guangxi (Project No. 2022KY0242).

Data Availability Statement

The original contributions presented in this study are included in the article.

Acknowledgments

The authors would also like to thank Collaborative Innovation Center for Exploration of Nonferrous Metal Deposits and Efficient Utilization of Resources for its support regarding the XRD and SEM texts.

Conflicts of Interest

Author Tao Zhang was employed by the Wengfu Group Limited liability Company. Author Yanguang Li was employed by the Changzhou Longcheng Powder Equipment Co., Ltd. Author Ruhua Chen was employed by the Guangxi Yunying New Material Technology Co., Ltd. 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.

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Buildings 15 01510 g001
Figure 1. Particle size distribution of the raw materials.
Figure 1. Particle size distribution of the raw materials.
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Figure 2. XRD patterns of the raw materials.
Figure 2. XRD patterns of the raw materials.
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Figure 3. Flexural strength (a) and compressive strength (b) of series S samples.
Figure 3. Flexural strength (a) and compressive strength (b) of series S samples.
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Figure 4. Heat flow (a) and cumulative hydration heat (b) of the composite pastes.
Figure 4. Heat flow (a) and cumulative hydration heat (b) of the composite pastes.
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Figure 5. Chloride migration coefficient and electric flux of series S samples.
Figure 5. Chloride migration coefficient and electric flux of series S samples.
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Figure 6. Corrosion resistance coefficient of series S samples for different soaking periods.
Figure 6. Corrosion resistance coefficient of series S samples for different soaking periods.
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Figure 7. XRD patterns of the composite pastes at 3 d (a) and 28 d (b).
Figure 7. XRD patterns of the composite pastes at 3 d (a) and 28 d (b).
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Figure 8. TG–DSC results of the composite pastes. (a) TG, (b) DSC.
Figure 8. TG–DSC results of the composite pastes. (a) TG, (b) DSC.
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Figure 9. SEM images of samples S0, S1, S3, and S6 at 28 d curing age.
Figure 9. SEM images of samples S0, S1, S3, and S6 at 28 d curing age.
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Figure 10. Element distribution of fracture surface of sample S3.
Figure 10. Element distribution of fracture surface of sample S3.
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Figure 11. Elemental analysis of three selected spots in sample S3.
Figure 11. Elemental analysis of three selected spots in sample S3.
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Figure 12. Cumulative (a) and incremental (b) pore volumes of series S samples.
Figure 12. Cumulative (a) and incremental (b) pore volumes of series S samples.
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Figure 13. Porosities (a) and pore volume fractions (b) of series S samples.
Figure 13. Porosities (a) and pore volume fractions (b) of series S samples.
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Table 1. Chemical compositions of the raw materials (wt%).
Table 1. Chemical compositions of the raw materials (wt%).
Raw MaterialSiO2CaOAl2O3Fe2O3MgOSO3Na2OK2OOthers
Cement24.7660.255.643.710.883.220.160.700.68
BOFS26.9529.675.6624.155.330.310.090.087.76
BRM14.4916.8220.3930.580.330.527.150.199.53
PG4.0736.980.360.270.0335.170.050.0223.05
Table 2. Mix proportion of the samples (kg/m3).
Table 2. Mix proportion of the samples (kg/m3).
Sample No.CementBOFSBRMPGSandWater
S0410.16175.78001757.82292.97
S1410.16117.1958.590.001757.82292.97
S2410.16117.1946.8811.721757.82292.97
S3410.16117.1935.1623.441757.82292.97
S4410.16117.1923.4435.161757.82292.97
S5410.16117.1911.7246.881757.82292.97
S6410.16117.190.0058.591757.82292.97
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MDPI and ACS Style

Hu, C.; Wang, Q.; Xiang, W.; Zhang, T.; Li, Y.; Chen, R. Study on Mechanical Strength and Chloride Corrosion Resistance of Composite Mortars Mixed with Steel Slag, Bayer Red Mud, and Phosphogypsum. Buildings 2025, 15, 1510. https://doi.org/10.3390/buildings15091510

AMA Style

Hu C, Wang Q, Xiang W, Zhang T, Li Y, Chen R. Study on Mechanical Strength and Chloride Corrosion Resistance of Composite Mortars Mixed with Steel Slag, Bayer Red Mud, and Phosphogypsum. Buildings. 2025; 15(9):1510. https://doi.org/10.3390/buildings15091510

Chicago/Turabian Style

Hu, Cheng, Qijie Wang, Weiheng Xiang, Tao Zhang, Yanguang Li, and Ruhua Chen. 2025. "Study on Mechanical Strength and Chloride Corrosion Resistance of Composite Mortars Mixed with Steel Slag, Bayer Red Mud, and Phosphogypsum" Buildings 15, no. 9: 1510. https://doi.org/10.3390/buildings15091510

APA Style

Hu, C., Wang, Q., Xiang, W., Zhang, T., Li, Y., & Chen, R. (2025). Study on Mechanical Strength and Chloride Corrosion Resistance of Composite Mortars Mixed with Steel Slag, Bayer Red Mud, and Phosphogypsum. Buildings, 15(9), 1510. https://doi.org/10.3390/buildings15091510

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