Study on the Alkali–Sulfur Co-Activation and Mechanical Properties of Low-Carbon Cementitious Composite Materials Based on Electrolytic Manganese Residue, Carbide Slag, and Granulated Blast-Furnace Slag

Abstract

Industrial solid waste is characterized by complex mineral phases and various components. Low-carbon cementitious materials can be prepared through precise regulation based on the material composition and properties of various industrial solid wastes. In this study, electrolytic manganese residue (EMR), carbide slag (CS), and granulated blast-furnace slag (GBFS) were used as alternatives to cement to prepare multicomponent solid waste cementitious materials. The effects of the proportions of EMR and CS on the cementitious activity of GBFS and the activation mechanism of alkali and sulfur were studied. The results showed that with increasing EMR content, the strength first increased and then decreased. At a GBFS content of 20%, CS content of 2%, and EMR content of 8%, the compressive strength was highest, reaching 45.5 MPa after 28 days of curing, mainly because the OH⁻ in CS and SO₄²⁻ in EMR synergistically stimulated the active components in GBFS. Hydrated products such as ettringite and hydrated calcium silicate (C–S–H gel) were generated and interlaced with each other to improve the densification of the mortar. Overall, the proposed system provides an avenue to reduce or replace the production of cement clinker and achieve the high-value-added utilization of industrial solid waste.

1. Introduction

Cement is an inorganic hydraulic powder material with good workability, mechanical properties, and durability, making it the most widely and commonly used building material worldwide [1]. However, cement production is often associated with mineral resource shortage, excessive energy consumption, and excessive CO₂ emissions. It is reported that for every 1 ton of cement produced, ~800 kg of CO₂ gas is generated. Moreover, the total emissions from cement production account for ~8% of the world’s total CO₂ emissions, making cement production a significant contributor to the carbon emission industry [2,3]. With the intensification of the global greenhouse effect, energy conservation and carbon reduction have become the future development directions of the cement industry. Therefore, many scholars have proposed the utilization of various industrial solid wastes (such as fly ash, granulated blast-furnace slag [GBFS], and silica fume) as supplementary cementitious materials [4,5,6]. These materials not only exhibit certain hydration abilities but also play a role in filling pores. Accordingly, a series of green and low-carbon cementitious materials have been developed [7,8,9]. GBFS is a byproduct of the iron-making process. It contains numerous silico-aluminate minerals and exhibits a volcanic ash effect [10,11]. Generally, GBFS activity can be stimulated by alkali, sulfate, and other materials, as shown in

Table A1. Comparative table of similar technologies.

Type	CS-GBFS	EMR-GBFS	CS-EMR-GBFS
Principle	Alkali-activated	Sulfate-activated	Alkali–sulfur co-activation
Compressive strength	3 d > 20 MPa, 28 d > 30 MPa	3 d > 17 MPa, 28 d > 44 MPa	3 d > 20 MPa, 28 d > 45 MPa
Hydration heat	24 h heat release > 100 J/g	72 h heat release > 250 J/g	72 h heat release > 250 J/g
Type of hydration products	C-(A)-S-H	AFt	C-(A)-S-H, AFt
Advantage	High early strength, fast setting time.	High EMR content, and the later strength data are considerable.	Excellent data for each age.
Deficiency	The cost is high, and the later strength is not considerably improved.	EMR requires high temperature treatment and high energy consumption.	-

in Appendix A.

Carbide slag (CS) is a byproduct of industrial acetylene production, and its main components are Ca(OH)₂ and a small amount of CaCO₃ [12,13]. In recent years, CS production has steadily increased with the growing demand for acetylene, reaching an expected annual production of ~5.6 × 10⁷ tons per year. Using CS is quite challenging, owing to its high alkalinity. Most enterprises opt for on-site storage [14,15], and there is still untapped potential yet to be explored. This paper discusses utilizing CS as an alternative to an alkali activator to enhance GBFS activity, aiming to reduce costs and mitigate the environmental issues associated with alkali activators. Numerous studies have demonstrated that CS possesses a certain alkali excitation effect. The combination of CS and GBFS yields the best effect, but adding some auxiliary material is often required to obtain ideal strength [16,17,18].

Electrolytic manganese residue (EMR) is an industrial solid waste produced through the electrolysis of metallic manganese, and its main components include CaSO₄·2H₂O and SiO₂ [19]. It has been reported that every ton of electrolytic manganese production results in the generation of 10 to 12 tons of EMR. Over the years, the cumulative amount has exceeded 150 million tons, with an annual utilization rate of only ~10%. This is attributed to the complex composition of EMR, which includes harmful ions such as Mn²⁺, Cd²⁺, and NH₄⁺ [20,21]. At present, most enterprises resort to open-air stacking and in situ burial methods, which have the potential to cause major disasters in the ecological environment and human life [22]. As EMR is a sulfur-rich material (with an SO₃ content of approximately 17–25%), it can be considered similar to gypsum. Studies have shown that EMR can be combined with GBFS and clinker/Ca(OH)₂ to prepare cement-based cementitious materials, and its mechanical properties have been found to be superior to those of ordinary Portland cement (OPC) after 28 days of curing [23,24]. According to the above, EMR holds potential as a building raw material, but its optimal performance is often realized when used in conjunction with alkaline raw materials.

Therefore, to reduce carbon emissions in the cement industry and realize the utilization of industrial solid waste, this study utilized harmless modified EMR and CS to enhance the cementitious activity of GBFS through alkali–sulfur co-activation. The mechanical properties of the multicomponent cementified solid waste material were explored, and the activation process of the system was studied from the aspects of hydration heat, hydration products, and microstructure. Furthermore, a theoretical method for preparing CS–EMR–GBFS-based high-quality cementitious material is proposed. This approach offers a novel avenue for the utilization of industrial solid waste, providing significant economic and environmental benefits.

2. Materials and Methods

2.1. Raw Materials and Analysis

P.O42.5 cement produced by Xingan Conch Cement was used in this experiment. The cement type was ordinary Portland cement (OPC). The performance indexes of the cement are shown in

Table 1. Basic performance indexes of cement.

	Density (kg/m3)	Specific Surface Area (m2/kg)	Flexural Strength (MPa)		Compressive Strength (MPa)
			3 d	28 d	3 d	28 d
OPC	3.20	360.80	5.2	7.5	24.5	46.4

.

The GBFS utilized in this experiment was provided by Liugang Group. Its main component was C₂S, and it had a density and specific surface area of 2.80 kg/m³ and 450.13 m²/kg, respectively. The EMR used was obtained from an enterprise in Guiping and was treated safely. The main components of the EMR included SiO₂ and CaSO₄·2H₂O. The Mn²⁺ solidification rate was >99%, and the NH₄⁺ removal rate was >98%, both of which met the national standards. CS was provided by an enterprise in Yulin. Its main component was Ca(OH)₂, and its density and specific surface area were 2.98 kg/m³ and 580.46 m²/kg, respectively. The chemical compositions of all raw materials, obtained via X-ray fluorescence spectrometry (

Table 2. Chemical composition of raw materials (wt%).

	Fe2O3	Al2O3	TiO2	SiO2	CaO	MgO	Na2O	K2O	MnO	SO3	Others
OPC	3.71	5.64	0.3	24.76	60.25	0.88	0.16	0.7	0.32	-	3.28
GBFS	0.81	11.79	1.94	25.26	57.54	-	-	0.7	0.54	1.16	0.26
EMR	11.03	5.09	0.26	29.98	20.14	2.55	2.24	0.71	9.50	17.06	1.44
CS	0.63	1.58	0.04	4.80	92.07	0.14	0.03	0.02	0.04	0.62	0.05

), were consistent with the phase analysis of the raw materials, as demonstrated in the X-ray diffraction analysis (Figure 1).

Figure 2 illustrates the particle size distribution and cumulative curve of the raw materials. The particle size of OPC ranged from 0.14 to 174.98 μm, with a D50 of 3.3 μm. The particle size of GBFS ranged from 0.11 to 171.54 μm, with a D50 of 2.8 μm. The particle size of EMR ranged from 0.9 to 47.34 μm, with a D50 of 2.1 μm. The particle size of CS ranged from 0.8 to 150.82 μm, with a D50 of 2.7 μm.

2.2. Experimental Methods

2.2.1. Preparation and Curing Procedures

In the early stage of this study, the mechanical properties of multicomponent solid waste cementitious materials without cement were studied. However, due to the low dissolution rate of OH⁻ in the early stage of CS, the active groups that GBFS can dissolve are less present, so the early mechanical properties are poor, which is not conducive to the application of practical engineering. Therefore, this study mainly mixed industrial solid waste with cement to prepare cementitious materials.

As depicted in Figure 3, the three types of solid waste (i.e., GBFS, CS, and EMR) were obtained after 40 min of grinding and 100 mesh screening, and GBFS, CS, and EMR were fully mixed according to different proportions to replace 30% cement and prepare mortar test blocks with dimensions of 40 mm × 40 mm × 160 mm. The test number was EGC0-18. The effects of different ratios of GBFS, CS, and EMR on the properties of mortar were studied through a series of microscopic test methods, and the specific ratios are shown in

Table 3. Proportioning design of multicomponent solid waste cementitious materials.

Experiment Number	Cement/%	EMR/%	GBFS/%	CS/%	W/C	Sand/g
PO425	100	-	-	-	0.5	1350
EGC0	70	-	30	-
EGC1	70	0	25	5
EGC2	70	1	25	4
EGC3	70	2	25	3
EGC4	70	3	25	2
EGC5	70	4	25	1
EGC6	70	5	25	0
EGC7	70	0	20	10
EGC8	70	2	20	8
EGC9	70	4	20	6
EGC10	70	6	20	4
EGC11	70	8	20	2
EGC12	70	10	20	0
EGC13	70	0	15	15
EGC14	70	3	15	12
EGC15	70	6	15	9
EGC16	70	9	15	6
EGC17	70	12	15	3
EGC18	70	15	15	0

. After forming, the mortar was placed in an environment of 20 ± 2 °C for 24 h of demudding. Subsequently, the mortar was placed in a curing box at 22 ± 1 °C and with a humidity of 97 ± 2% for curing until the specified age.

2.2.2. Test Methods

(1)

Density and specific surface area test: The raw material density test method was based on GB/T 208-2014 [25] “Cement Density Test Method”, and the specific surface area was determined in accordance with GB/T 8074-2008 [26] “Cement Specific Surface Area Test Method”.

(2)

Particle size distribution test method: The particle size distribution of the prepared powder was assessed using the Morphologi 4-ID particle size and shape analyzer (Malvern Panalytical, Malvern, UK).

(3)

Mechanical property test: The bending and compressive strength of the mortar at 3 d, 7 d, and 28 d were tested using a mortar press in accordance with the GB/T 17671-1999 [27] “Cement Mortar Strength Inspection Method (ISO Method)” standard.

(4)

Hydration heat test: The hydration heat release process of the slurry after 72 h was examined at 25 °C using an isothermal calorimeter (I-CAL4000/8000) manufactured by Calmetrix, Boston, MA, USA.

(5)

X-ray diffraction test: The mineral composition of the sample powder was analyzed using an X-ray diffractometer (X’PERT PRO) (Malvern Panalytical, Malvern, UK). The diffraction angle ranged from 5° to 80°, and the rate was set at 4°/min.

(6)

Scanning electron microscopy test: A scanning electron microscope (JSM-6380LV, JEOL Ltd., Tokyo, Japan) was employed to observe the micro-morphology of the sample under the following conditions: voltage 5 kV, current 5 μA, magnification 5000× g, scale 10 μm, and glided sample surface.

(7)

Thermogravimetric differential thermogravimetry test: Approximately 3 mg of the sample was weighed and placed into the crucible. The thermogravimetric analyzer (Q500 IR) (Newcastle, DE, USA) was utilized to conduct tests in a nitrogen atmosphere, with a heating rate of 10 °C/min.

3. Results and Discussion

3.1. Compressive Strength

The compressive strength of each group of cementitious materials is shown in Figure 4a–c. The incorporation of only EMR or CS hindered the strength development of the cementitious materials because EMR or CS are not ideal as a single activator. With the addition of EMR and CS, the compressive strength of each multicomponent solid waste cementitious materials first increased and then decreased, indicating that the addition of appropriate amounts of EMR and CS effectively stimulated the hydration activity of GBFS and improved the strength. Sample EGC11 (GBFS content of 20%, EMR content of 8%, and CS content of 2%) exhibited the optimal strength, and the 28 d compressive strength was 45.5 MPa. The strength of the specimen improved, owing to the ability of EMR and CS to fill the pores and enhance the density of the mortar [28]. Additionally, the sulfate phase in EMR and the free alkali substances in CS effectively stimulated the hydration activity of GBFS, leading to the generation of more hydration products [29,30].

Figure 4d–f shows the distribution of the compressive strength of the multicomponent solid waste cementitious materials system. With the increases in the EMR content and curing time, the compressive strength increased; thus, the extension of curing time was beneficial to the development of 3 d, 7 d, and 28 d compressive strengths, especially for the 28 d compressive strength, mainly because SO₄²⁻ in the EMR could continue to react with GBFS to generate more AFt in the later stage and AFt was the main hydration product. However, under excessive EMR, the strength significantly decreased, which was related to the large amount of inert material SiO₂ contained in the EMR. Moreover, the compressive strength of each age was optimal at the GBFS content of 20%; therefore, considering the utilization rate of solid waste and the mechanical properties of mortar, this study mainly explored the multicomponent solid waste cementitious materials system with a GBFS content of 20% (group EGC7-12).

3.2. Thermal Analysis of Hydration

Figure 5 illustrates the hydration heat curve of the multicomponent solid waste cementitious material over 72 h. Figure 5a displays the hydration heat release rate, with the first heat release peak rapidly forming within 0–1 h. This initial peak corresponded to the exothermic dissolution of aluminate- and sulfate-phase substances in the cementitious material. In the following 2–3 h, the cementitious material continued to hydrate into the induction stage, leading to the generation of some hydration products, such as C–S–H gel and Ca(OH)₂. Compared with the induction stage of the EGC0 group, the induction stage of the EGC7-12 group was shortened after EMR and CS additions. In addition, during the acceleration stage (4–13 h), the EGC0 group reached a peak of 2.75 × 10⁻³ W/g at 10.2 h. With the decrease in the CS content, the second exothermic peak of the EGC7-12 group was delayed mainly because CS incorporation increased the pH value and the Ca²⁺ concentration and reduced the time to reach Ca²⁺ saturation, thereby promoting hydration [31]. Between 14 and 20 h, the third exothermic peak, attributed to the generation of AFt [32], appeared with an increase in the EMR content. The time at which the third exothermic peak occurred was also delayed.

The cumulative heat release of hydration of the cementitious material is shown in Figure 5b. After the addition of EMR and CS, the cumulative heat release of hydration increased with the increase in the EMR content. The cumulative heat release of hydration in the EGC11 group over 72 h was 264.81 J/g, representing 109.65% of that of the EGC0 group (241.50 J/g). This indicates that the EMR and CS additions effectively enhanced the hydration rate and degree of GBFS.

3.3. X-ray Diffraction Analysis

Figure 6 shows the X-ray diffraction (XRD) patterns of multicomponent solid waste cementitious materials at different ages. In addition to the hydration products of the C–S–H gel, the hydration products of each group mainly included AFt, Ca(OH)₂, and some unhydrated C₂S and C₃S. At 3 d, the EGC0 group exhibited a diffraction peak of AFm, mainly owing to the occurrence of insufficient SO₄²⁻. However, after EMR incorporation, the concentration of SO₄²⁻ increased, and the AFm diffraction peak disappeared and transformed into an AFt peak. The EGC0 group that was aged for 28 d exhibited significantly weakened Ca(OH)₂ diffraction peak intensity, while the group with the appropriate amount of CS exhibited enhanced Ca(OH)₂ diffraction peak intensity, attributable to the existence of residual Ca(OH)₂ after the incorporation of excessive CS and the Ca(OH)₂ generated during hydration. This situation was more significant in the EGC7-9 group with increasing CS content. However, with the decrease in the CS content, the Ca(OH)₂ diffraction peak intensity of the EGC10-11 group did not decrease, which indicates that the hydration rate of GBFS could be improved under the addition of an appropriate amount of CS. Moreover, after the EMR incorporation, the concentration of dissolved SO₄²⁻ increased, and the reaction between the dissolved SO₄²⁻ and the calcium aluminate produced by GBFS promoted AFt formation. The diffraction peak showed an enhanced trend in the XRD pattern, indicating an increase in AFt generation. Therefore, according to the XRD pattern, the hydration activity of GBFS was effectively stimulated by CS and EMR addition, and more hydration products were generated, which is consistent with the results of the mechanical properties.

3.4. Thermogravimetric Differential Thermogravimetry Analysis

Figure 7 shows the thermogravimetric differential thermogravimetry (TG-DTG) analysis curves of the EGC0 and EGC7-12 groups on day 28. At 40–800 °C, the sample exhibited significant mass loss, mainly caused by the loss of chemically and physically bound water and the decomposition of AFt, C–S–H gel, Ca(OH)₂, CaCO₃, and other products.

As shown in Figure 7, three weight loss peaks mainly occurred in the whole test stage. The peak at 50–200 °C corresponds to the evaporation of physically bound water and the decomposition of AFt and C–S–H/C–(A)S–H gel [33], and the peak near 350 °C to 500 °C is related to Ca(OH)₂ decomposition [34]. The peak near 600–700 °C is related to CaCO₃ decomposition [35]. The weight loss of the sample at 50–200 °C is positively correlated with the increase in the EMR content, indicating that the increase in the EMR content and the decrease in the CS content were beneficial for the generation of hydration products, particularly AFt. In addition, all the groups featured Ca(OH)₂ decomposition peaks with different weight loss values at 350–500 °C. The EGC7 group, with the highest CS content, displayed the highest Ca(OH)₂ weight loss peak, attributable to the presence of excessive CS and consistent with the XRD results.

Table 4. Mass loss rate of samples at 50–500 °C.

Samples	Mass Loss Ratio (%)
	50–200 °C	350–500 °C
EGC0	7.89	3.05
EGC7	7.73	5.26
EGC8	8.37	5.21
EGC9	8.42	4.83
EGC10	8.47	3.84
EGC11	8.78	3.40
EGC12	9.27	2.94

presents the mass loss rates of the samples in each group. The EGC7 group exhibited a slightly lower mass loss rate than the EGC0 group. This is attributable to the single-doping of CS, which not only reduced the GBFS content, thereby diminishing the number of active components, but also resulted in a deficiency of SO₄²⁻, leading to a reduction in AFt generation. The EGC8-12 group demonstrated a higher mass loss rate than the EGC0 group, with the EGC12 group doped with EMR exhibiting the highest mass loss rate. This observation is attributable to the generation of more AFt in the EGC12 group, while the lack of CS incorporation correspondingly resulted in fewer dissolved GBFS groups and lower C–S–H gel generation. Therefore, the co-incorporation of CS and EMR more effectively stimulated the activity of GBFS, which also proves that the mechanical properties of the EGC11 group were better than those of the EGC12 group.

3.5. Scanning Electron Microscopy Analysis

The morphology of the multicomponent solid waste cementitious material was characterized through a scanning electron microscopy (SEM) test to illustrate the changes in GBFS hydration products under alkali–sulfur co-excitation (Figure 8 and Figure 9). Generally, the hydration products exhibited varying micro-morphologies. Among them, the C–S–H gel exhibited a reticular morphology, AFt exhibited a needle-like rod morphology, and Ca(OH)₂ exhibited a hexagonal plate morphology. As shown in Figure 8a, the EGC0 group was the control group. On day 3, a large amount of incomplete GBFS, with smooth and glassy surfaces and a reduced quantity of hydration products, was found. As shown in Figure 8b–d, with the addition of CS or EMR, the hydration products generated were relatively simple, but with the addition of CS and EMR, small amounts of AFt, C–S–H gel, and other hydration products were slowly generated, and the amount of GBFS was reduced. This indicates that the early activity of GBFS was effectively improved under alkali–sulfur co-activation, leading to higher strength. This observation was consistent with the 3 d compressive strength data.

AFt, C–S–H gel, and Ca(OH)₂ hydration products were generated in the EGC0 group after aging for 28 d, and the amount of GBFS decreased, indicating that the GBFS hydration degree deepened over the hydration time (Figure 9a). Compared with EGC0-28 d (Figure 9a), EGC7-28 d, EGC11-28 d, and EGC12-28 d (Figure 9a–d) exhibited a large number of hydration products, and the amount of AFt was positively correlated with the EMR addition amount, indicating that EMR incorporation promoted AFt generation, which is consistent with the test results presented in Section 3.4. Moreover, a comparison of Figure 9a–d reveals that the EGC11 group exhibited the fewest pores and that a large amount of C–S–H gel was enveloped in AFt, showing an interleaved growth state and a relatively tight structure, which were mainly reflected in the mechanical properties of the samples.

3.6. Discussion

In this study, the cementitious activity of GBFS was enhanced through alkali–sulfur co-activation, and the strength of the cementitious material system first increased and then decreased with the increase in the EMR content. The key factor influencing strength was the generation of AFt, which is also one of the main hydration products, and it is mainly formed by Al₂O₃ and gypsum in alkaline environments [36]. Therefore, this study employed three types of industrial solid waste that met the above conditions to promote the hydration reaction and consequently generate more hydration products, particularly AFt. The optimal reaction ratio and reaction mechanism of the three waste materials were studied. Figure 10 illustrates the reaction mechanisms of the multicomponent solid waste cementitious materials.

As shown in Figure 10a, mechanical grinding and GBFS activation were conducted to refine GBFS and increase the hydration reaction area to enhance the generation of hydration products. Moreover, under the influence of high-energy impact, GBFS can promote the depolymerization of the vitreous body, leading to the breakage of surface bonds and lattice defects. A large number of aluminate and silicate groups can dissolve in an aqueous solution, promoting the formation of C–S–H gel and AFt. As shown in Figure 10b, in the presence of insufficient EMR and excessive CS, the early stage generation of AFt was limited, which affected the early strength of the sample. However, as the hydration reaction progressed, a small amount of AFt was generated in the later hydration stage mainly because the cement contained a small amount of gypsum phase to provide SO₄²⁻ to participate in the AFt reaction. Therefore, the main hydration product providing strength in this system was the C–S–H gel, of which the chemical reaction formula is shown in Equation (1) [32].

$${SiO}_2+{xCa\left(OH\right)}_2+\left(n-1\right)H_{2}O\to xCaO·{SiO}_2·n{H}_{2}O$$

(1)

In contrast, as shown in Figure 10d, in the presence of insufficient CS and excessive EMR, the AFt formation rate was higher in the early stage, which effectively improved the early strength of the cementing material, and a large amount of AFt was generated in the late hydration stage; however, the AFt morphology was long and fine, the C–S–H gel amount was small, and the structure density was poor. The AFt generation chemical reaction is shown in Equation (2) [37].

$${Al}_2{O}_3+3\left({CaSO}_4·2H_{2}O\right)+3{Ca\left(OH\right)}_2+23H_{2}O\to 3CaO·{Al}_2{O}_3·3CaS{O}_4·32H_{2}O$$

(2)

As illustrated in Figure 10c, the incorporation of appropriate CS and EMR contents played a positive role in both the early and late hydration of the gelling material. This was primarily attributed to the generation of a significant amount of AFt and C–S–H gel hydration products, with both products interlacing and forming relatively dense structures.

3.7. Prediction of Economic and Environmental Benefits

As mentioned above, employing supplementary cementitious materials to replace or partially replace cement clinker is not only a method for saving energy, reducing emissions, and achieving sustainable development in the cement industry but also the primary choice for addressing the disposal of industrial solid waste. According to these objectives, the ratio of the CS–EMR–GBFS-based cementitious material was designed, and the CO₂ emission and cost loss were predicted and analyzed. The energy consumption and electric carbon emissions generated by mechanical grinding were estimated at 40 kWh/t and 0.997 kg/kWh, respectively; the grinding time was 40 min, and the electricity cost was 0.6 RMB/kWh. The results show that the CS–EMR–GBFS-based composite cementitious material can effectively reduce costs and carbon emissions (

Table 5. Calculation of economic cost and carbon emission of multicomponent solid waste cementitious materials.

	Cost (RMB/t)	Carbon Emission (kg/kg)	Compressive Strength at 28 Days (MPa)
EMR	20	0.007	-
CS	60	0.067	-
GBFS	300	0.083	-
Cement	400	0.8	42.5
EGC0	370	0.5849	42.9
EGC7	362	0.5843	39.2
EGC8	361.2	0.5831	40.1
EGC9	360.4	0.5819	43.2
EGC10	359.6	0.5807	44.8
EGC11	358.8	0.5795	45.5
EGC12	358.0	0.5783	40.0

and Figure 11). The strength of the optimal group, EGC11, was higher than that of the cement group, and the cost and carbon emission of the cement group were only 88.70% and 72.44%, respectively. The cost price of the EMR raw material was determined internally by the research group, while the cost prices of other raw materials were determined according to local prices. Additionally, the information about carbon emissions was drawn from previous studies [32,38].

4. Conclusions

In this study, EMR and CS were employed to improve the activity of GBFS through alkali–sulfur co-activation. A CS-EMR-GBFS multicomponent solid waste cementitious material system was designed, and its mechanical properties, microstructure, and hydration behavior were explored. The conclusions are as follows:

• EMR and CS effectively enhanced the cementitious activity of GBFS and improved the mechanical properties of the multicomponent cementitious materials, with the most significant improvement observed in early strength. Notably, the EGC11 group, featuring 20% GBFS content, 8% EMR content, and 2% CS content, exhibited the optimal performance, achieving a 28 d compressive strength of 45.5 MPa, with lower costs and carbon emissions than conventional cement.
• The addition of 30% GBFS alone reduced the hydration reaction rate and the total cumulative heat release. However, the incorporation of CS and EMR effectively increased the hydration reaction rate and the total cumulative heat release of the slurry. This suggests that alkali–sulfur co-activation effectively enhanced the cementitious activity of GBFS and the degree of hydration reaction.
• The main hydration products of the CS–EMR–GBFS solid waste cementitious material were AFt and C–S–H gels. With the increase in the EMR content and the decrease in the CS content, the AFt and C–S–H gel contacts continued to increase, and a large amount of AFt was interspersed and grew in the C–S–H gels.