A Scenario Simulation of Material Substitution in the Cement Industry under the Carbon Neutral Strategy: A Case Study of Guangdong

Abstract

The Chinese government promises to reach peak carbon dioxide (CO₂) emissions by 2030 and strives to achieve carbon neutralization by 2060. Against this background, achieving emission reduction in the cement industry is in the spotlight. Material substitution is unmistakably an effective means of CO₂ emission reduction in cement production. In this paper, the three-scenario analysis approach is employed to forecast the production demand, technology development of raw meal replacement, and clinker substitution in the cement industry to try to achieve the goal of carbon neutrality. This study established a model by which to simulate the carbon emissions in the cement industry during 2020–2060 to analyze the contribution of emission reduction. Through developing new cement admixtures and improving the pretreatment of alternative calcareous materials, by 2060, under the three carbon neutrality scenarios, the clinker-to-cement ratio (CCR) falls to 0.60, 0.575, and 0.56, respectively, and the percentage of clinker produced from low-carbon raw materials reaches 13%, 17%, and 20%. In addition, the CO₂ emission level is down by 57%, 61%, and 63 % in comparison to that of 2020. This study can render practical suggestions for the cement industry to achieve carbon neutrality.

1. Introduction

Cement manufacturing, a carbon-intensive industry, contributes 7–8% to global carbon emissions [1]. The carbon dioxide (CO₂) generated in the production of cement clinker makes up roughly 60% of cement emissions [2]. As the climate crisis arising out of the greenhouse effect becomes acuter, putting CO₂ emissions in the cement sector under control becomes a crucial task in moving toward a low-carbon transformation. Mitigating the emissions from cement production while supporting sustainable urban development is a critical component of climate adaption [3].

There are many ways to reduce carbon emissions in the cement industry, such as changing raw materials [4,5,6] and improving the efficiency of mud kilns [7,8] or carbon capture technology [9,10]. The International Energy Agency (IEA) has pointed out an important direction for the development of low-carbon cement, namely, to replace part of the clinker with mixed materials so as to reduce the clinker production process [11]. Reducing the clinker-to-cement ratio (CCR), as a key factor, poses an enormous potential for early emission reduction [12,13]. Extensive research has attempted to replace some of the cement in concrete with more environmentally friendly materials [14,15,16,17,18,19,20,21]. Progressive change can be achieved in a relatively easy and cost effective way so long as proper materials are found [22]. Yet the availability of proper materials is limited. To ensure safe buildings, plenty of research is needed to test the properties of the new cement [15,18,23,24,25,26,27,28]. To what extent the cement clinker can be substituted by the environment-friendly admixture needs to be further studied [19].

The cement industry, on the other hand, is understood as one with a lot of potential to diversify its waste utilization. It can consume enormous volumes of waste as an industrial center for environmental issues [29]. Using byproducts as alternatives to traditional raw materials helps strike a balance between ecosystems and contributes to society’s development [14,30,31]. Some cement manufacturing companies are also exploring approaches of reducing emissions by replacing limestone in raw meals, recycling, and using various industrial and construction waste residues to produce low-carbon cement. Other companies have completed three stages of transformation: laboratory research, industrial testing, and stable operation of the production line [32,33,34,35,36,37,38]. Meanwhile, many by-products await exploration, some of which might be used in cement production or in the development of new types of cement.

China, at the 75th UN General Assembly, proposed achieving carbon neutrality by 2060. All potential solutions should, therefore, be pursued in a waste-no-time manner [39]. China produces roughly 55% of the world’s cement, and its CO₂ emissions account for over 50% of the cement industry as a whole. China will remain the major source of CO₂ emissions from industrial activities in the future [40,41]. In recent years, limited attention has been given to the assessment of low-carbon paths in this field. Decision-makers need more insight into the potential for scalable, sustainable alternatives [4]. Though some studies have suggested calculation tools and models to obtain the emission reduction effect of material substitution [42,43,44], it is evident that there is a lack of regional empirical models in relation to carbon neutrality in particular.

The purpose of this study is to examine the possibility of reducing CO₂ emissions through raw material substitution and clinker substitution in the cement production process. Energy conservation and emissions reduction are major concerns of Guangdong, one of China’s frontrunners in the industrial sector. The province sees cement production pick the crown of the country, with 178 production enterprises, 83 cement clinker lines, and 97.31 million tons of designed clinker capacity [45]. This paper, therefore, pinpoints the province of Guangdong as the research object. This paper presents three scenarios to forecast cement demand and the technical application of low-carbon raw meals and clinker substitution in 2020–2060 and analyzes the emission reduction potential of low-carbon raw materials and clinker replacement throughout the province. Although prediction and analysis have been conducted to measure the contribution of raw material substitution to emission reduction in the cement industry according to some books, the algorithms employed are only confined to directly evaluate carbon emission factors at the national level. Furthermore, during the research process, we found that due to the degree of coordination between regional governments in the circulation of industrial waste and the impact of local industrial environment, it is necessary to select alternative raw materials at the provincial level and conduct corresponding research on their emission reduction contribution. This paper identified the local supply and recycling rate of low-carbon calcium raw materials in Guangdong and estimated the carbon emission factor of the annual industrial process of the cement industry so as to improve the scientificity of the scenario forecast results. We highlighted the differences in promoting raw material substitution technologies in the cement industry among different regions, which can shed light on the analysis and research on the emission reduction. This paper also compared the impacts of setting a carbon neutrality target at different times on the cement industry’s emissions reduction behavior.

This paper is structured as follows: Part 2 is dedicated to the key parameters and calculation methods used in the scenario forecasts, and future demand forecasts for cement products and raw material substitution are covered in detail as well; Part 3 presents the scenario projection results from the perspective of carbon emissions and emission reduction drivers; while Part 4 and Part 5 draw conclusions on scenario projections and provide recommendations for further policy optimization.

2. Methods and Key Parameters

2.1. Methodology of Carbon Emission Calculation

According to the Intergovernmental Panel on Climate Change (IPCC), the accounting method for CO₂ released from industrial processes usually includes three tiers: Tier 1, Tier 2, and Tier 3 [46]. Tier 2 is most fit to calculate the CO2 emissions of the cement industry in this paper, which is a balanced method in terms of data availability and accuracy.

Formula (1), based on IPCC’s second level method, which is used to calculate the carbon dioxide emissions of each industrial process, is as follows:

$$E_t{=A}_t{\times \mathit{EF}}_t,$$

(1)

where:

$E_t$ is the total CO₂ emissions of industrial processes in t years;

$A_t$ is the activity level in t years, that is, the production of cement clinker;

${\mathit{EF}}_t$ is the CO₂ emission factor of industrial processes in t years.

2.2. Forecast of Future Cement Demand in Guangdong

The province of Guangdong is a major contributor to China’s cement production. The intensification of market competition and the acceleration of restructuring amid enterprises heighten the cement industry concentration steadily. The province pivots its focus to emerging industries as its urban construction becomes more sophisticated. Between 2016 and 2020, cement output grew at an average annual rate of 3%. In 2021, the province saw the market’s overall demand for cement remain relatively flat. The inventory of local cement enterprises continued to rise with the influx of external cement. The cement industry carried out kiln shutdown as scheduled in July 2021 to relieve inventory pressure, resulting in a decrease in the kiln line operating rate. The growth trajectory of cement demand in the future, therefore, was not obvious.

According to the relationship between per capita cement output and per capita Gross Domestic Product (GDP) in developed countries, the changing trend of cement demand is basically the same. In the beginning, cement output and GDP are inverted “U” curves, then decrease [47]. Wei [48] found that both urbanization rate (UR) and GDP per capita can indicate that cement production decreases after reaching its peak.

In this study, a mathematical model was established to expound the early relationship between per capita cement demand and per capita GDP. The formula is as follows:

$$\ln \left(C_t\right){=\beta }_0{+\beta }_1·\ln \left(G_t\right){+\beta }_2·{\left(\ln \left(G_t\right)\right)}^2{+\beta }_3·{\left(\ln \left(G_t\right)\right)}^3{+\dots +\epsilon }_t,$$

(2)

where:

t represents the year;

$C_t$ denotes the per capita cement output of Guangdong in t year;

$G_t$ measures the level of economic development in t year, expressed by GDP per capita;

$\beta$ typifies the variable coefficient, distinguished by the following corner marks;

${\epsilon }_t$ indicates a random disturbance term.

The formula adopts a logarithmic form to reduce data volatility and eliminate heteroscedasticity. The cement production, GDP, and population data of Guangdong from 2000 to 2020 can be obtained from the official website of Guangdong Statistic Bureau [49]. Future population and GDP can be predicted based on Leslie’s population matrix difference model and time series model. Cement demand in Guangdong, therefore, can be obtained (Figure 1). Polynomial regression analysis using UR and cement demand per capita leads to a fitting curve and validates prediction results. The results show that the deviation between the two prediction curves is less than 5%.

The forecast result of cement demand is listed below because it is the main parameter of the subsequent scenario forecast. Figure 2 shows that the demand for cement in Guangdong reaches its peak around 2020, with a peak of 171 million tons. This demand declines rapidly after a period of gradual development. The demand for cement drops to 149 million tons in 2030 and to about 100 million tons in 2060.

2.3. Forecast of the Future Application of Raw Material Replacement and Clinker Substitution in Guangdong

2.3.1. Analysis of Prospects for Raw Material Substitution

The application of industrial solid waste as cement raw material can bolster the sustainable development of cement production and promote a sound management mode for industrial wastes [31]. The substitution of low-carbon calcareous raw meals in clinker production provides a significant opportunity for symbiosis and the utilization of byproducts from other industrial processes [47].

A ton of cement clinker typically requires 1.3 tons of limestone raw materials. Limestone can be replaced with low-carbon raw meals to reduce carbon emissions by 10–40% [50]. In this paper, red mud (from the chemical industry) and steel slag (from the metallurgical industry) are culled as the main substitutes. They are separately added to raw meals to replace limestone and form two new raw meal formulae. In these three scenarios, the comprehensive use of these formulae replaces the traditional raw material formula.

Red mud is the residue left after the extraction of alumina in the chemical industry. Each ton of alumina produced can generate 1.0–1.6 tons of red mud. Due to its high calcium oxide content, red mud can be used as a building material. It can reduce the proportion of limestone in the raw meal formula and obtain a certain amount of process carbon emission reduction. The production experience of Shandong Aluminum Plant indicates that if the proportion of red mud in raw meals is 20%, it poses no negative impact on cement, clinker calcination, or equipment operation [51]. It is estimated that the corresponding process emission factor is about 0.393 tCO₂/tcl. In 2020, Guangdong produced 5.28 or so million tons of alumina and 5.81 million tons of red mud [49].

Steel slag can expedite limestone decomposition and improve the burnability of raw meals. To reduce production costs, some cement companies at home employ steel slag proportioning to make cement clinker. Many researchers increase the content of steel slag by improving the sintering process and screening the granularity of steel slag. Based on the production data of the enterprises, if steel slag is used to replace 15% of the raw material, the corresponding process emission factor will be 0.375 tCO₂/tcl [52]. Steel slag accounts for 10–15% of crude steel output. In 2020, the crude steel output of Guangdong stood at 85.04 million tons, approximately, which can supply 8.5 million tons of steel slag [49].

The application of industrial waste slag to cement clinker calcination is still at the experimental stage. A lot of repeated tests are needed to ensure the high quality of fired cement clinker in terms of strength, structure, mineral distribution, and other properties. At the same time, strengthening the pretreatment process of industrial waste slag can increase the mixing amount of industrial waste in raw meals, and ensure the quality of cement clinker. To apply and promote the findings of existing experimental studies in industrial production and improve the utilization of industrial waste are high on the agenda of current technological development.

2.3.2. Analysis of Application Prospect of Clinker Substitution

Although clinker is the primary resource for cement production, it can be substituted to a certain extent with a mix of fly ash, plaster, and clay. Cement production can decrease its energy consumption and CO₂ emissions by increasing the proportion of mixed materials and reducing the use of clinker [43].

The use of supplementary materials such as fly ash, ground-granulated blast furnace slag, and other potential industrial wastes plays an important role in diminishing the environmental impacts [14]. The clinker-to-cement ratio (CCR) fluctuates anywhere between 0.58 and 0.87 worldwide, with an average value of 0.65 [11]. The extreme value of the substitution rate may hit 0.5 [38]. The United Nations Technology Roadmap—Low-Carbon Transition in the Cement Industry—has set the expected goal of reducing the CCR to below 0.65 by 2030 and to below 0.6 by 2050 [50].

According to our investigation, Guangdong’s CCR arrived at 0.80 in 2020 [45]. Some cement plants have started using cement kilns to treat industrial waste, urban sludge, and other resources, but only as a fuel substitute [45]. The emission reduction potential of clinker substitution is still to be developed. The CCR reduction can be achieved in the future by deep processing of existing mixes and innovative use of various new concrete admixtures.

2.4. Scenario Setting

There are two kinds of parameters that affect CO₂ emissions in industrial processes: (i) activity level (main products output); and (ii) emission factors, which are mainly affected by the technological level, management level, production types, substitution ratio of raw materials, CO₂ recycling ratio, and policy control. In this study, three scenarios were developed for different carbon neutrality targets: the “carbon neutrality 60” scenario (CN60), the “carbon neutrality 50” scenario (CN50), and the “carbon neutrality 50 intensification” scenario (CN50+), taking into account the variation of the above parameters. Delphi methodology is a process of forecasting or decision-making using the collective opinion of a panel of experts on a complex topic [53]. Here, we use the Delphi method to set the scenario conditions in combination with the opinions of Guangdong cement industry experts [45].

CN60: Against the backdrop of the long-term goal of achieving carbon neutrality by 2060, the adoption of appropriate policy measures helps decrease CCR in a slow way. The proportion of low-carbon raw material substitution increases with the advances in technology and management. The utilization rate of red mud in cement raw materials ascends to 55% by 2060, while that of steel slag climbs to 10% [45]. The CCR drops to 0.65 in 2030 and 0.6 in 2060 [11].

CN50: Considering the long-term goal of achieving carbon neutrality by 2050, strengthening policy measures to gradually reduce the CCR, improve technological progress and management, and increase the proportion of low-carbon raw material substitution is a must. The CCR drops to below 0.65 in 2030, and below 0.6 in 2050 [11]. By 2060, the industry should maximize the use of low-carbon raw material substitutes, with the utilization rate of red mud in cement raw materials reaching 65% and the utilization rate of steel slag in cement raw materials reaching 15% [45].

CN50+: From 2020 onwards, deep emission reduction measures have been taken to achieve a low level of the peak, rapid reduction of CCR, further improvement of technology and management, and fast increase of low-carbon raw material replacement rate. The CCR decreases to 0.6 in 2030 and to 0.55 in 2050 [11]. By 2060, the industry maximizes the use of low-carbon raw materials, reaching 70% utilization of red mud in cement raw meals and 20% utilization of steel slag in cement raw meals [45].

2.5. Main Parameters

In this paper, the base year is set to 2020, and the forecast scenarios are set to 2060 and 2050. The data for the base year are mainly from the Statistical Yearbook of Guangdong Province [49]. Future activity levels and emission factors are projected as follows.

2.5.1. Activity Level

The activity data used to calculate the CO₂ emissions from cement production are derived from clinker production, which is the product of cement production and the CCR.

As mentioned earlier, 2020 saw Guangdong’s CCR come to 0.80 on average. In the CN60 scenario, the CCR decreases to 0.6 in 2060 from 0.8 in 2020. Under the CN50 scenario, the CCR drops to 0.55 from 0.8 in 2020, while the CN50+ CCR slides to 0.53 from 0.8. The estimated future output of clinker based on the predicted cement output and CCR is shown in

Table 1. Forecast results of clinker demand in the cement industry.

	Scenario	2020	2025	2030	2035	2040	2050	2060
CCR (clinker-to-cement ratio)	CN60	0.8	0.73	0.65	0.64	0.63	0.62	0.6
	CN50	0.8	0.72	0.63	0.62	0.60	0.58	0.55
	CN50+	0.8	0.71	0.6	0.59	0.58	0.55	0.53
Clinker demand (10,000 t)	CN60	13,660	11,842	9690	8181	7037	6636	6025
	CN50	13,660	11,680	9392	7862	6704	6207	5523
	CN50+	13,660	11,518	8945	7486	6382	5906	5322

.

2.5.2. Emission Factor

Based on the industry survey in Guangdong, the emission coefficient of the cement clinker process in the base year is 0.530 t CO₂/t clinker. This is close to the emission coefficient of a new dry kiln. Considering the current low utilization rate of industrial waste and the emission factor of Guangdong, the “Proportion of raw material replacing clinker output” in the province in 2020 is assumed to be zero.

Assuming that the relevant industrial capacity is adjusted in tandem with the cement industry, the level of supply of alternative raw materials remains unchanged. Yet the CCR reduction results in a corresponding increase in the proportion of cement clinker produced from alternative raw materials.

A Raw Material Replacement (RMR) scenario (consistent cement demand, substitution of raw material formulations only, no clinker substitution) was introduced to calculate the output rate of cement clinker under three scenarios. The RMR scenario achieves 100% recycling of industrial slag. Based on the availability of red mud and steel slag above, it is calculated that in 2060, the ratio of red mud cement clinker production reaches 14% and the proportion of steel slag cement clinker hits 16%. Further, it is possible to obtain year-by-year clinker production ratios for the three formulations under the RMR scenario from 2020 to 2060.

The percentage of clinker production for each formulation under the three carbon neutrality scenarios was calculated according to Formula (3).

$$w_{\mathrm{i}t}{=u}_{\mathrm{i}t}{\times w}_{\mathrm{i}t\mathrm{R}}{\times C}_{\mathrm{i}t\mathrm{R}}/C_{\mathrm{i}t},$$

(3)

where:

i is used to distinguish different formulations containing red mud or steel slag;

$w_{\mathrm{i}t}$ is the proportion of clinker output in formula i under the carbon neutrality scenarios in t year;

$w_{\mathrm{i}t\mathrm{R}}$ is the proportion of clinker output in formula i under the RMR scenario in t year;

$C_{\mathrm{i}t\mathrm{R}}$ is the CCR of formula i under the RMR scenario in t year;

$C_{\mathrm{i}t}$ is the CCR of formula i under the carbon neutrality scenarios in t year;

$u_{\mathrm{i}t}$ is the utilization rate of industrial waste in cement raw meals of formula i in t year.

In this paper, the Formula (4) was introduced to forecast future emission factors:

$${\mathit{EF}}_t=\sum {\mathit{EF}}_{\mathrm{it}}{\times w}_{\mathrm{i}t},$$

(4)

where:

${\mathit{EF}}_t$ is the CO₂ emission factor of industrial process in t year (tCO₂/tcl);

${\mathit{EF}}_{\mathrm{i}t}$ is the CO₂ emission factor (tCO₂/tcl) of cement clinker produced by formulation i;

$w_{\mathrm{i}t}$ is the proportion of cement clinker output (%) produced by formulation i.

2.6. Summary of Scenario Parameter Settings

To compare the CO₂ emissions reduction among the three scenarios, business as usual (BAU) is introduced into the research as a comparison scenario. In the BAU scenario, there is neither raw material replacement nor clinker substitution.

Table 2. Scenario parameter setting.

			2020	2025	2030	2035	2040	2050	2060
CCR		BAU	0.8	0.8	0.8	0.8	0.8	0.8	0.8
		CN60	0.8	0.73	0.65	0.64	0.63	0.62	0.6
		CN50	0.8	0.72	0.63	0.62	0.59	0.57	0.55
		CN50+	0.8	0.71	0.60	0.59	0.58	0.55	0.53
Clinker output (10,000 tons/y)		BAU	13,661	12,977	11,926	10,194	8879	8591	8033
		CN60	13,661	11,842	9690	8181	7037	6636	6025
		CN50	13,661	11,680	9392	7862	6704	6207	5523
		CN50+	13,661	11,518	8945	7486	6382	5906	5322
Proportion of raw material replacing clinker output (%)	Red mud	BAU	0	0%	0%	0%	0%	0%	0%
		CN60	0	1.07%	2.40%	3.64%	4.92%	7.57%	10.40%
		CN50	0	1.28%	2.93%	4.48%	6.10%	9.57%	13.41%
		CN50+	0	1.40%	3.31%	5.07%	6.91%	10.83%	14.98%
	Steel slag	BAU	0	0%	0%	0%	0%	0%	0%
		CN60	0	0.23%	0.51%	0.77%	1.04%	1.60%	2.20%
		CN50	0	0.34%	0.79%	1.20%	1.64%	2.57%	3.60%
		CN50+	0	0.46%	1.10%	1.69%	2.30%	3.60%	4.98%
Carbon emission factor		BAU	0.528	0.528	0.528	0.528	0.528	0.528	0.528
		CN60	0.528	0.526	0.524	0.523	0.521	0.517	0.513
		CN50	0.528	0.526	0.524	0.521	0.519	0.514	0.508
		CN50+	0.528	0.526	0.523	0.520	0.517	0.511	0.505

is presented here to illustrate all the parameter settings in the scenario analysis.

3. Results and Analysis

3.1. Carbon Dioxide Emissions and Cumulative Emissions from Cement Process

Under the previous scenario assumptions, the prediction results for carbon dioxide emissions from the cement industry process in Guangdong Province are calculated year by year. This is shown in Figure 3. It shows that based on the three scenarios, the cement process CO₂ emission in the province stands at 72.12 million tons in 2020. Then it begins to decline.

Under the CN60 scenario, the emissions of CO₂ from industrial processes in cement come to 50.79 million tons by 2030 and 30.89 million tons by 2060, 57% lower than the emission level in 2020.

Under the CN50 scenario, emissions of CO₂ from industrial processes in cement come to 49.12 million tons by 2030 and 33.09 million tons by 2050, 56% lower than the 2020 level. By 2060, the carbon emissions of the CN50 scenario amount to 28.05 million tons, 61% lower than that of 2020.

In the CN50+ scenario, the CO₂ emissions from cement-related industrial processes reach 46.72 million tons by 2030, 5% lower than that of the CN50 scenario during its peak. By 2050, CO₂ emissions arrive at 30.17 million tons, a reduction of 58% from 2020. By 2060, the carbon emissions of the CN50+ scenario come to 26.88 million tons, 63% lower than that of 2020.

The cumulative emissions show that in 2060, under the CN60 scenario, the CCR drops to 0.6, the carbon emission factor falls to 0.513, and the cumulative carbon emissions are 1.783 billion tons. Under the CN50 scenario, the CCR drops to 0.55, the carbon emission factor slides to 0.508, and the cumulative carbon emissions are 1.707 billion tons. In the CN50+ scenario, the CCR descends to 0.53, the carbon emission factor decreases to 0.505, and the cumulative carbon emissions are 1.644 billion tons. Cumulative emission results show that by 2060, each 1% increase in the proportion of clinker produced from low-carbon raw meal formulations reduces cumulative carbon emissions by 735 MtCO₂, and each 1% reduction in the CCR reduces cumulative carbon emissions by 877 MtCO₂.

3.2. Emission Reduction Potential of Raw Material Replacement and Clinker Substitution

In this study, there are two sources of emission reduction in the industrial process in the cement industry: (i) substitution of clinker; and (ii) replacement of low-carbon raw materials. A comparison of three scenarios for emission reductions in 2060 is shown in Figure 4.

Under the CN60 scenario, the CCR drops from 0.8 to 0.6. Compared with the BAU scenario, carbon dioxide emissions decreased by 24% through clinker substitution, contributing 89% to the total emission reduction. Under the CN50 scenario, the CCR is lowered to 0.55. Compared with BAU, the replacement of clinker further reduces CO₂ emissions by 30%, accounting for 89% of the total emission reduction. Under the CN50+ scenario, the CCR descends to 0.53, and the replacement of clinker cuts CO₂ emissions by 32.3% based on the BAU scenario, contributing 88% to the total emissions reduction.

Under the CN60 scenario, low-carbon materials are added to the raw meal formula to replace calcareous materials. The proportion of clinker output produced by low-carbon raw meals reaches 13%, the CO₂ emissions are 3% less than that of BAU, and the contribution of emission reduction is 11%. Under the CN50 scenario, the proportion of clinker produced by low-carbon alternative raw materials reaches 17% and the CO₂ emission is 4% less than that of BAU and accounts for 11% of the emissions reduction. Under the CN50+ scenario, the production proportion of low-carbon alternative raw material clinker is 20%, further reducing emissions by 4%, and the contribution of emission reduction is 12%. Under the three scenarios, with the reduction of the CCR and the application of low-carbon alternative raw materials, the emission reduction effect is enhanced. The driving force for clinker substitution is far greater than that for low-carbon raw meal substitution. This may be because of the decline of CCR which makes it difficult to play the role of low-carbon raw meals in reducing emissions.

As can be seen from Figure 5, the emission reduction contributions of both raw material substitution and clinker substitution under the three scenarios are concentrated in 2020–2045, and the emission reduction contributions are lower in 2045–2060. It is similar to the previous forecast curve for cement demand in terms of emission reduction contribution. Further consideration must be taken that the emission reduction effect of material substitution technology is strongly related to the change in cement demand. The peak emission reduction contribution of the CN60 scenario occurs around 2035, whereas the peak emission reduction contribution of the CN50 and CN50+ scenarios occurs around 2030. Substituting raw materials and clinker reduces the urgency of mid-term carbon neutralization emission reduction and transfers it to the early stage (2020–2030). From a long-term perspective, there is not much room for progress in this technology. There is a limit to the reduction of the CCR due to the limitations of the cement properties. The replacement ratio of low-carbon replaceable raw materials in the formulation is fixed. Therefore, in the early stage of carbon neutrality, the most significant carbon reduction effect is achieved by widely promoting cement substitution technology and reducing cement demand. In the middle and late stages of carbon neutrality, cement demand is at a low level and there is limited room for technology development. Therefore, the emission reduction effect is not obvious and the emission reduction potential is small.

4. Conclusions

On the back of the historical data of Guangdong, this study systematically analyzed the future demand of cement products and the application prospects of low-carbon raw material replacement and clinker substitution in the province. Then it established three scenarios oriented to carbon neutrality, with a focus on the long-term carbon emission reduction potential, cumulative carbon emission ceiling, and emission reduction driving factors of raw material substitution measures under different carbon neutrality scenarios.

• This study analyzed the future demand for cement products in Guangdong and found that demand peaks around 2020 and declines to 100 million tons by 2060;
• In the pre-carbon neutrality period, with the strong promotion of alternative technologies and the sharp reduction in cement demand, material substitution measures make an outstanding contribution to emission reduction;
• There are two factors driving substitution technology in the cement industry—the decline of the CCR and the recycling of low carbon materials. By comparison, the driving effect of the former is greater;
• The timing to set the carbon neutrality target affects the upper limit of cumulative carbon emissions and the distribution of abatement pressure scales over time. Setting targets in advance is conducive to prioritizing the deployment of policy resources, ramping up the emission reduction efforts in the early stage, and alleviating the pressure of emission reduction in the middle and late stages.

5. Policy Implications

This paper makes a number of recommendations. The target timing of carbon neutrality affects the distribution of resource allocation and emission reduction pressure throughout the process. Policymakers can prioritize the deployment of policy resources until 2030 to increase the intensity of early emission reduction measures. Improving the industrial carbon pricing mechanism sends a strong economic signal to exhort companies to make low-carbon reforms.

In recent years, the demand for cement in areas such as Guangdong, where infrastructure is well developed, has reached its peak. More attention needs to be paid to infrastructure construction, fixed asset investment, and other downstream industries to ascertain cement supply and demand and avert overcapacity.

Meanwhile, when applying the raw material replacement in the cement industry we should take several key factors into consideration: durability, strength, and standards compliance. More related research on the performance of the improved cement should be accomplished.

Efforts must be made to progressively establish a complete waste collection network in the future. Only when the nation and localities develop and implement waste policies to regulate waste management will it be possible to achieve a greater share of substitution and reduce carbon emission factors. An endeavor should be made to enhance interregional government cooperation to promote industrial waste flow and the role of cement kiln co-processing.

The acceptance of new materials by consumers at all levels of society influences the way cement is produced. Progress must be made in disseminating material substitution technology among architects, engineers, contractors, and clients.

The use of by-products in cement production can avoid pollution and elevate the environmental value. Serious efforts should be made to give full play to the synergistic treatment of cement kiln waste, clever use of industrial waste, and promotion of superfine powder to replace ordinary mixing materials, as well as to increase the amount of mixing materials and reduce the level of CCR.