Economic Analysis of Geopolymer Brick Manufacturing: A French Case Study

This paper presents an economic analysis of manufacturing geopolymer bricks for use in the construction sector. The manufacturing processes of both geopolymer bricks and traditional fired bricks were investigated. For this study, we collected and analyzed all phases of geopolymer brick production from the extraction of raw materials to storage. Seven formulations of geopolymer bricks based on clay and waste bricks were analyzed. We considered the cost of raw materials and logistics operations in the production line of brick manufacturing. The results of this study prove that the manufacturing cost of geopolymer bricks based on clay provides an economic gain of 5% compared to fired bricks for the same compressive strength of 20 MPa. In the case of waste bricks, for the same production cost, the compressive strength of the geopolymer bricks is double that of fired bricks. Hence, this study shows the economic interest in the industrial production of geopolymer bricks. It also confirms that future research is needed that focuses on necessary changes to the current industrial production chain required for the manufacture of geopolymer bricks.


Introduction
After the economic crisis in 2008, construction activity in France grew rapidly. This activity was followed by a strong demand for building materials. The production of these materials caused pressure on limited natural resources and an increase in construction waste and CO 2 emissions. In 2018, CO 2 emissions related to human activities reached a world historical level of 37.1 billion metric tons [1].
In France, the construction sector is responsible for about 40% of total energy consumption [2]. This value only represents the consumption related to the building process, without considering the industrial part of manufacturing and transport of building materials. In 2011, the CO 2 emissions due to the construction sector were estimated to be 10% of total CO 2 emissions, of which 52% was attributed to the concrete industry. In addition, the construction industry produces 75% of waste in France, making it the largest waste producer [2].
The pressure of economic and environmental costs is motivating academic and industrial parties to develop innovative building materials. These targeted materials must respond to the challenges of recycling construction waste, reducing CO 2 emissions, conserving non-renewable natural resources, and reducing costs at the industrial level. In this context, geopolymer-based materials show promise for replacing traditional materials in the building industry due to their interesting properties and low environmental impact [2].
The term geopolymer was invented by Joseph Davidovits in the 1970s [3]. Materials comparable to geopolymers were created in the Soviet Union starting in the 1950s [4,5]. These materials have also been called soil cements [6][7][8][9]. They generally consist of pozzolanic materials such as kaolin [10][11][12], 2 of 12 metakaolin [13][14][15], blast furnace slag [16][17][18], fly ash, and ceramic wastes [19,20]. These materials are activated by an alkaline solution usually containing varying amounts of dissolved silicate [21]. Geopolymer is a term that refers to a range of synthetic aluminosilicate polymeric materials, often called alkali-activated binders. Geopolymer materials can be produced from a range of natural and synthetic pozzolanic solids activated with alkaline solutions such as sodium hydroxide and sodium silicate.
Geopolymers have a wide range of applications due to their useful properties, such as their resistance to acid/sulphate attacks [22][23][24], freeze/thaw [22,25], and high temperatures [22,26]. In the construction sector, geopolymers are referred to as green concrete [27,28] due to their ability to reduce CO 2 emissions and lower production energy [21].
Geopolymers have been applied in various contexts: geopolymer cement and concrete, flame-retardant high-tech applications, aircraft and automotive interiors [3,29], seawater applications [30], immobilization of toxic metals and wastes [31][32][33], heat-resistant pavement [34], structural elements [35], geopolymer concrete pipes [36], ceramic materials [3], electrical fuses [3], and fire-resistant particleboard [3]. Geopolymers have the potential to be used in a variety of applications due to their durability, chemical and thermal resistance, rapidly evolving mechanical strength, and economic and environmental benefits as industrial by-products [3,37]. Since 1972, geopolymer applications have been developed in France, Europe, and the USA. In 1979, a French scientific organization, the Geopolymer Institute, was created [3]. Geopolymers are used in different applications, based on 30 patents registered and issued in several countries [3].
In the literature, studies on the economic feasibility of geopolymer materials are limited [38][39][40]. Geopolymers can act as a binder to replace other binders such as Portland cement pastes in concrete products [40]. Geopolymer bricks based on waste bricks and clay were investigated in a previous study [41]. The environmental impact of these geopolymer bricks was evaluated [42]. The results of these studies showed that these geopolymer bricks could be a possible alternative to fired brick (FB) based on their mechanical properties and environmental impact.
The objective of this study was to develop an economic analysis for the implementation of a new brick based on geopolymer materials, which could serve as an alternative to the fired brick manufactured at the French brickworks.
In this study, an economic analysis of the production cost was carried out using different geopolymer brick formulations based on waste bricks and clay. The production costs of both the economic feasibility and mechanical properties were analyzed to study the technical feasibility. The production cost of one metric ton of brick was determined based on the cost of ingredients in the French market. Hence, this novel study focused on developing a product database for the production of building materials in France, assessing the change needed to incorporate the product in the chain of production, and presenting a case study in the field of masonry with geopolymer bricks.

Research Objectives
The traditional process of producing fired bricks is considered energy-intensive and uses natural materials, mainly clay. In this study, attention was paid to the manufacture of geopolymer bricks and the implementation of this process as a substitute for the brick production process.
The manufacturing process of traditional bricks includes transporting raw materials to the factory, crushing, storing in silos, dosing, dry mixing, mixing with water, and preparing the blocks. The paramount step for fired brick is the use of a high temperature kiln that cures the bricks at a temperature above 1100 • C and ends with packaging and storage at the factory.
The manufacturing process of geopolymer bricks follows the same preparation process with the elimination of a high temperature curing phase, which is costly from economic and environmental points of view.
In geopolymer bricks, hardening is based on alkaline activation between the solid materials used (clay, sand, and brick waste) and alkaline activators (hydroxide and sodium silicate). With the elimination of the high temperature curing phase, this new manufacturing process consumes less energy than the conventional fired brick process. The different phases of these two brick manufacturing processes are illustrated in Figure 1. In geopolymer bricks, hardening is based on alkaline activation between the solid materials used (clay, sand, and brick waste) and alkaline activators (hydroxide and sodium silicate). With the elimination of the high temperature curing phase, this new manufacturing process consumes less energy than the conventional fired brick process. The different phases of these two brick manufacturing processes are illustrated in Figure 1. In this study, a comparison between the cost of production of fired bricks and geopolymer bricks was carried out to evaluate the economic value of the use of the geopolymer bricks in brickwork.

Cost Evaluation Method
The cost evaluation of bricks consists of the final cost of the bricks (based on the production chain) and the cost of raw materials used in the manufacturing process. This evaluation is composed of three steps: (1) Step 1: Brick formulation and geopolymer references: • Reference geopolymer brick formulation; • Determine characteristics of raw material; • Study different formulations of geopolymer bricks. (2) Step 2: Calculation of the initial cost: • Determination of unit prices for the different materials used; • Identification of the different phases of production of geopolymer bricks; • Calculation of the global cost of geopolymer and fired brick production for the different formulations studied. (3) Step 3-Business case analysis: • Identification of parameters; • Calculation of indicators related to the chosen parameters; • Performance analysis based on fired brick of the Briqueterie du Nord de la France (BdN); • Demonstration of the most efficient geopolymer brick formulations.

Materials and Formulations Used in the Geopolymer Formulations
Elimination of the high temperature curing step in the geopolymer brick manufacturing Geopolymer brick process Fired brick process In this study, a comparison between the cost of production of fired bricks and geopolymer bricks was carried out to evaluate the economic value of the use of the geopolymer bricks in brickwork.

Cost Evaluation Method
The cost evaluation of bricks consists of the final cost of the bricks (based on the production chain) and the cost of raw materials used in the manufacturing process. This evaluation is composed of three steps: (1) Step 1: Brick formulation and geopolymer references: • Reference geopolymer brick formulation; • Determine characteristics of raw material; • Study different formulations of geopolymer bricks. (2) Step 2: Calculation of the initial cost: • Determination of unit prices for the different materials used; • Identification of the different phases of production of geopolymer bricks; • Calculation of the global cost of geopolymer and fired brick production for the different formulations studied. (3) Step 3-Business case analysis:

Materials and Formulations Used in the Geopolymer Formulations
The solid materials used in the preparation of geopolymer bricks were waste brick (WB), clay, sand, and ground granulated blast furnace slag (GGBFS). The chemical composition of these materials is presented in Table 1.
The analysis of the chemical composition of the solid precursors indicated that the waste brick had a high content of 73.106% of SiO 2 compared to 12.68% for Al 2 O 3 . The value 6 of mass ratio SiO 2 /Al 2 O 3 classifies the waste bricks as a siliceous material [43]. A similar chemical composition of the waste bricks was achieved for the clay with 73.676% for SiO 2 and 13.59% for Al 2 O 3 . In the case of GGBFS, SiO 2 and CaO were the two main components with a minority of Al 2 O 3 . The composition of the sand displayed that the main phase was composed of SiO 2 , which accounted for 89.99% of its total mass.
The alkaline activators used in the preparation of the geopolymer consisted of a combination of hydroxide (NaOH) and sodium silicate (Na 2 SiO 3 ). The mass composition of sodium silicate contained 27% SiO 2 , 8% Na 2 O and 65% H 2 O. The sodium hydroxide solution was prepared with a concentration of 8M from solid NaOH capsules of 98% purity.
The compositions of the seven geopolymer brick's formulations studied in this research are illustrated in Table 2. These geopolymer brick formulations were presented in previous studies and are prepared with clay and waste bricks [41,42]. GC and GWBi represent the geopolymer brick's formulations based on clay and waste brick respectively. The value i varies from 1 to 5 to refer to the five geopolymer brick formulations based on waste bricks.

Parameter Used in the Economic Analysis
The parameter used in this study to evaluate the economic analysis of fired and geopolymer bricks was the compressive strength of the different formulations. The compressive strength values for waste geopolymer bricks are based on a study carried out by Youssef et al. (2019) [41,42]. In this study, a new geopolymer brick formulation based on clay was added. The reference-fired brick was manufactured by the brickworks in the north of France and is called FB. The mechanical strength of the fired brick was 20 MPa. Table 3 presents the compressive strength of the geopolymer and the fired bricks (FB).

Cost of Fired Brick Manufacturing: Data Source
In brickwork, the different types of fired bricks are differentiated by their mass in metric tons. For this reason, the production cost of geopolymer bricks was evaluated in metric tons of brick to facilitate the comparison with fired bricks. In this section, the data source for the production cost of fired bricks is based on the annual business model of fired brick production at the brickworks in the north of France. This business model for French brickwork was used to derive the actual cost of one metric ton of fired bricks produced in France. Table 4 presents the production cost of one metric ton of bricks according to the parameters used in the business model of the fired brick production at the French brickworks. In this model, the following data that covers the production stage of fired bricks are considered: (1) Extraction of raw materials (clay and sand); (2) Energy consumption: use of natural gas, electricity, and fuel throughout the production chain and in the factory premises; and (3) Maintenance and humanpower. Table 4 provides the business model of the annual production of fired bricks at the French brickwork case. This table is divided into three stages: The first stage shows the materials costs, the labor cost, and the annual cost of fired brick production in one year in this French brickworks case. The second section presents the quantity of fired bricks produced, which corresponds to the costs consumed in the first section. The third section demonstrates the cost of 1 metric ton of fired bricks calculated from the first two sections.

Cost of Geopolymer Brick Manufacturing
This part of the study focused on the production cost of geopolymer bricks. This cost had two data sources: (1) the French market to find the cost of the ingredients used in the geopolymer brick's formulations and (2) the business model for the French market brickworks used to calculate the production stage of the geopolymer bricks. This calculation covers the production of the geopolymer bricks, from the raw materials to storing of bricks.  Table 5 presents the geopolymer brick's ingredients and its cost on the French market. This cost represents the average cost of the different French suppliers.

Natural Gas and Domestic Fuel Oil Consumption
According to data from the French brickworks, the total amount of consumed natural gas is equal to 670.8 kWh for each metric ton of fired bricks produced. The kiln consumes 50% of the total amount of natural gas. However, in the manufacture process of geopolymer bricks, the absence of curing saves 50% from this total natural gas consumption and therefore the consumption of natural gas will be reduced to 335.4 per metric ton of geopolymer bricks produced.
For domestic fuel oil, the same amount used in the production of fired bricks is used in the manufacturing process of geopolymer bricks.

Electric Power Consumption
The geopolymer bricks were manufactured at low temperature and the kiln stage was eliminated from the manufacturing process. This temperature was much lower than that used in the manufacture of traditional bricks, which is between 1100 • C and 1400 • C.
The other machines present in the industry are used in the manufacture of geopolymer bricks. Molding, drying, and supplying by conveyor belts do not depend on the materials used. Moreover, the crushing and sieving system used in the production of fired bricks will still be involved in the case of geopolymer bricks. The electric power consumption in the production of geopolymer brick waste is showed in detail in Table 6. The weekly cost of electric power consumption obtained corresponds to an annual cost of 1,739,103 kWh. Therefore, the production cost of one metric ton of geopolymer bricks corresponds to EUR 10.23 based on the unit price of EUR 0.1483/kWh of electric power paid by the brickworks.

Maintenance and Labor Cost
The kiln represents 30% of the total maintenance cost in the factory, which means a reduction from EUR 13.41 to 9.387/t of geopolymer bricks produced without curing. Regarding labor, the cost remains the same at EUR 13.42 per metric ton of brick produced.

Global Cost of Geopolymer Brick Manufacturing
After collecting initial data for the geopolymer brick production chain, an overall economic assessment was conducted to determine the cost of production according to different formulations of geopolymer bricks based on clay and waste bricks. Table 7 displays a global assessment of the cost of producing a metric ton of geopolymer bricks according to the seven formulations studied. Table 7. Global assessment of the cost of a metric ton of geopolymer bricks according to the 7 formulations studied.

Results and Discussion
The production cost of one metric ton of bricks was calculated for the different geopolymer and fired bricks formulations, based on the compression strength obtained in our previous work [41,42]. The results are illustrated in detail in Figure 2.
The values obtained showed a variation in the cost of production of one metric ton of geopolymer bricks according to the ingredients of each formulation. For geopolymers based on waste bricks, the cost of Na 2 SiO 3 dominates the costs of the other ingredients in the formulation.
The clay-based geopolymer brick has the lowest production cost of EUR 114/t, resulting in a financial gain of 4.64% compared to the traditional fired brick for the same compressive strength of 20 MPa. The cost of geopolymer bricks based on waste bricks evolves proportionally with the quantity of GGBFS. The GWB1 formulation has a production cost of EUR 120/t for a compressive strength of 38.96 MPa. This formulation is cost-effective from an economic and technical point of view. The geopolymer brick formulations increase production cost from 4.23% to 17%, with a proportional increase in compressive strength from 94.8% to 350%. By classifying geopolymer bricks in grade according to their compressive strength, these results correspond to the literature [38,39] where the cost of production of geopolymer concrete is higher than ordinary concrete at higher grades of formulations.

Results and Discussion
The production cost of one metric ton of bricks was calculated for the different geopolymer and fired bricks formulations, based on the compression strength obtained in our previous work [41,42]. The results are illustrated in detail in Figure 2. The values obtained showed a variation in the cost of production of one metric ton of geopolymer bricks according to the ingredients of each formulation. For geopolymers based on waste bricks, the cost of Na2SiO3 dominates the costs of the other ingredients in the formulation.
The clay-based geopolymer brick has the lowest production cost of EUR 114/t, resulting in a financial gain of 4.64% compared to the traditional fired brick for the same compressive strength of 20 MPa. The cost of geopolymer bricks based on waste bricks evolves proportionally with the quantity of GGBFS. The GWB1 formulation has a production cost of EUR 120/t for a compressive strength of 38.96 MPa. This formulation is cost-effective from an economic and technical point of view. The geopolymer brick formulations increase production cost from 4.23% to 17%, with a proportional increase in compressive strength from 94.8% to 350%. By classifying geopolymer bricks in grade according to their compressive strength, these results correspond to the literature [38,39] where the cost of production of geopolymer concrete is higher than ordinary concrete at higher grades of formulations.
The interpretation of the results showed that both GC and GWB1 formulations are economically acceptable and represent a technical feasibility for the construction sector.
These results demonstrated that the production cost of geopolymer bricks depends on the components of the formulation. The production of geopolymer bricks is economically feasible. The decision to use this method is related to its technical feasibility and depends on well-defined parameters such as compressive strength. The results of this study can be added to the database of investors and production companies to clarify their decisions regarding geopolymer use at the industrial level.

Conclusions
In this study, we performed an economic analysis of the use of geopolymer brick at the industrial level. The research presents a French case study of the brickworks in the North of France. Different geopolymer brick formulations based on clay and waste bricks were studied. The production cost of The interpretation of the results showed that both GC and GWB1 formulations are economically acceptable and represent a technical feasibility for the construction sector.
These results demonstrated that the production cost of geopolymer bricks depends on the components of the formulation. The production of geopolymer bricks is economically feasible. The decision to use this method is related to its technical feasibility and depends on well-defined parameters such as compressive strength. The results of this study can be added to the database of investors and production companies to clarify their decisions regarding geopolymer use at the industrial level.

Conclusions
In this study, we performed an economic analysis of the use of geopolymer brick at the industrial level. The research presents a French case study of the brickworks in the North of France. Different geopolymer brick formulations based on clay and waste bricks were studied. The production cost of one metric ton of bricks and the compressive strength of the geopolymer bricks were the two parameters used to evaluate the feasibility of production of geopolymer bricks at the industrial level. The determination of the production cost of the geopolymer bricks was based on the annual business model of the brickworks, which was used to find all data sources needed.
The results of this study demonstrated that the production cost of geopolymer bricks changes significantly depending on the ingredients used in the formulation. The geopolymer brick based on clay gives a financial gain of 5% compared to traditional fired brick for the same compressive strength of 20 MPa. In the case of the geopolymer bricks manufactured with waste brick, an improvement of 100% in compressive strength can be achieved with the same production cost as fired bricks. These results can be considered as a database for use in the production of geopolymer-based building materials at the industrial level.