Natural stone materials with so many various types and different feature,that used for a lots of stone projects.For example, we know those famous like as natural granite and marble stone,that often did in popular stone tiles and stone sculptures for high class projects. In those materials, there also have a special type stone mateiral, that is blue limestone. Just as word said, this material is one of a limestone and also with own special use and popular application.
Judging from the current domestic and international demand for limestone, the worlds annual demand is about 1.2 billion tons, but 80% is for general use. High-quality lime has a large market gap due to low resources and low output. In recent years, countries in the Asia-Pacific region have to import about 1.1 million tons of limestone from China each year due to insufficient domestic limestone resources. Experts predict that the domestic demand for high-quality limestone will increase at a rate of 250,000 tons per year, and the Asia-Pacific region will increase at a rate of 300,000 tons per year. As a professional blue limestone factory from China, we hope can supply some basic info for customers reference
Limestone is a common non-metallic mineral and a valuable resource with a wide range of uses. Limestone is a trade name for limestone as a mineral raw material. Limestone has been widely used in the history of human civilization because of its wide distribution and easy accessibility in nature.
As an important building material, it has a long history of mining. In modern industry, limestone is the main raw material for the manufacture of cement, lime, and calcium carbide. It is an indispensable flux limestone in the metallurgical industry. After superfine grinding, high-quality limestone is widely used. Used in the manufacture of paper, rubber, paint, coating, medicine, cosmetics, feed, sealing, bonding, polishing and other products. According to incomplete statistics, the total ratio of limestone and building stones consumed in cement production, lime production, metallurgical flux, and limestone consumed by ultrafine calcium carbonate is 1:3
Just as material name said, that blue limestone is a limestone material. When we want to know and understand this material in very well, we have to know what is limestone too. The main component of limestone is calcium carbonate (CaCO3). Lime and limestone are a large number of raw materials used in construction materials and industries. Limestone can be directly processed into stone and burned into quicklime. Quicklime CaO becomes slaked lime by absorbing moisture or adding water. The main component of slaked lime is Ca(OH)2, which can be called calcium hydroxide. The slaked lime is prepared into lime slurry, lime paste, etc., which is used as coating material and brick adhesive. Whatever in Chinese market or other European market, this material always have big range use.
Compare with Chinese Granite, Chinese Marble, and Basalt Bluestone,this mateiral with own feature.The main component of limestone is calcium carbonate. Its main chemical property is to decompose into calcium oxide and carbon dioxide at higher temperature. In addition, there are some chemical properties as follows.
Limestone reacts with all strong acids to form calcium salts and release carbon dioxide. The reaction speed depends on the impurities contained in limestone and their crystal size. The higher the impurity content and the larger the crystal, the lower the reaction rate. The reaction speed of dolomite is slower than that of limestone. Judgment method of dolomite and limestone: a small amount of bubbles are generated when 10% hydrochloric acid is dropped on dolomite, and when dropped on limestone, odorless bubbles are generated violently. The gas generated can make the clarified lime water turbid
Chlorine and hydrogen chloride react very slowly with CaCO3 in the dry bath state and at room temperature, and only start to accelerate after 600C to form CaCl2; sulfur dioxide has no significant effect on CaCO3 in either gaseous or liquid state at room temperature; while nitrogen dioxide ( NO2) reacts with CaCO3 at 15 to produce Ca(NO3)2, NO and CO2
After short introduce, we can know what is structure of limestone and it is with own special physical feature. As a important type of limestone, the Blue Limestone also with those above feature.In addition, that also with own special style too. Then we can say some about this Blue Limestone material.
Jiaxiang,Shandong is the area with the largest storage of blue limestone(limestone). Blue Limestone slabs (blue limestone, gray limestone) generally contain about 50% CaO, and the MgO content is between 2.5-3.5.Three angles 3.7-3.8, water absorption 0.75%, bending strength 10.0MPa, glossiness around 60, compressive strength around 15.5mpa, density 2800 kg/m3.At the same time, the Blue Limestone also with own special feature. For exaple, that style as the texture is hard, the compressive strength is strong, the gloss is good, and it will not weather, which meets the requirements of the national first-class environmental protection product. It is widely used for indoor and outdoor building decoration, especially for gardens, squares, municipal administration, etc., showing its advantages.
Just as we introduced, the Blue Limestone can be cut in different shapes products. As it with very good physical data and performance. In general, we can cut blue limestone into can be further processed into various plates: matte board, paving slate, antique stone, pickling surface, sandblasting board, fire board, litchi noodle, chopped axe stone, square stone, step stone, curb stone, railing board Stone, tombstone, special-shaped stone, craft stone carving, relief, block, slab, etc.
The Blue Limestone often did various surface methods for different projects.At the daily life, when we do outdoor paving stone slabs, then the flamed and bush hammered is most popular. If we want to use Blue Limestone for interior floor, then the honed and flat surface is most popular. Indeed, this blue limestone can do almost all types popular surface methods, the detailed as:
The BLue Limestone also with various types from various areas. The famous mainly from China, Vietnam, and Belgium,etc. Of course, the most popular and famous blue limestone from Jiaxiang,China. Why so many peoples choose Blue Limestone from China?
Since becoming the worlds largest stone producer, exporter and consumer country in 2005, Chinas stone industry has maintained rapid growth for eight consecutive years, and has accounted for nearly 20% of global stone processing and production. Become a hot spot in the world market and continue to drive the development of the global stone industry.Just as we said, blue limestone mainly used in high-end real estate projects. Common star hotels, high-end clubs, villas, and mid-to-high-end communities need to use a large number of different varieties of stone for interior and exterior decoration. In addition, in the global market, more and more art puzzles, stone art modeling, and stone columns are used in halls, colonnades, doorways, elevator entrances and other parts. In particular, traditional stone consuming countries such as the United States, Germany, Italy, Spain, etc., are using a large number of medium and high-end blue limestone products due to their architectural style, living tradition, and environmental protection.
In the China, there have more than 200 big and small blue limestone factories in China. Those factories mainly located in Jiaxiang,China. As the quarry supply in stable,then make more and more customers import this materials from Qingdao,China now. Of course, the good quality and competitive price always the most important for blue limestone developing in China.
With the improvement of living and living standards, the proportion of stone used on the floor, cabinets and walls in home decoration has also increased significantly. There have more and more peoples start to use Blue Limestone for construction and decoration now.This material belongs to enviroment friendly stone material, that can meet most areas and countries quality request.
Cement production has undergone tremendous developments since its beginnings some 2,000years ago. While the use of cement in concrete has a very long history (Malinowsky, 1991), the industrial production of cements started in the middle of the 19 th century, first with shaft kilns, which were later replaced by rotary kilns as standard equipment worldwide. Today s annual global cement production has reached 2.8 billion tonnes, and is expected to increase to some 4 billion tonnes per year in 2050 (Schneider et al., 2011). Major growth is foreseen in countries such as China and India as well as in regions like the Middle East and Northern Africa. At the same time, the cement industry is facing challenges such as cost increases in energy supply (Lund, 2007), requirements to reduce CO2 emissions, and the supply of raw materials in sufficient qualities and amounts (WBCSD, 2008).
In this chapter, the environmental impact of cement production will be described. The chapter will first focus on the most common cementitious product: ordinary Portland cement (OPC) and will then evaluate the main perspective in terms of reduction of cement production s environmental impacts. To do so, we will describe the improvement perspective in the cement sector as well as the alternative products that could, at least partially, replace OPC.
Cement production is a thermal energy intensive process, which requires heating solid particles up to 1450C and cooling it down. The process generates hot and CO2 rich exhaust streams. Fin order to study energy efficiency of the process, authors like Mujumdar et al. (2006, 2007) developed detail models of process units, while others highlighted energy and exergy performances of plants (Kolip et al 2010). Some authors have studied the integration of cogeneration units in cement industry as an option of waste heat recovery (Wang et al 2008). The previously mentioned studies are considering, in detail, thermodynamic performances, but they are not investigating the heat integration inside the process. Some other authors, such as Murray et al (2008), Kaantee (2004), Mokrzycki (2003) have focused their analysis in the use of alternative/waste fuels, but they did not show the impact and the potential of these fuels on the heat integration between streams.
This paper explores the use of process integration techniques to improve the energy efficiency of cement plants, focusing on the dry route cement production and the integration of alternative fuels. Flow sheeting modeling, Pinch Analysis and mixed integer linear optimization techniques are applied to study an existing cement production facility.
Cement production is one of the largest industries in the world. Annual world production in 2013 was approximately 4 GT (of which, about half was in China). It is produced in kilns at around 1400oC (2500oF), and approximately 750 kg (1650 lb) of CO2 are released for each tonne (2205 lb.) that is made. This is 400 m3 (524 yd3) of gas; and CO2 normally forms only 0.04% of air. Cement production is responsible for around 7% of worldwide greenhouse gas emissions. The only larger contributors are electricity generation and transport.
Most of the CO2 released when cement is made comes from the chemical reaction. The limestone from which it is made is calcium carbonate, and when this is heated it gives off carbon dioxide, and forms calcium oxide. Thus, while some benefit has been obtained by making the process more energy efficient, there is little scope for any further reductions.
Numerous different solutions to this problem have been proposed, including carbon capture and inventing completely new cements; but the only effective method currently used to achieve significant reductions in greenhouse gas emissions is the use of cement replacements.
One process that has not been extensively investigated is carbon sequestration. In this process, the hydrated cement reacts with CO2 in the air, slowly reversing some of the processes that took place in the kiln when the cement was made (this is the carbonation process; it also causes reinforcement corrosion, see Section 25.3.2). It is estimated that this may reduce the carbon footprint of the cement industry by 35%.
Cement production is an energy-intensive process. The cost of energy constitutes more than 60% of the cost of the cement; hence cement plants have to consider minimizing the cost of energy when planning production. However, there are several challenging issues regarding the production plan. First, there are some operational constraints for the production process itself, such as keeping a proper level of inventory. Second, electricity prices are not fixed; they change on an hourly basis. Hence the cost of the electricity consumed may change substantially depending on the time of production. In this study, we developed a mixed integer programming model to minimize the cost of production (including energy, labor, and storage) by shifting working times to hours with low energy costs and trying to maintain activities during hours with high energy costs.
Cement production processes can be categorized as dry, semidry, semiwet, and wet processes depending on the handling of raw material before being fed to the rotary kiln. Nowadays, almost all new plants are based on the dry process and many old wet plants are also remodeled to dry or semidry processes. Dry cement manufacture has three fundamental stages: preparation of feedstocks, production of clinker, and preparation of cement [15,16].
Preparation of feedstock. This stage includes the process of siege, crushing, and prehomogenization. Typical raw materials used for cement production have 85% cayenne, 13% clay or blackboard, and under 1% each of materials such as silica, alumina, and iron ore. These feedstocks are crushed into particles with a diameter of less than 20mm and mixed with a prehomogenization pile .
Clinker production. As shown in Fig.6.6, the feedstock first enters the raw material to make a fine powder (raw feed), where 85% of the material is slightly smaller than 88m. Then, the feed is transferred to the homogenizing silos to impair the material difference. After that,the meal is thrown into the precalciner tower to start the chemical change to cement. Precyclone towers intermix with raw feed and almost 1000C of exhaust gas to recover energy, preheat feed, and initiate chemical reactions that result in cement. Gases straight from the kiln, but in precalciner facilities, gasoline, and air are provided by a combustion vessel inside the tower and kiln. Typically, 60% of burned calciner and more than 90% calcination have been reached before the material enters the rotary kiln. Inside the kiln, temperatures reach approximately 1400C to complete the process of chemical reactions and produce calcium silicates, called clinkers, with a diameter of 1025mm. The gas from the preheater tower is usually blended in a rawmill, which will help stabilize the future feedstock. After flowing through the rawmill, the gases are eventually released by a dust collector, which also obtains good particles when feedstuffs are milled. The dust will then be recycled into homogenizing silos and served as part of the kiln feed.
Preparation of cement. This stage completes the manufacturing process where clinker nodules are milled into cement. Following clinker milling, the cement is ready for use as a binder in various concrete mixes.
The cement production process, for example, starts with mining of limestone, which is then crushed and ground to powder. It is then preheated to save energy before being transferred to the kiln, the heart of the process. The kiln is then heated to a high temperature of up to 1480 degrees to convert the material to a molten form called clinker. The clinker is then cooled and ground to a fine powder with other additives and transferred to storage silos for bagging or bulk transportation (Portland Cement Association, 2014). The production of cement is either through the wet or dry process with the dry process as the preferred option because of the lower energy intensity. Cement production accounts for about 5% of total anthropogenic emissions (IFC, 2017). Cement-based structures constitute the largest surface area of all man-made structures (Odigure, 2009). World cement demand was about 2.283 billion tons in 2005, 2035 million tons in 2007, and 2836 million tons in 2010 with an annual estimated increase of about 130 million tons (Madlool, Saidur, Hossaina & Rahim, 2011; Odigure, 2009). World total cement production for 2016 was about 4.2 billion tons with emerging markets playing a dominant role (IFC, 2017). The energy intensity of cement production ranges from 3.6 to 6.5 GJ/ton depending on production process and location of the production (Hammond and Jones, 2011; Ohunakin et al., 2013; Worrell et al., 2000).
Cement production is one of the largest contributors to CO2 emissions. SCMs have been partially or completely used as replacement of cement or fine aggregates in construction to reduce the demand of cement and corresponding CO2 emissions (Al-Harthy etal., 2003; Babu and Kumar, 2000; Bondar and Coakley, 2014; Cheng etal., 2005; Jia, 2012; Khan and Siddique, 2011; Kunal etal., 2012; Limbachiya and Roberts, 2004; Lothenbach etal., 2011; Maslehuddin etal., 2009; Najim etal., 2014; Nochaiya etal., 2010; Siddique, 2011; Siddique and Bennacer, 2012; Toutanji etal., 2004). Some of the established SCMs are fly ash, silica fume, blast furnace slag, steel slag, etc. Pozzolanic materials, such as fly ash, steel slag, and cement kiln dust (CKD) when used as replacement to cement, improve the long-term performance of concrete as the pozzolanic reaction takes time. But, the early age strength of SCMs is a concern, as the reduction in cement content causes lesser hydration and, consequently, lesser formation of CSH gel (Lothenbach etal., 2011). The problem of low early strength of SCMs can be solved by using carbonation curing at early ages.
Apart from CO2 sequestration, carbonation curing has also been found to act as an activation mechanism for SCMs (Monkman etal., 2018). Many studies have tried to assess the effect of ACC on use of SCMs (Monkman and Shao, 2006; Sharma and Goyal, 2018; Zhan etal., 2016; Zhang etal., 2016; Zhang and Shao, 2018). ACC not only enhances the hydration degree of alternative cementitious materials but also improves the early age performance of concrete. Monkman and Shao (2006) assessed the carbonation behavior of blast furnace slag, fly ash, electric arc furnace (EAF) slag, and lime. All four materials reacted differently when subjected to carbonation curing of 2h. Fly ash and lime showed highest degrees of carbonation, followed by EAF slag, whereas ground granulated blast slag (GGBS) showed least reactivity towards CO2. Calcite was the major reaction product from fly ash, lime, and EAF slag, whereas aragonite was produced by carbonation of GGBS. Sharma and Goyal (2018) studied the effect of ACC on cement mortars made with CKD as cement replacement. ACC was found to improve the early age strength of cement mortars by 20%, even for mortars with higher CKD content. Several studies tried to assess the CO2 sequestration ability of steel slag binders (Bonenfant etal., 2008; He etal., 2013; Huijgen etal., 2005; Huijgen and Comans, 2006; Ukwattage etal., 2017). Presence of C2S component in steel slag makes it a potential cementitious material that could act as a carbon sink for CO2 sequestration (Johnson etal., 2003).
Zhang etal. (2016) in their study found that fly ash concrete was more reactive to CO2 as compared with OPC concrete. With the reduction in OPC content, a porous microstructure was generated due to insufficient hydration reaction. The enlarged distance between cement grains facilitated higher possibility of reaction with CO2, and hence, a higher degree of CO2 sequestration. The performance of SCMs subjected to carbonation curing is majorly dependent upon fineness of material and water content postcarbonation. Finer particle size of SCMs provides a higher specific area for effective carbonation reaction. Due to this, it was observed in many studies that concrete made with SCMs had better reactivity toward CO2 than OPC (Monkman and Shao, 2006). Water content postcarbonation also plays a dominant role in determining the performance of SCMs. Sufficient water content postcarbonation is necessary for complete hydration and pozzolanic reaction of SCMs (Monkman and Shao, 2006).
In Europe, cement production decreased by 26.9% from 1990 to 2012, whereas CO2 emissions decreased by 38.6%, showing an improvement in the cement production (CEMBUREAU, 2014). However, to reach the objectives of various sustainability programs, further efforts must be made in order to improve every step in the concrete production line. For concrete, the main solutions for reducing the environmental impact of modern construction are (Flatt et al., 2012):
Some other technical solutions to improve cement production are also of interest, including CO2 capture and storage. If this solution were to present a major impact on the final objective, it would need technological breakthroughs that are still in the research phase and are not planned to be ready for users before 2030, but they could potentially capture up to 45% of the CO2 produced by cement (IEA and WBCSD, 2010). By 2050 the baseline emissions will be 2.34 gigatonne (Gt) but will be reduced to blue emissions of 1.55Gt by the contribution of energy efficiency (10%), use of alternative fuels and other fuel switching (24%), clinker substitution (10%) and carbon capture and storage (56%) (IEA and WBCSD, 2010).
The worldwide use of blended cement in the production of cement is already a commonly used improvement, with significant investments for research made by cement producers (Table 15.7). Many blended cement types exist because of the great variability of usable SCMs. These cement types are produced by replacing part of clinker with SCMs, which leads to cement with unchanged or improved properties for both general and special applications. The same properties must be maintained; otherwise, for a functional unit (concrete beam) and on a product scale (cement), more cement may be necessary to obtain the same durability. Therefore the beneficial impact of replacing a part of clinker can be useless (Li et al., 2004). In the European context, binary cement incorporates up to 35% of each type of SCM even in the case of inert mineral fillers, and ternary cement uses up to 80% in mass replacement of clinker (EN 197-1, 2001). A final trend is the development of quaternary binder, but a lot of improvements remain necessary in order to ensure a better understanding of the interactions between clinker and SCMs.
As the CO2 resulting from the decarbonation of limestone during the calcination process is a fixed amount by clinker volume, the two major solutions are optimisation of the heating process to reduce the energy needed to reach 1450C and the use of blended cements.
The improvement of a specific burning process leads to no or very little change in the reduction of CO2 emissions, but a change from a wet process to a dry process with preheating and precalciner kilns can lead to significant improvements (WBCSD, 2013). The energy used by a wet kiln is estimated to be between 5.9 and 6.7GJ/tonne of clinker, whereas a kiln with preheating and precalciner kilns uses only 2.9 to 3.3GJ/tonne of clinker (reduction by 50%). Shifting the cement production from wet to dry with preheating and precalciner kilns can lead to a reduction of 20% (International Energy Agency, 2010) of the energy needed and 17% in the amount of CO2 emitted per tonne of clinker (Damtoft et al., 2008). It can be seen that the increase in part of the clinker produced by this technology could partially overcome the increase in cement production (WBCSD, 2013). These savings could be increased by the use of more alternative fuels (Nielsen and Glavind, 2007) (to coal, which actually accounts for 60% of the fuel used in cement production).
The use of SCMs in concrete is different from using them to produce blended cements. There is no guarantee on the potential strength achieved by a mixture of cement and SCM because of the great variability in the physicochemical properties of SCM. In order to control the amount used in concrete, use of SCM has been standardised through the k-value concept (Smith, 1967). This concept is based on the potential reactivity of each SCM, which helps in fixing a maximal replacement rate of cement to achieve the same mechanical and durability properties. The k-value for each addition differs depending on the type, on the concrete exposure conditions (frost, salt, sulphate, etc.)and on the local national standards. Depending on the type of SCM, the volume used and the targeted concrete strength, the savings in terms of CO2 emissions can be more than 20% (Table 15.9).
The previous solutions for improving the environmental aspect of concrete are widely used and remain of interest for further development, and some new, challenging solutions are also being studied but will need either breakthrough technology or huge investments in development. So far emissions of CO2 are inherent to cement production, so finding ways to prevent this gas from getting into the atmosphere need to be explored, as illustrated next.
Carbon capture and sequestration (CCS): This process consists basically of capturing the CO2 before it is released into the atmosphere and then compress it and store it underground (in mines, caves, oceans). Unfortunately, currently this process remains quite expensive and energy-consuming. Nevertheless, it is a new technology which can be improved in the future. On the other hand, it can also be argued that far from dealing with the problem, CCS is just a way to avoid the problem and leave it for later. Therefore it is totally in contradiction with sustainable development, which is defined by the Brundtland report (United Nations, 1987) as a development that meets the needs of the present without compromising the ability of future generations to meet their own needs.
Biofuel production: Although this approach is not yet totally explored, some researches have shown that captured carbon can be used in the production of algae that can then be transformed to biofuel, agricultural fertilizer or even animal protein (Potgieter, 2012).
Electrochemical carbon reduction (ECR): This process involves creating a reaction which will transform carbon into formic acid. This product is often used in the pharmaceutical industry. It is usually manufactured with high energy consumption but ERC requires less energy (Potgieter, 2012).
The first approach will be to reduce the volume of CO2 in the production of cement which is emitted into the atmosphere. But the most interesting solution in the short-term will be the development of alternative binders with a lower environmental impact, and some proposed solutions already provide excellent results on a laboratory scale or event in pilot projects (Aldred and Day, 2012; Duxson and Provis, 2008; Owens et al., 2010). Alkali-activated cements are aluminosilicatepozzolana-based materials (glass furnace slag, natural volcanic glass, manmade glass, fly ash, metakaolin). The activation occurs between the alumina-rich pozzolana and a strong alkali base, which dissolves the silicate and aluminate groups to form a cementitious gel to form the structure of the matrix. The so-called geopolymer is proven to have similar mechanical properties as cement-based concrete with a lower environmental impact (Duxson et al., 2007). This solution is already implemented in Australia by using fly ash and slag (Duxson and Provis, 2008). This solution is, however, hindered by some practical aspects, including the robustness of the design of the mix, the heat needed for a proper reaction to occur in a reasonable amount of time, the limited amount of available aluminosilicate compounds, the handling of the alkaline activator on the job site, the cost, and the environmental impact of the activator (Flatt et al., 2012).
Belite-rich cement, with a combination of calcium sulphoaluminate and calcium sulphoferrite, have been tested with success. Compared to ordinary Portland cement, belite-rich cement contains relatively higher belite (C2S) and lower alite (C3S) contents (Chatterjee, 1996). Belite-rich cement produces performances comparable to cement with the production of 2030% less CO2 (Li et al., 2007).
Some specially designed concretes have been developed with the eco-efficiency of products at a structural level in mind. This is particularly the case of HPC, including SCC (Hossain et al., 2013; Sonebi and Bartos, 1999, 2002). First, SCC will not act directly on the environmental aspect of sustainability, but rather on economical and societal aspects. When properly designed from the beginning, a construction made of SCC brings economic benefits by increasing the productivity because of the higher casting rate and the reduction in manpower which results in the elimination of vibration. This latter aspect also has a major societal aspect because it reduces the noise at construction sites and concrete factories and removes the risk of injury to workers related to crowded construction sites and vibration (Nielsen, 2007). The use of SCC in concrete factories (Yahia et al., 2011) can also be a solution for increasing mould service life and saving energy. In the case of concrete pipes, this reduction can be about 1.0GWh (De Schutter et al., 2010). Note also the reduced need for post-treatment of a surface by plaster, which accounts for 0.57kg of equivalent CO2 per m2, or by paint because of the better finish of concrete surfaces (Witkowski, 2015). This latter aspect can also increase the CO2 uptake by concrete carbonation because the concrete surface has no applied post-treatment. The major issue of SCC is that proportioning of a mix involves a significant amount of cementitious material in order to improve the workability of the concrete. This problem can be overcome with the development of high-performance chemical admixtures, use of high SCM content (Diederich et al., 2013), and an adequate selection of the granular skeleton of solid particles to achieve proper rheological properties of concrete. The latter approach has allowed the production of Eco-SCC with 40% fewer CO2 emissions than standard vibrated concrete, along with a 150-year service life (Mansour et al., 2013).
The development of high-strength concrete and high-strength, fibre-reinforced concrete is also a new approach to sustainability in construction materials. These concrete types are designed with a relatively greater amount of binder (cement and SCM) and chemical admixture, which achieves better performance than conventional concrete, including 316 times more compressive strength, 10 times more flexural strength and 10100 times more durability than conventional concrete does (Wang et al., 2015). These high performances allow a reduction in the size of elements for similar structural performance, therefore leading to a lower volume of concrete for the same structure. This reduction in volume can lead to a reduction of 65% in raw materials consumed, 51% in the primary energy used, and 47% in CO2 emissions (Batoz and Rivallain, 2009).
Currently in the United Kingdom, concrete debris is not sent to landfills but is treated so it can have a second life in the construction sector. Indeed, concrete is a material that can be fully recycled. In 2011 recycled and secondary aggregates represented about 5.3% of all aggregates used in concrete (Concrete Centre, 2011). This material is used mainly in road construction, but recycled concrete aggregates (RCA) can count for up to 30% of the aggregates in a concrete mix. In the United Kingdom recycled and secondary materials represent 28% of the total aggregates used in the marketplace, the highest in the Europe. The precast concrete industry provides greater opportunities for using recycled aggregates over to 20% (Concrete Centre, 2011). However, the following issues need to be considered when using RCA:
CO2 emissions from cement production are incurred through the consumption of fossil fuels, the use of electricity, and the chemical decomposition of limestone during clinkerization, which can take place at around 1400C. The decarbonation of limestone to give the calcium required to form silicates and aluminates in clinker releases roughly 0.53t CO2 per ton of clinker . In 2005, cement production (total cementitious sales including ordinary Portland cement (OPC) and OPC blends) had an average emission intensity of 0.89 with a range of 0.650.92t CO2 per ton of cement binder . Therefore, the decarbonation of limestone contributes about 60% of the carbon emissions of Portland cement, with the remaining 40% attributed to energy consumption, most of which is related to clinker kiln operations; the WWF-Lafarge Conservation Partnership  estimated that the production of clinker is responsible for over 90% of total cement production emissions.
In view of the fact that the requirement for decarbonation of limestone presents a lower limit on CO2 emissions in clinker production, and that there exist technical issues associated with the addition of supplementary cementitious materials (SCMs, including fly ash and ground granulated blast furnace slag), which restrict the viability of direct Portland cement supplementation by SCM above certain limits, the possibility to reduce CO2 emissions using Portland chemistry is limited. The WWF-Lafarge Conservation Partnership  expects that the emissions intensity of cement, including SCM, could be reduced to 0.70t CO2 per ton of cement by 2030, which still amounts to around 2 billion tons of CO2 per annum worldwide, even if cement production does not increase from its current level.
Fig. 10.6 shows the CO2 emissions of various binder designs as a function of Portland cement content. There have been a limited number of life-cycle analyses (LCA) of geopolymer technology. One reasonably extensive research program carried out in Germany  has provided information regarding the selection of precursors and mix designs for a range of geopolymer-based materials. However, geographic specificity plays a significant role in a full LCA, so there is the need for further studies considering different locations in addition to a wider range of mix designs spanning the broader spectrum of geopolymers. The main carbon-intensive and also the most expensive ingredient in geopolymer cement is the alkali activator, which should be minimized in mix design. McLellan et al.  provided further detail, while Habert et al.  concluded that geopolymer cement does not offer any reduction in carbon emissions; such a conclusion needs to be drawn with caution.
Sodium carbonate is the usual Na source for the production of sodium silicate. The different processes for conversion of Na2CO3 (or NaOH) and SiO2 to sodium silicate, via either furnace or hydrothermal routes, differ by a factor of 23 in CO2 emissions, and up to a factor of 800 in other emissions categories . It is therefore essential to state which of these processes is used as the basis of any LCA. Moreover, the best available data for emissions due to sodium silicate production were published in the mid-1990s , so improvements in emissions since that time have not been considered. Sodium carbonate itself can be produced via two main routes, which vary greatly in terms of CO2 emissions. The Solvay process, which converts CaCO3 and NaCl to Na2CO3 and CaCl2, has emissions between 2 and 4t CO2 per ton of Na2CO3, depending on the energy source used. Conversely, the mining and thermal treatment of trona for conversion to Na2CO3 has emissions of around 0.14t CO2 per ton of Na2CO3 produced plus a similar level of emissions attributed to the electricity used. This indicates an overall factor of 510 difference in emissions between the two sources of Na2CO3 .
A commercial LCA was conducted by the NetBalance Foundation, Australia, on Zeobonds E-Crete geopolymer cement, as reported in the Factor Five report published by the Club of Rome . This LCA compared the geopolymer binder to the standard Portland blended cement available in Australia in 2007 on the basis of both binder-to-binder comparison and concrete-to-concrete comparison. The binder-to-binder comparison showed an 80% reduction in CO2 emissions, whereas the comparison on a concrete-to-concrete basis showed slightly greater than 60% savings, as the energy cost of aggregate production and transport was identical for the two materials. However, this study was again specific to a single location and a specific product, and it will be necessary to conduct further analyses of new products as they reach development and marketing stages internationally. Fig. 10.6 shows a comparison of the CO2 emissions of four different E-Crete products against the Business as Usual, Best Practice 2011, and a Stretch/Aspirational target for OPC blends. It is noted that in some parts of the world (particularly Europe), some of the blends shown here in the Stretch/Aspirational category are in relatively common use for specific applications, particularly CEM III-type Portland cement/slag blends, but this is neither achievable on a routine scale worldwide at present, nor across the full range of applications in which Portland cement is used in large volumes.
Environmental impact of cement production is calculated based on the data provided by Ecoinvent (2012). Detailed information on the production process and on all inputs can be taken from Knniger et al. (2001). The functional unit is the production of 1kg of Portland cement strength class 42.5 (CEM I 42.5 R). Average fuel for clinker production is composed of 6.81103MJ natural gas (high pressure), 3.74104kg light fuel oil, 2.55102kg heavy fuel oil, 3.54102kg hard coal and 3.91103kg petroleum coke. In addition 5.80102 kWh electricity (medium voltage) is considered. Besides 0.912kg of Portland cement clinker, an input of 0.063kg gypsum (not balanced, origin from flue gas desulphurization), 0.025kg additional milling substances (not balanced as it is taken as waste without environmental burdens, e.g. dust from the cement rotary kiln, fly ash, silica dust, limestone) and 3.50104kg ethylene glycol (process material for grinding) is taken into account. A total energy for grinding and packing of 4.85102 kWh (electricity, medium voltage) as well as transport processes corresponding to 4.40103 tkm (lorry, 16t) is necessary. The production of 1kg Portland cement CEM I 42.5R yields an environmental impact of 0.833kg CO2-eq. (GWP100), 2.241108kg CFC-11-eq (ODP), 4.211105kg C2H4-eq. (POCP), 1.138103kg SO2-eq (AP) and 1.702104kg PO43-eq. (NP).
Sweden: Cementa says that the decision by the Supreme Land and Environmental Court to reject its renewal application to continue mining limestone at its quarries in Gotland will create a crisis for consumers in the autumn of 2021. The quarries supply its integrated Slite cement plant. The producer said that the majority of Swedish cement production could cease in November 2021 following the expiry of the current licence in October 2021.
We are seriously concerned but also surprised by the court's ruling today, said Magnus Ohlsson, the chief executive officer of Cementa. Limestone has been mined in Slite for over 100 years, which has built up a huge knowledge bank about how the business affects the surrounding environment. Our application is solid and clearly shows that it is possible to conduct a continued sustainable limestone mining in the area. We must go through the decision carefully and then set up the strategy for how we will handle the situation, He added, For Sweden, our customers and for us and our employees, it is important that political decision-makers and authorities quickly draw up new guidelines for how the supply of critical building materials such as cement and concrete should work.
The subsidiary of Germany-based HeidebergCement originally received clearance in 2020 to renew its mining operations at the site until 2041. However, this was subsequently challenged. The current decision by the Supreme Land and Environmental Court was reached as they said they had insufficient evidence to assess the environmental impact of the application.
Uruguay: The Administacin Nacional de Combustibles, Alcohol y Portland (ANCAP) and the Administracin de Ferrocarriles del Estado (AFE) have signed an agreement to exchange logistics services, materials and real estate. Under the deal ANCAP estimates that 380,000tt/yr of fuel and 390,000t/yr of cement and limestone can be transported by rail. The arrangement also includes: offering preferential transport rates to ANCAP; moving cement and limestone between ANCAPs plants and quarries; conducting restorative work at ANCAPs Queguay limestone quarry and its integrated Paysand cement plant; and supplying rail ballast to AFE.
Lithuania: Germany-based Schwenk Zement has sought to increase its stake in 50% subsidiary Akmenes Cement to 97%. The company is also seeking the acquisition of a 75% stake in limestone supplier Kalcitas. The producer took over Mexico-based Cemexs stake in Akmenes Cement in 2019.
Indonesia: Semen Baturaja has signed a memorandum of understanding with Huadian Buket Asam Power. Under the agreement, the producer will supply the power company with limestone for its flue gas desulfurisation (FGD) process in exchange for fly ash, bottom ash and gypsum. The agreement will last two years until March 2023.
The cement producers managing director Sumsal Saifudin said, This collaboration is a form of synergy between the two companies to improve competitiveness, which is much-needed in facing an increasingly competitive industrial environment, by taking advantage of opportunities for the creation of new revenue streams and cost transformation.
Bangladesh: Protesters in Chhatak, Sunamganj District have accused LafargeHolcim Bangladesh of selling limestone illegally. The New Nation newspaper has reported that protesters allege that the company sold imported Indian limestone on the open market. They allege that the limestone was imported exclusively for use as a raw material in cement production under Bangladeshi tax law.
Colombia: The Regional Autonomous Corporation of Antioquia (CorAntioquia) approved the modification of the environmental license of Cemex Colombias upcoming 1.0Mt/yr Cementera del Magdelena Medio integrated cement plant in Maceo, Antioquia. The modification will allow for the production of up to 1.5Mt/yr of cement annually. It will additionally enable the company to extract up to 990,000t/yr of limestone and clay. The producer called the authorisation an important step towards the plants completion.
Cemex Colombia and Peru president Alejandro Ramrez said, "The modification of the environmental licence is a milestone that allows us to resume work to make this project a reality, through which it is expected that we will offer our materials for infrastructure and housing works in the country more efficiently."
India: Meghalaya Cement, Star Cement and Amrit Cement have been accused of illegally mining 1.8Mt of limestone in Meghalaya between 2013 and 2018. The Northeast Now newspaper has reported that the companies mined the limestone in a tribal area of the state without environmental, forest or wildlife clearance or No Objection Certificates (NOCs). Local cement producers also allegedly owe the state government around US$40m in related limestone mining licence fees. All three cement producers reportedly made donations to a local political party.
The state government is also investigating allegations that two of the cement producers have polluted two local rivers, Wah Lukha and Wah Lunar. The former river allegedly turned deep blue due to pollution.
Switzerland: The Federal Council has noted a report stating that, without extensions to raw material extraction licences, domestic cement production is set to decline by 36% from 2024. The Agence Tlgraphique Suisse has reported that local producers are already restricted by limited legally available limestone and marl reserves. At present the local cement sector provides 86% of Switzerlands 5Mt/yr domestic cement demand. The report by the Swiss Geological Survey states that acceptance of all proposed mining expansion projects in 2023 would delay the projected decline until the end of 2030.
India: The Indian Department of Mines and Geology has fined Trishul Cements around US$13.6m for the alleged unlawful extraction of 14,000t of limestone from the Konuppalapadu limestone mine in Andhra Pradesh. The Times of India has reported that the state government terminated its lease of the land in relation to Trishul Cements in February 2020. Investigations unearthed continued mining activity at the site in Anantapur District, along with two other companies sites in the Muchakota forest area of the district.
India: ACC plans to sell its National Limestone Company subsidiary to Ghadiya Group for around US$2.5m. National Limestone Company holds mining leases for limestone in the state of Rajasthan. Ghadiya Group operates in the construction and mining sector.
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Herein, we report on the development of a cement comprising ground granulated blast furnace slag, soda ash (sodium carbonate), and up to 68wt.% granular limestone. Mixture Design of Experiment (DOE) was utilized, with analysis of compressive strength, modulus of elasticity, hydraulic properties, cost, CO2 production, and energy consumption. Models were derived to understand the impact of mix design on performance and for optimization. Successful formulations are hydraulic and cure at room temperature, with strengths as high as 41MPa at 3d and 65MPa at 28d. These formulations, compared to OPC, are competitive in cost and performance and can reduce both CO2 production and energy consumption by up to 97%.