How to Reduce Carbon dioxide from cement?

Get an overview to learn the Basics of properties of cement and know how the carbon dioxide is being removed

                        

ABSTRACT

Concrete is the most widely used building material in the world because of its beauty, strength, and durability, among other benefits. Concrete is used in nearly every type of construction, including homes, buildings, roads, bridges, airports, and subways. And in an era of increased attention to the environmental impact of construction, concrete performs well when compared to other building materials. As with any building product, the production of concrete and its ingredients does require energy that in turn results in the generation of carbon dioxide, or CO2. The amount of CO2 produced during manufacturing and the net impact of using concrete as a building material is relatively small. The following features of concrete construction help minimize its carbon footprint.

Atmospheric concentrations of CO2 are expressed in units of parts per million by volume (ppm). Since the beginning of the Industrial Revolution in the late 1700s, the concentration of CO2 in our atmosphere has increased by about 100 ppm (from 280 ppm to 380 ppm). The first 50 ppm increase took place in about 200 years, from the start of the Industrial Revolution to around 1973; the next 50 ppm increase took place in about 33 years, from 1973to 2006. It is estimated that 14% of the CO2 in the atmosphere is due to burning fossil fuels. It is also estimated that 64% of the CO2 added to the atmosphere since 1850 is due to burning fossil fuels.

INTRODUCTION

Cement is an important construction ingredient around the world, and as a result, cement production is a significant source of global carbon dioxide (CO2 ) emissions, making up approximately 2.4 percent of global CO2 emissions from industrial and energy sources (Marland 1989). Cement is produced in large, capital intensive Production plants generally located near limestone quarries or other raw carbonate mineral sources as these sources are the principal raw materials used in the cement production process. Because the production plants are expensive, the number of plants in a country is generally limited (less than 100). Carbon dioxide is emitted as a by-product of clinker production, an intermediate product in cement manufacture, in which calcium carbonate (CaCO3) is calcinated and converted to lime (CaO), the primary component of cement. CO2 is also emitted during cement production by fossil fuel combustion. However, the CO2 from fossil fuels is specifically accounted for in emission estimates for fossil fuels.

Carbon dioxide is released during the production of clinker, a component of cement, in which calcium carbonate (CaCO3) is heated in a rotary kiln to induce a series of complex chemical reactions. Specifically, CO2 is released as a by-product during calcination, which occurs in the upper, cooler end of the kiln, or a precalciner, at temperatures of 600-900C, and results in the conversion of carbonates to oxides. The simplified stoichiometric relationship is as follows: At higher temperatures in the lower end of the kiln, the lime (CaO) reacts with silica, aluminum and iron-containing materials to produce minerals in the clinker, an intermediate product of cement manufacture. The clinker is then removed from the kiln to cool, ground to a fine powder, and mixed with a small fraction (about Five percent) of gypsum to create the most common form of cement known as Portland cement. Masonry cement is generally the second most common form of cement. Because masonry cement requires more lime than Portland cement, masonry cement generally results in additional CO2 emissions.

Cement Industry:-

Current scheme of cement plants with respect to environmental problems is a follows:-

• Reduction of emissions
• Use of waste materials as additions in input materials, cement and alternative fuel
• Reduction of noise emissions

Cement industry belongs to the most demanding branches of industry as regards the consumption of energy. The cost of energy is the most important part of the total cost of cement. The aim is to decrease the demand for fuel and electrical energy. In the 90th of the 20th century, environmental requirements joined previous requirements of energy savings. Consumption of energy and amount of emissions is influenced particularly by the process of production of cement clinker. In recent years, most modern cement plants converted to the dry production process with a multistage exchanger and precalcination. This dry production process has been used since 1990 in the Czech Republic together with using alternative fuels, which saves so-called clean fuels like natural gas and heavy oil. However, the content of carbon in alternative fuels is usually higher. Therefore, these fuels often go against the reduction of CO2emissions. There is a possibility of using biomass as fuel; however, it is still limited in particular by its lower heating capacity compared to other types of fuels.

Emission of greenhouse gases:-

Declared emission of CO2 to one ton of cement clinker is 900 to 1000 kg at specific consumption 3500 to 5000 MJ/t of clinker, depending on the type Of fuel.Fig.1 Overview of CO2 emissions of cement industry. The emission of CO2 to one ton of cement decreases because of grinding cement with mineral additions. The following waste materials are used for grinding of cement: blast furnace slag, fly ash, waste types of gypstone from desulphurization processes, or chemical productions. Savings in the area of fuel emissions of CO2 will depend on the accessibility of alternative fuel and biomass. The emission of CO2 produced by the combustion of carbonaceous fuel is directly proportional to the consumption of heat. Declared emission at specific consumption of 3000 MJ/1t of clinker with the combustion of black coal is 0.32 t of CO2. The use of natural gas reduces emission by 25 % (Austrian report, 1997). In 1995, cement plants of developed European countries committed themselves to the reduction of emissions by up to 20 %, in particular by means of the introduction of more effective furnace processes.

Overview of CO2 emissions of cement industry

CO2 and other gases:

Calcination is the basic process of firing clinker. This chemical reaction begins with the decomposition of calcium carbonate CaCO3 accompanied by the emission of calcium oxide CaO and emission of carbon dioxide. The process of clinkering follows at the temperature around 1400 - 1500°C, where carbon dioxide reacts with silicon oxide, aluminum oxide, and iron oxide to silicates, aluminates, and ferrites of calcium and form cement clinker. Approximately 60 % comes from the process of calcination and 40 % from the process of combustion of fuel. There are more harmful emissions produced during the process of firing clinker: carbon monoxide CO, nitrogen oxides NOx- also greenhouse gases, sulphur dioxide, and dust.

The limited ability to reduce CO2 emissions in ordinary Portland cement along with increasing governmental regulations on emissions necessitates the development of alternative cement binders and consequently the creation of ‘‘greener” concepts for building materials . Manufacturers of cement prepared production of other types of cement for general purpose in accordance with valid European standard EN 197-1 [11], with respect to current environmentally and energetically demanding production of Portland cement and with respect to the necessity of reduction of greenhouse gasses. The main guidelines of construction with this cement are the following :

• Effective
• Economical
• Environmentally friendly

Blended cement contains more than one additional component apart from the clinker. In Czech conditions, it is usually slag, limestone, and fly ash. The use of more components makes it possible to make use of their characteristic properties and enhance end-use property of cement. Portland cement with limestone contains clinker and only one additional component – limestone (L, LL). Finely ground limestone has a positive effect on the workability of fresh concrete, decreases separation of water, and stabilizes coloring of concrete. On the other hand, the final strengths can decrease. Slag and fly ash decrease initial strengths. However, they have a positive effect on the development of strength and higher final strengths. These components usually also increase resistance to aggressive environments. Individual components can adjust granulometry of cement and thus control the development of hydration heat. Mentioned types of cement are sufficiently compatible with plasticizers in common use, like Portland cement.

Experimental part

The experimental part focused on the examination of characteristic properties of concrete. Three mix designs were used with three different types of cement. Common Portland cement was compared to two types of blended cement. Following characteristics of fresh and hardened concrete were observed:

1. Consistency (slump test, slump flow)
2. Air content in fresh concrete
3. Volume weight of fresh concrete
4. Compressive strength
5. Static elasticity modulus

Materials:-

Three mix-designs of aerated concrete with three different types of cement and identical doses of components were used. Cement used were

a) CEM I 42,5 R - Common Portland cement

b) CEM II/A-LL 42,5 R - Portland cement blended

with limestone

c) CEM II/A-M 42,5 R - Portland cement blended with 6-20 % slag, fly ash and limestone

Portland cement PC 42.5R (CEM I 42.5R)

Cement with a very high level of early and final strengths. Suitable for production of concrete precast elements and cement-based adhesives (tile and ETICS adhesives).

Composition:-

1. Portland cement clinker 95-100%
2. Gypsum and mineral fillers 0-5%

Properties:-

1. Very high strength development
2. High strength level

Application:-

1. Production of very high early strength in a wide variety of concretes, mortars and grouts.
2. Civil engineering (tunnels, bridges, overpasses)
3. Maintaining normal concrete production during cold weather (t<5°C).
4. Facilitating the early de-molding, handling and use of all types of
5. precast concrete products (railway sleepers, structural elements)
6. Production of tile adhesives and adhesives for insulation panels Cement with very high level of early and final strengths. Suitable for production of concrete precast elements and cement based adhesives (tile and ETICS adhesives).

CEM II/A-M 42.5R

Portland-composite cement with blended compounds of grinded slag and limestone. Cement with a high level of early and final strengths. Suitable for high strength and durable concrete cast by concrete pumps and for structural elements.

COMPOSITION:-

1. Portland cement clinker 80-94%
2. Grinded slag and limestone 6-20%
3. Gypsum and mineral fillers 0-5%

PROPERTIES

1. Moderate water demand
2. High strength development
3. Compatibility with concrete admixtures
4. Excellent workability retention
5. No concrete bleeding
6. High strength level

APPLICATION 

1. Production of high early strength in a wide variety of concretes, mortars and grouts.
2. Civil engineering (tunnels, bridges, overpasses)
3. Concrete with durability to freeze/thaw, frost/salt and water tightness
4. Precast concrete elements exposed to heat curing
5. Maintaining normal concrete production during cold weather (t<5°C).
6. Facilitating the early demoulding, handling and use of all types of precast concrete products
7. Cement based adhesives

CEM II/A-LL 42.5 R –PORTLAND LIMESTONE CEMENT

COMPOSITION:-

The main ingredients of CEM II/A-LL 42.5 are Portland cement clinker and selected limestone with high purity . Further calcium sulphate is added as a stabilizer.

• Portland clinker: 80 - 94%
• Additives: 6 - 20%

Applications:-

• Concrete goods industry
• Concrete precast industry
• Ready mix concrete industry

Evaluation of Tests:-

Concrete was mixed according to mix-designs. Fresh concrete was tested on consistency by Slump test in accordance with EN 12350-2 [14], Slump flow in accordance with EN 12350-5 [15] and air content in fresh concrete in accordance Testing specimens were made and then placed in water for the periods of 2, 7, 14, 28 and 90 days. Basic characteristic property of concrete - compressive strength - was determined on cubes with dimensions 150 x 150 x 150 mm. Static elasticity modulus, the elementary property for design of structures, was determined in accordance with ISO 6784 [13] on testing specimens with dimensions 400 x 100 x 100 mm.

Sr No.	Characteristics	Sample 1	Sample 2	Sample 3
1	Slump	220	230	230
2	Air content	5	4.7	5
3	Volume weight from fresh concrete	2330	2340	2300

Compressive Strength Results:( in MPA ) 

2  days	43	38	35
7  days	55.3	53.8	48.05
14 days	61	56	52
28 days	61.5	60.9	57.2
90 days	64.5	66.6	60.3

Conclusion

The report represents current state of cement industry and its reaction to the trend of reduction of CO2 emissions. Most European and global cement plants changed to more economical dry production process from more costly wet way. Another step of ecological approach of cement plants is using appropriate alternative fuels. Recently, the idea of Green cement become popular. These cements demand less energy for production and produce less CO2 emissions. These cements consist from clinker and usually waste products from other industrial branches. Fly ash and blast furnace slag are most frequently used. Limestone is the most frequently used replacement from the range of natural resources. Production of such blended cements (Portland cement and limestone) represents current trend of cement plants and blended cements are becoming popular in construction industry. The main reason

is properties of concrete made from such cements. The properties are the same or even better than those of concrete made from Portland cement, in particular in corrosive environments. The experimental part focused on assessment of basic characteristics of concrete with blended cement and cement with limestone in comparison with common Portland cement. Mix designs were identical with the only exception - type of cement. Workability of concrete was the same for all types of concrete and the same classing of consistency was reached. As for compressive strength, the generally known fact of slow development of initial strength of concrete with blended cement and cement with limestone showed. However, even if the initial strength and development of strength are lower, concrete can still reach comparable values of compressive strength at the required age of 28 days.

Development of static elasticity modulus in the period of 7 - 90 days was identical for all types of concrete. Nevertheless, in this case, it was cement with limestone, which reached better values than common Portland cement. Blended cement reached the lowest values of both compressive strength and static elasticity modulus; however, the difference was the only minor. Concrete as composite material is an important part of civil and industrial construction and it is still the most used composite construction material. Therefore it is necessary to support ecological thinking and contribute to global energy saving. Production of Green cements with more basic components and lower energetic demands is very important mainly because it can decrease production of CO2 and its environmental impact. However, ecological approach is not the only argument of Green cements, since they represent a technically adequate replacement of Portland cement, too.

REFERENCES:-

1. Bassioni, G., Global warming and construction aspects, Proceedings of the 7th International

Scientific and Practical Conference.

2. Gibbs, M., J., Soyka, P., Conneely, D., CO2emissions from cement production, Good

Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories.

3. Reference Document on Best Available Techniques in the cement and lime industries,

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