Process for producing blended cements with reduced carbon dioxide emissions

Abstract

A process for producing blended cement, where the cement contains Portland Cement mixed thoroughly with a microfiller and possibly a water reducing agent to a dry cement mixture and fine supplementary cementitious materials selected from the materials blast furnace slag, fly ash, quartz, silica, amorphous silicon dioxide, limestone and recycled concrete.

Description

[0001] The present invention related to process of producing hydraulic blended cement with a significantly reduced Portland clinker minerals content and correspondingly with an increased amount of supplementary materials.

BACKGROUND

[0002] It is well known that each ton of production of Standard Portland Cement is accompanied by the release of about one ton of carbon dioxide and that about half of this comes from the decarbonisation of limestone in the kiln and the other half from energy consumption, primarily in the kiln.

[0003] It follows that the only way in which the cement industry can achieve meaningful reductions in carbon dioxide emissions is via the reduction if Portland clinker production and increased use of fillers. The cement industry does not believe that more than about 2-3% further reduction in energy consumption is possible in Standard Portland Cement production.

[0004] The traditional methods of production of blended cement include intergrinding Portland cement clinker with different types of microfillers, e.g. blast furnace slag, fly ash, limestone etc. mainly in rotating ball mills. Such methods are not providing more than 20-25% of Portland clinker replacement by fly ash and approximately 30-50% by blast furnace slag, without significant negative influence on the cement performance, such as decrease of setting time, very low strength development during the curing period 0-28 days, etc. It takes up to 3 times longer time (2-3 months) to achieve a 28-days strength of traditionally Portland Cement concretes. At the same time the high volume fly ash (HVFA) cements do have significant benefits in comparison with traditional Portland cements. Concretes produced with such cements are characterized by high durability, such as a low chloride permeability, a high sulphate and an alkali-silica resistance, etc., see e.g. Malhotra, Concrete International J., Vol 21, No. 5, May 1999, pp. 61-66. According to Malhotra strength development of such concretes could be improved by significantly increasing the content of a binder, such as cement+a microfiller and significantly decreasing the amount of mixed water, but such approach require increased dosages of water reduced admixtures to keep acceptable consistency of concrete mixtures, which sharply increases the cost of the concrete.

[0005] Another method related to the present invention is a method described by the US Patent Appln. Publ. No. US 2002/0000179 for a “Method for producing a blended cementitious composition”. Said application suggests to introduce into the concrete mixtures of Portland Cement and traditional cementitious materials as fly ash, blast furnace slag, etc. very fine and highly reactive rice hull ash. This gives an improvement of early age strength and chloride permeability of the concretes.

[0006] Such method of producing concrete requires increased amounts, up to 400 kg per cubic meter, of a binder material, such as cement+fly ash+rice hull ash, in order to achieve a concrete which is comparable to Standard Portland Cement concretes at relative low water-to-binder ratios, such as less than 0.40. Those requirements bring significant technical and economical limitations for the application of said method by the ready mix concrete industry which produces about 95% of the concrete with a cement/binder content of 250-300 kg per cubic meter and a water to cement ratio of 0.60-0.70. Introduction of said method for the mentioned concrete mix design leads to a drastical decrease of the concrete strength development and increase of the setting time, which make it non-competitive with Standard Portland Cement concretes.

DISCLOSURE OF THE INVENTION

[0007] The present invention refers to the process for producing environmentally efficient blended cements with reduced carbon dioxide emissions for the preparation of concrete, where said cements contain Portland Cement mixed thoroughly with a microfiller and probably a water reducing agent to obtain a highly-active and dry cement mixture.

[0008] The present invention refers to a process for producing blended cement, where the cement contains Portland Cement mixed thoroughly with a microfiller and possibly a water reducing agent to a dry cement mixture and fine supplementary cementitious materials selected from the materials blast furnace slag, fly ash, quartz, silica, amorphous silicon dioxide, limestone anal recycled concrete and is characterized in, that said supplementary materials in a first step are being subjected to a grinding in a dry state to a specific surface of at least 1000 cm2/g (Blaine), in that in a second step the supplementary grinded materials are being subjected to a grinding together with at least 20% by weight of the total grinding mass of a highly reactive cement mixture in a dry state to achieve a specific surface of at least 3000 cm2/g (Blaine) which highly reactive cement mixture contains cement and at least one of the components a SiO2 containing microfiller and a polymer in the form of a powdery water-reducing agent which mixture have been previously been treated in a grinder with vibrating grinding media in which the cement particles are subjected to a large number of impact impulses giving the cement particles an increase in surface energy and chemical reactivity.

[0009] The said supplementary materials are subjected to a separate preliminary grinding to achieve a specific surface at least 1000 cm2/g (Blaine) and then to the joint grinding with at least about 20 weight percent, of the total grinding mass, of a highly reactive cement mixture to achieve a specific surface at least 3000 cm2/g (Blaine). This results in an improvement of hydraulic reactivity in the case blast furnace slag is used. The improvement of chemical reactivity with calcium hydroxide is achieved in the case of the use of silica or other substances containing silicon dioxide. The improvement is due to the surface modification of the particles of the said blend in the form of microdefects, microcracks and dislocations caused by strained induced dynamic transformations caused by the grinding process.

[0010] According to a very advantageous embodiment of the present invention, said highly reactive cement mixture has been manufactured according to a method according to the European Patent No. 0 696 262.

[0011] It is however also possible to use a cement mixture that has been treated in accordance with a corresponding process so as to obtain a compressive strength corresponding to that recited in EP 0 696 262.

[0012] European Patent Specification No. EP 0 696 262 describes a method of producing cement that can be used to producing cement that can be used to produce pastes, mortar, concrete and other cement-based materials of high bearing capacity with reduced water content, high mechanical strength and density and rapid strength development. This method includes the mechanical-chemical treatment of a mixture of cement and at least one component of two components, wherewith the first component is a microfill that contains silicon dioxide and the second component is a polymer in the form of water reducing agent. The cement and the first and/or the second component are mixed in the first stage in a dry state, wherewith the particles in the first and/or the second component are adsorbed on the cement particles. The mixture obtained in the first stage is treated in the second stage in a grinder with vibrating grinding media in which the particles in said mixture are subjected to a large number of impact impulses which change directions in a rapid sequence and therewith result in modification of the surface properties of cement particles in the form of considerable increase in surface energy and chemical reactivity. The duration of treatment in the second stage is sufficient for a cement paste cube having tie side length of 20 mm and compacted thoroughly under vibration and cured at +20 degrees C. under sealed conditions to obtain a one-day compressive strength equal to at least 60 MPa.

[0013] The European Patent No. 0 696 262 is hereby incorporated in the present patent application.

[0014] The present invention also relates to a method for producing a concrete mixture.

[0015] The method is used for preparing shaped concrete elements or structures and comprises the steps of firstly producing a blended cement according to the above said method and secondly mixing the said blended cement with sand and/or aggregate of greater dimensions and water, and thirdly casting a shaped element or the structure and hardening of the subject.

[0016] The present invention will be described more in detail in the following partly in connection with Tables and Figures, where

[0017] FIG. 1 is a diagram showing the average case for the particle size distribution of the blended cements produced according to the present invitation in comparison with traditionally Portland Cements and initial blend subjected to grinding according to proposed methods. It shows that the specific surface of the said blended cements is in line with the specific surface of tile commercially produced pure Portland Cements.

[0018] Table 1 and 2 respectively shows the strength development of the EN mortar, which is a European standard, having a cement-to-sand ratio of 1:3 and a water-to-binder ratio of 0.50, and concretes with ale blended cements containing high volume of fly ash produced according to the present invention and traditional blended cements.

[0019] Table 3 represents the strength development of the EN mortar (cement-to-sand ratio 1:3, and water-to-binder ratio 0.50) and concrete with blended cements containing a high volume of quartz filler produced according to the present invention.

[0020] Table 4 represents the strength development of the EN mortar (cement-to-sand ratio 1:3, and water-to-binder ratio 0.50) with blended cements containing a high volume of blast furnace slag produced according to the present invention and traditional blended cement.

[0021] In tables 4 and 5 HRC stands for High Reactive Cement as for example cement treated according to EP 0 696 262.

[0022] Table 5 represents the test results from the testing of chloride permeability (ASTM C 1202-94) of the concretes with blended cements containing a high volume of quartz filler produced according to the present invention.

[0023] It has been discovered that when supplementary cementitious materials selected front the group of materials, e.g. blast furnace slag, fly ash, quartz, silica or other substance containing amorphous silicon dioxide, etc., firstly subjected to a separate preliminary grinding to achieve a specific surface at least 1000 cm2/g (Blaine), and secondly subjected to joint grinding with at least about 20 weight percent of highly-reactive cement mixture to achieve a specific surface at least 3000 cm2/g (Blaine) the finally obtained blended cement has significantly better performance than traditional blended cements. The better performance relates to a higher early-age and long-term strength development, a finer porosity, etc. It has also a better performance than pure Portland Cement, such as a significantly higher environmental profile, a higher long-term strength development, a significantly lower chloride permeability, etc.

[0024] The above mentioned above grinding, both the separate and the joint stages, could be realized with the use of media milling equipment, e.g. tumbling ball mills, vibratory ball mills, planetary mills, stirred and centrifugal mills, and a non-media milling equipment e.g. roller, jet mills, etc.

[0025] According to one preferred embodiment of the present invention the blended cement contains from 20% by weight up to 80% by weight of said highly reactive cement mixture.

[0026] According to a first embodiment said supplementary cementitious material substantially consists of Class F fly ash.

[0027] According to a second embodiment said supplementary cementitious material substantially consists of Class C fly ash.

[0028] According to a third embodiment said supplementary cementitious material substantially consists of granulated blast furnace slag.

[0029] According to a fourth embodiment said supplementary cementitious material substantially consists of a quartz filler with a silicon dioxide content of at least 80% by weight

[0030] According to ASTM C 618 fly ash classified in two classes, Class C and Class F. Class F fly ash typically contains more than 70% by weight of silica, alumina, and ferric oxides, while Class C typically contains between 70% and 50% Class F produced as a by product of the combustion of bituminous coal Class C fly ash has a higher calcium content and produced as a by product of thi: combustion of sub-bituminous coal

EXAMPLES

[0031] The following materials have been used in these experiments: Standard Portland cement CEM I 42.5 according to EN-197 or Type I according to ASTM C 150, fly ash Class (FA), blast furnace slag (BFS), and quartz filler (Q). Chemical compositions of the said materials are presented by Table 6.

[0032] The cementitious supplementary materials have been subjected to separate grinding in the vibrating mill VBM 1518 to achieve a specific surface approximately 1500 cm2/g (Blaine).

[0033] Then the said fillers have been mixed in a dry state with a highly reactive dry cement mixture produced according to European Patent Specification No. EP 0696262 and containing 99% of PC and 2% of fly ash Class F. The mixing of the said components have been performed with a mixer called “Tonimix”, manufactured in Germany, with a rotation speed of 280 rpm during 3 min. to obtain a homogeneous blend.

[0034] The said blends have been subjected to further grinding in a rotating ball mill to achieve the specific surface of about 4500 cm2/g (Blaine).

[0035] During these two subsequent grindings the particles of cementitious supplementary materials are subjected to a surface modification in the form of microdefects, microcracks and dislocations caused by strained induced dynamic transformations. Such effects lead to the improvement of hydraulic reactivity in the case blast furnace slag is used and improvement of chemical reactivity with calcium hydroxide in the case of that silica or other substances containing silicon dioxide are used.

[0036] According to the test results the blended cements produced according to the proposed invention have specific surfaces in line with Standard Portland Cements, see FIG. 1, and the properties related to strength development and durability are significantly better than for traditional blended cements and pure Portland Cements, see tables 2-5.

[0037] FIG. 1. shows the particle size distribution for the blended cements produced according to the proposed grinding method and particle size distributions for the blends before grinding Please see the notations in the FIG. 1.

[0038] Due to a significant reduction of Portland clinker content implementation of such blended cements could significantly reduce the level of carbon dioxide and other “green house” gases emissions, where the reduction could be more than 50%, and the amount of energy required for Portland clinker production.

TABLE 6
Chemical composition
	Compound	PC	FA	BFS	Q
	CaO	62.4%	15.0%	35.5%	0.1%
	SiO2	17.8%	49.4%	34.0%	98.2%
	Al2O3	4.0%	19.6%	11.5%	0.2%
	Fe2O3	3.9%	5.2%	0.4%	0.3%
	SO3	3.2%	0.8%	3.4%	0.1%
	Na2O	<0.1%	0.3%	0.54%	0.3%
	K2O	0.3%	1.2%	0.56%	0.2%

[0039]

TABLE 1
Tests with fly ash for EN mortar (blended cement
produced according to the proposed invention.
	Compressive strength,
	MPa for fly ash, % weight
	Type of mi	0	30	40	50
	EN-mortar	18.6	23.8	18.6	14.4
	EN-mortar	42.7	52.9	46.8	43.7
	Concrete*,	14.0	13.8	13.5	13.0
	Concrete*,	33.8	43.7	36.1	35.0

[0040]

TABLE 2
Test with fly ash for EN mortar
(traditionally blended cements).
	Curing time, days
	Cement type	2	7	28
	80% PC + 20% fly ash	.5	23.6	35.8
	60% PC + 40% LFA	0.8	17.7	29.6

[0041]

TABLE 3
Tests with quartz filler for EN mortar
	Compressive strength, MPa
	for quartz filler,
	% by cement weight
	Type of mixture	0	30	40	50
	EN-mortar, 2 days	18.6	20.4	17.6	15.4
	EN-mortar, 28 days	42.7	44.9	43.8	42..7
	Concrete*, 2 days	14.0	13.8	13.5	13.0
	Concrete*, 28 days	33.8	36.7	36.1	35.0
	*Concrete with the binder content 300 kg/m3 and w/B ratio 0.65

[0042]

TABLE 4
Tests with blast furnace slag for EN mortar
	Slag	Compressive strength, MPa
	content,	for curing time, days
Type of mixture	%	2	7	28
100% PC	0	18.1	36.9	47.7
60% PC with slag	40	16.1	30.2	48.2
(traditional blend)
60% HRC with slag	40	19.5	38.4	55.6
30% HRC with slag	70	10.0	36.8	52.7
20% HRC with slag	80	8.0	30.2	49.9

[0043]

TABLE 5
Results from the testing of chloride permeability
(ASTM C 1202-94)
			Average value of
			“Charge
			passed” and	Evaluation of
Mix	Binder	w/b-	(SD)	chloride
No	type)	ratio	(Coulombs)	permeability
1	100% PC	0.45	3734	(165)	Moderate
2	100% PC	0.50	4030	(135)	High
3	100% PC	0.60	4828	(448)	High
4	50% HRC +	0.45	763	(62)	Very Low
	50% quartz
	filler
5	50% HRC +	0.50	821	(39)	Very Low
	50% quartz
	filler
6	50% HRC +	0.60	976	(106)	Very Low
	50% quartz
	filler

[0044] FIG. 1

[0045] Notations:

[0046] Q stands for reference blend of Standard Portland Cement and quarts filler (<1 mm), ratio 50/50 by weight.

[0047] EQ stands for the blend of Standard Portland Cement and quartz filler (50/50) unterground according to EMC method.

[0048] FA stands for reference blend of Standard Portland Cement and fly ash Class F ratio 50/50 by weight.

[0049] EFA stands for blend of Standard Portland Cement and fly ash Class F ratio 50/50 by weight unterground according to EMC method.

[0050] ST7 stands for Standard Portland Cement (Type I according to ASTM C 150).

[0051] IN4 stands for Rapid Hardening Portland Cement (Type III according to ASTM C 150 with higher fineness).

[0052] Calculated surfaces in m2/liter in brackets behind legends.

Claims

1. A process for producing blended cement, where the cement contains Portland Cement mixed thoroughly with a microfiller and possibly a water reducing agent to a dry cement mixture and fine supplementary cementitious materials selected from the materials blast furnace slag, fly ash, quartz, silica, amorphous silicon dioxide, limestone and recycled concrete characterized in, that said supplementary materials in a first step are being subjected to a grinding in a dry state to a specific surface of at least 1000 cm2/g (Blaine), in that in a second step the supplementary grinded materials are being subjected to a grinding together with at least 20% by weight of the total grinding mass of a highly reactive cement mixture in a dry state to achieve a specific surface of at least 3000 cm2/g (Blaine), which highly reactive cement mixture contains cement and at least one of the components a SiO2 containing microfiller and a polymer in the form of a powdery water-reducing agent which mixture have been previously been treated in a grinder with vibrating grinding media in which the cement particles are subjected to a large number of impact impulses giving the cement particles an increase in surface energy and chemical reactivity.

2. Process according to claim 1, characterized in, that said highly reactive cement mixture has been manufactured according to the method according to the European Patent No. 0 696 262.

3. Process according to claim 1 or 2, characterized in, that the blended cement contains from 20% by weight up to 80% by weight of said highly reactive cement mixture.

4. Process according to claim 1, 2 or 3, characterized in, that said supplementary cementitious material substantially consists of Class F fly ash.

5. Process according to claim 1, 2 or 3, characterized in, that said supplementary cementitious material substantially consists of Class C fly ash.

6. Process according to claim 1, 2 or 3, characterized in, that said supplementary cementitious material substantially consists of granulated blast furnace slag.

7. Process according to claim 1, 2 or 3, characterized in, that said supplementary cementitious material substantially consists of a quartz filler with a silicon dioxide content of at least 80% by weight.

8. Method for producing a concrete mixture, characterized in, that it comprises firstly the steps of claims 1 to 7 to produce said blended cement and secondly the step of mixing said blended cement with sand and/or aggregates of greater dimensions and water and possibly a water reducing agent and an air entraining additive.