PROCESS FOR CONTROLLING A CRYSTAL FORM OF ALITE IN PORTLAND CEMENT CLINKER

Abstract

The present invention relates to a process of controlling crystal form of Alite in Portland cement clinker, wherein the said Portland cement clinker is thermally treated in order to change the crystal form of Alite in Portland cement clinker, so as to improve performance of resulting Portland cement clinker. The said process of present invention is easy and feasible.

Description

FIELD OF THE INVENTION

The present invention relates to a process for controlling crystal form of Alite in Portland cement clinker, and particularly relates to a method for improving the performance of Portland cement clinker.

BACKGROUND OF THE INVENTION

Cement industry is growing rapidly in China. The output of cement in China in 2008 was around 1.45 billion tons, which took up around 50% of global cement total output and had been No. 1 cement producing country for 24 consecutive years all over the world. Due to the fact that Chinese economy is in the phase of rapid development, it is predicted that China's cement output will continuously increase at a rate of 10%. Although lots of cement is produced in China, the overall cement quality is relatively low, thus the lifetime of concrete work is influenced, therefore, the performance of cement has to be improved. Portland cement mainly consists of Portland cement clinker, plaster and composite material. In order to improve the performance of Portland cement, the performance of Portland cement clinker has to be improved. Portland cement clinker mainly consists of Alite, Belite, C₃A(3CaO·Al₂O₃) and C₄AF (4CaO·3Al₂O₃·Fe₂O₃). Alite is the main supplier to provide gelling property of Portland cement clinker, while it is also the main energy consumer. Therefore, the content of C₃S in clinker or its activity has to be improved in order to improve gelling property of Portland cement clinker, however, the increase of the content of C₃S in clinker will lead to increase of energy consumption, therefore, under the national demand of energy saving and emission reduction, one of the effective measures to improve the performance of cement clinker is to improve the activity of Alite in Portland cement clinker. At present, doping is the most commonly used method to improve the activity of Alite, wherein high-activity Alite is obtained via modification of its crystal form.

SUMMARY OF THE INVENTION

The object of present invention is to improve the performance of Portland cement clinker, providing a process for controlling crystal form of Alite in Portland cement clinker, as a result, the crystal form of Alite in Portland cement clinker is changed and therefore the performance of Portland cement clinker is improved.

In order to realize said object, the technical scheme of present invention is: a process for controlling crystal form of Alite in Portland cement clinker, wherein it includes the following steps:

• (1) The prepared Portland cement raw meal is calcined;
• (2) Portland cement raw meal is heated to 1400˜1600° C. at a rate of 1˜35° C. per min, and kept at said temperature and then naturally cooled;
• (3) When its temperature is at 600˜800° C., the said cooled clinker is heated at a rate of 1-35° C. per minute until it reaches 700˜1300° C., the said clinker is kept at said temperature, and then it is naturally cooled;
• (4) The said cooled clinker is ground to powder with the aid of ball mill;

Or it consists of the following steps:

• (1B) The prepared Portland cement raw meal is calcined;
• (2B) Portland cement raw meal is heated to 1400˜1600° C. at a rate of 1˜35° C. per minute, kept at said temperature and then it is transferred to a cooler, being cooled at a rate of 40˜80° C. per minute;
• (3B) When the temperature reaches 700˜1300° C., it is kept at said temperature;
• (4B) The said clinker is naturally cooled; the cooled clinker is ground to powder with the aid of ball mill.

The holding time of step (2), (3), (2B) and (3B) is preferred to be 5˜120 min, respectively. The specific surface area of ground powder of step (4) and (4B) is preferred to be 340˜360 m²/kg.

In step (1) and (1B), the prepared cement raw meal is calcined to form clinker according to regular processing parameters. Besides, calcined clinker could also be directly used in the following thermal treatment.

BENEFICIAL EFFECTS OF PRESENT INVENTION

The present invention relates to a process for controlling crystal from of Alite in Portland cement clinker, wherein Portland cement clinker is thermally treated so that the crystal form of Alite in Portland cement clinker is changed and the performance of Portland cement clinker is improved. The present process is easy and feasible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is XRD spectrum of Alite in cement clinker at different 2θ (the said clinker is produced by Huaihai Cement Factory), wherein FIG. 1-1 is XRD spectrum (2θ=32˜33°) of Alite in cement clinker without thermal treatment, FIG. 1-2 is XRD spectrum (2θ=51.5˜52.7°) of Alite in cement clinker without thermal treatment;

FIG. 2 is XRD spectrum of Alite in cement clinker at different 2θ (the said clinker is produced by Huaihai Cement Factory and is thermally treated); wherein FIG. 2-1 is XRD spectrum (2θ=32˜33°) of Alite in cement clinker after thermal treatment, FIG. 2-2 is XRD spectrum (2θ=51.0˜52.5°) of Alite in cement clinker after thermal treatment.

EMBODIMENT

The present invention is further illustrated with reference to the following examples, but the present invention is not limited to the following examples.

Example 1

• (1) The prepared Portland cement raw meal is heated to 1450° C. and calcined for 1 h; and then cooled;
• (2) The temperature of Portland cement raw meal is increased at a rate of 5° C./min until it reaches 1450° C., and kept at said temperature for 30 min, and then naturally cooled;
• (3) The said cooled clinker is heated at a temperature below 800° C., the temperature is increased at a rate of 10° C. per minute until it reaches 1100° C., subsequently, the clinker is kept at said temperature for 60 min and then naturally cooled;
• (4) The said cooled clinker was ground to powder with the aid of ball mill, the specific surface area of said powder is 340 m²/kg; the XRD spectrum of Alite in said clinker and the XRD spectrum of Alite in clinker of Xuchou Huaihai Cement Factory without thermal treatment are shown in FIG. 1 and FIG. 2; it can be seen that after calcination at 1100° C. for 60 min, the crystal form of Alite in Portland cement clinker of Huaihai Cement Factory is changed from M3 to M1.

(5) 4 g plaster was added to 96 g finally obtained cement clinker, the said mixture is stirred uniformly, subsequently, 29 mL water (ratio between water and cement w/c=0.29) was added, the said mixture was stirred and molded to form 20×20×20 mm samples, and the 3d and 28d compressive strength of the samples are determined. Samples are first cured in a curing box for 24 h, wherein the relative humidity is 90% and the temperature is 20±2° C., and then knockout sample is cured in a water curing case at 20±1° C. The comparison of resulting strength is shown in Table 1.

TABLE 1
Plaster strength of Portland cement clinker (MPa)
	Examples	3 d	28 d
	Xuzhou Huaihai Cement Factory	55.6	88.6
	(Portland cement clinker)
	Example 1	57.3	92.9

Example 2

• (1) The prepared Portland cement raw meal is heated to 1480° C. and calcined for 0.5 h; and then cooled;
• (2) The temperature of said Portland cement raw meal is increased at a rate of 10° C./min until it reaches 1500° C., and kept at said temperature for 60 min, and then it was naturally cooled;
• (3) The said cooled clinker is heated at a temperature below 700° C., the temperature is increased at a rate of 15° C./min until it reaches 1000° C., subsequently, the said clinker and kept at said temperature for 90 min, and then naturally cooled; the said clinker is ground to powder with the aid of ball mill, the resulting specific surface area of said powder is 350 m²/kg;
• (4) 4 g plaster is added to 96 g finally obtained cement clinker, the said mixture is stirred uniformly, subsequently, 29 mL water (ratio between water and cement w/c=0.29) is added, the said mixture was stirred and molded to form 20×20×20 mm samples, and the 3d and 28d compressive strength of the samples are determined. Samples are first cured in a curing box for 24 h, wherein the relative humidity is 90% and the temperature is 20±2° C., and then knockout sample is cured in a water curing box at 20±1° C. The comparison of resulting strength is shown in Table 2.

TABLE 2
Plaster strength of Portland cement clinker (MPa)
	Examples	3 d	28 d
	Xuzhou Huaihai Cement Factory	55.6	88.6
	(Portland cement clinker)
	Example 2	58.0	95.6

Example 3

• (1) The prepared Portland cement raw meal is heated to 1450° C. and calcined for 1 h; and then cooled;
• (2) The temperature of said Portland cement raw meal is increased at a rate of 5° C./min until it reaches 1450° C., and kept at said temperature for 60 minutes, and then the said mixture enters a cooling machine, and the temperature of said mixture is decreased at a rate of 55° C./minute;
• (3) The temperature is cooled to 1000° C., and the mixture is kept at said temperature for 60 minutes;
• (4) And then it was naturally cooled; the cooled clinker is ground to powder with the aid of ball mill, wherein the specific surface area of said powder was 360 m²/kg;
• (5) 4 g plaster was added to 96 g finally obtained cement clinker, the said mixture was stirred uniformly, subsequently, 29 mL water (ratio between water and cement w/c=0.29) is added, the said mixture is stirred and molded to form 20×20×20 mm samples, and the 3d and 28d compressive strength of samples are determined. Samples are first cured in a curing box for 24 h, wherein the relative humidity is 90% and the temperature is 20±2° C., and then knockout sample is cured in a water curing box at 20±1° C. The comparison of resulting strength is shown in Table 3.

TABLE 3
Plaster strength of Portland cement clinker (MPa)
	Examples	3 d	28 d
	Xuzhou Huaihai Cement Factory	55.6	88.6
	(Portland cement clinker)
	Example 3	58.5	105.0

Example 4

• (1) The prepared Portland cement raw meal is heated to 1450° C. and calcined for 1 h; and then cooled;
• (2) The temperature of said Portland cement raw meal is increased at a rate of 15° C./min until it reaches 1500° C., and kept at said temperature for 30 minutes, and then the said mixture enters a cooling machine, and the temperature of said mixture was decreased at a rate of 50° C. per minute;
• (3) The temperature is cooled to 1100° C., and then the mixture is kept at said temperature for 30 minutes;
• (4) And then it was naturally cooled; the cooled clinker was ground to powder with the aid of ball mill, wherein the specific surface area of said powder was 350 m²/kg;
• (5) 4 g plaster is added to 96 g finally obtained cement clinker, the said mixture was stirred, subsequently, 29 mL water (ratio between water and cement w/c=0.29) is added, the said mixture is stirred and molded to form 20×20×20 mm samples, and the 3d and 28d compressive strength of samples are determined. Samples are first cured in a curing box for 24 h, wherein the relative humidity is 90% and the temperature is 20±2° C., and then knockout sample is cured in a water curing case at 20±1° C. The comparison of resulting strength is shown in Table 4.

TABLE 4
Plaster strength of Portland cement clinker (MPa)
	Examples	3 d	28 d
	Xuzhou Huaihai Cement Factory	55.6	88.6
	(Portland cement clinker)
	Example 4	56.8	91.5

Claims

1. A process for controlling a crystal form of Alite in Portland cement clinker, wherein the method comprises: (1) the calcining prepared Portland cement raw meal to form a cement clinker, the calcining comprising; (2) increasing the temperature of the Portland cement raw meal at a rate of 1-35° C. per min to a first temperature of 1400-1600° C.;holding the temperature at the first temperature; andnaturally cooling the formed cement clinker;heat treating cement clinker after the temperature of the cement clinker is reduced from the first temperature to 600-800° C., the heat treatment comprising: heating the cement clinker at a rate of 1-35° C. per minute until the cement clinker reaches a second temperature of 700-1300° C.;holding the temperature of the cement clinker at the second temperature; andnaturally cooling the cement clinker; andgrinding the cement clinker after cooling from the second temperature.

2. The process according to claim 1, wherein the holding times of the calcining and heat treatment operations are each 5-120 minutes, respectively.

3. The process according to claim 1, wherein the specific surface area of the grounded clinker powder is 340-360 m2/kg.

4. The process according to claim 1, wherein the cooled clinker is grounded to a powder using a ball mill.

5. A process for controlling crystal form of Alite in Portland cement clinker, wherein the method comprises: calcining a Portland cement raw meal to form a cement clinker, the calcining comprising: heating the Portland cement raw meal to a first temperature between 1400-1600° C. at a rate of 1-35° C. per min;holding the temperature at the first temperature;cooling at a rate of 40-80° C. per min to a temperature of 700-1300° C.;holding the temperature at 700˜1300° C.; andnaturally cooling the formed cement clinker; andgrinding the cooled clinker to a powder.

6. The process according to claim 5, wherein the holding times of the calcining and heat treatment operations are each 5-120 minutes, respectively.

7. The process according to claim 5, wherein the specific surface area of powder of the grounded clinker is 340-360 m2/kg.

8. The process according to claim 5, wherein the cooled clinker is grounded to a powder using a ball mill.

9. The process according to claim 5, wherein cooling at a rate of 40-80° C. is performed using a cooling device.