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:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Application is the US National Phase under 35 U.S.C. §371 of International Application No. PCT/CN2010/075183, filed Jul. 15, 2010, which was published in Chinese as International Publication No. WO/2011/057505 on May 19, 11, 2010, and claims the benefit of CN 200910212646.5, filed on Nov. 13, 2009. Each of these references is hereby incorporated by reference in their entirety. 
     BACKGROUND 
     1. Field of the Inventions 
     The present inventions relate to a process for controlling the polymorph of Alite in Portland cement clinker, including, for example, methods for improving the performance of Portland cement clinker. 
     2. Description of the Related Art 
     The 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 China has been the No. 1 cement producing country in the world for 24 consecutive years. Due to the fact that the Chinese economy is in the phase of rapid development, it is predicted that China&#39;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. 
     SUMMARY OF THE INVENTION 
     Portland cement mainly consists of Portland cement clinker, calcium sulfate 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, C 3 A (3CaO.Al 2 O 3 ) and C 4 AF (4CaO.3Al 2 O 3 .Fe 2 O 3 ). Alite is the main contributor to the cementitious property of Portland cement clinker, while it is also the main energy consumer. Therefore, the content of C 3 S (CaSiO 5 ) in clinker or its activity has to be improved in order to improve the cementitious property of Portland cement clinker. However, the increase of the content of C 3 S 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, where high-activity Alite is obtained via modification of its crystal form. 
     An aspect of at least one of the inventions disclosed herein includes the realization that controlling the crystal form of Alite can improve the performance of Portland cement clinker, providing a process for controlling crystal form of Alite in Portland cement clinker. As a result of this process, 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 this object, the technical scheme of present invention is: a process for controlling the crystal form of Alite in Portland cement clinker, where the process includes the following steps: 
     (1) A 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 this temperature and then naturally cooled; 
     (3) When its temperature is at 600˜800° C., the cooled clinker is heated at a rate of 1˜35° C. per minute until it reaches 700˜1300° C. The clinker is kept at this temperature, and then it is naturally cooled; 
     (4) The cooled clinker is grounded to powder with the aid of a ball mill. 
     In another embodiment, a process for controlling the crystal form of Alite in Portland cement clinker includes the following steps: 
     (1B) A 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 this temperature and then it is transferred to a cooler, where it is cooled at a rate of 40˜80° C. per minute; 
     (3B) When the temperature reaches 700˜1300° C., it is kept at this temperature; 
     (4B) The clinker is naturally cooled; the cooled clinker is grounded to powder with the aid of ball mill. 
     The holding time of steps (2), (3), (2B) and (3B) is preferred to be 5˜120 min, respectively. The specific surface area of the grounded powder of steps (4) and (4B) is preferred to be 340˜360 m 2 /kg. 
     In steps (1) and (1B), the prepared cement raw meal is calcined to form clinker according to regular processing parameters. In alternative embodiments, calcined clinker could also be directly used in the following thermal treatment. 
     The present inventions relate to a process for controlling polymorph of Alite in Portland cement clinker, where the 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 
         FIGS. 1-1  and  1 - 2  are XRD pattern of Alite in a cement clinker at different 2θ (the clinker is produced by Huaihai Cement Factory) 
         FIG. 1-1  is an XRD pattern (2θ=32˜33° of Alite in a cement clinker without thermal treatment, 
         FIG. 1-2  is an XRD pattern (2θ=51.5˜52.7° of Alite in a cement clinker without thermal treatment; 
         FIGS. 2-1  and  2 - 2  are an XRD pattern of Alite in a cement clinker at different 2θ (the clinker is produced by Huaihai Cement Factory and is thermally treated); 
         FIG. 2-1  is an XRD pattern (2θ=32˜33° of Alite in a cement clinker after thermal treatment, and 
         FIG. 2-2  is an XRD pattern (2θ=51.0˜52.5° of Alite in a cement clinker after thermal treatment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present inventions are further illustrated with reference to the following examples. However, it may be understood that the present inventions are not limited to the following examples. 
     Example 1 
     (1) A prepared Portland cement raw meal is heated to 1450° C. and calcined for 1 h; and then cooled to form a cement clinker 
     (2) The temperature of the Portland cement raw meal is increased at a rate of 5° C./min until it reaches 1450° C., kept at this temperature for 30 min, and then is naturally cooled; 
     (3) The 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 this temperature for 60 min and then naturally cooled; 
     (4) The cooled clinker is grounded to a powder (e.g., with the aid of a ball mill. The specific surface area of this powder is 340 m 2 /kg. The XRD pattern of Alite in the 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 gypsum was added to 96 g of the cement clinker obtained as discussed above to form a mixture and this mixture is stirred uniformly, Subsequently, 29 mL water (ratio between water and cement w/c=0.29) was added and the mixture was stirred and molded to form 20×20×20 mm samples. The 3d and 28d compressive strength of the samples were determined. 
     Samples were first cured in a curing box for 24 h, where the relative humidity was 90% and the temperature was 20±2° C. Then a knockout sample was cured in a water curing case at 20±1° C. The comparison of resulting strength is shown in Table 1. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Compressive strength of Portland  
               
               
                 cement clinker paste (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) A prepared Portland cement raw meal was heated to 1480° C., calcined for 0.5 h, and then cooled; 
     (2) The temperature of the Portland cement raw meal was increased at a rate of 10° C./min until it reached 1500° C., and kept at this temperature for 60 min, and then it was naturally cooled; 
     (3) The cooled clinker was heated at a temperature below 700° C. The temperature was increased at a rate of 15° C./min until it reached 1000° C. Subsequently, the said clinker was kept at this temperature for 90 min, and then naturally cooled The clinker was grounded to powder (e.g., with the aid of a ball mill). The resulting specific surface area of this powder was 350 m 2 /kg; 
     (4) 4 g gypsum was added to 96 g of the cement clinker obtained as discussed above. The mixture was stirred uniformly. Subsequently, 29 mL of 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. The 3d and 28d compressive strength of the samples was determined. 
     Samples were first cured in a curing box for 24 h, where the relative humidity was 90% and the temperature was 20±2° C. Then, a knockout sample was cured in a water curing box at 20±1° C. The comparison of resulting strength is shown in Table 2. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Compressive strength of Portland  
               
               
                 cement clinker paste (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 was heated to 1450° C. and calcined for 1 h and then cooled; 
     (2) The temperature of said Portland cement raw meal was increased at a rate of 5° C./min until it reached 1450° C. and kept at this temperature for 60 minutes. Then, the mixture enters a cooling machine and the temperature of this mixture was decreased at a rate of 55° C./minute; 
     (3) The temperature was cooled to 1000° C. and the mixture was kept at this temperature for 60 minutes; 
     (4) 4 g gypsum was added to 96 g of the cement clinker obtained as discussed above, and the mixture was stirred uniformly. Subsequently, 29 mL water (ratio between water and cement w/c=0.29) was added. The mixture was stirred and molded to form 20×20×20 mm samples. The 3d and 28d compressive strength of samples was determined. 
     Samples were first cured in a curing box for 24 h, where the relative humidity was 90% and the temperature was 20±2° C., and then knockout sample was cured in a water curing box at 20±1° C. The comparison of resulting strength is shown in Table 3. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Compressive strength of Portland  
               
               
                 cement clinker paste (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) A prepared Portland cement raw meal was heated to 1450° C., calcined for 1 h, and then cooled; 
     (2) The temperature of this Portland cement raw meal was increased at a rate of 15° C./min until it reached 1500° C. and kept at this temperature for 30 minutes. Then, mixture entered a cooling machine and the temperature of mixture was decreased at a rate of 50° C. per minute. 
     (3) The temperature was cooled to 1100° C., and then the mixture was kept at this temperature for 30 minutes; 
     (4) 4 g gypsum was added to 96 g of the cement clinker obtained as discussed above and this mixture was stirred. Subsequently, 29 mL water (ratio between water and cement w/c=0.29) was added. The mixture was stirred and molded to form 20×20×20 mm samples. The 3d and 28d compressive strength of samples are determined. 
     Samples were first cured in a curing box for 24 h, where the relative humidity was 90% and the temperature was 20±2° C. Then a knockout sample was cured in a water curing case at 20±1° C. The comparison of resulting strength is shown in Table 4. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Compressive strength of Portland  
               
               
                 cement clinker paste (MPa) 
               
             
          
           
               
                 Examples 
                 3 d 
                 28 d 
               
               
                   
               
               
                 Xuzhou Huaihai Cement Factory  
                 55.6 
                 88.6 
               
               
                 (Portland cement clinker) 
                   
                   
               
               
                 Example 4 
                 56.8 
                 91.5