Inorganic pelletized perlitic lightweight granules and their preparation method and application

Abstract

The present invention discloses inorganic pelletized perlitic lightweight granules and a preparation process and use thereof. The present invention develops through encapsulation technology a novel type of lightweight particles, namely, inorganic pelletized perlitic lightweight granules comprising expanded perlite as a core material and a cementitious material as a shell material, forming a core-shell structure in which a perlite core is encapsulated in a cementitious shell. The cementitious material including cement and fly ash is coated onto the surface of expanded perlite particles through an encapsulation process by a pelletizer under controlled water spraying. The resulting inorganic pelletized perlitic lightweight granules are lower in cost and easier to produce, and have better fire resistance, higher crushing strength, and better compatibility with concrete. The inorganic pelletized perlitic lightweight granules can overcome the problems of conventional lightweight concrete, such as high water absorption and inconsistent performance.

Claims

1. Inorganic pelletized perlitic lightweight granules comprising expanded perlite as core and cementitious material as shell, and having a core-shell structure with the perlite core encapsulated by cementitious shell.

2. The inorganic pelletized perlitic lightweight granules according to claim 1, wherein the perlite core has a porous structure, and the cementitious shell has a dense structure.

3. The inorganic pelletized perlitic lightweight granules according to claim 1, wherein the cementitious material and expanded perlite have a volume ratio of 1:(0.3 to 3.0).

4. The inorganic pelletized perlitic lightweight granules according to claim 3, wherein the cementitious material and expanded perlite have a volume ratio of 0.860-2.890:1.

5. The inorganic pelletized perlitic lightweight granules according to claim 1, wherein the inorganic pelletized perlitic lightweight granules have a particle size of 0.5 to 20 mm; and/or the inorganic pelletized perlitic lightweight granules have a dry density of 580 to 1200 kg/m.sup.3.

6. The inorganic pelletized perlitic lightweight granules according to claim 1, wherein the expanded perlite is selected from expanded perlite with different size distributions.

7. The inorganic pelletized perlitic lightweight granules according to claim 1, wherein the cementitious material is selected from cement, or a mixture of cement and fly ash; and the mass ratio of cement to fly ash is 1:(0 to 1).

8. The inorganic pelletized perlitic lightweight granules according to claim 1, wherein the core-shell structure is formed via an encapsulation process with a pelletizer.

9. The inorganic pelletized perlitic lightweight granules according to claim 1, wherein the inorganic pelletized perlitic lightweight granules have a water absorption rate below 5.5%.

10. A preparation process of the inorganic pelletized perlitic lightweight granules according to claim 1, the preparation process including gradually encapsulating the expanded perlite with the cementitious material under water spraying in a pelletizer.

11. The preparation process of the inorganic pelletized perlitic lightweight granules according to claim 10, the preparation process comprising the steps of: S1. Mixing: required amounts of expanded perlite and cementitious materials are mixed to obtain a mixture of expanded perlite and cementitious materials; S2. Pelletization: required amount of water is sprayed to the mixture obtained in Step S1 to allow the cementitious material gradually encapsulating the expanded perlite under water spraying, thereby obtaining particles in which the surface of the expanded perlite is covered with the cementitious material; and S3. Curing: cured the inorganic pelletized perlitic lightweight granules obtained in Step S2 in a sealed environment for at least 1 day.

12. The preparation process of the inorganic pelletized perlitic lightweight granules according to claim 11, wherein the amount of water sprayed in the Step S2 is 20 to 35 wt % of the cementitious material, and/or the duration for water spraying is 10 to 60 minutes.

13. The preparation process of the inorganic pelletized perlitic lightweight granules according to claim 11, wherein the Step S2 is carried out in a pan pelletizer, where the pelletizer pan has an inclination angle of 20 to 60 degrees and a rotating speed of 10 to 60 r/min.

14. The preparation process of the inorganic pelletized perlitic lightweight granules according to claim 13, wherein after the cementitious material completely adhered to the surface of the expanded perlite, kept running the pelletizer for at least 5 minutes.

15. The preparation process of the inorganic pelletized perlitic lightweight granules according to claim 11, wherein the Steps S1˜S3 are repeated for 1-4 times, and the surface of expanded perlite is encapsulated with cementitious material in 2 to 5 pelletization processes.

16. The preparation process of the inorganic pelletized perlitic lightweight granules according to claim 15, wherein the amount of water sprayed in the first pelletization process of Step S2 is 20 to 35 wt % of the cementitious material, and the amount of water sprayed in the second pelletization process of Step S2 is 19 to 29 wt % of the cementitious material.

17. The preparation process of the inorganic pelletized perlitic lightweight granules according to claim 11, wherein the Step S1˜S3 further comprises: S1. Mixing: mixing specified amounts of expanded perlite and cementitious material and then moving the resultant mixture to a pan pelletizer, or alternatively mixing specified amounts of expanded perlite and cementitious material in the pan pelletizer, to obtain a mixture of the expanded perlite and the cementitious material; S2. Pelletization: starting the pan pelletizer with the inclination angle of the pelletizer pan being 20 to 60 degrees, and allowing the pelletizer pan rotate at a speed of 10 to 60 r/min, and then spraying water which is 20-35 wt % of the mass of cementitious materials within 10 to 60 minutes to the mixture of the expanded perlite and the cementitious material obtained in Step S1 to allow the cementitious material gradually attaching to the surface of expanded perlite, thereby obtaining particles in which the surface of the expanded perlite is covered with the cementitious material; and. S3. Curing: curing the particles obtained in Step S2 in a sealed environment for at least 1 day.

18. Use of the inorganic pelletized perlitic lightweight granules according to claim 1 in the production of lightweight concrete.

19. Use of inorganic pelletized perlitic lightweight granules prepared through the preparation process of the inorganic pelletized perlitic lightweight granules according to claim 10 in the production of lightweight concrete.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0055] FIG. 1 schematically shows the structure of the inorganic pelletized perlitic lightweight granule of the present invention.

[0056] FIG. 2 schematically shows the pelletization process of the inorganic pelletized perlitic lightweight granules of the present invention.

[0057] FIG. 3 is a photograph of pan pelletizer.

[0058] FIG. 4 is a photograph of the inorganic pelletized perlitic lightweight granules of the present invention.

[0059] FIG. 5 is an optical microscope image of the cross-section of inorganic pelletized perlitic lightweight granule of the present invention.

[0060] FIGS. 6a to 6c are SEM images of the inorganic pelletized perlitic lightweight granule of the present invention. FIG. 6a shows the core of the inorganic pelletized perlitic lightweight granule, FIG. 6b shows the shell of the inorganic pelletized perlitic lightweight granule, and FIG. 6c shows a core/shell interface of the inorganic pelletized perlitic lightweight granule.

[0061] FIG. 7 is a photograph of the cross section of the lightweight concrete of the present invention.

[0062] FIG. 8 is an optical microscope image of the cross section of the lightweight concrete of the present invention.

REFERENCE SIGNS

[0063] inorganic pelletized perlitic lightweight granule 100, expanded perlite 110, cementitious material 120, water mist 200.

DETAILED DESCRIPTION

[0064] The invention is a further development and extension of water capsule technique on the basis of the technique of patent applications of the present applicant (US 20180222806A1 and CN 201710079925.3). In order to obtain high performance lightweight particles for the production of lightweight concrete, the present invention develops a novel type of lightweight particles, namely, inorganic pelletized perlitic lightweight granules (as shown in FIG. 1 and FIG. 4), via the encapsulation technology. The inorganic pelletized perlitic lightweight granules include expanded perlite 110 as core and cementitious material 120 as shell, and have a core-shell structure with the porous perlite core encapsulated by dense cementitious shell. Compared with the water capsule of the previous applications, the inorganic pelletized perlitic lightweight granules of the present invention exhibit a lower cost, appropriate selection of materials, ease of production, superior fire resistance, higher crushing strength, and better compatibility with concrete.

[0065] As shown in FIGS. 5 and 6, it can be seen by optical microscopy and scanning electron microscopy that the expanded perlite has a porous structure, and it has an irregular shape and a coarse surface; the cementitious shell made from cementitious material has a dense structure; and the cementitious material firmly adheres to the surface of the expanded perlite, and a strong interfacial transition zone is formed between the expanded perlite and the cementitious material.

[0066] The present invention relates to the use of the inorganic pelletized perlitic lightweight granules 100 in producing lightweight concrete (as shown in FIG. 7). As shown in FIG. 8, under an optical microscope, the cementitious shell of the inorganic pelletized perlitic lightweight granule reacts with the cementitious binder material of surrounding concrete, resulting in formation of a high-strength interfacial transition zone between the inorganic pelletized perlitic lightweight granules and the concrete matrix, which facilitates the interfacial bonding between the inorganic pelletized perlitic lightweight granules and the concrete matrix.

[0067] In order that those skilled in the art understands and implements the present invention, the present invention will be further described in detail below in reference to specific embodiments.

Example 1

[0068] A kind of inorganic pelletized perlitic lightweight granules which include expanded perlite as core and cementitious materials as shell, having a core-shell structure with the porous perlite core encapsulated by the dense cementitious shell. The cementitious materials and the expanded perlite in the inorganic pelletized perlitic lightweight granules have a volume ratio (i.e., shell/core ratio by volume) of 1.6:1, and the cementitious materials contain cement and fly ash in a mass ratio of 1:0.5. The obtained inorganic pelletized perlitic lightweight granules have a particle size of no larger than 11 mm and a dry density of 850 kg/m.sup.3.

[0069] The preparation process of the inorganic pelletized perlitic lightweight granules includes the following steps:

[0070] S1. Mixing: required amounts of expanded perlite and cementitious materials were mixed and then moved to a pan pelletizer, or alternatively, required amounts of expanded perlite and cementitious material were mixed in the pan pelletizer, to obtain a mixture of expanded perlite and cementitious materials;

[0071] S2. Pelletization: the pelletizer was turned on and run with the inclination angle of the pelletizer pan being 20 to 60 degrees and the rotating speed of pelletizer pan being 10 to 60 r/min. Required amount of water (say 27 wt % of the mass of cementitious material) was sprayed automatically to the mixture obtained in Step S1 over 35 minutes to allow the cementitious material gradually encapsulating the expanded perlite under water spraying. After the cementitious material fully adhered to the surface of the expanded perlite, kept running the pelletizer for at least 5 minutes to obtain the inorganic pelletized perlitic lightweight granules; and

[0072] S3. Curing: cured the inorganic pelletized perlitic lightweight granules obtained in Step S2 in a sealed environment for at least 1 day.

[0073] Here, S1 mixing, S2 pelletization, and S3 curing steps were repeated for 1-4 times.

Example 2

[0074] A kind of inorganic pelletized perlitic lightweight granules which include expanded perlite as core and cementitious materials as shell, having a core-shell structure with the porous perlite core encapsulated by the dense cementitious shell. The cementitious materials and the expanded perlite in the inorganic pelletized perlitic lightweight granules have a volume ratio (i.e., shell/core ratio by volume) of 0.8:1, and the cementitious material contains cement and fly ash in a mass ratio of 1:0.3. The obtained inorganic pelletized perlitic lightweight granules have a particle size of no larger than 5 mm and a dry density of 700 kg/m.sup.3.

[0075] The preparation process of the inorganic pelletized perlitic lightweight granules includes the following steps:

[0076] S1. Mixing: required amounts of expanded perlite and cementitious materials were mixed and then moved to a pan pelletizer, or alternatively, required amounts of expanded perlite and cementitious material were mixed in the pan pelletizer, to obtain a mixture of expanded perlite and cementitious materials;

[0077] S2. Pelletization: the pelletizer was turned on and run with the inclination angle of the pelletizer pan being 20 to 60 degrees and the rotating speed of pelletizer pan being 10 to 60 r/min. Required amount of water (say 24 wt % of the mass of cementitious material) was sprayed automatically to the mixture obtained in Step S1 over 22 minutes to allow the cementitious material gradually encapsulating the expanded perlite under water spraying. After the cementitious material fully adhered to the surface of the expanded perlite, kept running the pelletizer for at least 5 minutes to obtain the inorganic pelletized perlitic lightweight granules; and

[0078] S3. Curing: cured the inorganic pelletized perlitic lightweight granules obtained in Step S2 in a sealed environment for at least 1 day.

[0079] Here, S1 mixing, S2 pelletization, and S3 curing steps were repeated for 1-4 times.

Example 3

[0080] A kind of inorganic pelletized perlitic lightweight granules which include expanded perlite as core and cementitious materials as shell, having a core-shell structure with the porous perlite core encapsulated by the dense cementitious shell. The cementitious materials and the expanded perlite in the inorganic pelletized perlitic lightweight granules have a volume ratio (i.e., shell/core ratio by volume) of 2.4:1, and the cementitious material contains cement and fly ash in a mass ratio of 1:0.7. The obtained inorganic pelletized perlitic lightweight granules have a particle size of no larger than 15 mm and a dry density of 1100 kg/m.sup.3.

[0081] The preparation process of the inorganic pelletized perlitic lightweight granules includes the following steps:

[0082] S1. Mixing: required amounts of expanded perlite and cementitious materials were mixed and then moved to a pan pelletizer, or alternatively, required amounts of expanded perlite and cementitious material were mixed in the pan pelletizer, to obtain a mixture of expanded perlite and cementitious materials;

[0083] S2. Pelletization: the pelletizer was turned on and run with the inclination angle of the pelletizer pan being 20 to 60 degrees and the rotating speed of pelletizer pan being 10 to 60 r/min. Required amount of water (say 31 wt % of the mass of cementitious material) was sprayed automatically to the mixture obtained in Step S1 over 47 minutes to allow the cementitious material gradually encapsulating the expanded perlite under water spraying. After the cementitious material fully adhered to the surface of the expanded perlite, kept running the pelletizer for at least 5 minutes to obtain the inorganic pelletized perlitic lightweight granules; and

[0084] S3. Curing: cured the inorganic pelletized perlitic lightweight granules obtained in Step S2 in a sealed environment for at least 1 day.

[0085] Here, S1 mixing, S2 pelletization, and S3 curing steps were repeated for 1-4 times.

Example 4

[0086] A kind of inorganic pelletized perlitic lightweight granules which include expanded perlite as core and cementitious materials as shell, having a core-shell structure with the porous perlite core encapsulated by the dense cementitious shell. The cementitious materials and the expanded perlite in the inorganic pelletized perlitic lightweight granules have a volume ratio (i.e., shell/core ratio by volume) of 0.3:1, and the cementitious material contains cement only. The obtained inorganic pelletized perlitic lightweight granules have a particle size of no larger than 0.5 mm and a dry density of 580 kg/m.sup.3.

[0087] The preparation process of the inorganic pelletized perlitic lightweight granules includes the following steps:

[0088] S1. Mixing: required amounts of expanded perlite and cementitious materials were mixed and then moved to a pan pelletizer, or alternatively, required amounts of expanded perlite and cementitious material were mixed in the pan pelletizer, to obtain a mixture of expanded perlite and cementitious materials;

[0089] S2. Pelletization: the pelletizer was turned on and run with the inclination angle of the pelletizer pan being 20 to 60 degrees and the rotating speed of pelletizer pan being 10 to 60 r/min. Required amount of water (say 20 wt % of the mass of cementitious material) was sprayed automatically to the mixture obtained in Step S1 over 10 minutes to allow the cementitious material gradually encapsulating the expanded perlite under water spraying. After the cementitious material fully adhered to the surface of the expanded perlite, kept running the pelletizer for at least 5 minutes to obtain the inorganic pelletized perlitic lightweight granules; and

[0090] S3. Curing: cured the inorganic pelletized perlitic lightweight granules obtained in Step S2 in a sealed environment for at least 1 day.

[0091] Here, S1 mixing, S2 pelletization, and S3 curing steps were repeated for 1-4 times.

Example 5

[0092] A kind of inorganic pelletized perlitic lightweight granules which include expanded perlite as core and cementitious materials as shell, having a core-shell structure with the porous perlite core encapsulated by the dense cementitious shell. The cementitious materials and the expanded perlite in the inorganic pelletized perlitic lightweight granules have a volume ratio (i.e., shell/core ratio by volume) of 3.0:1, and the cementitious material contains cement and fly ash in a mass ratio of 1:1. The obtained inorganic pelletized perlitic lightweight granules have a particle size of no larger than 20 mm and a dry density of 1200 kg/m.sup.3.

[0093] The preparation process of the inorganic pelletized perlitic lightweight granules includes the following steps:

[0094] S1. Mixing: required amounts of expanded perlite and cementitious materials were mixed and then moved to a pan pelletizer, or alternatively, required amounts of expanded perlite and cementitious material were mixed in the pan pelletizer, to obtain a mixture of expanded perlite and cementitious materials;

[0095] S2. Pelletization: the pelletizer was turned on and run with the inclination angle of the pelletizer pan being 20 to 60 degrees and the rotating speed of pelletizer pan being 10 to 60 r/min. Required amount of water (say 35 wt % of the mass of cementitious material) was sprayed automatically to the mixture obtained in Step S1 over 60 minutes to allow the cementitious material gradually encapsulating the expanded perlite under water spraying. After the cementitious material fully adhered to the surface of the expanded perlite, kept running the pelletizer for at least 5 minutes to obtain the inorganic pelletized perlitic lightweight granules; and S3. Curing: cured the inorganic pelletized perlitic lightweight granules obtained in Step S2 in a sealed environment for at least 1 day.

[0096] Here, S1 mixing, S2 pelletization, and S3 curing steps were repeated for 1-4 times.

Example 6

[0097] A kind of inorganic pelletized perlitic lightweight granules which include expanded perlite as core and cementitious materials as shell, having a core-shell structure with the porous perlite core encapsulated by the dense cementitious shell. The cementitious materials and the expanded perlite in the inorganic pelletized perlitic lightweight granules have a volume ratio (i.e., shell/core ratio by volume) of 0.8:1, and the cementitious material contains cement and fly ash in a mass ratio of 1:0.5. The obtained inorganic pelletized perlitic lightweight granules have a particle size of no larger than 11 mm and a dry density of 850 kg/m.sup.3.

[0098] The preparation process of the inorganic pelletized perlitic lightweight granules includes the following steps:

[0099] S1. Mixing: required amounts of expanded perlite and cementitious materials were mixed and then moved to a pan pelletizer, or alternatively, required amounts of expanded perlite and cementitious material were mixed in the pan pelletizer, to obtain a mixture of expanded perlite and cementitious materials;

[0100] S2. Pelletization: the pelletizer was turned on and run with the inclination angle of the pelletizer pan being 20 to 60 degrees and the rotating speed of pelletizer pan being 10 to 60 r/min. Required amount of water (say 27 wt % of the mass of cementitious material) was sprayed automatically to the mixture obtained in Step S1 over 35 minutes to allow the cementitious material gradually encapsulating the expanded perlite under water spraying. After the cementitious material fully adhered to the surface of the expanded perlite, kept running the pelletizer for at least 5 minutes to obtain the inorganic pelletized perlitic lightweight granules; and

[0101] S3. Curing: cured the inorganic pelletized perlitic lightweight granules obtained in Step S2 in a sealed environment for at least 1 day.

[0102] Here, S1 mixing, S2 pelletization, and S3 curing steps were repeated for 1-4 times.

Example 7

[0103] A kind of inorganic pelletized perlitic lightweight granules which include expanded perlite as core and cementitious materials as shell, having a core-shell structure with the porous perlite core encapsulated by the dense cementitious shell. The cementitious materials and the expanded perlite in the inorganic pelletized perlitic lightweight granules have a volume ratio (i.e., shell/core ratio by volume) of 2.4:1, and the cementitious material contains cement and fly ash in a mass ratio of 1:0.5. The obtained inorganic pelletized perlitic lightweight granules have a particle size of no larger than 11 mm and a dry density of 850 kg/m.sup.3.

[0104] The preparation process of the inorganic pelletized perlitic lightweight granules includes the following steps:

[0105] S1. Mixing: required amounts of expanded perlite and cementitious materials were mixed and then moved to a pan pelletizer, or alternatively, required amounts of expanded perlite and cementitious material were mixed in the pan pelletizer, to obtain a mixture of expanded perlite and cementitious materials;

[0106] S2. Pelletization: the pelletizer was turned on and run with the inclination angle of the pelletizer pan being 20 to 60 degrees and the rotating speed of pelletizer pan being 10 to 60 r/min. Required amount of water (say 27 wt % of the mass of cementitious material) was sprayed automatically to the mixture obtained in Step S1 over 35 minutes to allow the cementitious material gradually encapsulating the expanded perlite under water spraying. After the cementitious material fully adhered to the surface of the expanded perlite, kept running the pelletizer for at least 5 minutes to obtain the inorganic pelletized perlitic lightweight granules; and

[0107] S3. Curing: cured the inorganic pelletized perlitic lightweight granules obtained in Step S2 in a sealed environment for at least 1 day.

[0108] Here, S1 mixing, S2 pelletization, and S3 curing steps were repeated for 1-4 times.

Example 8

[0109] A kind of inorganic pelletized perlitic lightweight granules which include expanded perlite as core and cementitious materials as shell, having a core-shell structure with the porous perlite core encapsulated by the dense cementitious shell. The cementitious materials and the expanded perlite in the inorganic pelletized perlitic lightweight granules have a volume ratio (i.e., shell/core ratio by volume) of 0.3:1, and the cementitious material contains cement and fly ash in a mass ratio of 1:0.5. The obtained inorganic pelletized perlitic lightweight granules have a particle size of no larger than 11 mm and a dry density of 850 kg/m.sup.3.

[0110] The preparation process of the inorganic pelletized perlitic lightweight granules includes the following steps:

[0111] S1. Mixing: required amounts of expanded perlite and cementitious materials were mixed and then moved to a pan pelletizer, or alternatively, required amounts of expanded perlite and cementitious material were mixed in the pan pelletizer, to obtain a mixture of expanded perlite and cementitious materials;

[0112] S2. Pelletization: the pelletizer was turned on and run with the inclination angle of the pelletizer pan being 20 to 60 degrees and the rotating speed of pelletizer pan being 10 to 60 r/min. Required amount of water (say 27 wt % of the mass of cementitious material) was sprayed automatically to the mixture obtained in Step S1 over 35 minutes to allow the cementitious material gradually encapsulating the expanded perlite under water spraying. After the cementitious material completely adhered to the surface of the expanded perlite, kept running the pelletizer for at least 5 minutes to obtain the inorganic pelletized perlitic lightweight granules; and

[0113] S3. Curing: cured the inorganic pelletized perlitic lightweight granules obtained in Step S2 in a sealed environment for at least 1 day.

[0114] Here, S1 mixing, S2 pelletization, and S3 curing steps were repeated for 1-4 times.

Example 9

[0115] A kind of inorganic pelletized perlitic lightweight granules which include expanded perlite as core and cementitious materials as shell, having a core-shell structure with the porous perlite core encapsulated by the dense cementitious shell. The cementitious materials and the expanded perlite in the inorganic pelletized perlitic lightweight granules have a volume ratio (i.e., shell/core ratio by volume) of 3.0:1, and the cementitious material contains cement and fly ash in a mass ratio of 1:0.5. The obtained inorganic pelletized perlitic lightweight granules have a particle size of no larger than 11 mm and a dry density of 850 kg/m.sup.3.

[0116] The preparation process of the inorganic pelletized perlitic lightweight granules includes the following steps:

[0117] S1. Mixing: required amounts of expanded perlite and cementitious materials were mixed and then moved to a pan pelletizer, or alternatively, required amounts of expanded perlite and cementitious material were mixed in the pan pelletizer, to obtain a mixture of expanded perlite and cementitious materials;

[0118] S2. Pelletization: the pelletizer was turned on and run with the inclination angle of the pelletizer pan being 20 to 60 degrees and the rotating speed of pelletizer pan being 10 to 60 r/min. Required amount of water (say 27 wt % of the mass of cementitious material) was sprayed automatically to the mixture obtained in Step S1 over 35 minutes to allow the cementitious material gradually encapsulating the expanded perlite under water spraying. After the cementitious material completely adhered to the surface of the expanded perlite, kept running the pelletizer for at least 5 minutes to obtain the inorganic pelletized perlitic lightweight granules; and

[0119] S3. Curing: cured the inorganic pelletized perlitic lightweight granules obtained in Step S2 in a sealed environment for at least 1 day.

[0120] Here, S1 mixing, S2 pelletization, and S3 curing steps were repeated for 1-4 times.

Example 10

[0121] A kind of inorganic pelletized perlitic lightweight granules which include expanded perlite as core and cementitious materials as shell, having a core-shell structure with the porous perlite core encapsulated by the dense cementitious shell. The cementitious materials and the expanded perlite in the inorganic pelletized perlitic lightweight granules have a volume ratio (i.e., shell/core ratio by volume) of 0.86:1, and the cementitious material contains cement and fly ash in a mass ratio of 1:1. The expanded perlite used was Type I expanded perlite with particle size distribution as shown in Table 1. The obtained inorganic pelletized perlitic lightweight granules have a dry density of 673 kg/m.sup.3 and a particle size distribution as shown in Table 2.

Example 11

[0122] A kind of inorganic pelletized perlitic lightweight granules which include expanded perlite as core and cementitious materials as shell, having a core-shell structure with the porous perlite core encapsulated by the dense cementitious shell. The cementitious materials and the expanded perlite in the inorganic pelletized perlitic lightweight granules have a volume ratio (i.e., shell/core ratio by volume) of 1.388:1, and the cementitious material contains cement and fly ash in a mass ratio of 1:0.5. The expanded perlite used was Type I expanded perlite with particle size distribution as shown in Table 1. The obtained inorganic pelletized perlitic lightweight granules have a dry density of 855 kg/m.sup.3 and a particle size distribution as shown in Table 2.

Example 12

[0123] A kind of inorganic pelletized perlitic lightweight granules which include expanded perlite as core and cementitious materials as shell, having a core-shell structure with the porous perlite core encapsulated by the dense cementitious shell. The cementitious materials and the expanded perlite in the inorganic pelletized perlitic lightweight granules have a volume ratio (i.e., shell/core ratio by volume) of 2.890:1, and the cementitious material contains cement only. The expanded perlite used was Type II expanded perlite with particle size distribution as shown in Table 1. The obtained inorganic pelletized perlitic lightweight granules have a dry density of 1072 kg/m.sup.3 and a particle size distribution as shown in Table 2.

Example 13

[0124] A kind of inorganic pelletized perlitic lightweight granules which include expanded perlite as core and cementitious materials as shell, having a core-shell structure with the porous perlite core encapsulated by the dense cementitious shell. The cementitious materials and the expanded perlite in the inorganic pelletized perlitic lightweight granules have a volume ratio (i.e., shell/core ratio by volume) of 2.822:1, and the cementitious material contains cement only. The expanded perlite used was Type III expanded perlite with particle size distribution as shown in Table 1. The obtained inorganic pelletized perlitic lightweight granules have a dry density of 1058 kg/m.sup.3 and a size range of 4.75˜16.0 mm.

[0125] The inorganic pelletized perlitic lightweight granules of Examples 10 to 13 were prepared by a two-step encapsulation process. A pan pelletizer, as shown in FIG. 3, was used for carrying out the encapsulation process. The pelletizer was equipped with a sprayer at the upper left portion of the pan, and the sprayer is able to automatically spray water into the pan. The encapsulation process includes the following steps:

[0126] 1. The first stage encapsulation process involves the steps: [0127] a) The angle of the pan relative to the horizontal plane was set to be 45°; [0128] b) A specified amount of expanded perlite was added into the pelletizer; [0129] c) A specified amount of cementitious material was added into the pelletizer; [0130] d) The pelletizer was turned on and run at a rotation speed of the pan of 5 r/s for about 1 minute to mix the expanded perlite and cementitious materials (i.e., S1 mixing); [0131] e) The speed of pan was increased to 20 r/min, and water was automatically sprayed to the pan by the nozzle until the water to cementitious material ratio attained 0.216 to 0.324; After the cementitious material completely adhered to the surface of the expanded perlite, kept running the pelletizer for at least 5 minutes to further dense the cementitious shell and obtain the inorganic pelletized perlitic lightweight granules (i.e., S2 pelletization); and [0132] f) The pelletizer was turned off for transferring the resultant particles (semi-finished particles) to a sealed environment and cured for 24 hours (i.e., S3 curing).

[0133] 2. The second stage encapsulation process involves the steps: [0134] a) A specified amount of semi-finished particles obtained in the first stage were added into the pelletizer; [0135] b) A specified amount of cementitious material was added into the pelletizer; [0136] c) The pelletizer was turned on and run at a rotation speed of the pan of 5 r/s for about 1 minute to mix the expanded perlite and cementitious materials (i.e., S1 mixing); [0137] d) The speed of pan was increased to 20 r/min, and water was automatically sprayed to the pan by the nozzle until the water to cementitious material (added in step b) ratio attained 0.192 to 0.288; After the cementitious material completely adhered to the surface of the expanded perlite, kept running the pelletizer for at least 5 minutes to further dense the cementitious shell and obtain the inorganic pelletized perlitic lightweight granules (i.e., S2 pelletization); and [0138] e) The pelletizer was turned off for transferring the resultant particles (finished particles) to a sealed environment or an environment that can avoid moisture loss and cured for 7 days (S3′ curing).

[0139] In Examples 10 to 13, the main difference amongst various types of expanded perlite used are their size distribution. Table 1 shows the size distribution of the three types of expanded perlite used in the examples of the present invention. The size distribution of the inorganic pelletized perlitic lightweight granules obtained in Examples 10 to 12 are shown in Table 2.

TABLE-US-00001 TABLE 1 Size distributions of the expanded perlite I, II, and III (cumulative percentage of mass retained on sieve) Types of expanded perlite Sieve size (mm) I II III 4.75  0.0 wt %  1.1 wt % 22.5 wt % 2.36 68.0 wt % 84.7 wt % 85.9 wt % 1.18 87.6 wt % 90.0 wt % 88.5 wt % 0.60 93.3 wt % 91.7 wt % 92.4 wt % 0.30 94.3 wt % 91.9 wt % 96.9 wt % 0.15 95.4 wt % 94.2 wt % 97.9 wt % 0.075 98.0 wt % 98.2 wt % 98.9 wt % <0.075 100.0 wt %  100.0 wt %  100.0 wt % 

TABLE-US-00002 TABLE 2 Size distribution of the inorganic pelletized perlitic lightweight granules obtained in Examples 10 to 12 (cumulative percentage of mass retained on sieve) Inorganic pelletized perlitic lightweight granules Sieve size (mm) Example 10 Example 11 Example 12 10.0  0.0 wt %  0.0 wt %  5.4 wt % 4.75  2.8 wt %  7.9 wt %  81.0 wt % 2.36 85.4 wt % 87.3 wt %  99.3 wt % 1.18 98.6 wt % 95.6 wt %  99.9 wt % 0.60 99.6 wt % 98.3 wt % 100.0 wt % 0.30 99.6 wt % 99.3 wt % 100.0 wt % 0.15 100.0 wt %  99.5 wt % 100.0 wt % 0.075 100.0 wt %  99.9 wt % 100.0 wt % <0.075 100.0 wt %  100.0 wt %  100.0 wt %

[0140] Examples 10 to 13 examine the effects of the size distribution of expanded perlite, the composition of shell materials and the volume ratio of shell/core on the performance of the inorganic pelletized perlitic lightweight granules, as summarized in Table 3. The thickness of the shell of the inorganic pelletized perlitic lightweight granules obtained in the examples increased going down Table 3. It can be seen from Table 3 that, when different expanded perlite, different shell materials and different shell/core ratios were employed, inorganic pelletized perlitic lightweight granules having different densities and strengths were prepared. Such inorganic pelletized perlitic lightweight granules having tailorable performance can be used for the production of lightweight concrete with different performance.

TABLE-US-00003 TABLE 3 Performance of inorganic pelletized perlitic lightweight granules 7-day Types of Shell/core Dry 1-hour water crushing expanded Composition of ratio by density absorption strength Example perlite shell materials volume (kg/m.sup.3) rate (%) (MPa) 10 I 50% cement 0.860 673 5.1 1.54 50% fly ash 11 I 65% cement 1.388 855 2.6 4.29 35% fly ash 12 II 100% cement 2.890 1072 1.2 5.47 13 III 100% cement 2.822 1058 0.6 6.20

Application Example 1

[0141] The inorganic pelletized perlitic lightweight granules obtained in Example 10 were used to prepare concrete containing 540 kg/m.sup.3 of cement, 60 kg/m.sup.3 of silica fume, 60 kg/m.sup.3 of fly ash, 549 kg/m.sup.3 of the inorganic pelletized perlitic lightweight granules, 430 kg/m.sup.3 of limestone, 180 kg/m.sup.3 of water, and 8.4 kg/m.sup.3 of superplasticizer (e.g. naphthalene and polycarboxylate based superplasticizers).

Application Example 2

[0142] The inorganic pelletized perlitic lightweight granules obtained in Example 11 were used to prepare concrete containing 600 kg/m.sup.3 of cement, 735 kg/m.sup.3 of the inorganic pelletized perlitic lightweight granules, 120 kg/m.sup.3 of limestone, 170 kg/m.sup.3 of natural coarse aggregates, 180 kg/m.sup.3 of water, 7.0 kg/m.sup.3 of superplasticizer, and 0.5 kg/m.sup.3 of viscosity modifying agent (such as acrylic copolymer, polyvinyl alcohol, and polyvinylpyrrolidone based viscosity modifiers).

Application Example 3

[0143] The inorganic pelletized perlitic lightweight granules obtained in Example 11 were used to prepare concrete containing 600 kg/m.sup.3 of cement, 735 kg/m.sup.3 of the inorganic pelletized perlitic lightweight granules, 290 kg/m.sup.3 of limestone, 180 kg/m.sup.3 of water, and 6.7 kg/m.sup.3 of superplasticizer.

Application Example 4

[0144] The inorganic pelletized perlitic lightweight granules obtained in Example 12 were used to prepare concrete containing 540 kg/m.sup.3 of cement, 60 kg/m.sup.3 of silica fume, 1027 kg/m.sup.3 of the inorganic pelletized perlitic lightweight granules, 190 kg/m.sup.3 of limestone, 180 kg/m.sup.3 of water, 7.0 kg/m.sup.3 of superplasticizer, and 0.5 kg/m.sup.3 of viscosity modifying agent.

Application Example 5

[0145] The inorganic pelletized perlitic lightweight granules obtained in Examples 11 and 13 were used to prepare concrete containing 450 kg/m.sup.3 of cement, 150 kg/m.sup.3 of fly ash, 565 kg/m.sup.3 of the inorganic pelletized perlitic lightweight granules (Example 11), 345 kg/m.sup.3 of the inorganic pelletized perlitic lightweight granules (Example 13), 100 kg/m.sup.3 of limestone, 180 kg/m.sup.3 of water, and 4.2 kg/m.sup.3 of superplasticizer.

[0146] The concrete of aforementioned application examples 1 to 5 was prepared following the below procedures:

[0147] 1) Specified amounts of cement, silica fume (if present), fly ash (if present), inorganic pelletized perlitic lightweight granules, limestone, natural coarse aggregates (if present), and water were weighed;

[0148] 2) Specified amounts of superplasticizer and viscosity modifying agent (if present) were weighed and added into the weighed water;

[0149] 3) The cement, silica fume (if present), fly ash (if present), limestone, lightweight expanded perlite inorganic particles, and natural coarse aggregates (if present) were added into the mixer and dry mixed for at least 1 minute;

[0150] 4) The mixture of water, superplasticizer, and viscosity modifying agent (if present) were added into the mixer and wet mixed for at least 3 minutes;

[0151] 5) The resultant fresh concrete mixture was placed into the molds;

[0152] 6) The concrete mixture was properly cured for at least 7 days after concrete placement to avoid moisture loss.

[0153] Application examples 1 to 5 provided a basis to investigate the effects of the type and amount of the inorganic pelletized perlitic lightweight granules on the performance of concrete. The results of concrete produced are shown in Table 4. It can be seen from Table 4 that the inorganic pelletized perlitic lightweight granules with a thick shell can be used to produce high-strength, lightweight concrete, while the inorganic pelletized perlitic lightweight granules with a thin shell can be used to produce normal-strength, lightweight concrete. Comparing the results of application examples 1, 2 and 3, it can be seen that when less limestone but more inorganic pelletized perlitic lightweight granules with thick shell were employed (application examples 2 and 3), the resultant concrete had a higher density, and significantly enhanced 7-day compressive strength and 28-day compressive strength. Comparing the results of application examples 1 to 4, it can be seen that the inorganic pelletized perlitic lightweight granules with thicker shell can provide concrete with a higher strength. As fly ash and two different types of inorganic pelletized perlitic lightweight granules with and without fly ash were included, the concrete prepared in application example 5 is more environmentally friendly and economical than the concrete prepared in other application examples.

TABLE-US-00004 TABLE 4 Effects of type and amount of inorganic pelletized perlitic lightweight granules on the performance of concrete Application example 1 2 3 4 5 Type of Inorganic Example Example Example Example Example Example inorganic pelletized 10 11 11 12 11 13 pelletized perlitic perlitic lightweight lightweight granules granules Types of I I I II I III expanded perlite Composition of 50% cement 65% cement 65% cement 100% cement 65% cement 100% cement shell materials 50% fly ash 35% fly ash 35% fly ash 35% fly ash Concrete Cement 540 600 600 540 450 composition Silica fume 60 / / 60 / Fly ash 60 / / / 150 Inorganic 549 735 735 1027 565 pelletized perlitic lightweight granules (Example 10/11/12) Inorganic / / / / 345 pelletized perlitic lightweight granules (Example 13) limestone 430 120 290 190 100 Natural coarse / 170 / / / aggregate Water 180 180 180 180 180 Superplasticizer 8.4 7.0 6.7 7.0 4.2 Viscosity / 0.5 / 0.5 / modifying agent Result 7-day 31.6 44.4 45.4 50.6 35.6 compressive strength (MPa) 28-day 40.9 51.4 53.4 68.9 45.2 compressive strength (MPa) Equilibrium 1695 1854 1847 1967 1765 density (kg/m.sup.3) Dry density / 1680 1672 / 1605 (kg/m.sup.3)

[0154] It is obvious that the above-mentioned embodiments of the present invention are merely examples to clearly illustrate the present invention, but not intended to limit the embodiments of the present invention. For those of ordinary skill in the art, other changes or modifications in different forms can be made on the basis of the above description. It is unnecessary and impossible to list all the implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.