DUAL-SCALE TOUGHENED CEMENT-BASED COMPOSITE MATERIAL AND USE THEREOF

Abstract

Disclosed are a dual-scale toughened cement-based composite material and use thereof. The cement-based composite material includes a cementitious material, a polymer monomer, an initiator, a crosslinking agent, and fibers, wherein functional groups of the polymer monomer include a carbon-carbon double bond and a carboxyl group; and the fibers include steel fibers and/or synthetic fibers, the synthetic fibers including one or more selected from the group consisting of polyvinyl alcohol fibers, polypropylene fibers, glass fibers, and carbon fibers.

Claims

1. A dual-scale toughened cement-based composite material, comprising a cementitious material, a polymer monomer, an initiator, a crosslinking agent, and fibers; wherein functional groups of the polymer monomer comprise a carbon-carbon double bond and a carboxyl group; and the fibers comprise steel fibers and/or synthetic fibers, the synthetic fibers comprising one or more selected from the group consisting of polyvinyl alcohol fibers, polypropylene fibers, glass fibers, and carbon fibers.

2. The dual-scale toughened cement-based composite material as claimed in claim 1, wherein the carboxyl group is replaced with a group that is hydrolysable into a carboxyl group.

3. The dual-scale toughened cement-based composite material as claimed in claim 1, wherein the polymer monomer comprises one or more selected from the group consisting of acrylamide monomers, acrylic polymer monomers, a butyl methacrylate monomer, an ethylene dimethacrylate monomer, and a hydroxyethyl methacrylate monomer.

4. The dual-scale toughened cement-based composite material as claimed in claim 1 or 2, wherein a mass ratio of the cementitious material to the polymer monomer is in a range of 100:(0.1-10), and the fibers account for 0.5-3 vol. % of the dual-scale toughened cement-based composite material.

5. The dual-scale toughened cement-based composite material as claimed in claim 1, wherein the steel fibers each have a diameter of 300-1200 m and a length of 20-120 mm; and the synthetic fibers each have a diameter of 5-100 m and a length of 3-40 mm.

6. The dual-scale toughened cement-based composite material as claimed in claim 1 or 2, wherein the initiator comprises one or more selected from the group consisting of persulfate, sulphite, an organic peroxide-ferrous salt system, a multi-electron transfer hypervalent compound-sulphite system, and a non-peroxide initiator; and a mass ratio of the polymer monomer to the initiator is in a range of 100:(0.5-5).

7. The dual-scale toughened cement-based composite material as claimed in claim 1, wherein the crosslinking agent is a polyamino crosslinking agent; and a mass ratio of the polymer monomer to the crosslinking agent is in a range of 100:(0.3-5).

8. The dual-scale toughened cement-based composite material as claimed in claim 7, wherein the crosslinking agent comprises one or more selected from the group consisting of N,N-methylenebisacrylamide, hexamethylenetetramine-hydroquinone, polyethyleneimine, p-phenylenediamine, and dimethylaminoethyl methacrylate.

9. The dual-scale toughened cement-based composite material as claimed in claim 1, wherein the cementitious material comprises cement.

10. The dual-scale toughened cement-based composite material as claimed in claim 1, further comprising an aggregate and/or an admixture.

11. The dual-scale toughened cement-based composite material as claimed in claim 10, wherein the aggregate comprises sand and/or gravels.

12. The dual-scale toughened cement-based composite material as claimed in claim 9 or 10 or 11, wherein a mass ratio of the cement to the aggregate is in a range of 1:(1-3).

13. The dual-scale toughened cement-based composite material as claimed in claim 10, wherein the admixture comprises silica fume and/or fly ash.

14. The dual-scale toughened cement-based composite material as claimed in claim 9 or 10 or 13, wherein a mass ratio of the admixture to the cement is not larger than 1.

15. The dual-scale toughened cement-based composite material as claimed in claim 6, wherein the persulfate comprises one or more selected from the group consisting of ammonium persulfate, potassium persulfate, and sodium persulfate.

16. The dual-scale toughened cement-based composite material as claimed in claim 6, wherein the sulphite comprises sodium sulphite and/or sodium bisulphite.

17. The dual-scale toughened cement-based composite material as claimed in claim 6, wherein the organic comprises tert-butyl peroxide-ferrous salt system hydroperoxide-ferrous sulfate.

18. The dual-scale toughened cement-based composite material as claimed in claim 6, wherein the multi-electron transfer hypervalent compound-sulphite system comprises sodium chlorate-sodium sulphite.

19. The dual-scale toughened cement-based composite material as claimed in claim 6, wherein the non-peroxide initiator comprises ammonium ceric nitrate-thiourea.

20. Use of the dual-scale toughened cement-based composite material as claimed in any one of claims 1 to 19 in building materials.

21. The use as claimed in claim 20, wherein the use comprises the steps of mixing the polymer monomer, the initiator, the crosslinking agent, and water to obtain an in-situ polymerization solution; mixing the cementitious material and the in-situ polymerization solution to obtain an in-situ polymerization modified cement-based slurry; mixing the in-situ polymerization modified cement-based slurry and the fibers to obtain a dual-scale toughened cement-based composite slurry; and pouring and curing the dual-scale toughened cement-based composite slurry.

22. The use as claimed in claim 21, wherein the dual-scale toughened cement-based composite slurry is prepared at a temperature of 0-60 C.

23. The use as claimed in claim 21, wherein a mass ratio of the cementitious material to water is in a range of 1:(0.35-0.4).

24. The use as claimed in claim 21, wherein mixing the cementitious material and the in-situ polymerization solution is performed by stirring, the stirring comprising a first stirring and a second stirring, wherein the first stirring is performed at an autorotation rate of 135-145 rpm and a revolution rate of 57-67 rpm for 1-3 min; and the second stirring is performed at an autorotation rate of 275-295 rpm and a revolution rate of 115-135 rpm for 60-120 s.

25. The use as claimed in claim 21, wherein mixing the in-situ polymerization modified cement-based slurry and the fibers is performed by stirring, the stirring being performed at an autorotation rate of 135-145 rpm and a revolution rate of 57-67 rpm for 1-5 min.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] FIG. 1 is a scanning electron microscope (SEM) image of the test specimen obtained in Comparative Example 2.

[0045] FIG. 2 is an SEM image of the test specimen obtained in Example 4.

[0046] FIG. 3 is an SEM image of the test specimen obtained in Example 4.

[0047] FIG. 4 is an SEM image of the test specimen obtained in Example 4 after soaking in 1 wt. % hydrochloric acid for 60 s.

[0048] FIG. 5 is an SEM image of the test specimen obtained in Example 4 after soaking in 1 wt. % hydrochloric acid for 60 s.

[0049] FIG. 6 is an SEM image of the test specimen obtained in Example 4 after soaking in 1 wt. % hydrochloric acid for 60 s.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0050] The present disclosure provides a dual-scale toughened cement-based composite material, comprising a cementitious material, a polymer monomer, an initiator, a crosslinking agent, and fibers: [0051] wherein functional groups of the polymer monomer include a carbon-carbon double bond and a carboxyl group; and [0052] the fibers include steel fibers and/or synthetic fibers, the synthetic fibers including one or more selected from the group consisting of polyvinyl alcohol fibers, polypropylene fibers, glass fibers, and carbon fibers.

[0053] In the present disclosure, unless otherwise specified, the components are each commercially available goods well known to those skilled in the art.

[0054] The dual-scale toughened cement-based composite material according to the present disclosure includes the cementitious material. In some embodiments of the present disclosure, the cementitious material comprises cement. In some embodiments of the present disclosure, the cement is ordinary Portland cement. In some embodiments of the present disclosure, a grade of the ordinary Portland cement is grade 32.5, grade 42.5 or grade 52.5.

[0055] In some embodiments of the present disclosure, the dual-scale toughened cement-based composite material further comprises an aggregate and/or an admixture.

[0056] In some embodiments of the present disclosure, the aggregate comprises sand and/or gravels. In the present disclosure, there is no particular limitation on sand, and sand well known to those skilled in the art may be used. In the present disclosure, there is no particular limitation on gravels, and gravels well known to those skilled in the art may be used. In some embodiments of the present disclosure, a mass ratio of the cement to the aggregate is in a range of 1:(1-3), and preferably 1:(1.5-2.5).

[0057] In some embodiments of the present disclosure, the admixture comprises silica fume and/or fly ash. In some embodiments of the present disclosure, a mass ratio of the admixture to the cement is not larger than 1.

[0058] The dual-scale toughened cement-based composite material according to the present disclosure includes the polymer monomer. In the present disclosure, functional groups of the polymer monomer include a carbon-carbon double bond and a carboxyl group. As an alternative technical solution, functional groups of the polymer monomer include a carbon-carbon double bond and a group that is hydrolysable into carboxyl group. In some embodiments of the present disclosure, the polymer monomer includes one or more of acrylamide monomers, acrylic polymer monomers, a butyl methacrylate monomer, an ethylene dimethacrylate monomer, and a hydroxyethyl methacrylate monomer. In some embodiments of the present disclosure, the acrylamide monomers include one or more of acrylamide, hydroxymethyl acrylamide, and N-isopropylacrylamide. In some embodiments of the present disclosure, the acrylic polymer monomers include sodium acrylate.

[0059] In some embodiments of the present disclosure, a mass ratio of the cementitious material to the polymer monomer is in a range of 100:(0.1-10), preferably 100:(1-7), and more preferably 100:(3-5).

[0060] The dual-scale toughened cement-based composite material according to the present disclosure includes the initiator. In some embodiments of the present disclosure, the initiator includes one or more of persulfate, sulphite, an organic peroxide-ferrous salt system, a multi-electron transfer hypervalent compound-sulphite system, and a non-peroxide initiator. In some embodiments of the present disclosure, the persulfate includes one or more of ammonium persulfate, potassium persulfate, and sodium persulfate. In some embodiments of the present disclosure, the sulphite includes sodium sulphite and/or sodium bisulphite. In some embodiments of the present disclosure, the organic peroxide-ferrous salt system comprises tert-butyl hydroperoxide-ferrous sulfate. In some embodiments of the present disclosure, the multi-electron transfer hypervalent compound-sulphite system includes sodium chlorate-sodium sulphite. In some embodiments of the present disclosure, the non-peroxide initiator includes ammonium ceric nitrate-thiourea.

[0061] In some embodiments of the present disclosure, a mass ratio of the polymer monomer to the initiator is in a range of 100:(0.5-5), preferably 100:(0.8-3), and more preferably 100:(1-2).

[0062] The dual-scale toughened cement-based composite material according to the present disclosure includes the crosslinking agent. In some embodiments of the present disclosure, the crosslinking agent is a polyamino crosslinking agent. In some embodiments of the present disclosure, the crosslinking agent includes one or more of N,N-methylenebisacrylamide, hexamethylenetetramine-hydroquinone, polyethyleneimine, p-phenylenediamine, and dimethylaminoethyl methacrylate.

[0063] In some embodiments of the present disclosure, a mass ratio of the polymer monomer to the crosslinking agent is in a range of 100:(0.3-5), preferably 100:(0.4-3), and more preferably 100:(0.5-2).

[0064] The dual-scale toughened cement-based composite material according to the present disclosure includes the fibers. In the present disclosure, the fibers include steel fibers and/or synthetic fibers, the synthetic fibers including one or more of polyvinyl alcohol fibers, polypropylene fibers, glass fibers, and carbon fibers.

[0065] In some embodiments of the present disclosure, the steel fibers each have a diameter of 300-1200 m. In some embodiments, the steel fibers each have a length of 20-120 mm. In some embodiments of the present disclosure, the synthetic fibers each have a diameter of 5-100 m. In some embodiments, the synthetic fibers each have a length of 3-40 mm.

[0066] In some embodiments of the present disclosure, the fibers account for 0.5-3 vol. %, preferably 1-2.5 vol. %, and more preferably 1.5-2 vol. % of the dual-scale toughened cement-based composite material.

[0067] The present disclosure also provides use of the dual-scale toughened cement-based composite material described in the above technical solutions in building materials.

[0068] In some embodiments of the present disclosure, the use comprises the steps of [0069] mixing the polymer monomer, the initiator, the crosslinking agent, and water to obtain an in-situ polymerization solution; [0070] mixing the cementitious material and the in-situ polymerization solution to obtain an in-situ polymerization modified cement-based slurry; [0071] mixing the in-situ polymerization modified cement-based slurry and the fibers to obtain a dual-scale toughened cement-based composite slurry, and [0072] pouring and curing the dual-scale toughened cement-based composite slurry.

[0073] In the present disclosure, the polymer monomer, the initiator, the crosslinking agent, and water are mixed to obtain an in-situ polymerization solution.

[0074] In some embodiments of the present disclosure, the dual-scale toughened cement-based composite slurry in said use is prepared at a temperature of 0-60 C., and preferably 0-40 C.

[0075] In some embodiments of the present disclosure, mixing the polymer monomer, the initiator, the crosslinking agent, and the water is performed by mixing the polymer monomer and the water to obtain a polymer monomer solution, and mixing the polymer monomer solution, the initiator and the crosslinking agent.

[0076] In the present disclosure, there is no particular limitation on the means for mixing the polymer monomer, the initiator, the crosslinking agent, and water, and any means well known to those skilled in the art may be used, such as stirring. In some embodiments of the present disclosure, the stirring is performed by magnetic stirring. In some embodiments, the stirring is performed for 5-10 min.

[0077] After obtaining the in-situ polymerization solution, the cementitious material and the in-situ polymerization solution are mixed to obtain an in-situ polymerization modified cement-based slurry.

[0078] In some embodiments of the present disclosure, a mass ratio of the cementitious material to water is in a range of 1:(0.35-0.4), preferably 1:(0.38-0.4), and more preferably 1:0.4.

[0079] In some embodiments of the present disclosure, mixing the cementitious material and the in-situ polymerization solution is performed by stirring. In some embodiments, the stirring comprises a first stirring and a second stirring. In some embodiments of the present disclosure, the first stirring is performed at an autorotation rate of 135-145 rpm. In some embodiments, the first stirring is performed at a revolution rate of 57-67 rpm. In some embodiments, the first stirring is performed for 1-3 min, and preferably 1.5-2.5 min. In some embodiments of the present disclosure, the second stirring is performed at an autorotation rate of 275-295 rpm. In some embodiments, the second stirring is performed at a revolution rate of 115-135 rpm. In some embodiments, the second stirring is performed for 60-120 s, and preferably 90-100 s.

[0080] In some embodiments of the present disclosure, the dual-scale toughened cement-based composite material further includes an aggregate and/or an admixture. In some embodiments, the aggregate and/or admixture are used at the same timing with that of the cementitious material.

[0081] In the present disclosure, after obtaining the in-situ polymerization modified cement-based slurry, the in-situ polymerization modified cement-based slurry and the fibers are mixed to obtain a dual-scale toughened cement-based composite slurry, and the obtained dual-scale toughened cement-based composite slurry is poured and cured.

[0082] In some embodiments of the present disclosure, mixing the in-situ polymerization modified cement-based slurry and the fibers is performed by adding the fibers to the in-situ polymerization modified cement-based slurry. In some embodiments of the present disclosure, mixing the in-situ polymerization modified cement-based slurry and the fibers is performed by stirring. In some embodiments, the stirring is performed at an autorotation rate of 135-145 rpm. In some embodiments, the stirring is performed at a revolution rate of 57-67 rpm. In some embodiments, the stirring is performed for 1-5 min, and preferably 2-3 min. In some embodiments of the present disclosure, the fibers adhered onto the mixing apparatus are scraped into the in-situ polymerization modified cement-based slurry.

[0083] In the present disclosure, there is no particular limitation on the pouring, and any pouring well known to those skilled in the art may be adopted. In some specific embodiments of the present disclosure, the dual-scale toughened cement-based composite slurry is subjected to molding, shaking, smoothing, covering with a film and demolding in sequence. In some embodiments of the present disclosure, the shaking is performed 30-90 times, preferably 50-70 times, and more preferably 60 times. In some embodiments of the present disclosure, the covering with a film is performed by using a film of a cling film. In some embodiments of the present disclosure, the covering with a film is performed for 24 h.

[0084] In some embodiments of the present disclosure, the curing is performed by a standard curing. In some embodiments, the standard curing is performed at a temperature of 18-22 C. In some embodiments, the standard curing is performed at a the humidity of not lower than 95%.

[0085] In order to further illustrate the present disclosure, a dual-scale toughened cement-based composite material according to the present disclosure and its use are described in detail below with reference to the following examples, which are not to be construed as limiting the scope of the present disclosure. Obviously, the described examples are only some but not all of the examples of the present disclosure. Based on the examples in the present disclosure, all other examples, which are obtained by those of ordinary skill in the art without inventive labor, should fall within the scope of the present disclosure.

Example 1

[0086] 45 g of acrylamide monomer and 600 g of water were stirred, obtaining a polymer monomer solution. The obtained polymer monomer solution, 0.6 g of ammonium persulfate and 0.3 g of N,N-methylenebisacrylamide were mixed, and magnetically stirred for 5 min, obtaining an in-situ polymerization solution.

[0087] 1500 g of ordinary Portland cement (P.O grade 42.5) and the in-situ polymerization solution were stirred first at an autorotation rate of 135-145 rpm and a revolution rate of 57-67 rpm for 2 min, and then at an autorotation rate of 275-295 rpm and a revolution rate of 115-135 rpm for 90 s, obtaining an in-situ polymerization modified cement-based slurry.

[0088] 7.2 g of polyvinyl alcohol fibers (having a diameter of 40 m and a length of 12 mm) were added to the obtained in-situ polymerization modified cement-based slurry. The resulting mixture was stirred at an autorotation rate of 135-145 rpm, and a revolution rate of 57-67 rpm for 2 min. The fibers adhered onto the mixing apparatus were scraped into the dual-scale toughened cement-based composite slurry. The stirring was continued for another 1 min. The dual-scale toughened cement-based composite slurry was molded, shaken for 60 times, smoothed, covered with a film for 24 h and demolded, and then subjected to standard curing at a temperature of 18-22 C. and a humidity of not lower than 95%.

[0089] In this example, the fibers accounted for 0.5 vol. % of the dual-scale toughened cement-based composite material: a mass ratio of the cementitious material (ordinary Portland cement) to the polymer monomer (acrylamide monomer) was 100:3; a mass ratio of the polymer monomer (acrylamide monomer) to the initiator (ammonium persulfate) was 100:1.33; and a mass ratio of the polymer monomer (acrylamide monomer) to the crosslinking agent (N,N-methylenebisacrylamide) was 100:0.67.

Example 2

[0090] Example 2 was performed according to the technical means as described in Example 1, except that 14.4 g of polyvinyl alcohol fibers were used.

[0091] In this example, the fibers accounted for 1 vol. % of the dual-scale toughened cement-based composite material; a mass ratio of the cementitious material (ordinary Portland cement) to the polymer monomer (acrylamide monomer) was 100:3; a mass ratio of the polymer monomer (acrylamide monomer) to the initiator (ammonium persulfate) was 100:1.33; and a mass ratio of the polymer monomer (acrylamide monomer) to the crosslinking agent (N,N-methylenebisacrylamide) was 100:0.67.

Example 3

[0092] Example 3 was performed according to the technical means as described in Example 1, except that 21.6 g of polyvinyl alcohol fibers were used.

[0093] In this example, the fibers accounted for 1.5 vol. % of the dual-scale toughened cement-based composite material: a mass ratio of the cementitious material (ordinary Portland cement) to the polymer monomer (acrylamide monomer) was 100:3; a mass ratio of the polymer monomer (acrylamide monomer) to the initiator (ammonium persulfate) was 100:1.33; and a mass ratio of the polymer monomer (acrylamide monomer) to the crosslinking agent (N,N-methylenebisacrylamide) was 100:0.67.

Example 4

[0094] Example 4 was performed according to the technical means as described in Example 1, except that 28.8 g of polyvinyl alcohol fibers were used.

[0095] In this example, the fibers accounted for 2 vol. % of the dual-scale toughened cement-based composite material: a mass ratio of the cementitious material (ordinary Portland cement) to the polymer monomer (acrylamide monomer) was 100:3; a mass ratio of the polymer monomer (acrylamide monomer) to the initiator (ammonium persulfate) was 100:1.33, and a mass ratio of the polymer monomer (acrylamide monomer) to the crosslinking agent (N,N-methylenebisacrylamide) was 100:0.67.

Example 5

[0096] Example 5 was performed according to the technical means as described in Example 1, except that 60 g of acrylamide monomer, 1 g of ammonium persulfate, 0.5 g of N,N-methylenebisacrylamide, and 28.8 g of polyvinyl alcohol fibers were used.

[0097] In this example, the fibers accounted for 1.7 vol. % of the toughened cement-based composite material: a mass ratio of the cementitious material (ordinary Portland cement) to the polymer monomer (acrylamide monomer) was 100:4: a mass ratio of the polymer monomer (acrylamide monomer) to the initiator (ammonium persulfate) was 100:1.33; and a mass ratio of the polymer monomer (acrylamide monomer) to the crosslinking agent (N,N-methylenebisacrylamide) was 100:0.67.

Example 6

[0098] Example 6 was performed according to the technical means as described in Example 2, except that 0.225 g of ammonium persulfate was used.

[0099] In this example, the fibers accounted for 1 vol. % of the dual-scale toughened cement-based composite material: a mass ratio of the cementitious material (ordinary Portland cement) to the polymer monomer (acrylamide monomer) was 100:3; a mass ratio of the polymer monomer to the crosslinking agent was 100:0.5: a mass ratio of the polymer monomer (acrylamide monomer) to the initiator (ammonium persulfate) was 100:0.5; and a mass ratio of the polymer monomer (acrylamide monomer) to the crosslinking agent (N,N-methylenebisacrylamide) was 100:0.67.

Example 7

[0100] Example 7 was performed according to the technical means as described in Example 2, except that 0.45 g of ammonium persulfate was used.

[0101] In this example, the fibers accounted for 1 vol. % of the dual-scale toughened cement-based composite material; a mass ratio of the cementitious material (ordinary Portland cement) to the polymer monomer (acrylamide monomer) was 100:3; a mass ratio of the polymer monomer to the crosslinking agent was 100:1: a mass ratio of the polymer monomer (acrylamide monomer) to the initiator (ammonium persulfate) was 100:1; and a mass ratio of the polymer monomer (acrylamide monomer) to the crosslinking agent (N,N-methylenebisacrylamide) was 100:0.67.

Example 8

[0102] Example 6 was performed according to the technical means as described in Example 2, except that 0.675 g of ammonium persulfate was used.

[0103] In this example, the fibers accounted for 1 vol. % of the dual-scale toughened cement-based composite material: a mass ratio of the cementitious material (ordinary Portland cement) to the polymer monomer (acrylamide monomer) was 100:3; a mass ratio of the polymer monomer to the crosslinking agent was 100:1.5; a mass ratio of the polymer monomer (acrylamide monomer) to the initiator (ammonium persulfate) was 100:1.5: a mass ratio of the polymer monomer (acrylamide monomer) to the crosslinking agent (N,N-methylenebisacrylamide) was 100:0.67.

Example 9

[0104] Example 6 was performed according to the technical means as described in Example 2, except that 0.9 g of ammonium persulfate was used.

[0105] In this example, the fibers accounted for 1 vol. % of the dual-scale toughened cement-based composite material; a mass ratio of the cementitious material (ordinary Portland cement) to the polymer monomer (acrylamide monomer) was 100:3; a mass ratio of the polymer monomer to the crosslinking agent was 100:2: a mass ratio of the polymer monomer (acrylamide monomer) to the initiator (ammonium persulfate) was 100:2: a mass ratio of the polymer monomer (acrylamide monomer) to the crosslinking agent (N,N-methylenebisacrylamide) was 100:0.67.

Example 10

[0106] Example 10 was performed according to the technical means as described in Example 2, except that the polyvinyl alcohol fibers have a diameter of 15 m.

[0107] In this example, the fibers accounted for 1 vol. % of the dual-scale toughened cement-based composite material: a mass ratio of the cementitious material (ordinary Portland cement) to the polymer monomer (acrylamide monomer) was 100:3; a mass ratio of the polymer monomer (acrylamide monomer) to the initiator (ammonium persulfate) was 100:1.33; and a mass ratio of the polymer monomer (acrylamide monomer) to the crosslinking agent (N,N-methylenebisacrylamide) was 100:0.67.

Example 11

[0108] Example 11 was performed according to the technical means as described in Example 2, except that hydroxymethyl acrylamide monomer was used to substitute acrylamide monomer in Example 2.

Comparative Example 1

[0109] 1500 g of ordinary Portland Cement (P.O grade 42.5) was added into a mixing pot, and stirred in a mortar mixer at an autorotation rate of 135-145 rpm and a revolution rate of 57-67 rpm for 2 min. 600 g of water was added thereto, and the resulting mixture was stirred at an autorotation rate of 135-145 rpm and a revolution rate of 57-67 rpm for 2 min, and then stirred at an autorotation rate of 275-295 rpm and a revolution rate of 115-135 rpm for 90 s. The resulting slurry was then molded, shaken 60 times, smoothed, covered with a film for 24 h, and demolded, and then subjected to standard curing at a temperature of 18-22 C., and a humidity of not lower than 95%.

[0110] In this comparative example, no polymer monomers, initiators, crosslinking agents and fibers were used.

Comparative Example 2

[0111] 1500 g of ordinary Portland cement (P.O grade 42.5) and 600 g of water were stirred at an autorotation rate of 135-145 rpm and a revolution rate of 57-67 rpm for 2 min, and then stirred at an autorotation rate of 275-295 rpm and a revolution rate of 115-135 rpm for 90 s, obtaining a cement-based slurry.

[0112] 28.8 g of polyvinyl alcohol fibers (having a diameter of 40 m and a length of 12 mm) were added to the cement-based slurry, and the resulting slurry was stirred at an autorotation rate of 135-145 rpm and a revolution rate of 57-67 rpm for 2 min. The fibers adhered onto the mixing device were scraped into the dual-scale toughened cement-based composite slurry. The stirring was continued for another 1 min. The resulting slurry was molded, shaken 60 times, smoothed, covered with a film for 24 h, and demolded, and then subjected to standard curing at a temperature of 18-22 C. and a humidity of not lower than 95%.

[0113] In this comparative example, no polymer monomers, initiators and crosslinking agents were used, and the fibers accounted for 2 vol. % of the cement-based composite material.

Comparative Example 3

[0114] 45 g of acrylamide monomer and 600 g of water were stirred, obtaining a polymer monomer solution. The obtained polymer monomer solution, 0.6 g of ammonium persulfate, and 0.3 g of N,N-methylenebisacrylamide were mixed and magnetically stirred for 5 min, obtaining an in-situ polymerization solution.

[0115] 1500 g of ordinary Portland cement (P.O grade 42.5) and the in-situ polymerization solution were stirred at an autorotation rate of 135-145 rpm and a revolution rate of 57-67 rpm for 2 min, then stirred at an autorotation rate of 275-295 rpm and a revolution rate of 115-135 rpm for 90 s. The resulting slurry was molded, shaken 60 times, smoothed, covered with a film for 24 h, and demolded, and subjected to standard curing at a temperature of 18-22 C., and a humidity of not lower than 95%.

[0116] In this comparative example, no fibers were used, and a mass ratio of the cementitious material (ordinary Portland cement) to the polymer monomer was 100:3; a mass ratio of the polymer monomer (acrylamide monomer) to the initiator (ammonium persulfate) was 100:1.33; and a mass ratio of the polymer monomer (acrylamide monomer) to the crosslinking agent (N,N-methylenebisacrylamide) was 100:0.67.

Comparative Example 4

[0117] 1500 g of ordinary Portland cement (P.O grade 42.5) and 600 g of water were stirred at an autorotation rate of 135-145 rpm and a revolution rate of 57-67 rpm for 2 min, and then stirred at an autorotation rate of 275-295 rpm and a revolution rate of 115-135 rpm for 90 s, obtaining a cement-based slurry.

[0118] 14.4 g of polyvinyl alcohol fibers (having a diameter of 40 m and a length of 12 mm) were added to the cement-based slurry. The resulting slurry was stirred at an autorotation rate of 135-145 rpm and a revolution rate of 57-67 rpm for 2 min. The fibers adhered onto the mixing device were scraped into the dual-scale toughened cement-based composite slurry. The stirring was continued for another 1 min. The resulting mixture was molded, shaken 60 times, smoothed, covered with a film for 24 h, and demolded, and then subjected to standard curing at a temperature of 18-22 C., and a humidity of not lower than 95%.

[0119] In this comparative example, no polymer monomers, initiators and crosslinking agents were used; and the fibers accounted for 1 vol. % of the cement-based composite material.

Comparative Example 5

[0120] 45 g of polyacrylamide, 600 g of water and 1500 g of ordinary Portland cement were stirred at an autorotation rate of 135-145 rpm and a revolution rate of 57-67 rpm for 2 min, and then at an autorotation rate of 275-295 rpm and a revolution rate of 115-135 rpm for 90 s, obtaining a polymer-modified slurry.

[0121] 14.4 g of polyvinyl alcohol fibers (having a diameter of 40 m and a length of 12 mm) were added to the polymer modified slurry. The resulting slurry was stirred at autorotation rate of 135-145 rpm, and a revolution rate of 57-67 rpm for 2 min. The fibers adhered onto the stirring device were scraped into the resulting toughened cement-based composite slurry. The stirring was continued for another 1 min. The toughened cement-based composite slurry was molded, shaken 60 times, smoothed and covered with a film for 24 h, and demolded, and then subjected to standard curing at a temperature of 18-22 C. and a humidity of not lower than 95%.

[0122] In this comparative example, the fibers accounted for 1 vol. % of the dual-scale toughened cement-based composite material: a mass ratio of the cementitious material (ordinary Portland cement) to the polymer (polyacrylamide) was 100:3: the polymer was polyacrylamide rather than one obtained from the in-situ polymerization of the monomer.

Comparative Example 6

[0123] 45 g of acrylamide monomer and 600 g of water were stirred, obtaining a polymer monomer solution. The polymer monomer solution, 0.6 g of ammonium persulfate and 0.3 g of N,N-methylenebisacrylamide were mixed and magnetically stirred for 5 min, obtaining an in-situ polymerization solution.

[0124] 1500 g of ordinary Portland cement (P.O grade 42.5) and 14.4 g of polyvinyl alcohol fibers (having a diameter of 40 m and a length of 12 mm) were stirred at an autorotation rate of 135-145 rpm and a revolution rate of 57-67 rpm for 3 min, obtaining a cement-based material-fibers dry material. The cement-based material-fibers dry material and the in-situ polymerization solution were stirred at an autorotation rate of 135-145 rpm and a revolution rate of 57-67 rpm for 2 min, and then at an autorotation rate of 275-295 rpm and a revolution rate of 115-135 rpm for 90 s, obtaining the dual-scale toughened cement-based composite slurry. The fibers adhered onto the stirring device were scraped into the dual-scale toughened cement-based composite slurry. The stirring was continued for another 1 min. The dual-scale toughened cement-based composite slurry was molded, shaken 60 times, smoothed, covered with a film for 24 h, and demolded, and then subjected to standard curing at a temperature of 18-22 C. and a humidity of not lower than 95%.

[0125] In this comparative example, the fibers accounted for 1 vol. % of the dual-scale toughened cement-based composite material; a mass ratio of the cementitious material (ordinary Portland cement) to the polymer monomer (acrylamide monomer) was 100:3: the cementitious material and the fibers were mixed first, and the resulting cement-based material-fibers dry material and the in-situ polymerization solution were mixed.

Comparative Example 7

[0126] Comparative Example 7 was performed according to the technical means as described in Example 2, except that 144 L of tetramethylethylenediamine instead of 0.3 g of N,N-methylenebisacrylamide was used.

[0127] In this comparative example, the fibers accounted for 1 vol. % of the toughened cement-based composite material: a mass ratio of the cementitious material (ordinary Portland cement) to the polymer monomer (acrylamide monomer) was 100:3; a mass ratio of the polymer monomer (acrylamide monomer) to the initiator (ammonium persulfate) was 100:1.33; and a mass ratio of the polymer monomer (acrylamide monomer) to the crosslinking agent (tetramethylethylenediamine) was 100:0.248.

Comparative Example 8

[0128] Comparative Example 8 was performed according to the technical means as described in Example 3, except that: 1.225 g of ammonium persulfate and 1.225 g of sodium sulphite were used as initiators instead of the ammonium persulfate mono-initiation system; and the crosslinking agent N,N-methylenebisacrylamide was used in an amount of 0.045.

[0129] In this comparative example, the fibers accounted for 1.5 vol. % of the toughened cement-based composite material: a mass ratio of the cementitious material (ordinary Portland cement) to the polymer monomer (acrylamide monomer) was 100:3; a mass ratio of the polymer monomer (acrylamide monomer) to the initiator (ammonium persulfate) was 100:2.5; a mass ratio of the polymer monomer (acrylamide monomer) to the initiator (sodium sulphite) was 100:2.5: a mass ratio of the polymer monomer (acrylamide monomer) to the crosslinking agent (N,N-methylenebisacrylamide) was 100:0.1.

[0130] The test specimens of Examples 1 to 11 and Comparative Examples 1 to 7 were subjected to flexural strength test according to GB/T 17671-1999 Method of testing cementsDetermination of strength (ISO method). The test results are shown in Table 1.

TABLE-US-00001 TABLE 1 Results of flexural strength test performed on test specimens of Example 1-11 and Comparative Examples 1-7 (MPa) 7 days 28 days Example 1 7.2 8.3 Example 2 8.4 10.3 Example 3 9.4 11.1 Example 4 12.2 14.3 Example 5 10.7 12.4 Example 6 7.2 8.4 Example 7 8.8 10.2 Example 8 9.8 11.6 Example 9 9.2 10.7 Example 10 7.4 8.7 Example 11 8.9 10.8 Comparative Example 1 4.8 5.6 Comparative Example 2 7.1 8 Comparative Example 3 7.5 8.5 Comparative Example 4 5.6 6.8 Comparative Example 5 6.6 7.5 Comparative Example 6 7.7 8.6 Comparative Example 7 6.8 7.9 Comparative Example 8 7.3 8.4

[0131] As can be seen from Table 1, the dual-scale toughened cement-based composite material according to the present disclosure has 7-day flexural strength of 7.2-12.2 MPa and 28-day flexural strength of 8.3-14.3 MPa, which shows an increase by 50-150% compared with the cement-based material without modifying substances (i.e., Comparative Example 1). That is to say, the flexural strength is greatly improved, and the toughness is excellent.

[0132] SEM was performed on the test specimens obtained in Example 4 and Comparative Example 2. The SEM images obtained are shown in FIGS. 1 to 6, wherein FIG. 1 is the SEM image of the test specimen obtained in Comparative Example 2, FIGS. 2 and 3 are the SEM images of the test specimen obtained in Example 4, and FIGS. 4 to 6 are the SEM images of the test specimen obtained in Example 4 after soaking in 1 wt. % hydrochloric acid for 60 s.

[0133] As can be seen from FIG. 1, when 2% polyvinyl alcohol fibers are used alone for modification, the fiber surface is relatively smooth with little hydration products attached.

[0134] As can be seen from FIGS. 2 and 3, the polymer obtained from the in-situ polymerization of acrylamide and the hydration product covers the fiber surface, which increases the bonding properties and interfacial strength between the fibers and the cement matrix. The in-situ polymerization and fibers act together and thus extremely improve the properties of the dual-scale toughened cement-based composite material, particularly the flexural strength.

[0135] As can be seen from FIGS. 4-6, the polymer produced by the in-situ polymerization is attached to the fiber surface and the polymer network produced through the in-situ polymerization can be clearly observed.

[0136] While the foregoing are merely preferred embodiments of the present disclosure, it should be noted that numerous modifications and variations can be made by those skilled in the art without departing from the principles of the present disclosure. These modifications and variations should be considered to be within the scope of the present disclosure.