DRY PREMIXTURE FOR FLEXIBLE CONCRETE AND METHOD FOR ITS PREPARATION AND USE THEREOF

Abstract

The invention relates to a cementitious powder blend comprising, based on total weight—45-90 wt % Portland cement; pref. 50-80 wt %—0-25 wt % siliceous fly ash; pref. 5-20 wt %—0-25 wt % limestone; pref. 5-20 wt %—5-30 wt % polyvinylalcohol, pref. 5-15 wt %. The PVA preferably has—a size distribution with D.sub.10=170-270 μm, D50=370-450 μm. D.sub.90=690-850 μm and D.sub.100=1000-1300 μm; and—an ester value in the range of 1-250 mg KOH/g, as determinable by EN-ISO 3681:1998 and/or wherein the polyvinyl alcohol has a viscosity of a 4% aqueous solution at 20° C. in the range of 1-40 mPa.Math.s, as determinable by EN-ISO 12058-1:2002. A substantial part of the PVA may be present in the form of hybrid particles composed of Portland cement and the polyvinylalcohol. Further, the invention relates to concrete composed of the cementitious powder blend, water and aggregate as well as flexible concrete products made therefrom. The cementitious powder blend is used for—for the preparation of a paving of a road or other infrastructural element; for the preparation of a base course for a road or other infrastructural element; for the manufacture of a floor of a building; for the repair of a concrete structure; for grouting; or—as an injection into a concrete structure.

Claims

1. A cement powder blend comprising, based on total weight 45-90 wt. % Portland cement; 0-25 wt. % siliceous fly ash; 0-25wt. % limestone; and 5-30wt. % polyvinylalcohol.

2. The cement powder blend according to claim 1, wherein the polyvinylalcohol has a size distribution with D.sub.10=170-270 μm, D.sub.50=370-450 μm, D.sub.90=690-850 μm and D.sub.100=1000-1300 μm.

3. The cement powder blend according to claim 1, wherein the polyvinyl alcohol has an ester value in the range of 1-250 mg KOH/g, as determinable by EN-ISO 3681:1998.

4. The cement powder blend according to any of the preceding claims claim 1 comprising 50-80 wt. % Portland cement; 5-20 wt. % siliceous fly ash; 5-20 wt. % limestone; and 5-15 wt. % polyvinylalcohol.

5. A method for preparing a cement powder blend according to claim 1, comprising dry-blending the polyvinylalcohol, the Portland cement, the fly ash and the limestone.

6. A construction slurry of the cement powder blend according to claim 1 and water in a weight to weight ratio water to the Portland cement in the range of 0.2-0.7.

7. The construction slurry according to claim 6, wherein the construction slurry is a cement slurry.

8. A hardened construction cement slurry of the cement powder blend according to claim 1.

9. The hardened construction cement slurry according to claim 8, wherein at least a substantial part of the polyvinyl alcohol is present in the form of hybrid particles composed of Portland cement and polyvinylalcohol.

10. The hardened construction cement slurry according to claim 8, having an expansion of 0-25% determined with sample length measurements during curing at 60° C.

11. The hardened construction cement slurry according to claim 8, having a stiffness of 0.5-1.5 N/mm.sup.2 measured by means of direct tensile strength at 28 days.

12. Concrete composed of a cement powder blend according to claim 1, aggregate and water.

13. Concrete according to claim 12, comprising 6-24% wt. of the cement powder blend of claim 1; 4-16% wt. water; 20-50 wt. % fine aggregates (0-4 mm); 35-60 wt. % coarse aggregates (4-20 mm); with the proviso that the total aggregate content is 60-90 wt. %.

14. A product, comprising concrete according to claim 12.

15. The product according to claim 14, wherein the product is selected from the group consisting of infrastructural elements, such as roads, parking terrains, airplane-landing strips, railway embankments, sound barrier walls and sewers; buildings, such as parking garages, industrial buildings, storage halls, retail centers, residential buildings; concrete ware, such as concrete pipes; and elements for pre-fab buildings, such as pre-fab walls, pre-fab floors, pre-fab ceilings.

16. The product according to claim 15, wherein the product is a building, comprising a floor made of said concrete.

17. (canceled)

18. The cement powder blend according to claim 3, wherein the polyvinyl alcohol has an ester value in the range of 7-150 mg KOH/g.

19. The cement powder blend according to claim 18, wherein the polyvinyl alcohol has an ester value in the range of 7-10 mg KOH/g.

20. The cement powder blend according to claim 18, wherein the polyvinyl alcohol has an ester value in the range of 130-150 mg KOH/g.

21. The cement powder blend according to claim 1, wherein the polyvinyl alcohol has a viscosity of a 4% aqueous solution at 20° C., as determinable by EN-ISO 12058-1:2002, in the range of 1-40 mPa.Math.s.

Description

EXAMPLE 1

Formulation with Low Shrinkage

[0053] A formulation with 20 wt. % of polyvinyl alcohol with ester value of 8 mg KOH/g, viscosity 28 mPa.Math.s (of a 4% solution in water at 20 ° C.) and D.sub.10=233 μm, D.sub.50=440 μm, D.sub.90=767 μm and D.sub.100=1132 μm combined with 80% CEM I 42.5 cement was prepared. The resultant powder blend was mixed with water (in a weight to weight ratio water to powder blend of 0.6) to form a cement slurry (cement paste) at 60° C. The mixture was fully sealed and with water on the surface and cured. Shrinkage of the hardened cement slurry was determined by means of length change measurements using a micrometer. The results of the test are presented at FIG. 1. Results for a composition according to the invention (top) are compared with the results of CEM I 42.5 (bottom).

EXAMPLE 2

Formulation with Low Stiffness

[0054] A formulation with 7 wt. % of polyvinyl alcohol with ester value of 8 mg KOH/g, viscosity 28 mPa.Math.s (of a 4 (N) solution in water at 20 ° C.) and D.sub.10=233 μm, D.sub.50=440 μm, D.sub.90=767 μm and D.sub.100=1132 μm combined with 60 wt. % cement CEM I 42.5, 19 wt. % limestone and 14 wt. % fly ash was prepared. The resultant powder blend was mixed with water (in a weight to weight ratio water to powder blend of 0.6) to form a cement slurry (cement paste) at 20° C. The mixture was fully sealed with water on the surface and cured . up to 28 days. Then the direct tensile strength of the hardened cement slurry was determined (following AASHTO T314-07) and stiffness was calculated from the strain-stress diagrams. The results of the test are presented at Table 1 and compared with the results of CEM I 42.5.

TABLE-US-00001 TABLE 1 Results of stiffness calculation E (N/mm.sup.2) Std CEM I 42.5 1.520 0.11 Formulation with PVA 0.891 0.09

Example 3

Demonstration of Physical Bond Between Cement Calcium Phases and Polyvinyl Alcohol

[0055] A formulation with 7 wt. % of polyvinyl alcohol with ester value of 8 mg KOH/g , viscosity 28 mPa.Math.s (of a 4% solution in water at 20 ° C.) and D.sub.10=233 μm, D.sub.50=440 μm, D.sub.90=767 μm and D.sub.100=1132 μm combined with 60 wt. % cement CEM I 42.5, 19% limestone and 14 wt. % fly ash was prepared. The sample was cured after mixing at 60° C. with water (in a weight to weight ratio water to powder blend of 0.6) and fully sealed with water on the surface up to 28 days.

[0056] Then the cured sample was examined by means of SEM microscopy. The results are presented in FIGS. 2A and 2B. What is noticed is that there are portlanclite phases bound with polymer phases.

Example 4

Comparison of Cement Paste According to the Invention with a Standard Cement Paste on Properties Relevant for Paving Application

[0057] Direct tensile strength (AASHTO T314-07) tests were performed after 28 days of water curing.

[0058] Stiffness was determined by means of four point bending test (NEN-EN 12697-26) on concrete samples after 28 days of water curing for three different temperatures T=−10, 5 and 20° C. The test were performed on 50×50×450 mm prisms.

[0059] Fatigue was measured by means of four point bending (NEN-EN 12697-24) on concrete samples at 30 Hz, using different strain levels (90,120,180 and 210 microstrain) at 20° C. The tests were performed on 50×50×450 mm prisms.

[0060] Leutner shear test was performed on asphalt—concrete samples for two different temperatures according to standard prEN 12697-48:2011 after 28 days of water curing. Test samples were made by casting 6 cm concrete on an asphalt concrete plate and using cores of 10 cm diameter from the combination plate for the test.

[0061] Compressive and bending strength was measured on standard cement mortars according to EN 196-1 after 1, 2, 7 and 28 days. The strain-stress diagrams were acquired and stiffness was calculated.

[0062] Table 2 shows the Average Results of the direct tensile strength test.

TABLE-US-00002 TABLE 2 Tensile dL at strength Fmax Stiffness (MPa) (mm) (N/mm2) Reference 2.16 0.12 1.4 cement paste according to 2.20 0.26 0.8 the invention (flexible paste)

[0063] The results show that cement paste according to the invention exhibits lower stiffness while it can elongate (dL) more than twice as the reference cement paste before failure occurs. This is an indication that the material has a ductile fracture behaviour, which behaviour was confirmed by a plotting a force-displacement diagram (FIG. 3, reference at the left, flexible paste according to the invention at the right).

[0064] The diagram in FIG. 4 shows the stiffness-temperature dependency at 8 Hz (reference=top line, concrete according to the invention=bottom line) using the 4 point bending test. The dependency between stiffness and temperature is higher compared to conventional concrete with a difference of approximately 1800 MPa between low temperature (−10° C.) and high temperature (20° C.). Compared to asphalt, the stiffness of a concrete according to the invention varies less as a function of temperature a lower dependency on temperature. In this respect it can thus can be seen as a product category on its own.

[0065] An interesting aspect describing the behaviour of the flexible concrete according to the invention in fatigue is that there was an initial drop in stiffness after only a few cycles. Thereafter the samples endured many more cycles until the test was stopped without significant change in stiffness. The sample after this test was intact and no cracks were detected. This behaviour is illustrated for a sample tested at 120 micro-strain in FIG. 5.

[0066] The Leutner shear test results showed an average shear strength of 2.01 MPa at 10° C. and of 1.53 MPa at 20° C. The two layers had a good adhesion and the shear strength was higher than the requirement for thin coating; i.e. a tensile strength at 10° C. of 1.5 MPa.

[0067] In summary, from the results of the various tests it was concluded that a flexible concrete according to the invention (made using a powder blend according to the invention) has a ductile behaviour in all different mixes tested: paste, mortar and concrete. This property distinguishes the flexible concrete from normal concrete mixes. The ductility presented can have an effect in how a road is constructed and allow for less or no joints that will increase driving comfort. This property will not compromise the environmentally friendly aspect of concrete roads as the material remains a cement based material.

[0068] Another important property of the flexible concrete is that the ductility is not directly connected to its strength which allows strength optimization without sacrificing the ductile character. This is also not common for normal concrete where there is a relationship between mechanical properties and elasticity. The flexible concrete presented an excellent fatigue performance which indicates that a pavement can withstand a lot of cycles of loading and unloading before failure occurs. This means that the flexible concrete has good durability allowing less repairs. A combination of this property with high durability expected due to cementitious character of the flexible concrete makes it an excellent option for pavements.

[0069] The stiffness of the flexible concrete lies in the area of asphalt instead in that of concrete and there is some dependency with temperature and frequency but it is less strong than for asphalt. This means that Flexible concrete will be less sensitive to temperature variation.

[0070] Usage of this material can vary as it has a good affinity both with concrete and with asphalt. This would allow usage in different pavement layers on top of already existing layers as a combination layer or even as a repair material.