GB1592788A

GB1592788A - Concrete body

Info

Publication number: GB1592788A
Application number: GB47970/77A
Authority: GB
Original assignee: Gschwend & Stadler Inst Privat
Current assignee: Gschwend & Stadler Inst Privat
Priority date: 1976-11-19
Filing date: 1977-11-17
Publication date: 1981-07-08
Also published as: ATA763077A; JPS5711869B2; ES237743Y; CS208737B2; BR7707630A; SE7712999L; AT374778B; FR2371394B1; DE2750711A1; ES237743U; ES464231A1; JPS5364233A; DE2750711C2; FR2371394A1; CH612462A5; SE422785B; IT1087288B; JPS56125508A; JPS6156727B2

Abstract

The concrete body consists at least partly of reflective concrete containing Portland cement, a hard filler, a pigment and crystal glass beads (E). The refractive index of the filler is at least approximately equal to that of the crystal glass beads. The particle size of the filler is smaller than that of the crystal glass beads. The crystal glass beads are approximately half exposed at the surface (D). Preferably the concrete body has a basic body (A) of normal grey concrete which is covered at least partly with a layer (B) of reflective concrete. In order to produce the concrete body, the dry components of the reflective concrete are mixed and water added. The resulting viscous mortar is either filled into a mould in an approximately 10 mm thick layer, the mould thoroughly vibrated and the concrete body pressed, or it is filled into a tubular hollow mould and moulded by centrifugal casting. After the concrete body is removed from the mould and allowed to harden, the surface of the crystal glass beads is exposed by etching with an acid. The concrete body can be used for reflective markings. <IMAGE>

Description

(54) CONCRETE BODY (71) We, INSTITUT FÚR PRIVATWIRTSCHAFT, GSCHWEND & BR< STADLER, a Swiss body corporate of Greifenstrasse 9, CH-9001 St. Gallen, Switzerland, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to reflective concrete, a process for its manufacture and its use for reflecting markings on road surfaces.

Safety on the roads is a requirement of our time which continues to arise. It is less tiring for car drivers to drive on light roads, thereby reducing the danger of accidents. This is also true of sufficient reflex-markings which reflect the light from headlamps. In Switzerland, two main types of road-surfaces are used, namely black asphalt and concrete.

Black asphalt surfaces are made from a mixture of heated bitumen and gravel, sand and stone chips. After surfacing, the roads have to be compacted with a road roller. At the beginning, asphalt surfaces are black, but lighten over the years to black-grey. They are black when wet.

Concrete is a mixture of portland cement, gravel, sand and water which hardens chemically after mixing and forms a building material. The colour is white; with age the concrete surface becomes white-grey. At night and when wet it remains light grey. The degree of lightening of a concrete road surface is about double that of an asphalt surface. The concrete surface has a service life 3- to 4times longer than the asphalt surface. The maintenance costs as opposed to the asphalt surface are respectively much lower. On the other hand, the costs for surfacing with concrete are much higher; but the additional expenditure is worthwhile which is why only concrete surfaces are used on motorways.

Reflecting signal markings are often used for marking centre lines, edge lines and pedestrian crossings. One can proceed by using a spray machine to spray a paint binding agent onto the road surface at the same time sprinkling it with fine glass balls. After sufficient drying, the markings produced in this way can be driven over. They light up brightly in the headlamps of a vehicle and are clearly visible at night. The disadvantage is that the service life of these markings is limited and, depending on the intensity of use of the road, they must be renewed at regular intervals. The costs for the repeated renewal are substantial if one considers the relatively short lifetime of the markings produced in this way. Therefore, permanent solutions have been sought for years.

Further, there are the "cats' eyes" which are especially produced in Switzerland and England and which can be built into concrete or asphalt surfaces.

One embodiment relates to a structure of electric steel castings which comprises lens systems held in moulding material on its two sides. Another embodiment relates to a casting with a built in rubber part with 2 reflecting-lenses on each side.

When driving over these latter cats' eyes, the rubber part is pushed down by the weight of the car; the lenses are cleaned of dust and dirt each time. The reflection effect of this type of signal device is very good but both products have the big disadvantage that they protrude I to 2 cms. from the road surface. These signal devices are dangerous for cars moving at high speeds, especially in icy, winter conditions. During snow clearance, the cats' eyes can be ripped out of their anchorage points in the road surface.

It has now been found that durable reflex-markings may be made of hard concrete and can be built into road surfaces, preferably concrete surfaces.

One aspect of our invention provides reflective concrete comprising white portland cement, a white quartz filler, titanium dioxide, and colourless crystal glass balls in an amount of 5070 /n by weight of the total mixture, the particle size of the filler being smaller than that of the crystal glass balls and a surface layer of said crystal glass balls being exposed to about half their depth on the surface of said reflective concrete.

The invention also provides a reflective concrete body of which at least part of the surface comprises reflective concrete as defined above. For example, a body of normal grey concrete may be at least partly covered with a layer of said reflective concrete.

The accompanying drawing illustrates in cross-section a reflective concrete body forming one embodiment of the present invention.

Referring now to the drawing, in the embodiment illustrated the concrete body has a base A of normal grey concrete which is at least partly covered with a layer of reflective concrete, generally being 8 to 10 mm thick. The filler is preferably quartz powder with the trigonal trapezohedral crystal structure of A- quartz, with a particle size of up to 0.5 mm, especially up to 0.2 mm and with a refractive index of at least 1.2, in particular 1.55. The colourless crystal glass balls have preferably a diameter of 0.2 to 0.6 mm, in particular 0.3 mm, and a refractive index of at least 1.55, in particular 1.55. The titanium dioxide (rutile) achieves an additonal lightening of the white portland cement.Titanium dioxide was shown to have a reflex reflective value 15% higher than that of e.g. magnesium oxide at an observation angle 6f 20 degrees, when used in a test of reflex reflectors. This value is due to the fact that the mirror reflection component is higher in titanium dioxide than in magnesium oxide. The addition of titanium dioxide in relation to the amount of portland cement, should not exceed 5%.

The reflective concrete of our invention may be made by the steps of (a) thoroughly mixing said portland cement, filler, pigment and crystal glass balls in a dry condition, and adding sufficient water to form a thick mortar; (b) casting this mortar in a mould to form a concrete body; and (c) etching a surface of said concrete body to expose a layer of the crystal glass balls by treatment with an acid, preferably with phosphoric acid.

By compressing the reflective cement body with a pressure of at least 300 kg/cm2, a very compact bonding between the crystal glass balls, portland cement, filler and the pigment is obtained. The reflective concrete is normally vibrated before compression so that about 40 to 50 uniformly packed layers of crystal glass balls are contained in an approximately 10 mm thick layer of reflective concrete.

This has the advantage that by abrasion of the first layer of glass balls, the next layer is exposed.

The reflective concrete bodies according to the invention are very weatherresistant and are easily produced and installed in concrete road surfaces. They can be manufactured by mass-production on fully and semi-automatic production installations. Normally slabs of 3 to 4 cm thickness are produced. But one can also produce cylindrical bodies, e.g. tubes, by centrifugal casting or compression moulding techniques. For the production of central or edge lines, one can use for example slabs with a width of about 10 cm which can be installed in concrete road surfaces end to end or at intervals as markings. The slabs are conveniently installed flat and evenly into the surface so that there are no protruding parts which could cause blows to the vehicles driving over them.

Measurements of white reflective concrete have shown that the reflex reflectivity at an angle of incidence of light from 0 to 50 degrees does not substantially change. It has also been determined that the reflex reflectivity of dry, reflective concrete is 75 times stronger than that of dry, grey concrete. When wet, the reflective concrete still reflects 42 times more strongly than normal grey concrete. The loss of reflex reflectivity in a wet condition mainly depends on the type of wetting.

The layer of reflective concrete can, for example, have the following composition: Range: Preferably: Crystal glass balls 50 to 70% 60% Trigonal trapezohedral quartz powder, refractive index 1.55 10 to 30 /n 20% White portland cement 15 to 25 /n 18own Titanium dioxide 1.5 to 4.5 /n 2% 100% For the production of a reflective concrete body according to the invention, one can proceed as follows: The mixture of the above mentioned components is firstly thoroughly mixed in a dry condition in a forced circulation mixer and then the necessary quantity of water is added until a thick mortar is formed.

This is filled into steel forms at a thickness of about 10 mm to produce slabs in slab-producing machines. The steel form can also have a lining of rubber or hydrophobic plastic. The form is then thoroughly vibrated whereby the glass balls contained in the mortar are evenly arranged at the bottom of the form. Then normal, grey concrete (core-concrete) is filled into the form and thoroughly vibrated again and compressed at 300 kg per cm2. The slabs can be removed from the forms and stored in rows immediately. The full hardening time is 29 to 30 days.

The slabs thus removed from the forms do not yet show any reflective effect because the cement-mixture still covers the top layer of the glass balls (point C in the drawing). The slabs or moulded pieces are now immersed in a 9% solution of phosphoric acid. This corrodes the surface of the white cement. The duration of the corrosion of the surface depends on the diameter of the crystal glass balls. The corrosion should go so far until at least 50 /n of the top layer of glass balls is still anchored in the concrete, as shown in the drawing at D. With a corrosion period of about 14 to 15 minutes, the top layer with crystal glass balls of 0.3 mm diameter is so exposed that good 50 /n of the top glass balls are still anchored in the concrete.

For crystal glass balls with a diameter of 0.6 mm, the exposure of the surface takes about twice as long. The slabs are cleaned under running water with a hard brush to remove cement remains. The reflective layer can now develop its effectiveness (point F of the drawing) in that it is now able to reflex reflect the light from car headlamps, whereby an optimum reflex reflection is obtained for a reflective concrete body mounted in road surfaces at an angle of incidence of light of 20 degrees. But even at an angle of incidence of light of for example 50 degrees, excellent results are obtained. This means that the material also shows excellent reflex reflectivity when standing upright.

The reflective concrete bodies according to the invention have very good frost-resistance as well as bending tensile and compressive strengths. They are suitable, amongst others, for the following ranges of application.

a) Road traffic: Dividing lines in the road surface, bicycle lines in the road surface, pedestrian crossings in the road surface, curb stones, gutters, sign-posts, curve-posts, pavement edges, marking stones before rail crossings, markings on road and rail tunnels, markings on bridges, markings for stands of traffic police, portable marking stones for building sites and accident spots.

b) Rail traffic: Marking of network signals, line signals, point indicators, marking of railway crossings and tunnel entrances.

c) Sea traffic: Marking of harbour piers, bridge piers, harbour dams, landing steps, landing places.

d) Air traffic: Marking of landing strips and run-ways, signalization of airports in the military range (night-landings on unlit strips, whereby the reflective concrete markings can be seen only by the pilot in the plane's headlamps), marking of danger zones.

e) As an advertising or decorative display, utilizing a stationary or rotating source of light.

Claims

WHAT WE CLAIM IS:

1. Reflective concrete comprising white portland cement, a white quartz filler, titanium dioxide, and colourless crystal glass balls in an amount of 5070 /^ by weight of the total mixture, the particle size of the filler being smaller than that of the crystal glass balls and a surface layer of said crystal glass balls being exposed to about half their depth on the surface of said reflective concrete.

2. Reflective concrete according to claim I, wherein said filler is quartz powder with the trigonal trapezohedral crystal structure of quartz having a refractive index of 1.55.

3. Reflective concrete according to claim 1 or 2 wherein the narticle si7e nf said filler does not exceed 0.5 mm.

4. Reflective concrete according to claim 3 wherein the particle size of said filler does not exceed 0.2 mm.

5. Reflective concrete according to any of the preceding claims wherein said crystal glass balls have a diameter in the range of 0.2 to 0.6 mm.

6. Reflective concrete according to claim 5 wherein said crystal glass balls have a diameter of at least 0.3 mm.

7. Reflective concrete according to any of the preceding claims comprising, by weight, 5C70% of colourless crystal glass balls; 10--30 trigonal trapezohedral quartz powder of refractive index 1.55; 1525 /n white portland cement; and 1.54.5% titanium dioxide.

8. Reflective concrete according to claim 7 comprising, by weight, about 60 / of colourless crystal glass balls; about 20% trigonal trapezohedral quartz powder of refractive index 1.55; about 18% white portland cement; and about 2% titanium oxide.

9. Reflective concrete according to claim 1, substantially as hereinbefore described.

10. Reflective concrete, substantially as illustrated in the accompanying drawing.

11. A reflective concrete body of which at least part of the surface comprises reflective concrete according to any of the preceding claims.

12. A reflective concrete body according to claim 11 comprising a portion of normal grey concrete which is at least partly covered with a layer of said reflective concrete.

13. A reflective marking especially on or adjacent a roadway, comprising a reflective concrete body according to claim 11 or 12.

14. An advertising or decorative display comprising a reflective concrete body according to claim 11 or 12 and a stationary or rotating source of light.

15. A process for the manufacture of reflective concrete according to any of claims 1-10 comprising the steps of (a) thoroughly mixing said white portland cement, white quartz filler, titanium dioxide and colourless crystal glass balls in a dry condition, and adding sufficient water to form a thick mortar; (b) casting this mortar in a mould to form a concrete body; and (c) etching a surface of said concrete body to expose a layer of the crystal glass balls by treatment with an acid.

16. A process according to claim 15 wherein said mortar is vigorously vibrated and compressed in said mould.

17. A process according to claim 16 wherein said mortar is compressed at a pressure of about 300 kg/cm2.

18. A process according to claim 15 wherein said mortar is cast by a centrifugal casting process.

19. A process according to any of claims 15-18 wherein said acid comprises phosphoric acid.

20. A process according to any of claims 15-19 wherein normal grey concrete is also cast in contact with said mortar to form a concrete body having a reflective surface layer.

21. A process according to claim 15, substantially as hereinbefore described.