GB2389583A

GB2389583A - Resilient paving blocks

Info

Publication number: GB2389583A
Application number: GB0306411A
Authority: GB
Inventors: Bruce Alexander Cook
Original assignee: BRUCE COOK ROAD PLANING Ltd
Current assignee: BRUCE COOK ROAD PLANING Ltd
Priority date: 2002-03-20
Filing date: 2003-03-20
Publication date: 2003-12-17
Anticipated expiration: 2023-03-20
Also published as: GB0306411D0; GB0206553D0; GB2389583B

Abstract

A resilient paving block is formed form a mixture of aggregate and a foamed bitumen binder. The foamed bitumen if formed by spraying hot bitumen 14 into an expansion chamber 1 into which cold water 16 and compressed air are also sprayed. The foamed material is then mixed with aggregate, pressed and cured. At around 60 {C for about 72 hours. In a preferred embodiment, the aggregate comprises recycled asphalt planings. An additive to accelerate structural stiffness gain may be added, ideally this is a pozzolanic binder chosen from Portland cement, pulverised fuel ash or quicklime. Colouring agents may also be added.

Description

1 A Block and a Method For Making Blocks 3 This invention relates to a

block and to a method of 4 making blocks and particularly but not exclusively 5 to a flexible block and to a method of making 6 relatively flexible blocks to be used as paving 7 stones using a high proportion of recycled 8 materials.

10 Conventional concrete blocks are used in a number of 11 paving applications such as foot paths, cycle ways, 12 decorative areas and driveways. Typically, cement 13 is used to bind the aggregate used in concrete 14 blocks and although adequate, such blocks are 15 susceptible to cracking, deformation and rutting and 16 can be brittle particularly if point loads are 17 applied. Moreover, known blocks typically do not 18 comprise a significant proportion of recycled 19 materials because of the high costs traditionally 20 associated with recycling and variability of quality 21 of recycled feed aggregate.

r 1 According to the present invention there is provided 2 a method of making a block, the method comprising 3 the steps of: 4 providing an aggregate material; 5 adding a foamed binder to said aggregate 6 material; 7 forming a block from the combination of said 8 aggregate material and foamed binder.

10 Preferably, the method also includes the step of ll curing the block. Preferably, the curing involves 12 heating a block to a temperature in the range of 13 20 C to 100 C preferably 60 C for a period in the 14 range of 12 to 90 hours, preferably 72 hours.

15 Preferably, the block is cured by placing them in an 16 air convection tunnel. Typically, moisture is 17 substantially driven out of the block during the 18 curing step.

20 Preferably, the method includes the step of 21 compacting the combination of said aggregate 22 material and foamed binder. Preferably, the 23 compacting is performed by a vibratory press.

25 Preferably, the block is used as a paving surface 26 material.

28 Preferably, the method includes providing a means to 29 disperse the binder into microscopic bubbles which 30 attach to the aggregate, or more preferably the 31 fines in the aggregate.

( l Preferably, the binder is dispersed into microscopic 2 bubbles by adding cold water to the binder and more 3 preferably by adding cold water and compressed air 4 to the binder.

6 Most preferably, the air in the bubbles is driven 7 out by the compacting step.

9 According to a second aspect of the present 10 invention there is provided a resilient paving 11 block.

13 Preferably, the block according to the second aspect 14 to the invention is formed by the method according 15 to the first aspect of the invention.

17 Preferably, the block comprises at least 90wt% 18 aggregate and a binder.

20 Preferably, the block comprises up to 5wt% binder.

22 Preferably, the block comprises 2.5wt' - 3.5wt% 23 binder.

25 Optionally, further additives are added to the block 26 to aid accelerate structural stiffness gain and aid 27 effective curing. The additives may be a pozzolanic 28 binder such as 1-2wt% ordinary Portland cement, 5 29 10wti pulverized fuel ash or quicklime.

( 1 Preferably, the block comprises about 96wt% 2 aggregate. Preferably, the block comprises 1-4wt% 3 bitumen.

5 Preferably, the aggregate is recycled aggregate.

6 Preferably, the aggregate is recycled asphalt 7 planings although other recycled aggregates may be 8 used. Preferably' the block comprises 9096wt% 9 aggregate.

11 Preferably, the aggregate does not exceed 8mm 12 nominal size, that is, the aggregate will preferably 13 pass through an 8mm screen mesh. Preferably the 14 aggregate is relatively cold and relatively damp 15 before the binder is added.

17 Preferably the binder is a bitumen, and more 18 preferably the block comprises 1-4wt% bitumen.

20 Optionally a pozzolanic binder is added to the 21 block. For such embodiments the block may comprise 22 1-12wtt pozzolanic binder. The pozzolanic binder 23 may be ordinary Portland cement, pulverized fuel ash 24 or quicklime.

26 Optionally, the block is coloured by addition of any 27 suitable colouring pigment, preferably red, yellow 28 or black pigments.

30 Most preferably, the block comprises 88wt% recycled 31 asphalt planings, 3wt% bitumen and 2wt% ordinary 32 Portland cement blend and 7% pulverized fuel ash.

r 2 An embodiment of the invention will now be described 3 by way of example only with reference to the 4 accompanying drawing in which: 5 Fig. 1 is a diagrammatic view of an expansion 6 chamber that mixes water with bitumen to make 7 foamed bitumen.

9 Foamed bitumen has been used previously as a base 10 material for roads as described in the operating 11 manual for a Wirtgen KMA 150 mixing plant the 12 disclosure of which is incorporated herein by

13 reference.

15 With reference to Fig. 1, hot bitumen 12 flows into 16 the expansion chamber 1 through an upper inlet 14 17 while cold water is sprayed into the chamber 1 via a 18 side inlet 16. Compressed air is also injected into 19 the chamber 1 via a second side inlet (not shown).

20 Typically the chamber 1 will be pressurized to 21 30psi.

23 The bitumen 12 contacts the cold water and under the 24 pressurised conditions produces a bitumen foam for 25 6-7 seconds. The bitumen foam comprises millions of 26 microscopic bubbles 10 which attach to fines in the 27 aggregate (not shown). The foamed bitumen is 28 sprayed out from outlet 18 onto the aggregate in a 29 twin pugmill mixing chamber (not shown).

31 The mixture is then shaped and compacted using a 32 vibratory press (not shown) into individual blocks,

1 typical dimensions of which may be 200mm to 220mm in 2 length by 90mm to llOmm in width by 60mm to lOOmm in 3 height. An example of a suitable hydraulic press is 4 a Shlosser7 Block press and an example of a suitable 5 mechanical press is an Atlas 5507U press. When the 6 blocks are compacted, the air is driven out of the 7 bubbles causing the bitumen to form a mortar with 8 the fines which squeezes onto the coarse aggregate 9 causing the material to set relatively solid.

11 To determine the optimum curing temperature of the 12 blocks, a sample of around 30kg of the mixture was 13 made into twelve blocks as described above. Three 14 blocks were air cured, three were oven cured at 15 40 C, three were oven cured at 60 C and three were 16 oven cured at 80 C. The preferred curing 17 temperature was found to be 60 C.

19 The blocks may also be cured by exposing them to 20 ambient temperatures (in the range of 12-20 C) for 21 six to seven days.

23 The blocks are then preferably cured by placing them 24 in a convection tunnel (not shown) which raises a 25 temperature to 60 C for approximately 72 hours in a 26 tunnel of 12x4m. The moisture contained in the 27 blocks is thus driven out.

29 Certain embodiments of the block may be cured for 1 30 48 hours at temperatures ranging from ambient up to 31 80 C.

( 1 Optionally a pozzolanic binder such as 1-2wtt 2 ordinary Portland cement, 5-8wt% pulverized fuel ash 3 or quicklime is added in order to accelerate the 4 stiffness gained to aid curing rather than to bind 5 the aggregate. These binders hydrate the excess 6 moisture from the blocks and combine with the foamed 7 bitumen to form a strong mortar binding the 8 aggregates together.

10 The aggregate is recycled asphalt planings such as 11 that recovered from the resurfacing of motorways, 12 national road network or private roads/car parks 13 although it could be made from bituminous planings, 14 crushed concrete, brick rubble or any other suitable 15 material.

17 The grain size of the aggregate should be no larger 18 than 8mm, and be well graded from 0.075mm to 8mm.

19 The feedstock aggregate grading of a preferred 20 embodiment falls within the following specification

21 limits Sieve Size (mm) % Passing 10.0 100

8.0 75 - 100

6.3 68 - g5 5.0 60 - 88

3.35 46 - 74

1.18 28 - 51

0.60 20 - 35

- - 0.30 15 - 25

_ _ _ 0.075 10 - 20

_

( 1 The particle size distribution of the aggregate is 2 determined by the washing and sieving method as 3 detailed in British Standard 812, Part 103.

5 The curing will also serve to reinvigorate the added 6 bitumen.

8 The block may be coloured by addition of colouring 9 agents such as red, yellow or black pigments.

11 In preferred embodiments, the blocks contain 88wt% 12 recycled asphalt planings, 7wt% pulverized fuel ash, 13 3wt% foamed bitumen and 2wt% ordinary Portland 14 cement blend. Utilising less bitumen could cause 15 the blocks to crumble and be friable whereas a 16 higher proportion of bitumen may render the block 17 malleable and lack resistance to permanent 18 deformation.

20 To determine the optimum fluid content, four samples 21 were prepared at a range of moisture content but 22 with the same added foamed bitumen. The samples 23 were measured after being compacted to determine the 24 combined moisture and foamed bitumen content giving 25 the maximum dry compacted density.

27 In more preferred embodiments, the block comprises 28 6wt% water making a total fluid content of Dwt% (6% 29 water and 3% bitumen.) Certain other embodiments 30 can have between 4-8% water and 2-4% bitumen.

1 An advantage of certain embodiments of blocks in 2 accordance with the present invention are that they 3 are made from around 95wt% recycled material and so 4 are both cost effective and environmentally 5 friendly.

7 A further advantage of certain embodiments of blocks 8 in accordance with the present invention is that 9 they are resistant to cracking and rutting compared 10 to known concrete blocks.

12 Moreover, for certain embodiments of the invention 13 the cost of production of the blocks in this way is 14 considerably less than the production costs of the 15 conventional blocks due to the smaller amounts of 16 binder required compared with, for example, the 17 amount required for concrete blocks. Certain 18 embodiments of the blocks may cost only 70% of the 19 cost of known concrete blocks.

21 Certain embodiments of the invention benefit from 22 the fact that the blocks require less bitumen 23 because the foaming of the bitumen during 24 manufacture increases its efficiency at binding the 25 aggregate.

27 A further advantage of certain embodiments of the 28 invention is the relative flexibility of the blocks 29 when compared to conventional concrete blocks which 30 are generally relatively brittle.

( 1 The blocks according to the invention may be used in 2 a variety of different applications including 3 pedestrian precincts, car parks in environmentally 4 sensitive locations, transport interchangers, 5 decorative areas and domestic use such as house 6 drive, pathways and patios.

8 Certain blocks made in accordance with the invention 9 will be bound together predominantly with bitumen 10 rather than cement so they have what is known as a 11 flexible binder which will give them many 12 engineering advantages when they are laid in situ 13 including but not limited to improved performance 14 and good resistance to cracking and deformation.

15 Moreover certain blocks made in accordance with the! 16 present invention are not brittle and can withstand 17 a point load being applied to them without cracking 18 or fracturing.

20 Preferably, the blocks made in accordance with the 21 present invention comply with BS6717 or an 22 equivalent standard.

24 Improvements and modifications may be made without 25 departing from the scope of the invention.

Claims

l Claim"

3 1. A method of making a block, the method 4 comprising the steps of: 5 providing an aggregate material; adding a foamed binder to said aggregate 7 material; B forming a block from the combination of said 9 aggregate material and foamed binder.

11
2. A method as claimed in claim l, wherein the 12 method also includes the step of curing the block.

14
3. A method as claimed in claim 2, wherein the 15 step of curing the block involves heating the block -

16 to a temperature in the range of 20 C to 100 C.

18
4. A method as claimed in claim 3 wherein the step 19 of curing the block involves heating the block to a 20 temperature of around 60 C.

22
5. A method as claimed in any one of claims 2 to 4 23 wherein the block is cured for a period in the range 24 of 12 to 90 hours.

26
6. A method as claimed in claim 5 wherein the 27 block is cured for around 72 hours.

29
7. A method as claimed in any one of claims 2 to 30 6, wherein the block is cured by placing it in an 31 air convection tunnel means.

1
8. A method as claimed in any preceding claim 2 wherein the method includes the step of compacting 3 the combination of said aggregate material and 4 foamed binder.

6
9. method as claimed in claim 8, wherein the 7 step of compacting the aggregate material and foamed 8 binder is performed by a vibratory press.

lo
10. A method as claimed in any preceding claim, 11 wherein the method includes the step of dispersing 12 the binder into microscopic bubbles which attach to 13 the aggregate.

15
11. A method as claimed in claim lo, wherein the 16 binder is dispersed into microscopic bubbles by 17 adding cold water thereto.

l9
12. A method as claimed in claim lo or claim 11, 20 wherein the binder is dispersed into microscopic 21 bubbles by adding compressed air thereto.

23
13. A method as claimed in any one of claims 10 to 24 12 when dependent upon claim 8, wherein air in the 25 microscopic bubbles is driven out by the compacting 26 step.

28
14. A method as claimed in any preceding claim, 29 wherein the aggregate is recycled aggregate.

31
15. A method as claimed in claim 14 wherein the 32 aggregate is recycled asphalt planings.

2
16. A method as claimed in any preceding claim, 3 wherein the method includes the step of using the 4 block as a paving surface material.

6
17. A resilient paving block.

8
18. A block as claimed in claim 17, wherein the 9 block comprises at least 90wtt aggregate and a 10 binder.

12
19. A block as claimed in claim 18, wherein the 13 block comprises up to 5wt% binder.

15
20. A block as claimed in claims 19 wherein the 16 block comprises 14wt% bitumen.

18
21. A block as claimed in claim 20, wherein the 19 block comprises 2. 5wt% - 3.5wt% binder.

21
22. A block as claimed in any one of claims 17 to 22 21, comprising 9096wt% aggregate.

24
23. A block as claimed in any one of claims 17 to 25 22 wherein the binder is a bitumen.

27
24. A block as claimed in any one of claims 17 to 28 23, wherein the block comprises at least one 29 additive to accelerate structural stiffness gain 30 and/or aid effective curing.

1
25. A block as claimed in claim 24 wherein the at 2 least one additive is a pozzolanic binder.

4
26. A block as claimed in claim 23, wherein the 5 block comprises 112wt% pozzolanic binder.

7
27. A block as claimed in claim 25 or 26, wherein 8 the pozzolanic binder is ordinary Portland cement, 9 pulverized fuel ash or quicklime.

11
28. A block as claimed in any one of claims 17 to 12 27 wherein the block is coloured by addition of any 13 suitable colouring pigment.

15
29. A block as claimed in any one of claims 17 to 16 28 wherein the aggregate does not exceed 8mm nominal 17 size. l9
30. A block comprising around 88wt% recycled 20 asphalt planings, around 3wt% bitumen, around 2wt% 21 ordinary Portland cement blend and around 7% 22 pulverized fuel ash.