GB2445795A

GB2445795A - A material formed from recycled asphalt and construction material and pulverised fuel ash

Info

Publication number: GB2445795A
Application number: GB0700982A
Authority: GB
Inventors: Derek Fordyce; Bogdan Marinescu
Original assignee: PROFICIO TECHNOLOGY Ltd
Current assignee: PROFICIO TECHNOLOGY Ltd
Priority date: 2007-01-18
Filing date: 2007-01-18
Publication date: 2008-07-23
Also published as: GB0700982D0

Abstract

A hydraulically bound material for a roadway is made from separated components of: (a) recycled asphalt (asphalt arisings); (b) crushed brick and block, (c) crushed concrete arisings, and (d) additional hydraulic binder containing pulverised fuel ash. The mixture has an asphalt arisings content in the range 10% to 30%, the additional hydraulic binder content in the range 3% to 10% and either the crushed concrete content or the crushed brick and block in the range 30% to 50%. The material is mixed with moisture, from 6% to 14%, and compacted to form a roadway. The hydraulic binder may also comprise ferrocrete.

Description

I

Roadway Layer and Method The invention relates to material for use in roadways and corresponding methods.

Increasingly there is interest in using recycled materials in roadway construction, and attention has turned to the possibility of using roadway arisings, i.e. pieces of removed roadway, and forming aggregrates form these. Such an approach has considerable benefits for the environment.

One type of aggregate is known as a hydraulically bound material which is defined by a British standard as "a mixture that hardens by hydraulic and/or poxxolanic and/or suiphatic and/or carbonatic reaction, which usually has a workability to suit compaction by rolling and which is generally used in bases, sub-bases and capping layers" (British Standards Institution 2003).

Two recent Transport research laboratory reports TRL6 11 and TRL 615 address these issues, in particular the use of sustainable low-energy roadway construction andmaintenance. Various categories of material are defined. In particular, a B4 material is defined that includes asphalt planings in a hydaulically bound material. To meet the standard, a material must meet certain requirements.

There is thus a need for a material meeting these requirements at low cost and low energy usage.

A particular problem with the production of hydraulically bound material from recycled material such as roadway arisings is the lack of consistency in recycled material that inevitably arises since it is generated from roadways made in many different ways and with different materials.

According to the invention there is provided a material blend according to claim 1.

The crushed concrete and brick and block together form a water inert mixture that forms the basic structure of the mixture. The use of brick and block as well as concrete create a blended system. The crushed concrete includes concrete dust which acts as a weak hydraulic binder, and creates what is known as an ultra-slow setting hydraulic system. The asphalt arisings provide ductility. The use of separated materials improves the consistency of the resulting formulation.

A particular benefit of the invention is the use of pulverised fuel ash (PVA) in the additional hydraulic binder. PVA is a waste product of power stations. The PVA acts as cement, speeds up the setting and improves the binding.

Optionally, ferrocrete may also be used as part of the additional hydraulic binder.

In wet form, as used, the hydraulically bound material includes 6% to 14% moisture and the rest is the material blend as set out above.

The invention also relates to a method according to claim 8.

The method may further include sieving the components to remove particles with a size greater than a predetermined maximum grading size in the range 10mm to 30mm.

The method may further include mixing the material blend with 6% to 14 % moisture to provide.the hydraulically bound material.

The method may then include laying the hydraulically bound material and compacting it with a rammer for example to form the base course of a roadway.

The laid hydraulically bound material has good indirect tensile strength properties which can lead to a structural advantage in roadway formulation. in particular, a reduced thickness of capping layer can be laid on the top of the hydraulically bound material of the invention compared with conventional base layers.

For a better understanding of the invention, embodiments will be described, purely by

way of example.

In a first embodiment, separate asphalt planings, bricks and blocks, and concrete powder were obtained.

These were obtained from a recycling facility and mixed. The mixture was sieved to a nominal maximum grading size of 20mm. A first mixture with 20% asphalt planings and a second mixture with 70% asphalt planings were tested. In each case, the amounts of brick and block and crushed concrete were the same as each other, so the ratios were 20:40:40 and 70:15:15 respectively.

The first and second mixture were both then mixed with 6% hydraulic binder; in both cases two experiments were performed, using pulverised fuel ash in one experiment and a mixture of pulverised fuel ash and ferrocrete in the other.

These mixtures were both then moistened to a moisture content of 6% to 14% and compacted with a rammer, following which they were left for 48 hours unsealed. Both gave good cohesion setting and hardening.

However, the second mixture was still plastic after 10 weeks and exhibited poor stability. It was not proceeded with.

Thus, good results were obtained using a relatively low amount of asphalt.

The PFA binder speeds up the setting to suitable times, and may also deliver pozzolanic reactions in which the PFA reacts with free cement and released June to enhance binding.

The asphalt in the form of planings enhances ductility.

A roadway was finished by laying a capping layer on the mixture to a thickness 40mm.

The improved strength and ductility properties of the mixture as set out above meant that the capping layer could be thinner than using conventional bases.

By using separated asphalt planings, crushed brick and block and crushed concrete, some measure of control over the mixture is obtained meaning that roadway construction can proceed relatively reliably even using recycled materials.

Claims

1. A material blend comprising a blend of (a) asphalt arisings; (b) crushed brick and block, (c) crushed concrete, (c) wherein the asphalt arisings content is in the range 10% to 30%, and the crushed brick and block content in the range 30% to 50%; further comprising: (e) from 3% to 10% of an additional hydraulic binder containing pulverised fuel ash.

2. A material blend according to claim 1 wherein the crushed asphalt arisings, crushed brick and block, and crushed concrete, all come in the form of particles with a maximum particle size of 20mm.

3. A material blend according to claim 1 or 2 wherein the additional hydraulic binder is present in an amount from 5% to 8%.

4. A material blend according to claim 1, 2 or 3 wherein the additional hydraulic binder is pulverised fuel ash.

5. A material blend according to claim 1,2 or 3 wherein the additional hydraulic binder is a blend of 30% to 80% pulverised fuel ash and the rest of the additional hydraulic binder is ferrocrete.

6. A hydraulically bound material consisting of 6% to 14 % moisture and the remainder being the material blend of any of claims I to 5.

7. A hydraulically bound material consisting of 10% to 12 % moisture and the remainder being the material blend of any of claims 1 to 5.

8. A roadway comprising a laid layer of a hydraulically bound material of claim 6 or 7 and a top layer including asphalt, the thickness of the top layer being at most 45mm

9. A method of making a hydraulically bound material, comprising: providing separated components of: (a) recovered asphalt; (b) crushed brick and block, (c) crushed concrete arisings, and (d) additional hydraulic binder containing pulverised fuel ash.

mixing the separated components (a) to (d) to provide a material blend, wherein the mixing is carried out in the proportions with the asphalt content in the range 10% to 30%, the crushed concrete content in the range 30% to 50%, the additional hydraulic binder content in the range 3% to 10% and the remainder being crushed brick and block.

10. A method according to claim 9 or 10 further comprising mixing the material blend with 6% to 14 % moisture to provide the hydraulically bound material.

11. A method of making a roadway, including preparing a hydraulically bound material using a method according to claim 9 or 10; laying the hydraulically bound material; and compacting the hydraulically bound material with a rammer.

12. A method according to claim 11 further comprising laying a top layer including asphalt to a thickness of at most 45mm to complete the roadway.