A construction material

Abstract

A construction material comprising a foamed bitumen binder, carbon negative aggregate particles and a filler material, wherein the carbon negative aggregate particles and filler material are dispersed within the foamed bitumen. The carbon negative aggregate particles comprise a solid precursor material selected from paper sludge combustion material, pulverised fuel ash, kiln dust, limestone particles, chalk particles, marble particles, Portland cement, sand, silt, and mixtures thereof that have been reacted with carbon dioxide (CO2) to form a solid aggregate material. The construction material may comprise 1-10 wt% of the foamed bitumen binder, 20-60 wt% of the carbon negative aggregate particles, and 20-60 wt% of the filler material. The filler material may comprise road planings, and the construction material may further comprise pulverised fly ash and / or cement. The pulverised fly ash may be present in an amount of 5-10 wt%. A paved structure comprising a layer of the construction material is further defined. The paved structure may comprise a surface layer formed from a non-permeable asphalt composition, a permeable asphalt composition, a non-permeable or permeable concrete composition, and the layer of the construction material may be located beneath the surface layer.

Description

The present invention relates to a construction material that includes a carbon negative aggregate material and to a paved structure that includes a layer of the construction material. It is desired to provide an environmentally friendly impact for paved surfaces by including within the paved structure a component which is carbon negative. In other words, a component which utilises or traps more carbon than is used in its production. In addition, it is desired to remove or minimise the amount of tar that is used in the preparation of paved surfaces, as there are concerns about the environmental impact of using tar in such applications. It is estimated that the production of 1000 tonnes of the carbon negative aggregate material captures as much carbon dioxide as planting 4000 new trees. According to a first aspect of the invention, there is provided a construction material comprising a foamed bitumen binder; carbon negative aggregate particles; and a filler material, wherein the carbon negative aggregate particles comprise a solid precursor material selected from paper sludge combustion material, pulverised fuel ash, cement kiln dust, limestone particles, chalk particles, marble particles, Portland cement, sand, silt and mixtures thereof which has been reacted with carbon dioxide to form a solid aggregate material; and wherein the carbon negative aggregate particles and the filler material are dispersed within the foamed bitumen. It should be noted that the carbon negative aggregate particles are effectively a manufactured aggregate material. Accordingly, they are not directly substitutable for conventional aggregate material, which is typically quarried or dredged stone or gravel materials. In view of this, the carbon negative aggregate particles must be formed into an acceptable construction material before they can used in paved surfaces and other construction products. It has been found that the use of a foamed bitumen material provides a significantly larger surface area than liquid bitumen and therefore better coats the carbon negative aggregate particles and the filler material. Furthermore, the foaming process reduces the viscosity of the bitumen and this further results in better coating of the carbon negative aggregate particles and filler material. The filler material is present in the construction material to provide additional strength to the construction material. In an embodiment of the invention, the construction material comprises l-10wt% of the foamed bitumen binder; 20-60wt% carbon negative aggregate particles; and 20-60wt% of the filler material. Suitably, the construction material comprises 2-5wt% foamed bitumen binder; 30-50wt% carbon negative aggregate particles; and 30-50wt% filler material. Such formulations provide a construction material that has the desired physical characteristics. The filler material suitably comprises road planings. The skilled person is aware that road planings may also be referred to as crushed tarmac, tarmac scalpings, crushed asphalt, road scrapings or tarmac chippings. Road planings are obtained from a surface layer of a tarmaced area, such as a highway or footpath. The surface layer is then crushed or milled to provide the road planings. Road planings are generally considered to be environmentally friendly as they contain bitumen which is a natural substance. It also is considered to be a recycled material, which provides an alternative to quarried or dredged aggregate stocks. The construction material may further comprise pulverised fly ash. This component may act similarly to cement and is considered to provide additional durability to the construction material. For example, the fly ash component may be present in the construction material in an amount of 5-10wt%. In addition to the fly ash or as an alternative to the fly ash, the construction material may further include cement, such as Portland cement, for example. The cement may provide an additional binding element and may also increase the durability of the construction material. It may also provide additional desirable physical characteristics to the construction material. The cement may be present in the construction material in an amount of 0.1 to 5wt%. According to a second aspect of the invention, there is provided a paved structure comprising a layer of the construction material as defined anywhere hereinabove in connection with the first aspect of the invention. As noted above, the paved structure may be used in the preparation of roads, paths (e.g. pavements, sidewalks, etc.), parking lots, airports, schools, universities and such like. In the context of the present invention the term "paved" includes a structure which has a surface layer formed from a substantially continuous layer (such as asphalt or concrete) and a structure which has a surface layer formed from a number of close-set discrete elements which together substantially cover the surface of the structure (i.e. a discontinuous layer). Based on the above, the skilled person will appreciate that a surface layer formed from a concrete material may comprise a substantially continuous layer of a concrete composition or it may comprise a surface layer comprised of concrete block which define gaps between adjacent blocks and / or within each block. In an embodiment of the invention, the paved structure comprises a surface layer formed from a non-permeable asphalt composition, a permeable asphalt composition, a non-permeable concrete composition or permeable concrete composition; and the layer of construction material is located beneath the surface layer. The carbon negative aggregate particles are known. For example, WO2007 / 096671 describes a process for incorporating carbon dioxide into an aggregate material by reacting a precursor solid material with a little water in a carbon dioxide-rich environment. The result is a manufactured aggregate material in which carbon dioxide is effectively locked. The precursor materials are typically waste fines from certain processes (e.g. quarrying and combustion processes), which are then combined and carbonated to form the carbon negative aggregate material. As the formed aggregate materials consume more carbon dioxide that is generated in the manufacturing process, they are said to be carbon negative aggregate materials. It is estimated that the carbon negative aggregate material can be incorporated into the paved structure in an amount whereby one square metre of the paved structure will have an equivalent effect of planting one new tree. In order to further increase the environmentally friendly nature of the paved structure, the surface layer may be a water-permeable surface layer. Permeable paved surfaces are known and these were developed to allow the movement of water, for example rainwater, through the surface to prevent or minimise flash flooding and erosion. Such surfaces have been used for roads, paths, parking lots, airports, schools, universities and such like. Accordingly, permeable paved surfaces are considered to be more environmentally friendly than non-permeable paved surfaces. Accordingly, in an embodiment of the invention, the surface layer may comprise a permeable asphalt composition or it may comprise a pervious concrete layer. The pervious concrete layer may be formed from a permeable concrete composition or it may be formed from discrete concrete blocks wherein gaps are defined between adjacent blocks and / or each block defines at least one channel therethrough. For example, each block may define therethrough one or more gaps, voids or conduits. In embodiments in which the surface layer is water-permeable, water, such as rain water, is permitted to permeate or infiltrate through the surface layer. In order to capture the water that has permeated through the surface layer, a reservoir layer may be provided between the permeable surface layer and the carbon negative aggregate layer. The reservoir layer permits the storage of a volume of the water therein. Suitably, the reservoir layer comprises an aggregate material and / or a soil material. Advantageously, the reservoir layer may act to filter out contaminants and / or pollutants from the water as it passes through the reservoir layer under the action of gravity. Accordingly, the water towards the bottom of the reservoir layer may have been purified to some extent. The reservoir layer may include one or more outlet pipes which act to direct the water in the reservoir layer away from the paved structure, for example to a collection point, a storage container or area, or an existing waterway. Suitably, the or each outlet pipes are located towards the bottom of the reservoir layer. In other words, the or each outlet pipe may be located in a lower portion of the reservoir layer. The skilled person will appreciate that the features described and defined in connection with the aspect of the invention and the embodiments thereof may be combined in any combination, regardless of whether the specific combination is expressly mentioned herein. Thus, all such combinations are considered to be made available to the skilled person. Embodiments of the invention will now be described, by way of example only. The following examples were prepared and tested: Example No. Bitumen Carbon negative aggregate particles Road planings PFA Cement 1 3wt% 30wt% 60wt% 6wt% lwt% 2 3wt% 40wt% 50wt% 6wt% lwt% 3 3wt% 50wt% 40wt% 6wt% lwt% 4 3wt% 30wt% 60wt% 7wt% Nil 5 3wt% 40wt% 50wt% 7wt% Nil 6 3wt% 50wt% 40wt% 7wt% Nil 7 5wt% 40wt% 50wt% 4wt% lwt% 8 5wt% 40wt% 50wt% 5wt% Nil It was found that all of the example formulations exhibited acceptable physical characteristics for use in paved structures.

Claims

1. A construction material comprising a foamed bitumen binder; carbon negative aggregate particles; and a filler material, wherein the carbon negative aggregate particles comprise a solid precursor material selected from paper sludge combustion material, pulverised fuel ash, cement kiln dust, limestone particles, chalk particles, marble particles, Portland cement, sand, silt and mixtures thereof which has been reacted with carbon dioxide to form a solid aggregate material; and wherein the carbon negative aggregate particles and the filler material are dispersed within the foamed bitumen.

2. A construction material according to Claim 1, wherein the material comprises l-10wt% of the foamed bitumen binder; 20-60wt% carbon negative aggregate particles; and 20-60wt% of the filler material.

3. A construction material according to Claim 2, wherein the material comprises 2-5wt% foamed bitumen binder; 30-50wt% carbon negative aggregate particles; and 30-50wt% filler material.

4. A construction material according to any of Claims 1 to 3, wherein the filler material comprises road planings, [define road planings]5. A construction material according to any of Claims 1 to 4, wherein the construction material further comprises pulverised fly ash.

6. A construction material according to Claim 5, wherein the pulverised fly ash is present in an amount of 5-10wt%.

7. A construction material according to any of Claims 1 to 6, wherein the construction material further comprises cement.

8. A construction material according to Claim 7, wherein the cement is present in an amount of 0.1-5wt%.

9. A paved structure comprising a layer of the construction material as defined in any ofClaims 1 to 8.

10. A paved structure according to Claim 9, wherein the paved structure comprises a surface5           layer formed from a non-permeable asphalt composition, a permeable asphaltcomposition, a non-permeable concrete composition or permeable concrete composition; and the layer of construction material is located beneath the surface layer.10