Areas of potential use of recycled materials in road construction

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Bituminous material

Approximately 7.5 million tonnes of waste bituminous materials are produced each year within the United Kingdom. An estimated 80% of these are reused, less than 5% are recycled and the remainder are tipped. The majority of road planings are used as an unbound fill which is not the optimum use of this valuable material. Although the DoT specification now allows 10% addition of reclaimed material to a bituminous mix (see 3.5.1), for technical reasons not all reclaimed material can be recycled for this use.

Recycling of bituminous bound road material has been carried out throughout the world, especially in Europe and the USA, for many years. In the United Kingdom applications are limited, although a rudimentary form of Retread was used as early as 1937. Several techniques are available for recycling both carriageways and footways. These are summarised in Table 3.1.

Table 3.1 : Carriageway recycling processes a o u o u

In-situ hot

Repave

Typically involves heating and reprofiling the top 20mm of surfacing, and overlaying with 20mm of virgin material. 50% of new material is thus saved.

Remix

Similar to Repave, but the original top 20mm of surface is rejuvenated, then intimately mixed with the virgin material before compacting. Offers similar savings of new material to Repave.

In-situ cold

Retread

Retread involves scarifying the pavement to a depth of 75mm, adding virgin aggregate if required, spraying with bituminous emulsion, reprofiling and compacting. In use in the UK for over 40 years, and up to 50% cheaper than conventional methods.

Shallow Recycling

Similar to Retread, but shallower (50mm) and much quicker. Deep Recycling

Deeper than Retread, up to 350mm, and offers structural repair by use of ccmcnt and water, ccmcnt and bitumen, or foamed bitumen as the binder.

Central Plant hot/cold

Central Plant

Both hot and cold mix recycling at a central plant offer much greater quality control than can be achieved in situ. Up to 60% addition of reclaimed material was successfully incorporated in a trial on the ABBE at Ashford in Kent.

Table 3.2 shows the potential for recycling of bituminous material by illustrating the extent of the practice overseas. In many of these countries, the lack of a readily available supply of hardstone aggregate has altered the economic equation in favour of recycling. Financial incentives have been used in the Netherlands and legal requirements have been used in Germany to encourage the use of recycled materials.

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Table 3.2 : Percentages of reclaimed bituminous material in a recycled mix

Country

Percentage of Reclaimed Material in a Bituminous Recycled Mix

Austria

20-70%

Australia

25%

Belgium

30%

Czech Republic

Up to 100%

Denmark

30% +

France

50%

Germany - former Federal Republic

30-70%

Holland

10-30%

Italy

Up to 70%

Japan

% not specified

Spain

30-35%

Switzerland

70%

USA

50%

USSR

% not specified

Use of other alternative materials in road construction

Estimates of annual UK usage of alternative materials, excluding bituminous planings, vary between around 26 million tonnes (Whitbread et al, 1991) and 39 million tonnes (BACMI, 1991). Whichever figure is valid, Table 3.3 clearly demonstrates the considerable potential for their increased use as secondary materials in road construction.

Many waste materials in their natural form can only be used in basic bulk fill applications. Some are already highly valued in other applications, while others could be used in more technically demanding applications with appropriate incentives. The optimum use of a secondary material is when it is used at the highest level commensurate with its characteristics. Thus use of a material as bulk fill when it may be suitable as a surface layer aggregate is not making best use of its potential. Table 3.3 summarises the potential uses of waste materials in highway construction.

Table 3.3 Potential uses of waste materials in highway construction (Sherwood & Collins, 1993)

Table 3.3 Potential uses of waste materials in highway construction (Sherwood & Collins, 1993)

Fill

Unbound Capping Layer

Unbound Sub-Base

Cement Bound Road-base Material

Bituminous Bound Road-base Material

Concrete Aggregate or Additive

Surface Dressing Aggregate

Crushed Concrete

3

3

3

3

2

3

0

Bituminous Planings

3

3

3

2

3

0

0

Demolition Wastes

3

2

2

2

2

1

0

Blast Furnace Slag

3

3

3

3

3

3

3

Steel Slag

1

1

1

1

3

1

3

Burnt Colliery Spoil

3

2

3

2

1

0

3

Unburnt Colliery Spoil

3

1

0

2

0

0

0

Spent Oil Shale

3

3

2

3

1

1

0

Pulverised Fuel Ash

3

1

1

3

3

3

0

Furnace Bottom Ash

3

2

2

3

1

2

0

China Clay Sand

3

3

2

3

3

3

1

Slate Waste

3

3

3

3

3

3

0

Incinerator Ash

3

2

2

1

1

1

0

Potential for use assessed as

2 = Intermediate

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The following boxes take each waste material arising from construction/demolition previously listed in Section 2 and summarises their potential uses and applications as recycled and/or reused materials, their acceptability as recycled or secondary reuse products and any associated market influences. Reliable data and information on the properties and performance of reused/recycled material is paramount to creating and encouraging end markets. Design has a very important role to play in producing recycled/reused products that can be competitive with primary products.

RECYCLED CONCRETE

Uses*

Acceptability

Market Influences

Type of Debris General Bulk Fill

Base/Fill for Drainage

Road Construction

Aggregate for Concrete

  • a) Crushed demolition
  • b) Clean, graded mixed
  • c) Clean, graded concrctc

Suitable

Suitable

Usually suitable Usually suitable

Highly suitable Highly Suitable

Not usually suitable

Suitable in some cases(sub-base only)

Suitable

Not suitable

Suitable in some cases

Suitable in some cases

Notes:

  • Applications at present and possibly in the future, (a) Crushed demolition debris, mixed crushed brick and concrete that has been scrccncd and hand-sorted to remove excessive contamination, but still contains a proportion of wood or other impurities.
  • b) Clean graded mixed debris: mixed crushed brick and concrete which has been grade d and contains little or no contaminants.
  • c) Clean graded concrctc: cnishcd and graded clean concrete containing less than 5% brick or stony material and little or no contaminants.

Source: (Lindsell and Mulhcron, 1985)

Concrctc is cither plain or reinforced. If reinforced, extraction of the ferrous reinforcing bars is achieved by passing the crushed material under a sclf-clcaning band magnet. There has been considerable research into the use of recycled concrete aggregate for new concrctc (Nixon 1978, for example). Acceptance of recycled concrete aggregate depends on the results of trials. A barrier to wider use is the difficulty in producing a material conforming to existing standards (CIRIA RP 461, 1994).

About 30 million cubic metres of ready mixed concrete were delivered in Great Britain in 1989 (BACMI estimate also quoted by British Geological Survey, 1992). About 56 million tonnes of aggregate (coarse and fine) was required in its production. A plentiful supply of a high quality natural aggregate poses stiff competition for recycled concrete aggregate, but as indicated above, the market size is large.

Uses

Acceptability

Market Influences

RECYCLED STONE MASONRY AND NATURAL SLATE

  • second-hand roofing slate
  • refurbishmcnt/to match existing building appearances
  • general bulk fill if poorly sorted

Stone cladding may require removal to the stone masons for re-shaping and cutting to size. If used as crushed aggregate for fill the stone may require sieving and contaminant removal.

There exists some demand for second-hand masonry materials such as cut stone and roofing slate. There is a need for the demolition contractor to sell the stone at a price to justify careful removal. Stone masons only usually buy stones if they know they can be rc-workcd and used on a current (or imminent) project. Thus, the coincidence of supply and demand and the associated economics may limit recycling (CIRIA RP 461, 1994).

Uses

Acceptability

Market Influences

BRICKS

Mixed crushed brick and concretc have the following applications:

Type of Debris*

General Bulk Fill

Base/Fill for Drainage

Road Construction

Aggregate for Concrete

  • a) Crushed demolition
  • b) Clean, graded mixed
  • c) Clean, graded brick

Usually suitable

Usually suitable

Highly suitable

Not usually suitable

Suitable in some cases (sub-base only)

Usually s tillable

(sub-base only)

Suitable in some cases

Suitable in some eases

* Notes:

  • a) Crushed demolition debris, mi xed crushed brick and concrete that has been screened and hand-sorted to remove cxccssivc contanunation, but still contains a proportion of wood or other impurities. Ib) Clean graded mixed debris: mixed crushed brick and concrete which has been graded and contains little or no contaminants.
  • c> Clean graded brick - crushed and graded clean brick and masonry containing less than 5% other stony material and little or no contaminants. (Stony material is used here to mean concrctc, natural stone and ceramic materials.)

Source: Institute of Demolition Engineers, 1985.

Figures 3.1 to 3.3 show a few of the processing stages required to obtain graded aggregate from mixed brick and cement demolition debris. Bricks arc also recovered separately and used second-hand for aesthetic purposes e.g. internal fireplaces, facing ctc.

Some bricks arc fired at low temperatures making them unsuitable for external use. Such bricks arc difficult to identify visually, since their appearance is similar to that of external bricks.

In Denmark, high disposal taxes arc levied on cach tonne of demolition waste, and thus it has bccoinc economical to reclaim demolition bricks for re-firing. Rc-ftring makes separating the bricks from the mortar much easier (by brushing) and eliminates the need to separate facing bricks from commons. However, the process has a high energy consumption and is therefore unlikely to bccomc adopted practice in the UK.

Construction practicc strongly influences the extent to which building materials can be recovered. The use of cement based mortars as opposed to traditional lime based mortars makes it more difficult to rccovcr bricks without damaging them. Re-firing can reduce such damage. At present work is in progress at BRE to design mortars with better bonding to brickwork in order to reduce rain penetration. Such mortars may also increase the difficulty of reusing bricks.

Bricks with a high sulphate content or with adhering gypsum plaster should be avoided since there have been failures due to sulphate attack (Nixon, 1978), With respect to demolition debris containing brick, higher strength bricks may give less fines material making compaction more difficult.

Careful dismantling of brick structures tends to be labour intensive, and thus costly. Sorting and cleaning is also expensive and a local market is required to make recovery economically viable.

TILES/CLAY PIPES

  • second-hand use for aesthetic cffcct
  • crushcd and mixed with other demolition debris as general fill. Only undamaged, good condition tiles and pipes can be reused.

Second-hand use is highly dependent upon the coincidcncc of supply and demand. Transport and storage costs may be limiting.

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Figure 3.1 Mixed brick and concrete undergoing crushing and processing operations at the Bakker Recycling Plant, the Netherlands

Figure 3.2 Hand sorting of the crushed debris

Figure 3.1 Mixed brick and concrete undergoing crushing and processing operations at the Bakker Recycling Plant, the Netherlands

Figure 3.2 Hand sorting of the crushed debris

Figure 3.3 Graded brick and concrete aggregate, stockpiled for sale

ASPHALT

Uses

  • reuse of asphalt road planings as aggregate fill
  • reuse of road planings in sub-base courses.

Acceptability

Since road planings arc sourccd from general re-surfacing work they arc relatively clcan, despite some contamination with tyre rubber and oil. In the UK, road construction materials arc spccificd by composition which limits the rc-usc of road planings. It can be readily demonstrated by test that road planings can be reused in road sub-base courses with no appreciable loss of performance (Department of the Environment, 199 If). However, ageing of the bitumen binder can pose complications.

Market Influences

Reuse is dependent upon immediate market availability and associated transport costs. Storage can prove problematic, since space is required and slight ground contamination is possible.

Uses

Acceptability

Market Influences

SOILS

  • landscaping
  • garden soil (high quality)
  • general bulk fill
  • contaminated soils may undergo processing for vitrification. There arc two main glass products from vitrification
  • high quality aggregate (approx 75mm)
  • large cast glass blocks (seawall defence materials).

Good quality, uncontaininatcd soils arc often in demand; however contaminated soils often pose a disposal problem. The vitrification process vitrifies contaminated soils to form a bulk glass which is highly inert in nature and has excellent resistance to leaching. The vitrification process will take asbestos, incinerator ash and metal slag i.e. hazardous materials too.

Good quality soils arc in high demand in urban areas and good prices can be obtained. However, transport costs arc often high. The vitrification process has a large market potential which to date is untapped.

PAPER/CARDBOARD

Uses

  • cellulose insulation
  • rccyclcd/cardboard production (wood pulp)
  • incineration fuel.

Acceptability

Paper cardboard is used in construction and demolition, but collection and transportation costs usually make recycling economically unviable. It is not known whether cellulose insulation and recycled paper/cardboard production arc the most environmentally beneficial options when compared to incineration.

Market Influences

One means of increasing the use of recycled paper products in construction is to increase the market share of cellulose insulation. In principle this could absorb around 0.5 million tonnes of waste paper per year.

TIMBER/WOOD

Uses • floorboards, rafters, doors, window frames (reuse)

  • manufacture of pine furniture, repair of agricultural buildings (reuse)
  • DIY and new construction projects (reuse)
  • temporary shoring, temporary formwork
  • site survey pegs and plant stakes (off-cuts from reprocessing)
  • animal bedding (shavings and sawdust)
  • chipboard manufacture
  • wood pulp production (low grade)
  • pyrolysis
  • energy recovery (incineration)
  • lightweight fill material for correction of landslides and slope failures (sawdust or woodchips) (USA)
  • RDF production (refuse derived fuel mix)
  • mulch
  • composting

Acceptability The main problem in timber reuse is the existence of a wide range of contaminants i.e. nails, screws, heavy metal preservatives, paints, diseases, fungicides etc. However nails, screws, bolts and nuts can be recovered for scrap. In Denmark treatment plants arc available to strip paints and, providing there is no decomposition, the wood can be reused directly. Wood is considered a deleterious contaminant of demolition waste, which also applies to any other putrcsciblc or compressible material (Collins, 1992).

Market Influences In the UK old timber is rarely used in new construction. However, there still exists today a strong market for old timber for conservation and heritage applications. Chipboard manufacture is not commercially viable at present since it requires a regular supply of cheap, clean, infestation free wood which is not available from current demolition sources. Woodpulp production is also not viable at present (Bergeson, 1992).

GLASS

Uses

  • sheet glass (0.65 million tonnes per annum, UK)
  • thermal insulation (0.1 million tonnes per annum, UK)
  • glasphalt' paving.

Acceptability

The chemical composition of post consumer cullct makes it unsuitable for flat glass applications but it could be used for thermal insulation. ' Glasphalt' has been recently used by Westminster City Council and by the USA on a trial basis.

Market Influences

The need to remove contamination e.g. metals, plastics, paper establishes a technical barrier, and the high cost of cullct compared to raw materials represents an economic barrier. However, there is an energy saving when using cullct as opposed to raw materials in the manufacture of glass building products (Atkinson, Collins and West, 1994).

METALS

Uses

  • recycling of metals from construction in the manufacture of new metal
  • reuse of metal components.

Acceptability

Most of the metal content of demolition and construction waste is already recovered as it commands such a high price (Lindsell and Mulheron, 1985). Demolition of metal structures is usually straightforward and the comprehensive recycling of metals from construction conserves much of the energy of refining from ore and the natural mineral sources required for new primary metal production. Metal components arc rarely reused but arc usually recycled. Still more could be achieved if metal components were reused rather than rccyclcd which implies the need for storage sites and quality assurance testing facilities for suitable components (CIRIA RP461, 1994). To aid recovery the metals need to be clean, and better design for ease of recovery is required. With respect to ferrous metals, corrosion may cause problems. Ferrous metals within reinforced concrete require separation and cut-up into manageable pieces. Copper wire reclamation potential depends on thickness of wire. Individual telephone cabling is not considered worthwhile, but 13 amp wires and anything above arc collected by totters from local authority skips.

Market Influences

The construction industry is a potential market for its own metallic wastes. The aluminium and steel smelting industries in the UK would like more to be recovered from building waste. This aside, sincc the scrap metal markets arc profitable, no further work is urgently required in encouraging the reuse and recycling of metallic construction waste.

PLASTICS

Uses Kibert (1993) usefully summarises all the relevant issues and up-to-date information concerning the use of recyclcd polymers in construction materials. It includes: general policy, the economics and latest technologies of polymer recycling; polymer classifications and consumption; trends in polymer use in construction products; and provides information regarding the products and their market success and performance to date.

New Uses for Recycled Plastics Packaging

Pira International April 1990 - April 1993 (unpublished report)

During the period April 1990 - April 1993, Pira International was responsible for running a multiclient project which looked at new uses for recycled plastics from the packaging industry.

The objectives of the project were:

To compile a database outlining the latest developments in the area of plastics recycling. Throughout the life of the project, interim reports were prepared listing innovative technologies and new legislation.

To identify blends which were likely to occur in the collection of plastics from the packaging industry. These included a small percentage of polypropylene in high density polyethylene from bottles, and polyvinyl chloride in low density polyethylene arising from the collection of film.

To characterise the performance of these blends and to investigate the improvement in the mechanical properties arising from the addition of' compatibilisers'.

To identify new uses which could either incorporate a percentage of recycled plastic in their manufacture or be made entirely from recycled plastic. Several of these uses arose from the construction industry, for example:

Plastic pallets arc replacing wood, and as such offer an opportunity to incorporate large quantities of rccyclatc.

• Geosynthetics

Describing a range of products such as sheet and netting, these arc generally polymctric in nature. Many arc made to high standards but some versions could incorporate recycled plastic.

• Road Surfaces

Bitumen can be prone to cracking or creep under extremes of temperature. Tests have shown that the incorporation of plastic can improve the resistance to both of these effects.

Many pipes arc produced to very high standards which rccyclatc may not be able to meet. Colour inay also be a problem where bright shades arc required. Some manufacturers, however, already use recyclcd plastics in pipes.

• Timber Substitute

The use of recycled plastic to make fences and s ignposts is well recognised. In addition to a product which takes the placc of timber for external applications, there now exists a product which very closely models the appearance of wood for furniture or other interior decoration.

One company now produces an industrial strapping product from 100% recyclcd plastic.

Panels for interior decoration can be produced from recycled plastic as an alternative to chipboard. Produced by the appropriate process, an original and unusual aesthetic effect is achieved which is complemented by tough and durable mechanical resistance.

Acceptability Recycled plastics have a lower technical performance than virgin materials and technical standards require modification to allow use of recycled plastic construction components. The energy costs of reprocessing usually exceed that of virgin materials.

Market Industry is forecasting that the use of plastics in construction will increase dramatically in the future.

Influences This demand creates a large potential market for recycled polymers.

Use of plastics in construction products faccs both technical and economic barriers at present. This is mainly due to the high expense of collection, transportation, separation and cleaning of contaminated material.

Plastics products in existing buildings arc diverse in nature and have generally been designed to have a very long lifetime. Therefore only small quantities are available for recovery when a building is refurbished or demolished. Thus plastics used in construction with a rccyclcd content will most probably have been sourccd from post consumer polymers of alternative waste streams (Kibert, 1993).

OILS

It can be arranged for oil recycling companies/specialists to collect any waste oils on site. However, adequate storage must be provided, and a waste management licence may be required.

PAINTS/SOLVENTS/CHEMICALS

Some chemicals and solvents can be recycled, but due to the generally low volumes used require adequate storage facilities prior to periodic collection, which is usually undertaken by recycling contractors. Waste management licences may be required.

Uses

Acceptability Market Influences

PLASTER/GYPSUM

as fill in road and rail works in stabilised base courses retarder in cement expansive cement production manufacture of plaster building products e.g. glass reinforced gypsum (GRC) (patented by BRE) for strong and fire-resistant partition walls, ceiling and floor slabs e.g. gypsum polymer composite (GPC).

The sulphate content can attack concrete.

There is a plentiful supply of this natural mineral and careful removal and collection is not usually economical, especially in demolition where time restraints arc also prevalent. Manufacturers of gypsum wallboard recycle both production and site waste, but collection and return to works is a restriction with respect to the latter.

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