Section A Introduction (Back to Contents)

Waste generation has an important effect on the balance of environmental acceptability of an activity. The use of excess material constitutes a negative impact with no redeeming social benefit and the disposal of that waste causes further problems. If the waste is inert, it will occupy space and cause disruption during disposal. If it is a hazardous material, it also has the potential to cause continued and widespread ecological harm.

Thus, it is apparent that steps to minimise the production of waste are a vital part of any programme to reduce environmental impact. The construction industry in the United Kingdom is a major consumer of energy and resources and also a major producer of waste. The exact amount of waste is unclear; different texts use different measures or have different values. However, it is certain that the quantities involved are large.

Since 1976 the Construction Industry Research and Information Association [CIRIA], the Building Research Establishment [BRE] and the Chartered Institute of Building [CIoB] have reported that wastage rates are underestimated by the industry [CIRIA 1983 pp1, 10]. Recent reports indicate that few companies know the cost of their waste [CIRIA 1995 p10]. It is thus thought important to attempt to determine what levels of wastage are tolerated currently to allow an informed decision on targets for waste reduction.

The aims of this study were to:

• Review the available information on the composition, volume and cost of waste from construction.
• Assess the adequacy of this information for the setting of targets for waste reduction, with particular reference to the waste of ready-mixed concrete.
• Review the available methods of disposal of waste concrete and other hard wastes ^G.
• Verify any reported levels of waste of wet ^G [terms marked ^G are defined in the glossary] ready-mixed concrete using data from a major civil engineering site and assess the relationship between the quantity of waste and the size of the concrete pours ^G.
• Assess the costs of this waste.
• Recommend environmentally responsible methods of waste minimization suitable for all concrete and for surplus wet concrete in particular.

This section reviews industry practice and the published literature regarding the waste produced by construction to determine the extent and reliability of the information available. The estimates of the volumes concerned are compared and a summary produced. The proportions of the waste taking the different disposal routes are then considered.

The review then examines the waste of ready-mixed concrete, identifying its causes, methods of disposal available and the importance of the efforts to reduce the amount of concrete waste.

There are inadequate data on the total volumes of waste generated by the industry, the materials that constitute the waste stream and the proportion of it available for recovery. CIRIA [1992, p 22] concludes that

Construction requires large amounts of materials. CIRIA [1995] reports that the U.K. industry uses 400 Mtpa^G [million tonnes per annum] of a wide range of materials [p41]. Waste quantities are also likely to be large, partially due to the following reasons:

1. Construction is asked to produce large products using materials with low intrinsic value.
2. Many of the products require the generation of waste – for example, a hole in the ground will produce arisings^G. This is recognised in some texts [e.g. CIRIA 1995 p2].
3. Much work included as construction is waste disposal for other industries. The removal of contaminated soil to allow redevelopment or prevent pollution accounts for a substantial proportion of the work currently available but produces a disproportionate amount of "waste". Removal and disposal of contaminated material formed over 20% of turnover of one medium-sized UK civil engineering company [Nuttall, 1998].
4. The statistics generally include demolition waste. Construction is probably unique in that it already has to deal with almost all its products at the end of their useful lives. This concept of producer responsibility is now becoming recognised in other industries, possibly as a result of European Commission interest [Anon 1998a] but the disparity in approach prevents true comparisons with other sectors of industry.

B3 Estimates of the rates of waste production and recycling in U.K. construction  (Back to Contents)

        [a] "Hard" waste  (Back to Contents)

Several recent publications have provided estimates of the production of construction waste in increasingly lurid terms:

and incredibly:

There is considerable discussion of the amount of material available for reuse. Collins [1997, p36] reports figures of hard demolition waste arisings of 24 Mtpa, with a recycling rate of 50%. This comprises mainly concrete, stone and brick, but reaches an estimated 70 Mtpa when other construction hard waste, timber and surplus excavated material is included.

This accords with other values quoted: the 1990 production of 24 million tonnes of controlled (hard) waste estimated by Whitbread et al [1991] and the upper limit of the amount of demolition waste alone of 25 Mtpa given in the survey for the Institute of Demolition Engineers by Lindsell [1990]. BS 6543 [1985, table 1] suggests a value of 20Mtpa of demolition waste.

Other values have been suggested. CIRIA [1995, p2] records estimates of 32Mtpa published by Waste Age and quoted in Waste Management Paper No. 1 [DoE, 1992]. Collins [1997 p36] however, gives a value of 40Mtpa with a recycling rate of 30%, in addition to his figures above, for hard construction and demolition arisings.

These differences are partly due to differences in definitions of waste and reuse. The reported figures are broken down into constituent parts in Table 1, principally by reference to Collins [ibid.] and the report by Howard Humphreys and Partners [1994].

The large discrepancy noted in footnote 4 to Table 1, between the estimates of the quantity of soil generated as waste, is probably due to the method of assessment. For example, if surplus clay from a road cutting is taken off one site and is used to form an embankment at another site, it is subject to waste control regulations [Environment Act 1995] and so may be counted in the "waste" figures.

Table 1 indicates that 75% [52Mtpa] of construction waste is landfilled, with only 25% [18Mtpa] recovered (Note: Howard Humphreys & Partners [1994] value of 63% recycling includes materials used in landfill engineering). However, only 6% of the waste is disposed of unnecessarily, constituting about 4 Mtpa with the potential for recovery. This is small in comparison with the consumption of aggregates in England and Wales of 240 Mtpa in1991 [DoE, 1992] and full recovery of these materials will only slightly reduce primary aggregate demand.

Data regarding the other materials produced as waste are no more consistent. According to Lindsell [1990] wood, steel, plastic and other metals and debris constitute only 7% of demolition waste and so probably amount to 3Mtpa. CIRIA [1995, pp21 & 41] concludes that 10Mtpa (12Mm³ pa @ 0.8 t/m³ = about 10Mtpa)of timber waste and [an almost certainly incorrect figure of] 20Mtpa (CIRIA gives a figure of 9Mm³ pa, which @ 2.2 t/m³ bulked weight = about 20Mtpa. This is inconsistent with the estimates of total waste generation given previously in this reference and elsewhere) of metal waste arise annually from the UK Construction Industry, citing Whitbread et al [1991] and the preliminary results of a study by the CIoB. The apparent error probably lies in the quoted CIoB data, but as this was not referenced, it could not be checked.

Landfill operators use 36% of total construction waste to build their roads, containment cells and cover layers. There is concern that increased recycling will divert excessive amounts of engineering fill from landfills, requiring operators to purchase replacement materials [Anon 1998g]. This may be a specious argument, implying that good quality primary aggregate^G will be purchased for these purposes, increasing the negative environmental impact of aggregate extraction. As recovery increases, "waste" inert fill will acquire a value and the landfill operators will have to purchase their requirements. The cost of landfill will thus increase, reducing its competitiveness with other means of disposal. Secondary aggregates^G will still be cheaper than primary aggregate in most of the country so the demand for primary aggregate will only increase if the total aggregate demand increases more than the amount of recovery.

Figures collected for 1997 to assess the landfill tax indicate that the quantity of active waste^G sent to landfill has fallen three times as fast as inert waste [Anon 1997]. Consequently, less engineering fill is needed to service landfill sites.

Landfill sites will become less available, due to Government pressure [Brown, 1998; Anon, 1998d; Anon, 1998e], regulatory requirements for increased environmental impact analysis [Anon, 1998f] and lack of sites [CIRIA 1995 p1]. This will also decrease the demand for engineering materials at landfill sites.

Of more concern is the changing composition of the waste sent to landfill. The "traditional" waste comprised largely domestic ash and inert building and construction rubble. As construction waste is comparatively easy to recover and forms a large proportion of all waste [up to 60% - CIRIA 1995 p51], there is pressure to divert this from landfills. Domestic refuse now contains more putrescible matter and plastic, and industrial wastes are increasingly active. Thus new landfill sites are required to contain increasingly harmful mixtures of materials. This is not a reason to maintain the wasteful use of construction materials to dilute the wastes sent to landfill but should provide further incentives to recover these other materials.

Several texts, including CIRIA [1995] and Collins [1997], compare the recycling performance of the UK with that of other E.U Countries. Collins refers to a report by the Commission of the European Communities, which shows that only the Netherlands recycles more of its construction and demolition waste than the UK [60% compared to the UK’s 39%]. De Vries [1993 p10] reports a recycling rate of 50% in the Netherlands. CIRIA [1995 p86] gives details of waste recovery in Denmark, indicating that 10% was recycled in 1985, with a target of over 40% to be recovered by 2000. However, it quotes a total Danish construction waste figure of less than half that in the Commission Report [Collins, 1997].

Accurate comparison is difficult as the bases for the figures for the different countries are unclear and differently specified, but it is concluded that the UK is achieving better recovery rates than most E.U Countries.

The British ready-mixed concrete industry supplied 30 million cubic metres of concrete in 1989 [72 Mt] [BACMI estimate in CIRIA 1995 p33] with a current value of about £1.5 billion. In heavy civil engineering, the cost of concrete is significant. For example, one medium-sized heavy construction contractor spends £8 million annually on concrete from a turnover of £200 million p.a. [Nuttall 1998]. It is thus both a notable proportion of turnover and a large sum, so waste will have similarly important effects on profitability. The high price of concrete reflects the environmental costs of the high fuel and primary aggregate requirements of its production, so concrete waste has a similarly important environmental impact.

Concrete is identified as a major proportion of the hardened material waste in the texts reviewed in section B3 but most of this is "post-consumer" waste derived from demolition. The figures above demonstrate that the quantity of wet concrete waste could be significant. No estimates of the quantities were found in the texts reviewed.

According to CIRIA [1995 pp42, 45], principal reasons for concrete waste during construction are:

1. Design flaws
2. Design changes
3. Time pressures
4. Site practice

1. Design flaws.

Inefficient design can increase concrete consumption significantly. Structural sections designed larger than necessary because of inappropriate specifications or methods of analysis result in cost for the extra concrete used. There may be a saving for steel reinforcement through using a thicker section and, conventionally, these are balanced using the material purchase and use costs. To make an effective environmental impact comparison it is important to ensure that the costs fully internalise all environmental effects [CIRIA 1995 p27].

Specifying complicated shapes or differing concrete mixes also increases the level of waste. Abrupt section changes or difficult shapes may require the section to be poured in a number of separate pours. It is common to order a small surplus of concrete to avoid the cost or delay of reordering to make up any shortfall. The proportion of waste increases as the pour volume decreases. Similarly, the use of different mix specifications requires separate deliveries of each type of concrete, with the consequent fixed waste volume above, plus the transport energy costs of the extra vehicles running part empty. If a single mix is used, the deliveries can be combined with a single "safety margin" of waste. This may cause the concrete to be over-specified for one of its duties, which will involve a cost in additional cement or higher quality aggregate.

Design for a longer life can increase the efficiency of use of materials [CIRIA 1995 p28]. There are associated difficulties: it must be ensured that there will be a continued need for the facility for the longer life considered or the design needs to be sufficiently flexible to allow conversion cheaply to a new use. Also, there is no assurance yet that the materials commonly used will have the longevity required. Demonstrated life for different materials is estimated in Table 2, which shows that there is little evidence yet to support the use of reinforced concrete for conditions of long design life.

Designs rarely accommodate the needs of the demolition industry to facilitate the recycling of materials after the project is decommissioned. Using incompatible materials in composite structures makes recycling more difficult [CIRIA 1995 p24 - 25]. Gypsum in plaster prevents the use of crushed concrete as aggregate in new concrete because of the risk of sulphate attack. The cardboard facing to plasterboard, in turn, restricts the recovery or disposal of the gypsum [CIRIA 1995 p17]. Certain new designs may improve this: Canadian engineers have developed a system of concrete bridge decks without reinforcement, which will assist the recovery of the concrete on demolition as there is no steel to remove [Anon 1998b].

2. Design changes.

The designs of many construction projects change significantly during the construction phase [Anon 1998c]. There are numerous reasons for this, some justifiable and others with potential for improvement. Time pressure, considered in more detail below, can cause changes. Other reasons for the level of change are:

• Uncertain nature of the conditions in which the work will be effected. Ground conditions are never wholly apparent before design [Jones 1998b]. Often, the risk is accepted that waste may occur on modifying the design as required rather than undertaking expensive preliminary investigations to confirm the conditions.
• The long duration of construction projects may allow the design to be modified to suit changes in the market, research or legislation.
• Errors may become apparent in the original design.

3. Time pressures

The construction phase of a project is usually conducted in a short time when compared to the inception and planning or the operation phases. The pressure on time is enshrined in the forms of contract that are usually used for construction work: for example clauses 41 to 46 of the ICE. 5^th Edition Conditions of Contract [ICE1986] and clauses 28 to 29 of the G.C.Works/1 Edition 2 [DoE 1997].

This pressure can prevent a designer finding the optimum design in time to suit the construction programme and is more marked in the current conditions where "design and construct"^G and "lane rental"^G contracts are increasingly used. A wasteful design may be chosen if it offers a shorter construction period – for example the use of a higher cement content in concrete for precast construction^G as it provides higher early strength to allow early handling and erection.

Demolition creates a large proportion of construction industry waste. The fastest demolition methods are the least successful in producing reusable and recyclable material. Generally materials suffer greater damage when demolished quickly, reducing the recovery potential [CIRIA 1995 pp51, 58]. There is also likely to be more cross-contamination of materials. This makes recycling more difficult [as sorting is needed] or reduces the quality and value of the resultant material. For example, excessive amounts of brick in a crushed concrete aggregate will prevent it being used for concrete or for high quality layers in pavement construction^G.

The pressure on the time available for design and construction is partly generated by the artificially high value ascribed to time by interest rates when compared to the values used for materials. The pressure is increased by the length of the various approval and planning stages for major projects compared to the construction periods. Since it is vital that improvements in the planning and environmental control procedures do not extend the approval process unduly, several legislation systems place time limits on the stages of environmental impact analysis that are under the authorities’ control [Bond and Mortimer 1997].

4. Site practice

Additional concrete must be supplied above that required to form the design section, because of the testing and delivery of the material.

Quality control of concrete production requires frequent sampling for testing of rheological^G properties, strength or other attributes.

Delivery of the concrete involves an element of waste, as it is impossible to get all the concrete out of the agitator truck^G. This reduces with large pours as the trucks refill with fresh concrete so the waste only occurs once in the pour.

A major cause of industrial injury is the poor manual handling of excessive loads [HSE 1996]. The Health and Safety Executive encourages machine handling in preference to the control of the size of loads to be handled manually. The use of machine handlers on site requires more and better site haul roads, using hardcore, crushed aggregates and concrete in the heavily trafficked areas. There is thus a conflict between the minimisation of the use of materials and the need to improve safety in construction.

CIRIA [1997 p6] prioritises the methods of disposal, once the amount of waste produced is accepted as follows:

1. Reuse
2. Recycle
3. Find best practical environmental option [BPEO] for the disposal of the remaining materials.

1. Reuse

Reuse of wet concrete is difficult. Once the cement meets the water, the hydration reaction commences. Generally, it is taken that after two hours from its start, the reaction has progressed too far for the material to be used [Highways Agency 1994] although this varies with the cement type. There are limited opportunities for a supplier to find an alternative use for the waste concrete in this period.

Frequently the purchaser will make provision to use surplus material by having a mould ready to receive it. The need to place all the concrete quickly means that the alternative use may not require the same quality of concrete. Such downgrading causes an element of waste [CIRIA 1995 p vii].

There have been efforts to invent a chemical additive to "freeze" the reaction, awaiting a new use for the concrete. No cost-effective product has yet been found.

2. Recycle

The wet concrete can be washed out to recover the aggregate, the cement being allowed to react with copious water without gaining any strength. The aggregate can then be graded and returned to the batching plant^G for reuse. The water containing the reacted cement can be reused with fresh water to mix further concrete. However, the volumes of wash water from even a small load of waste concrete far exceed that which can go back into the mix. The recovery process produces a large volume of turbid, alkaline waste discharge, which needs to pass to a treatment works. The sediment tends to block conventional sewers and discharge of the quantities involved requires special authority. Most machinery currently available to do this separation can only receive a small quantity of concrete at a time, so the agitator truck is required to discharge the waste material for a considerable period. This prevents it delivering concrete, adding further to the high purchase and operating costs of the separator. Because of the costs and the under-utilisation of the equipment, the ready-mixed concrete companies charge four to five times the purchase price of the concrete to take it back.

Although separation recovers 2 tonnes of aggregate for each cubic metre of wet concrete recycled, 0.4 tonne of cement and its locked-in energy value is lost. As the cement is the most expensive constituent, requiring primary aggregates and a large fuel input in its manufacture, the gain from wet recycling is small, while the costs are high.

The concrete can be allowed to harden and then either roughly crushed for use as hardcore or more carefully processed to produce a consistent, graded aggregate. Often, the former process will take place on the site at which the concrete was originally delivered, replacing other imported low-grade materials.

Larger crushing plants, with control of their feedstock, produce a good quality aggregate that will replace high specification crushed granite or crushed limestone as sub-base^G for pavement construction. This provides the same degree of aggregate recovery as the wet process, with the added benefit of the weight of the hardened cement [an additional 20%] and avoiding the problem of disposal of the waste water.

There have been experiments to use crushed concrete as an aggregate for the production of further concrete. De Vries [1993] reviews experience in the Netherlands where, with further processing, a ‘recycled concrete aggregate’ [RCA]^G has been used in a number of large structures. Collins [1997] reports the use of RCA in the new "Environmental Building" at BRE. Both writers identify a number of problems with RCA concrete:

• Aggregate variability requires the use of stronger concrete to ensure satisfactory performance.
• Additional testing is needed to control quality.
• The aggregate has a higher water demand^G and so needs additional cement to give the same quality. Alternatively, weaker concrete can be produced requiring larger structural sections.
• Additional trials are needed to determine the characteristics of each RCA source.
• At present, suitable reliable sources of RCA are not always available.
• There is an increased risk of chemical contamination deleterious to the concrete; for example sulphate or chloride contamination.
• Contamination with brick aggregate reduces the strength of concrete that can be achieved.
• The specification for RCA is stricter than for sub-base so crushers tend to produce the lower grade material while there is adequate demand.
• The mechanical properties of the hardened concrete are adversely affected. Although strength is acceptable, drying shrinkage^G and the creep coefficient^G are both higher. This may require larger section sizes, for example in long-span beams.

In addition, production of RCA produces large volumes of sediment-laden, alkaline water for disposal.

However, both writers also note that the prestige associated with using recycled materials in new construction could outweigh the disadvantages. In the Netherlands 12% replacement of natural aggregate by RCA is permitted, which may be a suitable use for the product. This is felt to have a negligible effect on

the mechanical properties of the concrete [De Vries, 1993 and Collins, 1997].

3. BPEO for disposal

Surplus hardened material may be used as fill on the site to which it was delivered, perhaps by adjustment to the design levels. If this is genuinely the best option then there should be no difficulty in obtaining the necessary permissions. It will avoid the haulage of the waste from the site and may reduce the amount of transport delivering material.

There is no opportunity for energy recovery from hardened concrete. The material is incombustible and much of the energy used in the manufacture is lost in the exothermic hydration reaction.

At present, there appear to be few alternatives to sending unused waste concrete to landfill. Sea dumping may be an option as the material is almost inert. This should only be necessary if the value of the transport to a suitable crusher exceeds the value of the material for recovery. There will be a need for some inert material of engineering quality as long as any waste is sent to landfill so the value of the material can be partially realised in this way.

CIRIA [1995 pp18 - 21] assesses the suitability and priority for waste minimization of different materials. Concrete is listed as having high potential for reuse and recycling and intermediate potential for waste reduction. No detail is given of the criteria used for this assessment, but it appears to take a qualitative view of the difficulties of disposal, the environmental impacts of the waste and of the production of the material and the beneficial uses available for the waste. It also uses a ranking matrix based on the environmental hazard posed by the material and the environmental benefit of recovery or waste minimization. This assesses concrete as being of high priority for such efforts because:

• a large volume is produced
• it has a high environmental benefit ranking
• it poses a low environmental hazard.

The low hazard level to which CIRIA [1995 p20] refers relates to hardened concrete: disposal of wet concrete waste presents more problems as discussed in Section B6[c]. However, this does not invalidate the priority given to concrete waste reduction in the CIRIA report.

Some studies have looked at the composition of construction waste and estimates are available for the total volume produced by the industry. Costs were not ascribed to these estimates.

Reuse and recycling of materials is common but can be increased. Crushed concrete can be used successfully in place of crushed rock for unbound construction but its use as aggregate for concrete, whilst feasible, is not yet justified economically or environmentally.

The review identified that it is important to reduce the waste of ready-mixed concrete for the following reasons:

• It has a high value to the industry.

• It has received inadequate attention in other studies.

• It has been identified as a high priority material for waste minimisation.

The information examined during this review is inadequate for setting targets for the reduction of waste of most construction materials and no estimates were found of the wastage of wet ready-mixed concrete or its cost.

The method was designed to measure the amount of wet ready-mixed concrete that is wasted and so estimate its cost.

It used data from the construction of an urban dual carriageway trunk road including many large structures. The scheme cost over £30 million and required more than 50 000 cu.m. of concrete over a period from 1993 to 1997. Records of concrete placed during 1995 were studied, as this was a representative period of the construction. During that year 18 500 cu.m. of ready-mixed concrete was supplied to the site, 13 500 cu.m. of which was for structural use [the remainder being used for drainage, footpath and road construction].

Amongst other information, the engineers responsible for each pour recorded the volume required by the design, the measured volume of the moulds used to contain the concrete and the amount of concrete supplied to the site for individual elements of the construction. From these records, data were abstracted to allow the following three assessments:

• Volume of reinforcement contained in a structural concrete pour.
• Sampling for the quality control testing of the delivered concrete.
• Residual material in the drums of the agitator trucks.

In each case, graphical means were used to seek a relationship between the size of a pour and the amount of concrete waste, and to compare the pour size with the proportion of waste. Because of the spread of results encountered and the lack of an application for such a relationship if it was identified, no further steps were taken to measure the extent of the correlation.

The mean waste rate was obtained in each assessment by comparing the total annual concrete supply to the intended requirement.

The validity of the data was assessed and, where values used were recorded incorrectly or insufficiently accurately, the data were rejected. A number of records claiming zero waste were eliminated from assessments 1 and 2.

Assessment 3 was carried out to investigate the effect of the waste caused by the site practices identified in Section B6[b]. Reinforcement volume was calculated from measured reinforcement weights in a selection of the pours considered. Sampling quantities were measured by counting standard units taken by the technician. Residual material quantity was estimated from the known drum dimensions and an assessment of the thickness of the grout remaining after discharge.

Because the volume of the reinforcement was not deducted by the recording engineers when the pour size was below 200 cu.m. the first of these adjustments caused the waste figures to be larger than previously calculated. A number of records of zero waste previously excluded as being unreliable were reinstated, as the adjusted value would give a minimum estimate of the actual waste.

An estimate of the cost of wet concrete waste in the U.K. was prepared from the assessed wastage rates, using a mixture of quoted prices and costs known to be representative of the market.

Numerical results are given in Table 3 below.

No clear relationship was established between the volume of individual pours and the amount of associated waste. [Figure 1.] The overall spread of results showed an increase in the maximum amount of waste with the volume of the pour, but the majority of the results indicated a possible fall in the waste volume with increasing pour size. This is supported by the comparison of the pour volume with the proportion of waste generated [Figure 2].

The comparison of the waste volumes and proportions with the actual measured pour volume showed, unsurprisingly, that the amount of waste was generally less than the comparisons above indicate. The data showed a weak positive relationship but insufficiently precise to be of assistance in predicting waste. [Figure 3.]

The final comparison of waste volume and adjusted pour volume showed a similar weak positive relationship, but again it was not sufficiently precise to be of use. [Figure 4.]

Costs of the waste concrete are given in Table 4.

Several factors affected the validity of the results of this study. The method used data that were prepared during normal construction of the scheme. Different people recorded the values, without any cross-auditing to moderate or calibrate the results, but within the accuracy required for this study this variance probably did not affect the result.

The data were requested as part of a larger recording exercise so it was not apparent to the recorders that a study of the data would subsequently be made. Of more importance was the likely bias resulting from the reluctance of some recorders to report large wastage figures on work for which they were responsible. Because of the contractual basis on which most projects are let, the construction industry is generally conscious of the cost of obvious waste and attempts to reduce it. This may cause the assessments to underestimate the actual level of waste.

The data were not sufficiently detailed to determine the precise volumes intended by the designer, nor were the measurements of the larger pours accurately determined prior to the pour. Usually, the volume is measured again when the pour is nearing completion to ensure that sufficient is delivered. This also allows refinement of the volume ordered and so improves the waste rate.

In several of the reports, the quantity used was not known precisely as, in order to reduce the cost of transport, two small loads of concrete had been combined on a single delivery. This provided a further opportunity for a recorder to mask excessive losses.

The reports were only available for the concrete placed during the construction of the structural components of the study scheme. This constituted about 73% of the concrete used. However, it is also the part where measurements can be made more accurately and where it would appear to an observer that the wastage rates are lowest. Techniques for the construction of the roads and footpaths require smaller amounts of concrete placed in less easily confined locations so usage is less controllable. The overall waste rate is thus likely to be higher than the figure derived from this study.

All the data were obtained from a single scheme, with a consistent set of management techniques, supply conditions and work types. Variations would be expected between sites where these conditions differ. It is not apparent how much of an effect this would have on the range of results obtained.

The spread of results obtained for each of the relationships examined implies that there are a number of other variables influencing the amount of waste. However, the study has provided information to set a target for reduced concrete waste.

No data were found during the review so no comparison can be drawn with previous work. The assessment of U.K. waste of wet concrete of 2 to 3 Mtpa does not conflict with the published estimates of hard waste.

The construction and demolition industry generates about 70 Mtpa of waste, although the estimates differ. Little assessment of the resultant cost was found and the information is inadequate to identify the composition of the waste or to allow the setting of targets for waste reduction. There is increasing pressure on available landfill sites for the disposal of the waste and the production of the wasted materials has adverse environmental effects.

Some materials, such as steel and iron, are already recycled. The industry recovers 18 Mtpa of concrete and other hard materials and a further 4 Mtpa currently have the potential to be recovered. Concrete has been identified as a high priority material for recovery from waste, but no estimates were found of the amount of waste of wet concrete.

Excess ready-mixed concrete may have a purchase cost of £60M per annum to the construction industry and probably forms 4 % of the concrete purchased [3Mtpa]. The total cost of the waste, including disposal, is about £71 M and the associated loss of earnings is a further £2 M.

It generates a small [3%] proportion of the hard waste produced by the construction and demolition industry so its avoidance will not significantly affect the supply of materials for the construction of landfills and for crushing for reuse.

0.4% of waste wet concrete is currently unavoidable, being part of the production and testing process. The reasons for the remaining 3.5%, 2.5Mtpa, were not apparent from the factors investigated in this study and may be avoidable. A target can be set from this to promote waste reduction.

Reuse of the waste wet concrete is not practical or environmentally beneficial, except within the purchasing site.

Recycling of the hardened material into a concrete aggregate [RCA] is practical and sufficiently documented to allow its use. It has numerous disadvantages over concrete made from natural primary aggregates, mainly resulting in additional production costs but also causing adjustments to the design of slender structural sections. It requires higher cement contents than primary aggregate concrete, with an associated environmental cost. Low levels [less than 12%] of replacement of primary aggregate with RCA cause no practical difficulties.

The waste concrete can also be crushed into a successful sub-base, in direct competition with high quality primary aggregates such as crushed granite and limestone.

Some engineering-quality inert fill is needed to operate landfill sites. This will decrease as the number of landfill sites reduces.

Energy recovery is not practical and landfill is the best environmental option for the disposal of any hardened concrete that cannot be recycled.

1. It is recommended that attempts are made to reduce the volume of excess ready-mixed concrete ordered by:
• Planning of pours to allow amalgamation of deliveries.
• Accurate measurement of the volumes required.
• Preparing non-critical uses for any surplus material.
2. The remaining surplus should be allowed to harden where it can be kept as free of contamination as possible to gain the best value at disposal to a crusher.
3. Recycled aggregate should be used wherever possible for the unbound layers of pavement construction.
4. Concrete aggregate should not be processed commercially for use in concrete production until the full demand for aggregates for unbound construction has been diverted to secondary aggregates. Two exceptions to this would be if a large, good quality source of such aggregate was immediately available or if there was prestige or political benefit attached to using recycled aggregates in concrete.
5. All waste materials, and in particular hardened inert materials, should be separated as far as practical to minimise disposal costs and to maximise revenue.
6. A target should be set for the wastage of ready-mixed concrete of 2.5% of the quantity delivered, after adjustments for the inevitable losses.

• The quantity and content of the waste produced by heavy civil engineering works should be investigated, as inadequate data are available.
• Further investigation is needed of measures to improve the quality of recycled aggregate for unbound construction produced by crushers, to maximize the environmental value of the materials.
• The extent of the variation of wastage rates for ready-mixed concrete between different sites and types of work should be investigated to validate the results of this study.