Recycling reclaimed road material in hydraulically bound layers

Proceedings of the Institution of Civil Engineers

http://dx.doi.org/10.1680/tran.13.00056

Paper 1300056

Received 28/04/2014 Accepted 24/06/2014

Keywords: environment/recycling & reuse of materials/roads & highways

ICE Publishing: All rights reserved

Transport

Recycling reclaimed road material inhydraulically bound layersGaspar, Stryk, Marchtrenker et al.

Recycling reclaimed road materialin hydraulically bound layersj1 Laszlo Gaspar PhD, DSc

Research Professor, KTI, Budapest, Hungary

j2 Josef Stryk PhDHead of Infrastructure Department, CDV, Brno, Czech Republic

j3 Stefan Marchtrenker MEng, DIHead of Department of Concrete and Building Products, SmartMinerals GmbH, Vienna, Austria

j4 Regis De Bel PhDSenior Researcher, BRRC, Brussels, Belgium

j5 Finn Thøgersen MScSenior Researcher, Danish Road Directorate, Hedehusene, Denmark

j6 Thierry Sedran PhDDeputy Head, Materials for Transportation Infrastructure Laboratory,IFSTTAR, Bouguenais, France

j7 Karmen Fifer Bizjak PhDHead of Geotechnics & Traffic Infrastructure Department, ZAG,Ljubljana, Slovenia

j8 Fredrik Hellman PhDResearcher, VTI, Linkoping, Sweden

j9 Helen Ahnberg PhDResearch and Consulting Engineer, Swedish Geotechnical Institute,Linkoping, Sweden

j10 Ciaran McNally PhDLecturer, School of Civil, Structral & Environmental Engineering,University College Dublin, Dublin, Ireland

j11 Maria Arm PhDSenior Researcher, Swedish Geotechnical Institute, SGI, Linkoping,Sweden

j12 Zsolt Bencze MScResearcher, KTI, Budapest, Hungary

j1 j2 j3 j4 j5 j6

j7 j8 j9 j10 j11 j12

The European Direct-mat project provided a significant contribution to increasing recycling reclaimed road wastes.

Part of the project was dedicated to the recycling of various reclaimed road materials in new hydraulically bound

layers. This paper summarises the results of the project and the activities of the eight contributing European

countries. Several examples from countries outside the project are also provided to give a comprehensive overview.

The paper highlights the main trends of relevant practice worldwide (particularly in Europe) and draws conclusions

for practitioners.

1. IntroductionAn initial overview is presented of current practices concerning

the recycling of reclaimed road materials into new hydraulically

bound road layers. Cement concrete pavements and lean concrete

base courses are mainly considered here, but in some cases

pavement layers using lime or fly ash are also dealt with. The EU

RTD framework programme sponsored this project, the aim of

which was to present the different philosophies of various

European countries on the recycling of hydraulically bound road

pavement layers. The overview is based on the major activities in

Austria, Belgium, the Czech Republic, Denmark, France, Hun-

gary, Slovenia and Sweden, and considers relevant literature as

well as information collected in interviews with local experts.

Not every type of data source was available in each country

mentioned. From the separate tables presented, it is clear from

which countries some data could not be obtained. This review

was compiled as part of the activities of the ‘Direct-mat’ project

(DIsmantling and RECycling Techniques for road MATerials –

sharing knowledge and practices). The eight participating coun-

tries compiled national reports on their relevant experience, but

some information from other countries (mainly Germany) is also

utilised.

1.1 Recycling concrete pavements

Concrete highway pavements are used and recycled to various

extents across Europe and some countries have long experience

with this technology, as outlined in Table 1. In countries such as

Denmark (Thøgersen, 2010), Hungary (Gaspar, 2010) and

1

Sweden, the production of concrete pavements and cement-bound

base layers reached a peak around 1970. However, due to serious

durability problems such as alkali–silica reaction, reflective

cracking and loss of friction, most sections were later covered

with asphalt overlays or were removed. As a consequence, few

concrete road structures have been built in the past four decades.

However, in most of these countries there has been a moderate

rebirth of concrete pavement technology in recent years.

Nowadays, activities in this field vary across Europe due to

different road construction philosophies. In 2008, there were just

105 km of concrete roads in use in Hungary and 87 km in

Sweden; however, in Austria, 38% (1420 km) of the motorways

were made of concrete and up to 70% of the new motorways

being built were using concrete pavements. In France (Sedran,

2010), about 1% of the toll-free national roads, 10% (1410 km)

of the highways and about 3% of motorways were constructed

with concrete pavements. Concrete pavements and cement-bound

base layers have been used in Denmark, but cement-stabilised

sub-grades have never been employed. The expected service life

of motorways constructed using cement concrete pavements is

highly dependent on construction quality and proper maintenance.

In optimal conditions, a service life of up to 40–50 years can be

expected.

Considerable differences exist between countries in the field of

concrete recycling, as can be seen from the data in Table 1.

Recycling of road materials has become normal practice in

countries such as Austria, Belgium and the Czech Republic where

concrete pavements are used in a high percentage of highway

systems. In these countries, special organisations deal with this

technique and include representation from national recycling

companies. In other countries (e.g. Hungary), the use of recycled

road materials in cement concrete pavements cannot be con-

sidered a common technology. In Slovenia, research has been

carried out on the use of industrial by-products (steel slag, fly ash

and crushed concrete from building demolition) in new concrete.

Waste concrete from road construction has not been targeted in

research so far, but it is often used as embankment material

(Fifer-Bizjak, 2010).

1.2 Regulations, specifications and the promotion of

recycling

As would be expected, regulations covering this topic are in place

in the majority of countries surveyed. In most European coun-

tries, general regulations exist on the need for greener construc-

tion processes and these are supplemented by detailed technical

specifications for special applications. In several countries,

demolition material from roads is classified as waste and is not

permitted to be recycled in new constructions. It is possible to

promote recycling by putting rather high taxes on materials

deposited in landfills, as is the case in Austria, the Czech

Republic, Denmark, Slovenia and Sweden. Furthermore, recy-

cling can be promoted by other methods such as supporting the

research and training of involved professionals, as is the practice

in Slovenia. Under legislation in France and Belgium, disposal of

waste is only allowed for ‘ultimate waste’ (i.e. waste that cannot

be treated or reused); all other waste must be recycled.

There are national differences in the legislation concerning waste

treatment. As expected, countries with higher taxes on landfill

deposits are experiencing an increase in the recycling of con-

struction waste. In this context, the approach of taxing waste

disposal in landfills can be taken as an effective tool in promoting

recycling activities.

AT BE CZ DK FR GE HU SE SI IE

Year of first concrete pavement 1904 1913 1930 1923 1939 1888 1927 1925 1957 No data

Length of concrete pavement

network: km

1420 2618 376 100 150 3100 105 87 ,50 ,50

Age of concrete pavement

network: years

0–50 0–60 2–37 15–75 5–70 0–50 2–30 4–38 3–40 10–40

Beginning of concrete recycling 1989 Early

1980s

Early

1990s

No data 1976 No data Late

1990s

No data 1987 No data

Present concrete recycling High High High None Low High Low Low Low None

Yearly volume of hydraulically

bound waste produced: Mt

1.8 3.5 1.2 0.04 269 No data Few Few No data No data

Proportion of hydraulically bound

material recycled: %

90 95 .80 100 40 No data No data No data No data No data

Table 1. Historical development and present situation of recycling

of concrete road structures in some European countries

(AT, Austria; BE, Belgium; CZ, Czech Republic; DK, Denmark;

FR, France; GE, Germany; HU, Hungary; SE, Sweden; SI, Slovenia,

IE, Ireland)

2

Transport Recycling reclaimed road material inhydraulically bound layersGaspar, Stryk, Marchtrenker et al.

In addition to taxes on waste deposited in landfill sites, taxes on

natural gravel were introduced in 1997 to assist recycling

practices in Sweden (Hellman et al., 2011). As outlined in Table

2, there are also taxes on the use of natural aggregates in

Denmark, France, Sweden and Slovenia. The materials used in

road structures must satisfy given environmental and technical

criteria (standardised tender specifications, technical specifica-

tions, European standards etc.).

In spite of low concrete recycling activities in some countries,

there are several valid national specifications in this field. In

Belgium, France and Slovenia, recycled aggregates are required

to satisfy the same performance criteria as natural materials,

while in France a specific previous experimental validation is

needed for the approval of the use of recycled aggregate. The

French regional technical guide (DREIF, 2003) covers the main

regulations for the use of recycled road materials that do not

conform to relevant European and national specifications. In

Belgium, numerous different specifications and organisations for

recycling exist, with the objective of generalising the CE label

that already ensures the quality level of most recycling sites.

Regulations also exist governing the size fraction of recycled

products that may be used and these depend on the pavement

layer concerned; this is summarised in Table 3. The impurity

thresholds are identical to those specified for natural aggregates.

However, in Austria, additional impurity requirements are defined

for recycled aggregates (OBR, 2009).

There are national standards specifying concrete recycling in

countries where it is a widely used technique. Otherwise,

technical guidelines and recommendations are valid, as listed in

Table 4.

Sweden has general recommendations for excavated material,

detailing if it should be treated as waste or used with the same

criteria as for virgin materials (SRA, 2007). In Hungary, technical

guidelines and specifications have been issued recently (Balazs et

al., 2005; MAUT, 2006). Belgium has issued standard tender

specifications, where some aspects of recycled materials for new

hydraulically bound layers are considered, for example selective

demolition, milling depth and maximum size of blocks for block

cracking. The Austrian Association of Recycling in the Construc-

tion Industry has issued guidelines with general requirements for

recycled materials classified according to their technical and

environmental properties (OBR, 2009). In France, there is a

AT BE CZ DK FR HU SE SI IE

Existing legislation Yes Yes Yes Yes Yes Yes Yes Yes Yes

Taxes on natural aggregates: Euro/t No No No 0.40 0.20 No 1.45 1.80 No

Taxes on hydraulically bound

material waste: Euro/t

8.00 No 4.30–6.70 50.00 No No 48.00 1.18 75.00

Table 2. Taxes on natural aggregates and waste in European

countries


In situ recycling Yes Yes Yes Yes Yes Yes Yes Yes Yes No

Mobile plant recycling Yes Yes Yes No No Yes No No No No

Fixed plant recycling Yes Yes Yes No No Yes No No No No

Size fractions of recycled product: mm .4 0/32, 32/63, 0/63 4/16, 16/32, 4/32 — ,63 Many — — — —

Impurity threshold values Yes Yes Yes No Yes Yes No No No No

Table 3. Recycling techniques and specifications used for

hydraulically bound layers in European countries


National standard reference Yes No No No No Yes No No No No

National technical guide reference Yes No No No Yes Yes Yes No Yes No

Special technical criteria to recycle hydraulically bound road materials No No No No No No No No Yes No

Table 4. Specifications and criteria for concrete recycling

3


guideline for classification of crushing and mixing materials for

site recycling (Setra and CFTR, 2003).

2. Recycling road materials in hydraulicallybound layers

2.1 Recycling unbound road materials

Current European practices on recycling unbound materials in

new hydraulically bound layers (cement concrete pavements and

lean concrete bases) are summarised and compared in Table 5.

In the Czech Republic, recycling of unbound materials in new

layers is common practice and therefore no special technique or

machinery is needed. Accordingly, the requirements concerning

the recycling of this material are the same as in the case of natural

aggregates. Unbound materials from sub-bases or base layers are

commonly recycled; they are demolished, sorted and recycled in

situ or elsewhere. Their properties (grading, resistance etc.)

should be the same as those of natural aggregates (CSN, 2008).

2.1.1 Technical requirements

Special technical requirements for recycling unbound materials

are not available in either Austria or Belgium. The requirements

on aggregates and mix design are dependent on the type of new

layer. In Austria, unbound material is usually recycled in situ,

back into the same road. Unbound material coming from sub-

bases are stabilised by cement (BRV, 2008).

2.1.2 Pavement design using recycled materials

In Belgium, software developed by public authorities is used for

the design of new roads. The thicknesses of the layers are defined

to obtain a lifetime for the pavement (30–40 years for concrete

pavements). As inputs, sub-grade properties, traffic load, climate

and adhesion between layers are used. For some pavement types,

the user can also choose a predefined type of layer according to

standard tender regulation.

In Austria, the principles of pavement design, depending on load

class and construction type, are given in standards and guidelines.

Generally, there are no differences between the principles for

pavement design whether natural or recycled aggregates are used

(BRV, 2008).

In France, the construction of pavements using in situ treatment

methods is comprehensively described in a guide (Setra and

CFTR, 2003) and general principles are explained in a design

manual (Setra and LCPC, 1997). Construction with recycled

aggregates is almost the same as when natural aggregates are

used, even though particular care is needed for

j additional quality assurance on the construction site to ensure

homogeneity of recycled aggregates

j laboratory mix design to avoid the negative influences of

higher porosity and water absorption of recycled aggregates.

Agrela et al. (2011) investigated the physical and chemical

characteristics of mixed recycled aggregates in order to find

criteria for their acceptance in concrete. Water absorption and

gypsum content were found to be appropriate quality indicators.

2.1.3 Practical experience

In most of the countries reviewed, no practical experiences

concerning the recycling of unbound materials were reported,

although such techniques are common in some countries. This

could be attributed to the fact that the reuse of unbound materials

does not require special techniques and longstanding favourable

experiences are known. In France, an in situ treatment with

satisfactory behaviour after 19 years of traffic with 500 trucks per

day was reported (Direct-mat, 2010).

2.2 Recycling hydraulically bound materials

The review of international practices found that most countries

do not have specific national regulations on the recycling of

hydraulically bound materials into new hydraulically bound road

layers. However, some countries (Austria, Belgium, Czech Re-

public, France and Hungary) have examples of the use of

recycled aggregates from concrete in new hydraulically bound

layers; these are outlined in Table 6.

2.2.1 Regulations

The use of crushed concrete as aggregate in new cement concrete

is forbidden in Belgium. It is, however, possible to use crushed

concrete aggregates in other cement-based mixtures such as lean

concrete, sand–cement or porous concrete. In Slovenia, the use of

recycled aggregate in a concrete pavement is not allowed. In

Austria, recycled concrete aggregate (RCA) can be used in lower

concrete layers with the following technical requirements for the

old concrete (Osterreichische Forschungsgesellschaft, 2011)

j resistance to frost and de-icing chemicals

j contains ,20% bituminous material

j resistance to alkali–silica reaction by the fraction larger than


Is technique practised? Yes Yes Yes No Yes Yes No No No No

In which layer? Base Base Sub-base — Sub-base and base Base — — — —

Table 5. Recycling of unbound material in new hydraulically

bound layers

4


4 mm using the accelerated test 0/4 (and subsequent long-

term test).

The Czech Republic does not have specific regulations on RCAs

(Ministry of Transport of the Czech Republic, 2009); instead,

standard requirements on aggregates for hydraulically bound layers

are employed (Ministry of Transport of the Czech Republic, 2009).

In addition to these requirements, the aggregates are also tested for

chloride content, water-soluble sulfates and alkali reactivity as

these properties are likely to be detrimental to the concrete.

In Hungary, a technical guideline dealing with the use of recycled

aggregates in concrete has been issued (Balazs et al., 2005). This

includes many aspects, including requirements, performance,

suggestions for application and test methods. The aggregates are

classified based on standard aggregate tests such as density, water

absorption, apparent viscosity, particle size, grading, water-

soluble sulfates, chloride content, frost resistance and resistance

to de-icing agents. Physical properties are characterised by Los

Angeles, micro-Deval and compressive strength measurements

(Balazs et al., 2005).

In France, no specific regulation is used for recycling concrete

into hydraulically bound layers, but some documents classify the

aggregate for concrete which is valid also for recycled aggre-

gates; these concentrate on soluble sulfates and the influence of

recycled aggregate on setting time.

Oikonomou (2005) gives a Greek perspective of the three types

of RCA specified by Rilem (masonry rubble, concrete rubble and

a blend of recycled aggregates and natural aggregates). A new

Greek specification on this topic was recommended with limits

for specific gravity (>2.20 kg/m3), water absorption (<3%),

foreign ingredients (<10%), organic ingredients (<0.5%) and

harmful elements (<50 �g/l arsenic, <100 �g/l lead, <5 �g/l

cadmium).

In the USA, RCAs require the same tests as performed on virgin

aggregates (Wilcken and Fleischer, 2000).

In Germany, the requirements for recycled aggregates for con-

crete are specified in the relevant standard (DIN, 2002). These

include a minimum particle density (>2000 kg/m3) and maxi-

mum values for particle density range (< �150 kg/m3) and water

absorption (<10% after 10 min). German researchers (Zilch and

Roos, 2000) investigated if the existing standards were appro-

priate for the design of concrete with RCAs. Creep, shrinkage,

crack interlock and bond behaviour with recycled aggregates

were examined and it was found that concrete with increasing

content of recycled aggregate will behave increasingly like lean

concrete. The ‘traditional’ German design methodology can be

applied if the aggregate fraction above 4 mm is replaced; other-

wise, a modification is needed in the design. Concrete pavements

damaged by alkali–aggregate reaction are not allowed to be used

as recycled aggregate (FGSV, 1998). It is required that the

following properties of the old concrete are evaluated

j type and condition of the concrete pavement

j strength

j existing freeze–thaw damage

j aggregate properties

j condition of the mortar

j content of impurities

j air void characteristics.

2.2.2 Research results

There are limited research results available in this field as the

techniques applied are rather dictated by practical experience. It

is, however, obvious from a number of road projects that it is

possible to use recycled aggregate from concrete structures as

aggregate in new concrete layers with good results. A Czech

study based on laboratory testing has shown that


Is technique practised? Yes Yes Yes Rarely Yes Yes Few No No No

Regulations in place? Yes Yes No No Yes Yes Yes No Yes Yes

New layer type Allc Base Base Surface, base All

Max. RAPa content: % 20 No No limit No No 30 No 20 No

AARb test Yes No Yes No Not specific Yes No Yes

Chloride content: % No 0.02–0.10 No Yes Yes No

Acid-soluble sulfate: % Yes No ,1 No ,0.7 (aggregate)

,0.2 (concrete)

Yes No Yes

a Reclaimed asphalt pavement.b Alkali–aggregate reaction.c Excluding wearing courses.

Table 6. Recycling of hydraulically bound materials in new

hydraulically bound layers

5


j recycled aggregate influences the concrete mixture

consistency

j the density of the concrete decreases

j compressive strength decreases by 10–15%

j modulus of elasticity decreases by 15–20%

j creep increases by up to 50%

j shrinkage increases by 20–40% (Stryk, 2010).

Researchers in the FP5 Samaris project (F Sinis and M Gonzales,

unpublished project technical report, ‘Guide on techniques for

recycling in pavement structures’, 2006) characterised the follow-

ing properties of some road recycling materials (crushed con-

crete, crushed mixed materials)

j low aggregate abrasion resistance (Los Angeles value ¼ 25–

30, micro-Deval value ¼ 15–50)

j rough texture, high angularity

j higher porosity and water absorption than those of natural

aggregates (2–6%)

j methylene blue value (cleanliness): 2–4 g/100 g.

Belgian and Spanish researchers have shown that RCAs can

replace natural aggregates in roller-compacted concrete if appro-

priate quality control parameters are met (Delhez et al., 2004). In

Spain, Etxeberria et al. (2004) investigated the influence of the

percentage of recycled aggregate used and the heterogeneity of

recycled particles on the durability of recycled aggregate con-

crete. Alkali reactivity of fine aggregates in mortar was found to

be an important influencing parameter.

In Germany, Springenschmid (1995) studied the recycling of

concrete damaged by alkali–silica reaction. It was found that if

the alkali content of concrete was sufficiently high, detrimental

expansions and cracking were observed in the secondarily mixed

concrete containing recycled aggregate. However, when low alkali

cement was used the expansion did not exceed the critical limit.

Recycled aggregates from primary concrete containing blast-

furnace slag cement showed no damage in the secondary concrete.

Another German researcher (Wassing, 2002) investigated the

influence of fine particles from recycled concrete on the hydration

process. It was concluded that recycled aggregate can have

chemically active constituents with the potential to affect the

chemical reactions in the hydraulic materials and their technical

properties. This was particularly associated with the fine particle

size fractions of recycled concrete. It was shown that there is a

correlation between chemical–mineralogical features of carbo-

nated recycled aggregates and the hydration process. The com-

pressive strength of mortars containing recycled aggregates was

significantly lower than that of reference mortars with natural

sand. The former generally have a reduced setting time.

Another German investigation dealt with the influence of RCAs

on the durability of concrete (Kerkhoff and Siebel, 2002). The

influence of crushed concrete and varying quantities of crushed

sand on durability and the deformation features of concrete were

examined. Compared with concrete using natural aggregates, no

reduction in strength or durability was detected. However, a high

proportion of crushed concrete sand was found to lead to changes

in the deformation behaviour, with a decrease in the modulus of

elasticity and an increase in shrinkage and creep.

Kottas et al. (1997) dealt with the effect of recycled aggregate on

resistance to frost–thaw action. They concluded that, for concrete in

pavements directly loaded by vehicles, only the fraction above

4 mm should be replaced with recycled material. When assessing

recycled aggregates, it was found that the structure and porosity of

the old concrete cement matrix were the decisive factors. The frost–

thaw resistance of concrete manufactured using recycled aggregate

was affected mainly by water absorption and old concrete strength.

Sodeikat and Fleischer (1996) concluded that the higher the ratio of

recycled aggregate, the higher the moisture expansion and shrink-

age of new concrete. This effect can be initiated by the cementitious

component of recycled aggregates, since moisture expansion in

concrete is mainly caused by the cement matrix. Furthermore, the

additional capillary pores of the old cement matrix increase the

pore volume for water movement in new concrete.

Research has also been conducted into the potential environmen-

tal impact of using recycled concrete. Blankenagel (2005) found

that recycled material originating from highways in cold climates

may have been subjected to de-icing compounds that, over time,

have concentrated within the concrete structure. Chloride concen-

trations of 0.37–0.68 kg/m3 were recorded in RCA in an Amer-

ican investigation (Yrjanson, 1989). Such salts could be leached

from aggregate into the immediate environment, depending also

on the proximity of free water and the moisture susceptibility of

the pavement layer. In acidic environments, calcium hydroxide

can be readily dissolved, leading to increased concentrations of

calcium ions and elevated pH levels in the concrete. In addition,

calcium hydroxide can react with carbon dioxide in the air to

form calcium carbonate, an inert but not cementitious compound

(Mindess et al., 2003). While this carbonation process reduces

the available calcium and hydroxyl ions that may be leached, it

also limits the amount of self-cementing that may occur in the

recycled concrete. Depending on the movement of pore water

through the pavement structure and the extent to which carbona-

tion occurs first, ions can be leached out of the layer into the

pavement sub-grade and surrounding soils. Water flowing into

and out of the pavement accelerates leaching and compromises

the durability of the affected layers.

Kriech (1992) concentrated on the usability of recycled concrete

material as a clean fill. The major concern identified was that

accidental spills from vehicles onto the road surface could

contaminate the pavement and the surrounding road site; this

possible contamination could make the material unsuitable for

use in clean fill applications below the water table. The com-

pounds of interest were polycyclic aromatic hydrocarbons (PAHs)

6


and heavy metals. The main results obtained on test sites were as

follows.

j The leachate results of cement concrete samples were almost

identical to those of hot-mix asphalt and similar to soil.

j Very low concentrations of leachable metals (barium,

chromium etc.) were detected.

j No measurable amounts of PAHs were detected.

A German research team investigated the leaching behaviour of

recycled construction materials under real operating conditions

(Baasch and Goetz, 2004). Their results show that no reliable

forecast about pollutant discharge under filled conditions can be

derived from any single laboratory procedure.


In Austria and the Czech Republic, several motorway sections

have been built using recycled aggregate from demolished con-

crete pavements. The recycled material is used as aggregate in

lower hydraulically bound layers, but not in the wearing course.

The material is crushed and tested to fulfil the technical require-

ments. In Austria, the fine material (0/4) is used to improve the

stability of the sub-base (Marchtrenker, 2010). The 4/32 fraction

is applied as aggregate in the new base course. A similar

approach is used in the Czech Republic where the 4/16 and 16/32

fractions of the recycled aggregate are used in combination with

the 0/4 fraction of the natural aggregate in the concrete mix

(Stryk, 2010). In Belgium, an experimental road trial utilised the

fractions 6.3/20 and 20/32 for the crushed concrete in a new base

course. Generally, good experiences were gained on these road

projects and the road quality is comparable to that of roads built

with virgin aggregate.

Research and experimental road projects from Belgium show

positive results for the use of crushed concrete as aggregate in

various applications (De Bel, 2010).

j Crushed concrete sand (0/4 fraction) stabilised with cement

was used as sub-base. The experimental road has had a good

bearing capacity.

j Mechanical and durability tests of roller-compacted concrete

with recycled aggregate showed good results. Results from

freeze–thaw testing suggest good winter properties.

j Concretes with different contents of recycled aggregate met

the standard requirements. However, the workability tends to

increase the water demand, reducing the quality of concrete.

An American research report emphasised that economic con-

siderations are the primary reason for the use of recycled aggre-

gates in cement concrete pavements (Won, 2005). In this

particular case the performance of an experimental section

containing 100% RCAs was found to be comparable to one

manufactured using natural aggregate. No significant adjustment

in paving conditions was necessary. Recycled aggregates did not

have a pronounced effect on compressive strength, but recycled

fine aggregates did have an adverse influence on flexural strength.

The use of both recycled coarse and fine aggregates was found to

reduce the modulus of elasticity significantly. No change in

tensile strength was observed. The coefficient of thermal expan-

sion for concrete containing 100% recycled aggregate was found

to be much higher than for virgin aggregate concrete. In some

cases, construction difficulties were encountered.

In Australia, a two-stage mixing approach was developed to

improve the quality of recycled aggregate concrete for high-grade

applications (Eickschen and Siebel, 1999). Optimal performance

of recycled aggregate concrete using the two-stage mixing ap-

proach was obtained by using about 20% recycled aggregate

substitution. The effect of the two-stage mixing approach can be

attributed to the porous nature of recycled aggregate, and hence

pores and cracks can be successfully filled up during the pre-

mixing process. This resulted in denser concrete, improved

interfacial zones around recycled aggregate and a higher strength

in comparison with concrete using traditional mixing approaches.

The possibility of utilising recycled aggregates for heavily

trafficked highways was investigated by German researchers

(Katsakou and Kollias, 2007). It was concluded that if the

aggregates recycled from old concrete had not been subjected to

damage from frost or de-icing chemicals, then testing of the

resistance to frost and de-icing chemicals of the recycled aggre-

gates was not necessary if the aggregates were to be used in

concrete layers with lower cement content.

A demonstration project in the USA on recycling cement concrete

pavements evaluated their long-term performance (Cleary, 2011).

A moderately cracked concrete pavement had been recycled and

its performance monitored over a 10-year period. The recycled

concrete pavement aggregate was evaluated in four test sections

comprising two control sections, one test section of a cement-

treated base with recycled concrete pavement aggregate and one

test section using recycled aggregate in a cement concrete

pavement and cement-treated base. All test sections performed

generally well (in terms of faulting, roughness, performance level,

joint distress), with the cement-treated base and cement concrete

pavement sections with RCAs showing slightly more distress.

American experts investigated the long-term performance of

recycled cement concrete pavement (Cross et al., 1996). They

reported on test sites, pavement design and construction issues, as

well as the results from 10-year monitoring of test sections. The

main problem encountered during the recycling process was from

the reinforcing steel of the old pavement: it slowed down the

preparation process of the recycled aggregate and resulted in a

material loss of 15–20%. To increase the rate of recycling, a

37.5 mm maximum aggregate size was applied instead of 19 mm.

During the replacement, the recycled concrete performed better

and less slough-off at the outside edge was observed. The

performance of all sections after two million 80 kN single axle

loads (ESALs) was satisfactory.

7


In Switzerland, a concrete with 100% recycled aggregate (includ-

ing fraction 0/4) was tested with the following results (Werner,

1996).

j The use of impact crushers allowed the production of high-

quality recycled aggregates.

j Recycled aggregates should be separated into three or four

fractions.

j Before using recycled aggregates for new concrete, it should

be wetted for at least 48 h in order to waterlog the cement

stone.

j Cement content should be increased in comparison to

concrete with natural aggregates.

j Chloride content in old concrete is low and therefore this is

not an important factor.

A concrete pavement section with 100% recycled aggregates was

still performing adequately after 5-year trafficking.

An American bulletin provides background information on

recycling concrete pavements into RCA for use in bases, sub-

bases, new concrete mixtures, granular fill and so on (ACPA,

2009). The publication details economic and environmental

reasons for recycling concrete pavements, the methods and steps

of producing RCA, and the performance of concrete pavements

constructed using RCA. Recommendations and guidelines for

using RCA in various applications are also provided.

2.3 Recycling reclaimed asphalt

The common European practice on asphalt recycling into new

hydraulically bound layers is summarised in Table 7. Generally,

reclaimed asphalt is reused in new asphalt layers, by hot

treatment or as aggregate in new unbound granular layers. How-

ever, Austrian, Belgian and Czech regulations allow various

routes to recycle asphalt in new hydraulically bound layers.

2.3.1 Regulations

In Austria, the use of concrete rubble containing up to 20%

bituminous material is permissible in lower courses (BRV, 2008).

The recycling of reclaimed asphalt in concrete pavement is

generally not allowed by Belgian regulations. Nevertheless,

asphalt aggregates can be used in hydraulically bound, well-

graded bases; in the Walloon region it can be used in lean

concrete, porous concrete and roller-compacted concrete. The

reclaimed asphalt is usually recycled with the addition of sand

treated with cement.

The Czech Republic has published a basic regulation (Ministry

of Transport of the Czech Republic, 2009) containing informa-

tion on recycling where cement is used as binder. Recycled

bound courses can be used as a base (sub-base) course

(without traffic intensity limitation) or binder course (only for

cement combined with bituminous emulsion or foamed bitumen

as a binder, and just for low traffic intensity).

France has also published a guideline (Setra and CFTR, 2003) for

in situ treatment, including the use of bituminous layers to build

new sub-base and base layers.

A German bulletin deals with the recycling of asphalt granulate

in hydraulically bound base courses (FGSV, 2002). The document

deals with construction principles, raw materials, mixtures of

construction materials, execution and testing.

In Belgium, asphalt containing tar can be recycled only by means of

cold techniques; recycling in new hot-mix asphalt layers is

forbidden. When used as aggregate, the grading of the asphalt

rubble has to be modified by crushing and screening (De Bel, 2010).

2.3.2 Technical requirements

In Austria, no information on standards or specifications is avail-

able, except for the requirement mentioned in Section 2.3.1 and

the common technical requirements for aggregates. In Belgian

specifications, the technical requirements for asphalt aggregates

are the same as those for common aggregates. In the Flemish

region, there are no Los Angeles value requirements for asphalt

aggregates recycled in well-graded (sub)-bases (MFC DEI, 2000).

The Czech recommendations for recycled aggregates in hydrauli-

cally bound layers include requirements for aggregate fractions,

maximum volume of fines, quality of fines and maximum oversize

(Ministry of Transport of the Czech Republic, 2009).

2.3.3 Mix design

In Austria, there are no particular mix design requirements.

However, the higher the asphalt content in the recycled aggregate,

the lower the permitted water/cement (w/c) ratio.

In Belgium, the Flemish specifications (MFC DEI, 2000) indicate

that asphalt aggregates can be recycled in base layers treated with


Is technique practised? Yes Yes Yes No Yes Yes No No Yes Yes

For which layers? All Base Surface and base All Base Base

Are there regulations in place? Yes Yes Yes No Yes Yes No No Yes Yes

Table 7. Reclaimed asphalt material in new hydraulically bound

layers

8


cement and with an addition of a minimum 15% of sand. In the

case of in situ recycling with cement, preliminary crushing of

materials is required if more than 10% of the material is above

80 mm.

Czech requirements for recycled hydraulically bound mixtures

refer to grading, density, optimum water content, moisture, mini-

mum compressive strength and tensile splitting strength require-

ments (CSN, 2008).

2.3.4 Principles for pavement design

The principles of French pavement design for recycled aggregates

are the same as for natural aggregates, but changes in the

properties of constituents should be directly considered. Mean

values of these properties are presented in a guideline (Setra and

CFTR, 2003).

For many years now, recycling using hydraulically bound mix-

tures has been used in the UK for the structural maintenance of

roads to produce new 150–300 mm thick base layers (IPHBM,

2014). Deep-lift, in situ recycling has been used for almost

50 years but has become more prevalent and recognised in the

last 20 years with the advent of more powerful mixer–rotavators

capable of pulverising existing asphalt layers prior to the addition

of liquid or powder binders to the ‘granulated’ pavement. The

binders/additions used might typically be

j 6% cement, sometimes with coal fly ash to improve grading

j 3% foamed bitumen with 2% cement and usually 5–10% coal

fly ash for grading correction.

A report by Merrill et al. (2004) includes the use of ‘cold ex situ’

recycling, with central production of recycled mixtures for

transportation to the point of use. This work also covers a broader

range of binders including the lime/fly ash combination and the

use of lime with granulated blast-furnace slag.


Austrian researchers obtained good results in the laboratory and

on a test road section with reclaimed concrete containing up to

20% asphalt in a new concrete pavement (mainly in the lower

layers). According to another report, asphalt content up to 40%

can be used with the same w/c ratio as with mixtures using

natural aggregates (BWAS, 1998). In 1997, a motorway test

section was built with 35% of asphalt content using 4/32 aggre-

gate and a w/c ratio of 0.38. There were no problems during the

construction works, and the requirements of standards and

specifications were fulfilled.

Experience in Belgium indicated that a proper mix design for a

well-graded base with asphalt aggregate needs the addition of 15%

sand. The use of 5% cement can meet the requirements if the

moisture content is close to the optimum. The water content greatly

influences the material properties. Several test sections were stud-

ied with well-graded (sub)base containing asphalt aggregate

treated with cement. The asphalt aggregate contents varied from 80

to 90%, and were stabilised with 3–7% cement. Even after several

years, the pavements present no sign of settling or cracking.

In France, recycled bituminous material has been used in new

hydraulically bound layers with satisfactory results using the

following technique. First, the bituminous wearing course was

milled and part of this product (40% of the total amount of

aggregate) was recycled at a concrete plant. The product was then

used as a 100 mm white-topping layer to replace the existing

layer (Grob et al., 2003).

A Greek study reported tensile (uniaxial and flexural) and

compressive testing on mixtures of crushed aggregate and milled

bituminous materials with respective proportions by mass of

100/0, 75/25, 50/50, 25/75, 0/100 (Tam et al., 2008). All the

mixtures were bound with 3% or 5% cement and 52% water. It

was found that this type of recycled product produced a genera-

tion of new materials with different and enhanced properties

compared with ordinary cement-bound granular materials. Both

strength and modulus of elasticity decreased as the proportion of

milled bituminous material in the mix increased. The rate of

decrease in tensile strength was lower than that of compressive

strength; similarly, the rate of decrease in the modulus of

elasticity was lower than that of corresponding strength.

2.3.6 Research results

In France, recent research work has revealed the influence of the

replacement of natural aggregate by reclaimed asphalt pavement

(RAP) on road concrete properties (compressive strength, tensile

strength, modulus of elasticity, fatigue behaviour, cracking ten-

dency). The results can be used for the development of rational

mixture proportioning of concrete with RAP and they supply

information for the design of pavements using the French method

(Mathias et al., 2009).

3. ConclusionAfter reviewing practices across Europe, it can be concluded that

the typical obstacles to the (wider) use of cement concrete

recycling in road pavement structures come from the following

main sources.

j In some countries there are limited total lengths of roads with

cement concrete pavements. This is due to a combination of

reasons, including the failure of earlier concrete test sections,

unfavourable surface characteristics of cement concrete

pavements and/or fear of future rehabilitation difficulties with

these pavements.

j Since very few cement concrete pavements are built in some

countries, the possibility of recycling crushed road materials

is limited to lean concrete or cement stabilisation base

courses when hydraulically bound layers are investigated.

These lower structural pavement layers often need relatively

low-quality and/or local aggregates and, consequently, their

(partial) replacement by recycled road materials cannot be

9


necessarily economic. This is especially valid when reclaimed

cement concrete is used in unbound road pavement structural

layers or even embankments.

j Several European countries have taken the practical decision

not to extend the length of their road networks. Instead, they

have focused on the rehabilitation and/or widening of (adding

more traffic lanes to) existing road sections. In these cases

there are technologies available to allow the use of recycled

cement concrete pavement materials.

j The lack of appropriate national (or regional) specifications

in cement concrete recycling continues to act as an obstacle

to environmentally friendly road rehabilitation techniques.

j Sometimes there is a (usually unfounded) fear of excessive

heterogeneity and/or low quality of crushed road materials.

This concern is more pronounced when reclaimed asphalt is

intended for reuse in cement-bound layers.

To overcome these hindrances, the following proposals are made.

j Cement concrete pavements could be promoted by

highlighting the favourable long-term experiences of several

countries (e.g. Belgium, Austria, Germany) in the field,

concentrating on the relatively low lifecycle costs of heavily

trafficked cement concrete pavements compared with those of

asphalt pavements.

j New national research programmes (international literature

reviews, laboratory tests, design, construction and monitoring

of experimental or test sections etc.) should be initiated to

obtain reliable information about the economic,

environmental and performance features of various recycling

techniques of hydraulically bound layers.

j Increased national dissemination of favourable (local or

foreign) results obtained with the use of recycled road

material in cement concrete pavements or base courses

should be encouraged. This should include the positive

outcomes from the national research programmes mentioned

earlier and should be encouraged and coordinated by top road

administration organisations.

j State-level financial measures to promote recycling

procedures should be considered. These could include

subsidies and taxes on reclaimed road material deposits and

on the use of natural aggregates. National interests and those

of various stakeholders (designers, contractors, operators etc.)

should be drawn closer by appropriate decisions and

coordinated rules.

AcknowledgementThe research leading to these results received funding from the

European Community’s seventh framework programme (FP7/

2007–2013) under grant agreement number 218656.

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Recycling reclaimed road material in hydraulically bound layers

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