Optimising the use of RCA

Optimising the use of RCA

G Kohler
remex Baustoffrecycling AG

H Kurkowski
DEUTAG GmbH & Co KG

ABSTRACT. Up to now, recycable materials produced from road demolition and C&D waste have mainly been re-used in low quality applications in road construction and civil engineering works. Depending on the re-use being required by the Closed Substance Cycle and Waste Management Act and the producer's product responsibility, materials from site should be re-used on a relatively high level. As for concrete and masonry demolition waste, there is a requirement to use granulates of concrete and masonry for the production of ready-mixed concrete, and in concrete products or precast units.

Keywords. C&D waste, Closed Substance, Cycle and Waste Management Act, Concrete waste, Masonry demolition waste, Granulates, Ready mixed concrete, precast units.

Dr.-Ing. Guntram Kohler, is a member of the Board of remex Baustoffrecycling AG, Duisburg, and was born in Stuttgart in 1942. During 1962 - 1967 he studied Civil Engineering at the Technical University of Stuttgart. In 1967 - 1971 he was a Scientific Assistant and Senior Engineer at the Institute for Road Construction, Earthwork and Tunnelling, RWTH Aachen. In 1971 he obtained his doctorate degree and in 1972 received a Postdoctoral Scholarship at the University of California, Berkeley, USA. From 1973 to 1983 he held leading positions within the natural rock and asphalt industry. Since 1983, he has been part of the General Management of DEUTAG Asphalt, Cologne and remex, Duisburg.

Dipl. Ing. Dipl. Wirt. Ing. (FH) Harald Kurkowski, is Head of ATQ - asphalt technology and quality management of DEUTAG GmbH&Co.KG, Duisburg. In 1985 he took his final examinations in Civil Engineering at Bergische Universität Wuppertal. Since 1985, he has held various positions in the materials department and in quality management at DEUTAG and remex group. In 1996 he took his final examinations of supplementary studyon economical engineering at Technical College of Ruhr University, Bochum.

INTRODUCTION

The building materials recycling industry has used stationary plants in order to process concrete and masonry demolition waste into relatively pure, high quality granulates to meet the requirements of recycling.
By systematic planning of backbuilding, selective backbuilding, adequate logistics, separating storage on the recycling site and through the use of high-quality processing units these requirements can be met further.

Crushing of material to obtain an adequate particle shape for the production of concrete can be achieved by using impact milis. For the separation of light substances, particularly wood, which can still remain in the bulk material even after best pre-sorting on-site, the air classifying technique has been successfully employed. Moreover, a so-called jig technique is in operation and is currently being optimised.

Building Residuals and Their Recovery

Based on quantity estimations from ancient German states, carried out by the German Federal Statistics Department during the early to mid 1990's, the total quantity of waste arising per year has been projected to almost 300 million tons. A total quantity of waste of about 400 million tons per year has been estimated with building residuals arnounting to 75 per cent in weight and 60 per cent in volume. Most of the C&D waste arising from road demolition, rubble from construction sites and waste from construction sites can be recycled, whereas dug soil is mainly used for earth and causeway constructions, recultivation activities and back fills. Rubble from construction sites consists mainly of concrete demolition as well as brick and masonry. Asphalt demolition waste forms half of the total quantity (15 million tons) of road demolition waste and can be virtually all recycled into new asphalt.

Fig 1:

Building residuals in Germany

The clearing of construction sites and their renovation produces various C&D waste which amount to 14 million tons per year. This C&D waste is generally brought to sorting plants in a mixed form as it cannot be directly collected separately on large construction sites. Due to extensive adaptations in Eastern Germany, the total quantity of recyclable materials produced amounts to 100 million tons per year. Recycled building material amounts to 35 and 50 million tons, according to different sources, which consider the recycling rate to be approximately 50 per cent. Following systematic recovery politics, it is realistic to suggest that recycling rates up to 90 per cent can be achieved (Figure 2).

Fig 2:

Recycling of building materials

Up to now, mixed granulate is mainly used in earthworks, civil engineering works and road construction, which means that there is a large degree of a so-called DOWN-CYCLING. Aggregates with dose size fractions can be used for applications like water and gas drainage courses as well as for asphalt aggregates, low grade concrete and for scaffold materials. However, these are only produced in special cases.
As defined by the Closed Substance Cycle and Waste Management Act, October 1996, recycling clearly takes priority over disposal which consequently leads to re-use on a relatively high level. Because of the economic situation, and the fact that mineral substances have to be kept in the cycle, the re-use of building materials is increasingly taking place on a relatively high level at those sites where the materials come from.

The best conditions for recycling are to pick up the materials on site, as far as possible already separated according to origin and class, and leave them separated at the plant. This is the basis for a real RECYCLING PROCESS as shown in Figure 3.

Fig 3:

Recycling Process

Mixed building material should be sorted into fractions of pure quality, mineral or non mineral, so that they cnn be brought to an adequate processing and recovery.

Processing Technique

The building materials recycling industry has used stationary plants in order to process concrete and masonry demolition waste into relatively pure, high quality granulates to meet the requirements of recycling. By systematic planning of backbuilding, selective backbuilding, adequate logistics, separating storage on the recycling site and through the use of high-quality processing units these requirements can be met further. Important units in this process are the pre-sieving and segregation of ferrous scrap by overhead magnetic separators.

The use of picking belts enables separation of large disturbant substances, before material with a particle size of > 45 mm is transformed to granulates, mainly by impact crushers. After repeated segregation of seperated ferrous scrap, a fractional sieving and separation of light substances by air classifiers follows. This technique allows the production of well qualified, close size fraction granulate mixtures. Products being processed in this way are of high quality and can be assigned as recycling materials. This quality can be guaranteed by systematic quality monitoring and more intensive sampling and testing of the material characteristics (including environmental properties) than is the case for natural mineral substances (Figure 4).

Fig 4:

Flow sheet of an advanced recycling plant

Dry and Wet CIassifying

Conventional dry processing of recycling materials uses as its core the air classifier (Figure 5). The classification has to take place at relatively close size fractions in order to be able to adjust the air speed so that disturbant substances with slight bulk density and special particle shapes can be safely separated from the heavy mineral material. By reducing the air speed in the classifier, light substances can be separated and discharged from the process. These residues are usually brought to landfills or incineration/energetic treatment plants.

Fig 5:

Air classifier

Due to high demands e.g. on the production of concrete aggregates or on raw materials for the production of masonry, wet processing techniques become increasingly important. Density Separation using the jig technique are used in mining and ore extraction, and offer the best possibilities for the processing of recycling materials (Figure 6).

Density Separation

In order to achieve quality characteristics according to the standard DIN 4226, Part 1, wet processing can be used for the production of concrete aggregates, from mixed C&D waste, particularly concrete and masonry (mainly brick). Besides providing a dust-proof surface, the separation of materials of a density of < 2 g/cm³is possible. According to the current state-of-the-art, the only possibility is the so-called jig technique (Figure 6).

Fig 6:

Scheme of a jig

The fundamental principle of jigging is the fact that a pulsating water flow passes through a material mixture. A consequence of pulsation is stratification, i.e. the material mixture "settles" according to density, heavy substances concentrate at the bottom of the bulk material whereas light substances travel to the top. In the case of corresponding density differences of the materials, it is quite easy to separate them. Moreover, it is also possible to separate floating materials (wood, paper, foamed concrete, etc.).

Main factors influencing the efficiency of separation by jig are density differences of the material mixture, bulk parts of the different density fractions, particle shape, the kind of water movement and the discharge unit for the continuous discharge of the heaviest material course.

As to the main components of heterogeneous recycling building materials, the materials are to be distinguished according to Figure 7.

These density differences of heterogeneous recycling building materials are advantageous in order to achieve more homogeneous fractions.

Fig 7:

Bulk density

^{Technical
investigations in the Netherlands, where concrete aggregates were treated by
a} ^j^{ig
technique, which only removes disturbing substances from an heterogeneous recycling
mixture, were carried out. The jigging technique was tested by remex following
a research programme devised by "Baustoffkreislauf im Massivbau" [BIM]
(Recycling of Mineral Building Materials) of the German Committee for Reinforced
Concrete. Practical experiments were also undertaken by remex and Almineral.
The scientific part was carried out by K&M Krass & Mesters, Bochum.}

^{Figure 8 shows an example of these investigations and some of the results. As
a first step, recycling sand 0/4 and a light material 1, consisting of cardboard,
paper, wood, foamed concrete and a heavy material 1, a heterogeneous recycling
material 4/32 mm, was obtained from the initial fraction consisting of heterogeneous
recycling material (airclassified), (Figure 9). Heavy material 1, was separated
in a further step into a heavy material 2 which was enriched with natural rock
and concrete} ^- ^{size fraction 4/32 mm (Figure 10) and into a light material 2 with the
same size fraction, but enriched with brick.}

^{Light material
1, mainly consisted of disturbant substances, heavy material 1 could be considered
heterogeneous, but released from the floating components separated in light
material 1.

The difference
between heavy material 2 and light material 2 was recognised by colour. Heavy
material 2 mainly showed natural rock, gravel and concrete chips and only a
slight portion of red brick particles, while light material 2 was clearly enriched
with brick.}

Fig 8:

Splittings

Fig 9:

Raw material

Fig 10:

Heavy material 2, concrete/natural rock

The heavy material 1 and the density fractions from heavy material 2 and light material 2 showed that concrete and natural rock were enriched in the heavy fraction. However, the brick fraction increased in the so-called light material, although the concrete fraction including mortar still showed the main portion (Figure 11).

^{Fig 11:
Material
composition

^{With regard to physical}
^-
^{mechanical characteristics, the difference in the apparent densities
is clearly recognised. This results in clearly lower and therefore a more
convenient impact fragmentation value of heavy material 2 when compared to
the heterogeneous mixture and light material 2. Heavy material 2 shows, even
after spalling of size fraction 8/16 mm after 10 freezethaw changes, values
equal to those obtained for high qualified primary materials (Figure 12).}}

Fig 12:

Mechanical characteristics

^By ^{applying wet processing techniques, it is possible to produce washed sand
almost free of disturbant substances. lt is therefore possible that the company
Baustoffaufbereitung K&S GmbH, Büttelborn, can obtain concrete up to
B 25 according to the general admission of building supervisory boards for concrete
given the DIN 1045 standard.}

Equivalence of RC Aggregates and Natural Mineral Materials

^{In neighbouring
countries, e.g. the Netherlands, regulations have existed for years allowing
a certain amount of recyclable material to be used for the production of concrete
on a higher level, i.e. for strength class B II according to DIN 1045 standard.
Up to now, the practice in the German Federal Republic shows, however, that,
apart from a few special cases, only concrete of class B I up to strength class
B 15 can be produced with RCA, strict compliance with the DIN 4226 standard
is required.}

Fig 13:

RC concrete cube

^{General
admissions of building supervisory boards for special applications were given
by "Deutsches Institut für Bautechnik" (German Institute for
Building Technique), Berlin.}

^{Furthermore, a general admission was also given for size fractions 2 a, 2/8
and 8/16 mm. but with lower demands "vF" ("verminderter")
("v") (lower) [Widerstand gegen Frost "F"] (freeze resistance)
according to DIN 4226-1 standard up to strength class B 26. Also in this case,
concrete may not have special characteristics, eg. water resistant, freeze /} ^{dew salt resistant according to DIN 1045 standard, paragraph 6.5.7.}

^{The best known
example for the application of RCA for higher qualitied concrete B 25 and B
35 is the new construction
of the administration building of the foundation of environment in ^{Osnabrück
(Figure 14). As part of the research programme "Baustoffkreislauf im Massivbau"}
^[^{BIM]
(Recycling of Mineral Building Materials), a demonstration building in Darmstadt,
Vibler Weg, was built using of recycling aggregates. The topping-out ceremony
was in March 1998.}}

Fig 14:

Foundation of environment, Osnabrück

The experience so far gained from the total research programme has influenced the "Beton mit rezykliertem Zuschlag" (concrete with recycled aggregate) guidelines. The final version of these guidelines (12th draft, May 1998) and will shortly be published.

^{The DAfStB (German
committee for reinforced concrete) guideline is exclusively valid for the use
of concrete chips and crushed concrete sands. lts validity is temporary in so
far as the guidelines should be revised and expanded after completion of the
research project in 1999.
Table 1 shows the rates
of recycled aggregates according to the guidelines:}

Table 1:

Maximum rates of recycled aggregates, relating to the total aggregate

^{The
guidelines allow the production of concrete with recycled aggregate up to
strength class B 35, except for concrete with special characteristics, e.g.
water resistant concrete, B 25. A further restriction of the application of
the guidelines is the fact that concrete e.g. for exterior units may only
be produced with recycled aggregate, if it can be proved that there will be
no} ^{harmful reaction of alkali / silicic acid. In practice, this that recycled
concrete may only be used for interior units} ^- ^{a drastic restriction for the industry.}

^{In principle, however, these guidelines can be regarded positively. As to restricted
application, a special admission depending on} ^{a certain building or a general admission of building supervisory boards
is no longer necessary in Germany. These guidelines complete DIN 1045 and DIN
4226 standards.}

^{On the strength
of these guidelines, further special admission procedures for the use of recycled
materials is scarce. Against this background, we refer to the confirmed admission
for brick loaded recycling materials of remex Dresden. With the assistance of
the general admission of building supervisory boards, they are able to supply
chips for concrete up to strength class B 25 using recycled aggregate from processed
brick masonry (maximum brick content 80 per cent by weight); admitted size fractions
are 4/8-vF (lower freeze resistance), 8/16-vF and 16/32-vF. The supplement to
the DafStB guidelines will allow further fields of application. Futhermore,
guidelines for RC aggregates enriched with brick shall be included.

^{In the long run, the DIN 4226 standard will be replaced by a European standard
presented as a draft in February 1997, entitled "DIN EN 12620 Gesteinskörnungen
für Beton einschließlich Beton für Straßen}^-
^{und Deckschichten" (DIN EN 12620 Rock Granulations for Concrete
lncluding Concrete for Road and Surface Courses). The appeal period ended
at the end of March 1997 and the respective national committee has already
handled the appeals.}
^{This European standard includes aggregates from recycled materials, in addition
to natural and artificial aggregates, so long as they show an apparent density
of particles over 2.0 Mg/m}3^{. There is also the advice that "supplementary
demands for rock granulations of recycling material may be requested".
The responsible ad hoc committee CEN 154 Recycled Aggregates is carrying out
a special examination of demands, which will be included in the revision of
the Standard within 3 years after its introduction. Until then, further essential
ideas of research programmes initiated by the German Committee for Reinforced
Concrete are being integrated in a 3-years-programme (1996-1998) "Baustoffkreislauf
im Massivbau" [BIM] (recycling of mineral building materials). This prograrnme
is financed by the Federal Minister for Development and Research (BMBF) and
by industry with a total budget of more than 12 million DM and carried out
by leading research institutions.

Resulting from knowledge concerning the application of recycled aggregates,
it is recommended to proceed as follows:

1. RCA can be used in non-constructive concrete applications up to strength
class B 15.

2. Utilise RCA within the of admissions of building supervisory boards (presently
up to B 25).

3. Application of ,,DAfStB" (German committee for reinforced concrete)
guidelines for recycled concrete up to B 35, mainly for inferior units.

4. General admission e.g. on}
^{the occasion of special applications as to prestressed concrete, otherwise
in case of general equal treatment with primary materials according to the
regulations of CEN standards.}
REFERENCES}^{1.

^{KOHLER,
G Recyclingzuschläge für Stahlbeton (Recycling aggregates for
reinforced concrete), Deutscher Beton-Verein e.V., Vorträge auf dem
Deutschen Betontag 1997, Berlin, pp 290-305.}

2.
^{KOHLER, G and
PENZEL, U Planning, building and management of combi plants for processing
of building and industrial residuals, Proceedings of the XX International
Mineral Processing Congress: 21 ^- ^{26 September 1997, Aachen, pp 481-495.}}

3.
^{KOHLER,
G Recyclingpraxis Baustoffe (Experienced recycling of building materials),
Verlag TÜV Rheinland, Köln 1997.}

4.
^{MESTERS,
K and KURKOWSKI, H Density separation of recycling building materials
by means of hg technology, Mineral Processing, edition 10, 1997, pp 536-542.}

5.
^{DEUTSCHER
AUSSCHUSS FUR STAHLBETON (German committee for reinforce concrete DafStB-Richtlinie.
Beton mit rezykliertem Zuschlag (Concrete with recycle aggregates), 12.
Entwurf (Mai 1998).}

6.
^{DIN
EN 12620 Gesteinskörnungen für Beton einschließlich Beton
für Straßen und Deckschichten (Aggregates for concrete, including
those for use in roads and pavements German version prEN 12620, 1996.}}

1.	^{KOHLER, G Recyclingzuschläge für Stahlbeton (Recycling aggregates for reinforced concrete), Deutscher Beton-Verein e.V., Vorträge auf dem Deutschen Betontag 1997, Berlin, pp 290-305.}
2.	^{KOHLER, G and PENZEL, U Planning, building and management of combi plants for processing of building and industrial residuals, Proceedings of the XX International Mineral Processing Congress: 21 ^- ^{26 September 1997, Aachen, pp 481-495.}}
3.	^{KOHLER, G Recyclingpraxis Baustoffe (Experienced recycling of building materials), Verlag TÜV Rheinland, Köln 1997.}
4.	^{MESTERS, K and KURKOWSKI, H Density separation of recycling building materials by means of hg technology, Mineral Processing, edition 10, 1997, pp 536-542.}
5.	^{DEUTSCHER AUSSCHUSS FUR STAHLBETON (German committee for reinforce concrete DafStB-Richtlinie. Beton mit rezykliertem Zuschlag (Concrete with recycle aggregates), 12. Entwurf (Mai 1998).}
6.	^{DIN EN 12620 Gesteinskörnungen für Beton einschließlich Beton für Straßen und Deckschichten (Aggregates for concrete, including those for use in roads and pavements German version prEN 12620, 1996.}