In relation to the use of recycled aggregates in concrete the existing standards and technical specifications were screened in order to identify possible barriers. It was found that in the existing national standards in fact no explicit barriers were present.
Surprisingly however informal contacts brought about that the intention existed to take up explicitly in the new draft of NBN B15–101 (the Belgian implementation of EC2) that this standard was not applicable to recycled concrete!
As far as concerns official tender specifications it was found that the most recent of
them explicitly quoted that the materials to be used must be “new”. Yet in some older documents clauses were found in relation to the use of chrushed bricks [10]. Much of what was quoted however was to vague to be still useful. As an example following provisions were found in the 1979 version of the “General specifications for private-works”:
Clause 5.23.14. Masonry rubble.
Masonry rubble is obtained by chrushing hard bricks or other well-fired clay products. Bricks from demolished chimneys, ovens or stables may not be used.
The rubble may not contain any gypsum or saltpetre. Before use the rubble has to be saturated with water.
Relevant literature was consulted by the LIN working group in the process of drafting specifications for recycled concrete. Of particular interest was the RILEM report
“Recycling of Demolished Concrete and Masonry” as well as the link through the BBRI with the RILEM TC 121-DRG. The principle was adopted to draft the specifications along the lines of the recommendations which were in the process of elaboration in the aforementioned technical committee.
The essential elements of the worked out specification are given in the next tables, they consist in requirements for the aggregates (table 1), clear definitions of acceptable applications (table 2) and design values for the recycled concrete (table 3). Two types of material are distinguished and allowed to be used in recycled concrete, i.e. coarse aggregates GBSB-I and GBSB-II. Acceptable grading curves for the material (fig. 3) are those given in NBN B11–101, making exception of the gradings 2/4 and 2/7.
Table 1. Mandatory requirements in relation to the composition of recycled aggregates for concrete.
GBSB-I GBSB-II
Dry density (NBN B11–255) >1600kg/m3 >2100kg/m3 Water absorption at 24h. (NBN B11–255) <18% <9%
Content of material with a density<2100 kg/m3 - <10%
Content of material with a density<1600 kg/m3 <10% <1%
Content of material with a density<1000 kg/m3 <1% <0.5%
Content of broken natural stone, concrete, masonry or ceramic
material (asphalt excluded) >95%
Content of foreign materials (metals, glass, bitumen, soft material,
…) <1%
Fraction<80µm (NBN B11–209) <5% <3%
Organic material (NBN 589–207) <0.5%
Chloride content (NBN B11–202) <0.06%
Sulphate content (NBN B11–254) <1%
Table 2. Field of application for recycled concrete.
(A 100% substitution of the coarse aggregates by recycled aggregates is accounted for.
The sand to be used is of natural origin).
MAXIMUM ALLOWED
STRENGHT CLASS ALLOWED EXPOSURE CLASS
GBSB-I C16/20
• interior of buildings with dry environment (exposure class 1)
• components in non-aggressive soil and/or water not exposed to frost (exposure class 2a)
GBSB-II C30/37
• interior of buildings with dry environment (exposure class 1)
• components in non-aggressive soil and/or water (exposure class 2)
Table 3. Design values.
(Worst case values to be adopted in the absence of more accurate experimental results).
Coefficients to be applied on the values stated in prENV 1992–1–1 GBSB-I GBSB-II
Tensile strenght (fctm) 1 1
Modulus of elasticity (Ecm) 0.65 0.8
Creep (ф(∞,t0)) 1 1
Shrinkage (εcso) 2 1.5
Fig. 3. Grading curves for the recycled aggregates.
In a strict sense the specification worked out only apply for public works. It is however believed that they will also be used in the private sector and give a strong impulse to the use of recycled aggregates in concrete in general.
5 Environmental legislation
In the process of recycling there must of course carefully be watched that no contaminated material enters the circuit. The recycling industry is quite well aware of this fact and realises that if such would arrive this could be very harmful for the further development of the sector. In this respect the acceptance policy at the plants is of major importance. The origin of the waste must be known, suspected material is to be refused and control procedures have to be established. Selective demolition has to be promoted!
This is a necessity as well from a technical point of view as from an environmental point of view.
The recycling plants try to promote selective demolition by using different dumping tariffs for mixed and clean material. By the authorities a system of demolition permits should be made obligatory. It should be the responsibility of the owner to make a report on the use of the building and the materials involved. If during the demolition not reported suspected materials are found, an auto control by the contractor will in this way come into play. A follow-up of the waste stream is further also needed.
Anyway it is well realised that an integrated approach of demolition and further processing is needed [2]. The responsibilities of the waste transporter, demolition contractor and certainly also the commissioner of the demolition work, i.e. the building owner may not be underestimated and the responsibilities of each have to be clearly fixed. A lot of work still remains to be done in this respect.
Of cause it should also be clarified what is understood under contaminated waste. Here too a lot of work remains to be done and even a lot of knowledge is lacking.
What is to be considered as contaminated waste? Which materials should be refused?
What are acceptable limits of heavy metals, poly aromatic hydrocarbons and such? What are acceptable applications depending on certain pollutant concentrations?
Globally in this respect a similar approach as in the Netherlands is followed by OVAM in Flanders, i.e. a classification depending on leaching characteristics and the chemical composition of the materials (fig. 4). On some points however quite another orientation is followed, i.e. for example related to hydraulic bound materials where the chemical composition is considered in quite another perspective.
Fig. 4. Environmental qualification of recycled materials.
Actually heavy discussions are going on regarding this matter and research proposals have been forwarded. In anyway care should be taken not to be drowned in “ppm’s” and
“ppb’s” but rather realistic and workable solutions should be sought. It remains indeed a fact that most of the building and construction waste is in nature not harmful at all.
Another legal problem that has to be resolved is this of the legal status of recycled construction and demolition waste. Is recycled construction and demolition waste still waste? Obvious not! But how far must the processing go before this is the case?
Currently also this legal problem is being studied by OVAM and proposals are put forward to work towards a system of environmental attestation.
6 Conclusions
In relation to the problem of construction and demolition waste quite a lot of things are moving in Belgium. Yet a distinct difference exists between the North and the South of the country. Specific geographical differences between the regions account for this situation and will probably always result in a different economic interest in recycling
between the regions. Regarding environmental legislation a lot of work remains to be done and in this respect care should be taken not to be drowned in “ppm’s” and “ppb’s”.
Realistic and workable solutions should be sought. A coordinated approach in the different regions should be aimed at in order to prevent confusion. In this matter the National Confederation of the Building Industry (NCB) can and will play an important role. The latter even on an European level through its involvement in the FIEC and in EEC initiatives.
7 References
1. Problematiek van bouw-en sloopafvalstoffen. Voorbereidend rapport i.o. van de OVAM. WTCB-Recymat. Januari 1990. (In Dutch).
2. B.Simons & F.Henderieckx. Selective demolition. Guidelines and experiences in Belgium. RILEM 3th International conference, Odense 1993.
3. Problematiek van bouw-en sloopafval in het Brussels Gewest. Rapport i.o. van het BIM. WTCB-Recymat. Maart 1991. (In Dutch).
4. H.Motteu & E.Rousseau. Recycleren van afvalstoffen in de bouw. WTCB-tijdschrift zomer 1992. (In Dutch and French).
5. Provinciaal recyclage-initiatief van de Westvlaamse wegenbouwers. Bouwbedrijf nr.
17, 23 April 1993. p. 30. (In Dutch).
6. C.De Pauw, W.Goossens & J.Vyncke. Recycling of construction and demolition waste.
Plant concept. Organization and staffing. Essen, 1991.
7. C.De Pauw. Béton recyclé. CSTC-revue no. 2, juin 1980. (In French and Dutch).
8. C.De Pauw. Recyclage des décombres d’une ville sinistrée. CSTC revue, no. 4, décembre 1982. (In French and Dutch).
9. Hoe 80.000m3 gewapend beton veilig laten springen en recycleren. KVIV-WTCB studiedag. Antwerpen, 1987. (In Dutch).
10. B.Simons & J.Vyncke. Les Déchets de construction et de démolition. CSTC-revue printemps 1993. (In French and Dutch).