Re-use of construction and demolition residues and industrial wastes for the elaboration or recycled eco-efficient concretes

Production of residues from industries and construction and demolition sectors has increased during last years. The total amount of debris produced according to different estimations reaches values close to 42 million tonnes yr. Much of this waste has been thrown to landfill, without considering its potential for reuse, recycling or valuation. The aim of this research is to describe some of the physical and mechanical properties of different laboratory-mixed concretes, using various proportions of additional materials recovered from industrial waste and demolition rubble. The added materials are included either as admixtures (forestry residues, cork dust, steel fibre) or in partial substitution of natural aggregates (wire from electrical residues, tyre rubber, white ceramic, sanitary porcelain or shale). The laboratory tests have followed the standard EN protocols. Assay results were variable according to the nature of the material added to the mix: organic materials and shale, despite the steel fibre reinforcement, reduce the compression strength, but are suitable for the manufacture of lightweight concrete for agricultural pavements, with certain flexion resistance and a relatively good behaviour to impact. The substitution of natural aggregates with ceramic and porcelain wastes produces a signif icant increase in compression resistance, making them suitable for the manufacture of concrete with characteristic resistances above 40 MPa, which can be used both for structures or other agricultural elements: separators, feeders, slat floors. As a conclusion can be stated the possibility of reuse these wastes for the production of structural or non-structural concrete, with different applications in agricultural engineering. Additional key words: incorporated energy, recycling materials, rubble.


Introduction
For many years now, the councils of large and mediumsized urban centres, not only in Spain, but in Europe have been expressing growing concern over the collection, storage and, more recently, treatment of domestic waste.At the same time, public and political awareness about the issue of environmental degradation has heightened.This has led to the elaboration of the National Plan for Residues of  Residuos (PNIR)].This plan identifies two objectives: firstly, qualitative objectives aim to reduce the generation of construction and demolition residues at source, through correct management, re-evaluation and sorting in terms of recycling potential, and the closure of refuse tips and quarries.Secondly, quantitative objectives aim to achieve the controlled collection and correct management of 95% of wastes from construction and demolition from 2011 onwards, to reduce them by 15%, or reuse 15% by 2011, to recycle 40% of these types of wastes by 2011, to re-evaluate construction packaging materials by 2011, and to introduce selective collection and correct management of the same from 2008 onwards.In order to achieve these objectives, a variety of facilities will be required, such as evaluation and sorting plants, controlled refuse tips and transfer plants.
It has been estimated that some 200 million tonnes of rubble from the construction industry and building demolition is produced annually in the European Union (EU) (Aneiros Rodríguez, 2008).According to data from the National Plan for Residues of Construction and Demolition (2009), approximately 40 million tons are generated annually in Spain, the equivalent of 2 kg per inhabitant per day, a figure higher than that for domestic waste.According with Aneiros Rodríguez (2008) in the EU as a whole, 28% of these residues are recycled.The pioneering countries in this area are Holland, where 95% of construction residues are recycled, England, with 45%, and Belgium, with 87%, 17% of which is used in concrete production.In Spain, approximately 5% of total residues from construction and demolition is recycled, generally as road-fill and road sub-base or in buildings for pavements.
On the other hand the last decade has seen an alarming rise in the demand for aggregates in Spain.According to data for 2007, more than 450 million tonnes of aggregates is extracted annually in Spain, 65% of which is used in the production of concrete and asphalt.This spectacular increase in demand for aggregates, together with the obvious environmental restrictions on uncontrolled quarrying, has led to the proposal from within the sector for substituting recycled residues as an alternative to part of the aggregates used in concrete mixes.
Another significant aspect to consider is incorporated energy.One of the most important world-wide ecological objectives is the reduction of CO 2 emissions into the atmosphere (Kyoto Protocol, 1997).Indirectly, the construction industry is one of the principle sources of these emissions.Consider the enormous furnaces used in steel manufacture, or cement factories and the ceramics industry, or transport.These all include processes which invest energy in the production of construction materials, energy which can be termed incorporated energy.To give an idea of the magnitude of incorporated energy, it has been calculated that in order to produce one ton of steel, of bricks or of concrete, it is necessary to invest 60, 6 and 4 GJ of energy, respectively (Gordon, 2004).Furthermore, calculations suggest that of all the energy invested in the construction of a building, only 20%, approximately, corresponds to the actual construction process, whilst the remaining 80% is contained in the materials themselves (Presti, 2002).Thus, when a construction material is rejected as defective, or demolition is carried out, a large amount of incorporated energy is lost.It is necessary therefore, to develop practical methods for reusing these materials, and especially those representing most incorporated energy.According to data provided by Pilar Alaejos (Anon, 2001), one of the best means of recycling these residues is to incorporate them into mortar and concrete production.Such reuse would not only take advantage of the incorporated energy, but the number of refuse tips would be reduced.A concrete capable of incorporating these residues would be an eco-efficient material.In many cases, these possible uses will depend on the existence of pre-feasibility studies, as that proposed in this work.The main goal of this study is to show and demonstrate the real possibility of use construction and demolition residues or wastes from industrial sector to produce structural and non-structural concretes.
The first use of this type of eco-efficient concrete is an indirect one, but equally important as direct ones, concerning environment with a positive impact both ecological and landscape.This aspect is related directly with agricultural and forestry sector as is one of the most damaged with the presence of tips, mostly of them unlawful with lack of control.Also the possibility of reduction of quarries could positively affect the agro-forestry sector.
Whilst much research has investigated in detail the use of recycled aggregates in concrete production, such studies have basically focused on the reuse and recycling of aggregates from concrete.In our country mainly works by Sánchez and Alaejos (2003, 2005, 2006) reported the possibility of using these kinds of residues as a substitute for conventional coarse aggregates.They suggested a maximum percentage of 20%, due to the elevated absorption coefficient of this kind of material, although they also acknowledged the possibility of combining recycled aggregates with enhanced natural aggregates, and their use in structural concretes with a compression resistance equal to or less than 50 MPa.These studies suggested the possibility of use these eco-efficient concretes in the agricultural sector with a direct application in construction: structural with recycled concretes with ground white ceramic or sanitary porcelain (f ck greater than 25 MPa) in medium or small buildings (storehouses, animal housing, etc.) and non-structural (f ck less than 25 MPa) with a good traction behaviour in pavements or floors in animal housing for cows, sheep, etc. (recycled from cork dust with or without steel fibre), in forestry or garden paths, with recycled concretes from tyre rubber.In non-structural precast elements, with recycled concretes from shale or forestry residues, that give a more warm background in agricultural buildings.
Other interesting works about the possibility of reuse residues from construction and demolition are those published by Ryu (2002), Domínguez et al. (2004), Poon et al. (2004), Suárez et al. (2004), González and Martínez (2005), Evangelista and De Brito (2007), González et al. (2007), López et al. (2007), Rolón et al. (2007) and Guerra et al. (2008).The basic conclusion of all these studies is the real possibility of reuse recycled aggregates to produce concretes and mortars under certain conditions.Some of these studies also report a better durability behaviour of recycled concretes, this aspect is especially important for livestock o other agricultural buildings where aggressive environments are usually.
All these researches analyses the properties shown by the concretes thus mixed, where a percentage of the aggregates has been replaced by waste materials.The long-term aim of the work is to create ways of recycling different waste products, and in particular, waste materials from the construction industry and from demolition activities.
There are two objectives behind the development of this line of research: firstly, to find alternative sources of aggregates used in the construction industry, and secondly, to develop methods for recycling waste products, especially those which contain a significant amount of «incorporated energy».Given these objectives, the use of defective products produced by the ceramics industry is of great interest as these products have subjected to firing at high temperatures, endowing them with certain mechanical properties which may be profitably used in several contexts.
Another noticeable aspect is the inclusion in the recently published Spanish Standard for Structural Concrete, EHE-08 (2008) of a new annex of recycled concretes.This fact gives an idea of the importance and the real possibilities of this type of concrete.

Material
Two lines of research have been carried out to date.On the one hand, material for recycling was added directly to the concrete mix.The organic nature of these materials suggested a resultant low-resistance concrete, and therefore a concrete of characteristic resistance (f ck ) of 20 MPa was taken as the reference.The residues used in the production of these concretes included cork dust, cork dust with steel f ibre, and forestry residues.On the other hand, structural concretes were produced either by substituting a percentage of the aggregates with wire from electrical and electronic residues, tyre rubber, white ceramics, or sanitary porcelain, or by substituting the total fraction of coarse aggregates with shale from slag heaps (Truchas syncline, in the western Asturias-León region).In the latter cases (structural concretes), a structural concrete mix with a characteristic resistance of 30 MPa and 25 MPa respectively, was taken as the reference.
All assays used smooth silicate aggregates (maximum size 20 mm) and density was determined previously in the laboratory.The type of cement used is shown in Table 1.Dosage was designed to produce a plastic consistency, however, it was not always possible to achieve the desired consistency in all cases.
Using previous findings, and following De la Peña's granulometric module method (Arredondo, 1968), a water-cement ratio, and a theoretical dosage of water was established for each case, which later had to be corrected due to an excess of cement, aggregates humidity, or, in the case of concretes produced with cork dust, the high water absorption rate of cork.
All residues used were previously triturated and sieved until they were of the same size as the aggregate fraction they were to substitute.Table 2 shows the different proportions in which the various materials were added, either as an additional component or as a substitute for aggregates (sand or gravel) in the overall dosage of the different concretes assayed.Quantities were determined on the basis of the dosage for the reference, or control, concrete, which also served as the basis for comparison of results.
The methodology used was that typically used in the preparation of concrete test moulds.The aggregates were crushed and then sieved following European Standard EN 933-2 for sieving, and European Standard prEN 932-2 for crushing.The equipment used to test aggregates characteristics was previously calibrated following European Standard prEN 932-5.
Sand friability coefficients were determined following Spanish Standard UNE 83115-89.Gravel fragmentation resistance was determined using the Los Angeles test (EN 1097(EN -2:1998)).In all cases sand friability and gravel fragmentation were less of 40, value recommended by Spanish Standard for Structural concrete (EHE-08, 2008).Aggregates density and water content was determined following European Standards EN 1097-6:2000and EN 1097-6:2000 Mixing was carried out using a 250 L capacity mechanical concrete mixer.The components of the concrete mix were added to the mixer in the following order: first the water, next, part of the gravel followed by the gradual addition of cement, then the sand and the rest of the gravel.Mixing took 10 min approximately, after which a sample was taken to measure consistency using Abrams cone, according EN 12350-2.
The freshly-mixed concrete was used to fill 15 × 30 cm cylindrical moulds and 10 × 10 × 40 cm prismatic moulds following Standards EN 12390-1:2000 andEN 12390-1/AC: 2004.For each type of concrete, at least 11 cylindrical moulds and 3 prismatic moulds were filled.Cylindrical moulds were filled in three layers using a collector.Each layer was compacted using a standard steel rod, 600 mm long and 16 mm in diameter, with which they were each given 25 uniformly distributed blows to ensure amalgamation between the layers.Finally, the external surface of the moulds was vibrated lightly using a needle vibrator.
The prismatic specimens were filled using a collector and a filling hopper whose inner edge coincided exactly with that of the mould.They were compacted on a vibration bench using 50 blows, following which any excess concrete was removed.
All the specimens were covered with a sheet of plastic, and kept at 20°C for 48 h.After this, they were removed from their moulds and cured at 20°C and 95% relative humidity, following European Standard EN 12390-2:2000.Breakpoint tests were carried out after 7, 14 and 28 days.The cylindrical moulds were used to carry out compression tests following EN 12390-3:2001, and indirect traction tests (Brazilian test), following Standards EN 12390-6:2000 andEN 12390-6:2000/ AC:2004, using a universal press.The simple compression test was carried out using previously capped moulds.
The prismatic moulds were used to carry out flexotraction tests following EN 12390-5:2000and EN 12390-5:2000/AC: 2004, and subsequent compression tests, following EN 196-1:2005.European Standard EN 14158:2004 was followed to carry out impact assays on some of the moulds.Two types of mould were used for this test, comprising small pyramid-shaped plates (Type S), with a 193 × 193 mm upper face, 170 × 170 mm lower face, and 44-49 mm thick, and big plates (Type B), with a 190 × 390 mm upper face, 180 × 370 mm lower face, and 40-45 mm thick.
The number of moulds used for compression tests on each type of concrete is shown in Table 3.For all other tests, see Table 4.

Results
Results obtained for each type of concrete are presented in Table 5.As can be observed, the mean resistance f cm of experimental concretes with white ceramic and sanitary porcelain is greater than that of the reference concrete.
However, for all other experimental concretes, a reduction in characteristic resistance can be observed, compared to the reference concrete, indicating that structural applications would not be appropriate.Table 6 gives consistency, measured using Abrams cone.
As regards the indirect traction tests (Brazilian test), flexocompression tests and flexotraction tests, the same conclusions can be drawn as those respecting the compression tests: concretes mixed with white ceramic and sanitary porcelain show good resistance behaviour, whilst the remaining mixes show bad or very bad resistance behaviour, and are not appropriate for structural applications.
As can be seen in Table 5, the impact test was only carried out on those concretes not intended for structural use, that is, concretes with cork dust or forestry residues.For all these, fracture energy was highly variable, according to the dosage employed, but capacity for absorbing impact energy was surprising, although inferior to that of the reference concrete.Nevertheless, the difference was much less than that observed for all other resistance tests.It should also be noted that the two types of concrete for which best results were obtained were those incorporating forestry residues.

Discussion
Results obtained demonstrate the possibility of reusing different wastes from several industries, mining, forestry activities and construction and demolition as components of eco-efficient concretes.
Related with this subject there are similar works (Ryu, 2002;Sánchez and Alaejos, 2003, 2005, 2006;Domínguez et al., 2004;Poon et al., 2004;González and Martínez, 2005;Evangelista and De Brito, 2007;Rolón et al., 2007;among others); their results show that in many cases the concrete obtained present a loss of resistance.It is possible to establish the following: the use of materials as admixtures for concrete such as: shale, triturated wire and tyre rubber as a substitute for aggregates, as well as the incorporation of cork dust, cork dust with steel fibre and forestry residues as additional components reduce characteristic resistance in the resultant concretes, making them inappropriate for structural applications.These concretes could, however, be used for non-structural applications, for example for tiles or pavements in farms or others agricultural buildings (González et al., 2007).
Related with admixture of cork dust, the final concrete hardly reached a 10% of resistance compared with control concrete, but it keeps a good behaviour in the impact test: 6.1 J (5% dry aggregates) vs. 8.8 J of control concrete.The addition of 1% of forestry residues decrease the characteristic resistance of concrete up to values of 60%, compared with control, whilst the impact resistance is similar to the reference concrete, some concretes with these type of residues (2.8% pine) even improve these resistance.
In the same line is the concrete with electrical and electronic residues, the mean characteristic resistance (18.1 MPa) hardly reaches the requirements for mass concrete (established in 20 MPa according EHE-08).It is noticeable that the higher the proportion of wastes on the dosage, the worse the final resistance, which makes sense in these cases, where the added materials do not improve any of the properties of the material replaced.
The use of shale as coarse aggregate did not produce the expected resistance in concrete (Suárez et al., 2004), the final resistance was nearly 50% of the reference concrete.The behaviour of rubber addition in the proportion of 1% was much better than expected, obtaining a compression and indirect traction resistances approximately equal to the reference concrete.
A special case is concrete produced with white ceramic and sanitary porcelain wastes.These ones reached resistance values greater than the reference concrete.With the use of 20% of white ceramic in substitution of ordinary sand, the compression resistance of concrete has been of 55 MPa, a higher value compared with 36 MPa obtained for the reference concrete.In general, this resistance is maintained with other higher proportions of recycled aggregate (Guerra et al., 2008).Results obtained with sanitary porcelain are in the same line.In this case, the porcelain has replaced a part of the coarse aggregate (between 3 and 9%).The results show that the resistance of the new concrete remains similar to reference concrete in all tests: compression, indirect traction and flexion.
Therefore these recycled aggregates can be used to obtain structural concrete (López et al., 2007;Guerra et al., 2008).However, this conclusion does not agree with the results obtained by Correia et al. (2006) in concrete produced with ceramic wastes aggregates; in these studies a loss of resistance was observed in comparison with reference concrete and therefore nonappropriate for structural use.The explanation for this discrepancy may be due to the different origin of the waste used in each case.The studies developed for Correia used a direct debris from demolition and construction, containing other residues and dirt, this is the ultimate cause of the loss of resistance observed.In the other cases the ceramics residues used in the study comes from an industry wastes, clean, free of impurities.This waste is not contaminated with other components and have an adequate quality in order to obtain a structural concrete.The immediate consequence is: for a suitable reuse of these wastes a previous process is essential.This process must include separation and clean from other materials, nowadays these processes are not implemented in treatment plants.
Finally it can be considered the high amount of acquired energy contained in the recycled concrete using wastes as ceramic or porcelain, which have a previous oven thermal process, maintaining their resistance properties.These concretes can be described as structural and eco-efficient.Therefore we can conclude that recycled concrete with ceramic is an ecoefficient material.

Table 1 .
Cements used for different concretes

Table 2 .
Substitution/addition percentages of the different materials added to the concrete DA: dry aggregates.DG: dry gravel.G: gravel.S: sand.SF: steel fibre.WA: wet aggregates.WG: wet gravel.

Table 4 .
Number of moulds fractured in the various tests

Table 5 .
Mean values of results obtained for each type of concrete CD: cork dust.DA: dry aggregates.DG: dry gravel.G: gravel.RC: reference concrete.S: sand.SF: steel fibre.WA: wet aggregates.WG: wet gravel.