Recycled aggregates from construction and demolition waste (CDW) are commonly classed in coarse (CRA) and fine (FRA) fractions. Unlike CRA, which are ...
Fray International Symposium METALS AND MATERIALS PROCESSING IN A CLEAN ENVIRONMENT Volume 4: MATERIALS RECYCLING, SILICON FOR PHOTOVOLTAIC CELLS & BORON & BORATES Edited by Florian Kongoli, FLOGEN
PHYSICAL AND CHEMICAL-MINERALOGICAL CHARACTERIZATION OF FINE RECYCLED AGGREGATES FROM CONSTRUCTION AND DEMOLITION WASTE Fernando Rodrigues1 , Maria Teresa Carvalho1 , Manuel Francisco Pereira1, Luís Evangelista2 , Jorge de Brito1 1
2
Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa Instituto Superior de Engenharia de Lisboa, R. Conselheiro Emídio Navarro, 1 1959-001 Lisboa
Keywords: Construction and demolition waste, fine recycled aggregates, physical, mineralogical and chemical characteristics, Portuguese recycling plants ABSTRACT Recycled aggregates from construction and demolition waste (CDW) are commonly classed in coarse (CRA) and fine (FRA) fractions. Unlike CRA, which are now widely used in different applications including concrete, FRA (minus 4 mm fraction) are used as low-value products (for roads, landscaping and landfilling). One of the main reasons for this is the poor knowledge of their properties, which prevents their application in added-value products such as concrete. The development of a methodology to classify FRA aiming at their application in different applications relies on the physical/chemical-mineralogical characterization that is conditioned by the composition of the CDW and by the processing they were subjected to. This paper describes the experimental work carried out aiming at the characterization of this fraction of recycled aggregates and of its influence on the properties commonly used to predict concrete behavior. For this purpose, samples from 7 Portuguese CDW recycling plants were collected. The criteria to choose the plants were the geographical location and the type of CDW processing at the recycling plant. The former was due to the geological environment where the materials used in the construction were collected and to the building techniques employed, because they are most probably related with the composition of CDW and the resulting aggregates. The CDW processing diagram, equipment type and parameter settings may also affect the physical and the physical aggregate properties. The particle size analysis of each FRA was carried out and the over 1 mm fraction was manually separated in different materials (e.g. aggregates, wood and plastics) for composition evaluation. The inert fraction was grinded and dissolved in HCl for carbonates and other soluble minerals quantification. Then, a chemical-mineralogical characterization of the remaining sample by means of X-ray fluorescence and X-ray diffractometry was made.
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Finally, the physical properties of the aggregates that are commonly used to predict concrete behavior such as bulk density, water absorption and voids percentage were determined. The relationship between these and the physical/chemical-mineralogical characteristics was obtained leading to classification of FRA in different categories. It was found that FRA characteristics are defined mostly by the geological environment of the recycling plant. INTRODUCTION Construction is responsible for the annual consumption of 40% of natural resources such as stone and sand [1]. Sustainable development implies that such consumption must decrease as the use of construction and demolition waste (CDW) increases. Today, the recycling of coarse inert materials from CDW is common. The feasibility of the use of the CDW fine fraction (minus 4 mm) in valued products such as concrete has not yet been fully proved. Due to a poor knowledge of its properties its use remains restricted to roads, landscaping and land filling. However, studies carried out with artificial fine recycled aggregates (FRA), obtained from concrete pieces made and demolished in laboratory, showed that this material can be used in concrete with no limitation up to a 30% substitution of the natural aggregates [2]. The applicability of real FRA in concrete, however, relies on the knowledge of their physical/mineralogical-chemical properties that determine the concrete properties. It is expected that these properties are related to the composition of the CDW and the upstream processing diagram used to produce the FRA product. Assuming that in the constructions that originated the CDW the raw materials used are mainly extracted in the CDW plants’ neighborhood, it is expected that FRA composition is mainly influenced by their geographical location which is related to the regional geological resources and construction methodologies/types adopted. As well, the CDW processing plant design has impacts on the physical and chemical characteristics of the FRA product depending on the fragmentation equipment type (jaw, gyratory or hammer crusher) and parameter setting, screen type and size and, mainly, the processing diagram. The knowledge of the physical properties of the aggregates used in concrete is extremely important, since the properties of the final concrete depend directly on the quality of the aggregates [3]. The studied physical properties were those specified in standard EN 12620:2008 [4], which defines the requirements for the aggregates to use in concrete. Only the properties that are applicable to the fine aggregates were studied. The water absorption by the fine recycled aggregates is commonly referred as quite high [5] [6] [7]. This is one of the major difficulties of the application of these aggregates, since they tend to absorb the water needed during concrete mixing. Therefore, the knowledge of this property is also quite important to define the correct content of water in the mix. This study aimed determining of the influence of the physical, mineralogical and chemical characteristics of FRA on the concrete properties. Ten products from seven CDW processing plants were characterized. The plants were chosen so that different geographical location and geological environment as well as CDW processing could be analyzed. PROCESSING PLANT AND SAMPLED PRODUCTS Table I lists the processing plants used in this study and the category of each sample. Figure I shows the location of the seven plants chosen for this study. The geographical dispersion of RTR, VAL, ARV, AMB and the group of TRI, SGR and VIM ensure that different types of 302
construction are analyzed. While RTR, SGR and VIM are located near large size towns, the others are located in predominantly rural areas. In what concerns the geological environment, RTR and VAL are located in regions where granitic rocks are abundant, while the others are located in geological units where carbonate rocks dominate (Portuguese West and Algarve Mesocenozoic borders). In what concerns the processing diagrams, in all plants, metals, such as iron and steel, plastics, paper and cardboard are manually or automatically separated and sent to the corresponding recycling industries. The inert fraction is then crushed and screened. Crushing is made either in jaw or hammer crushers. The crusher and screen parameter settings vary from plant to plant. The crushing and classification diagrams are different. Table I. List of the recycling plants. category of each sample Recycling plant Sample Category Name Abbreviation code AMB-c Aggregates mostly from concrete AMBILEI AMB AMB-m Aggregates from a mix of CDW ARVELA ARV ARV Aggregates from a mix of CDW RETRIA RTR RTR Aggregates from a mix of CDW SGR #1 Aggregates from a mix of CDW from the first screening S.G.R. SGR SGR #2 Aggregates from a mix of CDW from the second screening TRINOVO TRI TRI Aggregates from a mix of CDW VALNOR VAL VAL Aggregates from a mix of CDW VIM #1 Aggregates from a mix of CDW from the first screening VIMAJAS VIM VIM #2 Aggregates from a mix of CDW from the second screening AMB
PROCESSING DIAGRAM OF AMBILEI Recycling Industries
Reception and weighing of the CDW Recycling Industries
Plastics Paper Wood
Manual waste removal
Metals
Jaw crusher
Magnetic Separation
0-50 mm
Storage
303
Metals
PROCESSING DIAGRAM OF ARVELA
ARV Reception and weighing of the CDW
Recycling Industries
Plastics Paper Wood Iron and Steel
Manual sorting
Metals
Magnetic separation
Screening
0.6 – 32.5 mm
Plastics Paper Wood Steel and Iron
+ 32.5mm Manual sorting - 0.6mm
Metals Magnetic separation
Mill hammer + 32.5mm Landfill
Screening - 0.6mm
0.6 – 32.5 mm
Storage
PROCESSING S.G.R. DIAGRAM OF RETRIA Incineration- Steelwork factories
Reception and weighing of the CDW
Not inert waste compound Landfill
Manual sorting
Screening (250 mm) + 250mm Magnetic separation Storage SGR #1
Metals Screening - 20 mm
+ 40 mm
Storage SGR #2 - 40 mm
Not inert waste compound
Manual sorting Recycling industries
Storage SGR #3
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PROCESSING DIAGRAM OF SGR
S.G.R. Incineration- Steelwork factories
Reception and weighing of the CDW
Not inert compound Landfill
waste
Manual sorting
Screening (250 mm) + 250mm Magnetic separation Storage SGR #1
Metals
Screening - 20 mm
+ 40 mm
Storage SGR #2 - 40 mm
Not inert compound
waste
Manual sorting Recycling industries
Storage SGR #3
TRI PROCESSING DIAGRAM OF TRIANOVO
Reception and weighing of the CDW
Manual sorting
Recycling industries
Plastics Paper Wood Iron and Steel
Screening
- 5mm
5-20mm
+ 20mm
Jaw crusher
Landfill
Mill hammer
+ 20mm Final screening
0-20mm
Storage
305
VAL PROCESSING DIAGRAM OF VALNOR Reception and weighing of the CDW
Recycling industries
Metal recycling
Plastic Paper Wood
Manual sorting Metals Metals
Magnetic separation
Jaw crusher +50mm Screening
- 10mm 10-50mm
Storage
Landfill
VIM
PROCESSING DIAGRAM OF VIMAJAS Reception and weighing of the CDW
Metals Manual separation
Landfill
1st screening
Metals recycling
- 45 mm + 45 mm Impactor crusher
Metals
Magnetic separation
Storage VIM #1
2nd Screening
Incineration
- 8mm + 8mm
Not inert waste coumpound
Triagem manual Wood
Aggregates Mill hammer
Biomass
-38mm + 38mm Storage VIM #2
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Figure I. Location in Portugal of the seven recycling plants studied. All the processing diagrams are included in annex. The sampled products are represented in colored gray blocks. Table II shows the main singularities of the seven diagrams. Although VAL has a product specification of 10-50 mm, the proportion of minus 4 mm is quite high. Two of the plants (VIM and SGR) produce two products containing minus 4 mm material. One plant, AMB, processes concrete (AMB-c) and CDW mixture (AMB-m) independently. Samples from the ten different products from the seven plants were then collected. Table II. Main singularities of the processing of CDW in the seven recycling plants.
Sample
TRI
VAL AMB
ARV
VIM #1
VIM #2
SGR #1
Sample specification (gauge in mm)
0-20
10-50 0-50
0.632.5
0-8
0-38
0-20
Not Not Screen size 5 mm presen prese 0.6 mm before crushing t nt Type of Hamm Hamm Jaw Jaw crushing er er Screening after Yes Yes No Yes crushing
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SGR #2
RTR
Not 20-40 availab le
45 mm
Not present
40 mm
Hammer
Not present
Jaw
Yes
Yes
No
PHYSICAL, MINERALOGICAL AND CHEMICAL CHARACTERIZATION PROCEDURE The mass of each sample is given in Table III. Table III. Mass of the collected samples
Sample name AMB-c AMB-m ARV RTR SGR #1 SGR #2 TRI VAL VIM #1 VIM #2
Mass collected (kg) 59.0 60.2 39.8 46.3 50.6 51.3 57.4 43.0 61.2 63.4
Each sample was subjected to the procedure illustrated in Figure II. Several representative subsamples of the primary samples were prepared for further analysis by division using a Jones splitter. Macroscopic Composition of the 1-4 mm fraction by manual sorting Size Distribution Sample
% Soluble Minerals in HCl - 4 mm
Screening
Division
Mineralogical Analysis (XRD)
Chemical Analysis (XRF)
+ 4 mm
Bulk Density Physical Properties
Water Absortion Apparent bulk density
Figure II. Procedure summary chart.
PARTICLE SIZE DISTRIBUTION Firstly, the particle size distributions were determined using the European standards for screen size selection, EN 933-2, [8] and execution method, EN 933-1 [9]. The importance of knowing the size distribution is also referred in standard EN 12620:2008. Figure III illustrates the method. A modification of this standard was made for the samples that were not washed before sieving, allowing the quantification of the fraction minus 63 μm, as seen in Figure IV.
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Figure III. Sieves and shaker used on size distribution.
Figure IV. Fraction minus 0.063 mm.
CHEMICAL AND MINERALOGICAL ANALYSIS OF THE FINE RECYCLED AGGREGATES After the particle size distribution was determined, the samples were screened at 4 mm. The fine fraction was quantified and divided in equal parts for subsequent analysis. Figure V and Figure VI show the fraction minus and plus 4 mm, respectively.
Figure V. Fraction minus 4 mm. (VIM #1)
Figure VI. Fraction plus 4 mm. (VIM #1)
The first analysis performed was the determination of the composition by material in the 1 -4 mm fraction. This analysis was made by manual sorting, where the minimum size of 1 mm is the one below which visual identification of the different materials is almost impossible. The calculation of the grade in carbonates and other soluble minerals was made by complete dissolution in HCl. Finally mineralogical analysis, by X-Ray diffraction (XRD), and chemical analysis, by X-Ray fluorescence (XRF), both semi-quantitatively, were carried out. PHYSICAL CHARACTERIZATION OF THE FINE RECYCLED AGGREGATES The bulk density and water absorption were calculated using the fraction 0.063-4 mm, resulting from the sub-sample washing in a screen with 0.063 mm sieve size. According to standard EN 1097-6 [10], the following physical properties were determined: -
The apparent particle density (ρa), which represents the ratio between the mass of a sample dried in an oven and its volume, including the internal pores, inaccessible by water, but excluding the pores accessible by water;
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The oven-dry particle density (ρrd), which represents the ratio between the mass of oven dried aggregate and the volume it occupies under water, including every pore, accessible or inaccessible by water; - The saturated surface-dry particle density (ρssd), which is the relationship between the mass of a sample of the aggregate, including the mass of water within the accessible pores, and its volume, including every pore. The water absorption was also determined, after immersion in water during 24 hours. -
The bulk density (ρb) and void percentage, v (%), were determined using the EN 1097-3 [11] that recommends the use of the complete size fraction (0-4 mm). According to the standard, the sample was first dried in an oven at 110ºC, for 48 hours. Then, a 1 liter bucket was used to determine the bulk density. The void percentage of the aggregate was calculated using the values of the bulk density and the oven-dry particle density. The results presented in Table IV are the average of three tests. Table IV. Summary of the experimental procedures. Sample size gap (mm)
Procedure
Macroscopic composition
1-4
Mineralogical analysis Chemical analysis Particle densities and water absorption determination Apparent bulk density and void percentage
0-4 0-4
Manual separation XRD XRF
0.063-4
NP EN 1097-6
0-4
NP EN 1097-3
RESULTS ANALYSIS OF THE PLANTS DIAGRAMS AND PARTICLE SIZE DISTRIBUTION The flowcharts used in the seven plants are quite different, leading to different products. The simplest diagrams are the ones used in SGR and in AMB. In what concerns inert material, in SGR diagram’s there is no crushing, i.e. processing is restricted to the classification by size. In AMB there is no classification by size, only crushing after the separation of the not inert materials. After sorting, all the plant feed is crushed making a unique product. At VIM there are 2 crushing stages leading to three inert products. At RTR, TRI and VIM, a fine fraction is separated before fragmentation, and then landfilled. This fine fraction has a maximum particle size that changes from plant to plant. For instance, in ARV the fine fraction corresponds to the minus 0.6mm product while in VIM it corresponds to the minus 45 mm. The diagrams differ also in the fragmentation and screening equipment type and parameter setting leading to the particle size distributions shown in Figure VII. Despite the differences in processing diagrams described above, four plants produce similar products: RTR, TRI, AMB and ARV. SGR and VIM have different particle size distributions because these plants produce one finer and one coarser product. VAL product exhibits a particle size distribution that is the result of the elimination of the minus 10 mm fraction. The other size particle size distributions correspond to regular crushed material. 310
Figure VII. Particle size distribution of the various samples. The differences in the distributions of both products of AMB are due to the fact that AMB-m (CDW mixture) is softer than AMB-c (concrete waste), so it produces a higher proportion of fine material. The observed particle size distributions, in some cases, do not correspond to the plants’ commercial products specifications. Table V shows some values taken from the observed particle size distributions. For instance, three plants (VAL, ARV, and SGR #2) have, in the final product, material with size below the specification. The recycling plants TRI and VAL produce a high percentage of material above the specification. These anomalies may be due, for example, to malfunction, incorrect sizing of the screens or screen surface deterioration. Table V. Products specifications and some particle size distribution values.
Product TRI VAL AMBm AMB-c ARV VIM #1 VIM #2 SGR #1 SGR #2 RTR
Product specification (mm) 0-20 10-50
Material with Material with Material with size particle size below particle size below 4 mm, the specification above the present in the (%) specification (%) sample (%) 20 27 25 30 8
0-50
-
5
44
0-50 0.6-32.5 0- 8 0-38 0-20 20-40 Not defined
15 75 Not defined
4 5 0 0 0 0 Not defined
37 40 80 22 84 30 40
Concerning the fraction with particle size below 4 mm, the object of this project, it appears that plant VAL produces a low percentage of this fraction, about 8% of its total production. Although higher than VAL, samples VIM#2 and TRI have also a low percentage of this fraction, i.e. 22% and 27% respectively. The fine product of plants VIM and SGR, denominated VIM#1 and SGR#1, are potentially the most interesting for application in concrete with fine recycled aggregates, as they have both more than 80% of material below 4 mm.
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COMPOSITION, MINERALOGICAL AND CHEMICAL ANALYSIS OF THE MINUS 4 MM FRACTION The overall results of the macroscopic composition, mineralogical and chemical analysis of the products are shown in Table VI. The macroscopic composition results show that in most of the seven plants sorting of other materials than inert ones is efficient, for there are only residual percentages of other materials present in the 1-4 mm fraction. Considering the complexity and heterogeneous nature of the analyzed materials, quantitative chemical and mineralogical analysis is not appropriate to perform a preliminary characterization of these products. These products could include inorganic and organic compounds, and crystalline and amorphous phases in their composition. Therefore the analysis of the chemical and mineralogical composition of the products was performed using XRD and XRF in a semiquantitative way, based in normalized results. The XRD results are normalized considering the highest reflections of the main minerals phases identified: quartz, calcite, K feldspar, Na feldspar, muscovite/illite and gypsum. Amorphous or other crystalline phase such as hematite, portlandite, calcium and/or aluminum silicates, are not included in this study because the reflections are generally low. The XRF results are normalized considering the kα (1 st order) of the main elements present. To do a global interpretation based in the ratios presented in the Table VI, this normalization should be taken in consideration, as different products have different grade of quartz and calcite. The values have been normalized by Si kα (I) reflection. This approach seems to be adequate to characterize the different products, in order to define differences/tendencies in their geographic/geologic domain, global composition and features related to the processing plant design. The grade in brick in VIM is much higher than in the other plants products, while in AMB-c and ARV it is much lower. These observations are corroborated by the iron content obtained in the chemical and mineralogical analysis. The grade of bricks is correlated to the content of hematite (Fe2O3), easily detectable in XRD (not in Table VI). Unlike the others, the SGR and AMB-m samples exhibit significant gypsum content. This can be observed macroscopically and by chemical analysis for the grade in sulfur is higher in these samples than in the other samples. This observation is explained by the fact that, unlike the other plants, in these two plants there is no upstream separation of a fine product containing the small gypsum particles. Differences in the regional building materials and techniques could be considered as well in order to explain some of the differences found. In what concerns calcite and other minerals soluble in HCl, RTR, VAL and SGR#2 products have the lowest content. These products present 16% to 22% in weight of HCl soluble minerals while in the others the ratio varies from 30% to 39%. These results of acid dissolution are fully confirmed by XRD and XRF results. SGR product, especially the coarser one (SGR#2), has a composition quite different from that of SGR#1, showing the results of the separation of fine materials in the processing treatment. After this separation, SGR#2 has the highest grade of quartz of the analyzed samples. Considering also the XRD results, it is concluded that the VAL and RTR products are a separate group, where quartz, feldspar and muscovite are dominant (see Qz/c and (Qz+KF+NaF)/c ratios in Table VI). This could be related to a regional geological framework that influences the composition of the building materials, namely sand and aggregate materials with dominant granitic composition. The K relative content is strongly correlated to the presence of feldspars and muscovite. The VIM products present intermediate content of feldspars but have higher content of calcite, suggesting also a regional control of the origin of the building 312
materials. The remaining products are very similar showing higher content of calcite (binder and/or aggregates) and purer sands. The observation of the -63 μm fraction analyses shows, as predicted, an improvement in binder materials content due to the presence of cement products, lime, gypsum and (more rarely) clay minerals. XRD and XRF results (not shown in Table VI) show a consistent increase in calcite and Ca and S elemental content. Table VI. Results of the macroscopic composition, mineralogical and chemical analysis of the samples. TRI VAL AMB-m AMB- ARV VIM#1 VIM#2 SGR#1 SGR# RTR Plant c
2
Composition Minerals Fraction 14mm (%) Brick Others Total Soluble fraction (% of fraction 0-4mm)
93. 3 5.6 0.4 100 37
92. 92.8 99 98. 89.9 6 7 7.2 6.8 0.7 1 8.6 0.2 0.4 0.1 0.3 0.1 100 100 100 100 100 18 30 37 39 32
85.6
94.4
13.5 0.1 100 36
4.1 0.5 100 22
92.7 94. 1 5.6 5.2 0.8 0.2 100 100 17 16
Fraction minus 63 μm (% of fraction 0-4 mm)
na
na
na
2.8
5.7
2.3
Muscovite/Illite 0.9 8.0 Gypsum 0.2 0.1
0.7 0.6
Mineralogical analysis Fraction 04mm Normalized XRD indicators (1) (% intensity of characteristic mineral reflections)
na
1.9
1.8
na
1.0 0.3 0.6 0.8 0.0 0.1 vestig vestig e e 50. 70.3 68. 66. 59.4 53.9 1 4 6 25. 4.4 7.4 2.5 8.1 12.8 7 11. 0.8 2.6 0.3 5.9 2.3 1 4.9 23.1 20. 30. 26.0 30.2 5 1 10. 3.0 3.3 2.2 2.3 1.8 2 17. 3.3 3.8 2.3 2.8 2.3 7 na na 2.0 na 2.6 1.6 na na 0.0 na 0.0 0.0 na na 39. na 45.1 41.3 0 na na 6.0 na 9.3 4.2
na
na
na
2.0
na
2.5
2.8
4.6
na
na
na
na
40.4
50.0
39.3
na na
na na
na na
52. 0 0.8 0.9
na na
1.1 1.4
0.8 1.0
1.2 1.4
26.9 32. 3 2.4 1.5 2.6 2.0
1.8 2.3
1.0
0.9 2.4
2.0
2.9
1.5
1.6
Quartz
76. 0 K Feldspar (Fk) 1.0 Na Feldspar 1.7 (NaF) Calcite 20. 3 Qz/c 3.7
(Qz+KF+NaF)/ c Mineralogical Muscovite/Illite analysis Gypsum Fraction minus Quartz (Qz) 63 μm (%) Normalized K Feldspar (Fk) XRD indicators (1) Na Feldspar (% intensity of (NaF) diagnostic Calcite (c) mineral reflections) Qz/c (Qz+KF+NaF)/ c Chemical Fe
4.6
3.9 na na na
313
1.0 1.2
0.5 0.5
64.6
3.4
82.8 72. 0 5.9 12. 0 3.9 9.0
15.9
6.4
4.1
13.0 14. 4 14.6 18. 6 0.4 1.6 3.8 1.4 64.1 48. 5 1.4 16. 2 3.4 0.0
13.9
5.1 1.4 3.8 46.7 4.3
1.0 v
5.0
1.9
analysis Fraction 04mm Normalized XRF indicators
Mn Ti Ca
0.0 0.0 0.1 0.1 7.1 2.7
0.0 0.1 5.9
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.1 0.1 0.1 0.1 0.1 6.9 12. 5.7 7.5 4.2 2.2 1.8 6 K 0.4 0.6 0.4 0.3 0.4 0.5 0.5 0.4 0.3 0.6 (2) Mg 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Ratio of Na nd nd nd nd nd nd nd nd nd nd elemental Cl 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 kα (I) intensity S 0.1 0.0 0.0 0.1 0.0 related to Si 3 4 0.10 4 0 0.07 0.06 0.21 0.12 4 Si 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Al 0.2 0.2 0.1 0.1 0.3 0.2 0.3 0.1 0.1 0.2 Fe/Ca 0.2 0.9 0.2 0.1 0.2 0.4 0.4 0.4 0.7 1.0 Fe/Al 8.6 11. 7.2 7.6 9.6 8.7 11.2 11.2 14.4 7.7 5 na - not available; nd - not determined; (1) indicator relatively abundant based only on the highest minerals reflection (normalized to a total of 100% of intensity) (2) indicator of relative abundance based on the ratio of the intensity of elemental kα (I) radiation (intensities normalized by Si kα (I)). Summarizing, the analysis carried out shows, as expected, that the mineralogical and chemical composition of the selected products are related to the geological environment of the plants location, upstream processing and type of construction. Therefore, further applications of these products must considerer their regional mineralogical and chemical differences in order to define the processing design plant and determine the best use. For instance, VAL’s sample composition is due to the high percentage of brick, used in the building construction in the area of CDW collection. PHYSICAL CHARACTERIZATION OF THE FINE RECYCLED AGGREGATES The values obtained for the differently calculated particle densities and the water absorption percentage, can be observed in Table VI. Table VI. Densities and water absorption. Sample name
ρa (kg/m3)
ρrd (kg/m3)
ρssd (kg/m3)
AMB-m AMB-c ARV RTR SGR#1 SGR#2 TRI VAL VIM#1 VIM#2 Average Relative standard deviation (%)
2601.2 2684.8 2645.6 2572.7 2637.6 2647.1 2649.0 2653.2 2644.0 3058.7 2679.4
2340.5 2225.2 2190.9 2284.2 2320.8 2382.1 2138.2 2357.6 2230.0 2670.7 2314.0
2440.7 2396.4 2362.8 2396.3 2440.9 2482.2 2331.0 2469.0 2386.6 2797.6 2450.4
Water absorption (%) 4.1 7.1 7.3 4.7 4.9 4.0 8.3 4.5 6.6 4.5 5.6
5.1
6.4
5.3
28.6
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ρa - apparent particle density; ρrd - oven-dry particle density; ρssd - saturated surface-dry particle density The bulk density (ρb) and void ratio results are shown in Table VII. Table VII. Apparent bulk density and void percentage. ρb Sample name v (%) (kg/m3) AMB-m 1441.8 38.4 AMB-c 1354.4 39.1 ARV 1332.1 39.2 RTR 1255.6 45.0 SGR#1 1383.0 40.4 SGR#2 1285.6 46.0 TRI 1305.9 38.9 VAL 1386.9 41.2 VIM#1 1291.5 42.1 VIM#2 1320.9 50.5 Average 1335.8 42.1 Relative standard deviation 4.2 9.3 (%) The same results are shown in Figure VIII and IX, for clarity’s sake. The apparent particle density (ρa) for most of the samples of the studied set of plants does not show a significant scatter. The maximum relative standard deviation is 5.1%. The plants that show the highest deviation from the average are VIM #2 and RTR. In fact, the apparent bulk density determined with the former sample is almost 400 kg/m3 higher than the average of the others plants while in RTR sample it is lower by more than 100 kg/m3 . In the VIM plant there are two stages of screening that remove at the beginning of the process the fine CDW fraction. So, the fines present in this sample, are mostly generated by crushing of the natural aggregates, which are denser than the mixture observed in other recycling plants.
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Figure VIII. Bulk density of the various samples.
Figure IX. Water absorption and void percentage of the various samples. Similar conclusions concerning other particle densities can be obtained, except for the bulk density, which presents a regular value for all plants, including VIM #2, with a standard deviation of 56.2 kg/m3. The obtained bulk density, which represents the mass of a certain volume of fine recycled aggregate in its normal state (without compaction), demonstrates that independently of the variation in other properties, the packing of particles is such that bulk density is almost the same in different plants. The void percentage represents the space unoccupied by any particles, in a given reference volume. The results of the various plants led to an average of 42.1%, with a standard deviation of 9.3%. Three plants showed values above the average, in particular the SGR #2, VIM #2 and RTR. The high void percentage obtained in VIM #2 and SGR #2 samples can be explained by the coarser particle size which avoids the compaction of particles. The smaller void percentage is obtained at the AMB plant, only with a small difference between the AMB-c and AMB-m. That fact shows that going without screening of the aggregates before crushing originates a much higher trend towards a better rearrangement of the particles, originating a higher bulk density and a lower void percentage. Water absorption is directly related with the difference between the saturated surface-dry particle density and the oven-dry particle density. Higher water absorption corresponds to a greater difference. This also holds for the number of pores accessible to water that exist on the particles. Processing of the aggregates may have an influence on this property, since fragmentation can generate fractures in the particles that are able to absorb and retain water. The water absorption 316
shows values with an average of 5.6%, and a coefficient of variation of 28.6%. Water absorption is the variable with higher coefficient of variation. As another investigation concluded, this is the most sensitive variable to the processing and composition of samples [12].The sample presenting the highest water absorption is TRI, with a value of 8.3%, remarkably higher than the average of 5.6%. As expected, VAL and RTR samples show lower water absorption compared with the aggregates obtained from limestone. Processing seems to have an effect on this property, since the plants with two screens, VIM and SGR, presented less water absorption on the coarser sample. Possibly, the fine aggregates present on the fraction from the coarser fraction sample may be originated from the disaggregation of the mortars, grinding the particles in their original natural fine aggregates, which possess low or no water absorption at all. The apparent bulk density does not seem to interfere with this property, since the bulk density of the apparent particle density of samples like VIM#2 and SGR#1 is quite different, but the water absorption is similar. The mineralogy of the particles does not seem to introduce a major influence on the physical characteristics of the fine recycled aggregates. For instance, VAL and AMB-m, with different mineralogical and chemical analysis exhibit similar physical characteristics. CONCLUSION The present work aimed at performing a physical, chemical and mineralogical characterization of the fine recycled aggregates (0-4 mm) from several Portuguese construction and demolition waste recycling plants. Tests were performed to determine size distribution, chemical and mineralogical analysis, particle density, water absorption, bulk density and void percentage. It was found that FRA characteristics are defined by the geological environment of the recycling plants. On the other hand, it was concluded that processing inherent to each recycling plant influences the size distribution, the bulk density and also the water absorption of the produced aggregates. The bulk density and void percentage appear to be influenced as well by processing.
ACKNOWLEDGEMENTS The authors thank to the FCT (Project FCD PTDC/ECM/108682/2008) for the financial support and to the plants responsible staff who authorized the sample and data collection. REFERENCES 1. Roodman, D., Lenssen, N. - A bulding revolution: how ecology and health concerns are transforming construction. Worldwatch Paper, Vol. 124, 1995; 2. Evangelista, L. - Concrete executed with fine recycled concrete aggregates (in Portuguese). Masters dissertation in Constrution, Lisbon, Portugal, 2007; 3. Coutinho, A. - Manufacture and properties of concrete (in Portuguese). LNEC, Lisbon, Portugal, 1994; 4. CEN : EN 12620:2003 - Aggregates for concrete. Brussels, Belgium, 2002; 5. Miranda, L. - Contribution to the development of production and control of the mortar with washed sand from recycled waste with class A from construction (in Portuguese), PhD
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Dissertation in Engineering, Polytechnic School of the São Paulo University, São Paulo, Brazil, 2005; 6. Angulo, S. - Characterization of recycled aggregates from construction and demolition waste and its influence on characteristics and behavior of concrete (in Portuguese), PhD Dissertation in Engineering, Polytechnic School of the São Paulo University, São Paulo, Brazil, 2005; 7. Leite, M. - Avaliation of the mechanical properties of concrete made with recycled aggregates from constrution and demolition waste (in Portuguese). PhD Dissertation in Civil Engineering, Porto Alegre, Brazil, 2001; 8. CEN: EN 933-2 - Tests for geometrical properties of aggregates - Part 2: Determination of particle size distribution - Test sieves, nominal size of apertures. Brussels, Belgium, 1996; 9. CEN: EN 933-1 - Tests for geometrical properties of aggregates - Part 1: Determination of particle size distribution - Sieving method. Brussels, Belgium, 1997; 10. CEN: EN 1097-6 - Tests for mechanical and physical properties of aggregates - Part 6: Determination of particle density and water absorption. Brussels, Belgium, 2000; 11. CEN: EN 1097-3 - Tests for mechanical and physical properties of aggregates - Part 3: Determination of loose bulk density and voids. Brussels, Belgium, 1998; 12. Angulo, S. - Variability of recycled coarse aggregates from construction and demolition waste (in Portuguese). Master Dissertation in Engineering, Polytechnic School of the São Paulo University, São Paulo, Brazil, 2000.
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