USE OF CONSTRUCTION WASTE GENERATED IN THE CITY OF ALMERÍA IN THE MANUFACTURE
OF BASES AND SUB-BASES OF RURAL ROADS AND CONCRETE OF LOW STRENGTH
E. Garzón*, S. Martínez-Martínez**, L. Pérez-Villarejo** and P. J. Sánchez-Soto***
* Department of Engineering, University of Almería, Almería, Spain
** Department of Chemical, Environmental and Materials Engineering, University of Jaén, Jaén, Spain
*** Institute of Materials Science of Sevilla, CSIC – University of Sevilla, Sevilla, Spain
e-mail: [email protected]
Introduction
❑ At the Andalusian level, three million tons were generated in 2015
and the percentage that is recycled is similar to that registered at
the national level, however there is 44% of construction waste that
goes to uncontrolled landfills (Moreno and Bueno, 2020). Although
there is a Territorial Master Plan for Urban Waste Management in
Andalusia, where there is talk of an annual production of
12.200.000 tons, which means 5 Kg./hab./day. In this plan, Almería
was assigned 862.588 tons/year, most of this rubble corresponding
to municipalities with more than 5.000 inhabitants, where the
construction index registered the highest values in the years of the
construction boom (Decreto 218, 1999).
❑ On this point Aguilar (1997) indicates that the factors that influence
the volume and composition of the RCDs are: type of activity, either
construction or demolition, type of construction, age of the building,
volume of activity in the sector and policies in force in housing
matter. Regarding the importance, wood is more relevant in the
demolition of old houses, metals in the demolition of industrial
buildings, bituminous products are limited to repair works and road
expansion and plastics appear in recent construction works. Based
on the above, this research work has been carried out in the
municipality of Almería, in order to take advantage of construction
waste in earthworks and in the manufacture of concrete.
Experimental
❑ Aliquots of this material have been studied by different experimental techniques
such as: X-ray diffraction, X-ray fluorescence, scanning electron microscopy on
a sample previously metallized with gold, chemical analysis by dispersive
energies X-ray analysis and oven test up to 1000 ºC .
❑ On the other hand, its mechanical behavior has been determined by carrying
out the following tests:
▪ Texture according to UNE 103101 (1995) and Atterberg limits according to
UNE 103103 (1994) and UNE 103104 (1993).
▪ The material has been subjected to different degrees of compaction with a
normal proctor “1/2PN” (PN13 blows), “PN” (PN26 blows), “2PN” (PN52
blows) following the UNE 103500 (1994) standard.
▪ California Bearing Ratio (CBR) on the original material samples following
the UNE 103502 (1995) standard.
❑ With another part, HA-25/B/20/L type concretes were made with gravel,
standardized sand (100%), cement (CEM V/A SPV 32.5N) (UNE-EN 197-1,
2000), water and Sikament 390 additive (concrete 1), concrete 2 where 48%
recycled sand and 52% normalized sand were introduced and concrete 3 with
100% recycled sand. The dosage for this type of concrete was as follows:
gravel (1000 Kg/m3), sand (820 Kg/m3), cement (320 Kg/m3), additive at 1% of
the weight of cement and water (160 l). And its consistency (UNE 80303, 1990)
and compressive strength at 7 and 28 days were determined (UNE-EN 12390-
2, 2001, UNE-EN 12390-3, 2001, UNE-EN 12390-4, 2001).
Conclusions
❑ Construction waste generated in the metropolitan area of Almería can be reused as esplanades or sub-bases of roads
and highways, since it is a granular material with a very high CBR (36). However, its granulometry is not adequate and
the sulfur level is above 1%. These restrictions can be overcome by acting on the crushing machine, so that a larger
recycled aggregate is generated. And on the selective waste process, eliminating the gypsum responsible for the high
relative levels of sulfur.
❑ However, its use as a substitute for sand, for the manufacture of concrete, can only be used in percentages lower than
10% by weight of recycled aggregate, since higher percentages give very low compressive strength values, which
make its use unfeasible use in this application.
The authors would like to express appreciation for the support of Reciclados Almerienses 2005
Results and discussions
b) Application on rural roads:
The size of the aggregates leaving the crusher is between 0,08 mm - 25 mm. However, the characteristics of the
aggregates of this plant do not comply with the General Technical Conditions of Roads and Bridges (PG3) and Technical
prescriptions required in the Spanish standard UNE 146131 (2003), in its annex of “recycled aggregates” (Fig. 4), since its
granulometry is not included within the Spindle intervals (dashed lines). These deficiencies can be corrected by mixing
this material with another larger aggregate or by acting on the crushing machine in such a way as to increase the size of
the aggregate that comes out of the machine. It has also been observed that the dominant fractions are sand (56.9%) and
gravel with 38.4%, the rest is silt (4.7%). In addition, it has been impossible to determine the liquid and plastic limits
following the standards, since it is a material that does not present plasticity. All this allows this material to be classified as
GW (Well-graded gravel, sand-gravel mix, little or no fine grains), GP (Poorly graded gravel, sand-gravel mix, little or no
fine particles) or GM (Silty gravel, Gravel mix- sand, silt) according to the unified classification of Casagrande.
Figure 5 shows the evolution of density with increasing humidity when normal proctor energy is applied. Subsequently,
this curve is compared with those obtained at ½ PN and 2PN (Fig. 5). It can be observed that by increasing the
compaction energy applied to the rubble, there is an increase in the dry density. The decrease in required humidity is only
recorded when going from ½ PN to PN. However, going from PN to 2PN results in an increase in optimal humidity.
Observing that the differences between PN and 2PN are very small, this is associated with the fact that the efficiency in
the compaction energy applied to the soil decreases as the void index decreases and these decreases are high at the
beginning to decrease later.
In figure 6 is observed that the CBR is 36 to 100% of the PN, which makes it a selected soil (CBR≥20) for the formation of
esplanades (Art. 330 PG3). In addition, the swelling registered has been zero. This value is related to the majority
granulometric composition, formed by gravel and sand.
Figure 6: CBR of construction waste.
c) Application in the manufacture of concrete:
The results for the shape coefficient of the recycled aggregates do not meet the specifications of the EHE instruction for
structural concretes, since the percentage retained in the 8 mm and 16 mm aperture sieves is less than 0,2 (Table 2). In
the same way, with the dosage used it has been verified that the decrease in the Abrams Cone for the three concretes
has been between 0-1 cm. Which allows classifying these concretes in the group of dry consistency. Likewise, the
compressive strength at 7 days has been much higher in conventional concrete compared to concretes that incorporate
recycled sand, being concrete with 100% recycled sand the one that has registered the lowest levels of resistance to
compression. These differences have remained after 28 days. In Figure 7 it can be seen that by incorporating less than
10% of the plant's construction waste, the drops in compressive strength are not very high both at 7 and 28 days,
although the slope is greater at 28 days.
With these values of compressive strength so low, it is impossible to use it as sand to make concrete (Castilla, 2004).
These results confirm the need for a selection of the material that reaches the plant, so that it is used for the manufacture
of recycled aggregates: mortars, concrete, ceramic products. Eliminating debris with the presence of gypsum or wood that
generate very low compressive strength values.
Figure 1: Recycled plant details.
Figure 2: Sample of
recycled aggregate.
a) Physical and chemical characterization of the sample:
X-ray diffraction analysis of the crystalline phases present in the sample revealed the presence of quartz and
calcite as the major components, in addition to an average content of dolomite and albite, while illite,
chlorite/kaolinite, gypsum and iron oxides among other minor components. This composition reveals the majority
presence in the recycled material of lime mortar with quartz and limestone aggregates.
The iron oxide content of around 4,58% and of sulfur (1,23%) stand out, the latter related to the presence of
gypsum. This sulfur content is above the technical specifications (<1%) of the recycled aggregates standard
(Anexo PNE de norma UNE 146131, 2003). To avoid this problem, it will be necessary to carry out a selective
demolition, so that the construction elements where there is presence of gypsum are separated (Table 1).
The weight loss due to calcination at 1000 ºC is 15,30%, which is attributed to the presence of calcite and
dolomite. Subsequently, a study by electron microscopy was carried out, which facilitated the observation of a
very heterogeneous structure formed by particles of different sizes (Figure 3) and the presence of quartz crystals,
with their characteristic morphology.
Figure 4: Granulometric curve of recycled
Aggregate.
Figure 5: Evolution of humidity and dry density with
the compaction Energy of construction waste.
Figure 3: Scanning electron
microscopy (sample extracted
from an oriented aggregate
made from a mixture of
construction waste and distilled
water, left to stand (24 hours).
SiO2 (%) Al2O3 (%) Fe2O3 (%) K2O (%) CaO (%) MgO (%) Na2O (%)
39.13 9.55 4.58 1.62 21.42 3.50 0.68
TiO2 (%) P2O5 (%) S (%) Cl (%) Sr (%) Ba (%) Zn (%)
0.68 0.12 1.23 0.09 0.26 0.02 0.01
CBR index Value
100% compactation 36
95% compactation 27
Swelling Null
Shape coefficient (UNE
7238:1971)Retained on 4 mm
sieve0.237
Retained on 8 mm
sieve0.086
Retained on 16 mm
sieve0.015
Table 1: Elemental chemical composition of the construction waste sample.Table 2: Shape coefficient.
Figure 7: Compressive strength according to the
percentage of incorporation of recycled aggregate.