LABORATORY ANALYSIS OF RECYCLED AGGREGATES AND LIME

LABORATORY ANALYSIS OF RECYCLED AGGREGATES AND LIME
MIXTURES FOR USING IN PAVEMENT LAYERS
DINIZ Arthur Brito Nunes 1, a, MELO Ricardo Almeida de2,b
1Federal
University of Paraíba, Centre of Technology, Department of Civil and
Environmental Engineering Campus I, Cidade Universitária. CEP: 58051-900. João
Pessoa, Paraíba, Brasil
2Federal
University of Paraíba, Centre of Technology, Department of Civil and
Environmental Engineering Campus I, Cidade Universitária. CEP: 58051-900. João
Pessoa, Paraíba, Brasil
[email protected], [email protected]
Keywords: recycled aggregates, lime, base, pavement, mixtures.
Abstract. Recycled concrete aggregates can be used on pavement layers to minimize roads
construction costs and decrease environmental impacts in cities. Thereby, this study consisted in
analyzing the technical feasibility of using “Class A” recycled concrete aggregates and hydrated lime
(in the proportion of 1% to 6%) mixtures for low traffic pavements and comparing them with natural
aggregates. The materials were collected in USIBEN and in an asphalt plant. Tests were performed
such as particle size, compaction with intermediate energy and California Bearing Ratio (CBR). The
compositions of the mixtures were determined by “E” grading envelope specified by DNIT. The
compaction performed indicated optimum moisture contents of 16.9%; 14.7%; 15.1% and 15.9% for
lime contents of 1%, 2%, 4% and 6%; and results of 8% and 14.9% for natural and recycled
aggregates, respectively. With respect to maximum dry density, values of 1.734; 1.765; 1.765 and
1.718 g/cm³ were obtained for same lime contents, and of 2.011 and 1.830 g/cm³ for natural and
recycled aggregates, respectively. According to mechanical resistance, the CBR values of lime
contents had resulted in 147%, 155%, 112% and 87%, while that for natural and recycled aggregates
resulted in 45% and 61%, respectively. The results show that the mechanical properties of recycled
aggregates and lime mixtures are above the minimum specified values by DNIT for use in pavement
base. Therefore, one can say that using mixtures of lime and recycled aggregates is technically
feasible for pavement layers.
Introduction
Brazil's economic development in recent years are evident in the urban expansion and the growth
of the real estate sector that have generated a progressive increase in production of solid waste from
construction and demolition. This type of waste produced by the Brazilian construction industry
surpasses 31 million tons per year [1]. Moreover, only about one third of this material was delivered
to the public landfills while the rest was disposed of illegally [2]. In 2002, the National Council of
Environment (CONAMA), which is a Brazilian agency responsible for establishing standards and
criteria for licensing of effective or potentially polluting activities, published Resolution No. 307,
establishing guidelines, criteria and procedures for the management of construction waste in order to
minimize the environmental impacts of its improper disposal [3].
In this sense, research shows that recycled concrete aggregates have great potential for recycling
and reuse in various construction activities such as pavement construction in order to protect the
natural resources and reduce the environmental pollution of solid waste [4, 5]. Potential saving in cost
and time of recycling of construction and demolition debris has made the use of recycled concrete
aggregate (RCA) an attractive alternative to the highway engineer [6]. In this case, a smaller rubble
recycling technology is required in addition to reducing the environmental impacts caused by the
construction of pavements and the process of getting its raw materials, which makes the use of these
recycled materials advantageous.
Studies about physical properties, mechanical behavior, and durability of recycled concrete
aggregates are quite recent. Nevertheless, the use of concrete waste aggregates in construction of
pavements have been growing worldwide, particularly in Europe, where there is shortage of raw
materials and strict control of environmental impacts caused by the extraction of natural resources.
This has been an efficient way to manage the construction waste in favor of contributing to the proper
disposal of waste and an alternative to use them in places where obtaining natural aggregates is
troublesome [7].
One of the most advantageous alternative application for the recycled concrete aggregates (RCA)
is their use in layers (base and sub-base) of pavements with low traffic volume [8]. Leite et al. [2]
conducted a laboratory program by geotechnical characterization, bearing capacity and repeated load
triaxial tests to evaluate the feasibility of using aggregate from recycled construction and demolition
waste (RCDW) in pavement applications. The results have shown that the RCDW aggregate may be
utilized as coarse base and sub-base layer for low-volume roads.
Behiry [6] studied the feasibility of using recycled concrete aggregate (RCA) mixed with
traditional limestone aggregate (LSA) which is currently being used in base or sub-base applications
in Egypt. The results show that the adding of RCA improves the mechanical properties of the mixture
where the unconfined compressive strength (UCS) is taken as an important quality indicator.
Variables influencing the UCS such as cement content, curing time, dry density play important roles
to determine the performance of cement treated recycled aggregate (CTRA).
Motta [4] analyses recycled aggregates from São Paulo as a material to be used in base, sub-base
or subgrade reinforcement courses in urban roads of low-volume traffic, to replace conventional
materials. This study involved the analysis of recycled aggregate in natura, as well as its mix with
4% of lime or 4% of Portland cement, to promote a gain in strength. It was concluded that recycled
aggregate is promising for paving, given its satisfactory physical and mechanical properties,
comparable to traditional granulometrically stabilized materials or even to simple graded crushed
rock. The addition of lime or Portland cement is an excellent alternative concerning the increase in
strength of those recycled materials.
Helen et al. [9] compared mechanical performance of nature aggregates, concrete recycled
aggregates and flakes PET mixtures (in proportion from 0.5 to 4.0%) for granular pavement layers.
According to mechanical resistance, the CBR value of nature aggregates had resulted 45%, while that
for recycled aggregates resulted 61%. On the other hand, the CBR results did not show a particular
behavior tendency with addition of recycled PET flakes. Therefore, it was possible to conclude that
recycled aggregates are technically viable to build granular pavement layers (sub-base and base) from
low traffic flow, in spite of the variability of the CBR results to recycled aggregates and flakes PET
mixtures.
The NBR 15115/04 standard [10] provides the use of recycled concrete aggregates for base and
sub-base of low-traffic volume roads. In turn, the NBR 15116/04 standard [11] specifies the
requirements for the use of such materials in pavements. In some cases, hydrated lime is added as a
binder of recycled concrete aggregates to increase these materials’ strength [4, 6], and which needs a
proper water content for both compaction and lime hydration. Accordingly, a mixture is composed in
accordance with NBR 15116/04 [11] for the purpose of chemically stabilize the RCA and present
better mechanical performance [12].
Thus, the main objective of this research was to analyze the technical feasibility of using recycled
aggregates “Class A” mixed with hydrated lime to construct pavement layers (base and sub-base)
with low traffic volume. Therefore, materials were subjected to physical characterizing tests as well
as mechanical performance tests.
Methodology
Natural aggregates, recycled concrete aggregates (RCA, hereafter "recycled aggregates") and
hydrated lime were materials used in this study. All these materials were provided by companies and
recycling plants located in the state of Paraiba, Brazil.
Natural aggregates and lime were supplied in different grain sizes: 19 mm coarse aggregate, 12
mm coarse aggregate, stone dust, sand and hydrated lime. In this study, the lime was mixed with
recycled aggregates in percentages of 1%, 2%, 4% and 6% of the total weight of the respective
samples. Recycled aggregates were assigned in three grain sizes: sand, 12 mm and 25 mm coarse
aggregates.
Recycled and natural aggregates and its mixtures were characterized under standard laboratory
tests. Besides, the effect of compaction effort on its physical and mechanical properties were
analyzed. The following tests were carried out: sieve analysis, compaction with modified energy and
California Bearing Ratio (CBR). The results and conclusions about the use of recycled aggregates in
low-volume roads construction are presented.
Sieve analysis. The sieve analysis of materials were obtained from previous studies [9], which were
performed with the same materials of this research and in accordance with the Brazilian standard
DNER-ME 083/98 [13].
The tests were conducted with each size of the aggregates in three samples. The sieve analysis was
useful to know the maximum aggregate diameter and uniformity coefficient of uniformity (Cu).
According to NBR 15116/04 [11], coefficient of uniformity (Cu) is expected to be greater than 10 for
recycled aggregates.
The materials provided for this study have different grain sizes, so each of them was analyzed
separately for what proportions would be defined in order to compose the mixture would be adequate
for floor bases and sub-bases. Thus, it could be obtained mixing natural aggregates and recycled
aggregates mixtures with hydrated lime, respectively. The mechanical behavior of the mixtures were
compared in sequence.
The construction standard DNIT: ES 141/2010 [14] determines possible particle sizes for bases
composed of crushed materials. In this study, the specified range "E" was chosen because it represents
roads with low traffic volume, as recommended by NBR 15116/04 [11] for pavement bases built with
recycled aggregates. Table 1 describes the necessary percentage of passing material through the sieve
for the granulometric range "E".
Table 1 – Particle size range "E" for granular layers. Source: [14]
Standard sieve
Passing material percentage [%]
Permitted sieve variation
3/8”
100
±7
N° 4
55-100
±5
N° 10
40-100
±5
N° 40
20-50
±2
N° 200
6-20
±2
Compaction. Compaction tests were performed manually with modified energy to evaluate the effect
of compaction effort on the natural and recycled aggregates samples, as specified NBR 15116/2004
[11] and Brazilian standard DNER-ME 162/94 [15]. The results were used as parameters for the
attainment of the CBR tests.
California Bearing Ratio (CBR). The samples were prepared with optimum moisture contents
obtained in the compaction test. The CBR tests were conducted in accordance with the Brazilian
standard DNER-ME 049/94 [16].
Results
All results were compared and evaluated according to NBR 15116/04 [11] and DNIT: ES 141/2010
[14].
Sieve analysis of natural and recycled aggregates. The sieve analysis was done to aggregates for
three samples of each material fraction. After the sieve analysis, maximum aggregate diameter,
retained material percentage on the sieve 0.42 mm and coefficient of uniformity (Cu) were
determined, as recommended by NBR 15116/04 [11]. The results obtained for the average of three
samples are shown in Figures 1 and 2 and Table 2.
Table 2 presents the coefficient of uniformity (Cu) for natural and recycled aggregates.
Table 2 – Natural and recycled aggregates uniformity coefficients. Source: [9]
Type of aggregate
Aggregate diameter
Coefficient of uniformity (Cu)
Classification
19 mm coarse aggregate
2,6
Uniform
12 mm coarse aggregate
2,6
Uniform
Stone dust
22,2
Non uniform
Sand
5,0
Fairly uniform
25 mm fraction
2.5
Uniform
12 mm fraction
2.0
Uniform
Sand fraction
5.3
Fairly uniform
Natural
Recycled
According to Table 2, only the stone dust resulted in a coefficient of uniformity (Cu) which does
not satisfy the uniformity of the material [11]. Moreover, the values in Table 2 for the 12 mm coarse
aggregate, 19 mm coarse aggregate and sand that these materials have low uniformity coefficient,
therefore, they have uniform graduations.
Fig. 1 depicts the size distribution curves for natural aggregates.
Fig. 1 - Gradation curves for natural aggregates. Source: [9]
It can be seen from Fig. 1 that only the stone dust variation line is entirely located between the
band limits "E" [14] considering the tolerances for the design range. Coarse aggregates in fractions
of 12 mm and 19 mm crushed stone showed opened grain sizes with fine insufficiency, whereas the
sand fraction showed continuous granulometric curve. Therefore, granulometric stabilization was
necessary in order to obtain a sample average curve of the mixture within the standard limits and
improve the mechanical properties.
As shown in Table 2, values of coefficient of uniformity (Cu) did not meet the standard
requirement [11]. In addition, these results are an evidence for considerable empty spaces between
the solid particles of these recycled aggregates.
Fig. 2 depicts the size distribution curves for recycled aggregates.
Fig. 2 - Recycled aggregates gradation curves. Source: [9]
As shown in Fig. 2, 19 mm and 12 mm coarse aggregates showed open granulometric curves with
fine material insufficient, while the sand presented a continuous curve, being the only that falls in the
“E” range [14] , considering the tolerances for the project range. Therefore, the granulometric
stabilization is necessary to the achievement of recycled aggregates mixtures framed on the "E" range
in order to obtain good mechanical performance.
On what was found, the particle size stabilization was used to define the proportions of each
aggregate in the mixtures proposed (natural aggregates, recycled aggregates with powdered hydrated
lime), reaching gradation curves that stay within the defined range limits "E" and correcting decreases
in mechanical properties resulting from the empty spaces or the characteristics of the material itself.
The granulometric stabilization was achieved using a spreadsheet. The results are shown in Table 3.
Table 3 - Granulometric stabilization for recycled and natural aggregates [9]
Material
Recycled
aggregate
Natural aggregate
Sieve percentage in granulometric stabilization (%)
25 mm fraction coarse
aggregates
12 mm fraction coarse
aggregates
-
Sand
fraction
0
16
-
84
19 mm coarse aggregates
12 mm coarse aggregates
Stone dust
River sand
0
23
11
66
The particle size stabilization performed to the natural aggregates resulted in an average curve
within the limits of the range "E". As for the recycled aggregates, the average curve is not fully
reached within the specified threshold, since the percentage of fines (% passing the 0.074 mm sieve)
is less than the lower limit described by the standard DNIT: ES 141/2010 [14]. However, this is not
a requirement for recycled aggregates for application to pavements mentioned in NBR 15116/04 [11]
and therefore, the obtained mixture was used in this study.
Subsequently, it was determined the coefficient of uniformity (Cu), maximum aggregates diameter
and passing material percentage in the 0.42 mm sieve for the granulometric curves of mixtures. The
results shown in Table 4 show that mixtures are satisfactory before the standards used as references.
Table 4 – Properties of aggregates mixtures [9]
Natural
aggregates
Recycled
aggregates
Specified
standards
Coefficient of uniformity (Cu)
15
12
> 10
Maximum aggregate diameter (mm)
9.5
9.5
≤ 63.5
Passing 0.42 mm sieve percentage
41
29
10% to 40%
Passing 0.075 mm and 0.42 mm sieves percentages
ratio
0.1
0.1
< 2/3
Propriety
Compaction. After the characterization of the materials, the mixtures were performed with natural
aggregates, recycled aggregates and these materials mixed with lime according to pre-established
proportions in order to perform compaction tests.
Table 5 shows the results of compression test in terms of optimum moisture content and maximum
dry density.
Table 5 - Proctor compaction tests’ results
Type of aggregates (%)
Lime (%) OWC (%)
Maximum dry density (g/cm³)
Natural - 100
0
8,0
2.011
Recycled - 100
0
14,9
1.830
Recycled - 99
1
16,9
1.734
Recycled - 98
2
14,7
1.765
Recycled – 96
4
15,1
1.765
Recycled - 94
6
15,9
1.718
According to the results of Table 5 and Fig. 3, recycled aggregates mixtures showed density reduction
and optimum moisture content increase comparing to natural aggregates. Since the grading of each
aggregates is similar, this difference is mainly attributed to the physical properties of natural
aggregates which has the highest particle density and is less porous and the addition of lime, because
it is a finer material. Recycled aggregates has higher water content where can absorb nearly twice the
amount of water compared with natural aggregate. This absorption can minimize water infiltration
into and under highways that use recycled aggregates as road base material [6].
Fig. 3 - Relationship between optimum moisture and lime content in the maximum dry density
results for recycled aggregate mixtures
However, a standard in the compaction results for mixtures with recycled aggregates was not
observed as shown in Fig. 3. It was expected an inverse relationship between the optimum moisture
content and maximum dry density, which has not happened in all mixtures. The literature also points
to a difficulty in obtaining a standard for the compaction curves of recycled aggregates and its
respective mixtures, which can be explained by several factors such as granulometric differences,
material heterogeneity, origin of the material and compaction energy [17].
California Bearing Ratio. The results of the CBR tests are listed in Table 6 and Fig. 4.
Table 6 – California bearing ratio tests’ results
Type of aggregates [%]
Lime [%]
Maximum dry density (g/cm³)
CBR [%]
Natural - 100
0
2.011
45
Recycled - 100
0
1.830
61
Recycled - 99
1
1.734
147
Recycled - 98
2
1.765
155
Recycled – 96
4
1.765
112
Recycled - 94
6
1.718
87
It can be seen in Table 6 and Fig. 4 that the recycled aggregate mixtures with hydrated lime reached
the highest CBR values among aggregates mixtures. The tests results showed that recycled aggregate
mixture with hydrated lime content of 2% was the most resistant. According to the Federal Highway
Administration [18] typical CBR values for recycled concrete aggregates are between 94% and 148%.
As specified by the Brazilian standard procedure [13], the recycled aggregate must reach a CBR value
of at least 60%.
Fig. 4 – Relationship between maximum dry density and the lime content in the CBR results for
recycled aggregate mixtures
It is observed in Fig. 4 that the addition of hydrated lime resulted in the increase in CBR values to
some extent, since as a thin material is led to a reduction of the maximum dry density, impairing the
strength of the mixture in percentages of 6% onwards.
It was state in earlier study that by repeating the CBR tests with mixed recycled aggregates, there
was a difference of 20% in the previous results, which shows a difficulty in obtaining a standard on
test results for this material [2]. These unexpected events may be related to the heterogeneity of the
material and difficulty achieving the optimum moisture content.
The aggregates mixtures that showed CBR results higher to 60% (recycled aggregates mixtures
with hydrated lime) can be considered as technically feasible to construct pavement bases with low
traffic volume.
Conclusions
The materials showed good characteristics in terms of granulometry, ratio of passing in the 0.072
mm and 0.42 mm sieves and maximum aggregate diameter. The granulometric stabilization was
necessary to obtain the most appropriate gradation curve as possible as well as the coefficient of
uniformity specified by the Brazilian standards [11, 14], so that all the general requirements could be
met as regards the use of recycled aggregate in pavements.
The CBR results showed that mixtures with lime showed high resistance and therefore are
technically viable for use in base pavements that have low traffic volume.
However, further studies are required due to the heterogeneity of recycled material, which in
addition to other factors causes the variability of the CBR results, preventing the taking of concise
conclusions about this kind of material. In addition, the material must be assessed through further
tests, such as the resilience modulus and compressive strength.
Acknowlegdements
The authors would like to thank CAPES - Brazilian Federal Agency for the Support and Evaluation
of Graduate Education by the scientific initiation scholarship granted to the first author, NOVATEC
and EMLUR companies to have assigned the materials, and Engineering Project Consulting LTDA
for the technical and physical support in achieving the California bearing ratio.
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