Open Access Library Journal
How to cite this paper: Ayan, V., Omer, J.R., Azadani, S.M.N., Limbachiya, M.C. and Khavandi, A. (2014) Water Absorption
Study in Recycled Aggregates for Use as Pavement Material. Open Access Library Journal, 1: e605.
http://dx.doi.org/10.4236/oalib.1100605
Water Absorption Study in
Recycled Aggregates for Use as
Pavement Material
Vahid Ayan1*, Joshua R. Omer2, Seyed Masoud Nasr Azadani3, Mukesh C. Limbachiya2,
Alireza Khavandi4
1Department of Civil Engineering, Islamic Azad University (IAU), Islamshahr Branch, Tehran, Iran
2Sustainable Technology Research Center, Kingston University London, London, UK
3Department of Railway Engineering, Iran University of Science & Technology, Tehran, Iran
4Department of Civil Engineering, Faculty of Engineering, University of Zanjan, Zanjan, Iran
akhavandi@iu st.a c.ir
Received 4 June 2014; revised 15 July 2014; accepted 25 August 2014
Copyright © 2014 by authors and OALib.
This work is licensed under the Creative Commons Attribution International License (CC BY).
http://c reativec ommons.org/licenses /b y/4.0 /
Abstract
Water absorption properties of recycled materials play an important role in pavement perfor-
mance. The performance of aggregates changes after absorbing water, then it affects highways
layers such as base, subbase, capping. This is why these materials must comply requirements of
codes and standards. With regard to the increasing trend of application of recycled aggregates in
highways layers, this issue needs more investigation. This research is only a part of our large re-
search programme on three different purposed mixes of unbound subbase mixture below: 1)
100% Recycled Concrete Aggregate (RCA); 2) 100% Lime Stone (NA); 3) 50% RCA + 50% Re-
claimed Asphalt Pavement (RAP). Water absorption for each mix has been performed in different
size fraction with pyknometer and wire basket methods. The relationship between density, grad-
ing and water absorption and its comparison for mixes would be indicating the changes in behav-
iour of aggregates and future performance of subbase. Laboratory testing showed that 100% Lime
Stone had the higher densities than other mixes and water absorption value of 100% RCA was
about 40% higher than 50% RCA + 50% RAP in 31.5 mm - 4 mm fraction.
Keywords
Water Absorption, Recycled Aggregate, Reclaimed Asphalt Pavement, Density, Subbase
Subject Areas: Civil Engineering, Environmental Sciences
*Corresponding author.

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1. Introduction
During the last two decades, various researches were carried out to investigate the possibility of using construc-
tion and demolition waste. RA and RCA are subjects of debate in so far as application in road bases and subbas-
es are concerned. Evaluation showed that RCA and RA from different sources have different mechanical proper-
ties based on their origin [1].
In a research by Park (2003), tests were carried out for physical and compaction properties of two different
recycled aggregates obtained from a housing redevelopment site (RCA-1) and a concrete pavement rehabilita-
tion project (RCA-2). This research revealed that the bulk specific gravity and water absorption values were
2.53%, 2.54%, 1.43% and 1.77% for RCA-1 and RCA-2, respectively [2]. Elsewhere, physical and mechanical
tests were carried out on crushed clay brick (CB) from partition wall and RCA by Poon and Chan (2006). The
particle sizes of the RCA were: 40 mm, 20 mm, 10 mm and <5 mm and the water absorption values were: 3.17%,
2.17%, 2.29% and 10.3%, respectively. The aggregates size of CB was 20 mm, 10 mm and <5 mm with water
absorption results 18.4%, 19.5% and 30.9%, respectively. It was concluded that CB had the highest water ab-
sorption value, followed by RCA and natural aggregate. The high amount of adhered mortar attached to the CB
particles led to increase in the water absorption value [3].
Another research was carried out on the utilization of RCA in rigid pavements. A part of this study was the
construction of a Portland Cement Concrete Pavement (PCCP) section using RCA and a field study of the per-
formance of the pavement. Based on the results of the tests it was concluded that use of fine RCA is not practical
because of its high water absorption rate [4]. Investigations were carried out on 11 RA samples obtained from 10
demolition sites and a recycling plant. The study revealed that in most samples, the water absorption of 10 mm
aggregates was higher than 20 mm aggregates. It was inferred that smaller size aggregates had more cement
mortar which absorbed more water than larger size aggregates. In addition a correlation was found to exist be-
tween particle density, porosity and water absorption [5].
Existing regulated tests to determine the density and water absorption were developed for natural aggregates,
however, and several problems arise when they are applied to recycled aggregates, especially fine recycled ag-
gregates. These difficulties mostly are because of their cohesiveness and binding properties. Rodrigues et al.
(2013) described the main problems encountered with these tests and proposed a new method to measure the
density and water absorption of fine recycled aggregates that removes them. They used sodium hexametaphos-
phate solutions in the water absorption test to improve its efficiency, minimizing cohesion between particles and
helping to release entrained air [6].
The main theme of this research is to compare the water absorption properties of different recycled aggregates
and their mixes according to BS EN 1097-6:2000 [7].
2. Materials
The research concentrated on investigating the suitability of three kinds of aggregates which all are Type 1 un-
bound mixture for subbase [8] (Figures 1(a)-(c)):
1) 100% Recycled Concrete Aggregate (RCA) which is indicated with the notation T-1.
2) 100% Lime stone as the natural aggregate (NA) which is indicated with the notation T-2.
3) 50% Recycled Concrete Aggregate (RCA) + 50% Reclaimed Asphalt Pavement (RAP) which is indicated
with the notation T-3.
(a) (b) (c)
Figure 1. (a): A sample of T-1; (b): A sample of T-2; (c): A sample of T-3.

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The grading curves of three above aggregates, the upper and the lower range of Type 1 unbound mixtures
given according to MCHW Series 800 are illustrated in Figure 2.
For all three kinds of aggregates; the mixture designation is 0/31, 5 (aggregate sizes are expressed as d/D or
lower limiting sieve size/upper limiting sieve size), the Maximum fines content is UF9 and Oversize is OC75
which meet the requirements of MCHW Series 800 requirements [8] [9].
3. Current Specifications
The determination of water absorption was based on the provisions outlined in the three documents: BS EN
13285:2003, MCHW Series 800 and DMRB HD 35/04 [8]-[10]. Four types of unbound mixtures for subbase
application are defined by MCHW Series 800. To determine water absorption rate, BS EN 1097-6 requires that
the method selection should be based on the particle size range as outlined below [7]:
Particle size range Method used
31.5 mm - 63 mm Wire-basket method
4 mm - 31.5 mm Pyknometer method
0.063 mm - 4 mm Pyknometer method
Preparation of test portions in both wire-basket and pyknometer methods included sampling and reduction
which were performed in accordance with BS EN 932-1 and BS EN 932-2, respectively [11] [12].
Density measurements included: 1) oven-dry particle densities (ρrd); 2) saturated and surface-dry density (ρssd);
3) apparent particle density (ρa). The parameter ρrd is the characteristic used to calculate the volume occupied by
the aggregate, for various mixtures of RCA, NA and RAP, respectively. In addition to these solid particles, the
voids including permeable and impermeable voids (but not including the voids between particles) must be con-
sidered when calculating the masses of aggregates. Interpretation of ρssd is based on aggregates soaked in water
for 24 hours to satisfy the water absorption requirement. The weight of aggregates and water within the voids
filled during the soaking time (but not including the voids between particles) were calculated to find the mass in
air of each mixture. (ρa), pertained to the relative density of aggregates not including the permeable pores.
4. Method Statements
The method statements for wire-basket and pyknometer method are summarized in Figure 3 and Figure 4, re-
spectively:
In the wire-basket method, the prepared test portion was placed in a wire-basket and immersed in water for a
period of 24 hours, so all entrapped air was removed. To dry the surface of saturated aggregates, the test portion
transferred to a second dry soft absorbent cloth and was spread and turned until all visible films of water were
removed, but the aggregate still had a damp appearance. The oven-dry mass was achieved by placing the test
portion in an oven set at a temperature of 110˚C ± 5˚C for as long as necessary for the specimen to reach a con-
stant mass.
Figure 2. Grading curves for the tested aggregates.

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Figure 3. The stages of wire basket method.
In the pyknometer method, the prepared test portion was immersed in water pyknometer for the soaking peri-
od of 24 hours to remove all entrapped air. According to BS EN 1097-6:2000 the pyknometer including aggre-
gates and water must stand in the water bath and keep the test portion at a temperature of (22 ± 3)˚C for (24 ±
0.5) hours [7]. In this research, to get a higher accuracy, the pyknometer and the refill water was placed in a cur-
ing room, which was maintained at a temperature of 20˚C for 24 hours (Figure 5 and Figure 6). Achieving sat-
urated and surface-dried aggregates for particles size between 4 mm and 31.5 mm was exactly the same as ag-
gregate particles size between 31.5 mm and 63 mm. In order to assess whether the surface dry state has been
achieved for aggregate particles between 0.063 mm and 4 mm, the metal cone mould test was applied.
5. Test Results and Discussions
According to mentioned method statements and other requirements of BS EN 1097-6:2000 water absorption test
carried out on three kinds of subbase mixtures. The test results for materials of different particle sizes are sum-
marized in Figures 7-10.
The bar charts in Figures 7-10 compare the densities (ρa, ρrd, ρssd) and water absorption rates (WA24) for 24 h
immersion periods. To calculate these densities, the density of water was obtained at the temperature recorded
when the apparent mass in water of the basket containing the sample of saturated aggregate (M2) was deter-
mined.
The tests result showed that natural aggregates had the highest apparent particle density (ρa), particle density
on an oven-dried basis (ρrd), particle density on a saturated and surface-dried basis (ρssd) for particles in all rang-
es. Conversely, they had the lowest water absorption for particles in all fractions.
As seen in Figures 7-10, for a given kind of density (ρa, ρrd, ρssd) the trend of variation of the density with par-
ticle size is consistent for all three materials types (T-1, T-2 and T-3). The presence of the cement mortar adher-

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Figure 4. The stages of pyknometer method.
Figure 5. The pyknometer, squeeze bottle and plastic pot in the curing room.
ing to the stone particles in the RCA creates a relatively weak, porous and cracked layer [13] thereby resulting in
a decreased density of the RCA relative to NA. It is likely that the porous layer described above, in addition to
residual unhydrated cement, lead to an increase in the water absorption rate of RCA [1].
As the density of cement mortar (around 1.0 - 1.6 Mg/m3) [14] is less than that of stone particles of about 2.60

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Figure 6. Keeping the temperature of test portion and water constant at 20˚C in
the curing room.
Figure 7. ρa values for subbase material.
Figure 8. ρrd values for subbase material.

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Figure 9. ρssd values for subbase material.
Figure 10. WA24 values for subbase material.
Mg/m3, the smaller the particle density, the higher the cement mortar content adhering to the RCA. The reason
for the particle densities being lower in RCA as compared to NA is due to the relatively high porosity and low
density of the cement paste adhering to the RCA particles. High porosity between the RCA particles would be
filled with void or cement instead of denseportions [1].
Furthermore, particle densities of coarse aggregates are larger than those of fine aggregates, implying that a
higher amount of cement mortar is attached to the fine aggregates. This behavior affects the water absorption
rate of RCA in the sense that fine aggregates of RCA have a higher water absorption rate, a pattern which is
consistent with the findings reported by Tam and Le (2007) [14].
In the mix of RCA and RAP (T-3), bitumen coated particles in reclaimed asphalt pavements are observed
mostly in the 31.5 mm - 4 mm particle size range. Thus the particles in the size range of 4 mm - 0.063 mm are
less coated with bitumen in T-3 and only a very small part is coated (Figure 11 and Figure 12). These observa-
tions make the water absorption value of T-1 about 40% higher than T-3 in 31.5 mm - 4 mm, but the water ab-
sorption of T-1 and T-3 are relatively close in the fine particles.
The particles in the size range 63 mm - 31.5 mm of T-3 are mostly crushed concrete aggregates. This is why
the water absorption and apparent particle density of coarse particles of T-3 are close to those of T-1. Figure 13

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Figure 11. The fine particles of T-3.
Figure 12. The fine particles of T-1.
Figure 13. T-3 coarse after empting.
shows the particles after emptying the aggregates from the basket on to dry clothes and Figure 14 shows them
after reaching constant mass.

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Figure 14. T-3 coarse in constant mass.
6. Conclusions and Recommendations
This paper presents the result of an investigation of water absorption on the use of recycled concrete and re-
claimed asphalt pavement as aggregate in unbound subbase materials and then their comparison with natural
aggregate behavior. Prior to the study, the mixture and grading requirement category were first evaluated. The
following differences were found between the natural aggregate, recycled concrete aggregate and the mixture of
recycled concrete aggregate with reclaimed asphalt pavement:
In RCA’s samples, the water absorption rate of large size aggregate is less than that of small size aggregate,
inferring that larger size aggregate may have less cement mortar adhered to its surface, leading to a lower water
absorption rate as illustrated in the Figure 8. It is included that adhering cement mortar to material’s surface will
lead to higher water absorption and this is mostly valid for fine particle sized materials.
The water absorption rates of recycled aggregates (T-1 and T-3) are generally higher than that of natural ag-
gregate. In another research by author [1] performed tests on RCA such as durability and strength tests showed
that the higher water absorption can directly influence these properties. Durability test like soundness of subbase
aggregates by use of sodium/magnesium sulphate and strength tests like compaction and California Bearing Ra-
tio (CBR) are very significant requirements in construction of base and subbase layer of highways. The presence
of RCA in T-1 and T-3 increased the optimum moisture content and decreased the maximum dry density as a re-
sult of the higher water absorption and the low particle density of the recycled concrete aggregates. The conse-
quent decrease in CBR values (specially soaked CBR values) of T-1 and T-3 can be created by these factors as
well. Tendency to higher water absorption increased the loss under cycles of immersion in saturated solutions of
sodium sulfate followed by oven drying. Moreover, it worsened resistance against internal expansive for
cederived from expansion of water on freezing.
Presence of RAP in mixes decreases water absorption properties and makes them suitable for drainage pro-
pose which is very important for unbound subbase applications.
Water absorption of RAP is 1% [5]. Adding the RCA and as a following result existing the cement in the mix
T-3 increases water absorption rate by 6% in coarse particles and 120% in fine particles. In one hand, it seems
that adding 50% RAP to RCA decreases the water absorption rate and makes it suitable for subbase applications.
But, on the other hand our further researches [1] showed that this replacement decreased the strength property of
subbase such as CBR values. This is why, it is needed an optimum mix design of RAP and RCA both decrease
the water absorption and increase strength and durability.
References
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[3] Poon, C.S. and Chan, D. (2006) Feasible Use of Recycled Concrete Aggregates and Crushed Clay Brick as Unbound

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