Second LACCEI International Latin American and Caribbean Conference for Engineering and Technology
(LACCEI’2004)“Challenges and Opportunities for Engineering Education, Research and Development”
2-4 June 2004, Miami, Florida, USA
High Performance Construction Materials From
C&D Waste Aggregate and Recycled Plastics
Khaled Sobhan, Ph.D.
Assistant Professor, Florida Atlantic University, Boca Raton, FL 33431, USA
Abstract
This project deals with the innovative recycling of Construction and Demolition (C&D) waste
aggregate, fly ash and recycled HDPE plastic strips obtained from post-consumer water
containers into a fracture resistant construction material for highway pavements. According to a
1998 USEPA estimate, a total of 196 million tons of C&D wastes were generated in the U.S. in
1996, out of which 24-66% were concrete materials. Regionally, data from Florida Department of
Environmental Protection (FDEP) indicates that nearly 25% of the Municipal Solid Waste
(MSW) stream in Florida comprises of construction and demolition (C&D) wastes, 33% of which
is concrete materials. Similarly, due to the widespread availability of fly ash as a waste material,
and its cementitious characteristics under certain conditions, there is lot of potential for utilizing
fly ash as an alternative construction material. Moreover, a 1992 USEPA study showed that
almost 20% by volume of the available landfill space is occupied by waste plastics. The current
study combines these three solid waste materials into a high performance Roller Compacted
Concrete, which is inherently resistant to the formation of load induced tensile fracture due to the
presence of recycled plastic strips acting as micro reinforcements within the brittle matrix. Some
guidelines are provided on the mix-design and properties of the new composite for ready
incorporation into pavement construction. Such innovative recycling of solid wastes in highway
applications will conserve not only our natural aggregate resources but also the rapidly depleting
landfill spaces, and at the same time help mitigate the crucial solid waste disposal problem in the
U.S. and other developing countries.
Keywords: Recycled, waste plastic, concrete, fly ash, landfill
1. Introduction
The research described in this paper systematically tests and evaluates an alternative, roller
compacted concrete (RCC) pavement foundation material consisting more than 90% by mass of
recycled waste products namely crushed aggregate, fly ash, and shredded plastics. One of the
long-range goals of this research endeavor is to provide valuable insights into the durability and
performance of the new composite. The scope of the current paper is limited to static laboratory
investigation for providing some performance-based mixture design guidelines such that adequate
strength and toughness is achieved for use as a high-quality pavement foundation. In the recent
years, major emphasis has been placed on the rehabilitation and maintenance of existing highway
facilities, rather than building entirely new pavement structures. The increasing availability of
reclaimable aggregates from demolished infrastructure elements (such as bridge and pavements)
and the concurrent gradual decline in available landfill spaces for the disposal of construction
debris have created a need-driven opportunity for greater use of recycled aggregates in the
construction and rehabilitation of pavement systems. Similarly, due to the widespread
availability of fly ash as a waste material (Ahmed and Lovell, 1992), and its cementitious
characteristics under certain conditions, there is lot of potential for utilizing fly ash as an
alternative construction material in highway applications. From a mechanistic standpoint, a brittle
material will undergo failure due to formation and propagation of tensile cracks. To inhibit tensile
crack propagation, and thus to potentially enhance the service life of the pavement layer,
shredded-plastic strips obtained from recycled high density poly ethylene (HDPE) as found in
post-consumer milk and water containers were used as randomly oriented micro-reinforcement
within the matrix. According to data published by the EPA (1992), the solid waste stream in the
United States in 1988 included 14.4 million tons of plastics, which occupied 20% by volume of
the available landfill space. Therefore, innovative use of recycled plastics as fiber/strip
reinforcement of pavement layers is not only environmentally significant, but has the potential of
becoming a new and effective strategy for rehabilitation and maintenance; this will ultimately
result in savings to both the highway agency and the user.
2. Objectives
The specific objectives of the study were (a) to propose mixture proportions for RCC based on
performance-based lab testing, (b) to determine the compressive and split tensile strength of the
composite, and (c) to evaluate the effectiveness of recycled plastic fibers in enhancing the
mechanical characteristics of a lean RCC pavement material.
3. Materials
Type I Portland cement and Class C fly ash were used as stabilizing agents whose proportions
varied from 4% to 8% (by mass of the total RCC mixture). Plastic fibers were obtained from
recycled high density polyethylene (HDPE) as found in milk or water containers. Amount of fiber
varied between 0.25% to 1.25% (by mass) with lengths varying from 19 mm to 76 mm, and width
of 6.35 mm. Reclaimed aggregate was obtained from a plant called Jobe Concrete (El Paso, TX),
which collects demolished concrete products, separates the reinforcements and impurities, and
crushes into 1-inch or 2-inch sized aggregate suitable for pavement base or subbase applications.
The fly ash was obtained from Mineral Solutions (formerly The American Fly Ash Company)
located in Naperville, Illinois. This fly ash complies with ASTM C618 specifications.
4. Specimen Preparation and Curing
Based on initial modified Proctor compaction tests on various mix proportions of aggregate,
cement, and fly ash, all specimens used in this study were prepared at a constant unit weight of 19
kN/m3, and at a molding water content 9%. The experimental program consisted of unconfined
compression tests, and specially instrumented split tensile tests. Twenty-one different mix designs
were selected for preparing 15.24 cm (6-in) x 30.48 cm (12-in) cylindrical specimens to evaluate
the strength and toughness characteristics under unconfined compression and split tension modes.
Table 1 shows the details of all these mixtures, which included recycled crushed aggregate and
various combinations of cement, fly ash, and shredded recycled plastic fibers. Mixtures 1 through
3 are unreinforced specimens and were used as control specimens. Fiber reinforced specimens
contained either 0.25% or 0.5% (by total dry mass of the mix) of plastic strips, which were 19
mm to 76 mm in length, and 6.35-mm in width. The specimens were sealed cured in the lab for
about 24 hours after which they were demolded and transported to a 100% humidity room for
curing. All tests were conducted with a 90-KN INSTRON servo-hydraulic testing machine. As an
extension to the standard ASTM method for split tension tests (ASTM C496), two horizontal
linear variable differential transformers (LVDTs) were attached at the longitudinal and vertical
mid height of the specimens to measure the tensile deformation of the horizontal diameter due to
compressive loading in an orthogonal direction (as shown in Figure 1). This method permitted an
evaluation of the toughness characteristics of the composite.
TABLE 1 Mixture Design Matrix for Compression and Split Tension Tests
Compression Tensile
Tests
Tests
Mixes
Mix Design
Mix-1
8% Cement


Mix-2
4% Cement + 4% Fly Ash


Mix-3
8% Cement + 8% Fly Ash


Mix-4
8% Cement + 0.25%, 50.8-mm Fibers


Mix-5
4% Cement + 4% Fly Ash + 0.25%, 50.8-mm Fibers


Mix-6
8% Cement + 8% Fly Ash + 0.25%, 50.8-mm Fibers


Mix-7
8% Cement + 0.50%,2" Fibers


Mix-8
4% Cement + 4% Fly Ash + 0.50%, 50.8-mm Fibers


Mix-9
8% Cement + 8% Fly Ash + 0.50%, 50.8-mm Fibers


Mix-10
8% Cement + 0.25%, 76.2-mm Fibers


Mix-11
4% Cement + 4% Fly Ash + 0.25%, 76.2-mm Fibers


Mix-12
8% Cement + 8% Fly Ash + 0.25%, 76.2-mm Fibers


Mix-13
8% Cement + 0.50%, 76.2-mm Fibers


Mix-14
4% Cement + 4% Fly Ash + 0.50%, 76.2-mm Fibers


Mix-15
8% Cement + 8% Fly Ash + 0.50%, 76.2-mm Fibers


Mix-16
8% Cement + 0.25%, 19-mm Fibers


Mix-17
4% Cement + 4% Fly Ash + 0.25%, 19-mm Fibers


Mix-18
8% Cement + 8% Fly Ash + 0.25%, 19-mm Fibers


Mix-19
8% Cement + 0.50%, 19-mm Fibers


Mix-20
4% Cement + 4% Fly Ash + 0.50%, 19-mm Fibers


Mix-21
8% Cement + 8% Fly Ash + 0.50%, 19-mm Fibers


5. Experimental Results
5.1 Compression and Split Tensile Strengths
Figure 2 shows the average 28-day compressive and split tensile strengths for all mixtures. The
maximum strength was achieved by the mixture containing 8% cement and 8% fly ash, having a
compressive strength of 14 MPa (2000 psi) and a split tensile strength was 1.5 MPa (175 psi)
indicating a remarkably strong stabilized base course material despite the fact that 92% or more
of this composite contains waste products. It is found that the compressive strength drops when
50% of the cement is replaced by fly ash (i.e. comparing Mixes 1 and 2), and significantly
increases when the amount of cementitious material is doubled by adding fly ash to the composite
(i.e. comparing Mixes 1 and 3). For all mixtures, the inclusion of fibers had a detrimental effect
on compressive strength compared to a corresponding unreinforced mix. However, a similar
comparison reveals that for most mixes, the split tensile strength remained approximately same or
showed noticeable improvement due to the inclusion of fibers.
Figure 1: Schematic of Split Tensile Tests
5.2 Toughness Characteristics
In order to evaluate the effectiveness of the fibers in improving the post-peak load bearing
characteristics, the area under the split tensile load-deflection curve was calculated (details can be
found in Sobhan and Mashnad, 2001). This quantity is termed the absolute toughness and is a
measure of the energy absorption capacity of the material. These toughness values are also
plotted in Figure 2 for the various mixtures. It is observed that for most mixes the specimens
incorporating 51-mm fiber in general produced the higher toughness values and clearly showed
the beneficial effects (improvement in toughness) of fiber inclusions.
5.3 Effect of Fiber Length
In order to determine an optimum fiber length based on performance, the strength and toughness
values were plotted against the fiber length for all mixes as shown in Figure 3. It is found that for
both 0.25% and 0.5% fiber contents, the “best” performance was achieved with the 51-mm fiber.
6. Conclusions
The study presented in this paper showed a systematic way of characterizing a new composite
roller compacted cementitious material, and selecting mix-design based on performance. Due to
stabilization and reinforcement (achieved mostly with recycled materials), the selected mix with
4% cement, 4% fly ash, 92% aggregate and 51-mm fiber is likely to outperform conventional
granular pavement foundation materials obtained from natural resources. Moreover, this new
composite contains more than 96% by mass of waste materials, which potentially makes it an
attractive alternative construction material from both environmental and economical standpoints.
8. References
Ahmed, I., and C. W. Lovell. Use of Waste Materials in Highway Construction, State of the
Practice and Evaluation of the Selected Waste Products, Transportation Research Record
1345, TRB, National Research Council, Washington, D. C., 1992, pp. 1-9.
Environmental Protection Agency. Characterization of Municipal Solid Wastes in the United
States: 1992 Update. Report No. EPA 530-R-97-019, EPA, Washington, D. C., 1992, pp. 2-12
Kandhal, P. S., and M. Stroup-Gardiner. Overview: Flexible Pavement Rehabilitation and
Maintenance, ASTM Special Technical Publication. No. 1348, 1998, pp. 1-3.
Sobhan, K. and Mashnad, M. (2001). “A Roller Compacted Fiber-Concrete Pavement Foundation
with Recycled Aggregate and Waste Plastics,” Transportation Research Record 1775,
Journal of the Transportation Research Board, pp. 53-63.
Sobhan, K. and R. J. Krizek. Fiber-Reinforced Recycled Crushed Concrete as a Stabilized Base
Course for Highway Pavements. First International Conference on Composites in
Infrastructure, ICCI’96, Tucson, AZ, January 15-17, 1996, pp. 997-1011.
Acknowledgement
The work was sponsored by the Recycled Materials Resource Center at the University of New
Hampshire, with funds received from the FHWA/USDOT.
Mix-21
Mix-20
Mix-19
Mix-18
Mix-17
Mix-16
Mix-15
Mix-14
Mix-13
Mix-12
Mix-11
Mix-10
Mix-9
Mix-8
Mix-7
Mix-6
Mix-5
Mix-4
Mix-3
Mix-2
16
14
12
10
8
6
4
2
0
Mix-1
Compressive strength, MPa
(a)
Mix-1
Mix-2
Mix-3
Mix-4
Mix-5
Mix-6
Mix-7
Mix-8
Mix-9
Mix-10
Mix-11
Mix-12
Mix-13
Mix-14
Mix-15
Mix-16
Mix-17
Mix-18
Mix-19
Mix-20
Mix-21
Mix-2
Mix-3
Mix-4
Mix-5
Mix-6
Mix-7
Mix-8
Mix-9
Mix-10
Mix-11
Mix-12
Mix-13
Mix-14
Mix-15
Mix-16
Mix-17
Mix-18
Mix-19
Mix-20
Mix-21
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Mix-1
Tensile strength, MPa
(b)
Absolute toughness, kN.m
(c)
180
160
140
120
100
80
60
40
20
0
Figure 2: Strength and Toughness for Various Mixes
2.00
1.75
Tensile Strength, MPa
1.50
1.25
1.00
0.75
0.50
0.25
0.00
Compressive Strength, MPa
12
9
6
3
0
Absolute toughness, MPa 10-6
175
150
125
100
75
50
25
0
0
25
50
75
100 0
Fiber Length, mm
25
50
75
Fiber Length, mm
0.25% Plastic fiber
0.50% Plastic fiber
8% Cement
4% Cement + 4% Fly Ash
8% Cement + 8% Fly Ash
Figure 3: Effect of Fiber Length on Strength and Toughness
100