Recycling of Plastic Bottles for Use as a Lightweight Geotechnical Material

Recycling of plastic bottles for use as a lightweight geotechnical material.


In order to build road embankments, fill in behind retaining walls, and backfill above underground pipes, geotechnical fills are employed. Fill that is lighter helps structures be erected more cheaply by reducing the burden. A brand-new, thin geo-material was created by adhering recycled plastic bottles in their post-consumer form.

This project aims to investigate the potential of this novel material as a light-weight geotechnical fill. Design, methodology, and approach – Aspects of the mechanical and physical properties of the recycled plastic bottle blocks were examined through a preliminary laboratory and field investigation.Behind a retaining wall on a bicycle route, field tests of this novel material are currently being conducted.

Results – It was discovered that this novel material has a very low average density of 32.63 kg/m3 (2.04 lb/ft3) and that 59.5 percent of a block is formed of recycled plastic bottles. The plastic bottle waste stream that is collected from a recycling facility is gap-graded, with roughly 25% of the bottle volume being in 2l bottles and the remaining 75% being in 500ml bottles.Small ten-bottle samples subjected to unrestricted compression testing yielded strengths of 60 kN/m2 (1,250 lb/ft2) or more.

Practical applications – Test results suggest that this material could be used as a light-weight geotechnical fill over soft soils or behind retaining walls, as an energy-absorbing crash barrier for highway, race track, or airport safety, as ground and building insulation for Arctic construction, as floating barriers or platforms for offshore work, or for acoustic or vibration dampening for manufacturing processes.

Originality/value – The utilization of a significant amount of recycled plastic bottles as a green geotechnical engineering material is explored in this paper. There is a description of an ongoing field research as well as engineering parameters for this novel material.The knowledge provided here is the initial step in comprehending this new topic with regard to applications in civil engineering.

Keywords: Geotechnical engineering, plastics, and recycling Case study paper type


Natural resources from the area are often used to make geotechnical fills. Roadway embankments, retaining walls, and backfilling above subterranean pipelines are all constructed using fills. These structures may be built more affordably the lighter the load they support. Additionally, because of significant settlement, building on soft ground has always been a difficult problem for geotechnical engineers.

The rise in overburden stress is a factor in settlement. A desirable way to lessen settlement of soft underlying soils is to control the total weight of fill, particularly by using recycled material (Pierce and Blackwell, 2003). Since the early 1960s, expanded polystyrene has been successfully applied in geotechnical applications (Stark et al., 2004). Expanded polystyrene, sometimes known as geofoam in geotechnical applications, was the subject of patents granted in 1971 and 1973 (Monahan, 1993).

Large chunks of geofoam up to 1:25m by 4m by 0:6 m (4 ft by 16 ft by 2 ft) are created. Expanded polystyrene is a distinctive material with a density that ranges from 12 to 29 kg/m3 (0.70 to 1.80 lb/ft3), or roughly 1-2 percent that of dirt.

So a geofoam embankment that is 30 m (100 ft) long would weigh almost the same as a soil embankment that is 0.3 m (1 ft) long. Despite being lightweight and having a low density, geofoams are sturdy enough to handle the majority of loads that are encountered. They are sturdy enough to withstand typical loads that are low in density and geotechnical applications, is encountered.

The benefits of geofoams are as follows:.

  • They are compact
  • They act as thermal insulators
  • They manage the flow of fluid
  • They reduce tremors
  • They are sound structurally

In addition to several benefits, expanded polystyrene geofoam blocks also negative aspects, such as:

Environmental impact – Some methods of geofoam manufacture contribute to the ozone problem in the atmosphere. The Montreal Protocol of the United Nations prohibits the manufacture of ozone-depleting substances after 2010 (United Nations Environment Programme, 2000)

.Cost – Blocks range in price from $25/m3 to $80/m3, depending on the density of the geofoam. $50/m3 (between $0.75 and $1.50 per square foot) (Negussey and Jahanandish, 1993); thus, petroleum-based goods. This could result in serious issues if a gasoline or oil. A car wreck along a geofoam road embankment causes a leak. 1993 (Monahan). Geofoam blocks are flammable even if they are flame-retardant. Although geofoam blocks are available, they are rarely used because of their fire resistance. Blocks are more expensive than regular geofoam, costing 5–10% extra. (1993; Negussey and Jahanandish).

Block moving – Underneath the construction site, Geofoam blocks could cause the underlying structure to crack.

Animal and insect damage — Due to geofoam’s insulating capabilities, animals and insects may burrow into the foam, diminishing its structural strength and integrity.

Despite the fact that geofoams have many benefits, there are some drawbacks. Limitations include environmental effect, high expense, and incompatibility with petroleum-based products. their widespread application. Even with limited application, the volume of lightweight fill placed is quite large. Some examples of the volumes of geofoam employed in past projects are:

A shopping mall foundation in New York, 28,000 m3 (950,000 ft3); the I-15 reconstruction project in Salt Lake City, 100,000 m3 (3:5 £ 106 ft3); 120 projects between 1971 and 1991 in Norway, 250,000m3 (8:8 £ 106 ft3); and 1,665 projects between 1985 and 1995 in Japan, 1,020,000m3 (36 £ 106 ft3) (Negussey, 1997).
The University of Alabama has created a lightweight geomaterial that addresses the main drawbacks of geofoam and is made from recycled plastic bottles. Large quantities of waste (plastic bottles) that are ordinarily landfilled are used in the post-consumer plastic bottle fill. 4 billion) of the 1.8 billion kilos

Only 360 million kilos (797 million pounds) or 19.9 percent of the bottles that were sold on US shelves in 2002 (National Association for PET Container Resources, 2002) were recycled. Due to the fact that waste plastic bottles do not require further manufacturing processing, unlike the creation of recovered plastic boards or fabrics, the suggested use of waste plastic bottles as a fill is more cost-effective than recycling.

Lightweight recycled plastic bottle fill

Recycling programs are run by communities and organizations all over the world to collect post-consumer materials like paper, metal, glass, and plastic. Unfortunately, the enthusiasm shown by society during collecting does not match the financial gain from using a significant amount of recycled material. Recycling waste is all too frequently dumped in landfills.

With the new recycled plastic bottle fill, less expanded polystyrene might potentially be used, which would reduce the cost of lightweight geotechnical fill applications. Recycling plastic bottles is better for the environment than making expanded polystyrene blocks. Instead of needing to melt and treat the waste plastic, recycling bottles in their post-consumer form saves energy expenses and landfill space.

The only material expense of making this lightweight fill is from the adhesive binding agent that is used to glue the bottles together since recycled bottles make up the majority of this novel geo-material. Additionally, if an oil or gasoline spill were to happen, plastic bottles would not dissolve because they are compatible with petroleum products. These benefits have influenced many to choose plastic bottles as an eco-friendly lightweight fill.
This regenerated heterogeneous material has a wide range of variations, just like natural soils. Among the variables are bottle size, which can be large, tiny, or random; caps, which can be capped or uncapped; adhesive, which can be urethane, cement, PETE, bitumen, rubber, shrink wrap, geogrid, or another; and bottle orientation, which can be oriented or random;

bottle orientation – orientated, random;

confined or unconfined during cure; small, medium, or large samples; axial or transverse sample test orientation; low, room, or high test temperature; and wet or dry test condition.
Engineering properties may be impacted by any of these factors. A collection of important mechanical, physical, and chemical properties is shown in Table I. Due to the size of the test matrix, it was first determined what the basic characteristics of typical samples were. Compressive strength was assessed for small ten-bottle samples, whereas density and grain size distribution were determined for samples measuring 0:61 £ 0:61 £ 0:61 m (2 £2£2ft).

Preliminary laboratory results

Post-consumer PETE bottles and a binding agent are used to create the lightweight recycled plastic bottle fill. Although many asphaltic adhesives as well as a construction adhesive were tested in the preliminary research, the focus was on commercially available polyurethane foam as the binding agent. The function of the glue is not well understood at this stage of the research.

When compared to urethane foam, the construction glue generated lesser strength and less recoverable deformation, and the asphaltic adhesives were difficult to work with and gave inconsistent results. Expandable backfill made of urethane foam has been used in civil engineering to put roadside signage for transportation purposes. Urethane foam can be used in civil engineering applications below ground for 20 years or more (Boehm, 2005) .In a wooden mold, five blocks of urethane foam filling with a volume of 0.227 m3 (8 ft3) were created.

After the mold had been filled with solely plastic bottles, it was once again weighed. The weight of the plastic bottles was derived from this. Each bottle’s size and kind (water, soda, juice, etc.) were noted when a sample was put together. Additionally, whether the bottle was cap-on or cap-off was noted. These data allowed for the determination of the new lightweight fill’s density, grain size distribution, and sample statistics.

Mechanical properties

Compressive strength

Compressive modulus

Shear strength

Shear modulus

Impact strength

Creep strength

Fatigue strength

Physical and chemical properties


Grain size distribution


Thermal conductivity

Acoustic transmission

Vibration dampening


Electrical resistance

Corrosion resistance

Recycling of plastic
Recycling of plastic

When a load is applied, the pressure in a bottle that has a cap will rise and then gradually decrease over time. The lightweight fill has a density of 32.63 kg/m3 (2.04 lb/ft3) on average. Approximately 80% of a sample’s weight comes from the bottles, and 20% comes from the polyurethane adhesive.
Each laboratory sample of the light-weight fill material had its grain size distribution plotted, as seen in Figure 1. A typical geotechnical grain size distribution plot uses axes that are similar to those of this figure, but with a small difference. As opposed to effective particle diameter, the abscissa is measured in milliliters of bottle volume, and the ordinate is measured in percent smaller by volume.

Figure 1 shows that the material created from a typical recycled plastic bottle waste stream is gap graded and contains a sizable amount of bottles between 500 ml and 2 l (home use size) in volume. The grain size distributions are strikingly comparable despite the material’s appearance of extreme randomness.
A number of tiny samples were created and tested for compressive strength in addition to the five large blocks of lightweight fill that were manufactured. To employ the least amount of urethane foam while increasing the contact surface area, ten identical plastic bottles were assembled.

The bottles in the little samples were capped and placed four up and six down. An illustration of a small sample kept together with urethane is shown in Plate 2.


The loading rate used for the compressive strength tests was 12mm/min (0.5in/min). Because the pressure inside the sealed bottles has increased, it is assumed that the loading rate will have an impact on the compressive strength. Analysis and comparison of the test findings from the small samples with the geofoam’s strength characteristics took place.

The little plastic bottles acquired roughly half the compressive strength (stress) of commercially available geofoams, as illustrated in Figure 2.The facts are encouraging because the plastic bottle material is stronger than many soils used in construction, despite preliminary results showing that the plastic bottles are not as robust as geofoam.

construction. It should be noted that big chunks of material were used to create the stress-strain data for the geofoam. The plastic bottle material will eventually be examined in this research endeavor using a sample size akin to that.

Case study

A small field installation of the lightweight recycled plastic bottle fill was constructed at Lake Lurleen State Park in Tuscaloosa County, Alabama, USA. The site is a switchback on a rough mountain bike trail. The switchback is located approximately 1 km (0.6 miles) from the nearest vehicle access point. Lightweight fill was selected due to a lack of quality fill material at the site and the haul distance from the nearest access point.

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