In 1995, New York turned discarded milk jugs and detergent bottles into a pier deck; 2 years later, the recycled plastic had held its key engineering properties

Discarded plastic bottles are often associated with a long-lasting waste problem, but in the 1990s, researchers and manufacturers began exploring whether the same material could serve as a durable alternative to timber. In December 1995, recycled plastic lumber was used to build part of a pier in Old Field, New York. The structure provided a chance to test how the material held up under real outdoor conditions, including sunlight, rain and changing water levels.

From household plastic waste to pier decking

According to a study published in Resources, Conservation and Recycling in 1998, the plastic lumber was manufactured by TRIMAX, a company based in Ronkonkoma, New York. Its feedstock consisted mainly of post-consumer high-density polyethene (HDPE), a type of plastic commonly used in milk and water jugs, shampoo bottles and detergent containers. The material was created using an extrusion method, in which plastic was melted and forced through a die to form long profiles. These profiles could then replace traditional wood in construction projects like decking, fencing, and benches, among others. The pier was constructed at West Meadow Creek, Old Field, Long Island. It measured 1.2m x 9.1 m, and the recycled plastic profiles made up some of its deck sections.


The use of plastic lumber in a water-bound structure offered several advantages over timber. Plastic lumber is less prone to decomposition than natural wood and can withstand attack by marine creatures that damage timber structures. In addition, the use of plastic lumber in a water body would minimise the use of timber preservatives, which could leach out into the nearby water bodies. Nevertheless, lack of susceptibility to rot does not mean that a material is structurally sound. This is because plastic can deform or soften under continuous loading and UV light.

What two years of testing revealed

Sampling was conducted on the pier intermittently over the course of two years before sending the materials back to the lab for engineering tests. Measurements of dimensional stability, surface hardness, resistance to compression, and the modulus of elasticity (i.e., the stiffness of the material upon the application of force) were taken. Results were varied yet promising on multiple fronts. Dimensional stability, in-plane compression modulus, and Shore D surface hardness of the recycled plastic lumber stayed consistent with or above what was observed prior to the material being installed.

The modulus of elasticity, however, varied considerably. During the first 12 months of outdoor exposure, it fell from an initial value of 1,370 to 750, a decrease of about 45 per cent. The researchers reported these values in the paper, but the unit should be verified against the original data before being added. During the second year, the value rose towards its original level. This variation matters because the modulus of elasticity measures a material’s stiffness and helps indicate how much it deforms under an applied force.

A promising use for plastic waste, with limits

Pier Project was one of several attempts to find uses for recycled plastic waste produced by households. Utilising waste plastic to produce durable building materials would result in less disposal and reduced need for raw materials. This project was focused on using plastic for marine structures that would be subject to decay caused by wood-eating marine life.

The 1997 study also notes that certain organic substances and metallic ions were released by the plastic surfaces, but their concentrations in the adjacent river water were very small. Thus, it provided information on how recycled plastic products behave in an actual aquatic environment, though it does not prove that all formulations would behave the same way environmentally.

The study at West Meadow Creek, however, was limited to one product and one pier. Moreover, the study period was too short to conclude the lifespan of plastic-lumber piers. The pier was also not used heavily during the observation period. Despite this, the experiment indicated that discarded milk jugs and detergent containers could be converted into decking materials that maintained many key characteristics even two years later.