Grantee Research Project Results

Final Report: Melt Recyclable Polymer Concrete Using Recovered Concrete Aggregate and Unique Thermosetting Thermoplastic Polycarbonate

EPA Contract Number: 68HERC20C0036
Title: Melt Recyclable Polymer Concrete Using Recovered Concrete Aggregate and Unique Thermosetting Thermoplastic Polycarbonate
Investigators: Cameron, Randy E.
Small Business: Instrumental Polymer Technologies, LLC
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2020 through August 31, 2020
Project Amount: $100,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2020) RFA Text |  Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR – Sustainable Materials Management

Description:

Concrete is the most consumed human-made product on Earth. The world produces 10 billion tons of concrete each year to build infrastructure for human society and exhales more than 2.2 billion tons of carbon dioxide in the process. It's not only being used to build structures, but roadways are increasingly being paved with concrete rather than asphalt. Concrete consists of a binder, usually Portland cement, and aggregate, which happens to be the most mined raw material in the world. Mining for aggregate leaves scars on the Earth, destroys valuable farmland, while using an extensive amount of energy, and creating much waste. Because of this, developing effective methods of recycling concrete has become increasingly important. Recycling concrete as concrete aggregate not only protects natural resources of aggregate and land but also eliminates the need for concrete's disposal.

Unfortunately, recycled concrete aggregate, (RCA) can only be added to new cement concrete at levels of up to 35%. Any higher than this and the physical integrity of the concrete begins to suffer. While it is beneficial to develop technologies aimed at improving cement so that it could incorporate more RCA, there is another, more impactful environmental problem that needs to be addressed. And that is that cement concrete is increasingly being replaced by polymer concrete, which introduces a whole new set of environmental issues. Polymer concrete's higher compressive, tensile and impact strength, fast cure, low permeability, low density and better resistance to chemicals and corrosive environments offer new opportunities in architectural design. But its higher strength and longevity also make it much more difficult to grind up and recycle or biodegrade. Furthermore its unsustainable and toxic roots pose a problem for the environment. If polymer cement is the material of the future, then a project to develop an environmentally friendly version that can utilize RCA as a very high percentage of its aggregate would be extremely useful. And that is the goal of this project.

Polymer concrete is aggregate bound by polymers like epoxy or polyester, rather than cement. Its high tensile strength, excellent adhesion, low density, low shrinkage and water impermeability offer longevity and opportunities in design that conventional Portland cement concrete can't achieve. It's most often used in areas of high wear. The market for polymer concrete is growing strong with a compounded annual growth rate (CAGR) of 6.3% with the United States holding 70% of the current global market. Nevertheless, its growth is highly hindered by the fact that the resins used in polymer cement are two-component systems that have a very short work-life. After mixing the aggregate and resins, workers have less than two hours to apply the material. Because thermosetting cures are exothermic, mixing of large volumes of polymer concrete shortens the work-life even more.  And the situation is worse when the temperature is hot. Nevertheless the growth rate shows there is a drive from designers to use more polymer concrete.

Unfortunately the increasing use of polymer concrete systems is a detriment to the environment and to workers. Not only are the epoxy and polyester resins that are used derived from toxic and unsustainable raw materials, but the resin systems themselves are often toxic. This is because small molecules and oligomers with low viscosity and high reactivity are used in order to wet the aggregate well and react quickly. For example, styrene, which is often used in the polyester resin systems, is a very thin and volatile liquid. But it is also suspected to promote lymphohematopoietic cancers. Furthermore, the cured polymer concrete is also an environmental problem. It cannot be melt recycled (like asphalt can) and, because of its stronger strength, is more difficult than cement concrete to grind and use as aggregate.

Thus there are two sources of tension in the polymer concrete market. One is the designers desire to expand the use of polymer concrete in to more complex, larger volume designs, but the two-component thermosetting nature of polymer concrete hindering large scale application of it. And the other is the environmental concern that replacing cement concrete or asphalt with polymer concrete is only exacerbating a bad situation.

Summary/Accomplishments (Outputs/Outcomes):

The research objective of this project was to develop a new type of polymer concrete, using recycled concrete aggregate, (RCA), along with a proprietary thermosetting thermoplastic polycarbonate.  It needs to be strong enough to incorporate a large percentage of RCA, but with application characteristics of that of asphalt. The concept of a thermosetting thermoplastic is an invention by Instrumental Polymer Technologies, LLC (IPTECH), and is a plastic that is a crosslinked under ambient conditions, so it performs like other highly crosslinked thermoset resins like epoxies. However, it has a chemical functionality built in so that upon heating to a certain temperature the resin fragments and becomes a liquid. Upon cooling the plastic once again crosslinks. In other words, the crosslinking is reversible. Consequently the plastic processes like a thermoplastic, but performs like a thermoset plastic. If designed correctly the fragmented segments are small so the "melted" or fragmented material is very low viscosity. This is a key factor in the polymer concrete designed in this project. The objective is to have the high performance properties of current polymer concrete, but will be applied and recycled like asphalt. The polymer is derived from inexpensive, sustainable raw materials.

During Phase I IPTECH developed a version of thermosetting thermoplastic aliphatic polycarbonate for use in polymer concrete by focusing on achieving a low fragmentation ("melt") viscosity, an appropriate cure time and physical properties as well as a fragmentation temperature that was high enough for external use (above 90°C). During Phase I IPTECH was able to demonstrate a version of this thermosetting thermoplastic that fragmented at approximately 95°C and became a low viscosity, easily processable, liquid at 120°C. Upon cooling the material once again underwent ring opening polymerization and was a solid within an hour of cooling. Ultimate hardness was achieved in 24 hours. This will be a huge advantage over asphalt, which takes three days before a heavy load can be applied.

IPTECH filled the material at 120°C with recycled concrete aggregate (RCA) to a level in which there was only 10% resin and 90% RCA, as is the common loading level of polymer concrete and asphalt. This material was easily processable at 120°C and cured even faster than with the neat resin. Physical properties including compression strength, tension strength and flexural strength were tested and found to be better than asphalt and slightly less than epoxies. Consequently the results of Phase I are a success. This is particularly interesting since our system used 100% RCA as aggregate and we are comparing it to epoxy polymer concrete containing normal aggregate.

IPTECH also performed testing on the polymer concrete using thermosetting thermoplastic and RCA after immersing the material in water for a month. Surprisingly the material was even stronger after immersion. This is probably because the samples had an extra month of cure. During Phase II we will explore catalysts for accelerating the cure of material and allow for faster strength build up.

Conclusions:

IPTECH has begun discussions with polymer concrete manufacturers who develop and sell product for use in roadways as well as molded furniture and architectural forms. IPTECH currently produces and sells aliphatic polycarbonate polyols for use in coatings and will be able to use these facilities for producing the resin for this technology.