Polymers

 

Raw materials for Ground Consolidators – A green solution

 

GC’s are a durable and a sustainable alternative for various traditional constructions for prevention or repair of erosion hotspots.  GC’s can be made of many different materials. We used steel and a wide assortment of modern composite plastics. 
The research of GC constructions is supported by the Dutch “Rijkswaterstaat” as they believe new types of raw materials give new opportunities for  minimizing the “load” on our environment during and after the products lifecycle.

 

Durability

Traditionally especially rock, gravel, concrete and steel slag are widely used for erosion protection, in various assortments, with or without a  geotextile filter layer. These materials form a protective layer against erosion and a high weight is therefore needed.
In a GC application this is totally different: the sand which is kept together by the GC package forms the protective layer. The amount of material to be added is therefore much lower.
Furthermore, the edges of the protective GC layer are not “sharp”, which prevents the development of new erosion spots. Also the layer is somewhat flexible and will therefore accommodate (seasonal) changes in the bottom profile. Therefore it is expected that the GC layers require less corrections and maintenance which leads to less trouble and lower costs (measured over multiple years).

 

Sustainable

Obviously it is essential that the use of GC’s has no (negative) chemical impact whatsoever on the environment during or after use. With material specialists we designed the materials in two different “cradle-to-cradle” cycles:

  1. Technical cradle-to-cradle
    The GC’s and the GC- mattresses are designed and applied in such a way that they can be removed after their useful lifetime in the protective layer, and properly recycled. The raw materials can be used within new GC’s (or similar products), thus giving a closed loop for the polymer component. For example, in an artificial reef we used natural fibers and barite minerals, kept together with polypropylene polymer.Also basalt fibers can be used. These composites will not lose any material to the environment during their lifetime. This gives a heavy composite which can be properly recycled which closes the raw materials loop.
    In extremely sensitive areas one could also consider the use of biopolymers with an extremely long decay (composting) time at room temperature, e.g. PLA with basalt. This might e.g. be interesting for erosion protection of a pipeline in a sensitive environment like the Dutch Waddenzee or in a coral reef restoration project around the great barrier reef. If some material would unforeseen be lost to the environment it will not contribute to any "plastic soup". The basic aim of such construction however is that one is able to recycle the material after its usefull life.

  2. Biological cradle-to-cradle
    The GC’s and the GC mattresses are designed in such a way that biodegradation will occur within a timeframe tuned to the required lifetime of the construction. Innovative polymers based on PLA (poly lactic acid, made out of corn) are mostly used. These are strengthened with natural fibers like hemp or flax or mineral fibers like basalt, and if needed weighted with natural lime or barite. These materials can be mixed with e.g. Solanyl (based on reclaimed potato, grain, root and/or seed flour based resources) to tune composting. The composting will give nutrition for plants which can be used for new biopolymers etc, which closes this loop.   

 

Proof of principle

There is a lot of talking about cradle-to-cradle. Well, we did it, examples are shown here:

 

In collaboration with Wageningen University Research, GreenGran Hongkong, Inverko Compounding (recycling) and Anome Projects a complete technical cradle-to-cradle cycle was executed and completed in 2013. Rijkswaterstaat supported this project financially, as they believe modern composites will establish themselves into a “green” alternative for rock, gravel, geotextile, concrete or steel slag in several applications within civil engineering. Thousands of GC’s which were used during 3 years for a slope protection project in Rotterdam were tested, recycled, cleaned, milled and used as raw material in injection moulding, in various blends. Subsequent test results were convincing.

 

In a further test a few 40 cm GC’s were dumped into the IJsselmeer. A Boskalis survey ship with multibeam found them immediately back. So, in a clean-up project we seem to be able to find even individual GC’s back. However, we do not expect to loose any GC’s. We do not find individual GC’s around the projects, the interlocking seems OK even after many thousands high and low tides.

In summary: we are able to fully reclaim and recycle GC projects and use the composite as raw material for further projects. This shows the feasibility of the technical cradle-to-cradle principle.

 

The proof of principle of the biological cradle-to-cradle is still underway, a.o. in the reed fixing project and in the Burgers’Zoo tests. Typically these GC’s are used as temporary stabilizer where plants like reed or maze reed have to take over. We foresee further applications in temporary erosion protection mattresses, where the higher initial costs easily balance with later savings as removal is not necessary anymore. 
As composting is a biological process done by micro-organisms we cannot perform accelerated life tests, and exact decay is yet unknown. We are aiming for strength during ~10 years.  After ~3 years we see now some early signs of degradation in some material variations, as planned. Only some barite (“sand”) will finally remain, which shows we have a really nice “green” construction!

In January 2014 Anome Projects will start several series of tests with new biopolymers (composites), in collaboration with Pezy, CMB, StendenPre Hogeschool and Rodenburg Biopolymers.

 

For further info or great ideas mail to Lieuwe Boskma