London – Bridgestone Corp. is optimising technology for using rubber granulate from scrap tires as a cement additive in geoengineering products, a company manager reported at the recent IRC 2019 conference.
Rubber granulate has been found to offer an effective means of improving the ductility of cement treated clay while still maintaining its very low permeability, Ashoke Karmokar said at the event held 3-5 Sept in London.
The use of rubberised cement in civil and geotechnical engineering applications, he suggested, could represent a significant outlet for scrap tires – thereby, helping the industry to meet its circular-economy goals.
A particular target is the use of dredged clay as sealing/filling material in geotechnical engineering applications, which is usually treated with cement for to increase its strength and reduce permeability.
However, due to embrittlement following curing cement-treated clays cannot follow the contour of structures under deformation: cracks generation severely hampering the low permeability characteristics.
In Bridgestone’s tests, clay slurry with about 280% water-content was made by adding water to dredged clay collected from the marine bed of the Tokyo Bay area. Portland cement was then mixed into the clay slurry.
Next, commercially available scrap tire derived granulated rubbers with grain size ranging 1-3mm were added and mixed well to prepare cement-treated clay samples.
The mixture was poured into moulds and kept in the controlled atmospheric chamber and cured for a standard 28 days period.
X-ray CT scans of the rubberised clay showed that cracks only appeared around the rubber, grain as opposed to widespread crack generation in the clay-matrix of cement-treated clay material, the London conference heard.
According to the Bridgestone presenter, the performance enhancement is probably due to differences in Poisson’s ratios of rubber and cement treated clay-matrix.
“Minute cracks those developed successively around the rubber particles prevent the growth of wide cracks as happens typically in cement treated clay material, according to Karmokar.
The use of rubberised cement treated clay avoids these problems, enabling their use in many geotechnical structures where deformation is also a crucial consideration, said the Bridgestone manager.
“Development of this technology portfolio would likely open up new avenues for recycling scrap tire derived rubber, and thus expected much to help in realising a circular economy in the industry,” he concluded.