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An invisible culprit is weakening our concrete, research finds

 

A team of researchers has found trace amounts of organic matter in concrete and asphalt can cause premature deterioration of the building materials.

Phthalates, diesel exhaust particulates, surfactants, and windshield washer fluids have all been found to cause the phenomenon.

But rather than preventing these fine particulates from entering the concrete in the first place, better post-production testing has been proposed by researchers to understand the useful lifetime of any given structure.

Current methods of assessing concrete and asphalt deterioration use surface cracks and basic chemical tests, but the researchers found this to be inadequate as the root cause of deterioration.

Research team member Akihiro Moriyoshi, from Hokkaido University in Sapporo, Japan, said the findings affect everyone and further research will be required to remediate this invisible threat.

“Road managers, building owners and the general public are also at great risk, but they are unaware of this phenomenon,” Moriyoshi said.

Moriyoshi gave examples of New York’s World Trade Centre towers on 11 September, 2001 and a bridge in Minneapolis both falling due to weak structural integrity, caused by the decay of organic matter within the concrete.

“The concrete dust scattered around the collapse of the US World Trade Centre had an average diameter of 0.05mm, which is the same size as white flour powder. This indicates that the concrete had already been disaggregated before it collapsed,” Moriyoshi explained.

One promising method used by the research team involved analysing damaged concrete samples using a CT scanner, where disaggregation of the samples showed in black.

Simply put by the professor, “damage caused by the disaggregation phenomenon cannot be evaluated from the surface of the structure”.

“For this reason, new and existing structures can be evaluated accurately using the new Micro Focus CT Scanner (CT) evaluation method.

“Using this evaluation method, it is possible to accurately determine the repair time and repair depth of concrete structures. In addition, the soundness of new structures can be accurately evaluated.”

The research compared the deterioration times of samples from modern day concrete, with 120-year-old concrete samples as a control.

“One hundred and twenty years ago, cement was made from only three materials: clay, limestone and silica stone, and no additives or wastes were used,” Moriyoshi explained.

“In modern cement manufacturing, in addition to this raw material, more than 40 per cent of waste is used during manufacturing, which greatly affects the deterioration and cracking of concrete.”

Moriyoshi’s work is published by the PLOS One online journal.

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