Japanese scientists have found that the deterioration of modern concrete and asphalt structures is because of the presence of trace quantities of organic matter in these structures.
Cement and asphalt are vital to modern construction materials, with cement being used for the construction of various buildings and structures, while construction companies primarily use asphalt for highways and runways. Experts have widely used both for these purposes since the 1800s. But it has been observed that modern concrete and asphalt structures deteriorate much faster than historical structures – the reason for this was unknown.
With this knowledge, a team of scientists from six institutions across Japan – including Akihiro Moriyoshi, a professor at Hokkaido University – have found that trace quantities of organic matter in modern concrete structures and asphalt pavements drives the deterioration of these structures.
The deterioration of modern concrete structures and asphalt pavements is a major issue, experts have said. The features that lead to deterioration include cracks, disaggregation (breakdown into fine white powder), and delamination (separation into layers). These deteriorated structures are unsafe for their intended purposes: rapid deterioration reduces the expected lifespan of structures, increasing the costs for maintenance or replacement.
To tackle this, the scientists set out to develop an alternative method to assess the rate of deterioration in concrete. They based the current method on the width of surface cracks in concrete and a simple chemical test; however, it only gives an incomplete picture of the level of damage.
During their experiments, the scientists found that a strange odour developed when commercial cement was mixed with water. With this, they hypothesised that organic matter was responsible for the odour, and investigated the effect it has on the deterioration of concrete.
The scientists developed the one-dimensional transient moisture permeation apparatus to reproduce the field of environmental conditions that concrete structures and asphalt pavements are exposed to, in the laboratory, over a period of 24 hours. When combined with CT scans, this method can be used to evaluate the precise extent of the damage, the team said.
The researchers tested a variety of asphalt samples from Japan dating back to 1960 – a number of concrete samples from across the world were also tested, and a 120-year-old concrete sample was used as a reference.
The team showed that there are several organic molecules, from diverse sources, present in modern concrete structures and asphalt pavements: phthalates, diesel exhaust particulates, surfactants, and windshield washer fluids. Such molecules are either introduced during the manufacturing process – the contents of phthalates, phosphate compounds, and AE water-reducing agents present in commercially available cement are 0.0012 per cent, 0.12 per cent, and 0.25 per cent, respectively – or absorbed from the environment, and cause rapid deterioration of concrete structures and asphalt pavements.
Of the organic matter present in cement, phthalates have the highest effect on deterioration, more than phosphates and AE water-reducing agents, the researcher explained. Organic matter in water accelerates the deterioration of asphalt pavements.
The scientists also showed that crack width and length are the best determinants of concrete damage, while the degree of formation of amorphisation is the best determinant of deterioration. They believe their findings can develop novel formulations for long-lasting concrete structures and asphalt pavements.
The researchers’ findings, which include novel methods to assess deterioration, were published in the journal PLOS ONE.