Scientists reveal the causes of concrete and asphalt degradation
Japanese scientists have found that the deterioration of modern concrete and asphalt structures is due to the presence of trace amounts of organic matter in these structures.
Cement and asphalt are essential for modern building materials, where cement is used for the construction of various buildings and structures, while construction companies mainly use asphalt for highways and runways.
Experts have used both extensively 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 – has discovered that trace amounts of organic matter in modern concrete structures and asphalt pavements cause the deterioration of these structures.
According to experts, the deterioration of modern concrete structures and asphalt pavements is a major problem. 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 purpose: rapid deterioration reduces the expected life of structures, increasing maintenance or replacement costs.
A close-up of a bridge, with worn asphalt pavement and concrete.
To address this, the scientists wanted 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 provides an incomplete picture of the extent of the damage.
During their experiments, the scientists found that a strange odor was created when commercial cement was mixed with water. With this they hypothesized that organic matter was responsible for the odor and investigated the effect this has on the deterioration of concrete.
The scientists developed the one-dimensional transient moisture permeability device to reproduce the field of environmental conditions that concrete structures and asphalt pavements are exposed to in the laboratory over a 24-hour period.
In conjunction with CT scans, this method can be used to evaluate the precise extent of the damage, the team said.
CT scans show cracks in damaged concrete. A and B have cracks in the first layer, while C and D have cracks in the second layer. GBS, GHY, TMS, MS TSS and GR refer to different types of aggregates in the mortar.
The researchers tested a variety of asphalt samples from Japan dating back to 1960 – a number of concrete samples from around the world were also tested, and a 120-year-old concrete sample was used as a reference.
The team showed that there are different organic molecules, from different sources, present in modern concrete structures and asphalt pavements: phthalates, diesel exhaust particles, surfactants and windscreen washer fluids.
Such molecules are either introduced during the manufacturing process – the phthalates, phosphate compounds and AE water reducing agents content in commercially available cement is 0.0012 percent, 0.12 percent, and 0.25 percent, 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 greatest effect on spoilage, more so 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 amorphis formation is the best determinant of deterioration.
They believe their findings can develop new formulations for durable concrete structures and asphalt pavements. The researchers’ findings, including new methods to assess deterioration, were published in the journal PLOS ONE.