Scientists reveal that the deterioration of modern concrete and asphalt structures is due to the presence of traces of organic matter in these structures.
Cement and asphalt are essential to modern building materials; cement is used for the construction of various buildings and structures, while asphalt is mainly used for highways and tracks. They have been widely used for these purposes since the 1800s. It has been observed that modern concrete structures and asphalt structures tend to deteriorate much faster than historic structures, but the reason for this phenomenon was unknown.
A team of scientists from six institutions, including Hokkaido University Emeritus Professor Akihiro Moriyoshi, revealed that the presence of traces of organic matter in modern concrete structures and asphalt pavements lead to deterioration of these structures. Their results, which include new methods to assess deterioration, have been published in the journal PLOS ONE.
Deterioration of modern concrete structures and asphalt pavements is a major problem. Characteristics that lead to deterioration include cracking, weathering (decomposition into a fine white powder) and delamination (separation into layers). These deteriorated structures are not safe for their intended purposes; rapid deterioration reduces the expected life of structures, thereby increasing maintenance or replacement costs.
Scientists set out to develop a new method to assess the rate of deterioration of concrete. The current method is based on the width of the surface cracks in the concrete and on a simple chemical test; however, this only gives an incomplete picture of the level of damage. During their experiments, the scientists noticed that a strange odor developed when commercial cement was mixed with water. They hypothesized that organic matter was responsible for the odor and studied the effect it had on the deterioration of concrete.
Scientists developed the one-dimensional transient moisture permeation apparatus to accurately reproduce the field environmental conditions to which concrete structures and asphalt pavements are exposed, in the laboratory, over a 24-hour period. When combined with CT scans, this method can be used to assess the precise extent of damage. They 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 benchmark.
Scientists have shown that there are a number of organic molecules, from various sources, present in modern concrete structures and asphalt pavements: phthalates, diesel exhaust particles, surfactants, and windshield washer fluids. These molecules are either introduced during the manufacturing process – the contents of phthalates, phosphate compounds and water reducing agents AE present in commercially available cements are 0.0012%, 0.12% and 0.25%, respectively – or absorbed by the environment, and cause rapid deterioration of concrete structures and asphalt pavements.
Among the organic matter present in cement, phthalates have the greatest effect on deterioration than phosphates and AE water reducing agents. Organic matter in water accelerates the deterioration of asphalt pavements. Scientists have also shown that the width and length of cracks are the best determinant of concrete damage, while the degree of amorphous formation is the best determinant of deterioration. They believe their findings can be used to develop new formulations for long-lasting concrete structures and asphalt pavements.
Source of the story:
Material provided by Hokkaido University. Note: Content can be changed for style and length.