Uncovering Causes of Modern Concrete and Asphalt Deterioration

Photo credit: Ken Kistler, CC0 1.0

Concrete has dominated the modern construction industry since the start of its commercial manufacturing in the nineteenth century. Asphalt concrete, a specific variety of concrete used for paving and typically referred to as “asphalt,” gained popularity during this same period. As the foremost option for road construction, asphalt’s popularity rose in conjunction with the commercial automobile industry. Today, concrete is the most commonly used building material in the world, and second only to water as the world’s most widely used substance.

Despite worldwide popularity, concrete and asphalt structures can fall short of their expected lifespans. Modern concrete and asphalt structures are known to deteriorate far faster than their historical counterparts. Deterioration takes many forms: cracks, breakdown into fine particles, interior hollowing, and separation into layers. All forms of deterioration threaten the integrity and safety of structures, translating into decreased lifespans and increased maintenance or replacement costs.

When compared to the endurance of historical concrete, widely studied processes like aggregate expansion, chemical damage, and rebar corrosion (in reinforced structures) present only a partial picture of deterioration root causes for modern concrete structures and asphalt pavements. A paper recently published by the journal PLOS ONE sheds light on one significant additional cause of deterioration.

The paper authors—a team of researchers drawn from six diverse institutional environments (medicine, manufacturing, higher education, and consulting)—began their inquiries with the unexplained odor that emanates from commercial cement when mixed with water. The researchers hypothesized that the odor derived from organic matter. From there, they examined the presence of organic matter in relation to concrete deterioration.

Currently, scientists and inspectors determine deterioration rates through surface crack measurements and a chemical test. This team of researchers used a micro focus CT scanner, like those used in medical settings, to develop cross-sectional images of asphalt and concrete samples. The samples originated from a variety of geographical locations and time periods where unexplained asphalt and concrete damage had occurred. After procurement, researchers exposed the samples to test conditions reproduced from moisture permeation levels calculated in the field. This permeation process enabled the team to accurately represent the real-world relative humidity of summer.

Researchers determined that asphalt and concrete samples contained organic molecules from a variety of sources: phthalates, surfactants, windshield washer fluids, and diesel exhaust particulates. Comparisons between CT scans showed that phthalates, chemicals used to increase the durability of plastics, had the most significant effect on concrete and asphalt deterioration. For the first time, researchers demonstrated that organic matter levels, whether introduced during the production process or real-world exposure, were indicators for the deterioration present in modern concrete and asphalt.

The researchers believe that their findings will contribute to the development of enduring concrete and asphalt materials and structures. To read more about the study and findings, click here.