Newark, DE 19716
University of Virginia
351 McCormick Dr.
P.O. Box 400742
Charlottesville, VA 22904-4742
University of Delaware
University of Virginia
Funding Source(s) and Amounts Provided (by each agency or organization)
UD $150,000 (Match)
Total Project Costs
Reinforced concrete is used worldwide for roads, bridges, buildings, and hazardous material storage — structures meant to last 50 years or more. As the concrete ages, chloride attack, alkali-silica reaction (ASR), and freeze-thaw cycles cause cracking, which weakens the structure and makes the concrete and reinforcing steel vulnerable to further damage. In Delaware, ASR damage is widespread in roadways. ASR occurs when the aggregates have high concentrations of reactive silica, which is a common feature of aggregates sourced in the Mid-Atlantic states. If, during the design phase, the aggregates are known to cause ASR, the concrete mixture can be adjusted to prevent future problems. However, in existing structures, ASR effects are only identified when visible cracks develop, after extensive chemical changes and internal damage have already occurred.
ASR is a chemical reaction between the alkaline cementitious materials and reactive silica present in certain aggregates. When there are available cations in the concrete pore solution, reactive silica in the aggregate, and sufficient moisture, a gel-like material forms in the concrete, absorbs water and expands, exerting tensile forces within the concrete matrix and causing cracking. External water easily penetrates the cracked concrete, exacerbating ASR and increasing the potential for other kinds of damage, further deteriorating the concrete. Because the chemistry of ASR-affected concrete differs from that of undamaged concrete, we hypothesize that its microbial population will also be different.
In water quality, food safety and soil sciences, microbes are used as bio-indicators for system health. I propose to identify microbial species found only in alkali-silica reaction (ASR)-damaged concrete, for use as a bio-indicator for this type of damage. Developing a bio-indicator for ASR-related damage would enable production of a rapid, simple test that could be used to identify ASR-induced damage before visible cracking has occurred. This work will contribute to the MATS-UTC focus area of coastal infrastructure resiliency by enabling earlier diagnosis of a problem that is especially common in this area.
During the past 2 years, Maresca’s laboratory at UD has developed a method for extraction of DNA from concrete and cultivated more than 15 bacterial species from the same samples. We have shown that the bacterial communities in and on concrete, as identified by DNA analysis, include more than 200 species and are unique to the concrete environment. Many of the species in these samples have tough membranes and are related to bacteria found in deserts and soda lakes – other dry, alkaline environments. The cultivated bacteria are a limited but representative subset of those identified by DNA analysis.
The MATS UTC research team, led by UD, proposes to identify microbial biomarkers of ASR dam-age by applying these new techniques to both laboratory-made concrete samples and core samples obtained from ASR-damaged roadways in Delaware and Virginia. In 2013, we prepared ASR-prone con-crete cylinders using materials from the Delaware Department of Transportation (DeIDOT). We prepared a parallel set of test cylinders that included fly ash, DeIDOT’s standard protocol for prevention of ASR. These cylinders were placed on the green roof, and one of each set has been harvested every 6 weeks since then. By analyzing microbial communities in ASR-prone and mitigated test cylinders left outside to weather over the course of 2 years, we will identify microbial species present in undamaged samples and those that thrive best as the chemistry of ASR-prone concrete changes. We will also use these samples to develop methods that require less sample material, and to develop and test assays for specific bacteria.
To confirm that any bio-indicators – either of damage or of “normal” concrete – identified in our laboratory samples are relevant in field assessments, we will compare these results with the microbes identified in ASR-damaged road samples. Maresca and Harris have contacts with DeIDOT and the Virginia Department of Transportation, respectively, and will obtain core samples from ASR-affected roadways, as well as samples from nearby, undamaged roadways. This ﬁeld component will be crucial both to demonstrate the efficacy of the developed tests and to determine whether our results are specific to materials used in Delaware or can be applied throughout the mid-Atlantic.
Although microbes have long been known to degrade concrete and have more recently been employed to repair it. the study of concrete as a unique environment hosting a variety of microbes capable of different effects on their milieu has been neglected. The methods developed as part of this research will contribute both to improved diagnosis of ASR-type damage to concrete, and to a better fundamental understanding of the natural populations acting in and on concrete as it weathers.
Researchers from UD and the University of Virginia (UVA) will conduct research from a multi-disciplinary perspective. Maresca, a microbiologist in UD‘s Civil and Environmental Engineering department. will lead the analysis of microbial communities in concrete. Harris, an expert in civil infrastructure, has a mobile laboratory for rapid evaluation of transportation infrastructure (MOBLab), which is well suited for field studies. He also has a number of ongoing collaborations with the Virginia Center for Transportation Innovation and Research, the research arm of the Virginia Department of Transportation. His contribution will primarily focus on obtaining ﬁeld samples of ASR-damaged concrete from different localities and undamaged samples from the same general areas. As we develop easier tests for ASR-associated microbes, we propose to supply the MOBLab with the equipment and reagents necessary to deploy these tests in the ﬁeld.
To extend roadway lifetimes, potential problems must be identiﬁed early enough that repair, rather than replacement, is feasible. Early bio-indicators of damage would allow DOTS to implement chemical remediation for ASR before visible cracking and structural damage have occurred. A bio-indicator is a rapid, simple, and inexpensive tool that would provide data to support early identiﬁcation and remediation of roadways susceptible to speciﬁc types of damage. Because this approach could extend roadway lifetimes, state and local DOTS could stretch limited funds. Earlier diagnosis of a problem that is especially common in the Mid-Atlantic Coast region will contribute to the MATS-UTC focus area of coastal infrastructure structure resiliency. In addition, characterization of microbes native to concrete environments will contribute to a better understanding of the mechanisms of life in dry, salty, alkaline conditions, and to the development of future tools in bio-repair of concrete.
Results from project research will be published in peer reviewed journals and will be presented at large national conferences. Researchers will work collaboratively with the Delaware Department of Transportation to implement project outcomes into new DOT speciﬁcations. as appropriate. Wherever possible, new ﬁeld projects will be conducted as “Demonstration Projects”., which will be open to a variety of researchers and other employees from various DOTS throughout the MATS consortium area.