Autogenous Healing of Concrete in the Drinking Water Industry

Sponsor: American Water Works Association Research Foundation

Co-PIs: Marc Edwards (Virginia Tech)

Corrosion, the degradation of materials through physicochemical interaction with the environment, has profound economic, social, and public health consequences. In the United States it is estimated that the annual cost of corrosion ranges from $200 to $271 billion, or about 3.1% of the nation's gross domestic product. As a result of these societal costs, a significant research effort has been expended to characterize atmospheric corrosion processes, the corrosion of metal reinforced concrete bridges and roads, and corrosion in the defense industry. Unfortunately, comparatively little research expenditure has gone towards the investigation of the processes responsible for the corrosion of concrete drinking water infrastructure.

Though poorly studied, it is typically believed that cracks in concrete pipe and lining allow access of corrosive water to reinforcing metal, which then corrodes, expands and causes pipe failure via spalling or attack on reinforcing metal. Under some circumstances, the hairline cracks that develop in concrete can repair themselves through reactions with constituents in the water. If the chemistry is favorable, the cracks fill with deposits, preventing access of water and corrosive ions to metal wires or rebar. This phenomenon has been termed “autogenous healing” and has recently been studied in the nuclear power industry in some detail . If the combination of water chemistry and concrete is not conducive to the self-repair of hairline cracks, these cracks may increase in size with potentially catastrophic consequences.

The rate at which concrete corrodes controls the longevity of water treatment plants, cement water mains and ductile iron pipe lined with cement. Accordingly, a thorough understanding of the processes responsible for concrete corrosion is of fundamental concern to the water treatment industry. We are currently conducting an in-depth examination of the factors responsible for both concrete corrosion and the autogenous healing of cracks within the concrete. This work is the first known study to systematically investigate this important phenomenon in drinking water. By carefully examining the effects of water chemistry on concrete corrosion and autogenous repair, we intend to develop an experimental database that may provide a basis for an index that will enable treatment plant operators to readily evaluate the aggressiveness of a given water toward their concrete infrastructure. The current work will be a firm step towards that longer term goal. This project consists of three interrelated tasks: Task 1 – Evaluation of the effect of water chemistry on concrete corrosion and autogenous healing; Task 2 – Identification of autogenous precipitates via in-situ Raman spectroscopy, and Task 3 – Determination of the level of restoration possible by various modes of autogenuous repair.

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