Concrete Curing pH Level Impacts for Minimization of Harm to Aquatic Species
Construction and maintenance actions regularly require state Department of Transportation(s) (DOT) to cast concrete structures below the ordinary high water lines of streams. Recently-cast concrete is known to increase the pH level of water it contacts, which has the potential harm to aquatic species. This and other in-water work are typically done within dewatered work areas. Restoring flow too early may result in harm to aquatic organisms and enforcement actions by environmental regulators. Restoring flow too late may unnecessarily delay removal of work area isolation structures, delay restoration of full fish passage through the stream crossing, conflict with in-water work timing requirements, and extend project schedules. Excessive delay may therefore harm natural resources, project budgets and schedules.
Because freshly set concrete can affect the pH of water it contacts, the concrete must be isolated from stream flow, usually by diverting the stream using a pipe or parallel channel, until the curing process sufficiently reduces the probability of an adverse effect to aquatic habitat. However, the precise effect of recently-set concrete on the pH level of water is not well understood. Specifically, it is not clear how long it takes for curing concrete’s effect on water pH to be reduced to a level that minimizes potential to harm to aquatic species. Understanding this timing is important for ensuring that following cast-in-place operations, DOT’s restore flow to streams at the appropriate time and can demonstrate to regulators using reliable data that these practices will not result in harm.
This is a relevant topic anywhere grout and concrete products are used in aquatic habitats, in addition to being a statewide issue in states such as Oregon.
The objective of this research is to develop field applicable pH reduction curves for curing concrete to inform in-water work processes for DOTs and their regulatory agencies. This research should encompass a multi-parameter model that includes the effects of variables such as: 1) concrete and grout type used by state DOTs in aquatic applications, 2) volume of water and duration of contact with concrete (which is a function of water velocity, length of concrete structure along the stream, and the hydraulic radius of the concrete portion of the channel), and 3) water temperature. Additionally, mitigation factors that enable more efficient construction should be explored including: low pH cement, quick drying cement, and sealants.
DOTs may presume that the effects of pH on fish of various species and life stages are well understood by agencies state Fish and Wildlife Agencies and/or the National Marine Fisheries Service (NMFS); however, these agencies are not expected to be authorities on the specific effects of concrete on the pH of flowing water. More information about the effects of recently cast-in-place concrete on pH of flowing water is needed to ensure that regulations are informed by good science, impacts are minimized, and appropriate water quality contract specifications are used for state DOT construction projects.
In 2016, the California Department of Transportation’s Division of Research published the results of a preliminary investigation to identify the existing body of knowledge on the topic (https://dot.ca.gov/-/media/dot-media/programs/research-innovation-system-information/documents/preliminary-investigations/pcc-and-water-ph-pi-revised-2-1-16-a11y.pdf). This investigation was motivated in part by the California Department of Fish and Wildlife’s requirement that Portland cement concrete be isolated from flowing water for 30 days. The research found some relevant past research, but found significant gaps and was not focused on the specific products used in states such as Oregon. A follow-up inquiry to Caltrans in May 2019 found that although the report identified potential next steps including further research, the investigation’s champions had retired from Caltrans and no further action had been pursued. Caltrans’ preliminary findings may be an appropriate point to build upon in conducting further research. In 2014 the published research evaluating techniques to meet pH standards during in-stream construction that might
Also potentially useful for this proposed research effort are prior investigations into pH remediation techniques, such as a 2014 Maryland State Highway Administration study (Identification of Techniques to Meet pH Standard during In-Stream Construction (maryland.gov)) and a 2014 RMIT University study (The impact of curing compounds on the leaching from concrete).
· Literature Review and Data Acquisition that includes: 1) state DOT survey for precedent data and development of concrete and grout product list commonly used, 2) industry data if available, 3) identification of knowledge gaps needed to estimate the appropriate curing time before water containing aquatic organisms is returned to the structure.
· Laboratory and Field-scale experiments that identify ideal curing time and pH conditions for aquatic species site return that includes pH effects post-water return (up to 1yr)
· Laboratory and Field-scale experiments that explore the feasibility (pilot) the use of remedial solutions.
· Report that highlights recommendations, reviews the state of practice, and details the methodology, findings, and limitations of the research study.
Depending on timing and budget considerations, it may be appropriate to explore the potential to reduce the delay of streamflow restoration by applying effective curing compounds, including the effects of the most effective and available compounds on the receiving waters.
Stormwater professionals including hydraulic engineers, water resource specialists, and biologists within DOTs are likely to be responsible for implementing this research. This research may likely inform project delivery budget and timelines, so prior to full implementation, field-scale pilots may be needed/expected.
The AASHTO Natural Resources Subcommittee of the Committee on Environment and Sustainability and the AASHTO Technical Committee on Hydrology and Hydraulics may be interested in these research results and assist with implementation.
|Sponsoring Committee:||AEP70, Environmental Analysis and Ecology
|Research Period:||Longer than 36 months|
|RNS Developer:||Cory Engel, Oregon DOT; Cory.C.ENGEL@odot.state.or.us; 503-986-6641 Kira Glover-Cutter, Oregon DOT; Kira.M.GLOVER-CUTTER@odot.state.or.us; 503-986-2851|
|Index Terms:||Concrete curing, Curing agents, pH value, Water pollution, Water quality management, |