FY2022 NCHRP PROBLEM STATEMENT OUTLINE

1. Problem Title
Concrete Curing pH Level Impacts for Minimization of Harm to Aquatic Species

2. Background
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.

3. Literature Search Summary
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. 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. Caltrans’ preliminary findings may be an appropriate point to build upon in conducting further research. In 2014 the Maryland State Highway Administration published research evaluating techniques to meet pH standards during in-stream construction that might also be useful for this proposed research effort (Identification of Techniques to Meet pH Standard during In-Stream Construction (maryland.gov)).

4. Research Objective
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.

Expected Tasks:
• 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.