Development of Concrete Mix Designs/Matrix of Materials, Performance Properties, and Construction Field Sampling and Testing Expectations During Construction
Status: in contracting
To address climate change mitigation goals, alternative concrete paving mixtures are being investigated that are claimed to have a lower global warming potential (GWP) at time of construction with equal or better long-term performance compared to conventional concrete paving mixtures currently in use by MnDOT. This study is to develop a matrix of test sections for installation at MnROAD in 2022 to meet the objectives identified in the following three NRRA Initial Idea Development documents:
- Use of Alternative Pozzolanic Materials Towards Reducing Cement Content in Concrete Pavements
- Use of Carbon Dioxide for Sustainable and Resilient Concrete Pavements
- Alternative Cementitious Materials – Geopolymer Concrete
The study will include the formation and management of a Technical Advisory Panel (TAP), development and finalization of the matrix of test sections, establish mixture performance criteria for acceptance of all mixtures, assessment of environmental impact of each proposed mixture, coordination with cement supplier and concrete producer to facilitate mixture production, and the development of a construction quality assurance (QA) testing plan.
The objective of this study is to develop the final matrix of test sections and construction QA plan for the construction of a MnROAD experimental section consisting of 16 to 20 test cells to assess the environmental impact and constructability of various concrete paving mixtures designed to reduce environmental impact with the opportunity to assess in-service performance in the coming years.
Task 1: Technical Advisory Panel (TAP) management
This task will form and manage the TAP that will advise NRRA and the project team on the conduct of this study. The TAP will be composed of 6 to 8 volunteers who are recognized for the knowledge and work in concrete, concrete pavements, and commitment to greenhouse gas reduction.
There will be a virtual kick-off meeting with the TAP held within 30-days of contract execution to discuss project scope and tasks. Additional TAP meetings will be held virtually at the project mid-point and near the end of the project, to report progress and to elicit feedback.
- Deliverable: A progress report will be prepared and submitted to the TAP two weeks prior to each meeting. Meeting notes will be prepared and submitted to NRRA appointed Technical Liaison (TL) 2 weeks following each meeting, The TAP meeting notes will be finalized after TAP review and submitted with the progress report.
- Due date: April 14, 2023
Task 2: Develop and finalize matrix of test sections
The following initial criteria have been identified for selection of the materials to be tested:
- Ability to meet specified concrete performance properties, identified as part of this project.
- Constructability as reflected by workability.
- Implementation potential, including material availability, and ability to be integrated into conventional concrete production and placement.
- Environmental impact, assessed from material acquisition through placement and ultimately over the entire life cycle (includes use of life cycle assessment and environmental product declarations [EPDs]).
- Materials supplier cooperation to conduct trial batching to meet desired properties.
First and foremost, materials selected for inclusion in this study must meet basic engineering properties to ensure constructability and potential performance. Initially, the project team will request a range of information from the suppliers, documenting the availability, performance, and sustainability attributes of their material. For conventional materials that have provided submissions to any NRRA member states, that information will be used. Based on the initial submissions, a final matrix of potential materials will be selected, and that list will be provided to TAP for approval.
After selection for inclusion, it will be the responsibility of the material suppliers to work with independent laboratories to complete laboratory mixture designs for use during construction. The research team will review the results of these mixture design studies and verify compliance with the pre-established mixture properties.
The properties of the fresh concrete must render a material that is workable (i.e., able to be mixed, transported, placed, consolidated, and finished with minimal loss of homogeneity) for a minimum of 90 minutes if batched at a concrete plant and 30 minutes if batched on-site using volumetric mixers. Some properties of fresh concrete that should be evaluated include: Slump (AASHTO T 119), Unit Weight (AASHTO T 121), Set Time (ASTM C403), V-Kelly (AASHTO TP 129, Air Content (AASHTO T 152), Maturity (AASHTO T 325), Box Test (AASHTO TP 137), SAM (AASHTO TP 118).
Hardened properties of concrete must provide for a pavement that will perform structurally and have the durability to provide long-term performance. Testing for these properties falls into two broad categories: constituent acceptance tests and mixture acceptance tests. Constituent acceptance testing includes aggregate testing such as F-T durability (AASHTO T 161) and alkali-silica reactivity (ASR), which is based on testing in compliance with AASHTO R 80.
For this experiment, one combination of aggregate sources will be selected for all mixtures and that aggregate shall be a source pre-approved by MnDOT for use in concrete pavement construction. The approach to ASR testing is more complicated with the wide range of materials to be evaluated. Some materials, such as geopolymers, are commonly thought to be non-susceptible to ASR. Other materials, such as Carbon Cure, are thought to not directly impact ASR in either a positive or negative manner. And with Carbon Cure, preparing test specimens is problematic. Therefore, careful thought needs to be given to a process for evaluating these materials combinations.
The team envisions a two-phased approach where prior to construction, the combination of materials to be used (i.e., cement, SCM, aggregate) shall be evaluated using ASTM C1567 as a pre-screening test to ensure to the extent possible that the as-placed mixtures will not experience ASR. The second phase will be laboratory evaluation of the tested materials to further understand their individual ASR characteristics. As part of this initial planning project proposed here, a detailed ASR testing plan will be provided that evaluates the individual materials for long-term ASR potential. The expectation is to execute that plan after the placement has been completed.
Mixture design acceptance testing will be conducted for all concrete included in the experiment, although additional interpretation may be required for some alternative cements (e.g., geopolymers). Where applicable, the same tests will be performed on all materials. In some cases, however, a test may be ill suited for a certain material and alternative tests will be sought. The following tests will be considered:, Flexural Strength (AASHTO T 97) Elastic Modulus/Poisson’s Ratio (ASTM C469), Compressive Strength (AASHTO T 22), Coefficient of Thermal Expansion (AASHTO T 336), Unrestrained Volume Change (AASHTO T 160), Concrete Resistivity (AASHTO TP 119), Time to Critical Saturation (ASTM C1585), Formation Factor (AASHTO PP 84), Deicing Salt Damage (AASHTO T 365), Air Voids in Hardened Concrete (ASTM C457), Petrographic Analysis of Hardened Concrete (ASTM C856).
One note is that concrete resistivity is affected by many factors, a principal factor being the conductivity of the pore solution. This can be quite variable for different cementitious systems and thus the results of the resistivity test are also variable. It is therefore recommended that each concrete specimen be soaked in a solution of known conductivity to normalize this variable (in accordance with AASHTO) thus permitting calculation of the Formation Factor. Efforts will be expended to validate this approach for the range of materials included to assess the value in pursuing Formation Factor as a viable quality assessment tool.
The current thoughts on the potential matrix of 20 test sections (note that there will be 16 test sections total) are included in Table 1. This is expected to change as the project progresses and preliminary testing, constructability, and the level of material suppliers’ collaboration is assessed.
- Deliverable: Preliminary and Final Matrix of Test Sections including supporting test data and agreements by materials suppliers to participate in construction.
- Due date: March 14, 2022
Task 3: Establish mixture performance criteria for construction acceptance
This task will consider the preliminary test results obtained in Task 2 and establish mixture performance criteria for use in construction quality assessment based on the unique nature of each material. Most criteria will be uniformly applied across all material types, including most workability and strength requirements. Some materials may require on-site mixing using volumetric mixers. In these cases, workability requirements will be adjusted to accommodate the alternative method of mixture production.
Other properties will be affected by material type including shrinkage and resistivity. Shrinkage results will be considered in the context of the literature and criteria set based on the class of material. Experimentation will need to be conducted to ensure that the standard approach to determination of the Formation Factor using a soak solution of known conductivity is sufficient to normalize the results of all materials under consideration.
Of special concern is durability testing related to ASR and freeze-thaw durability. ASR is a result of the dissolution of certain silica minerals present in aggregates that occurs in the high pH environment present in hydrated portland cement paste pore solution. The dissolution alone is not sufficient to cause damaging ASR, as the presence of calcium ions in the pore solution plays a key role in the formation of ASR gel that is both expansive and damaging. Although our understanding of the ASR mechanism in portland cement concrete is not perfect, it is such that reasonable test methods and mitigation strategies have been developed to avoid damaging ASR in most cases. The understanding of ASR susceptibility in alternative cement systems is not advanced. Therefore, particular focus will be placed on establishing criteria to avoid ASR in these systems.
Similarly, resistance to freeze-thaw damage is an unknown for many of these alternative systems. Those systems based on a hydrated cementitious paste will likely have similar behavior to conventional portland cement-based systems, although this will need to be verified. In these cases, protection of the paste is obtained through the entrainment of an acceptable air-void system: assessed through testing of the air content in fresh concrete (total air and SAM number) and in hardened concreter (i.e., ASTM C457). It is uncertain how resistant some of the non-portland cement-based are to freeze-thaw damage and therefore the evaluation of ASTM C666 results will be critical to set criteria for acceptance.
- Deliverable: The deliverable for this task will be the establishment of mixture performance criteria for acceptance for all mixtures.
- Due date: April 14, 2022
Task 4: Preliminary assessment of environmental impact of each mixture
The key goal of this project is to assess the environmental impact of each mixture, assessing the benefit in comparison to MnDOT’s conventional paving mixture. It is known that roughly 90% of the embodied GWP of conventional paving concrete, at the gate exiting the concrete plant, is due to the production of portland cement clinker. As such, one approach to reducing the GWP over the life cycle is to reduce the amount of portland cement clinker in concrete without compromising performance.
Strategies for reducing GWP include partially replacing portland cement with less carbon intensive materials (e.g., ground limestone, SCMs) or entirely replacing portland cement with an alternative low GWP cement. In addition, reducing the total amount of cementitious materials in the concrete through mixture optimization (i.e., optimize the aggregate grading) is another effective strategy.
To understand the impact of the various materials to be tested in this experiment, it is essential to conduct a rigorous assessment in accordance with established procedures to determine the environmental footprint of each material. The tool to accomplish this is an environmental life cycle assessment (eLCA) conducted according to the principles and framework described in ISO 14040 standards. A detailed eLCA is outside the scope of this effort but in recent years, LCA tools have been developed in accordance with ISO 14040 specifically to assess the eLCA of pavements including Athena Pavement LCA, the FHWA’s LCA PAVE, and the eLCAP program developed at the University of California – Davis.
These tools, which are suitable for a preliminary analysis, will be evaluated for applicability to this study for assessment of the environmental impact of each material. Initially, the analysis will focus on material acquisition through end of construction, but this can be extended as pavement performance data is obtained. Existing material data bases are sufficient to assess conventional concrete paving materials (e.g., Portland cement, PLC, fly ash, natural pozzolans, etc.) but do not contain environmental production data on specialty SCMs, alternative cements, or carbon sequestration materials. It is recommended that material suppliers of specialty products agree to share environmental production data with the research team. Preferably this data would be collected by an independent third-party. Without this data, it would be difficult to honestly assess the environmental impact of these alternative systems.
- Deliverable: A preliminary eLCA that considers material acquisition through construction phase for each material based on material supplier provided data.
- Due date: June 30, 2022
Task 5: Coordinate with cement supplier and concrete producer
This task is to facilitate coordination between the cement supplier and local concrete producer to ensure that each understands the capabilities and limitations of the alternative materials and what must be done during construction. This facilitation will require virtual and in-person meetings.
For most materials, little facilitation will be needed other than to make sure all parties understand the unique elements of production. In some cases, the local concrete producer will not be able to directly assist the material supplier in production. In these cases, the research team will facilitate contact with alternative producers capable of mixture production including coordinating transfer of aggregates for use in production.
- Deliverable: Meeting logs and notes describing the facilitation activities between cement suppliers and concrete producer(s).
- Due date: April 14, 2023
Task 6: Development of construction quality assurance testing plan
The recommended construction quality assurance testing plan will be based on the criteria established in Task 3. This plan will have three parts. The first part will include a plan for inspection of the concrete plant during production. It is assumed that the plant will be certified. At a minimum, the plan will include a checklist that verifies that certification is current, and all calibrations are up to date. Aggregate stockpiles will be inspected for moisture content and segregation, cementitious materials and admixtures verified, and general plant operations observed. Additional testing at the plant may be recommended.
The second part will be a typical sampling and testing plan for construction to ensure that the concrete as delivered meets basic mixture requirements as presented in Table 2. It is noted that not all tests may apply to all materials. For cases where a specific test may not apply, surrogate testing will be explored to capture comparable information based on the work done in Task 3.
In addition to basic construction sampling and testing listed in Table 2, the third part of the construction quality assurance plan will be for additional concrete samples to be collected from production concrete to conduct the following testing: Unrestrained volume change (AASHTO T 160), ASR accelerated mortar beams (AASHTO T 303), Time to critical saturation (ASTM C1585), ASR long-term concrete prism (ASTM C 1293), Freeze-thaw durability (AASHTO T 161), Air Voids in hardened concrete (ASTM C457), Petrographic analysis of hardened concrete (ASTM C856).
Again, not all tests may apply to all materials and for cases where a specific test may not apply, surrogate testing will be explored to capture comparable information based on the work done in Task 3. It is noted that specimen acquisition, handling, and curing for this additional suite of tests will require special treatment beyond what would normally be exercised in conventional construction.
- Deliverable: A construction sampling and testing plan including broader concrete specimen acquisition, handling, and curing plan for advanced testing.
- Due date: May 1, 2022
Task 7: Construction consultation
In this task, the project leads will be available for consultation during the construction phase to assist in coordinating the construction of the MnROAD test site. Most consultations will occur virtually, although two trips to the MnROAD facility have been assumed, one to conduct a preconstruction meeting and a second during construction to address issues that may have arisen.
- Deliverable: Notes from consultations held summarizing issues and derived solutions.
- Due date: December 31, 2022
Task 8: Draft final report
A draft final report will be prepared detailing the work conducted in Tasks 1 through 7. This draft final report will be submitted to NRRA appointed TL 4 months prior to the end of the contract.
- Deliverable: A draft final report will be prepared and submitted to MnDOT 4 months prior to the end of the contract.
- Due date: January 31, 2023
Task 9: Editorial review and publication of final deliverables
This task is to produce a final, published report that meet with MnDOT’s editorial guidelines and standard. NCE has technical editors on staff that will assist with this task.
- Deliverable: A final publishable report that meets MnDOT’s Editorial Guidelines and standards.
- Due date: April 14, 2023
Principal Investigator: Thomas Van Dam, Ph.D., P.E., principal, Nichols Consulting Engineers Chtd., firstname.lastname@example.org
Subcontractor: Larry Sutter, Ph.D., P.E., Sutter Engineering LLC, email@example.com
Technical Liaison: Maria Masten, MnDOT, firstname.lastname@example.org
Technical Advisory Panel (TAP) - email the TAP
Contact us to join this TAP
- Mark Finnell, Wisconsin DOT
- Maria Masten, Minnesota DOT (TL)
- Kevin W. McMullen, P.E., Wisconsin Concrete Pavement Association
- Joseph Podolsky, Minnesota DOT
- Brett Trautman, Missouri DOT
- Initial Project proposal (doc), 4/21/2021