The primary purpose of the Concrete Laboratory is to conduct research to develop a better, more durable, cost-effective, and sustainable concrete infrastructure by:
- Investigating and characterizing concrete component materials used for highways including cement, aggregate, supplementary and alternative cementitious materials, and admixtures.
- Assessing and improving durability aspects of concrete.
- Developing and evaluating new test methods or enhance existing testing procedures.
- Collaborating with academia and industry in advancing new emerging technologies.
- Performing forensic investigations requested within the Agency, by State departments of transportation (DOTs), and other governmental agencies.
The Concrete Laboratory conducts research in many areas related to concrete materials, such as fly ash, slag cement, and alternative cementitious materials with little or no hydraulic cement. The laboratory collaborates with academia, other government agencies, and industry, leveraging expertise in conducting research to address issues of national significance. The Concrete Laboratory is inspected by the Cement and Concrete Reference Laboratory (CCRL) and accredited by the American Association of State Highway and Transportation Officials (AASHTO) Materials Reference Laboratory.
Recent Accomplishments and Contributions
Assessment and Validation of Concrete Durability Testing Procedures in Support of AASHTO PP84-17
Summary: As part of an effort to promote more durable, longer-lasting, and more cost-effective concrete infrastructures, FHWA, in partnership with State DOTs, academia and the industry, has been working on establishing a new mindset for concrete mixtures design and quality assurance procedures, moving from a prescriptive to a performance approach.
A suite of new and modified testing procedures was proposed under the FHWA’s Performance Engineered Mixtures (PEM) initiative, and incorporated into the AASHTO procedures, PP-84-17. These procedures cover several categories; each consists of several testing procedures that are requiring assessment, refinement, and validation before they can be implemented. The concrete lab at TFHRC was charged with assessing and validating eleven new and modified concrete durability-related testing procedures.
As these procedures are balloted and approved by AASHTO, they will be integrated into a performance-related specifications (PRS) program. The impetus behind the PEM program is to help State DOTs shift from prescriptive to performance specifications, while giving them the freedom to use prescriptive specifications in the interim.
The primary objectives of the TFHRC study are:
- Assess, refine, and validate durability-related test methods as depicted in the AASHTO, PP-84-17, and when necessary, recommend changes to these test methods.
- Shepard these test methods through the AASHTO Committee on Materials and Pavements (COMP).
- Conduct ruggedness evaluation.
- Determine the test precision and bias.
Assessment and Validation of New Rapid ASR Tests
Summary: Although Alkali-Silica Resistivity (ASR) has been the focus of extensive research since the late 1930s, there is still no reliable test method to evaluate its prevention and mitigation measures reliably. Many of the exposure blocks in North America, including the ones in Texas and Canada, are failing and exhibiting signs of ASR despite passing the two-year Association of State Highway and Transportation (ASTM) C1293. It is the consensus of the concrete community that ASTM C1293 can properly detect ASR in reactive aggregate; however, when it is used with supplementary cementitious materials (SCMs) as a mitigation or prevention treatment, its reliability has been inconsistent. The main issue with the test is said to be the leaching of alkalis.
Two new test methods, AASHTO T380—Miniature Concrete Prism Test (MCPT), and Concrete Cylinder Test (CCT) have been identified as testing procedures that potentially address the shortcomings of the ASTM C1293, help prevent alkali leaching, and assess ASR mitigation and prevention measures. The MCPT takes only eight weeks to complete, while the CCT takes up to nine months.
This research, in collaboration with Oregon State University and University of Texas Austin, focuses on examining the reliability of two new tests methods—Concrete Cylinder Test (CCT) and Miniature Concrete Prism Test (MCPT)—in assessing ASR mitigation measures. The primary objective of this research is twofold:
- Examine the use of CCT and MCPT as accurate and accelerated test methods in evaluating ASR mitigation measures and compare with the data at various exposure sites in North America.
- Determine the proper test duration and expansion limits for the proposed test methods.
Reducing the Specimen Size of Concrete Flexural Strength Test for Safety and Ease of Handling
Summary: This project evaluated the feasibility of using smaller specimen sizes. A total of 22 concrete mixtures were prepared with varying water to cementitious ratios (w/cm), coarse aggregate types, and maximum nominal sizes. In addition, an interlaboratory study (ILS) for the determination of the precision of the test procedure was carried out in collaboration with the American Society for Testing and Materials (ASTM) and 22 laboratories.
- AASHTO T23 and AASHTO T97 have been revised and allow for the use of the smaller size beams.
- Several stakeholders have already started using the smaller size beams.
Super Air Meter (SAM) for Assessing Air-Void System of Fresh Concrete
Summary: The Concrete Laboratory, in Collaboration with Oklahoma State University, examined the feasibility of using SAM as a quick scanning tool for measuring air system of fresh concrete. The product of this research was balloted and approved as an AASHTO provisional test.
- DOTs from 28 States are in the process of implementing SAM.
- A provisional test method has been prepared and submitted to AASHTO to be balloted in February 2015.
Impact of Deicing Salts on Transport Properties of Concrete
Summary: This study aimed to evaluate the combined effect of diffusion and absorption on transport properties of concrete samples exposed to deicing salts. Plain concrete, 30 percent fly ash F and 50 percent slag cement concrete mixtures, with w/cm of 0.42 or 0.50 were exposed to NaCl, CaCl2, and MgCl2 continuously or in wet and dry cycles for up to a year. The rate of absorption and the apparent diffusion coefficient were found to depend on the mixture design, exposure conditions, and cations of the salts in solution. Results showed the importance of careful interpretation; transport testing results depend on the exposure history and testing protocols. Relying solely on test results without understanding concrete’s exposure history and the factors that affect individual tests can be misleading.
Influence of Aggregate Characteristics on Concrete Performance
Summary: This was a collaborative project between Turner-Fairbank Highway Research Center (TFHRC) and the National Institute of Standards and Technology (NIST), and evaluated and quantified the effect of aggregate characteristics that are not normally considered on concrete mechanical performance. The results have demonstrated that for similar mixture proportions, the selection of coarse aggregates can have a measurable influence on concrete performance for both mechanical and transport properties. The incompatibility of certain paste and aggregate properties likely promote the development of interfacial stresses, potentially causing microcracking, weakening the bond between the two phases, and lowering the measured concrete strength. The results also demonstrated that selection of an optimum aggregate for a specific concrete application will require knowledge of the binder used; some aggregates performed better with the ordinary concrete than they did in the ternary blends and vice versa. The bond between aggregates and paste/mortar greatly influences mechanical properties of the produced concrete.
- Held the Third Biannual workshop on Alternative Cementitious Materials and Alkali-Silica Reaction (ACM/AAR) at TFHRC with attendees and presenters from FHWA, State DOTs, industry, and Academia. A summary report can be obtained upon request.
- The Concrete Laboratory, in support of STEM awareness and education, participates in several educational events including Transportation YOU, Summer Mini Camp, Girls Mentoring Program: “I Love Me", Bring Your Child to Work Day, and others.
The Concrete Laboratory’s capabilities include mixing, proportioning, and conducting tests on cementitious paste, mortar, and concrete. The Laboratory is equipped with facilities for evaluating early-age properties and hardened concrete properties (e.g., rheological properties, setting, and calorimetry); concrete volume changes; concrete durability including freezing and thawing, permeability, ions penetrability, and alkali-aggregate reaction; and mechanical properties, including strength and modulus of elasticity.
Services are focused on research and investigations at TFHRC or in cooperation with other governmental agencies, as well as academia and industry. Services also include performing forensic investigations requested within the agency, by State DOTs, and other governmental agencies.
The Concrete Laboratory can monitor hydration reactions over time using an isothermal calorimeter (Figure 1) or semiadiabatic calorimeter. Workability is assessed with a flow table, a vebe consistometer, and a dynamic shear rheometer (Figure 2). A super air meter (SAM) is used to measure the air-void system of fresh concrete (Figure 3).
Figure 1. Photograph. Isothermal Calorimeter.
Figure 2. Photograph. Dynamic Shear Rheometer.
Figure 3. Photograph. Super Air Meter
Curing and Conditioning of Samples
The curing room contains three temperature-controlled curing tanks that automatically maintain constant water level and temperature, a walk-in environmental chamber, and a shrinkage room. Here concrete specimens are cured under standard or other controlled conditions, and are used to maintain a specific curing or conditioning environment while studying curing-related properties, such as degree of hydration, maturity, and shrinkage (free, autogenous, chemical, and restrained).
The Concrete Laboratory includes facilities for investigating the effects of chemical and environmental exposure on concrete, including automated freeze-thaw chambers (Figure 4) with the capacity for 17 specimens, computer-controlled chloride penetration test equipment and the formation of calcium oxychloride, using a LTDSC (low temperature differential scanning calorimeter) (Figure 5).
Figure 4. Photograph. Freeze-Thaw Chamber.
Figure 5. Photograph. LTDSC.
The chemical reactions through pore solution expression (Figure 5), pore solution chemical analysis (Figure 6) and pore solution resistivity with the cell resistivity (Figure 7) or probes (Figure 8). A surface resistivity apparatus (Figure 9) and a bulk resistivity meter (Figure 10) measure concrete resistivity.
Figure 10. Photograph. Surface Resistivity Apparatus.
Figure 11. Photograph. Bulk Resistivity Apparatus.
The titration apparatus (Figure 12) is used to determine the chloride content in concrete and the coefficient of thermal expansion (CTE) test apparatus (Figure 13) is used to evalaute the thermal effects in concrete. The Concrete Laboratory is also involved in assessing other distress mechanisms such as alkali-aggregate reaction and sulfate attack.
Figure 12. Photograph. Titration Apparatus.
Aggregates used for concrete can now be characterized by their shape, angularity, and texture using the Aggregate Image Measurement System (AIMS) shown in figure 14.
Figure 13. Photograph. CTE Apparatus.
Figure 14. Photograph. AIMS Apparatus.