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
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.
Isothermal Calorimetry and Rheological Measurements as Tools to Evaluate Early Age Performance of High-Volume Fly Ash (HVFA)
Summary: This study evaluated the viability of using isothermal calorimetry (IC) or rheological measurements to predict early age properties of mixtures containing different amounts of fly ashes regardless of their types, source of origin, physical properties, and chemical composition. A series of paste and mortar mixtures containing different fly ashes (Class F fly ash and Class C fly ash) with replacement levels of 20, 40, and 60 percent, with high and low alkali cement evaluated.
- IC was confirmed to be a good screening and versatile tool to monitor the hydration process and to detect incompatibilities, such as delayed setting time.
- IC was found to be a good tool for setting time and compressive strength predictions at early ages.
- The rheological methodology used in this study may give an indication of setting delay,
- The rate of change of yield stress may be a good predictor of setting behavior, but more research is needed to confirm this. On the other hand, the rate of change of plastic viscosity was not found to be a good predictor of performance.
- IC is being used by many cement and concrete laboratories in assessing the early age properties of cementitious materials.
- AASHTO subcommittee on materials is now recommending the IC results to be included in cement mill report.
- Several ASTM new test methods are available or under ballot, such as ASTM C1679 and ASTM C1753/C1753M and a standard is under preparation to use calorimetry as an indicator of setting time.
Enhancing the Performance of HVFA Concrete using Fine Limestone Powder or Nanoparticles
Summary: This study was divided in several phases. Phases I and II were conducted in collaboration with NIST and examined the effectiveness of fine limestone powder in improving the early age properties of HVFA concrete mixtures. Mixtures were prepared where 40–60 percent of the cement was replaced by fly ash or a combination of fly ash and limestone powder. In the third phase, pastes and mortars were modified with an in-house prepared and commercially available nano-aluminosilicate and calcium silicate hydrate (C-S-H), replacing 1–3 percent of the fly ash in the mixtures. The results of the study showed that fine limestone can considerably improve setting times and transport properties. On the other hand, the effect of the nanoparticles depends on cement alkali content, the fly ash, chemistry and size of the nanoparticles and the dosage. In some cases, the use of nanoparticles can be detrimental to the setting and compressive strength.
- The standard specifications ASTM C595 and AASHTO M240 included a new type of cement (Portland Limestone Cement).
- The American Concrete Institute (ACI) created a new subcommittee on proportioning with ground limestone and prepared a report which is under ballot.
- ASTM is in the process of preparing a specification for ground limestone fines for use in concrete.
- At least 20 State DOTs have started using Portland limestone cement (PLC).
- 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.
Concrete, mortar, and paste mixers of various sizes and types are available in the Concrete Laboratory, including a high-shear paste mixer (figure 1) and a high-intensity concrete mixer (figure 2).
Figure 1. High-Shear Paste Blender.
Figure 2. Photograph. High-Intensity Concrete Mixer.
The Concrete Laboratory can monitor hydration reactions over time using an isothermal calorimeter (figure 3) or semiadiabatic calorimeter and through pore solution extraction (figure 4). Workability is assessed with a flow table, a vebe consistometer, and a dynamic shear rheometer (figure 5). A super air meter (SAM) is used to measure the air-void system of fresh concrete.
Figure 3. Photograph. Isothermal Calorimeter.
Figure 4. Photograph. Pore Selection Extraction Setup
Figure 5. Photograph. Dynamic Shear Rheometer.
Figure 6. 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 7) with the capacity for 17 specimens, computer-controlled chloride penetration test equipment, a surface resistivity apparatus (figure 8), equipment to measure the resistivity of pore solutions (figure 9), and a titration apparatus (figure 10). The thermal effects are evaluated using coefficient of thermal expansion (CTE) test frames (developed in-house and obtained commercially). The Concrete Laboratory is also involved in assessing other distress mechanisms such as alkali-aggregate reaction and sulfate attack.
Figure 7. Photograph. Freeze-Thaw Chamber
Figure 8. Photograph. Surface Resistivity Apparatus.
Figure 9. Photograph. Resistivity of Pore Solution Apparatus.
Figure 10. 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 12.
Figure 11. Photograph. CTE Apparatus.
Figure 12. Photograph. AIMS Apparatus.
Facilities are also available for testing the mechanical properties of concrete and composites. Mechanical properties are measured with two universal testing machines with capacities of 4,500 kilonewtons (1 million pound-force) and 2,225 kilonewton (500,000 pound-force), a beam tester with a capacity of 130 kilonewtons (30,000 pounds), a compressometer/extensometer, and four creep frames.