Concrete Laboratory

Overview: Researchers in the Concrete Laboratory investigate concrete component materials used for highways including cement, aggregate, supplementary and alternative cementitious materials, and admixtures. Investigators assess durability aspects of concrete, develop and evaluate new test methods or enhance existing testing procedures, as well as performing forensic investigations requested within the Agency, by State departments of transportation (DOTs), and other governmental agencies.

Laboratory Description and Capabilities:The Concrete Laboratory batches, mixes, and conducts tests on cementitious paste, mortar, and concrete. The Laboratory is equipped with facilities for evaluating plastic 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, modulus of elasticity

Laboratory Equipment: Concrete, mortar, and paste mixers of various sizes and types are available in the Concrete Laboratory, including a high-shear paste mixer and a high-intensity concrete mixer (figure 1).

Figure 1. Photograph. High-Intensity Concrete Mixer.

Early-age evaluation capabilities include monitoring the hydration reactions over time using Isothermal Calorimeter (figure 2) or semiadiabatic calorimeter and through pore solution extraction. Workability is assessed with a Vebe Consistometer and a Dynamic Shear Rheometer (figure 3). Super Air Meter (SAM) is used to measure air-void system of fresh concrete.

Figure 2. Photograph. Isothermal Calorimeter.

Figure 3. Photograph. Dynamic Shear Rheometer.

The curing room contains three temperature-controlled curing tanks and a walk-in environmental chamber.  Here concrete specimens are cured under standard or other controlled conditions, and are used to assess 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, such as automated freeze-thaw chambers (figure 4) with the capacity for 17 specimens, computer-controlled chloride penetration test equipment, and a surface resistivity apparatus (figure 5). The thermal effects are evaluated using coefficient of thermal expansion 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 4. Photograph. Freeze-Thaw Chamber.

Figure 5. Photograph. Surface Resistivity Apparatus.

Aggregate used for concrete can now be characterized by their shape, angularity, and texture using the Aggregate Image Measurement System (AIMS).

Facilities are also available for testing the mechanical properties of concrete and composites. The mechanical properties are measured with a universal testing machine having a capacity of 4,500 kilonewtons (1,000,000 pounds), a beam tester with a capacity of 130 kilonewtons (30,000 pounds), a compressometer/extensometer, and four creep frames.

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.