General Info

Purpose

The AVA (Air Void Analyzer) is used to measure the air-void parameters (spacing factor and specific surface) of samples of fresh air-entrained concrete. Samples are taken after concrete has been placed in the structure and consolidated. It provides timely information to reveal problems with the air-void system.

Background

The durability of concrete subjected to wetting and cycles of freezing and thawing can be enhanced by deliberately introducing many, small and closely spaced air bubbles (air voids) in the cement paste. During freezing, the ice formed in the capillary pores of the paste will expand into adjacent air voids without damaging the paste, provided the air-void spacing and the size distribution of the air voids are within certain limits. The spacing factor (maximum distance from any point in the cement paste to an air-void boundary) and the specific surface (ratio of the surface area of the air voids to their volume) are two parameters that can be used to characterize the air-void system. In general, a good quality, frost resistant concrete requires a spacing factor less than 0.20 mm and a specific surface greater than 25 mm-1.

Fresh Concrete

The spacing factor and the specific surface of the air-void system are determined typically according to ASTM C457 “Test Method for Microscopical Determination of Parameters of the Air-Void System in Hardened Concrete,” or similar standards such as EN 480-11 “Admixtures for concrete, mortar and grout – Test methods – Part 11: Determination of air void characteristics in hardened concrete.” These methods require obtaining a sample from the hardened concrete on-site and preparing a properly polished specimen in the laboratory as illustrated in the photo to the left. The spacing factor and the specific surface are then determined manually by the linear traverse method using a microscope, or by an automated image analyses system. Determination of the air-void structure in this manner cannot produce timely information during construction, which would be needed to make adjustments to the concrete mixture if the measured parameters are not within specified limits.

Timely information is important, because practice has shown that the air-void structure created by air entraining agents can change easily during construction; for example, due to the type and dosage of normal or high-range water-reducing admixtures, by changes in sources of cementitious materials, by pressure influences during pumping of concrete, by high hydrostatic pressure, or by over vibration.

With the AVA, the air-void structure is measured after the concrete is placed but while it is still fresh, thereby providing timely information of the spacing factor and the specific surface of the airvoid system of the in-place concrete. The testing time is 25 minutes or less.

The AVA-3000 features:

  • The complete apparatus comprising the base unit, riser column, buoyancy dish, balance, and
    sample collection apparatus.
  • Laptop computer with AVA-3000 software.
  • Latest microprocessor technology with components minimized in size and number
  • Only one USB cord is used to connect the laptop computer and the base unit
  • Incorporates a mini balance that can withstand rough treatment during transport and/or testing
  • Elimination of the influence of external vibrations on the test results, including the introduction
    of a wind shield positioned on top of the riser column
  • Improved stirrer operation with constant rotational speed independent of the load applied on the
    stirrer
  • Incorporates a 35-L temperature bath tank for automated de-aerating and controlling the temperatures of the water in the riser column and the AVA release liquid for testing. The waterfilled tank may also function as ballast for stabilizing the base unit
  • In addition to the calculation of the spacing factor and the specific surface for chord length less than 2 mm, the AVA-3000 calculates the air-void parameters for chord length less than 1 mm, as required by the current ASTM C457 standard

Contact Hylec Controls for a quotation

Product Video