Purpose

The COMA-Meter ( COncrete MAturity-Meter) is used to measure the maturity of newly cast concrete at a depth of 80 mm from the surface for the following purposes:

  • Estimating the compressive strength at an early age using a pre-established strength-maturity relationship (see below for illustration)
  • Timing of pullout testing with LOK-TEST for early-age strength measurement
  • Evaluating the effective in-place curing temperature

Principle

A glass capillary contains a liquid for which the rate of evaporation varies with temperature according to the Arrhenius equation, which is the same function that is used to determine maturity of concrete from its temperature history (see pg. 75). The closed capillary is placed on a card with a calibrated scale indicating maturity in equivalent age at 20 ºC. The card is attached to a cap that fits into a transparent container. After the concrete is cast, the capillary tube is snapped at the zero mark on the scale, the cap is pushed into the container, and the container is inserted into the fresh concrete.
Coma-Meter_1The temperature within the container will stabilize quickly with the temperature of the surrounding concrete. The liquid in the capillary tube evaporates at a rate determined by the temperature and time. The level of the liquid, readable on the scale, measures the maturity of the concrete stated in M20 units, which is the number of equivalent days of curing at 20ºc.

 

 

Easy to use – Without electronics

For timing early and safe loading operations the COMA-Meter is used in conjunction with a reliable test system for in-place strength, that is the LOK-TEST or CAPO-TEST pullout testing (ASTM C 900).

The mix calibrated in the laboratory is based on compression of specimens perfectly consolidated and cured in water for perfect hydration (which is not the case with the structure), and it is assumed that the mix in the laboratory is identical to the mix used on site.

 

Technical specifications

  • Activation energy 40kj
  • Arrhenius Equation for maturity
  • Storage temperature 20ºc
  • Operating temperatures 0 to +60ºc
  • Variation 2%

 

Contact us for a quotation today!