Calcium Carbide Method (CM method) for Screed Residual Moisture Measurement
It goes about a well-known method for indirect moisture measurement. Here, the carbide method is subject to clearly erroneous influencing factors. Since the local practitioner has been used to this method of moisture measurement for decades, it still plays a role, even though decreasing, e.g. when assessing the adhesiveness of the floor coverings on the screed.
According to this method, calcium carbide reacts with water to calcium hydroxide and acetylene. The water comes from the previously obtained sample material (10 ... 50 g), which is crushed in the reaction vessel by the also present there steel balls, in the result of a 10-minute shaking and the moisture present in the container reacts with the calcium carbide. The gaseous acetylene causes a pressure rise that is measurable and can be correlated directly to the moisture content.
The reaction containers made of stainless steel and with the display of the container pressure via a pressure gauge, are applied for this purpose. The maturity of a screed can thus be determined indirectly but with sufficient accuracy with the help of the CM method.
Concrete Moisture Meter (follows Carbide Method)
Measuring function Measuring range Relative scale 0.0 ... 99.9% anhydrite 0.0 ... 3.5% (Weight percent) anhydrite 0.0 ... 1.5% (Calcium carbide method)* cement screed 0.0 ... 4.7% (Weight percent) cement screed 0.0 ... 3.0% (Calcium carbide method)* Concrete (weight percent) 0.0 ... 6.0% gypsum plaster 0.0 ... 10.0% (Weight percent) hardwood 0.0 ... 37.0% (Weight percent) softwood 0.0 ... 51.0% (Weight percent) *The calcium carbide method is approximate. Further specification Accuracy ± 0.5% Resolution 0.1% Power supply 2 x 1.5V AA batteries Uptime About 20 hours Automatic shutdown After 5 minutes of inactivity Menu languages English, German, Dutch, Spanish, French Display Graphically monochrome, 128 x 64 pixels, 61 x 33 mm, backlight Operating conditions 5 ... 40°C / 41 ... 104°F Dimensions 147 x 89 x 33 mm / 5.8 x 3.5 x 1.3 in Weight 200 g / < 1 lb (with batteries)