Coarse aggregates can contain 0-2% surface moisture by weight and fine aggregates even up to 10%. These numbers exclude absorbed water, which ranges typically from 0.5 to 4%. Ultimately, wet aggregates may contain moisture more than is desirable to preserve the water-cementitious material ratio (w/cm) in design limits without overdosing cement. In practice, moisture content of aggregates must be known to fractions of percent to minimize variability in concrete quality and to enable optimal usage of cement. Accurately measured moisture in aggregates allows optimizing strength, durability and shrinkage of concrete products. Also knowing the right moisture content prior to mixing permits faster mixing times, when there is no need to add water during mixing.
Optical detection of material moisture allows noncontact detection with clear advantages for concrete industry. Optical moisture sensors are based on absorption peaks by water molecules at near infra-red wavelengths. There have been optical moisture sensors available for process industry over tens of years, but they have not been widely used in concrete plants due to their high price compared to microwave sensors. However, development of optoelectronic components thanks to optical communication technology has enabled designing more optimal and economical sensors for measuring surface moisture in aggregates as Polarmatic’s Polarmoist Water Content Monitor WCM411.
Polarmoist is an outstanding optical moisture sensor designed for detecting moisture content of concrete aggregates. The sensor embeds a micro-processor and uses LED’s as light sources. Moisture content is determined as percentage of water by weight of dry aggregate. The sensor is most optimal when used above conveyors or silo feeders to detect moisture content in moving samples. A non-contacting remote measurement guarantees stable performance and long life time of the sensor.
Polarmoist has been extensively tested in concrete plants with different grades of stone material. By proper calibration the accuracy of measuring water content outperforms hand made reference measurements in the case of a limited number of samples and a large variation of moisture in a given batch.
Polarmoist has a serial and a current loop output and a wide power supply voltage range enabling easy integration to existing control systems.
Features and Benefits:
Remote optical measurement of moisture content
- Solid state design
- No moving nor wearing parts
- High accuracy and resolution
- Fast response
- Low noise
- Stable LED light sources
- Temperature compensated
- Easy to install and calibrate
- current loop 4-20 mA
- Power supply 9-30 VDC
Non-contact measurement, long lifetime due to solid state design, simple calibration, high accuracy and minimal maintenance are huge advantages over microwave probes to measure moisture in fine and coarse aggregates.
Concrete Batch Solutions
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