Economic Implications of Aggregate Moisture Measurements

Economic Implications of Aggregate Moisture Measurements

Considerable savings and higher quality of concrete may be gained by use of moisture sensors in the concrete industry worldwide. Currently it seems that measuring the moisture in the aggregates is far from being a systematic procedure.

Concrete strength is determined mainly by water to cement ratio (w/c). A typical dependence of strength on w/c is shown in Figure 1. If the water in aggregate is not measured accurately, the inaccurate amount of water must be compensated by additional cement. The inaccuracy is on the order of 2 percent or even more in fine aggregates, which are typically used about 1 ton per 1 m³ of concrete. This additional 20 kg of water requires 40 kg more cement per 1 m³ at w/c = 0.5 in order not to fall below the chosen level of computational strength of the concrete. Approximately half of this can be saved with the help of a precise moisture measurement of the aggregates.

Typical dependence of concrete compressive strength on water to cement ratio

Image 1. Typical dependence of concrete compressive strength on water to cement ratio

Considering the cement price to be 100 EUR per ton, the loss is about 2 EUR/m³. For a small concrete plant which produces annually about 20 000 m³ this means a loss of 40 000 EUR per year. Typically 1-3 optical sensors are installed into one factory, and given these figures the payback time of taking into use the optical sensor solution will be less than 1 year.

The world consumption of concrete is in the order of 4,2 109 m³. Measuring moisture accurately in concrete production could save the cost of cement worth roughly 8 000 MEUR/year. This means also less CO2 emissions.

In addition to the direct monetary loss there are indirect costs caused by the poor quality of the concrete and its shorter durability. Instead of a potential lifetime of 100 – 200 years, it can drop to around 50 or less if the quality of concrete will not be maintained.

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