Keeping an eye on moisture
In concrete batching plants the online measurement of moisture in raw materials allows more precise control of the batching process. Scantech International has developed the TBM260, a new system for measuring the moisture content of material in bins, a trial for which was conducted at the Holcim Darra plant in Queensland, Australia. By Steve Louden, Holcim (Australia) Pty & Ken Smith, Scantech International Pty Ltd, Australia.
Figure 1: installation of microwave antennae on the throat of a bin
The concrete batching process aims to load a concrete truck with the required quantity of concrete meeting the customer’s specifications. Sands and aggregates are automatically weighed and cement and water are added to produce concrete with the correct strength and slump specification. The measured weight includes the water present in the material. Therefore, variation in moisture can result in errors in the amount of dry material in the mix. Moisture in sand is the major problem as sand can contain up to 15 per cent moisture.
Online measurement of moisture in raw materials can avoid these problems. The moisture result can be used to calculate the correct wet weight of material for the optimum mix. The correct water addition can also be calculated, by taking into account the water already present in the raw materials. For best results the measurement technology must measure moisture directly in a bin and rapidly provide moisture data to the batching control system.
