The Water, Cement, Concrete relationship
The aggregate moisture sensor ensures that the batch is proportioned according to the DRY WEIGHT MIX DESIGN.
Accurate moisture or slump requires correction of the water added to the mixer.
A water dosing system ensures consistent moisture, slump and product quality.
Slump metering can give good results when the same mix design and batch size are used for long periods.
In predictive addition, a moisture measurement is made on the dry ingredients soon after they are added to the mixer. When a suitably accurate reading is acquired, the amount of water in the batch is calculated and, from the mix design data, the amount still required is calculated. The water can then be added quickly, through a volumetric meter or from a weigh scale. Because the moisture measurement is done on the dry material, sensitivity is at its highest and accuracy is maximized. In addition, any type of concrete can be made in this way, from dry cast to high slump values, with no loss in precision. And, because the actual batched weights of aggregates and cement can be factored into the calculation, all the errors can be eliminated. Speed is higher than the first type, above, but slower than metering the water in without feedback. AquaControl using MasterMix is a predictive addition system with all the refinements mentioned here.
Of course, this method requires more equipment than the first and is more expensive as a result. Also, since speed in reading the initial moisture is critical, the software for averaging the wide variations in sensor reading is complex and expensive to develop. If high quality, consistent product is necessary, however, this method is the best. Slump metering is effective in a limited number of applications and is low in cost.
There is no free lunch; the better systems cost more – but the payback could be impressive!
Note that once the complete system is installed, the water dosing system can be bypassed for less critical products, using metered water with no moisture feedback to gain faster mix times and more production per hour. The BatchTron controller allows this by saving your choice right in the formula.