Bobrowski et al. taught that concrete remaining in the mixing drum of delivery trucks can be reclaimed for use by adding a retarding admixture to stabilize the remainder concrete (See U.S. Pat. No. 4,964,917), optionally adding new concrete to the remainder (See U.S. Pat. No. 5,203,919), and then using an accelerator just before re-using the reclaimed concrete (See U.S. Pat. No. 5,247,617).
Hines et al. taught that the amount of admixture to be dosed into the truck returning from delivery can be calculated based on remaining load size and temperature of the concrete (See U.S. Pat. No. 6,042,258) and that admixture dosing could be done on an automated basis (See U.S. Pat. No. 6,042,259).
The present inventors believe that prior art methods for calculating the concrete load remaining in the truck after delivery are neither sufficiently accurate nor practically convenient. For example, it is known to weigh the mixing truck on a weight scale before and after delivery (See e.g., U.S. Pat. No. 5,752,768; U.S. Pat. No. 6,123,444; U.S. Pat. No. 8,020,431; and GB 2392502), but weight can vary due to imprecision of the scale and various other factors (such as fluctuation of fuel tank and other fluid tank levels).
It is also known to estimate concrete discharged from the drum by counting mixing drum rotations required to discharge a known volume of concrete. A typical concrete mixing drum has a pair of mixing blades mounted on the inner drum wall, helically arrayed about the rotational axis of the drum. The blades thus function in the manner of an Archimedes' screw device. When the drum rotates in the “charge” (loading or mixing) direction, the blades push concrete towards the closed end of the drum; and, when the drum rotates in the “discharge” direction, the blades push concrete towards and through an opening located at the opposite end of the drum. The concrete expelled through the drum opening can then be guided by a chute to the desired spot where it is to be placed. Often, the load will not be fully discharged, and the remainder will be returned in the mixing drum to the plant or moved to another placement location; and the remaining volume of concrete would typically be measured by rough visual approximation or by subtracting a rough estimate of the discharged amount from the amount of the original load.
To this point, the current practice of estimating the remainder load has been premised upon the assumption that the amount of concrete discharged from the drum can be calculated based upon the number of drum rotations required to expel the concrete from the drum. This relation is mentioned in various patents, including U.S. Pat. No. 5,752,768 of Assh (Col. 18, line 40 et seq.), U.S. Pat. No. 8,020,431 of Cooley, and U.S. Pat. No. 8,118,473 of Compton. However, the present inventors believe this assumption is predicated on a the underlying assumption that the number of rotations required to bring concrete to the drum opening is constant from load to load, and further that the amount of discharge for each drum rotation is also constant from load to load.
In U.S. Pat. Nos. 6,611,755, 6,892,131, and 7,489,993, Coffee et al. disclosed that Begin Pour and End Pour events (i.e., charging and discharge) can be based upon, among other approaches, the number of drum rotations in the discharge direction, and that the truck can be weighed as part of determining amounts of concrete remaining in the drum after the End Pour event. The number of discharge revolutions for the Begin Pour event is hitherto assumed or estimated to be 1 or 2 drum revolutions, regardless of the load size of the concrete. While this may be adequate for determining Begin Pour and End Pour events, the present inventors believe that a novel system and method are required for achieving high accuracy in calculating the amount of concrete remaining in the drum after partial discharge.