The first type is the drum mixer, which can be classified as non-tilting,
split drum, or titling drum mixers, as well as truck mixers or reversing
drum mixers. Characteristics of each type of mixer are shown in the table
|Type of Mixer||Characteristics|
|Non-tilting mixer||Single drum rotating about a horizontal axis. Fixed blades work the concrete towards the discharge end of the mixer, in order to provide a rapid rate of discharge. The typical capacity is 1 CY.|
|Split drum mixer||The drum, rotating on a horizontal axis, separates into two halves, allowing the concrete to be discharged cleanly and rapidly. No blades are required since cohesion to the top and bottom of the drum and cleats provide adequate charging and mixing. Typical capacity is 2.5 CY and provides a short mixing cycle and rapid discharge.|
|Tilting drum mixer||Are common in various sizes as shown in Figures 2 and 3. They are most suitable for concrete with large sized aggregate and, since they have a rapid discharge rate, are suitable for low workability concrete. Internal blades lift and tumble the ingredients onto itself. Two primary types exist: horizontal (one end has and opening for charging and a different end for discharging) and single drum (materials are charged and discharged through a single opening). The main difference between all mixers is the tilting mechanism. "Each manufacturer attempts to reduce installation height and maintain a relatively simple mechanism" (Dobrowolski, 18.2).|
|Reversing drum mixer||Rotate in one direction for mixing and in the reverse direction for discharge as shown in Figure 4. One set of blades exists for each operation. Provide efficient mixing with very little build up within the mixer. Are suitable with dry concrete mixes.|
|Drum Truck Mixers||Two types: rear discharge, as shown in Figure 5, and front discharge. Both utilize fins to mix and discharge the concrete and are powered by engine driven-variable speed hydraulic systems.|
The second type is the pan mixer, shown in Figure 6. A forced movement pan mixer has blades that are fixed to an assembly that agitates the concrete throughout the pan as the vertical shaft rotates. This mixer is most common where stiff or zero slump mixes are prevalent. "They have not gained acceptance in ready mix production because of the small size and reputation for high blade and liner wear" (Dobrowolski, 18.5). Pan mixers are most commonly found in precast concrete plants. Their capacity ranges from .25 CY to 2.5 CY.
The final type is the continuous mixer. A free-falling continuous mixer is a gravity-fed mixer, classified by its continuous movement. In this process the charging of materials and discharging of the mixed concrete is released in one, uninterrupted process. Continuous mixers utilize a continuous weigh batching system as well. Materials are typically fed into the mixer by a conveyor system. This mixer is most suitable when large quantities of mass concrete are required (i.e. dams, foundations, retaining walls and mass concrete filling). Stationary mixers are used in ready-mix concrete plants, while portable mixers are used on construction sites. Continuous mixers outperform batch mixers when "minor adjustments to the workability of the concrete" (Murdock, 151) are required.
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