2.5.1. Design and Configuration

Your RMC transit mixer, it is also an example of free fall non-tilting reversible mixer. So, here also, you can see, there is only one opening. You have spiral blade arrangement inside. So, when you feed in the material, you have to rotate in one direction. So, when you want to discharge the concrete out, you have to rotate in the opposite direction.

So, these are reversible drum rotating in one direction for mixing and the direction of rotation is reversed while discharging. So, you can see the picture. When the rotation is reversed, the concrete gets discharged out. So, it is mainly because of the spiral blade arrangement inside the drum.

In this section, we learn about the RMC transit mixer, which is a specific type of concrete mixer. It operates on the principle of free fall non-tilting mixing. This means that it does not tilt to discharge the concrete, rather it relies on a reversible drum that can rotate in two directions. When the drum spins to the one direction, it incorporates the concrete materials together. When it's time to discharge, it reverses the direction, allowing the concrete to flow out. This is made efficient by the spiral blade inside the mixer, which ensures that the ingredients are mixed thoroughly before being discharged.

Think of the RMC transit mixer like a blender. When you blend fruit for a smoothie, the blades mix everything together as they spin. Then, when you want to pour out the smoothie, you might rotate the blender or press a button to release it. Here, the mixer rotates one way to blend concrete, and then the opposite way to let it out, just like how a blender operates.

So far, we discussed about the free fall mixers. So, they have different categories as we discussed tilting type, non-tilting, non-tilting reversible type. So, different configurations are there. Now, let us move to the next category that is power mixer. So, here, the mechanism is different. Here, you are not dependent upon the free fall of the material. Here, we are dependent upon the rapid rotation.

So, these mixer machines will be rotated at a very high speed. So, there will be some paddles fixed to the shaft inside pan or the drum. So, these paddles will be rotating at a very high speed that enables the rapid mixing and homogeneous mixing of the concrete.

In this chunk, we see two types of concrete mixers: free fall mixers and power mixers. Free fall mixers utilize gravity to mix materials, which limits their efficiency with stiff mixes (i.e., concrete that doesn’t flow easily). On the other hand, power mixers rely on high-speed rotation of internal paddles to create rapid and thorough mixing. This makes them versatile, as they can effectively mix even thicker and more cohesive concrete mixtures that free fall mixers struggle with.

Imagine making whipped cream. If you just let the cream fall into a bowl and hope it mixes, you wouldn’t get very good results, just like a free fall mixer. Instead, you use a mixer that spins rapidly, which is similar to a power mixer. The fast spinning allows the cream to mix thoroughly into a fluffy texture, just like thick concrete does in a power mixer.

First, we are going to discuss about the pan mixer. It resembles the shape of a pan. You can see, there is a vertical shaft here and the paddles are connected to the vertical shaft. So, because of the rapid rotary motion of these paddles, you can have a thorough homogeneous mixing of the concrete. Another important thing to be noted with respect to the pan mixer is, you have a blade kind of arrangement, blade or scraper attached to the inside of the drum.

The pan mixer has a unique pan-shaped design with a vertical shaft at its center. Paddles attached to this shaft rotate at high speeds, allowing for effective mixing. An essential feature of the pan mixer is the inclusion of scraper blades that help prevent materials from sticking to the drum’s sides. This ensures more uniform mixing and less wastage, which is a common problem in conventional mixers without this design.

Think of a pan mixer like making pizza dough in a bowl. When you knead the dough, you scrape the sides of the bowl with your hands or a spatula to incorporate all ingredients evenly. The scraper blade in the pan mixer works similarly by avoiding sticking and ensuring all ingredients are blended well.

Now, we will discuss about the next type of power mixer which is trough mixer. So, it resembles a trough shaped drum. So, you can see the schematic picture of the trough mixer. You can have a single shaft or double shaft trough mixer. Early, pan mixer, the shaft was vertical but here you can see, the shaft is horizontal.

The trough mixer has a horizontal shaft and can have either a single or double shaft design. It’s shaped like a trough and has paddles arranged in a spiral pattern along the shaft. This design maximizes mixing efficiency due to the turbulence created when the paddles move, leading to thorough mixing. This type of mixer is known for its high productivity and effectiveness, particularly in mixing material quickly and uniformly.

Think of a trough mixer like stirring a pot of soup. If you use a long spoon to mix the ingredients, you can reach every part of the pot and ensure everything is well combined. The horizontal shaft and paddles in the trough mixer allow for comprehensive mixing, similar to how a long spoon mixes all components in a pot.

Another important thing, we have to note here is the mixing duration. The mixing duration is very critical. We have to make sure we meet at least a minimum mixing duration as stipulated by the guidelines of the manufacturer.

Mixing duration is a critical factor in producing concrete. Each type of mixer has its recommended minimum mixing time, which should be adhered to in order to ensure a homogeneous mix. Not mixing long enough can lead to uneven concrete, affecting its strength and durability, while mixing too long can start a chemical reaction in the cement leading to problems like losing workability.

Mixing concrete is like making a cake batter. If you don’t mix it long enough, the ingredients don’t blend well, leading to uneven texture. But if you mix it for too long, you could end up overworking the batter, affecting the final cake’s texture. Just like baking, getting the mixing duration right for concrete is essential for achieving the right result.

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