5.1. Concrete Batching Production Example

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.

A Ready-Mix Concrete (RMC) transit mixer is a specialized vehicle that mixes and transports concrete. It features a drum that rotates in one direction while mixing materials. When it's time to pour the concrete, the rotation is reversed, causing the concrete to flow out through a single opening. This design effectively utilizes a spiral blade arrangement inside the drum, ensuring that the ingredients are mixed properly before being discharged.

Imagine a blender in your kitchen; you spin the blades to mix all the ingredients together. When you want to pour out your smoothie, you flip a switch that changes the direction of the blades so the contents can flow out smoothly. The RMC transit mixer works on a similar principle, just with a much larger capacity and different materials.

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.

Concrete mixers can be classified primarily into three types: tilting, non-tilting, and non-tilting reversible mixers. Tilting mixers allow the drum to tilt for discharging concrete, while non-tilting mixers maintain a fixed position. The non-tilting reversible type can mix and discharge by reversing the drum's rotation, enhancing versatility in operations.

Think of a washing machine: some have a top that opens (tilting) so you can take out clothes easily, while others have a front door (non-tilting) that remains in place. In the case of concrete mixers, different types suit various construction site needs—just like you might choose a top-loader or front-loader based on your laundry habits.

Now, let us move to the next category that is power mixer. 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.

Power mixers operate differently from free fall mixers. Instead of relying on gravity to mix materials, they use high-speed rotating paddles. This method enables them to handle stiff and cohesive mixes efficiently, producing a more homogeneous concrete mixture in a shorter time compared to free fall mixers.

Consider a salad spinner: it uses high-speed spinning to quickly dry greens. Similarly, power mixers rapidly spin their paddles to mix concrete ingredients efficiently, allowing them to create a well-blended mix even when the ingredients are thick or hard to combine.

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.

The pan mixer effectively blends concrete using a shape similar to a frying pan. It features a vertical shaft with paddles attached that rotate rapidly to mix ingredients thoroughly. Additionally, scraper blades help prevent materials from sticking to the drum, ensuring the consistency of the mixture is maintained.

Think of how a traditional frying pan has a flat bottom and sides to keep ingredients together while stirring. Similarly, the pan mixer is designed to keep all the components of concrete contained while achieving a well-mixed product.

When we make the initial trial mixes, the free fall drum mixer, what happens is the most of the paste will stick to the sides of the drum.

In free fall mixers, during the initial mixing phase, the paste can often stick to the drum's sides, resulting in uneven mixtures. To address this issue, operators may perform a 'buttering' operation, where they run a trial batch with water to coat the drum, reducing material wastage during actual concrete mixing.

If you’ve ever tried to mix batter in a bowl and found it sticky, you might drizzle oil on the sides to help the mixture slide down. Using the 'buttering' technique in mixers is like that—using a bit of water to minimize sticking and help achieve a smooth, even mix.

Now, we will discuss about the next type of power mixer which is trough mixer. So, it resembles a trough shaped drum.

The trough mixer features a unique design resembling a long trough, with paddles arranged spirally along either a single or double shaft. This design aids in creating a more turbulent mixing action, which leads to better consistency in the concrete mixture.

Imagine stirring a large pot of soup with a long spoon. As you stir, the spoon moves through the ingredients, mixing them up effectively. Likewise, the trough mixer’s design allows for effective mixing over a larger area, making it efficient and productive.

Another important thing, we have to note here is the mixing duration. The mixing duration is very critical.

The duration for mixing concrete varies depending on the type of mixer and its capacity. Following the manufacturer's guidelines is crucial; insufficient mixing time can lead to poor homogeneity, while excessive time can harmful effects due to cement setting and loss of workability.

Think about making a cake. If you don’t mix the batter long enough, it won’t be smooth, but if you overmix it, the cake may become tough. Just like cake batter, concrete needs the right amount of mixing time to achieve an optimal, consistent mixture.

Now, how to calculate the productivity of your batch? Generally, we know that concrete is producing batches.

To assess concrete production productivity, you consider batch size and cycle time, which consists of loading, mixing, and discharging times. The actual output per hour is determined using the nominal batch size and the operational efficiency of the mixer.

Think of running a lemonade stand. If you know how much lemonade your jug can hold (batch size) and how long it takes to prepare a batch (cycle time), you can calculate how many jugs you can sell in an hour, guiding your sales strategy for the day.

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