Concrete Material is one of the terms that does not sound familiar to us. Concrete materials are used in the construction of civil engineering buildings. Each building requires different specifications. In order to achieve the desired quality of concrete, various processes must be considered, such as the dosage of concrete material, the stirring process, the casting process to the curing process.
This article will discuss the stirring process and the importance of using mixer equipment to achieve the desired concrete quality. One of the main benefits in the use of mixers is to achieve a state of homogeneity.
Benefits of using a Mixer
Mixer means a device for stirring or stirring in Indonesian. Mixers that serve for concrete mixing, are needed in mixing concrete materials to achieve the desired quality. The quality will be much better and more homogeneous when compared to manual mixing of concrete. The process of stirring concrete material by hand is better avoided except mixing in small volumes.
Based on SNI 03-3976-1995, the mixer equipment used must meet the following conditions:
- All equipment for concrete stirring must be in good condition and clean;
- The stirring machine should be at the speed recommended by the manufacturer of such machine;
Apart from based on the type of mixer, the length of the stirring process can affect the quality of concrete. The stirring time of concrete can affect the moisture content inside the cement or the hydration of the cement. Concrete mortar should be planned in such a way, so that the resulting concrete reaches the desired quality and can be easily worked on.
What are the types of Mixers available in the market?
There are several types of mixers that are commonly used and available in the market, including:
Tilting drum mixer
This mixer is drum-shaped, and works by rotating. During the stirring process, the mixer will work with the position of the mixer axis in a horizontal state. When the stirring process is complete, the cement will be removed by tilting the drum axis.
Non-Tilting drum mixer
Non-tilting drum mixer is also drum-shaped, and works by rotating. This type of mixer drum works in a fixed position, that is, horizontally both in the stirring process and the filling process.
Vertical Shaft Mixer
Vertical shaft mixers are often also referred to as turbine mixers. This mixer works by rotating the propeller or pedal on the vertical axis at the time of stirring. The propeller is installed in the center of the container and can be adjusted as needed. This type of mixer is excellent for stirring concrete materials with relatively dry characteristics.
Paddle mixer is a type of mixer that uses horizontally mounted knives. This mixer is suitable for use for relatively dry concrete mixtures. Paddle mixers are generally used in the production of precast concrete.
Continuous mixer mixes concrete by using spiral blades that can rotate at high speed. The spiral knife is placed on a large tube with an inclined position of 15 – 25 degrees against the horizontal line.
Mixer Truck / Mixer Truck
Truck mixer is a truck vehicle that has a large drum on the back. The drum on the truck vehicle can rotate for the process of stirring concrete. It is very beneficial to maintain the condition of the concrete material not hardening during the delivery process from the batching plant to the construction site.
There are two types of mixing trucks, namely:
- mixer type with cement fill dispensing system from behind the drum using inclined axis.
- mixer type with a fill removal system from the front of the drum that uses fins mounted on the drum and rotates in the opposite direction.
Standard Concrete Stirring Process
The stirring of concrete material based on location is divided into two, namely (1) mixing in the field (on site) and (2) concrete that is grieved in the batching plant and must be carried in a safe mix.
In accordance with SNI 03-3976-1995, the process of stirring concrete in the field is regulated with the following provisions:
- The concrete must be stirred in such a way that an even spread of the material is achieved and all the mortar must be removed before the mixer machine is replenished;
- Stirring should be carried out not less than 1 - 1/2 minute for any smaller or equal to 1 m3 Stirring time should be increased by 1/2 minute for each additional capacity of 1 m3 complain.
- Stirring should be continued for at least 1-1/2 minutes after all materials have been put into the stirring machine (or according to the specifications of the stirrer).
- During stirring, the viscosity of the concrete mortar should be monitored continuously by checking the slump on each new concrete mixture.
- The viscosity of concrete must be adjusted to the transport distance.
- If the production of concrete is carried out by a ready-mixed concrete company, then the uniformity of stirring must follow the applicable regulations.
- Detailed data recording should be carried out on:
- Time and date of stirring and casting;
- Proportion of materials used;
- The number of batches produced;
- The location of the final casting on the structure.
Things to pay attention to in the process of stirring concrete
Things that need to be considered in the concrete stirring process include:
- Segregation of concrete mixtures, is a condition in which sand and concrete corals separate from cement paste (a mixture of water and cement) which can occur during stirring, casting, as well as when transportation to the place of casting area. The main cause is too long stirring.
- The length of time the concrete after mixing is not directly cast. Based on the reference, the initial setting phase time of cement is 1 - 2 hours. Then the longest casting time is 1 hour. It can be different if the concrete material contains additional additives.
- Concrete stirring containers, containers when they are mixed before transportation and casting to avoid the possibility of segregation. In addition, also take into account the distance of the lips of the mixer with a container that is not too high.
- Concrete stirring location, this is done to avoid long waiting times, the possibility of segregation, cement initial setting and optimal cost, the concrete stirring location should be as close as possible to the foundry.