8.1
Mixing Concrete
Concrete mixing ensures a homogenous blend where aggregates are well-coated with cement paste. Concrete mixing is typically done using two main types…
The primary goal of mixing concrete is to stir its ingredients, ensuring the aggregates are evenly coated with cement paste, resulting in a uniform mixture.
Typically, concrete is mixed using batch mixers or continuous mixers.
Batch mixers process one complete batch at a time, mixing the ingredients and then discharging them before the next batch is introduced. There are four types of batch mixers: tilting drum mixers, non-tilting drum mixers, pan-type mixers, and dual drum mixers.
A tilting drum mixer uses internal blades to mix concrete, discharging the mixture by tilting the drum. Contrarily, a non-tilting drum mixer discharges the mix through a chute or by reversing the drum's rotation.
Mixing concrete in batches can be done in a pan-type mixer using paddles or in a dual drum mixer involving a two-stage mixing process within a tandem setup of drums.
Continuous mixers automatically and continuously receive ingredients, which are then uniformly combined using a drum-type mixer or a screw moving inside a stationary housing, resulting in a constant outflow of mixed concrete.
Lastly, to ensure the mixer's efficiency in yielding a uniform mix, samples at specific discharge points are collected and evaluated for consistency.
View the full transcript and gain access to JoVE Core videos
Q1: What is the primary goal of mixing concrete?
The primary goal of mixing concrete is to stir its ingredients, ensuring aggregates are evenly coated with cement paste, resulting in a uniform mixture. This uniform distribution is essential for achieving consistent concrete quality and performance across the entire batch.
Q2: What are the main differences between batch mixers and continuous mixers?
Batch mixers process one complete batch at a time, mixing ingredients and discharging them before the next batch begins. Continuous mixers automatically receive ingredients in a steady flow, uniformly combining them with constant outflow. Batch mixers offer flexibility, while continuous mixers provide consistent production rates.
Q3: How do tilting drum mixers differ from non-tilting drum mixers?
Tilting drum mixers use internal blades to mix concrete and discharge the mixture by tilting the drum. Non-tilting drum mixers discharge through a chute or by reversing the drum's rotation. Both are batch mixer types but employ different discharge mechanisms to empty their contents.
Q4: What are pan-type mixers and dual drum mixers used for in concrete production?
Pan-type mixers use rotating paddles about a vertical axis to blend concrete in batches. Dual drum mixers employ a two-stage mixing process within tandem drums, allowing sequential mixing. Both are batch mixer options that provide alternative mixing mechanisms for different production needs.
Q5: Why is mixer capacity important for achieving uniform concrete mixes?
Mixing a volume that is only a minor portion of the mixer's total capacity is inefficient and leads to inconsistent mixes. Similarly, overloading the mixer beyond its recommended capacity by more than 10% results in non-uniform mix. Operating within the mixer's optimal capacity range ensures proper ingredient distribution and concrete quality.
Q6: How is concrete mixer efficiency verified for consistency?
To ensure mixer efficiency in yielding uniform mix, samples are collected at specific discharge points and evaluated for consistency according to set criteria such as density, air content, slump, and compressive strength. This sampling process confirms that the mixer is properly combining all ingredients throughout production.
Q7: What types of batch mixers are commonly used in concrete production?
Four main types of batch mixers are used: tilting drum mixers, non-tilting drum mixers, pan-type mixers, and dual drum mixers. Each type uses different mechanisms for mixing and discharging concrete. After mixing is complete, concrete is typically ready for placing concrete or other downstream processes.