What Is Meant By Ready Mix Concrete?

What Is Meant By Ready Mix Concrete?

Ready-mix concrete (RMC) is a type of concrete made in a batch plant to meet specific project requirements and delivered to the job site ready for use.

There are two main types of RMC: barrel truck or in-transit mixers, which deliver wet concrete, and volumetric concrete mixers, which deliver dry concrete and mix it on site.

Some sources categorize RMC into three types: Transit Mix, Central Mix, or Shrink Mix. RMC is a mixture of cement, water, and aggregates like sand, gravel, or crushed stone, with washed aggregates and limited amounts of dirt and clay. An admixture may be added to improve workability and/or extend setting time.

What Are The Types Of Ready Mix Concrete?

Different types of ready mix concrete include:

• Standard Concrete: The most common type, made at a plant for consistent quality.
• Architectural & Decorative Concrete: Offers a structural and aesthetic finish with varied textures and colors.
• Accelerated Set Concrete: Quick-drying for fast formwork removal and construction sequencing, used for roads and runways.
• Fiber-reinforced Concrete: Made with micro/macro fibers for strength and crack resistance, used for structural and shrinkage reduction.
• Flowable Fill/CLSM Concrete: Fluid concrete used for laying pipes and cables, providing protection and quick work.
• Roller-compacted Concrete: Compacted in place, durable and cost-competitive, used for high flow infrastructure such as spillways.
• Self-consolidating Concrete (SCC): Self-leveling with high flow and compaction, resulting in high strength.
• Pervious Concrete: Highly porous, allowing water filtration, reducing flooding and heat concentration, used for parking lots and paths.
• Insulating Concrete: Forms for poured concrete walls that stay in place for insulation, recently developed by CEMEX.

What Is The Composition Of Ready Mix Concrete?

The crucial components of concrete mix and their functions:

• Cement – Though a small part of the mix, cement acts as the binding agent that holds everything together. It hardens the ready mix once placed. There are 5 types of cement for different concrete uses: Type I (residential), Type II (moderate sulfate), Type III (freezing climates), Type IV (special orders), and Type V (extreme sulfate). Types I and II are widely used in the US.
• Air and Water – A small amount of air entrainment (microscopic air bubbles) is necessary for the mix to work effectively. This ensures excess water can expand in the freeze-thaw cycle. Too much water weakens the hardened mix and causes shrinkage and cracking. A water to cement ratio of 0.4 to 0.6 is ideal, and a slump test can be performed to check solubility.
• Gravel and Sand – These aggregates make up 70% of the mix, making it economical. A good mix includes a proportionate amount of large (gravel) and small (sand) particles, with gravel making up most of the mix and sand filling any extra spaces.

What Are The Advantages Of Ready Mix Concrete?

The combination of materials in a batch plant starts the hydration process when water and cement are mixed.

Transit time from the plant to the job site and waiting time before pouring is crucial for distant locations, but can be extended by using admixtures, retarders, and alternative materials like fly ash or GGBFS.

Concrete must be poured continuously for large forms, otherwise a cold joint may appear.

Ready-mix concrete is produced in controlled conditions for consistent quality, with strict control over material testing, process parameters, and ongoing monitoring.

The ready-mix method eliminates issues with inconsistent input materials, batching, and mixing that can occur with site mix concrete.

Ready-mix concrete plants have faster production, reducing cement consumption by 10-12% through improved handling and mixing techniques and the use of admixtures and alternative materials.

Ready-mix concrete has less dependence on human labor, reducing the risk of human error and intensive labor needs.

Concrete shrinks as it cures, causing internal stress that must be accounted for and may require reinforcement or pre-stressed elements.

Ready-mix trucks, with a capacity of up to 32 tonnes, require roads capable of supporting their weight, but mini mix trucks with smaller 4 m3 mixers can access weight-restricted sites.

What Is The Ratio Of Ready Mix Concrete?

A typical concrete mixture consists of approximately 10% cement, 20% air and water, 30% sand, and 40% gravel, following the 10-20-30-40 Rule. The ratios may differ based on the cement type and other variables.