The construction industry has seen unprecedented growth in the use of Ready-Mix Concrete, however, the first use of RMC dates to 1903 which then progressed only to mega projects in India until the 1950s. The last two decades have seen tremendous use of RMC in residential & other infrastructure projects. If the term RMC is new and you are wondering about its use, application let us get to the basics of RMC!
What is Ready Mix Concrete?
Concrete is a mixture of Portland cement, water, coarse & fine aggregates mixed at the site. RMC as opposed to site concrete is mixed in a central batching or a mixing plant which is then transported in a truck-mixer and supplied in fresh condition to the site. RMC has the same composition & proportion as traditional concrete, since it is manufactured in a plant it has the added advantage of mixing concrete in precise proportions. This improves the concrete mix and standardizes the quality. This concrete mix is supplied in terms of cubic meters.
When will you need RMC?
Concrete is a useful and crucial material for any form of construction or renovation. Nevertheless, inexperienced users of concrete, in general, find it incredibly difficult to get the right mix on site. To secure suitable results for any task involving concrete is a risk. This poses one of the main reasons why ready-mix concrete is popular today. Secondly, when the concrete requirement is immediate or when needed in small quantities, mixing on-site is trouble, with RMC making small scale projects easily commissionable. RMC proves its advantages with ease of site handling at the site with minimal labor cost and low material wastage. Since the site condition & surroundings will not be harmed at large it is environmentally friendly.
Since RMC is manufactured in a plant. Now, how can RMC be transported?
The concrete must be transported from the mixer to the site maintaining the workability of the mix without segregation, loss of any constituents or ingress of foreign matter. It must be immediately used at the site to avoid rehandling or moving the concrete horizontally. The full load of concrete must be discharged within 30mins of the arrival at the site as specified by IS Code. However, RMC is available in different grades and value addition which may specify a different time and care for casting.
Are there different types?
Pioneering efforts of several manufacturers have bought in the various product range of RMC, these specialized ranges include lightweight concrete, high strength concrete, self-compacting concrete, Fiber Reinforced and several others which will be described in detail in the next blog. Watch this space!
Advantages of RMC?
Quality of Concrete - For one thing, the quality of concrete matters! In a traditional on-site concrete mix, quality control is a major concern. Manual labor and on-site equipment usually do not maintain an ideal water-cement ratio and grade of aggregates to precise quantity. Do not do you agree it’s a tricky job? With ready mix concrete, batch mixing can always guarantee an accurate proportion of all constituents since it is manufactured in a remote plant using state-of-the-art technology, engineering, and equipment with minimal manual labor.
Environmentally Friendly - Let us understand how RMC proves to be environmentally friendly and how the site will not be harmed. Secondly, pre-mixed concrete eliminates the storage of materials required at the site causing minimal or no harm to the site and its surrounding. The material required such as cement, sand, gravel, and the prep area to mix the concrete and all the arduous tasks are eliminated.
Cost-Effective - Since ready mix concrete is premixed and available to use immediately it reduces the labor and contracting charges required at the site & reduces a ton of money. The batching plant has control over the production and use of raw materials, the mechanized process reduces material wastage and overhead costs at the site.
Time Optimized Solution - RMC offers speedy construction, reduces problems associated with the site. Increased supervision & mechanized controls at manufacturing plants keep the delivery of concrete time-bound. An immediate requirement of a project can be met without pre planning buying of materials and managing equipment at the site.
For what are they used?
Ready-mix concrete can be used for all concrete works like traditional concrete works, it only needs additional care during transportation. Any concrete-based job such as foundational works, framed construction of columns & beams, laying or resurfacing pavement, walkways, driveways or even roadway can be quickly undertaken and completed without any obstruction to continued activities.
Now, are there any limitations to the use of RMC?
Well, of course, any material or service has its pros and cons. In this consideration, RMC is to be looked more of a service than just a material.
Setting Time - Concrete manufactured at the batching plant is mixed with admixtures or retarders that delay the setting time allowing the material to be transported to the site. RMC must arrive at the site with an optimum dose of admixtures that does not involve undue delay in its setting.
Good Formwork - The formwork cast at the site needs to be sturdy to withstand the load of the fresh concrete since RMC needs speedy pouring on site. The formwork needs to sustain the placement of speed concrete. IS code specifies the concrete to be cast within 30minutes of arrival at the site.
Slump & Stiffness of Concrete - Concrete supplied from the plant can either be stiff or more slumpy. The addition of water at the site will compromise the workability and pumping of concrete. Technical supervision at the site is necessary while discharging the concrete for any recommendation for re-handling concrete if necessary!
Types of Ready-Mix Concrete
Here’s what we are going to talk about the types of Ready-Mix concrete determined by the specific mix and constituents of the ingredients.
What are the three types of Ready-Mix Concrete?
● Shrink Mixed Concrete
● Transit Mixed Concrete
● Central Mixed Concrete
1.Shrink Mixed Concrete - The concrete is partially mixed in the batching or manufacturing plant to a specific consistency allowing further mixing of concrete while the mix is in transit. The secondary or continued mixing is carried out in the mountain drum of the transit truck mixer. The amount of mixing required during transit is determined by the amount of premixing completed at the batching plant. A slump test or necessary test is taken to determine the amount of mixing required during transit is best advised.
2. Transit Mixed Concrete - Transit mixed concrete is also known as dry-batched concrete. Ready- Mix concrete of this type includes mixing of all ingredients in the transit truck mixer as the name indicated. All the basic constituents including water are combined during the transit. When the truck is loading initially with all the ingredients, the mountain drum of the mixer rotates quickly at a very high speed eventually reducing the speed of the drum to slow rotations to an agitating normal speed.
Now the Transit mixer concrete is also available in three variations:
- Mixed at Job Site
During the transport, this variant of RMC revolves in the mountain drum at a slow speed. Approximately 2 rotations of every minute, 2 rpm. When the mix reaches the construction site before the mix is being removed from the truck, the drum rotates about 70 – 100 revolutions at a maximum speed of 12-15 rotations per minute (12-15 rpm). This helps the concrete mixture to attain a smooth texture.
- Mixed in Transit
As the name suggests, the concrete is completely mixed during the transit. During the transit, the mix is under a continual rotation of approximately 8 rpm is about 70 revolutions approximately. After achieving 70 revolutions, the rotation of the drum is slowed to an agitating speed. The speed of the drum is then about 2 rpm until the concrete reaches the site and is finally discharged.
- Mixed in Yard
The mix is complete when the concrete reaches the site. During transit, the RMC is kept at slow agitation to keep the mix in a stable texture without forming lumps. Once the truck reaches the site, the mountain drum will rotate at a speed of 12-15 rpm at roughly 50 revolutions until the mixture is ready to be discharged.
3. Central Mixed Concrete - Central mixed concrete is also referred to as wet batch concrete or premix plants or even central batching plant concrete. The concrete is mixed in a stationary unit in the plant before being transferred to the transit truck. During transit, the mountain drum primarily acts as an agitator. Central mixed concrete has a faster production rate than transit mix RMC. The quality of the RMC is higher, and the consistency is improved due to the stationary mixer unit. The intensity of the plant mixer tends to produce higher strength concrete because of thoroughly blended ingredients.
Value Added Ready-Mix Concrete
1.High Strength Concrete - HS concrete offers superior workability, high durability & compressive strength of 65 Mpa and above. The use of high strength concrete reduces concrete volume by 45% by reducing structural column/beam size. Used for Long span infrastructure, Structural elements, Column, Beam, Shaft.
2. Self-Compacting Concrete - High-performance concrete with properties like self-levelling and self-compacting is achieved with special admixtures. Reduced noise during casting, gives a smooth surface finish with high workability and reduced cost. Especially preferred for congested reinforcement sections where it’s difficult to vibrate sections while concrete placement. A generic application like slabs, beams, foundation & columns.
3. Fiber Reinforced Concrete - Fiber Reinforced concrete contains fibrous material which increases structural integrity & tensile strength compared to normal concrete. The fiber content in the concrete mix controls shrinkage cracks that occur during hydration. FRC can be an RMC mixed with additives or can be mortar mixed onsite, care must be taken to evenly mix the fiber content. The fibrous content of the concrete varies concerning the application. Depending on the structural design the fibers can replace steel rebars or reduce the usage of steel thereby lowering the cost of construction.
4. Steel Fiber concrete is used for road pavement, construction of bridges, decks & pavement for airfield structures.
5. Glass Fiber concrete – GFRC is a lightweight concrete mix used for creating structures with high aesthetic value. Commonly seen it's used in fluidic construction. Even used as façade cladding.
6. Synthetic Fiber Concrete is made of two fibrous types either microfiber or macro fiber. Microfiber is used for reducing cracks during shrinkage. Macro fiber is used for obtaining high tensile strength. Commonly used for Sidewalks, curbs & driveways.
7. Lightweight Concrete - Lightweight concrete is 50% to 75% lighter in weight than normal concrete. It has improved thermal insulation, lesser structural loading & higher resistance to fire. Generally used for floor screed for noise cancellation transferring through the floor slab. Construction of light weighs partitions, filler slabs, decks, bridges & piers.
8. Green Concrete - Sustainable alternative to concrete with lower embodied carbon. Green concrete meets sustainable goals with reduced use of ordinary cement. Every cubic meter of Green Concrete saves about 10-13% of Co2 emission. Green concrete controls sulfate & ion ingress, reduces hydration therefore best suited for marine & coastal structures.
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