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Ready-Mix Concrete is a type of concrete that is manufactured in a factory according to a set recipe, and then delivered to a worksite, often by truck. This results in a precise mixture, allowing specialty concrete mixtures to be developed and implemented on construction sites.
Ready-Mix Concrete is quality consistent, saves on storage space and logistics of arranging raw materials. Desired grade can be supplied as and when required.
Concrete Mix Design is the process of selecting suitable ingredients of concrete and determining their relative amounts with the objective of producing a concrete of the required strength, durability, and workability as economically as possible.
Grade of concrete refers to the strength of concrete after a period of 28 days, i.e. M20 grade refers to strength of concrete after 28 days as 2660N/mm2.
Concrete cubes are cast at regular intervals and the same cubes are tested to find out crushing strength on 7th and 28th day. The strength of the cube will indicate strength of concrete.
Slump is an indication of water cement ratio in concrete. More the slump more is the amount of water in concrete. In case of pump able concrete a slump of 80 to 120 mm is desirable. This high slump of concrete is achieved by designing the mix and adding certain admixture to concrete. The strength of concrete is not affected due to high slump of pump able concrete. Hydraulic cement, and fiber reinforcement, used as an ingredient of concrete or mortar, and added to the batch immediately before or during its mixing’.
A Slump test is one of fresh concrete tests. Slump test is made to measure the consistency of fresh concrete mix; it’s the most commonly used all over the world according toIS1199 1959. The main purpose of measuring consistency by slump test is to achieve acceptable fresh concrete workability. Also the slump test is one of the simple and important tests which help us to get a homogenous fresh concrete mix before casting. Slump test has a direct effect on compressive strength of the hardened concrete as slump test shows the water/cementing material ratio. In other words, when slump is big then water/cement ratio is big and the compressive strength of concrete is low.
The properties (strength, durability, impermeability & workability) of Concrete depend upon the following parameters:
The term ‘grading’ indicates the art of combining various sizes of the particles compositing the aggregate to produce a dense and economic concrete using minimum amount of cement per unit volume for the desired strength. The fundamental principle of grading is that smaller particles fill up the empty spaces in between larger particles. To secure the proper interlocking of various sizes of the aggregate, it is essential that the particle should be angular & shape.
Transit mixer is a truck mounted drum with a capacity to carry up to certain cubic meter concrete at a time.
Concrete is placed at site with the help of concrete pumps. These pumps come in various capacities. These pumps are hydraulically operated with diesel power, to pump up to 100 meters. However, placing at the desired level is our scope, leveling and compacting is to the clients’ scope.
Admixtures are any chemical additive to the concrete mixture that enhances the properties of concrete in the fresh or hardened state. IS1903 99 defines the term admixture as ‘a material other than water, aggregates, hydraulic cement, and fiber reinforcement, used as an ingredient of concrete and added to the batch immediately before or during its mixing’.
In normal use, the admixtures make up less than 5% of the cement weight, and are added to the concrete at the time of batching / mixing.
The most common types of admixtures are :
– Accelerators speed up the hydration (“hardening”) of the concrete.
– Retarders slow the hydration of concrete.
– Air-entertainers add and distribute tiny air bubbles in the concrete
Plasticizers can be used to increase the “workability” of concrete, allowing it be placed more easily, with less compactive effort. Super plasticizers allow a properly designed concrete to flow in place even around congested reinforcing bars. Alternatively, they can be used to reduce the water content of a concrete (water reducers) while maintaining workability. This improves its strength and durability characteristics
Plasticizers are chemical additives added to concrete to increase the workability of concrete. This is done without altering the water cement ratio. The strength of the concrete will not be affected.
After concrete is placed, satisfactory moisture content and temperature (between 50°F and 75°F) must be maintained, a process called curing. Adequate curing is vital to quality concrete.
Curing is the process of controlling the rate and extent of moisture loss from concrete to ensure an uninterrupted hydration of cement after concrete has been placed and finished in its final position. Curing also ensures to maintain an adequate temperature of concrete in its early ages, as this directly affects the rate of hydration of cement and eventually the strength gain of concrete.Curing of concrete must begin as soon as possible after placement & finishing and must continue for a reasonable period of time as per the relevant standards, for the concrete to achieve its desired strength and durability. Uniform temperature should also be maintained throughout the concrete depth to avoid thermal shrinkage cracks. Also protective measures to control moisture loss from the concrete surface are essential to prevent plastic shrinkage cracks.
In a nut shell, curing process is designed primarily to keep the concrete moist by controlling the loss of moisture from the body of concrete, during the given period in which it gains strength.
NO! Restrain masons at the site. Do not force Transit Mixer Operators to add water to ready mixed concrete. Consequences of such actions can be severe. Properly designed ready mixed concrete contains optimum water. Inform the ready mixed concrete supplier if workability (slump) of ready mixed concrete is not as expected. If required, dosing of admixtures along with a small quantity of water would be done by the ready mixed concrete supplier´s technical personnel.
Ready-Mixed Concrete mixes are supplied only after exhaustive laboratory and plant trials. To ensure consistent quality, incoming raw materials are regularly tested. Sampling and testing of ready mixed concrete is done every day as per BIS stipulations. At our Arunachala Ready-Mix Concrete, we invite you to visit our laboratories to witness the process.
A- Mix Concrete can deliver a minimum load size of 3 cubic meters.
Depending on the workability, the Ready-Mixed Concrete might be usable for up to 4 hours.
Standards specify that Ready-Mixed Concrete must be discharged from the transit mixer truck within 2 hours of the time of loading. It is also mandatory to make arrangements at site to ensure that full load of Ready-mixed Concrete is discharged within 30 minutes of arrival on site.
When the ready mixed concrete is transported to the construction site, the ready mixed concrete is pushed deeper into the drum attached to the back of the truck with the help of a spiral blade fitted within the drum. This is achieved by rotating the drum in one direction. This process is known as charging the transit mixer. At the construction site, the drum is rotated in the other direction, which forces the ready mixed concrete out of the drum. This process is known as discharging. The ready mixed concrete may be discharged directly into chutes, pumps or on to conveyor belts.
Pumps are designed to facilitate pumping of ready mixed concrete through the pipeline under high hydraulic pressure. When ready mixed concrete is pushed through the pipeline, it is separated from pipe line wall by a lubricating layer of cement, water and fine aggregates. Ready mixed concrete should have enough cohesiveness and workability for the mix to move easily through pipeline, bends, reducers and hoses
Concrete is used and sold on a cubic volume basis (usually by cubic feet although / some places will sell by cubic meter). When converting between cubic meters / cubic feet /cubic inches use the following conversion factors:
To calculate how much concrete you would need to order to pour a slab use the following formula:
Total cubic ft. of concrete required = *Slab thickness (in ft.) X Slab width (inft.) X Slab length (in ft.)