FAQ

What is Concrete?

Concrete is a composite building material made from the combination of aggregate and a cement binder. The most common form of concrete consists of Cement, mineral aggregates (generally gravel and sand) and water.

What are the roles of Major ingredients of concrete?

Cement- reacts with water to form “glue”.
Water- reacts with cement, the amount also determines strength
Aggregate (crushed rock, sand, gravel) – makes concrete stronger, more durable, and less costly
A properly proportioned concrete mixture will possess the desired workability for the fresh concrete and the required durability and strength for the hardened concrete. Typically, a mixture is by volume about 10 to 15 percent cement, 60 to 75 percent aggregates and 15 to 20 percent water. Entrained air bubbles in many concrete mixtures may also take up another 5 to 8 percent.

What is Ready-Mix Concrete?

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.

How is Ready-Mix Concrete better than site mix concrete?

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.

What is Concrete Mix – Design?

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.

What is grade of concrete?

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 2900 psi ( pound per square inch).

What tests are conducted to determine the strength of concrete?

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.

What tests are conducted to determine the strength of concrete?

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.

What is meant by slump?

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’.

What is the Slump test of Fresh Concrete?

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 to
(ASTM  C143-78). 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.

What are the factors that control properties of Concrete?

The properties (strength, durability, impermeability & workability) of Concrete depend upon the following parameters:

  • Grading of aggregates
  • Moisture Content of aggregates.
  • Water/Cement ratio
  • Proportioning of various ingredients of Concrete.
  • Method of mixing.
  • Placing & Compaction of Concrete
  • Curing of Concrete

What is aggregate gradation?

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 & sharp.

To calculate how much concrete you would need to order to pour a slab use the following formula:
*Slab thickness (in ft.) X Slab width (in ft.) X Slab length (in ft.) = Total cubic ft. of concrete

 Required.

What is a transit mixer?

Transit mixer is a truck mounted drum with a capacity to carry up to certain cubic meter concrete at a time.

How is concrete placed at site?

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.

What are the admixtures?

Admixtures are any chemical additive to the concrete mixture that enhances the properties of concrete in the fresh or hardened state. ACI 116R [2000] defines the term admixture as ‘a material other than water, aggregates, hydraulic cement, and fiber reinforcement, used as an ingredient of concrete or mortar, 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

What are plasticizers? Will the strength of concrete be affected by the addition of these plasticizers?

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.

What is concrete curing?

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.

Why curing is required to 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 or mortars.

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.

Can water be added to the ready mixed concrete at the site?

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.

How does one ascertain the quality of Ready-Mixed Concrete?

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 Codal stipulations. At our Shah Cement Ready-Mix Concrete, we invite you to visit our laboratories to witness the process.

What is the minimum load size Shah Cement Ready Mix Concrete can deliver?

Shah Cement Ready Mix Concrete can deliver a minimum load size of 5.5 cubic meters.

What is the duration for which the Ready-Mixed Concrete remains usable?

Depending on the workability, the Ready-Mixed Concrete might be usable for up to 4 hours.

Is there any time limit for unloading of Ready-Mix Concrete at site?

International 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.

How does a transit mixer work?

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.

How do pumps work?

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

How to Calculate Cubic Volume of Concrete?

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 yards / cubic feet cubic inches use the following conversion factors:

  • 1 cubic meter ( m3)  =  35.315 cubic feet (cft)

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.)

What is Reinforced Cement Concrete?

Reinforced concrete is concrete in which reinforcement bars (‘rebars’), grids, plates or fibers have been incorporated to strengthen the concrete in tension.
Concrete is strong in compression but weak in tension, thus adding reinforcement increases the strength in tension. For a strong, ductile & durable construction, the reinforcement shall have the following properties:

  1. High Strength
  2. High Tensile Strain
  3. Good bond to the concrete
  4. Thermal compatibility
  5. Durability in the concrete environment.

Reinforcement steel is higher strength bar but concrete is same, so is that building safe?

There is no benefit in using high strength steel with poor quality concrete.  It is essential that concrete & steel will fail together. Steel strength are higher but concrete strength is poor it would cause sudden failure in the section.