Pros and Cons of ready-mix concrete

Ready-mix concrete belongs to a concrete that is formed in a batch plant, on the basis of a predefined engineered mix design. Ready-mix concrete is generally supplied in two ways i.e. the barrel truck or in–transit mixers.

This type of truck supplies concrete in a plastic state to the site. And the volumetric concrete mixer. It supplies the ready mix in a dry state and then blendes the concrete on site.

Given below some pros and cons of ready-mix concrete :-

Pros of ready-mix concrete:

a. With Ready Mix Concrete (RMC), the construction process becomes fast with programmed delivery at site, automated operation with subsequent economy.

b. The costs of labor and site supervision are decreased significantly.

c. RMC maintains uniformity in quality with perfect & computerized control of sand aggregates and water according to mix designs.

d. Formation of RMC facilitates reducing cement wastage because of mass handling.

e. While producing RMC, no pollution occurs.

f. By using RMC in project, project time is curtailed significantly and it leads to huge savings in all phases.

g. Perfect control and economy in applying raw material leads to saving of natural resources.

Cons of Ready-Mix Concrete

Following are the cons of ready-mix concrete:

1. The materials are batched at a main plant, and the mixing starts at that very plant. So the transition time from the plant to the site covers longer distances and becomes complicated. Some sites locate at too remote distance, which may cause risk for ready mix concrete to be useless owing to setting.

2. It will create extra road traffic. Normally, Ready Mix Trucks are bigger in size and may take huge space in the road that will obstruct other traffic. Besides, access roads and site access should have the capacity to bear the heavier weight of the ready-mix truck plus load. (Green concrete is approx. 2.5 tonne per m³.) This issue can be resolved by using so-called ‘mini mix’ companies which employ smaller 4m³ capacity mixers to visit more-restricted sites.

3. Concrete’s constrained time span among mixing and curing signifies that ready-mix should be arranged within 210 minutes of batching at the plant. The time span can be rectified with modern admixtures perfectly, though, the amount and type of admixture that is included with the mix is very crucial.

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Published By

Rajib Dey

www.constructioncost.co

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How batching of concrete is done

Concrete is a multipurpose, long-lasting, eco-friendly, and inexpensive material as well as globally recognized construction material. To produce superior quality concrete, the components of concrete should be calculated properly and perfectly. Once mix design is set, the initial task should be batching materials.

Batching of concrete stands for the method of estimating and mixing necessary concrete ingredients both with weight or volume according to the mix design and implanting them into a mixture to form a consistent quality of concrete.

By perfectly computing all the material applied in the concrete formation, it becomes possible to maintain consistency of proportions in all consequent batches.

Why Batching of Concrete is Important?

Usually, following three types of batching are undertaken for concrete components:

01. Random Volumetric Batching: Batching devoid of any control on the size and shapes of applied containers leads to big errors and deviations like utilizing “ghamellas” i.e. – by tallying numbers of ghamellas. This method is totally unscientific, unrefined and should not be recommended even for a small project.

02. Volume Batching of Concrete: Volume batching of concrete is accomplished with the use of measurement boxes, locally named “farmas or gauge boxes”. Concrete components like aggregates ( Kapachi +Sand) and cement is calculated with farmas or gauge boxes and proper precaution should be maintained to ensure that the farmas or gauge boxes are filled excessively. To calculate the quantity of water, the water meter should be utilized when batching or use cans of water contain fixed volume.

03. Weigh Batching of Concrete: Weigh batching of concrete is accomplished with the use of a weigh batch or the weighing system on the batching plant. On big projects, automatic batching plants are set up to facilitate optimizing quality and uniformity.

Water is very vital material and therefore, maximum water should be used for batching. If the quantity of water is less, the functionality of concrete will be hampered whereas surplus water will minimize the strength of concrete. Water should be computed perfectly in litres.

The selection of batching method is based on the size of job, production rate and standards of batching performance.

Usually batching is performed with volume. Precision in batching is very crucial. It is better to perform weigh batching instead of volume batching. Volume batching is mostly effective where weigh batching is not possible. It is always recommended to incur additional cost for it, because in long term, it saves huge costs.

Note: The quantity of cement should also be calculated by maintaining the precision of ± 2 percent and the quantity of aggregates, admixtures and water should be calculated with a precision of ± 3 percent.

Article Source: gharpedia.com

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Published By

Rajib Dey

www.constructioncost.co

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On site demonstration of mixing and placing concrete

In this construction video tutorial you can get live demonstration of blending and positioning of concrete in the jobsite for slab or road.

Mixing: Mixing of concrete is one of the most crucial factors for obtaining good final properties and for this purpose proper equipment should be utilized.

So, it is suggested to employ ready-mixed concrete to get the best result. Mixing allocates the aggregate uniformly during the cement paste and it makes sure that all of the cement is completely saturated in water, and eliminates large air voids.

Besides, mixing separates agglomerated clusters of cement particles and facilitates air entraining admixtures to produce the perfect air void system. Undermixing can produce large flaws and therefore leads to poor strength, whereas overmixing consumes time and energy and can demolish entrained air voids. If the workability is lower, the more mixing energy and mixing time is necessary.

Placing: As soon as the concrete is blended sufficiently, it should be placed into the formwork to determine its final position and shape. If it is required to reinforce the concrete, the rebar should have been placed properly in order that the concrete can flow around it.

If the concrete mixing truck is available adjacent to the site, then the concrete should be directly poured into the forms. If it becomes difficult, the concrete is transmitted in buckets through a crane or wheelbarrow.

If it is impossible because of the necessary distance or the size of the job, the fresh concrete has to be pumped via a system of pipes or hoses to the site with the special concrete pumps. Concrete that is to be pumped contains more severe needs for workability.

If the concrete gets too dry, it will not pump properly, whereas if it gets too wet it will have a tendency to segregate. Segregation may also happen if the concrete is poured into the formwork too rapidly, because larger aggregate particles will be subject to be pushed downward.

In slab construction, the placing has to be initiated along the perimeter at one end of the work with each batch arranged against transmitted concrete earlier. It is suggested not to dump the concrete in independent piles and then level and work them jointly; nor should it be placed in large piles and carried horizontally into final position.

Watch the following video for more details.

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Published By

Rajib Dey

www.constructioncost.co

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Variation among Plastering and Pointing

Plastering: Plastering is the process for using mortar coats on the exterior of walls, columns, ceiling to provide a sleek finish. Mortar that is utilized in plastering may range from lime mortar, cement mortar or lime-cement mortar. Lime mortar that is utilized should contain fat lime to sand ratio of 1 : 3 or 1 : 4. If hydraulic lime is applied, it’s mix ratio (lime: sand) is 1 : 2. Cement mortar of 1 : 4 or 1 : 6 mix is mostly utilized for plastering, richer mix is applied for outside walls. Lime-cement mortar is the combination of lime mortar and cement mortar in the ratio of (cement : lime : sand) 1 : 1 : 6 or 1 : 1 : 8 or 1 : 2 : 8. Lime-cement mortar can save significant plastering cost.

Lime mortar is generally applied in 3 coats whereas cement mortar is used in two or three coats toward the stone and brick masonry. Cement mortar is used in two or three coats toward concrete surfaces.

Most often, one coat of cement mortar is used for concrete building blocks.

The first coat is useful for attaining level surface. The final coat produces smooth surface. When three coats are applied, second coat is called floating coat. The average density of first coat is 10 to 15 mm. The density of middle coat is 6–8 mm. The density of final coat is just 2 to 3 mm. When single coat is applied, the density remains among 6 to 12 mm. Such coats are useful for concrete surfaces not uncovered to rain.

Pointing: In some cases, special mortar finishing work is applied to the uncovered joints in place of providing plaster to the whole surface of the masonry. It is known as pointing. It comprises of slanting the joints to a depth of 10 mm to 20 mm and stuffing it with richer mortar mixes. Toward lime mortar, the ratio of pointing mix is 1 : 2 and for cement mortar pointing mix is applied in the ratio of 1 : 3. Pointing is mostly suitable for stone masonry as stones contain eye-catching colors and strong resistance power against water penetration. Pointing makes weaker part of masonry (i.e. to joints) more accurate and it enhances the aesthetic view of the masonry.

Given below, some points of variations among plastering and pointing.

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Published By

Rajib Dey

www.constructioncost.co

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