Ready-mix concrete is concrete that is manufactured in a factory or
batching plant according to a set recipe, and then delivered to a work site by
truck mounted in transit mixers.
This results in a precise mixture, allowing specialty concrete mixture
to be developed and implemented on construction sites. The first ready-mix
factory was built in the 1930s, but the industry did not begin to expand
significantly until the 1960s, and it has continued to grow since then.
Ready-mix concrete is often preferred over on-site concrete mixing
because of the precision of the mixture and reduced work site confusion.
Ready-mix concrete, or RMC as it is popularly called, refers to
concrete that is specifically manufactured for delivery to the customer's
construction site in a freshly mixed and plastic or unhardened state. Concrete
itself is a mixture of Portland cement, water and aggregates comprising sand
and gravel or crushed stone. Ready-mix concrete is bought and sold by volume -
usually expressed in cubic meters (cubic yards in the US).
Advantages of Ready Mixed Concrete:
1.Quality assured concrete:- Concrete is produced under controlled
conditions using consistent quality of raw material.
2.High speed of construction- Speed of construction can be vary fast in
case RMC is used.
3.Reduction in cement consumption by 10 – 12 % due to better handling
and proper mixing. Further reduction is possible if mineral admixtures or
cementitious materials are used.
4.Versatility in uses and methods of placing: The mix design of the
concrete can be tailor made to suit the placing methods of the contractor.
5.Since ready mixed concrete (RMC) uses bulk cement instead of bagged
cement, dust pollution will be reduced and cement will be saved.
5.Conservation of energy and resources because of saving of cement.
6.Environment pollution is reduced due to less production of cement.
7.With better durability of structure, their overall service life
increase and there is saving in life-cycle cost.
8.Eliminating or minimizing human error and reduction in dependency on
labour.
9.Timely deliveries in large as well as small pours.
10.No need for space for storing the materials like coarse and fine
aggregate, cement, water and admixtures.
11.No delay due to site based batching plant erection/ dismantling; no
equipment to hire; no depreciation of costs.
12.Reduced noise and air pollution; less consumption of petrol and
diesel and less time loss to business.
Disadvantages of ready-mix concrete:
1.The materials are batched at a central plant, and the mixing begins
at that plant, so the traveling time from the plant to the site is critical
over longer distances. Some sites are just too far away, however the use of
admixtures like retarder can be added.
2.Furthermore, access roads and site access have to be able to carry
the greater weight of the ready-mix truck plus load. (Green concrete is approx.
2.5 tonne per m³.) This problem can be overcome by utilizing so-called 'mini
mix' companies which use smaller 4m³ capacity mixers able to reach
more-restricted sites.
3.Concrete's limited time span between mixing and curing means that
ready-mix should be placed within 210 minutes of batching at the plant. Modern
admixtures can modify that time span precisely, however, so the amount and type
of admixture added to the mix is very important.
4.As the Ready Mixed Concrete is not available for placement
immediately after preparation of concrete mix, loss of workability occurs. In
addition, there are chances of setting of concrete if transit time involved is
more. Therefore, generally admixture like plasticisers/ super plasticisers and
retarders are used. Addition of retarders may delay the setting time
substantially which may cause placement problems. In addition, it may also
affect the strength of concrete. Therefore, it is necessary that the admixtures
i.e. plasticisers and super plasticisers/ retarders used in Ready Mixed
Concrete are properly tested for their suitability with the concrete. In case
loss of strength is observed, the characteristic strength may have to be
enhanced so that after loss of strength, required characteristic strength is
available.
