Properties and benefits of Reactive powder concrete (RPC)

Reactive powder concrete (RPC) stands for the generic name for a class of cementious composite materials which contain superior physical properties, specifically ultra high strength and ductility.

It is formed by mixing fiber reinforced, super plasticized silica fume, cement and quartz sand along with very low water cement ratio. It contains greater compressive strength since quartz sand is applied in place of ordinary aggregate.

Composition of RPC: RPC attains it’s superior properties with a very solid mix containing fine particles and fibers.

1. Low w/cm proportion : 0.16 to 0.24 (as low as 0.13)
2. Type 20M (like type II) Portland cement (no C3A less HoH)
3. Silica fume (25% by weight)
4. Water
5. High dosage of super plasticizer
6. Fine quartz sand (SG = 2.75)
7. Steel fibers (2.5 to 10% by volume) for hardening
8. No rebar necessary

It is cured in steam bath for 48 hours @ 190 degree F (88 degree C) as soon as it is set primarily. It is set under pressure at the molding phase.

Properties of RPC:

Compressive Strength

1. Greater compressive strength as compared to HPC.
2. It is a factor connected with stability of material.
3. Highest compressive strength of RPC is roughly 200 MPa.

Flexural Strength: Plane RPC comprises of extreme flexural strength as compared to HPC (up to 100 mpa). With steel fibers, RPC can attain extreme flexural strength.

Water Absorption: The ratio of water absorption or RPC is very low than HPC. This feature of RPC supports the desired properties of nuclear waste containment materials.

Water penetrability: Water penetrability is reduced in due course of time for all mixtures. 28th day penetrability of RPC is minor than HPC (almost 7 times lower). For water absorption, the application of fibres enhance the penetrability of both types of concrete.

Defiance to chloride ion penetration: It is raised if heat curing is accomplished in concrete. Heat cured RPC demonstrates higher value as compared to normal cured RPC. This characteristic of RPC makes it perfectly fit for being used in nuclear waste containment structures.

Homogeneity: It is enhanced by removing all coarse aggregates. Dry components to be applied in RPC remains under 600 micro meter.

Compactness: Application of pressure prior to and throughout concrete setting period.

Microstructure: Microstructure of the cement hydrate is altered by providing heat treatment throughout curing.

Material Ductility: Material ductility is enhanced through the inclusion of short steel fibres.

Advantages:
1. It has the ability to structurally combat with steel.
2. It has greater stability along with shear capacity that leads to substantial dead load curtailment.
3. RPC is utilized to withstand all but direct primary tensile stress.
4. Superior seismic performance by eliminating inertia load with lighter member.
5. Low and non-interconnected porosity reduces mass transfer, keeping penetration of liquid/gas non-existent.




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Published By

Rajib Dey

www.constructioncost.co

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Segregation of concrete – Causes and Remedies

Segregation means the partition of course materials (cement, sand, aggregates) from other mass. When the water quantity in the concrete mix is increased, the greater sized aggregates are detached thus results in segregation.

Therefore, concrete should be free from segregation as concrete not only gets weak but lack of consistency also brings unwanted properties in the hardened state. The segregation can be avoided with the choice of proper grading and careful handling.

Reasons for segregation :

Carrying concrete mixes for long distance.

Imperfectly proportioned mix where adequate matrix does not exist to unite the aggregates.

Dropping concrete from height places (underground foundation & rafts).

Vibrating concrete for long time.

Segregation is available in two types - Initially (in too dry mixes), the coarse aggregate is segregated or settling down from the rest of the matrix, secondly ( in too wet mixes ), the paste or matrix is detached away from coarse aggregate. In case of segregation, remixing for a short time may transform concrete again homogeneous.

The following precautions should be taken to get rid of concrete segregation :-

The concrete mix should be perfectly designed with best possible quantity of water i.e. not too wet nor too dry.

The proportion of the mix should be correct.

Ensure the concrete is mixed perfectly at the proper speed in a transit mixture for minimum two minutes.

Concrete should not become excessively wet or dry.

Refrain from arranging concrete from long height.

There should be proper transportation of concrete through shortest route.

Air entraining admixture and pozzolanic materials should be used in mix.

Select coarse and fine aggregate with approach specific gravity.

The vibrator should be used for exact time period (not too long or short).

Don’t permit concrete to flow.

The formwork should be firm.

The formwork should not be vibrated.

Video Source: Civil Engineers

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Published By
Rajib Dey
www.constructioncost.co
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Brief overview of concrete mix ratio

If cement is blended with sand, stone/aggregates and water, a paste will be developed and it can be applied to stick the building materials collectively. This paste is known as concrete.

The ration upon which the cement, sand, stones or aggregates are amalgamated, defines the strength of the concrete mix. Depending on these ratios, different types of concrete grades are accessible in the market. These concrete grades range from M10, M20, M30, M35, etc.

“M” denotes “mix”. Mix characterizes concrete with indicated ratios of cement, sand and aggregate. And the number after “M” denotes compressive strength of that concrete mix in N/mm2 after 28 days. As for instance, for M30 grade of concrete mix, its compressive strength after 28 days should have been 30 N/mm2.

Concrete mix ratio table

Given below, the standard chart table that displays different grades of concrete mix design together with their relevant ratios of cement, sand and aggregates required.

It is found that volume of sand is always retained half of that of aggregates in these standard mix designs. These proportions can be estimated and sustained with buckets or some other standard cubes which are easily utilized during the project. It is essential to keep up uniformity in each and every concrete mix produced throughout the entire project.

The site engineer/supervisor should take the responsibility to examine and implement it.

Water content ratio in concrete mix: The strength & adaptability of concrete is mainly dependent on water content. The adaptability of concrete (more fluid) will be increased with the higher quantity of water but it will decrease the concrete strength.

Contrarily, if the amount of water is low, adaptability of water will also be decreased. So, it becomes complicated to arrange such concrete in the structure. Required amount of water may differ for same volume of concrete for different grades of concrete. So, equilibrium should be maintained in the construction site throughout concrete mixing.

Video Source: Civil Engineering

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Published By
Rajib Dey
www.constructioncost.co
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Definition of M20 grade of concrete

In construction, there should be individual strength for each building element.

To maintain the strength of concrete for different elements, various types of concrete grades are required. The strength needed for foundation, beam, slab etc. will be different.

IS 456-2000 has specified the concrete mixes into a number of grades as M10, M15, M20, M25, M30, M35 and M40. In the following construction video tutorial, brief explanation is given on M20 grade of concrete.

In M20, M denotes Mix and 20 refers to the characteristic strength (fck) of that mix i.e. 20mpa. Cement, sand and aggregates are used for mixing in the ratio of 1 : 1.5 : 3. M20 signifies mixture of cement, sand and aggregate which are prepared in such a manner that a cement concrete cube of size 15 cm x 15 cm x 15 cm is formed with characteristic strength (fck) of 20mpa while examining it after being cured for 28 days.

The characteristic strength (fck) signifies the strength under which not over 5% of test results are predictable to fail.

Cement is always calculated with weight. Commonly it is applied in terms of bags. The weight of one bag of cement is 50 kg and it contains a volume of 35 litres (or, 0.035m3). A gauge box is employed for batching of fine and coarse aggregate by volume.

To get more brief information, watch the following video tutorial.

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Published By
Rajib Dey
www.constructioncost.co

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