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.




Read more

~~~~~~~~~~~~~~~~~~~~~~~~

Published By

Rajib Dey

www.constructioncost.co

~~~~~~~~~~~~~~~~~~~~~~~~

Impact of impurities in water on concrete properties

If the water applied for concrete preparation contain impurities, the properties of concrete is influenced in the following manner:

a) The strength & longevity of concrete is decreased because of the existence of the impurities in the mixing water. It is found that water with extreme amount of dissolved salts weakens the compressive strength by 10 to 30% as compared to potable water.
b) The setting time of cement is modified. Existence of Zinc chlorides delays the setting of concrete to significantly so that no strength test can be done at 2 and 3 days.

Contrary, the existence of calcium chloride speeds up the setting and hardening.
c) Existence of extreme chlorides leads to dampness, surface efflorescence & raise the corrosion of reinforcing steel.
d) Existence of algae in water decreases the bond among aggregate & comet paste & as a result the strength of concrete is reduced significantly.

e) Existence of sugar up to 0.15% by weight of cement delays the setting of cement and the early strength is decreased. When the quantity of sugar is raised to 0.2% by weight of cement ,setting is expedited.
f) The existence of vegetable oils provides detrimental effect on the concrete strength, specifically at later ages.

Name of Impurities - Allowable limit
1.Organic matter - 200 mg/lit
2.Inorganic matter - 3000 mg/lit
3.Sulfates ( as SO2 ) - 400 mg/lit
4.Chlorides (as Cl)
a) For plain concrete - 2000 mg/lit
b) For R. C. C. - 500 mg/lit
5.Suspended matter - 2000 mg/lit

Read more

~~~~~~~~~~~~~~~~~~~~~~~~
Published By
Rajib Dey
www.constructioncost.co
~~~~~~~~~~~~~~~~~~~~~~~~

Benefits and drawbacks of air entrained concrete

Air entrained concrete is formed by providing little air bubbles into concrete is called air entrainment. Air entrainment is performed with the use of air entraining Portland cement or air entraining agents like admixture.

The amount of air in such concrete is normally kept among four to seven percent of the volume of concrete.

Various types of methods like galvanometric method, volumetric method and pressure method are used to work out the concrete volume. The air bubbles mitigate internal pressure on the concrete by arranging chambers for water to be extended at the time of getting freezed.

Method - Air in concrete in integrated in the following ways:

 By utilizing gas forming materials like aluminium powder, zinc powder and hydrogen peroxide.  With the application of surface active agents that minimizes surface tension. These may contain natural wood resins and their soaps, animal or vegetable fats or oils, alkali salts of sulfonated or sulphated organic compounds.  With the help of cement dispersing agents.

Benefits - Given below, some of the benefits of air entrained concrete:

1. Workability of concrete is raised significantly.
2. The impact of freezing and thawing is reduced with air entraining agent.
3. Bleeding, segregation and laitance in concrete are decreased.
4. Entrained air makes the sulphate repelling strength of concrete.
5. Minimizes the chance of shrinkage and crack development in the concrete surface.

Drawbacks - Given below, some of the drawbacks of air entrained concrete:

a. The strength of concrete is reduced.
b. Air entraining agent can raise the porosity of concrete and consequently the unit weight is decreased.
c. Air-entrainment in concrete should not be performed if the site control is not superior because the air entrained in a concrete differs with the alteration in sand grading, errors in proportioning and workability of the mix and temperatures.



Read more

~~~~~~~~~~~~~~~~~~~~~~~~
Published By
Rajib Dey
www.constructioncost.co
~~~~~~~~~~~~~~~~~~~~~~~~