Uses of Self-Compacting Concrete
Self-compacting Concrete, or Self-Consolidating Concrete, generally called SCC, is a fresh concrete that runs under its own weight and does not want external oscillation to undergo compaction. Constructors use SCC in the building structures where it is troublesome to use vibrators for the consolidation of concrete.
Why is Compaction Needed?
After the liquid or paste concrete is poured in place and should be left to set, it should undergo the compaction process before it starts to harden. Compaction or Consolidation significantly enhances the final strength of concrete and improves bonding with reinforcement. It also increases the abrasion resistance and overall sturdiness of the concrete. Moreover, this process decreases the permeability of concrete and helps to minimize its shrinkage and creep characteristics.
What is SCC?
The SCC or Self-compacting concrete is a form of concrete that can flow under its weight, and that does not need to go through a separate compaction process to fill and flow through heavy reinforcement areas.
SCC has more or less equivalent cement binders and water ratios as the standard concrete mix. However, the variations in the mix cause the SCC to produce a higher strength without vibrating the concrete by forming better bonds between the hardened paste and the aggregates and reinforcements. You can pour SCC into structures more than five meters tall because due to its characteristics the aggregates will not get segregated. The self-compacting concrete can also be poured faster than the regular mix.
What are the Materials in SCC Mix?
To give the concrete paste diverse properties, somewhat different materials ratios are used in the SCC mix. These are as follows.
Cement: Grade 43 cement is used in self-compacting concrete, which must meet the physical properties according to IS:8112 code. The following table will give a better understanding of the cement used in SCC
| Physical Property | Ratios |
|---|---|
| Fineness (Cement will retain on 90-mm sieve) | 8-10 mm |
| Normal Consistency | 28% |
| Initial setting time (minutes) | 75 (30 Min) |
| Final setting time (minutes) | 215 (600 Max) |
| Crushing strength 3-days later | 23 MPa (22 Min) |
| Crushing strength 7-days later | 36 MPa (33 Min) |
| Crushing strength 28 days later | 45 MPa (43 Min) |
Aggregates
Fine aggregates in the SCC mix should not exceed 4.75mm diameter and the stone chips or coarse aggregates should be 16mm maximum in size. According to IS:383-1970 code the ratios should be set to code.
| Physical Tests | Coarse Aggregate | Fine Aggregate |
|---|---|---|
| Specific gravity | 2.67 | 2.66 |
| Fineness modulus | 6.86 | 2.32 |
| Bulk density | 1540 (kg/m3) | 1780 (kg/m3) |
Advantages of SCC:
- SCC always consolidates under own weight
- Reduced amount of water is needed in SCC mix
- Placing of concrete is easier and simpler with SCC
- It flows excellently around heavy reinforcements
- Finishing is much more aesthetic
- Higher strength than other types of concrete
- Better consistency in flow and slump characteristics
- Many reduced expenses in labor and equipment
- Less time to set the concrete
- Compared to normal concrete, much less quantity consumption
What Affects Self-Compacting Concrete - While the self-consolidating concrete is great for some uses, the constructor must remember that it can be affected by several factors and thus should not be used indiscriminately. The circumstances that influence the quality and performance of SCC are:
- Weather temperature can cause the quality to change in SCC
- Since SCC has a shorter setting time, a long haul can reduce the following characteristic of the mix
- Similarly, delays on the job site will reduce concrete design performance
- Adding water to semi-hardened SCC will not return its flowability to default and instead can cause strength issues
Special Attentions for SCC - Self-compacting concrete can be great for your building, but you need to be mindful of the following points while utilizing SCC:
- Loading mixers to their full capacity is not feasible for SCC. Since it has greater flowability than other types of mixes, spillages can occur easily, bringing contamination and environmental hazards.
- The fluid SCC mix exerts more pressure than normal concrete, so the framework must be built accordingly to withstand the load.
- In the case of building taller structures, instead of pumping it up, carrying it in lifts may be more appropriate.
- Trained and learned crews are needed to produce SCC, while unskilled laborers are fine making a standard concrete.
- While saving on the tools and labors, using SCC can add some extra costs in some cases, varying upon ready-mix providers.
Also, keep in mind that even though SCC does not require vibrating, in case of very congested reinforcements using a little vibration may be necessary.