Self-Compacting Concrete (SCC)

SCC stands for Self-Compacting Concrete or Self Consolidating Concrete. It has a high flowability for which it can spread in the formwork with ease and without any mechanical vibrator. This type of concrete has good flowability, stability & for the use of superplasticizer admixtures such as FOSROC Structuro 202 or BASF MasterEase 3602 gives the concrete a flow of around 550 mm - 650 mm in Flow table test without adding more water.

Some advantage of SCC over normal concrete is stated below:

•          The mix design for any grade of concrete is done with superplasticizer admixture (such as FOSROC Structuro 202 or BASF MasterEase 3602) which gives the concrete the ability for higher flow, greater compacting ability under its own self-weight & without the use of any mechanical vibrator.
•          Due to its flowability, SCC can occupy every corner of its formwork with ease and gives a better finish of the RCC surface than most of the normal RCC casting.
•          As for its property of self-compaction, it is generally preferred over normal concrete where there is a congestion of TMT work and use of mechanical vibrators is restricted. The bonding between the TMT bars & concrete also gets enhanced due to high flowability.
•          The superplasticizer increases the viscosity of concrete which enhances the pump-ability of the concrete.
•          It is more economic than normal concreting due to the fact it is more easily place-able via pump or Transit mixture & less manpower required for compaction, leveling as well as surface finish. It reduces the cost of labours & also increases the casting schedule of the RCC member.
•          Due to the addition of superplasticizer it is less prone to segregation than normal concrete.

Some drawbacks for SSC is:

•          When working with SCC especially when it is going to travel in transit mixture, we have to be very careful and what type of flow range we need at concrete pouring point, cause the flow deceases as time passes, it is generally termed as retention period of concrete. For example: if the flow at batching plant (concrete production) is 600 mm in 3 sec (T₅₀ Sec) and had to travel or wait for an hour then the flow will get low around 500 mm in 4.5 sec (T₅₀ Sec).
•          If the SCC is to be traveled by a transit mixer then fully loading the mixture is not a good idea, as the flowability is higher there is a chance of spillage.
•          The formwork has to be strong enough to withstand the fluid pressure of the concrete, generally for embedded / reusable wall tie (used for holding the aluminium shuttering) has to have a minimum load capacity of 25 N/mm².
•          Concreting with SCC is easier than normal concrete but making an SCC is harder, and care to be taken at batching plant constantly for a steady standard flow of concrete. Temperature can vastly change the standard of SCC for which minor adjustment of admixture dosage is required during a long casting.   
•          Some case of casting requires additional water at pouring point if the retention period has exceeded beyond allowable point to get the required flow, however for SCC it cannot be done as it will de-stabilize the concrete and can lead to segregation or bleeding of concrete.
•      In case of underground structure such as rain water harvesting tank, SCC concrete is not suitable as due to evaporation of water from mix can lead to shrinkage crack, which affects the permeability of the structure.