What is Self Consolidating Concrete?
Self Consolidating Concrete (SCC) is an innovative concrete that does not require vibration for placing and compaction. It is able to flow under its own weight, completely filling formwork and achieving full compaction, even in the presence of congested reinforcement. The hardened concrete is dense, homogeneous and has the same engineering properties and durability as traditional vibrated fully compacted concrete.
SCC shall be supplied by a competent concrete producer with a record of successfully producing this type of concrete at considerable volume and with high consistency.
What are the constituent materials of Self Consolidating Concrete?
The constituent materials for SCC are the same as those used in traditional vibrated concrete conforming to EN 206-1.
To achieve these requirements the control of the constituent materials needs to be increased and the tolerable variations restricted, so that daily production of SCC is within the conformity criteria without the need to test and/or adjust every batch.
What are the procedures for testing SCC Plasticity?
Slump-Flow Test: Test that aims at investigating the filling ability of SCC. It measures two parameters: flow spread and flow time T50 (optional). The former indicates the free, unrestricted deformability and the latter indicates the rate of deformation within a defined flow distance.
Measuring the largest diameter of the flow and the one
perpendicular to it.
L-Box, U-Box and J-Ring: Tests that aims at investigating the passing ability of SCC. It measures the reached height of fresh SCC after passing through the specified gaps of steel bars and flowing within a defined flow distance. With this reached height, the passing or blocking behavior of SCC can be estimated.
V-Funnel: The V-Funnel flow time is the period a defined volume of SCC needs to pass a narrow opening and gives an indication of the filling ability of SCC provided that blocking and/or segregation does not take place: the flow time of the V-funnel test is to some degree related to the plastic viscosity.
Column Test/Penetration Test: The test aims at investigating the resistance of SCC to segregation by penetrating a cylinder with a given weight into the fresh SCC sample. If the SCC has poor resistance to segregation, the cylinder will penetrate deeper due to the less amount of aggregate in the upper layer of the sample. Therefore the penetration depth indicates whether the SCC is stable or not.
What are the tests requirements for Self Consolidating Concrete?
|Laboratory tests||Field Tests|
|Slump-flow by Abrams Cone||600 – 750 mm||550 – 750 mm|
|T500mm slump flow by Abrams Cone||3 – 6 sec||3 – 10 sec|
|V-Funnel||6 – 25 sec||N.A.|
|5 minute V-Funnel||< 3 sec||N.A.|
|L-Box (3 bars)||> 0.80||N.A.|
Concrete specimens shall be moulded in a single layer without rodding and tapping.
Slump flow and VSI testing shall be performed as outlined in ASTM C 1611/C 1611M
SCC exerts greater formwork pressure than normal concrete because it generally takes a greater period of time for its thixotropy to develop “self-supporting” structure in the fresh material. This self-support occurs much earlier than initial set and is related to fresh concrete rheological behavior.
Formwork pressure can be measured by using pressure sensors mounted in formwork. Laboratory studies using PVC test columns have proven to be convenient and reliable methods for characterizing SCC behavior.
A better understanding of formwork pressure will lead to improved versions of formwork pressure models. Several formwork pressure models have been developed, and one common element is that all of the models require testing the candidate SCC and obtaining the value of a representative parameter to describe rheology, stiffening, or gelation. Such models represent great opportunity to improve prediction of formwork pressures in the field, allowing faster pour rates with greater confidence. These advances will make possible more economical construction with SCC.