Know what is Self-Compacting Concrete

Self-compacting concrete (SCC) is a flowing concrete mixture that is able to consolidate under its own weight. The highly fluid nature of SCC makes it suitable for placing in difficult conditions and in sections with congested  reinforcement. Use of SCC can also help to minimize hearing-related damages on the worksite that are induced by vibration of concrete. Another advantage of SCC is that the time required to place large sections is considerably reduced.

Self Compacting Concrete has to be designed and tested before it is produced and used for construction.

During SCC evaluation, the local materials such as cement, granules and sand and equipments have to be tested to find out the right concrete mix proportions and mixing times suitable for the element to be cast. Various kinds of fillers can result in different strength, shrinkage and creep but shrinkage and creep will usually not be higher than for traditional vibrated concrete.

Following are the properties of hardened self compacting concrete:

In all SCC mixes compressive strengths of standard cube specimens were comparable to those of traditional vibrated concrete made with similar water-cement ratios if anything strengths were higher. In-situ strengths of SCC are similar to those of traditional vibrated concrete, indeed somewhat higher when limestone powder is used as filler, probably because of a densifying mechanism and the observed lower susceptibility to imperfect curing, both attribute to this type of filler. In vertical element, in-situ strengths of both SCC and traditional vibrated concrete are higher at the bottom than at the top, vibration of in-situ strengths, for both types of concrete is much lower in horizontal elements, in this case the beams. These observations are characteristic of traditional vibrated concrete. The in-situ strengths of elements cast and cured outdoors in winter (the beams), whether SCC or conventional, were lower than those cast indoors at the same time (the columns).

Tensile strength was assessed indirectly by the splitting test on cylinders. For SCC, both the tensile strengths themselves and the relationships between tensile and compressive strengths were of a similar order to those of traditional vibrated concrete.

The strength of the bond between concrete and reinforcement was assessed by pullout tests, using deformed reinforcing steel of two different diameters, embedded in concrete prisms. For both civil engineering and housing categories, the SCC bond strengths, related to the standard compressive strengths, were higher than those of the reference concrete were.

Results available indicate that the relationships between static modulus of elasticity and compressive strengths were similar for SCC and the reference mixes. A relationship in the form of E/ (fc) 0.5 has been widely reported, and all values of this ratio were close to the one recommended by ACT for structural calculations for normal weight

traditional vibrated concrete. 

This property was assessed by loss of ultrasonic pulse velocity (UPV) after daily cycles of 18 years at o 30 C and 66 hours at room temperature. No significant loss of UPV has been observed after 150 cycles for the SCC or reference higher strength concrete.

None of the results obtained indicates that the shrinkage and the creep of the SCC mixes were significantly greater than those of traditional vibrated concrete.

The permeability of the concrete, a recognized indicator of likely durability, has been examined by measuring the water absorption of near surface concrete. The results suggest that in the SCC mixes, the near surface concrete was denser and more resistant to water ingress than in the reference mixes.

The evidence in hand and data from other source suggest that the durability performance of SCC is likely to be equal or better than that of traditional vibrated concrete.

The structural performance of the concrete was assessed by loading the full-size reinforced columns and beams to failure. For the columns, the actual failure load exceeded the calculated failure load for both types of concrete (SCC and traditional vibrated concrete). For the beams the only available comparison is between SCC and traditional vibrated concrete in the civil engineering category. Here the behaviour of the two concretes in terms of cracking moment, crack width and load-deflection was similar.

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