The Constructor

Properties of Hardened Self Compacting Concrete

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Properties of Hardened Self Compacting Concrete

1. Compressive strength of 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. The in-situ strengths of both types of civil engineering concrete, SCC and  traditional   vibrated concrete were closer to standard cube strengths than those of the housing mixes  again;  this is typical of higher strength concrete. 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). Overall,  we might conclude that the fresh self-compacting properties of the concrete have little effect on the in-situ strengths.

2. Tensile strength

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.

3. Bond strength

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.

4. Modulus of elasticity

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.

5. Freeze/thaw resistance

This property was assessed by loss of ultrasonic pulse velocity (UPV) after daily cycles of 18 years at 30C 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 (t he civil engineering mixtures).

6. Shrinkage and creep

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.

7. Some aspects of durability

Elements of all types of concrete have been left  exposed for future assessment of durability but some preliminary tests have been carried out. 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. Carbonation depths have been measured at one year. The civil mixes  (both SCC and reference) show no  carbonation. 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.

8. Structural performance

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  behavior  of the two concretes in terms of cracking moment, crack width and load-deflection was similar. Read More on Special concretes
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