2.5 Conclusions

percentages. The greater number of fractured aggregate in the SCC specimens was another indication of a better bonding between aggregate and cement paste.

Tomographic images of SCC (top row) and NC (bottom row) specimens after being tested in compression (from

The air entrainment was reduced in the SCC mix with the addition of finely divided mineral admixtures, such as fly ash and silica fume. Samples with the dimensions of 80 80 12 mm were acquired from both types of concretes at w/cm ratios of 0.30, 0.45, and 0.60 to study their air-entrained properties. Air voids larger than 200 microns only were considered for the analysis. The measurements showed that SCC samples exhibited half the amount of air voids compared to NC. Visual analyses of the "air voids" sizes and shapes revealed that SCC had smaller and more round-shaped voids than NC which presented slightly larger and

Moreover, while the air voids in the SCC appeared more clustered in certain areas of the cut specimen, the voids in NC were relatively well dispersed in the

2.4 Evaluation of air void content

left to right: top, middle, and bottom of specimen).

Compressive Strength of Concrete

Figure 3.

Figure 4.

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irregular shaped voids (by 15–20%) (Figure 4).

Distribution of air voids (white spots) in: (a) NC and (b) SCC.

This research verified that SCC achieved self-compactability and adequate flow under its own weight, without external vibration or compaction based on the mix proportion parameters and the materials used. The study also showed that splitting tensile and compressive strengths in SCC were higher than those of normal vibrated concrete due to the addition of chemical and mineral admixtures. Compressive strength had an average increase of over 60%, whereas the splitting tensile strength showed a 30% increase. The ratio between the splitting and compressive strength was similar to values found in the literature. Also, a better bonding between aggregate and cement paste was achieved in SCC due to the use of chemical and mineral admixtures, as the material has shown smaller aggregate-matrix interface microcracks than normal concrete. This characteristic affected both the splitting tensile and compressive strengths. Another indicator of the stronger aggregate-paste bonding was the greater percentage of the fractured aggregate in SCC (20–25%) compared to the 10% for normal concrete. Moreover, when compared to NC, the number of air voids in SCC was lower and they appeared relatively smaller and more rounded. These factors have contributed as well to the increase in strength of the SCC.
