• Computers and Concrete
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• v.5 no.2
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• pp.101-116
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• 2008

The microscopic determination of air void characteristics in hardened concrete, defined in EN 480-11 as the linear-traverse method, is an extremely time-consuming and tedious task. Over past decades, several researchers have proposed relatively expensive mechanical automated systems which could replace the human operator in this procedure. Recently, the appearance of new high-resolution flatbed scanners has made it possible for the procedure to be automated in a fully-computerized and thus cost-effective way. The results of our work indicate the high sensitivity of such image analysis automated systems firstly to the quality of sample surface preparation, secondly to the selection of the air void threshold value, and finally to the selection of the probe system. However, it can be concluded that in case of careful validation and the use of the approach which is proposed in the paper, such automated systems can give very good estimate of the air void system parameters, defined in EN 480-11. The amount of time saved by using such a procedure is immense, and there is also the possibility of using alternative stereological methods to assess other, perhaps also important, characteristics of air void system in hardened concrete.

• International Journal of Highway Engineering
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• v.16 no.6
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• pp.27-37
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• 2014

PURPOSES : The purpose of this study is to verify the causes of surface scaling at L-shoulder concrete structure. METHODS : From the literature reviews, mechanisms of frost damage were studied and material properties including strength, air void, spacing factor and scaling resistance of L-shoulder concrete structure were analyzed using core specimens taken by real fields. RESULTS : The spacing factor of air void has relatively high correlation of surface conditions : lower spacing factor at good surfacing condition and vice versa. If the compressive strength is high, even thought spacing factor does not reach the threshold value of reasonable durability, the surface scaling resistance shows higher value. Based on these test results, the compressive strength also provide positive effect on the surface scaling resistance. CONCLUSIONS : The main causes of surface scaling of L-shoulder could be summarized as unsuitable aid void amount and poor quality of air void structure. Secondly, although the compressive strength is not the governing factor of durability, but it shows the positive effect on the surface scaling resistance.

• The KSFM Journal of Fluid Machinery
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• v.6 no.3 s.20
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• pp.58-63
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• 2003

The performance of turbo pump drops rapidly and it gets into break-down when the void fraction reaches above the threshold value because the impeller flow passage is choked up with air bubbles. Phenomenological understanding of break-down and pumping recovery mechanisms under air-water two-phase flow conditions are therefore important for pump designers and essential assignment for researchers. In this paper, we investigated the characteristics of break-down and pumping recovery due to entrained air occurring inside a screw-type centrifugal pump which has a wide flow passage mainly through the findings of suction and discharge pressures, rotational speed, flow rate measurements and visualization.