An investigation of the effect of fly ash to the porosity of concretes using image analysis technique

Although air void or the porosity is one of the most important factors that affect the performance of hardened concretes, it is generally not considered in the design and analysis because of the difficulties of its quantification; for example, the air void content determination using ASTM C457 method proved to be expensive, time consuming and tedious. This paper presents an efficient and inexpensive technique to measure air void content in concretes through the use of semi-automated image analysis software. One of the main advantages of this software is that it provides image acquisition and documentation for each analysis. Plain concrete and fly ash concretes have been used for the air content measurement study. Three methods of curing of concretes namely air curing, sheet curing and pond curing have been used and the specimens have been tested at the ages of 3 days, 7 days and 28 days. A total of 108 specimens have been analysed using the image analysis technique. The study has shown that in both plain and fly ash concretes the void ratio decreases with the extended curing period. The plain and fly ash concretes exposed to pond curing for a period of twenty eight days have shown 60% and 58% less air voids respectively than their air cured counterparts. The significance of the fly ash additive has become evident from this investigation as there have been reductions in air voids after the normal curing period as follows: 29% in air cured specimens and 25% in pond cured specimens. The details of the testing methods and analysis of air voids are explained in detail in the paper.