Field and laboratory validation of the sequential air method

Experimental Study on the Stability and Distribution of Air Voids in Fresh Fly Ash Concrete

“…A low SAM number indicates a low spacing of air voids in concrete. From a conservative perspective, a SAM number equal to or below 0.2 is desired to achieve a spacing factor no larger than 0.2 mm [ 26 , 27 ]. At 0 min, all the fly ash concrete mixtures had a similar air content of 6 ± 1%, while the SAM number showed a relatively large difference, ranging from 0.07 to 0.27, reflecting the various qualities of the air void system.…”

“…However, this test is still conducted on hardened concrete, which is time-consuming. Both lab and field investigations have validated that an SAM number no greater than 0.2 for fresh concrete can be used to predict a spacing factor of 0.2 mm or less, which could ensure that the concrete has enough freeze–thaw resistance [ 26 , 27 ]. Glinicki and Zielinski [ 62 ] showed that a satisfactory air void system, i.e., spacing factor smaller than 0.2 mm, was obtained for concrete containing two types of circulating fluidized bed combustion fly ash immediately after mixing.…”

“…Figure 8 plots the correlation between SAM number and air content of fresh concrete at the different sampling times of 25, 50, and 75 min. Previous studies showed that a higher air content could result in a lower spacing factor based on the ASTM C457 test on hardened concrete [ 27 ]. This study showed that a higher air content tended to cause a lower SAM number and, thus, a lower spacing of air voids.…”

“…Studies have shown that air voids of different sizes in fresh concrete respond differently to sequential pressures: air voids no larger than 0.2 mm dissolved in solutions under the pressure, while air voids larger than 0.2 mm were just compressed under the pressure and then returned to their original size, so the size and spacing of air voids could be indirectly estimated by applying different pressures [ 24 , 26 ]. Both laboratory and field tests have proved that a SAM number of 0.2 or below could predict a spacing factor of 0.2 mm or below [ 26 , 27 ].…”

“…Compared with the AVA, the SAM is not expensive and is easily performed in the field. More importantly, both laboratory and field studies have proved that SAM number had a good correlation with the spacing factor and freeze–thaw durability factor [ 26 , 27 , 28 , 29 , 30 ], indicating that the SAM is a useful tool to ensure concrete structures have enough freeze–thaw resistance. For example, a spacing factor of 0.2 mm or below was recommended by the American Concrete Institute to ensure that concrete structures have adequate resistance against freeze–thaw damage [ 31 ], while a SAM number of 0.2 or below can be utilized to predict a spacing factor of 0.2 mm or below with 88% accuracy [ 26 , 27 ].…”