09-02-2013, 04:36 PM
Effect of Fly Ash on Volume Changes of Concrete
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INTRODUCTION
It has been generally reported that the use of fly ash in normal proportions does not significantly influence
the drying shrinkage of concrete. Typical of the conclusions of most researchers in this area are those
made by Davis et al. (1937), who commented as follows:
• For masses of ordinary thickness, such as are normally found in highway slabs and in the walls
and frames of buildings, the drying shrinkage at the exposed surfaces of concrete up to the age
of one year for fly-ash cements is about the same as, or somewhat less than, that for corresponding
Portland cement. At a short distance from the exposed surface the drying shrinkage up to the age
of one year is substantially less for concretes containing corresponding Portland cements.
• For very thin sections and for cements of normal fineness, the drying shrinkage of concretes
containing finely ground high-early-strength cements may be somewhat reduced by the use of fly
ash.
Procedure of Test
After filling the moulds, place them immediately in a moist
room or moist closet for 24 ± 2 hours. Then remove the specimens from
the moulds and immediately immerse in water at 27 ± 2°C and allow
them to remain there for six days.
Remove the specimens from the water and measure for length
using a length comparator. Protect specimens against loss of moisture
prior to reading for initial length. The temperature of the test
specimens at the time of initial measurement shall be 27 ± 2°C. Store
the specimens in a closet or room maintained at 27 ± 2°C and 50 ± 5
percent relative humidity. Measure the length of the specimens again28 days after the initial measurement. Place the specimens in the
comparator with the same end uppermost with respect to the position
of the specimens as when the initial measurement was made. When
making the measurements, the specimens, comparator, and the
reference bar shall be at a temperature of 27 ± 2°C.
Calculation — After the specimens are measured as in 12.7.2 at
the age of 7 and 35 days, calculate the average difference in length of
the three specimens to the nearest 0.01 percent of the effective gauge
length, and report this difference as the drying shrinkage.