The behavior of concrete mixes containing various amounts of fly ash
conforming to ASTM C-618, class c, was investigated. Twenty to fifty percent
of the port 1 and cement lvas replaced on a weight basis. Two tasks were investigated simultaneously. Task 1 investigated the freeze-thaw durability of
the various mixes using Procedure A, Resistance of Concrete to Rapid Freezing
and Thawing in Water (ASTM C-666). Task 2 investigated the effects of ambient
temperature. Concrete was batched and mixed at 55, 70, or 90 F (13,21,or
32 c) ; the influence of temperature on the quantities of mix water and air
entraining agent dosage and on the time of set was established. Slump, unit
weight, temperature, and air content were measured after initial mixing. The
speed of the mixer was then reduced to 2 rpm and the concrete was subjected
to agitation until it was unworkable; during this time the properties of the
mix were determined at 30-minute intervals. Task 1 results indicated that
all mixes tested exhibited high resistance to freeze-thaw action. As the percentage
of fly ash was increased it was possible to reduce the amount of mix
water; however, it was necessary to increase the dosage of air entrainment
admixture. The 28-day compressive strength concrete was not strongly influenced
by fly ash; a modest increase in strength was normally exhibited
with 30 and percent fly ash replacement. Although fly ash significantly
retarded the time of set, it appeared to slightly accelerate the rate of loss
of slump. The air void system in the hardened concrete appeared to be unaffected
by the percentage of fly ash.Final Report Dec. 1980 to July 1983N
