Mukherjee is replacement of fly ash up to 60

Mukherjee et al. (2013)
40 They observed the sump value decreases
with the increase of fly ash replacement from 40% to 70%. Generally, the
addition of fly ash with superplasticizer increases the workability of concrete
within a lower range of fly ash addition. The slump value will fall due to the
higher surface area of fly ash in high volume fly ash concrete. As the specific
gravity of fly ash (2.42) is less than that of cement (3.11) and the
replacement of cement was made by weight, the specific surface area of the mix
remain higher with higher replacement ratios.

Ravina and Mehta (1986)
7 found that class C fly ash has a
greater delay in setting time than the class F fly ash, due to its higher
sulfate contents. While it is apparent that the setting time is longer for
HVFAC , when there is replacement of fly ash up to 60 to 70%. Many researcher
concluded that the use of superplasticizer is necessary in HVFAC to ensure
workability, when low water to binder ratios less than 0.3 are used. The
reaction between cement and water is the primary cause of the setting of
concrete. Therefore, as the cement content decreases, it shows that the time
set would be increases. The delay in setting time can be up to two hours.

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Mittal et al. (2002)
2 They observed that use of fly ash
retards the setting time of concrete. As the setting characteristics of the
concrete depends on various parameters like concrete temperature, cement type,
type of fly ash, admixture and their relative quantities. In 350kg/Cum and
450kg/Cum cementitious concrete mixers the initial and final setting times are
determined and no significant changes in the setting time is observed. It is
probably due to the fact that retardation due to increase in percentage of fly
ash is compensated by the reduction in super plasticizer.

Wang 2006 52
Higher-calcium fly ash for the most part retard setting to a lesser degree than
low calcium fly ash, likely of the fact that the hydraulic reactivity of fly
ash increments with the increases of its calcium content .The impact of
high-calcium fly ash is harder to foresee in light of the fact that the
utilization of some of these type of fly ash with certain concrete admixture
mixes can promote either quick setting or retard time

2.2.2 DURABILITY

Fly
ash concrete has lower permeability than conventional concrete, which means
less water and chemical can enter the concrete. Therefore the fly ash enhances
the durability of concrete, particularly reducing the alkali-silica reaction,
freeze-thaw attack, corrosion susceptibility. High heat of hydration of OPC
concrete results in thermal cracking which effects its durability. The reduced
heat of hydration of fly added concrete can effectively address the above
concerns and improves its durability.

Mehta (2006) 36
The research has showed that HVFAC is more crack resistant than conventional
concrete, due to the decreased shrinkage. This is a results of the decreasing
mixing water, decreased water to cementitious materials(w/cm) ratios, and
decreased in the total volume of cement paste that is required in HYFAC. Also,
the decreased the heat of hydration at early ages reduced potential for thermal
shrinkage and cracking.

Quan and Kasami (2014)
13 The study presents effects of
durability improving admixture, air content, water-binder ratio, and fly ash
replacement ratio on the performance of fly ash concrete. The results show that
by using durability improving admixture in non air-entraining fly ash concrete the
compressive strength of fly ash concrete can be improved by 10%-20% and the
drying shrinkage is reduced by 60%.