Early Age Thermal Behavior of Bagasse Ash Concrete Under Different Ambient Temperatures
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Date
2019-07
Authors
Journal Title
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Addis Ababa University
Abstract
Bagasse ash can be optimized as a partial cement replacing material in a concrete mixture.
Other than guaranteeing mechanical properties, this pozzolana could be used as a thermal
retarder for mass concrete placement, despite the fact that its property was not examined
under various ambient temperatures. This research aims at studying the early age thermal
and mechanical properties of bagasse ash concrete under different ambient temperatures.
A semi-adiabatic temperature rise data of four different concrete mixtures (containing pure
Portland cement, 6.5%, 13% and 20% dosage of bagasse ash by volume) are determined.
Insulated concrete specimens of size 30*30*40cm
were cast and the internal heat of
hydration was measured at three different locations for every 30 minutes of interval. For
simulating different ambient temperatures, a chamber has been constructed in the AAiT
material laboratory. The temperature chamber is capable of simulating average ambient
temperatures of 25.15
3
0
0
, 35.54
0
and 43.77
C.
As the experimental outcomes indicate, there is reduction in early age compressive,
splitting tensile, and flexural strength of concrete containing different dosages of bagasse
ash. On the other hand, enhancement of strength is observed in bagasse ash concrete
specimens at late age testing (with exception of 20% replacement level). The laboratory
testing program revealed that, the presence of bagasse ash in the concrete mixture shifts
temperature rise-time curve, reduces the total heat of hydration and decreases the thermal
gradient in the specimens. Moreover, the total heat of hydration of all mixtures was
significantly influenced as the ambient temperature increased, but mixtures containing
bagasse ash show slower heat liberation rate relative to the control group.
Heat of hydration and thermal cracking risk were also simulated using Hacon-3 finite
element software. The FES results show a good agreement with the real measurement in
temperature gauges. The presence of bagasse ash in concrete up to 13% decreases the
cracking risk. However, incorporating bagasse ash at a higher dosage could retard the
strength development and consequently escalates the risk of cracking. This investigation
proves, the main driving force that controls early age cracking risk depends on both
strength development and heat liberation of concrete.
Description
Keywords
Bagasse ash, Semi-adiabatic temperature rise, Temperature chamber, Heat of hydration, Ambient temperature, Thermal gradient, Thermal cracking risk