Structural Engineering

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Browsing Structural Engineering by Subject "Ambient temperature"

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    Early Age Thermal Behavior of Bagasse Ash Concrete Under Different Ambient Temperatures
    (Addis Ababa University, 2019-07) Amanuel, Bersisa; Adil, Zekeria
    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.