Thermal conductivity of dry fly ashes with various carbon and biomass contents

ABSTRACT Huge amounts of fly ash - a substance that does not conform to the ASTM C618 classification due to its chemical properties - have been abandoned in landfills around the world, despite their self-cementing property. It has not been used in concrete making applications due to its large amounts of free lime and sulfate contents. The fly ash in these plants is dumped in landfills, causing serious environmental hazards. Fly ash is disposed to the landfills by belt conveyors after being humidified with water. Therefore, the fly ashes humidified in the landfill areas are hydrated in nature. This hydration is further intensified in landfills by rain and snow. Thus, the free lime content of fly ash decreases due to its long hydration process. In this work, the lightweight masonry blocks were produced by mixing normal and hydrated fly ashes or normal, hydrated fly ash and lime without Portland cement. The compressive strength, water absorption, sorptivity, density, porosity, and thermal conductivity values of the samples produced were determined. The results obtained from these tests showed that lightweight masonry blocks could be produced by using these waste materials in building applications.

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Modeling of Temperatures in Cementitious Monoliths

MRS Proceedings ◽

10.1557/proc-86-265 ◽

1986 ◽

Vol 86 ◽

Author(s):

S. Kaushal ◽

D. M. Roy ◽

P. H. Licastro

Keyword(s):

Thermal Conductivity ◽

Thermal Properties ◽

Thermal Stresses ◽

Heat Evolution ◽

Extreme Conditions ◽

Fly Ashes ◽

Exothermic Reactions ◽

Setting Times ◽

Reactive Additives ◽

Very High

ABSTRACTTemperatures in large cementitious monoliths (works) can rise very high due to unfavorable thermal properties such as low conductivity and high diffusivity of the monolith and the surrounding media. Heat moderation becomes necessary in such situations to avoid excessive thermal stresses. Moderation due to the addition of inert additives such as sand in mortars is compared to that obtained by the addition of reactive but low heat evolution substituents such as Class C and Class F fly ashes. Substitution of cement by slag has also been considered. The hydration temperatures for the extreme conditions (adiabatic) have been experimentally measured and compared to those predicted under real conditions. Such a simulation has been made by measuring the thermal properties and analyzing the temperature distribution due to exothermic reactions as predicted by a finite differences computer model. In general, lower temperatures can be maintained by increasing the thermal conductivity and heat capacity of the hydrating material. This material can be tailored for both heat evolution and setting times by incorporating inert additives such a sand (quartz) and/or reactive additives such as slag and fly ash.

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