Hilal, Ameer Abdulrahman
(2015)
Properties and microstructure of pre-formed foamed concretes.
PhD thesis, University of Nottingham.
Abstract
In construction buildings, use of thermal insulating materials is essential and beneficial not only by reducing the cooling/heating cost and the structural element sizes but also reducing the pollution of the environment which results from heavy use of fuel.
Foamed concrete is a lightweight material. In this research, by using the preformed foam method, foamed concrete mixes with/without lightweight aggregate (LWA), which are suitable for semi-structural or structural purposes with good insulation and durability properties, were designed and produced. Then, their behaviour and the effect of microstructure on their macro properties were established. As a result, the mechanical, thermal and permeation performance as well as damage behaviour of foamed concrete, associated with changes in its microstructure that result from inclusion of superplasticizer, additives (silica fume and fly ash) and LWA, were investigated.
The results showed that, for a given density, although the additives in combination led to increased void numbers, both void size and connectivity were reduced by preventing their merging and this resulted in a narrow void size distribution. As a result, the mineral admixtures (silica fume and fly ash) and superplasticizer combination provides improvement in the strength properties of foamed concrete. In addition, due to their making the cement paste denser and less porous, addition of additives and superplasticizer in combination led to slightly increased thermal conductivity in the dry state. However, owing to reduced water absorption, the thermal conductivity in the saturated state was slightly lower for mixes with additives than conventional mixes. Adding additives (individually or in combination) helped in reducing the water absorption, sorptivity and permeability of foamed concrete. However, inclusion of LWA resulted in increased sorptivity and permeability compared to the same density mixes, conventional or with additives in combination. From elasticity, fracture and fractal points of view, it was found that brittleness increases with additives while it reduces with inclusion of LWA. However, at a micro level, less damage occurred in mixes with LWA and the bond microcracks percentage increased with inclusion of additives.
Finally, although the findings of this study are encouraging for the potential of using modified foamed concrete with additives in semi-structural and structural applications, it was recommended that using it in reinforced structural elements such as beams, columns, slabs and reinforced walls or load bearing masonry walls needs to be experimentally examined and evaluated.
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