Experimental development of alternative lightweight concretes

Zwicky, Daia (School of Engineering and Architecture (HEIA-FR), HES-SO // University of Applied Sciences Western Switzerland)

It is difficult to compete with normalweight concrete: it is pourable, usually self-compacting, hardening reasonably fast, cheap and locally available in large quantities. Its excellent fire protection and good acoustic insulation for airborne sound are further advantages in construction. But, regular concrete is very heavy, being disadvantageous for transportation and hoisting and results in the fact that a concrete structure predominantly supports its self-weight. Also, concrete qualities applied in building construction usually provide a far too high strength, as geometry is often dictated by constructability (minimum dimensions for concreting). Concrete further provides poor thermal insulation and unpleasant user experience (it “feels” cold), and is rather challenging to recycle. Last but not least, concrete manufacture is largely based on non-renewable resources and has a high environmental impact. Thus, alternative lightweight concretes should be further developed. Starting from earlier developments on “wood-based concrete” (or wood-cement compounds WCCs), essentially consisting of Portland cement (PC) and other mineral binders and of up to 60% of untreated sawdust, this study aimed at improving their mechanical properties by integrating an aggregate skeleton from organic aggregates (fruit pits, crushed nut shells) and lightweight aggregates from largely available or renewable resources (expanded clay and glass). 15 different recipes for “WooCon” (from wood-concrete) were designed and evaluated, in a first phase, for possible self-compaction as a basic fresh-state requirement for their targeted application in prefabrication. In a second phase, basic mechanical properties of 5 retained WooCon recipes were evaluated, by testing elastic modulus, compressive strength, and their development over 28 days as a further important prefabrication requirement. These results were also used to modify predictive expressions for correlating compressive strength and elastic modulus. In a third phase, estimates of economic and ecological performances were established, in order to assess the competitiveness of the newly developed WooCon recipes. The fourth evaluation phase of long-term properties (shrinkage and creep) of the 3 most promising WooCon recipes is currently ongoing. The study results show that adding an aggregate skeleton to WCCs, i.e. converting them into WooCon, can notably improve workability properties, up to self-compaction. Compressive strength can be doubled and elastic modulus can be tripled. Strength development can be predicted by generally accepted expressions and can even reach very rapid early hardening. Elastic modulus can be correlated quite accurately to compressive strength. In all evaluated mechanical properties, a marked influence of the applied percentage of organic aggregates could be observed. Economic impacts of WooCon majorly reside in costs for organic aggregates and cement, and result in unit prices up to 2.5 times higher than regular lightweight concrete (LC); however, if contextualised for mechanical elements, WooCon can perform better than regular LC. Lime filler and cement are the major contributors to ecological impact (global warming potential, GWP) but the overall result shows 75-80% reductions in comparison to regular LC.


Keywords:
Conference Type:
full paper
Faculty:
Ingénierie et Architecture
School:
HEIA-FR
Institute:
iTEC - Institut des technologies de l'environnement construit
Publisher:
Eindhoven, The Netherlands, 12-15 August 2019
Date:
2019-08
Eindhoven, The Netherlands
12-15 August 2019
Pagination:
15 p.
Published in:
Proceedings of 2nd International Conference of Sustainable Building Materials (ICSBM 2019), 12-15 August 2019, Eindhoven, The Netherlands
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Note: The status of this file is: restricted


 Record created 2019-10-22, last modified 2019-10-29

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