The Physical Properties, Water Sensitivity and Long Term Durability Performance of Vegetal Concrete

  • Joseph Sheridan

Student thesis: Doctoral ThesisDoctor of Philosophy

Abstract

Vegetal concrete is a building material that is manufactured using a natural aggregate. This work develops a novel vegetal concrete mix using hemp and rapeseed straw and evaluates the physical properties, water sensitivity and long term durability performance of the concrete. The first part of the work characterised 24 different mixes made up of different binders (hydrated lime, metakaolin and Vicat natural hydraulic lime), bio-aggregate types (hemp and rapeseed straw), a linseed oil pre-treatment and a polyacrylic acid-based viscosity modifying admixture (VMA). The mixes were characterised regarding their bulk density, particle size distribution, water absorption, thermal and mechanical characteristics. The second part of the thesis is devoted to the long-term durability of vegetal concretes. Four of the original 24 mixes were selected for detailed durability testing and these mixes were: untreated hemp, hemp VMA, untreated rapeseed and rapeseed VMA. The mixes were studied for long term weathering and carbonation both in artificial conditions in the laboratory as well as in natural conditions in an outdoor environment. Organic and inorganic leaching was also studied as a secondary effect of long-term weathering. Finally, the suitability of the Washburn equation was determined for predicting the capillary rise of water in vegetal concretes.
The study concludes that the use of rapeseed aggregate in vegetal concrete gave promising results, and when compared to hemp responded well in both parts of the work. The use of a viscosity modifying admixture also led to very good results and is recommended for widespread use in vegetal concrete mixes. Greatly increasing the mechanical properties of the concrete as well as lowering the concrete’s water absorption without sacrificing the thermal conductivity. It was found that all of the mix types carbonated very quickly and responded relatively well to the long-term immersion testing; although the addition of a VMA clearly caused an increase in durability for both mix types. Comparing the two aggregates directly is difficult, and it can be concluded that both perform similarly regarding durability resistance of the mechanisms studied. However, it can be concluded that it was the hemp concretes that were more durable overall. This was because it was the hemp concretes that absorbed less water, and so suffered less strength reduction in the immersion tests. Both organic and inorganic leaching was found for all of the mixes as calcium ions as well as soluble organics such as sugars were identified in the experimental water; although again, the VMA mixes performed better by leaching less. Finally, the Washburn equation was proved to be a good start in terms of capillary rise prediction in vegetal concretes, although more work needs to be done to model the effect of gravity.
Date of AwardJul 2020
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SupervisorSu Taylor (Supervisor), Mohammed Sonebi (Supervisor) & Sofiane Amziane (Supervisor)

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