Effect of compaction on mechanical and thermal properties of hemp concrete

The influence of the casting process on the internal structure and physical properties of hemp-lime

“…This in turn could reduce possible stress concentrations or thermal bridges through the material thus influencing behaviour. The results indicate that this is not the case for the range of layer sizes considered here, however, the results of others who have plotted density with depth of larger specimens indicate that it may still have bearing at larger layer sizes [8].…”

“…The methods and specimen ages from casting were chosen based on combination of the British Standards for compressive strength testing of concrete and insulation products [24,25], as well as preceding studies on hemp-lime [8,11,15,17]. All specimens were removed from the temperature and humidity controlled curing room and tested at 28 days after casting.…”

“…The depth of layers, the degree of compaction and the direction of compaction with respect to the direction of thermal and mechanical loading are all variables within this process. The distribution of density within cast material is known to be dependent on depth within a single layer and globally a function of compaction [8,9]; it is also known that the casting process produces an orientated internal structure [10]. Taken together these variables will in part determine the internal topology of the material and thus have an influence on the physical properties.…”

“…Nguyen et al [8,9] found that static load compaction of fresh hemp-lime during casting can improve the peak compressive strength and stiffness of the material; the thermal conductivity was also seen to increase but to a lesser extent. The results are attributed to a reduction of inter particle voids that would reduce the volume fraction of thermally resistive air and increase the volume fraction of structural binder.…”

“…The application of any compaction has been shown to produce a preferential orientation of the particles towards stratified planes perpendicular to the compacting force [10] that is widely considered to produce observed anisotropic behaviour [8,[18][19][20][21]. The compressive strength, compressive stiffness and failure mode of compacted hemp lime have been shown to depend on whether testing is conducted parallel or perpendicular to the compaction force [21] as has thermal conductivity [8,20]. This paper considers how the variables of layer size and compaction affect the directional compressive behaviour and thermal conductivity of hemp-lime.…”