DRY-STACKED INSULATION MASONRY BLOCKS BASED ON MISCANTHUS CONCRETE

The present dissertation entitled “Dry-stacked insulation masonry blocks based on Miscanthus concrete” is carried out at the University of Luxembourg and financed by CONTERN Lëtzebuerger Beton. The principal aim of this project is to valorise the sustainability in the construction sector and improve the circular economy by using Luxembourgish Miscanthus to produce a masonry block. The latter should include bearing and thermal properties. Besides, a dry-stacked system should be adopted. The imposed aims are reached by developing a masonry block based on two materials connected by a dovetail connection. Furthermore, a dry-stacked system is adopted using a horizontally and vertically tongue-groove system. The present research demonstrates the approach performed to achieve these goals.
The process to reach the described aims is divided in five major steps. The first step consists of an analysis on the needed amount of mixture components with the aim of achieving the highest possible load-bearing capacity of concrete based on Miscanthus aggregates. It can be concluded that the variation of the amount of components affects the density, which has an increasing parabolic relation with the load-bearing capacity of the specimens. Furthermore, the long-term deformations considering shrinkage of Miscanthus concrete achieve in average 2350 𝜇𝑚/𝑚, which is the double of a lightweight concrete. However, comparing the long-term deformations of Miscanthus concrete with Hemp-concrete a benefit of at least 50 % can be considered.
Secondly, a machine-learning tool is applied to predict the compressive strength by introducing the mixture components and avoiding the need of creating time-consuming and costly experimental tests. Furthermore, it is possible to analyse the impact of each individual component on the load-bearing capacity. This tool has the ability of optimising the mixture according to the needs in compressive strength.
Next, a Miscanthus concrete mixture is used to manufacture rectangular masonry blocks and an analysis on their geometrical height and roughness imperfections is performed experimentally and numerically on the load-bearing capacity of walls and single masonry blocks. The roughness was investigated by measuring the contact surface. Accordingly, an exponential relation is identified between the applied compressive strength and the contact surface. The height imperfections show a low impact on the load-bearing capacity of the wall. This statement is also validated in the numerical calculation. Finally, an increase of the relation height to length of a wall reduces linearly the maximum achieved compressive strength.
The next step consists of investigating the use of a Mycelium-Miscanthus composite for insulation purposes and analyse different properties. The scanning electron microscopic analysis allows investigating the bond between Mycelium and Miscanthus. It can be concluded that the Mycelium webs enter the Miscanthus fibre and holds in the way the specimen together. Furthermore, a density of 122 kg/m3 and a thermal conductivity of 0.09 W/mK is measured in this bio composite, which is higher than a conventional insulation material. Besides, a fire resistance of category EI15 according to EN13501-2:2003 is measured. These results show a promising capacity of this composite as a building insulation. The last phase of this project consists of creating an interaction between all the parts by applying the investigated material properties into one masonry block with a geometry able to be applied in a dry-stacked masonry wall. The latter is applied by introducing a horizontal and vertical tongue-groove system in the masonry block. This block is divided in two parts, a bearing and insulation material, which are connected by a dovetail connection. A sensitivity analysis is performed in the wall by varying different properties of the masonry block, such as the thickness of the bearing and the insulation part, the angle of the dovetail connection or the position of tongue-groove system. An increase of the width of the bearing part has an increasingly linear impact on the load-bearing capacity. However, an increase of the thickness of the insulation part does not show any impact on the maximum achieved compressive strength. Furthermore, the impact of the geometrical imperfections like height and roughness are analysed. Subsequently, the needed thickness of the masonry block is calculated based on the imposed thermal transmittance value. A total thickness of the masonry block of 77 cm was determined. Therefore, it can be concluded that the thermal conductivity of the insulation part has to be improved to reduce the needed thickness of the masonry block. Finally, this thesis assesses the use of Miscanthus fibres in a masonry block, which has a bearing and insulation capacity. Furthermore, the tongue-groove system of the masonry block and the low Young’s Modulus of the Miscanthus mixture allow its application in a dry-stacked wall in the construction sector.