The development of novel infill materials for composite structural assemblies
This thesis presents experimental investigations on the development of new/suitable materials for lightweight wall systems. The physical and mechanical characteristics of different mix compositions of foam and ultra-lightweight concrete as well as numerical simulation using finite element analysis in order to describe and predict bonding strength between steel sheets and aerated concrete specimens are presented in the thesis.
A significant achievement of the research was to design a novel set-up of a flexible mechanism to eliminate the influence of undesirable effects of either bending and/or twisting of steel strips during pull-out tests to concentrate on pure uniaxial performance. Furthermore, this thesis provides primary quantitative information about bonding behavior between lightweight concrete and perforated steel strips, and a finite element model (FEM) of the interface behavior of both materials, establishing a basis for future research.
Galvanized plain and perforated steel strips with holes of various numbers and patterns were used in order to verify the effect of the anchorage of concrete embedded into holes. Significant improvements for strips with holes over strips without holes were confirmed through a comparative analysis of pull-out tests.
Diverse components were researched to obtain a lightweight concrete, such as a plasticizer, lightweight aggregates, foaming agents, and mineral admixtures. Three foam concrete (FC) mix compositions were prepared with desired densities of 800, 1000 and 1200 kg/m3, and ultra-lightweight concretes (ULWC) with desired densities of 150, 200, 250 and 400 kg/m3. The compressive strength obtained for FC varied between 0.91 and 23 N/mm2 while for ULWC between 0.07 and 2.1 N/mm2.
Differences between target and final densities were found. This may be due to the processing method, i.e. bubbles not able to resist the physical and chemical forces imposed during mixing.
Fire resistance has also been investigated as an important parameter of this ultra-lightweight concrete made with expanded polystyrene (EPS) beads potentially being used as infill material for wall panels. These infill materials should be designed with a density greater than 250 kg/m3, as the insulation failure criterion (160oC) applied during the fire tests indicated sufficient fire resistance compared with less dense lightweight concretes, demonstrating the percentage of cement being a significant parameter for fire resistance properties. In addition, an innovative ultra-lightweight concrete made with EPS beads was developed at 150 kg/m3 density, which can be a filler material for wall systems, if a suitable layer of fire insulation is added to reduce the fire effects.
A very good agreement of cohesive behavior between 3-D FEM modeling and experimental results was obtained with the simulation, i.e. the relationship between displacement and pull-out force in the simulation is similar to that observed in the experimental results of various lightweight concretes and various geometrical configurations of steel strips.