Mechanical performance of statically loaded flat face epoxy bonded concrete joints

One of the main challenges in the offshore renewable energy industry is the reduction in the levelised cost of energy of wind, wave and tidal devices. The use of concrete as the primary construction material in such devices presents a low unit cost, high marine durability alternative to steel, however, to maximise material efficiency factors such as mix constituent design, structural detailing and manufacturing processes have to take into account the specific conditions of the marine environment. Pre-cast segmental construction can be considered as one of the fastest and cheapest construction options. However the challenges regarding performance of epoxy bonded concrete in marine environment should be taken into account. This paper presents the results of an experimental programme on the performance of shear and tensile capacity of flat face concrete joints, focussing on the effect of substrate surface preparation, joint thickness, properties of epoxy resins, exposure to seawater and presence of joint defects on the ultimate failure load. The ultrasonic pulse velocity (UPV) method for detection of defects in the adhesive layer was examined and digital image correlation is used to observe the surface strain flow through the joint. The results indicate that the epoxy joints behave monolithically and remain undamaged under different types of static loading. The joints do not significantly interrupt the flow of strain but can locally affect the distribution of strain (and thus stiffness and stresses) in a structure. An increase in the density of the epoxy (and the filler content) leads to the increase in the joint strength and thicker joints are less affected by small defects in the bonding layer. The majority of tested specimens failed by cracking of concrete rather than by debonding of the joint, whilst compressive stresses acting on the joint can help to augment its shear strength. Sandblasting of bonded surfaces can improve performance of joints, whereas UPV testing may be used for quality control of epoxy-bonded joints

The effect of print parameters on the (Micro) structure of 3D printed cementitious materials

The extrusion-based 3D printing method is one of the main additive manufacturing techniques worldwide in construction industry. This method is capable to produce large scale components with complex geometries without the use of an expensive formwork. The main advantages of this technique are encountered by the fact that the end result is a layered structure. Within these elements, voids can form between the filaments and also the time gap between the different layers will be of great importance. These factors will not only affect the mechanical performance but will also have an influence on the durability of the components. In this research, a custom-made 3D printing apparatus was used to simulate the printing process. Layered specimens with 0, 10 and 60 min delay time (e.i. the time between printing of subsequent layers) have been printed with two different printing speeds (1.7 cm/s and 3 cm/s). Mechanical properties including compressive and inter-layer bonding strength have been measured and the effect on the pore size and pore size distribution was taken into account by performing Mercury Intrusion Porosimetry (MIP) tests. First results showed that the mechanical performance of high speed printed specimens is lower for every time gap due to a decreased surface roughness and the formation of bigger voids. The porosity of the elements shows an increasing trend when enlarging the time gap and a higher printing speed will create bigger voids and pores inside het printed material

Structural behaviour of layered beams with fibre-reinforced LWAC and normal density concrete

The hybrid concrete structures investigated in this project were beams composed of two layers of different types of concrete. Normal density concrete (NC) was used in the top layer combined with a layer of fibre-reinforced lightweight concrete (FRLWC). Hence, the beams had a low weight and the NC layer fulfilled the requirements for ductility in compression. The material properties of the FRLWC were investigated through small-scale tests, the uniaxial tension test, the 3-point bending test and a compressive test on concrete cylinders/cubes. The small-scale tests constituted the basis for obtaining design parameters used in the design of the larger hybrid beams. These beams had 0.5 and 1.0 % of steel fibres, and were subjected to a 4-point bending test in order to study the performance in terms of both shear and bending actions. Fibre counting was carried out in order to relate the performance to the number of fibres crossing the critical section, which turned out to have a considerable influence on the performance of the FRLWC. In general, the types of failure were as expected. This study shows that the concept of combining NC and FRLWC in one cross-section shows promising results, and no problem with the bond between the layers of concrete was registered. Steel fibre reinforcement of the lightweight concrete increased the ductility in tension, so the amount of conventional shear reinforcement could be reduced. The concept provides a low self-weight of the structure, practical solutions in the construction phase and good premises for more efficient building.acceptedVersion© Springer Verlag. This is the authors' accepted and refereed manuscript to the article. The final publication is available at https://link.springer.com/article/10.1617%2Fs11527-015-0530-