Monthly Technical Meeting – July 2018
The July technical meeting of the branch was held at the University of Cape Town at the end of July, and featured presentations by students currently studying at one of the local universities.
Branch Chairman, Mfundo Taliwe, welcomed everyone to the event and thanked visitors and students alike for their attendance. He then opened the proceedings by describing in some detail the aims and activities of the Concrete Society.
The first presentation was given by Jacques Kruger, who is studying structural engineering at the University of Stellenbosch. His topic was Nanotechnology for improved constructability with 3D printing of concrete (3DPC)
3D printing is fast becoming an integral part of the manufacturing sector. It has the ability to drastically reduce manufacturing times and cost, while also increasing quality. This industry 4.0 technology can also be applied in the construction sector, which has not yet experienced the benefits of industrialisation to the same extent as the manufacturing sector.
Early reports indicate that 3D printing of concrete can reduce construction times and waste by 50 and 30% respectively, presenting enough benefit to justify large-scale industry adoption.
Although it certainly is a technology to induce socio-economic excitement, much work remains before actual realization of the concept.
Jacques presented a background of 3DPC from an international perspective, depicting current projects and trends.
Next to present was Amy Moore a civil engineering Masters student at UCT. Her presentation covered an investigation into the effect of exposure zones in the marine environment, on the corrosion rate of reinforced concrete.
Southern Africa has a developing coastline in terms of infrastructure. Because structures in marine environments are exposed to seawater, which contain high quantities of chlorides, these structures are vulnerable to chloride induced corrosion. This results in the deterioration of the RC concrete structures, leading to high costs associated with maintenance, repair and rehabilitation. Research in this field is relevant and could perhaps result in minimising the need for repairs.
Amy went on to describe the various conditions for corrosion using case studies to illustrate these.
Reinforced concrete structures that are continuous across all three exposure zones (i.e. piles or quay walls) tend to show damage in the splash zone, while the tidal zone remains relatively unaffected. Conversely, structures that only exist in the tidal and submerged zone (i.e. tidal pool walls) tend to corrode significantly faster than they would if they had concrete in the splash zone. The function of the structure is also crucial, as a jetty slab that is used to offload fish or hold heavy repair equipment might experience further deterioration problems as opposed to a slab that is used for small craft mooring and recreational activities.
When designing a structure or performing a repair assessment, parameters such as the position of the structure along the coast, the type and function of the structure, the environmental exposure class, cover depth and quality of cover layer are all details to be considered. General blanketed descriptions that “the tidal and splash and spray zone are equal in severity” are not sufficient.
Fatigue behaviour of fibre-reinforced concrete was the topic of a presentation by Humaira Fataar, who undertook research to investigate the behaviour of steel fibre reinforced concrete due to cyclic loadings. She is a civil engineer at Stellenbosch University.
Fibre-reinforced concrete (FRC) is becoming a more popular construction material due to the positive contribution it makes to concrete. Fibres can be divided into two general geometric categories, namely micro fibres (length typically less than 15 mm) and macro fibres (lengths at least 30 mm). They can also be manufactured from different materials, the most common being steel, polypropylene, glass and PVA. Natural fibres can also be used. The greatest advantage of adding fibres to concrete is the improved post-cracking behaviour of concrete in tension and flexure. Micro fibres are often used for the reduction of the risk of plastic shrinkage cracking, or increasing the ductility of concrete in the case of Strain Hardening Cement-based Composite (SHCC). The Unit for Construction Materials (UCM) at Stellenbosch University has focused on a large number of aspects of FRC, but most recently the focus has been on the use of macro synthetic fibres and the creep of cracked FRC.
Humaira’s research investigates the fatigue behaviour of steel fibre reinforced concrete under cyclic loads. When cracks develop in concrete, fibres help in bridging the gap and reduces the progression of crack growth. However, research on the crack propagation of fibre-reinforced concrete under cyclic loadings is still lacking. Furthermore, research at a single fibre level is even more uncommon. This research aims to fill this knowledge gap by conducting fatigue tests on concrete beams as well as fatigue single fibre pull-out fatigue tests.
Brian Abala is a student at the University of Cape Town with CoMSIRU' and is a professional engineer (civil engineering) with the Engineers Board of Kenya. He presented the final paper of the day on Performance Requirements for Patch Repair Mortars on Cracking Resistance and Durability.
Concrete structures are characterised by premature deterioration thus the need for remedial measures. The cost of repair and maintenance of deteriorating concrete structures is high.
Costs from poorly designed or executed repairs, are often higher than the actual repair costs.
There are many repair standards, codes and guidelines with varying characteristic and performance requirements for concrete repair.
Brian’s research objectives were to investigate the compressive strength, shrinkage, tensile strength, elastic modulus and tensile relaxation that affect the long-term performance of PRMs; determine the durability and permeability performance, for the commercially available PRMs; and determine the age at cracking, width and area of cracks of commercially available PRM specimens.
Brian used twelve patch repair mortar samples from four different manufacturers which have been tested in the laboratory with varying outcomes. A platform for the development of performance requirements of PRMs is needed to project specifications and quality control.