Visit to University of Pretoria Civil Laboratory
Inland Branch members were recently treated to a site visit to the University of Pretoria Civil Laboratory. It was a great success and attracted a diverse audience.
There was a total of 18 attendees which ranged from readymix suppliers to consulting engineers. The meeting began with a brief discussion regarding different concrete tests led by Derek Mostert from the University of Pretoria.
Durability Index Testing – Jaco du Plessis (see left) from Go-Consult explains and demonstrates the three key durability tests and the equipment used.
Oxygen permeability, water sorptivity and chloride conductivity are tested. The Oxygen permeability test is suitable for the evaluation of materials and mix proportions for design purposes, and for research and development.
The test can also be used for quality control of concrete on site. It is very useful to assess the state of compaction, presence of bleed voids and channels and the degree of interconnectedness of the pore structure.
Sorptivity is a material’s ability to absorb and transmit water through it by capillary suction. Uptake of water by unsaturated, hardened concrete may be characterised by the sorptivity.
The Water Sorptivity test is used to determine the rate of absorption (sorptivity) of water by hydraulic cement concrete by measuring the increase in the mass of a specimen resulting from absorption of water as a function of time.
The chloride conductivity index is a quality control parameter used to assess the resistance of concrete to chloride ingress. It is determined from the chloride conductivity test which measures the electrical current flowing through a concrete specimen. The apparatus used allows for rapid testing under controlled laboratory conditions and give instantaneous results.
Modulus of Elasticity (E-value) – Derek Mostert (see right) conducted the test on a concrete cylinder and discussed the relevance of the E-value for engineers in practice.
Modulus of elasticity is a very important mechanical property of concrete. It represents the material stiffness of the concrete to an imposed stress. The higher the value of the modulus, the stiffer the material is.
Large Scale Beam Testing – The attendees viewed the failure of a large-scale reinforced beam and got an understanding of the relationship between steel and concrete as a composite material. In essence, the beam test consists of subjecting specimens to loading, either by two loads at third points or a single load at midspan. This test is normally done for floors, road, or airport pavements but may also be required for structural elements where flexural strength is critical.
The site visit was concluded with the Concrete Society thanking the University of Pretoria for opening up their laboratory
and sharing their knowledge and love for concrete with the members.