Evaluation of rock types for concrete aggregate suitability for the construction of a gravimeter vault and access road at the Matjiesfontein Geodesy Observatory site near Matjiesfontein, South Africa
CITATION: Van Wyk, P. R. & Croukamp, L. 2014. Evaluation of rock types for concrete aggregate suitability for the construction of a gravimeter vault and access road at the Matjiesfontein Geodesy Observatory site near Matjiesfontein, South Africa. Journal of the South African Institution of Civil Engineering, 56(2):30-36.
The original publication is available at http://www.scielo.org.za
Often the use of local rock material for construction purposes is overlooked in engineering, which could reduce costs in terms of procurement and transport, as well as being more environmentally friendly by minimising the introduction of foreign materials. The rock materials at and around the site of a rock vault for the Matjiesfontein Geodesy and Earth Observation Observatory (MGO) were tested to determine if local materials may be used for construction purposes. In order to do this, strength and durability tests were conducted according to several South African National Standards (SANS). Slake durability was also tested where the potential of certain rock types, such as tillite of the Dwyka formation and shale of the Karoo Supergroup, typically slake/disintegrate into long angular fragments. This angular fragmentation during crushing of rock into aggregate for concrete also affects the workability of concrete in a fresh state. Concrete design using crushed local rock material was conducted to analyse performance and to establish a mix design that would be sustainable throughout the lifetime of the project. Tillite of the Dwyka formation was found to satisfy all test prerequisites best with minimal slaking due to the arid conditions at Matjiesfontein. Quartzite (Table Mountain Group) is very durable, but further testing for alkali-silicate reactivity is needed. All concrete cube tests accomplished the 40 MPa cube stren,gth, which was the design requirement, but problems arose in the workability of the concrete when river sand from nearby non-perennial rivers was used as fine aggregate in the concrete. This relates to too many particles of the same size within the sand.