“Concrete itself has not changed but our understanding of its behaviour has deepened and the new SANS 51992 1 1 that comes into full effect in Decembe
“Concrete itself has not changed but our understanding of its behaviour has deepened and the new SANS 51992 1 1 that comes into full effect in December 2026 code now reflects decades of international research that includes new practises and stronger materials.”
This is according to Dr Kim Timm of Stellenbosch University speaking at the recent Concrete Society of Southern Africa (CSSA) roadshow seminars to familiarise the industry about the new code adding that it shifts focus to the practical realities of new materials and durability under the new code especially where high strength concretes are becoming more common well above 90 MPa.
Diving straight into the crux of the talk on materials and durability she stressed that in the South Africa’s National Annex there is a note of caution where higher strengths are technically permitted and engineers may specify 80 MPa or more, but they must demonstrate compliance through testing, particularly for shear behaviour, creep and shrinkage. In many cases, the Annex advises reverting to the conservative limits of 50–60 MPa unless robust evidence supports higher values. This balance, she added, reflects the country’s pragmatic approach to durability.
“Looking at the new code it will be evident that a critical change lies in the way compressive strength is defined. Where SANS 10100 relied on cube tests the Eurocode derived SANS 51992 1 1 code uses cylinder strength (fck). Although contractors might still cast cubes on site, designers must convert results using established tables because cylinder strength typically sits at 80–85 percent of cube strength and the code provides “cheat sheet” tables to simplify the conversion. This distinction is vital because if you ever put your cube strength directly into a cylinder equation, you’ll be over designing your reinforcement and undermining your structure.
“The code also introduces additional factors to account for long term effects. The ηcc factor adjusts compressive strength for creep and sustained loading while the Kt factor allows modest increases for age related strength gains. South Africa’s Annex aligns with the British approach setting ηcc at 0.85 rather than the Eurocode’s recommended 1.0 in order to reflect local material realities. These refinements ensure that design strengths more accurately mirror how concrete behaves over decades as opposed to just laboratory tests,” she said.
Timm shared insight into how durability models for creep and shrinkage have advanced and where SANS 10100 relied on empirical British data, the new code rather incorporates forty years of theoretical modelling. Shrinkage is now divided into drying shrinkage and autogenous shrinkage recognising both moisture loss and chemical reactions during hydration. The new models predict higher shrinkage values than the old code which is crucial for crack control and water retaining structures. Creep predictions are more difficult and avoids the overestimation common in earlier South African practice. This will improve long term performance especially in sensitive applications such as reservoirs and high rise slabs.
Reinforcement behaviour has also been updated where the old code had a more simple elastic plastic curve that flattened out after yield the SANS 51992 1 1 code allows for strain hardening for more efficient designs if the steel supplier can prove performance through testing.
Local studies have shown that South African steels often do not achieve the same hardening levels as European products so the Annex advises caution. As a result, Class B ductility remains the default ensuring structures fail gradually rather than suddenly. “We prefer ductile performance. If failure ever occurs we want warning not brittle collapse.”
She also warned against the casual use of mesh reinforcement in slabs which is becoming increasingly common in residential construction. Mesh often falls into Class A with lower ductility and may not provide the resilience required for structural elements. That is why is especially important for engineers to verify the class of steel before substituting mesh for conventional reinforcement particularly in critical applications.
The takeaway for concrete professionals is that SANS 51992 1 1 uses a more sophisticated understanding of concrete and steel tailored to South African practices. They key to successfully using it lies in mastering the requirements, converting cube to cylinder strengths, applying long term factors and ensuring ductility in reinforcement.
