Dr. Dipl.-Ing Wolfram Schmidt in the test hall of the Department of Safety of Structures. One of his concrete samples is being tested for tension and pressure.

Dr. Dipl.-Ing Wolfram Schmidt in der Prüfhalle der Abteilung Bauwerksicherheit. Eine seiner Betonproben wird auf Zug und Druck getestet.

Source: BAM, photo: Michael Danner

Wolfram Schmidt seeks the optimum, sustainable concrete – with the help of vegetable starch. He gathers knowledge and ingredients for his lab tests from Africa, as he reports.

"Here in the lab I mix small experimental sample blocks of concrete from sand, cement, limestone powder and water. In addition, many chemical additives are added to the mixture. They are special plasticisers and stabilisers developed specifically for high-performance concrete, which can now be found in almost every recipe. But today my ingredient list looks different: I add ash from burned African cassava shells to the concrete. The cassava – also known as manioc or tapioca in other parts of the world – contains a lot of starch and the ash from the burnt shells contains a high percentage of reactive silicon dioxide. Therefore, my colleagues and I came upon the idea to start tests on cassava. We want to gradually replace chemical and mineral additives in concrete: we are introducing vegetable starch into modern building chemistry and this is new.

So I add cassava and determine the flow behaviour of the concrete using a rheometer. I may add the ash from rice husks or other plants, for example, coconut and bagasse in the next experiment. Or I take the juice of the South African Acacia karroo (Sweet thorn), then I compare my bio-based mixtures with the chemically treated ones in the laboratory. We then pour the liquid concrete into silicone moulds and when it hardens, we get flat samples. We clamp the test samples into the large BAM test rig and test them for their tensile and compressive strength. I have also added long sisal fibre reinforcement to some samples in the silicone mould instead of chemical fibres. Thus we carry on with the experiments on bio-based ingredients all the time.

One can achieve a lot using simple means. I got the eye for this through BAM’s cooperation with African scientists. We are now building a common knowledge network. The goal of all this research is simple to describe: we are seeking the best concrete for the construction industry using readily available and cheap materials. Plant residues containing silica or starch are readily available. If our basic research continues to be successful for the African case, we will have to transfer some results to the high-tech West since we will be forced to tap into new raw material sources in the future. One will then probably use potato starch as a high-performance concrete ingredient instead of an expensive powder from a chemical factory.

This idea for a solution in concrete research has not been seen since the 1960s. In this respect, we are introducing a paradigm shift in our concrete laboratory. This work is unique as we explore everything from nanotechnology to the large scale and a number of disciplines from chemistry to engineering are represented. "