Evaluation of the combination of desert sand and calcium sulfoaluminate cement for the production of concrete. (20th May 2020) - Kaufmann, Josef
Highlights: Sand fraction of concrete and mortar replaced by desert sand. Calcium sulfoaluminate cement (CSA) used as binder instead of Portland cement. High water demand of desert sand compensated by formation of ettringite. Environmentally friendly concrete using local desert sand and low-CO2 CSA cement. Abstract: The production of concrete requires large quantities of sand. At first sight, sand seems to be a cheap, widely available and abundant resource, however, in some regions of the earth sand is getting rare because of the high demand. An alternative might be desert sand, which is available from many sources around the world, but is not yet widely used in concrete due to its narrow particle size distribution. In this study, a new concept of combining desert sands with a binder based on calcium sulfoaluminate cements (CSA) and gypsum is tested to obtain a suitable workability and packing density and hence allows for a high sand replacement level in standard concrete. Unlike typical CSA applications, a high gypsum content is used in order to produce a large amount of ettringite, which is able to bind large quantities of mixing water. The concept is applied on a series of pastes and concretes with different standard sand replacement levels. A very fine quartz sand is used as a model desert sand. Mechanical properties (compressive and bending strength) are determined and compared to reference systems based on ordinary Portland cement (OPC). It is shown that the formation of ettringite is capable to fill the voids between the small and narrow-sized desert sand particles leading to a very dense microstructure. Drying shrinkage data show volumetric stability and reduced shrinkage. Owing to the low CSA dosage and the low carbon dioxide emissions related to CSA production, the proposed concrete mixtures can be regarded as eco-friendly.