A team of researchers from the chemical company BASF, the ALBA Synchrotron and the “Universitat Politecnica de Catalunya · BarcelonaTech (UPC)” has determined how clays and superplasticizers interact in concrete pastes.
These results pave the way to improve the design of new superplasticizers more resistant to the clays that are generally found in the sands that are used for the production of concrete.
The preparation of mortar and concrete is a complex process, involving different chemical reactions that are difficult to replicate. The properties of the concrete improve when the amount of water is reduced: the concrete paste with less water has a higher density and, therefore, greater resistance to compression and bending, lower permeability and greater resistance to weathering; apart from reduce the change in volume of drying and wetting that minimizes shrinkage cracking. However, when the water content is reduced, the mortar and concrete become more viscous, which reduces their ability to work and increases the problems for their placement.
The polycarboxylate superplasticizers (PCE) make the concrete more fluid with less water, which substantially improves its manageability, and allows reducing the water content of the paste. However, polycarboxylate superplasticizers are very sensitive to clays that may contain the sand used in the production of mortar and concrete.
“The presence of clays in concrete pastes inhibits the dispersion capacity of polycarboxylate superplasticizers, thus decreasing their ability to make concrete fluid.” The previous used methodologies for characterization of the PCE-clays interaction did not consider the induced alterations. By centrifugation and drying processes in the PCE mixture, which made it impossible to measure it correctly, it was therefore necessary to measure the interaction in the fresh samples, avoiding the drying process,” says Pere Borralleras from BASF.
This research has been published in the magazine “Cement and Concrete Research”, the second highest impact factor magazine in construction and construction Technology.
Dyna, (2019). [online] Available at: https://www.revistadyna.com/noticias-de-ingenieria/una-nueva-metodologia-para-mejorar-resistencia-del-hormigon [Accessed 8 Mar. 2019].
Test related to concrete samples can be carried out in specialized climatic chamber to check their characteristics.