Researchers from BASF, the ALBA Synchrotron and the UPC propose a methodology to increase the strength of concrete

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An X-ray powder diffraction pattern of clay with increased PCE dosage: a) fresh paste with synchrotron light, b) hardened paste with a Cu Kα diffractometer.

Researchers from the UPC, the ALBA Synchrotron and the chemical company BASF have established how clays and superplasticisers interact in cement pastes using synchrotron light. These results pave the way for improving the design of new superplasticisers with enhanced tolerance to the clays contained in the sand used for concrete production.

Apr 05, 2019

The preparation of mortar and concrete is a complex process that involves chemical reactions that are difficult to replicate. By reducing the amount of water, the properties of concrete improve: the cement paste has a higher density, which yields higher compressive and flexural strength, lower permeability and greater resistance to weathering; and the volume change from drying and wetting is reduced, which minimises shrinkage cracking. However, reducing the water content may result in stiffer mortar and concrete, which reduces their workability and increases potential placement problems.

Polycarboxylate (PCE) superplasticisers provide more fluid cement with less water, that is, they substantially improve its workability despite reducing the water content of the paste. However, polycarboxylate superplasticisers are very sensitive to the clays contained in the sand used for mortar and concrete.

Therefore, it is vital to understand the interaction between polycarboxylate superplasticisers and clays to improve the performance of these complex mixtures. Researchers from BASF, the Department of Civil and Environmental Engineering at the Universitat Politècnica de Catalunya · BarcelonaTech (UPC) and ALBA have investigated the behaviour of fresh cement paste in the NCD-SWEET beamline at the ALBA Synchrotron’s facilities. This has helped the researchers to develop an on-site methodology that properly characterises the interaction between polycarboxylate and clay. The previous methodology would centrifuge and slightly heat the pastes, which led to errors due to the preparation of the sample. Synchrotron light can measure cement pastes with no need to prepare the sample first.

“The presence of clays in cement pastes inhibits the dispersion capacity of polycarboxylate superplasticisers, thus reducing their ability to make fluid concrete and cement. The methodologies previously used to characterise the interaction between PCE and clays did not consider the alterations induced by the centrifugation and drying processes in the PCE mixture, which made it impossible to measure it correctly. That is why it was necessary to measure this interaction in fresh samples and prevent the process of drying”, explains Pere Borralleras from BASF.

“Synchrotron light has been the key to this experiment, since it enabled the intercalation of plasticisers in fresh clay pastes to be measured, so the study is not biased by the preparation of the sample”, continues Ignacio Segura, a researcher from the UPC’s Department of Civil and Environmental Engineering, one of the coauthors of the paper together with Antonio Aguado, a researcher from the same department.

This new methodology will enable the development of better PCE superplasticisers (that are more resistant to ubiquitous clays) in the coming years. It will also help to increase sustainability in the process, since sand washing is a common practice that uses a lot of water. “Sustainability is present in all the experiments carried out at ALBA”, states the professor Miguel Ángel García Aranda, the scientific director of ALBA and a coauthor of this paper.

This research has been published by Cement and Concrete Research, a journal with the second highest impact factor in the fields of construction and construction technologies.