Effect of clay minerals on polycarboxylate superplasticizer and methods to improve the performance of concrete containing clay: a review

The polycarboxylate superplasticizer (PCE) has been widely used in concrete products, tunnels, bridges and water conservancy projects due to its excellent characteristics. With the rapid development of the construction industry and the depletion of high-quality raw materials for concrete, sand and gravel containing clay have been used in concrete, which reduces the properties of PCEs. Recent studies have found that many PCEs structures without PEG/PPG or polyamine side chains have been developed due to the influence of montmorillonite (MMT) in clay on the fluidity of concrete. However, the influence mechanism of clay minerals in concrete on PCEs and the improvement methods are not summarized, and this paper has systematically overviewed this aspect. Firstly, HPEG-PCEs and APEG-PCEs in the PCEs market have superior cost effectiveness for concrete, while specific efficient PCEs such as zwitterion PCEs are suitable for calcination of clay cement mixtures to reduce anthropogenic CO2 emissions. Secondly, the chemical adsorption of clay to PCEs in concrete leads to a sharp decline in concrete fluidity, in which montmorillonite has the greatest effect, followed by illite and kaolin. Finally, methods such as modifying clay, increasing or reducing the steric resistance of PCEs, introducing special functional groups and adding sacrificial agents are discussed to improve the fluidity of concrete containing clay by changing the structure of clay layers and PCEs, thus saving the construction cost caused by the amount of raw materials and PCEs. In addition, the efficient application and future research of clay minerals and PCEs are also prospected.