The Enhancement Methods of Polycarboxylate-Based Water Reducing Admixture Performance in Systems Containing High Amount of Clay Literature Review


Şahin H. G. , Biricik Ö., Mardanı Aghabaglou A.

6th International Conference on Engineering and Natural Science (ICENS), Belgrade, Serbia, 21 October - 25 December 2020, pp.14

  • Publication Type: Conference Paper / Summary Text
  • City: Belgrade
  • Country: Serbia
  • Page Numbers: pp.14

Abstract

The gradation, shape, texture and clay content of aggregate which constitute a large part of the concrete mixture affect both the fresh and hardened state performance of concrete mixtures. The clay content of crushed aggregate is higher than that of natural one. Demand for the crushed aggregate is increasing with the development of construction industry. It is known that in the case of concrete mixtures produced by utilization of aggregate having high methylene blue value, adversities such as loss of consistency and increase in water requirement may occur. The mentioned negative situations were explained by two different mechanisms. It was reported that the presence of clay in the system impairs the dispersibility of polycarboxylate-based waterreducing admixtures (PCE). On the other hand, the polyethylene oxide (PEO) side chains of PCE which presence in the cementitious system can be depleted by it enters the interlayer of clay. Thus, the water reducing admixture demand for providing constant consistency will increase. It was emphasized by the other researchers that both the mentioned conditions negatively affect the workability of the concrete mixtures. It was recognized from the literature that various studies were conducted to eliminate these negative effects. In order to eliminate the mentioned negative effects, methods such as increasing the PCE dosage and using sacrificial agents as well as the addition of polyethylene glycol (PEG) - grafted-lignin and pure PEG to the mixture were suggested by the researchers. However, it was reported that these methods are not economical. Therefore, it was emphasized that modified PCEs, which have better performance in the system having excess clay content as well as it is more economical than the other ones, need to be synthesized. For this purpose, it was recognized from the literature that modified PCEs were synthesized with some methods like adding functional groups, changing the length and shape of their side chains. In this study, a literature survey was carried out on changing the side chain shape of PCE, which is thought to be an effective way to prevent the adverse effects of clay. It was observed from the literature that admixtures having different side-chain shapes such as MA-β-CD-AA-SMAS-TPEG with the cyclicshaped, SPCE with the star-shaped, PCE-SF with the snowflake-shaped and PCE-Ls with the claw-shaped were synthesized. It was stated that in these modified PCE types, larger side chains are substituted with the linearshaped one of conventional PCE. Thus, it was declared that this method reduces the admixture demand for providing constant consistency by preventing access admixture side chains to interlayers of the clay.