Akademik Veri Yönetim Sistemi
6th International Conference on Engineering and Natural Science (ICENS), Belgrade, Sırbistan, 21 Ekim - 25 Aralık 2020, ss.14
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.