Controllable synthesis of terminal carboxyl hyperbranched polyester and their retarding effect on concrete

Concrete retarders could efficiently extend the hydration time of cement and maintain the plasticity of concrete slurry. However, some inherent shortcomings, such as a short setting time and poor compatibility, severely limits their application. To solve these problems, in this work, a series of carboxyl-terminated hyperbranched polymers (CTHP) were controllably synthesized and their retarding effects on the concrete setting were investigated. The results showed that the final setting time of concrete was increased by nearly 4 times as the addition amount of third generation CTHP was 1.5%, demonstrating an excellent retarding effect. Furthermore, the compressive strength was increased by 43% after 7 d of curing. The results of resistivity and Zeta potential demonstrated that CTHP could change the surface charge density of cement particles and affect the flocculation of cement particles and thus extend the retarding time. The results of Tg、XRD and SEM demonstrated that the CTHP could induce a decrease in the content of Ca(OH)₂ and an increase in the content of ettringaite (AFt) during the hydration procedure, drastically enhancing the strength of the concrete. These CTHP would demonstrate the enormous potential to commercial concrete for the rapid demand in the engineering field.