Effect of Linkage Bond between Backbone and Side Chain in Comb-Like Copolymer Dispersants on Early Properties of Concentrated Cement Suspensions

Comb-like copolymer, consists of backbone with ionizable group and charge neutral poly(ethylene oxide)-based “teeth” side chain grafted onto the backbone at frequent intervals, has been widely used as superplasticizer in concrete industry due to its unique properties compared to traditional polyelectrolyte dispersants, such as lower dosages, outstanding water reduction, excellent workability retention and lower shrinkage. It is easy to modify and adapt this molecular structure in order to maximize the targeted properties and also meet specific properties for different applications. However, modification attempts usually focused on the side-chain length and charge density. In fact, the linkage bond between backbone and side chain has greatly influence on the early behavior of cement suspensions due to copolymers with different linkage bond have different structure stability under the strong basic environment. In this study, two comb-like copolymer dispersants with different linkage group (ester and ether) were produced. The effects of the type of linkage bond in comb-like copolymers on the adsorption characteristics and hydration behavior of concentrated cement suspensions, were investigated by means of Total organic carbon analyzer(TOC),DSC-TG and calorimetric device and Environmental Scanning Electron Microscope(ESEM). Test results showed that the comb-like copolymer with ester linkage bond, has lower initial adsorbed amount, and thus not only accelerate the hydration rate, but also change its crystal shape of hydrated cement. This will help in the understanding of the structure-property relationship of comb-like copolymer and in the designing the molecular structure of new functional superplasticizer.