Effect of Chemical Structure on Fluidizing Mechanism of Concrete Superplasticizer Containing Polyethylene Oxide Graft Chains
M. Kinoshita, T. Nawa, M. lida, and H. lchiboji
Appears on pages(s):
adsorption; mixing time; superplasticizer
Methacrylic graft copolymers (hereafter referred to as graft copolymers) were synthesized to investigate the effects of chemical structures on the fluidizing mechanism of concrete superplasticizer containing polyethylene oxide graft chains. The cement-dispersing performance of graft copolymers is strongly affected by the length of the polyoxyethylene graft chains and is governed more by steric repulsion than electrostatic repulsion. Graft copolymers having longer graft chains and a relatively short backbone required a shorter mixing time and exhibited excellent fluidity immediately after mixing. Conversely, the fluidity-retaining capability was lower. The authors therefore synthesized a graft copolymer having different graft chain lengths to attain the high fluidity and fluidity-retaining capability, and investigated its properties. As a result, the graft copolymer having graft chains with different lengths was found to satisfy both performance requirements for fluidity and fluidity retention. Moreover, this copolymer was found to be adsorbed less onto cement particles, resulting in a low set-retarding effect. It was also confirmed that the cement-dispersing capability of graft copolymers varies depending on the cement type. Belite-rich low-heat portland cement with a low C3A content leads to high fluidity with a much lower dosage of graft copolymers than normal portland cement. These properties of graft copolymers and cement suggest their promising applicability to production of high performance concrete.