A Comprehensive Study of Interactions Occurring Between Superplasticizers and Clays, and Superplasticizers and Cement

The work documented in this thesis includes a wide range of research topics, namely (1) the interaction of polycarboxylate comb copolymers with different clay minerals; (2) a novel facile preparation method for PCE polymers using macroradicals; (3) a mechanistic investigation of cement – PCE superplasticizer incompatibility; (4) the nucleation and crystallization of ettringite under zero gravity conditions; and (5) the use of nano clay for early strength enhancement of Portland cement. It has been reported that PCE superplasticizers exhibit a strong sensitivity to clay contaminants occurring in aggregates. Because of this effect the dispersing performance of PCEs can be reduced significantly. To make it even more complicated, the negative effect from clay contaminants varies from case to case depending on the type of clay. To specify the mode of interaction between PCE polymers and clays, XRD analysis, adsorption and zeta potential measurements were carried out. Moreover, PCE structures exhibiting enhanced clay tolerance were proposed and successfully synthesized. Due to the limitation of the conventional synthesis methods of (meth)acrylate ester-based PCEs, a more simplified synthesis method starting from maleic anhydride and ω-methoxy poly(ethylene glycol) as sole raw materials was introduced in this study. The key in the polymerization process was the generation of ω-methoxy polyethylene glycol macroradicals obtained via hydrogen abstraction from MPEG. The third part of this thesis investigated the incompatibility problem occurring between most PCE polymers and specific cements. In the study, a wide range of ordinary Portland cements (OPCs) and structurally different PCE superplasticizer samples were chosen to probe their cement compatibility via the ‘mini slump’ test. The morphology of the ettringite crystals was observed under the SEM, and the role of the PCE polymers as morphological catalyst was elucidated. In the fourth part, early ettringite nucleation and crystal growth was investigated. The crystallization under idealized zero gravity conditions was studied on parabolic flights which offer 22 seconds of zero gravity. The morphology of ettringite crystals formed under zero gravity was compared with those produced in the earth’s gravity field and was found to be smaller, because at 0 g ion transport occurs only via diffusion and is not enhanced by convection. In the last part of the thesis, the use of nano kaolin as an efficient enhancer for the early strength of cement was studied. A thorough mechanistic study was also carried out to explain the strength enhancement effect. A correlation between the strength enhancement and particle size of nano clay was established.