The adsorption of polycarboxylate-based superplasticizer onto natural bentonite was investigated in aqueous solution using a batch technique with respect to initial adsorbate concentration, contact time, temperature, pH value and ionic strength. Lower pH value and higher ionic strength were proved to be favorable for the adsorption. The pseudo-first-order, pseudo-second-order and intraparticle diffusion models were used to describe the kinetic data and the kinetic constants were also determined. The experimental data fitted the pseudo-second-order model well. The Langmuir, Freundlich and Dubinin-Radushkevich (D-R) equations were applied to describe the equilibrium isotherm and the isotherm constants were also evaluated. The langmuir model agreed with the experimental well. Thermodynamic parameters (ΔG0, ΔH0 and ΔS0) indicated that the adsorption was endothermic and physical in nature.
Lowering the water/cementitious materials (W/CM) ratio is the key for the production of high-strength concrete and high-performance concrete, but there is a limit to lowering the W/CM ratio because the water added must be enough to fill the voids between solid particles and form water films coating the solid particles. Hence, an increase in packing density of the cementitious materials would allow a lower W/CM ratio to be adopted. This research aims to evaluate the effects of adding superfine cement (SFC) and condensed silica fume (CSF) on the packing density of cementitious materials, and study the roles of packing density and water film thickness in the rheological properties and compressive strength of cement paste. The results showed that the addition of SFC and/or CSF can significantly increase the packing density and water film thickness, and thereby greatly improve the rheological and strength performances of cement paste.
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