Synthesis and Performance of Anticlay Polycarboxylate Superplasticizers
Polycarboxylate superplasticizers (PCEs) have been extensively used in the areas of construction and building; however, the application limitation of PCEs has emerged owing to their sensitivity to clay. In this work, three anticlay PCEs were synthesized by introducing acrylamide (AM), methacryloxyethyltrimethyl ammonium chloride (DMC), or 3-[2-(methacryloyloxy) ethyl] dimethylammonio-propane-1-sulfonate (DMAPS) into the polycarboxylate copolymer of ethylene glycol monovinyl polyethylene glycol ether (EPEG) and acrylic acid (AA), denoted as A-PCE, D-PCE, and S-PCE, respectively. The structures of these superplasticizers were characterized by gel permeation chromatography (GPC) and Fourier-transform infrared spectroscopy (FTIR). Compared with the common polycarboxylate superplasticizers (O-PCEs), the resultant anticlay PCEs showed better dispersion as far as the fluidity of cement paste and mortar were concerned. With the content of 0.5% per weight sodium bentonite in place of cement, these anticlay PCEs exhibited better clay resistance than O-PCE. In addition, the compressive strengths of mortar and concrete by the addition of A-PCE, D-PCE, or S-PCE were slightly higher than those of O-PCE. Total organic carbon (TOC) revealed that the sensitivity of A-PCE, D-PCE, and S-PCE to clay was lower than that of O-PCE. X-ray diffraction (XRD) proved that the layer spacing of clay increased after treatment with superplasticizer. In combination of adsorption determination with XRD analysis, a possible mechanism was proposed. Unlike the PEG side chains inserting into the clay layers for O-PCE, the cations in functional groups entered the clay layers through cation exchange for anticlay PCEs preferentially.
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