Study on the Combination of Double Cationic Polymer Sacrificial Agent and Polycarboxylate Superplasticizer in Cementitious Materials Containing Clay

The clay attached to the inferior aggregate contaminates the concrete, which will have a serious negative impact on its workability and quality. The quaternary ammonium monocationic polymer (SP1) was synthesized from epichlorohydrin and dimethylamine by step-growth polymerization mechanism. Then, quaternary ammonium and quaternary phosphine dicationic polymer (SP2) was prepared via etherification reaction of SP1 with phosphorus tetrahydroxymethyl sulfate. This study attempts to improve the clay resistance of polycarboxylate superplasticizer (PCE) by combining SP1 or SP2 ionomers. The results of fluidity indicate that the fluidity increases with the addition of sacrificial agent, and the fluidity can reach 280 mm when the dosage of SP1 is 0.2%. Meanwhile, the presence of the sacrificial agent in PCE system can obviously improve the flow retention whole 120 min, showing the improvement in clay tolerance. The adsorption results suggest that the incorporation of sacrificial agent can affect the adsorption behavior, with a decline on MMT particles in total adsorption amount. XRD result demonstrate that the introduction of SP1 or SP2 into the PCE-MMT supernatant can compress the MMT layer spacing and avoid the interlayer adsorption for PCE. Specially, due to the synergistic action of double cations and hydroxyl groups, SP2 preferentially occupies the MMT surface, inhibits the spallation of clay and greatly reduces the surface area for adsorption, which is the main reason for improving the clay tolerance of PCE. This study provides promising solutions for PCE dispersion, with respect to cementitious systems contaminated by clay.