Selection of superplasticisers for improving the rheological and mechanical properties of cement paste with CNTs

Abstract Electrical conductivity (EC), pH, spreadability, viscosity, and temperature measurements were used to evaluate the impact of superplasticiser (SP) (lignosulphonates (A), polyacrylates (B), polycarboxylates (C)) on the cement paste with CNTs properties. Compared to the pure paste’s viscosity, SP(A), characterised with high EC values, causes the rise in the paste temperature and viscosity, but SP(C) and SP(B), with lower EC values, reduce the specified parameters. While interacting with CNTs, SP(C), SP(B) and SP(C + B) blend, lowers paste initial temperature, longer structure formation and hydration process. When SP(A) is used, the aforementioned processes take place in an opposite way. By interaction with CNTs and SP(A), more of ettringite and less of portlandite than in the other samples is formed. DTA/TG study confirmed that at least 2.4% of portlandite is formed in a sample with SP(A), more than 3.1% and 3.4% in samples with SP(C) and SP(B), and 4.1% in sample with SP(C + B). In the samples with a blend of SP and CNTs, the gain of compressive strength was achieved - up to 20% after 28 days of curing, in comparison to the samples with separately used SP’s, this could be related to the interaction effect between the CNTs and the blend of SP.