Rheological characterization of limestone calcined clay cement pastes with various generations of superplasticizers for pumping applications

The present study investigates the effect of commercially available superplasticizers (SP) of various generations, such as lignosulphonate, Sulphonated Naphthalene Formaldehyde (SNF) and Polycarboxylate Ether (PCE), on the fresh properties of Limestone Calcined Clay Cement (LC3) pastes which simulates the lubrication layer formed during the pumping of concrete. LC3 cementitious pastes with different w/b (0.25–0.55), corresponding to various concrete strength grades adopted in the construction industry, were investigated. The study involves superplasticizer optimization and rheological assessment of cementitious pastes. The findings highlight the efficacy of different generations of superplasticizers, the transient flow behaviour at varied shear rates and the solid volume fractions on the rheological behaviour of LC3 pastes. The research findings indicate that LC3 based mixtures, at optimized SP dosages with increased shear rates exhibit a notable transition in behaviour from shear thinning to shear thickening (crucial for controlling the discharge of concrete during pumping). Moreover, the study reveals that LC3 pastes containing lignosulphonate based SP demonstrate superior performance at lower solid volume fractions. On the other hand, PCE based SP combinations exhibit enhanced effectiveness at higher solid volume fractions. This research outcome helps with the rational selection of superplasticizers and its dosage for LC3 mixtures in high-shear applications, particularly for the purpose of mitigating shear thickening during pumping operations.