Enhancing workability of high-volume calcined clay blend cement pastes through optimized addition sequences of PCE superplasticizer

Abstract

The cementitious paste containing a high volume of calcined clay exhibits poor fluidity due to the thixotropic nature of the clay suspension. The study focuses on the impact of the stepwise addition of PCE and protein-based alkaline retarder (PAR) on the rheological properties of cement-calcined clay blends with varying calcined clay replacement levels. The addition sequences included prior addition (PA), simultaneous addition (SA), and delayed addition (DA) of PCE. The blends were evaluated based on their fluidity, rheology, and setting time. The results showed that the DA sequence notably improved the workability of the blends, minimizing the fluidity loss over 60 minutes and reduced the yield stress of the paste by up to 89.8 %. The adsorption of polymers on mineral particles was analyzed by total organic carbon (TOC), X-ray photoelectron spectroscopy (XPS), X-ray diffractometry (XRD) and Zeta potential test to reveal its mechanism. The results revealed a 17 % increase in polymer adsorption with the DA sequence, while the zeta potential of the blend experienced only a slight change. These findings suggest that the sequence of chemical admixture addition can significantly influence the working performance of cement-calcined clay blends. This provides new insights for improving the dispersion performance of these blends and promotes the application of limestone calcined clay cement.

Keywords

• PCE superplasticiser
• Protein-based retarder
• Surface coverage
• Workability
• Rheology