Evaluation of Rheological Properties of Cashew Nutshell Liquid Superplasticizer with Portland Cement

Abstract

This study investigates the rheological performance of Portland cement paste modified with a novel bio-based superplasticizer synthesized from cashew nutshell liquid (CNSL), an agro-industrial byproduct rich in phenolic compounds. The use of bio-derived admixtures is gaining attention in sustainable construction practices, offering a greener alternative to conventional petrochemical-based additives. In this work, the synthesized CNSL-based superplasticizer (CNSL-SP) was evaluated for its effectiveness in enhancing the flow behaviour of cement paste across various water-to-cement (w/c) ratios ranging from 0.2 to 0.4. Rheological properties were measured using a Brookfield CAP 1000+ viscometer under different shear rates, and CNSL-SP was dosed at concentrations between 0.5% and 3.0% by weight of cement. The results demonstrate a consistent decrease in shear stress with increasing CNSL-SP content, indicating improved dispersion and workability of the cement paste. The most effective dosage was observed between 1% and 2%, where the reduction in yield stress was substantial without compromising paste stability. At higher dosages, particularly beyond 2%, over-fluidity and potential segregation were observed, especially at elevated w/c ratios. These findings highlight the potential of CNSL-SP as a sustainable and cost-effective superplasticizer for concrete technology, particularly in regions with abundant cashew production. Moreover, the results provide a foundation for further investigations into the long-term mechanical performance and durability characteristics of CNSL-modified concrete. The use of renewable resources such as CNSL for performance-enhancing admixtures aligns with the broader goals of green engineering and environmentally conscious construction practices.