This study aims to investigate the effect of varying proportions of lime (L), gypsum powder (P) and pozzolan (Z) on the mechanical properties and microstructural characteristics of lime-based sand concrete. It also seeks to optimize the composition of the ternary binder using a mixture design methodology and to model the relationships between binder components and the resulting mechanical responses.
An experimental program was conducted using a mixture design methodology to systematically vary the relative proportions of lime, gypsum and pozzolan within the ternary binder system. The effects of the component proportions were evaluated in terms of compressive strength (Rc) and flexural strength (Rf) after 7 and 28 days of curing. Statistical models were developed to predict the mechanical responses. In addition, microstructural analyses, including X-ray diffraction (XRD) and optical microscopy, were performed to relate mechanical performance with hydration products and internal structure.
The results revealed that gypsum powder content (P) was the most influential factor affecting both compressive and flexural strengths. Among the tested mixtures, SC21, containing 0% L, 10% P and 0% Z and corresponding to a complete replacement of the lime-substitution fraction by gypsum, showed the best mechanical performance, with a 107% increase in compressive strength compared with the reference mix. Microstructural analyses showed that variations in binder composition influenced the nature and distribution of hydration products, which in turn affected the mechanical properties. The studied composites exhibited a relatively dense and homogeneous microstructure with good paste–aggregate bonding.
This study makes a novel contribution by investigating the lime-gypsum-pozzolan (L–P–Z) ternary binder system for sand concrete, which remains underexplored. In contrast to previous studies mainly focused on mortars or conventional concrete, this work examines how the specific characteristics of sand concrete influence binder reactions, microstructural development and mechanical performance. The combination of mixture design, mechanical testing and microstructural analysis enables the optimization of the binder composition and contributes to the development of improved lime-based sand concrete formulations.
