Eggshell Powder Used as Replacement in Building Materials

A research team from Najran Scientific University in Najran, Saudi Arabia, recently conducted a study on calcinated eggshell powder's use in lightweight foamed concrete.

Over the last few decades, the study shares, partial cement has been replaced with agriculture inorganic wastes, fly ash, and silica fume. Incorporating these particular waste items improves concrete performance and provides a clear environmental benefit as a result of their notable pozzolanic reaction, cost-effective, and reduced CO₂ emission.

Calcined eggshell powder (CESP) has been used to produce calcium phosphates since 1999 and can be used as a bio-waste material. Every year, the food sector generates enormous volumes of eggshells (ES), which are then dumped into landfills without being properly processed. ES is then moved from open landfills to enclosed sanitary dumps. The production of hazardous gas from this waste can harm the environment and human health. ES slightly differs from cement in terms of its chemical, physical, and mineralogical qualities, the research stated.

The Research

This study aimed to prepare CESP, which contained 98% calcium oxide powder with particle sizes ranging within 5–100 μm, from ES waste and use it to produce LWFC (lightweight foamed concrete), in consideration of its high calcium content. (Foamed or cellular concrete is made from a mortar or cement that is mixed with air. It is light on its own, flows easily, requires few aggregates, has relatively low strength, and provides excellent thermal insulation.)

Ten LWFC mixtures consisting of two densities of 600 kg/m³ and 1200 kg/m³ were produced and tested. Each density were made of mixtures with varying proportions of CESP, from 0% to 20%.

The ES was calcined at 900 °C to convert the CaCO₃ into CaO. The fresh, transport, mechanical, microstructural, and thermal properties were investigated. The findings revealed that the slump flow and setting times progressively decreased as the CESP proportion increased. The water absorption, sorptivity and intrinsic air permeability improved as the CESP proportions were increased from 5% to 20%.

The main materials used were ordinary Portland cement (OPC), fine sand, protein-based surfactant, potable water, and CESP.

The slump flow of LWFC mixes at 600 and 1200 kg/m3 with 5%, 10%, 15%, and 20% of CESP was measured and compared with those of the ES0-600 and ES0-1200 mixes. The increase in foam from 24 kg/m³ to 43 kg/m³, which reduced the density from 1200 to 600 kg/m³, slightly increased the slump depth from 247 mm to 251 mm. The addition of 5%, 10%, 15%, and 20% CESP reduced the slump flow by 2.39%, 3.59%, 4.38%, and 5.18% at 600 kg/m³ and by 2.02%, 3.64%, 4.45%, and 5.26% at 1200 kg/m³.

The Findings

The compressive strength, flexural strength, splitting tensile strength, modulus of elasticity, and drying shrinkage went through an initial increase and then a decrease, and the optimal CESP replacement rate was found to be 15%. As well, a marginal rise in thermal conductivity and diffusivity was observed as the proportion of CESP increased.

Based on the SEM and pore dispersion results, adding up to 15% CESP into both LWFC densities resulted in an improved microstructure and enhanced pore dispersion, leading to the formation of a greater amount of C–S–H compounds. The findings were substantiated by enhanced mechanical properties, transport characteristics, and SEM results.

The increase of foam from 24 to 43 kg/m³ reduced the dry density from 1200 to 600 kg/m³ and improved pore dispersion.

Results show that CESP can be a possible substitute for concrete in producing lightweight foamed concrete.

The study was shared by Science Direct, part of Elsevier Publishing Co.