Análise da influência da casca de ovo moída no melhoramento de solo da formação guabirotuba

Abstract

The search for sustainable and innovative solutions in civil engineering has led to the exploration of alternative materials for soil improvement and stabilisation, especially those with characteristics that impose restrictions on engineering projects, such as the Guabirotuba Formation soils found in the Curitiba-PR region. This study investigates the use of ground eggshell, potassium hydroxide, and micro silica as additives for the improvement of a soil from the Guabirotuba Formation. The main objective of this research is to analyse the influence of ground eggshell on the enhancement of this soil. The study aims to evaluate the mechanical behaviour of the soil improved with varying percentages of ground eggshell and micro silica, combined with potassium hydroxide, providing a technical basis for the application of these materials in paving. From an environmental sustainability perspective, this work promotes the use of agroindustrial waste, reducing reliance on non-renewable natural resources. The proportions of eggshell (0% to 5%) and micro silica (0% to 4%) were varied, while the soil, KOH content (1%), specific mass, moisture, and temperature were kept constant. The materials were characterized through grain size distribution, specific gravity, compaction, Atterberg limits, XRF, mini-MCV, and mass loss by immersion tests. The mixtures were assessed using pH, XRD, and SEM analyses. Mechanical strength tests included unconfined compressive strength (UCS) and tensile strength by diametral compression. The results indicate strength gains in most mixtures after a 60-day curing period, while a slight reduction in qu was observed at 7 days. Mixture 431 (4% ground eggshell, 3% micro silica, and 1% KOH) exhibited the highest UCS improvement (490%), reaching 1231 kPa at 60 days. Meanwhile, Mixture 041 (0% eggshell, 4% micro silica, and 1% KOH) achieved the highest UCS at 60 days (1555 kPa), at a 167% increase compared to the initial time. The tensile-to-compressive strength ratio ranged between 7.3% and 14.8%. SEM imaging revealed a denser and more homogeneous microstructure after 60 days of curing in mixtures with higher and balanced proportions of ground eggshell and micro silica. XRD analysis identified peaks corresponding to quartz, gibbsite, and calcite, though the presence of C-S-H could not be confirmed. The presence of micro silica and ground eggshell was noted in the mixtures, albeit with peak smoothing. This study demonstrates that ground eggshell, KOH, and micro silica can be effectively applied to improve clayey soils of the Guabirotuba Formation. The use of balanced proportions of ground eggshell and micro silica resulted in a soil with a dense and homogeneous microstructure after 60 days of curing, with few unreacted particles. Mixtures 431 and 541 exhibited the second-highest rupture stress among the studied mixtures.