Olive waste ash as a sustainable supplementary cementitious material in mortar productions

Abstract

The thesis explores the potential of olive waste ash (OWA) as a supplementary cementitious material (SCM) to create more sustainable cement mortar composites. It delves into the impact of substituting ordinary Portland cement (OPC) with varying percentages of OWA on mortar properties. Conventional cement production has significant environmental impacts, such as high energy consumption, greenhouse gas emissions, and resource depletion. To mitigate these effects, there is a shift toward sustainable alternatives. This study explores using calcined olive waste ash (OWA) as a partial replacement for cement in mortar production. The aim is to identify the optimal calcination temperature and particle size of OWA to maintain the mortar's properties. Research has shown that replacing cement with OWA can degrade the mechanical properties of mortar. Therefore, the study focuses on optimizing the combustion temperature and process duration to improve OWA quality. Specifically, OWA is calcined at 400°C and 600°C for 2 hours and tested in different particle size distributions (<90, 90-180 and 180-360 microns). The study evaluates the optimal OWA particle size and calcination temperature by measuring the strength activity index (SAI). It also examines the ideal replacement percentage for maintaining mechanical properties and minimizing the alkali-silica reaction (ASR). Additionally, capillary water absorption tests assess the mortar's durability and moisture resistance. The experimental plan includes a systematic approach to evaluate OWA as a supplementary cementitious material. The methodology involves selecting particle size distribution and calcination temperature, recognizing their impact on reactivity and workability. Phase 1 focuses on determining the best SAI results out of different calcination temperatures and particle sizes, then Phase 2 examines mechanical strength, durability, and material characterization of the optimum OWA known by Phase 1 to study different replacement percentages with cement. The methodology outlines a systematic approach, beginning with the selection of OWA particle size distribution, which is crucial for reactivity and workability. Optimization of calcination temperature follows, aiming to enhance pozzolanic properties. The study quantifies the strength activity index (SAI) to measure the ash's ability to improve mortar strength through chemical reactions. Durability tests evaluate resistance to environmental stresses, while mechanical strength tests gauge structural suitability. Material characterizations are conducted using SEM and XRD analysis. A series of mortar mixtures are designed with increasing OWA content, ranging from 5% to 20% replacement of OPC. Adjustments to the water-to-cement ratio (W/C) are made to balance workability and strength, with the addition of superplasticizers to maintain consistent flow across mixes. An extensive experimental plan is executed, examining particle size distributions and calcination temperatures (400°C and 600°C) to optimize Strength activity. Results indicate that finer particle sizes consistently enhance both flexural and compressive strengths, particularly at 600°C calcination. However, as OWA content increases, there is a gradual reduction in strength, albeit remaining within acceptable ranges for construction standards. The study also investigates the influence of OWA calcination temperature on mitigating alkali-silica reaction (ASR) in mortar mixes through accelerated mortar bar tests. While results show negligible ASR expansion, increasing expansion rates are observed over time, with subtle differences noted between calcination temperatures. Reduced the expansion is spotted while increasing OWA content. Furthermore, capillary water absorption tests reveal that higher OWA content leads to significantly greater absorption rates over time due to increased porosity. XRD results and SEM images provide insights into the microstructural changes induced by OWA addition, highlighting its participation in pozzolanic reactions and enhancement of calcium-silicate-hydrate (C-S-H) formation. Research shows that using OWA in cement mortars helps reduce waste and construction materials' carbon footprint, which is contributing in a more sustainable environment. The results highlight the significance of carefully selecting particle size and calcination conditions, and despite obstacles connected to increased porosity, they reinforce OWA's potential as a sustainable SCM. Overall, the thesis presents a comprehensive exploration of OWA's impact on mortar properties, offering valuable insights into its potential as a sustainable alternative in construction practices.