Sustainable Disposal of Pecan Shells

Urbanization acceleration has increased the consumption of natural resources and carbon footprint, pushing the need for sustainable development. Even though various construction materials are needed for infrastructure development, the most commonly used material is Ordinary Portland Cement for strength (OPC) and durability, while sand is used as a filler in the mixes prepared with OPC. The main goal of this study is to find a sustainable substitute for sand, which is locally available and currently being placed in landfills. One such material is pecan shells, and a thorough analysis of the literature led us to investigate the possible use of pecan shells in cement mortar mix. The pecan shells can be milled or ashed and then mixed in the cement mortar mix by substituting a portion of sand with pecan and tested as per ASTM- C109 guidelines, which provide the necessary ratios of OPC, sand, and water for a control mix. The study also sought whether adding pecan shells would improve the mortar's compressive strength in fly ash presence. Under ASTM C109, the extent of this study concentrated on assessing the compressive strength of 2-inch mortar cubes. The sand proportions substituted with pecan shells ranged from 2% to 5% in increments of 0.25%. Additionally, the evaluations included varying curing times of 3, 7, 14, and 28 days to track strength gain over time. The average strength gains for specimens at varying substituted proportions were 389 psi from 3 to 7 days, 382 psi from 7 to 14 days, and 498 psi from 14 to 28 days for milled pecan shells (MPS). MPS specimens with fly ash showed average strength gains of 291 psi from 3 to 7 days, 478 psi from 7 to 14 days, and 391 psi from 14 to 28 days. Ashed pecan shells (APS) with fly ash resulted in average strength gains of 475 psi from 3 to 7 days, 448 psi from 7 to 14 days, and 573 psi from 14 to 28 days. APS only specimens resulted in strength gains averaging 450 psi from 3 to 7 days, 513 psi from 7 to 14 days, and 455 psi from 14 to 28 days. This study offers important new perspectives on the viability of pecan shells as a sustainable material in cement mortar, benefiting the building sector both in terms of waste reduction and resource economy. The analysis suggested that the milled pecan shells with and without fly ash lowered the compressive strength; thus, milled pecan shells are unsuitable for use in cement mortar mix. However, a mixture of ashed pecan shells and sand additions performed favorably compared to the control specimens by 500 psi and could partially replace sand.