RHEOLOGICAL ASSESSMENT ON OPTIMAL MIX DESIGN OF BEANS POD ASH CEMENT BLENDED WITH SELF-COMPACTING CONCRETE
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Date
2024
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University Of Ilorin
Abstract
Characterization of fresh concrete using material science is crucial to the determination of concrete rheological properties. The aim of this study was to investigate the performance characteristics of optimal mix of calcined Beans Pod Ash (BPA) in Self-Compacting Concrete (SCC). The objectives of the study were to: (i) determine the pozzolanic or chemical oxides of BPA; (ii) characterize BPA based on performance parameters of pozzolanicity due to calcination; (iii) determine the rheological properties of freshly prepared calcined BPA-cement SCC; (iv) evaluate strength, durability and fresh properties of calcined BPA-cement SCC; and (v) evaluate the optimum concrete performance parameters as affected by variation of mixture parameters.
Bean pod was crushed and burnt using a gas burner. The resulting ashes were pulverized using hammer mill. Thereafter, the ashes were calcined at temperature ranging from 500oC to 900oC at 100oC interval and time ranging from 1-hour to 5-hours at 1-hour interval for sample population as obtained from design of experiment. Laboratory investigation conducted on BPA included chemical analysis for oxides composition, mineral contents, material morphology, and statistical analysis performed using central composite design of response surface method. The influence of mix parameters such as partial replacement of cement with BPA, super-plasticizer dosage, water-binder and fine-to-total aggregate ratios on compression and tensile strength, rheological properties, durability of SCC were investigated and statistical analysis performed using Taguchi Method.
The findings of the study were that:
the pozzolanic oxides of calcined BPA ranges from 30.46% to 35.02% for silica, 9.86% to 12.98% for alumina and 8.27% to 11.80% for iron oxides, at different calcination parameters;
calcined BPA exhibited a class C pozzolanic properties based on ASTM C618-12a specifications; and contains large amount of quartz and cristobalite, with optimum pozzolanic performance at 738.38oC burning temperature and 3.45-hours of dwelling time;
the concrete fresh property ranges from 3.03 Pa.s to 3.99 Pa.s for viscosity, 515 mm to 678 mm for slump flow, 0.7576 to 0.9037 for passing-ability and 10 secs to 65 secs for flow-ability, showing satisfactory response based on EFNARC (2002);
BPA is the most contributing factor to concrete properties with the highest percentage contribution of 86.39% for compressive strength, 81.81% for viscosity and 81.84% for slump flow; and a combination of super plasticizer, aggregates and BPA for concrete porosity at 81.33%, as obtained from analysis of variance results; and
the optimum concrete mix conditions for concrete strengths were attained at 0.35, 5%, 6% and 0.4 for water to binder ratio, percentage of cement replaced with BPA, super-plasticizer dosage, and ratio of fine to total aggregate, respectively.
The study concluded that the presence of optimum quantity of BPA, up to 15%, in SCC mix significantly influenced concrete workability, strengths and durability. Therefore, it is recommended that the use of BPA in concrete mix be promoted as pozzolan to produce durable concrete for sustainable concrete structure.
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Keywords
Concrete, Mix, Rheological, Design, Pod