Ultimate Load and Workability Optimisation of Coconut-Shell Plain-Concrete Beams Incorporating Sikament-NN

Fahrizal Zulkarnain; Ainurrasyid

doi:10.30736/cvl.v11i2.1741

Authors

Fahrizal Zulkarnain Universitas Muhammadiyah Sumatera Utara
Ainurrasyid Universitas Muhammadiyah Sumatera Utara

DOI:

https://doi.org/10.30736/cvl.v11i2.1741

Keywords:

Coconut-shell aggregate, Plain-concrete beam, Ultimate beam load, Sikament-NN, , Superplasticiser, Sustainable concrete

Abstract

Agricultural coconut-shell waste offers a renewable alternative to mineral aggregate, but its porous surface may reduce concrete workability and mechanical performance. This study evaluates whether Sikament-NN can compensate for these effects in plain-concrete beams. Twenty-one specimens measuring 600 x 150 x 150 mm were produced in seven mixtures: a normal-concrete control, three mixtures containing 1.5%, 1.7% and 1.9% coconut-shell fragments as partial coarse-aggregate replacement, and three corresponding mixtures incorporating 2.3% Sikament-NN by cement mass. Slump, 28-day compressive strength and ultimate beam load under central loading were assessed. Increasing coconut-shell content without admixture reduced slump from 100 to 75 mm and decreased mean ultimate beam load from 37.00 to 35.37 kN. Sikament-NN restored slump to 100-110 mm and maintained mean ultimate beam load between 36.50 and 36.87 kN. The mixture containing 1.9% coconut shell and Sikament-NN achieved 29.73 MPa compressive strength and a 36.80 kN ultimate beam load, retaining 98.78% and 99.46% of the control values, respectively. Because the archived test record did not preserve sufficient crack-pattern evidence to distinguish diagonal-shear failure from mid-span flexural-tensile failure, the response is reported as ultimate beam load rather than shear capacity. The findings indicate that Sikament-NN effectively offsets the workability loss and most of the mechanical-performance reduction associated with low-volume coconut-shell incorporation.

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