Febrianti, Meliana (2024) Pengaruh Penambahan Cangkang Kemiri Untuk Substitusi Sebagian Agregat Kasar Dengan Bahan Tambah Superplasticizer Terhadap Kuat Tekan Beton. Other thesis, Universitas Islam Riau.

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Abstract

Concrete is a mixture of cement, fine aggregates, and coarse aggregates bound together with water, with or without additional materials, forming a solid mass. As the use of concrete increases over time, the demand for aggregates in concrete production is very high, potentially leading to a reduction in the availability of natural resources for concrete structures. Alternatives for concrete mixtures need to be explored, such as using agricultural by-products that are no longer utilized, specifically candlenut shell waste (Sitorus et al., 2023). Candlenut shells can be maximally utilized as a partial replacement for coarse aggregates, which is expected to help reduce the negative environmental impact. The composition of candlenut shells, which includes CaO, SiO2, Al2O3, MgO, H2O, and Fe2O3, reacts to form a residual SiO2. This unreacted SiO2 can react with CSH gel-2 to produce a denser CSH gel-3, enhancing the cement paste and aggregate. However, there is a drawback of higher water absorption, necessitating the use of superplasticizer additives (Sutanto et al., 2021). Water-reducing superplasticizers are additives that can reduce water usage by up to 20% and improve concrete compressive strength by up to 40%. This additive can increase the concrete slump value to 8 inches or more, with the recommended dosage being 1%-2% of the cement weight used. This study aims to assess the effect of slump value using a pine nut shell mix with superplasticizer and the compressive strength of concrete using pine nut shells as a partial substitute for coarse aggregates, with mix variations of 0%, 2%, 4%, and 6% of the coarse aggregate weight and 1% superplasticizer by cement weight. This research method was conducted based on the standards of SNI 7656-2012 with a quality of K-250. The test specimens were cylindrical concrete measuring 15 x 30 cm with variations of candlenut shell at 0%, 2%, 4%, and 6% of the weight of the coarse aggregate, with an additional material of 1% superplasticizer by weight of cement, totaling 24 samples. The results of the research showed that the variations of candlenut shell concrete at 0%, 2%, 4%, and 6% as partial replacements for coarse aggregate had compressive strengths of 21,7 MPa, 29,7 MPa, 25,1 MPa and 22,7 MPa, respectively. Meanwhile, the addition of 1% superplasticizer concrete had a compressive strength of 40.7 MPa, which was one of the highest compared to other concretes. The mix of 1% superplasticizer + 2%, 4%, and 6% candlenut shell resulted in compressive strengths of 30,3 MPa, 30 Mpa and 25,6 Mpa, respectively. Based on the research findings, future researchers can explore variations in mixing candlenut shell with different ratios to enhance the compressive strength of concrete. Additionally, incorporating admixtures with candlenut shell could be investigated. As the amount of candlenut shell increases, the compressive strength tends to decrease due to the organic waste nature of the candlenut shell used in this study. However, the compressive strength achieved with candlenut shell usage meets the planned quality standards. The study concludes that increasing the amount of candlenut shell and adding superplasticizer has not yet shown a significant improvement in the compressive strength of the concrete.

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