Clay soil behavior often becomes problematic with building construction, it is about the shrink-swell behavior in clay when influenced by water content. Coconut husk fiber (coir fiber), in general, is an industrial waste which is still infrequent to be re-used. This study aims are to determine the effect of coir fiber addition for mechanical stabilization of clay soil in terms of CBR (California Bearing Ratio) value. Soil samples used for laboratory tests were collected from Ulee Glee area of Pidie Jaya Regency. According to AASHTO classification, the soil category is A-7-5 (25) while for USCS classification, the soil is OH (Organic High). The percentage of added coir fiber was 0%, 0.2%, 0.4% and 0.6% of the dry weight of the soil with a coir fiber length of 2 and 3 cm. Two treatments of clay-coir fiber mixing method were applied namely direct mixing and mixing by layers. The results of natural soil compaction test obtained that OMC (Optimum Moisture Content) value and dry soil weight (γdmax) was 26.8% and 1.34 gr/cm3 respectively. The highest CBR results were obtained for clay soil with 0.4% coir fiber 3 cm (direct mix) with CBR value = 17.7%. Furthermore, the lowest CBR value is 10% for percentage of 0.2% with coir fiber length 2 cm (by layer). In general, high organic clay soil with coir fiber mixture addition is able to increase the CBR values if compared to CBR of natural soil which is 8.15%. Thus, the use of coir fiber in this study is able to improve soil bearing capacity which is useful for construction material in the site.

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The types of wood in Banda Aceh used was seumantok, meranti, and sembarang wood. The process of wood leaves sawdust. The sawdust becames rubbish and could pollute the environment. There was five quality of woods, namely quality I - quality V. The purpose of this study is to optimize the sawdust of seumantok (quality I), meranti (quality II), and sembarang wood (quality III) to be processed into wood ash as a substitute for a part of cement in concrete with its percentage were 5% and 10%. The research method was experimentally in a laboratory-based on ASTM (American Society for Testing and Materials) and ACI (American Concrete Institute). The maximum diameter of the aggregate was 25.4 mm, and the compressive strength of concrete was 14.5 MPa with 21 specimens of cylindrical concrete. Concrete compressive strength results at 28 days with 5% wood ash variation and 10% respectively for quality I were 15.83 MPa and 14.20 MPa, quality II was 13.56 MPa and 12.75 MPa, and quality III were 13.79 MPa and 10.75 MPa. While the normal compressive strength of concrete was 15.86 MPa.

Finding alternatives to natural resources is important for a sustainable future and is essential to infrastructure projects. Among these replacements is the use of coffee waste as soil stabilizers. Coffee husk ash (CHA) is a solid waste obtained by the processing of coffee beans on a farm or factory. The main aim of this study is to determine the geotechnical properties of clay soil treated with CHA to develop a low-cost, environmentally friendly alternative composition. Laboratory tests were conducted to investigate the influence of CHA on the physical properties and the mechanical properties of clay. The CHA concentration was adjusted from 5% to 25% by the dry weight of clay in 5% increments. The clay classification of the mixture becomes coarser following the addition of the CHA. At 25% CHA, a peak UCS of 130.83 kN/m2 was measured compared with the untreated clay of 89.17 kN/m2. In addition, the cohesion values and internal friction angles of soil for 0% and 25% CHA increased from 80.1 kN/m2 to 148.7 kN/m2 and from 16.1° to 25.8°, respectively. It was found that CHA can improve the strength of clay by forming a pozzolanic and hydration process that fills soil voids and binds particles together.

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Industrial solid wastes have become a difficult problem in some developing countries, especially in Indonesia. The environmentally friendly issue regarding how to decrease industrial wastes by reuse or recycling process has become famous in recent years. Coffee husk ashes in this research were attained from burned waste coffee husk which can be considered as solid waste material from the coffee processing industry. In this study, clay soil obtained from Cot Bagie Village, Blang Bintang, Aceh was mixed with coffee husk ashes. Several soil physical properties test was conducted such as specific gravity, Atterberg limit, and grain size distribution by following ASTM standard. The physical parameter of soil was evaluated with the addition of 3%, 6%, 9%, and 12% coffee husk ashes by soil dry weight. The result shows that the physical properties of soil were improved if compared to untreated soil. A further mechanical laboratory test in soil mechanics was suggested for more advanced analysis of effect in soil-coffee husk ashes mixing.

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