Geopolymer is an inorganic polymer from activation of source materials that rich of silica and alumina with alkaline activator. Previous studies reveal that the geopolymer has engineering properties and durability, which is equivalent or higher than the Ordinary Portland Cement (OPC) concrete. This paper presents properties of geopolymer concrete prepared with local Palm Oil Fuel Ash (POFA) and Fly Ash (FA) from agro-industrial waste in Riau Province, Indonesia. The POFA and FA were activated by a combination of sodium hydroxide and sodium silicate. The specimens were cured at room temperature for 24 hours before steam cured for another 24 hours at 60OC. Hardened properties namely compressive strength, tensile strength, flexural strength and modulus of elasticity, and water penetration of both POFA and FA geopolymer concrete were determined at 7, 14 and 28 days. Results showed that local POFA and FA as geopolymer source materials could produce mix with strength 19-22.5 MPa at 28 days. The compressive strength, tensile strength, flexural strength and modulus of elasticity of both geopolymer tended to increase slightly with time. In general, the results suggest that the local POFA and FA are potential as source material to produce geopolymer concrete.

The concrete structure exposed to high temperatures can affect the strength of the structure. Limitations in the experimental method can be solved by mathematical modeling. This study aims to identify the stress and strain behavior that occurs at high-temperatures. The model is a cylindrical concrete with a diameter of 150 mm and a height of 300 mm. The concrete strength design is 25 MPa. The temperatures of the model are 100 °C, 200 °C, 300 °C, 400 °C, 500 °C, 600 °C, and 700 °C. The model analysis using LUSAS v. 16 Software to observe the properties of the concrete material due to exposure to high temperatures. The results of the study get the higher the temperature received by concrete, the strength of the concrete decreases. Concrete that burned to a temperature of 300 °C still had 82% available power, and at a temperature of 700 °C, the remaining concrete strength was 30%. The strain increases to 423% from normal conditions at a temperature of 700 ° C. Therefore, the results of the study can be used as a reference for structural engineers to know the behavior of the concrete that exposure to high temperatures.

This research investigates the behaviour of non-engineered reinforced concrete (RC) beams strengthened with embedded steel bars. Two RC beams, namely control beam (Beam-A) and strengthened beam (Beam-B) were fabricated and tested under shear loading. Beam-B was strengthened with four 12 mm steel bars embedded in the core of the concrete beam. The results showed that Beam-A experienced shear failure while Beam-B failed in flexural tension where most cracks developed in the flexural span. The embedded steel bars were proven to shift failure mode from shear failure on Beam-A to flexural one on Beam-B. Furthermore, the shear capacity of the strengthened beam was enhanced by 31% compared to that of the control beam.

Geopolymer hybrid concrete is prepared by activating fly ash bottom ash with an alkaline solution and curing with Ordinary Portland Cement (OPC). OPC could be added to the mixture to increase the reaction, promote hydration, and assist in curing at room temperature. Peat water is an acidic organic environment that may reduce the durability of concrete. The purpose of this research is to determine the effect of Portland cement on the properties of FABA geopolymer hybrid concrete exposed to peat water. Portland cement was used in geopolymer as an additive and a substitute. Compressive strength, porosity, and weight change were evaluated for both mixtures. The NaOH molarities were 10, 12, and 14M, the NaOH/sodium silicate ratios were 1.5, 2.0, and 2.5, and the Ordinary Portland Cement percentages were 0, 10, and 15%. Specimens were exposed to peat water for up to 91 days following 28 days of room temperature curing. The geopolymer mixture with 10M NaOH, 2.5M Ms, and 15% OPC had the highest compressive strength and the lowest porosity. The FABA geopolymer hybrid with OPC had a slightly greater compressive strength and a lower porosity than the geopolymer containing OPC as a cement replacement material. In addition, weight change is more stable in geopolymers containing OPC. Based on the performance of both mixes in peat water, it is recommended to use OPC as an additive in FABA geopolymer hybrid concrete.

Kayu adalah bahan yang umum digunakan baik secara struktural maupun non-struktural. Penggunaan kayu dalam bentuk struktural memerlukan spesifikasi tertentu. Kayu adalah bahan alami yang pertumbuhannya dipengaruhi oleh faktor lingkungan yang menyebabkan perbedaan kualitas kayu. Penelitian ini bertujuan untuk menguji dan memperoleh nilai kuat tekan sejajar serat kayu dan kuat geser kayu serta mengklasifikasikan kayu berdasarkan SNI 7973: 2013. Kayu tembusu (Fragraea fragrans) digunakan sebagai objek dalam penelitian ini. Hasil pengujian diperoleh nilai kuat tekan paralel kayu tembusu variasi A 16,31 MPa sehingga termasuk dalam kategori kayu dengan kode mutu E19. Nilai kuat tekan sejajar serat kayu kayu tembusu variasi B 16,26 MPa sehingga termasuk dalam kategori kayu dengan kode mutu E18. Modulus elastisitas kayu tembusu variasi A yang diperoleh adalah 3.555,95 MPa dan 5.324,24 MPa untuk variasi B. Nilai kuat geser kayu variasi A didapat sebesar 2,54 MPa dan untuk variasi B didapat 3,27 MPa. Penelitian ini bermanfaat untuk menganalisis kuat tekan sejajar serat, kuat geser kayu dan untuk penelitian lanjutan lainnya. Hasilnya diharapkan berkontribusi pada basis data ilmiah umum sifat mekanis kayu di Indonesia dan khususnya dalam desain komponen struktural tekan dan lentur serta untuk penelitian lebih lanjut.