Nanosilica produced from physically-processed white rice husk ash agricultural waste can be incorporated into geopolymer cement-based materials to improve the mechanical and micro performance. This study aimed to investigate the effect of natural nanosilica on the mechanical properties and microstructure of geopolymer cement. It examined the mechanical behavior of geopolymer paste reinforced with 2, 3, and 4 wt% nanosilica. The tests of compressive strength, direct tensile strength, three bending tests, Scanning Electron Microscope-Energy Dispersive X-ray (SEM/EDX), X-ray Diffraction (XRD), and Fourier-transform Infrared Spectroscopy (FTIR) were undertaken to evaluate the effect of nanosilica addition to the geopolymer paste. The addition of 2 wt% nanosilica in the geopolymer paste increased the compressive strength by 22%, flexural strength by 82%, and fracture toughness by 82% but decreased the direct tensile strength by 31%. The microstructure analysis using SEM, XRD, and FTIR showed the formation of calcium alumina-silicate hydrate (C–A–S–H) gel. The SEM images also revealed a compact and cohesive geopolymer matrix, indicating that the mechanical properties of geopolymers with 2 wt% nanosilica were improved. Thus, it is feasible for nanosilica to be used as a binder.

Sodium silicate is a commonly used activator in geopolymer that is produced commercially. In this study, rice husk ash (RHA) from agricultural waste was used to synthesize sodium silicate as an activator for geopolymer cement. This white ash was applied for producing sodium silicate with different molarities (8, 10, and 12) and then used to synthesize fly ash-based geopolymer cement. Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR) were applied to investigate the micro-characteristics of the geopolymerization products. Bulk density, water absorption, compressive strength, flexural strength, and fracture toughness were carried out to measure and evaluate the geopolymers with sodium silicate. The combination of 10 M NaOH with sodium silicate increased the compressive strength by 16.21% and the flexural strength and fracture toughness by 81.6%. However, sodium silicate combined with 12 M NaOH decreased compressive strengths by 13.23% and flexural strength and fracture toughness by 61.94%. The lowest water absorption value of 12.3% was obtained in a geopolymer paste using sodium silicate combined with 10 M NaOH, and the largest was 13.3% for sodium silicate combined with 8 M NaOH. The microstructure analysis showed the hydrated calcium alumina silicate gel (C–A–S–H) and the SEM image also revealed a compact geopolymer matrix. Thus, it can be concluded that sodium silicate from rice husk ash can be utilized as an activator or reactive material to produce geopolymer cement with a good geopolymer network.

The research was conducted to determine the bending capacity of high-strength reinforced concrete beams with the addition of three environmentally friendly synthetic fibers i.e., polypropylene fiber, tie wire fiber, and used rubber tires fiber. Four beams with a dimension of 15 x 30 x 220 cm were tested, including a beam for specimen without fiber as comparison. Specimens were designed to experience bending failure. Yield point of steel (fy) used for flexural and shear reinforcement was 407.43 MPa. The diameter of flexural tensile reinforcement was 15.8 mm, 11.9 mm for the compressive reinforcement, as well as 11.9 mm for the shear reinforcement. Concrete proportion incorporated 8% silica fume and 1.5% polycarboxylate ethers based superplasticizer ViscoCrete 10 from the cement weight. The maximum diameter of split was 15.9 mm, having 550 kg/m3 cement content and w/c-ratio 0.30. The target compressive strength was 70 MPa for cylinder 15/30 cm. The results showed that all beams experienced flexural failure as planned. Addition of fibers enhanced the bending behavior significantly, especially in flexural capacity, deflection and ductility. In comparison with high-strength reinforced concrete beam without fibers, the beam with polypropylene fiber had the increase of flexural strength of 115.24%, deflection of 306.56% and ductility of 298.9%; with tie wire fibers resulted in the increase of flexural strength of 117.39%, deflection of 160.52% and ductility of 148.0%; as well as with used rubber tires fiber produced the enhance of flexural strength of 112.13%, deflection of 184.56% and ductility of 178.3%. It can be concluded that the use of such environmentally friendly synthetic fibers can reduce the brittleness of high strength concrete, in which polypropylene fiber had delivered the best value and can be used very effectively than the other two types of fibers.

Reliable spectral displacement (SD) in a wide range of response periods is crucial in seismic vulnerability assessment for Banda Aceh-Indonesia as the city is founded on a thick-soft soil. This SD is excellent for estimating building drift ratio from which the vulnerability of building is assessed. SD can be obtained from conversion of the acceleration spectra (converted SD) and site response analysis (analyzed SD). In this paper, both converted- and analysed-SDs are developed for Banda Aceh’s soft soil case using three historical seismic events of the 2012 Simeulue II, the 2013 Mane-Geumpang, and the 2013 Bener Meriah earthquakes and three soil models from which acceleration-displacement response spectrum (ADRS) of Banda Aceh’s soft soil is proposed. This proposed ADRS is compared to the generic response spectra of Centre of Research and Development of Housing and Settlement (PUSKIM) Indonesia. It can be concluded that the Proposed ADRSs can be used as another source in determining the performance of a building beside the PUSKIM ADRSs. Furthermore, the developed SDs were used to calculate the drift of 2-, 3-, and 4-storey typical shop-house buildings at Banda Aceh-Indonesia.

Beach erosions have been faced as coastal problem and efforts to address the solution have been sought by the coastal researchers. One of the coastal protection structures that are commonly used are the system of groins. Various types of groins have been investigated and observed either in the Laboratory or directly in the field namely type of the forming material, length of the groins, the distance between the groins, and the width of the groin. However, groins with a zigzag shape are rarely investigated and studied. Hence, this paper reports on changes in beach profile due to the construction of single zigzag type of porous groins named GROPOZAG. The small scale of 1:20 physical model tests have been carried out at the Laboratory of River and Coastal Engineering in Engineering Faculty of Syiah Kuala University. Regular wave were generated in wave basin with 15 m long, 5 m wide, and 0.6 m deep. The influence of single groin length (Lg), and groins orientation perpendicular to the shoreline (θ) of 45°, 63°, and 90° under various wave steepness (H/L) of 0.0409, 0.0235 and 0.0200 with the beach profile of 1:20 slope are elaborated in this paper. Erosion or sedimentation is expressed in terms of sediment total volumes. It is found that groin with 90° orientation is more erosive than that of 45°. Straight porous groins erode more sediments than that of zigzag type porous groins. Zigzag porous groin is better in reducing erosion at the front head of the groin