Engineering Journal of Research and Development

EFFECTS OF RECYCLED CONCRETE AGGREGATE TYPES ON THE DURABILITY OF CONCRETE UNDER MARINE ENVIRONMENTS IN THAILAND

Assoc.Prof.Dr.Taweechai Sumranwanich, Aunchana Kijjanon, Lyna Prak — Tue, 31 Mar 2026 00:00:00 +0700

This paper investigates the effects of recycled concrete aggregate (RCA) types on the chloride penetration resistance and compressive strength of concrete exposed to marine environments in Thailand. Two types of recycled coarse aggregates were used: RCA obtained from precast concrete plants (RAA) and RCA from ready-mixed concrete plants (RAB), which were partially replaced with natural coarse aggregate (NA) at replacement levels of 10%, 25%, and 50%. The concrete mixtures were designed with a water-to-binder ratio of 0.40 and a fly ash-to-binder ratio of 0.30. Tests on chloride penetration resistance, reinforcement corrosion, and compressive strength were conducted after 2 and 7 years of marine exposure. The experimental results revealed that cement-fly ash concrete incorporating both types of recycled concrete aggregate exhibited higher resistance to chloride penetration and reinforcement corrosion than cement-only concrete with NA. However, the compressive strength of recycled aggregate concrete was lower than that of the control mix. When the percentage of recycled concrete aggregate replacement was considered, it was found that increasing the replacement ratio of recycled coarse aggregate led to reductions in chloride resistance, corrosion resistance, and compressive strength. Furthermore, concrete containing RAA showed higher chloride resistance and compressive strength than that containing RAB.

ENGINEERING PROPERTIES OF CLAY STABILIZED WITH EUCALYPTUS WOOD ASH AND STONE DUST FOR ROAD EMBANKMENT MATERIAL

Natapong Nuypet, Prof. Dr.Pittaya Jamsawang — Tue, 31 Mar 2026 00:00:00 +0700

Eucalyptus wood ash and stone dust are industrial by-products with the potential for reuse in civil engineering applications, particularly for improving the properties of clayey soils, which cannot be directly used as embankment materials due to their low shear strength, low bearing capacity, and high swelling behavior. This research aims to investigate the effects of partially replacing clay with eucalyptus wood ash and stone dust at various proportions to enhance soil strength and reduce the consumption of natural materials. The laboratory tests conducted include the California Bearing Ratio (CBR), swelling, and Direct Shear tests. All specimens were prepared at their Optimum Moisture Content (OMC) and Maximum Dry Density (MDD) in accordance with ASTM D1557. The test results indicate that the addition of eucalyptus wood ash helps densify the soil structure by filling voids, while stone dust increases the internal friction within the mixture. Consequently, the CBR value increased from 5% in natural clay to a maximum of approximately 33–42% at the optimal mixture proportion. Meanwhile, the cohesion (c) tended to decrease with increasing proportions of replacement materials, whereas the internal friction angle (φ) significantly increased. Overall, the mixture of eucalyptus wood ash and stone dust can effectively improve the engineering properties of clay, making it suitable for use as embankment fill material in accordance with the Department of Rural Roads standard DRR 201/2545.

DESIGNING AN INNOVATIVE DRYING AND STORAGE SYSTEM OF PADDY RICE: TOWARDS A PROTOTYPE FOR PRACTICAL IMPLEMENTATION

Tue, 31 Mar 2026 00:00:00 +0700

This research aimed to design a lab-scale innovative drying and storage system for paddy rice, which controlled the airflow velocity for uniform distribution through the grain bed. The experimental results showed that the deviation of the local air velocity compared to the overall average velocity was only 9.7%. The study also employed Ansys FLUENT computational fluid dynamics software to predict the airflow characteristics within the system, revealing a 10.6% difference between the numerical predictions and the experimental results. The results from this study were utilized to co-design a practical innovative drying system capable of holding up to 2.7 tons of paddy rice. This machine would help solve problems for farmers in Thailand and provide knowledge regarding airflow organization within drying systems.

PROPERTY IMPROVEMENT OF RECYCLED PLASTIC PELLETS FROM HIGH DENSITY POLYETHYLENE WASTE WITH COCONUT FIBER

Assoc. Prof.Dr.Jittra Rukijkanpanich, Panisara Juntra — Tue, 31 Mar 2026 00:00:00 +0700

This research aimed to improve the properties of recycled HDPE plastic pellets using coconut fiber as a reinforcing material. The recycled HDPE was obtained from post-consumer detergent bottles and shampoo bottles. Polyethylene-grafted Maleic Anhydride (PE-g-MA) was used as a compatibilizer. All raw materials were ground and mixed at the following weight ratios of HDPE: PE-g-MA: coconut fiber: 50:5:45, 60:5:35, 70:5:25, 80:5:15, and 90:5:5. The mixtures were then melt-blended using a twin-screw extruder at a temperature of 180°C. Subsequently, the samples were tested according to ASTM standards. The mechanical properties evaluated included tensile test, impact test, and hardness test. The physical property tested was the melt flow index (MFI). The research was divided into two stages: laboratory-scale experiments to determine the optimal mixing ratio, followed by validation of the selected ratio under production conditions in the factory. The results indicated that the composition ratio of 90:5:5 provided properties most comparable to those of 100% recycled HDPE. Moreover, this formulation could be successfully processed into plastic pallets, demonstrating its potential for practical industrial applications.

OPTIMIZATION OF PROCESS PARAMETERS FOR REDUCING SHORT SHOT DEFECTS IN INJECTION MOLDING: A CASE STUDY OF AN ELECTRICAL APPLIANCE FACTORY

akkaradeth ratsaree, Dr.Pholchai Chotiprayanakul — Tue, 31 Mar 2026 00:00:00 +0700

This research aims to determine the optimal process parameters for plastic injection molding in order to reduce the occurrence of short shot in AC power cord plug production. Short shot is one of the most critical defects affecting product quality and manufacturing efficiency in the studied factory. Production data collected between January and December 2024 showed that 19,957 defective parts were identified as short shot out of a total production of 1,674,504 parts, representing 1.2% of total production. To investigate the root causes of the problem, data collection and brainstorming sessions were conducted with the production team, followed by root cause analysis using a cause-and-effect diagram. Three key process parameters influencing short shot were identified: melt temperature, injection pressure, and injection speed. The injection molding process was then simulated using SolidWorks Plastics to analyze melt flow behavior and determine appropriate parameter ranges. A full factorial experimental design (3³ factorial design) was applied to evaluate the effects of these parameters on the filling behavior of molten plastic. Simulation results indicated that injection temperature and injection pressure significantly affected the filling behavior. The optimal process conditions for minimizing short shot were a melt temperature of 200 °C, an injection pressure of 90 MPa, and an injection speed of 70 mm/s, with a gate size of 10 sqr.mm. Validation experiments under actual production conditions confirmed the effectiveness of the optimized parameters. During the validation period, 411,643 parts were produced, of which 1,309 parts were identified as short shot, corresponding to a defect rate of 0.32%. These results demonstrate that appropriate optimization of process parameters can effectively reduce short shot and improve production quality in plastic injection molding processes.