Subyakto

Fast-growing sengon wood falls into the low durability and strength class. Enhancing the physical, mechanical, and fire-resistance properties of sengon can be an important step toward increasing its market value. This study aimed to determine the effectiveness of CaCO3 formation in enhancing physical, mechanical, and fire-resistance properties of sengon wood. The wood was impregnated in two steps with calcium chloride (CaCl2) and assisted potassium carbonate (K2CO3) at three concentrations (0.5, 1, and 2 mol/L). The results showed that the consequent CaCO3 mineralization process at moderate concentrations improved wood properties. The concentrations of 0.5 and 1 mol/L showed optimal overall performance in improving the properties of sengon wood, with 0.5 mol/L offering potential advantages in terms of treatment efficiency. In particular, mechanical properties were increased by about 20% compared to the control. The use of CaCO3 at 2 mol/L was less effective at improving mechanical properties. However, the physical and fire resistance properties were comparable to those of moderate concentrations of 0.5 mol/L and 1 mol/L. Based on this work, mineralization can be regarded as an alternative to improve wood properties, especially fire resistance, for environmentally friendly structural applications.

Mortar has been widely applied as a coating for various purposes on building infrastructures, including basements, water tanks, retaining walls, dams and building exteriors, where resistance to moisture and water is highly required. Various chemicals have been added to mortar to reduce its water permeability. However, they raise environmental problems, therefore, environmentally friendly additives are indispensable. The purpose of this study was to enhance the water resistance, compressive strength, and crack recovery ability of mortar with the addition of hydrochar from biomass. Hydrochar was prepared from the hydrothermal carbonization of coconut coir fiber at 150°C for 4 hours. The hydrochar was added to the mortar at different particle sizes and ratios to cement. Mortars were made by mixing cement, sand, water, superplasticizer, and hydrochar; and they were tested after 28 days. The results showed that the addition of 1 wt% hydrochar with a particle size of 150-250 µm reduced the water permeability of mortar, as evidenced by a 36.45% decrease in secondary water absorption and a 14.94% reduction in percentage of void. In addition, the compressive strength increased by 10.29% compared to the control mixture. Hydrochar can absorb water bubbles in the mortar mixture; however, excessive hydrochar causes the mortar to be more porous. The addition of hydrochar in mortar demonstrated superior crack recovery abilities because it functions as a connection medium to accelerate the recovery.

This study aims to produce mortar through the addition of oil palm shells (OPS)-activated charcoal and oil palm empty fruit bunch (OPEFB) hydrochar, which has high mechanical properties, self-healing crack capabilities, and pollutant adsorption abilities. The cracking of mortar and other cementitious materials is essential in anticipating and reducing building damages and ages due to various reasons, such as chemical reactions, foundation movements, climatic changes, and environmental stresses. This leads to the creation of self-healing mortar, which is produced by adding reductive crack size materials to form calcium carbonate (CaCO₃) and silicate hydrate (3CaO.2SiO₂.2H₂O, CSH). One of these materials is known as activated charcoal, which is obtained from oil palm shells (OPS) and oil palm empty fruit bunches (OPEFB) fibres. This is because the OPS-activated charcoal minimizes crack sizes and functions as a gaseous pollutant absorber. In this study, activated charcoal was used as fine aggregate to substitute a part of the utilized sand. This indicated that the utilized content varied between 1–3 wt.% cement. Also, the mortar samples were tested after 28 days of cure, including the mechanical properties and gaseous pollutant adsorption abilities. Based on this study, the crack recovery test was also performed at specific forces and wet/dry cycles, respectively, indicating that the mortar with the addition of 3% activated charcoal showed the best characteristics. Using 3% of the cement weight, OPEFB hydrochar subsequently varied at 1, 2, and 3% of the mortar volume, respectively. Therefore, the mortar with 3 and 1% of OPS-activated charcoal and OPEFB hydrochar had the best properties, based on mechanical, self-healing, and pollutant adsorption abilities.

The compatibility of oil-palm-trunk fibers and cement was investigated. Cold-water and hydrothermal carbonization treatments were applied on the fibers, and then the hydration temperature was measured to observe the compatibility. Calcium chloride (CaCl₂), as an accelerator, was added at 1.5, 3.0, 4.5 and 6.0% of cement weight. The results showed that cold-water treatment and hydrothermal carbonization of the fibers reduced the hemicelluloses and ash content, thereby increasing the compatibility. Fourier transform infra-red analysis showed that functional groups of untreated and treated fibers were almost identical, indicating that the addition of treated fibers did not interfere the hardening process of cement. The treatment of fibers resulted in reduced thermal stability of the cement-fibers mixture, and the addition of CaCl₂ decreased the hydration temperature of the mixtures, indicating that the chemical accelerated the hardening of the cement-fibers mixture. The addition of 1.5% CaCl₂ to the cement mixture with treated fibers was adequate to obtain a low inhibitory index. Field emission scanning electron microscopy showed that higher formation of calcium silicate hydrate and calcium carbonate was observed in the treated fibers compared to the untreated fibers. The board modulus of elasticity increased by 215% and 281% after the fibers underwent with cold-water treatment and hydrothermal carbonization, respectively.

The effective use of agricultural residues is desirable. In this study, the manufacturing of mouldings using sweet sorghum bagasse powder and citric acid as an adhesive was attempted. The effects of the application method and citric acid content on the bending properties and water resistance of the mouldings were investigated. Powder and liquid applications were used. The citric acid solid content based on the total weight of the mouldings was adjusted to 0, 15, 20, 25, and 30 weight percent. The dumbbell-shaped moulding was manufactured at 200 degrees C and 4 MPa for 10 minutes. The relationship between the bending properties and citric acid content differed depending on the application method; the powder application was effective for obtaining high bending properties with a lower citric acid content. The water resistance of the moulding was greatly affected by the application method when a low citric acid content was used, and it was affected by the citric acid content when a high citric acid content was used. According to the data measured from Fourier-transform infrared spectroscopy, it was easy to contain unreacted citric acid in the moulding with the powder application, and an ester linkage formed easily when the liquid application was used. It was suggested that the citric acid tends to work as an adhesive in the powder application, and it tends to modify the bagasse powder in the liquid application.

Bacteria as Self-Healing Agent in Mortar Cracks