Utilization of Sea Water to Production of Concrete in Terms of Mechanical Behavior

Supplies of fresh water in everyday life has increased, but the smaller the potential sources of water so we need to think of alternative uses of water for concrete construction work. This study aims to compare the compressive strength of concrete using sea water and fresh water with water cement ratio of 0.37. An experimental research was conducted by making specimens of concrete cylinder with a diameter of 150 mm and height of 300 mm. The study used specimens of concrete using sea water and fresh water. There were 32 specimens for each kind of concrete. The treatment of each specimen used sea water and fresh water in accordance with the type of mixing water. The immersion periods were 1, 3, 7 and 28 days. Mechanical testing of concrete was conducted by testing the compressive strength and elasticity, while the testing of concrete microstructure was conducted by using X-Ray Diffraction (XRD) and Scan Electron Microscopy (SEM). The results revealed that in the 28-day immersion period. The compressive strength values of the sea water concrete and fresh water concrete were 44.88 MPa and 44.03 Mpa respectively. The difference of compressive strength in the two types of concrete was not significant. The result of microstructure test in the 28-day period revealed that in the sea water concrete, there was a formation of Friedel’s salt (3CaO.Al2O3.CaCl2.10H2O) of 7.71%, tobemorite (3CaO.2SiO2.3H2O) of 58.66% and calcium hydroxide (Ca(OH)2) of 6.18%. In the fresh water concrete, there was a formation of tobermorite (3CaO.2SiO2.3H2O) of 51.35%, and calcium hydroxide (Ca(OH)2) of 22%. There was no formation of Friedel’s salt in the fresh water concrete because there was no mutual reaction between chloride and calcium hydroxide elements. From the regression analysis, showed that the difference of microstructure compressive strength differences caused by differences in the microstructure of the content of the two types of concrete.

Factorial Design for Studying the Properties of Recycled Aggregate Concrete Exposed to Aggressive Media

Recycled Aggregate Concrete (RAC) mixes (1.15: 2.3: 4.6) cement: fine aggregate (sand): coarse aggregate (demolition concrete waste), water / cement (0.5), and 50 % demolition aggregates were prepared according to standard procedure. The resistance of the recycled aggregate concretes towards chemicals was investigated throughout the attack of (Acid: acetic Acid HAC, and salt: Sodium Chloride NaCl) solutions. The test was carried out based on adopted experiments designed using Response Surface Methodology (RSM). A 2-operating parameter central composite design was adopted to study the impact of concentration of the HAC and NaCl solutions (0.1-0.45) Molar, and immersion period (0.57-6.9) day of the (RACs) specimens on weight loss, compressive strength and density. The results obtained confirmed that weight loss increases, but both compressive strength and density decreases after the aggressive solutions attack, however HAC seemed more aggressive. The decrease in compressive strength was (2.8-42) % and (3.2-10.8) %, while the decrease in density was (0.72-2.05) % and (0.6-1.8) % for the samples immersed in HAC and NaCl solutions respectively. The mathematical models presenting the effect of concentration of the aggressive media and immersion duration on weight loss, compressive strength and density were estimated, and the effects were optimized and modeled. The Analysis of Variance (ANOVA) revealed that an optimum compressive strength (37.8 and 34.8) MPa is obtained for the RACs immersed for 0.56 day at 0.1 Molar HAC and NaCl respectively.

Mechanical and thermal behavior of plantain peel powder filled recycled polyethylene composites

In the arduous search for ways to clean up the environment and produce viable materials from waste plastics; plantain peel powder filled low density polyethylene wastes (wLDPE) were developed through melt mixing and compression moulding techniques. Optimum properties were determined at 15, 55 and 30 % formulation of plantain peel powder, and Kankara clay respectively. Composition with optimum properties has tensile strength of 55.5 MPa, flexural strength of 50.45 MPa and elastic modulus of 2.30 GPa with corresponding minimal water absorption of 0.95% after 30 days immersion period at room temperature. The thermal properties investigated by Dynamic Mechanical Analysis showed that the composite has better thermal stability at higher temperature than wLDPE. Similarly, through creep analysis, the composite was observed to have better load bearing capability at elevated temperature than waste low density polyethylene material. These results indicate that incorporation of treated plantain peel powder and Kankara clay into wLDPE enhanced the mechanical, thermal and creep resistance of wLDPE. This implies load bearing capability and potential suitability for different wall tiles applications.

Characterization and Application of Bioactive Glass and Chitosan Nanoparticles for Tooth Enamel Remineralization

We investigated the remineralization of demineralized enamel surfaces through the application of bioactive glass (BG) and chitosan nanoparticles (CNPs). BG and CNPs were immersed in artificial saliva for 7 days. The resulting crystals were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Embedded enamel blocks were immersed in demineralization solution and then classified into five treatment groups: (1) No material applied; (2) toothpaste containing NaF (F); (3) CNP hydrogel; (4) distilled water slurry containing BG; and (5) CNP hydrogel containing BG (BG-CNP). The enamel blocks were immersed in an artificial saliva solution for 1 month; each material was applied twice per day. Nanoindentation testing of enamel surfaces was performed during the immersion period. We found that unidirectional rod-shaped crystals formed in the artificial saliva solutions treated with BG and BG-CNP, showing multiple XRD peaks for hydroxyapatite. The mechanical properties of enamel surfaces decreased markedly following immersion in the demineralization solution, and significantly recovered after 1 month of BG-CNP and BG treatment compared to other the specimens. Porous demineralized enamel surfaces were filled with a remineralization layer after immersion in saliva and application of NaF, BG, and CNP-BG. Thus, daily application of CNP-BG or BG facilitates enamel remineralization.

Moisture Absorption Behavior and Adhesion Properties of GNP/Epoxy Nanocomposite Adhesives

In the current work, an attempt has been made to investigate the effect of Graphene Nanoplatelets (GNP) reinforcement to water absorption behavior and mechanical properties of adhesive bonding with epoxy. Epoxy adhesive with various GNP content (i.e., 0.0~2.0 wt%) was utilized to joint aluminum adherend subjected to various immersion periods (i.e., 0~60 days). Subsequently, the effect of GNP reinforcement on water uptake, water absorption rate and tensile shear strength was investigated. Depending on GNP content, two distinct behaviors in water uptake and moisture absorption rate have been observed; specimens with lower GNP content (0.5~1.0 wt%) have demonstrated increased/retention of water uptake and water absorption rate regardless of immersion period. Meanwhile, at higher GNP content (1.5~2.0 wt%), decreased water uptake and water absorption rate are generally observed. At similar GNP content, regardless of immersion periods, water immersed specimens generally demonstrate higher or retention of shear strength when compared to specimens at 0-day immersion period. These observations suggest that the relation between moisture absorption behavior and mechanical properties of GNP-reinforced adhesive with GNP content are rather complex which might be attributed to the interplay of several possible mechanisms.

Biomass Enhancement of Stevia rebaudiana Bertoni Shoot Culture in Temporary Immersion System (TIS) RITA® Bioreactor Optimized in Two Different Immersion Periods

Stevia plant contains steviol glycosides, which are estimated to be 300 times sweeter than sucrose. However, conventional (in vivo) propagation of Stevia rebaudiana in Indonesia was not effective due to poor results. Therefore, an alternative method to propagate stevia plants is needed. One of them is by using in vitro method. Multiplication with a large quantity of stevia biomass in a relatively short period can be conducted by using TIS RITA® (Recipient for Automated Temporary Immersion System). This study aimed to evaluate the effect of the immersion period of the medium on growth and the medium bioconversion into the production of shoot biomass. The bioreactors were set up with 15 min and 30 min immersions periods, scheduled every 6 h, and incubated for 21 d. The result indicated that the immersion period affected the biomass and growth rate (µ). Amount of 30 min immersion showed a greater percentage of shoot multiplication, higher biomass, percentage of leaf growth, growth rate, and productivity compared to 15 min immersion. The pattern of sucrose, mineral, and inorganic compounds consumption followed the growth of plant biomass for both systems. In conclusion, 30 min immersion gave a greater efficiency medium bioconversion to plant biomass compared with 15 min immersion.

Effect of Salivary pH on Water Absorption and Solubility of Enhanced Resin- Modified Glass Ionomer Enhanced Resin- Modified Glass Ionom

The influence of immersion period and liquid pH on water absorption capacity and solubility of the resin-modified glass ionomer cement (RMGIC) raises the question of whether the critical pH of hydroxyapatite and fluoroapatite influences the water absorption capacity and solubility of enhanced resin-modified glass ionomer (ERMGI). Objective: This study was designed to investigate the effects of immersion periods and various pH levels of artificial saliva on the water absorption and solubility of RMGIC and ERMGI. Methods: Fifty-four disc-shaped specimens (15 mm x 1 mm) of enhanced RMGI (ACTIVATM BioACTIVE-RESTORATIVE, Pulpdent, Watertown, MA, USA) and 54 disc-shaped specimens (15 mm x 1 mm) of RMGIC (Fuji II LC Capsules, GC Corp, Tokyo, Japan) were prepared. Both materials were divided into 9 groups based on artificial saliva pH (pH 7, pH 5.5, and pH 4.5) and immersion time (1, 7, and 14 days). Water absorption and solubility were measured based on ISO 4049: 2009. Data were analyzed statistically using one-way ANOVA. Results: The results showed significant differences in water absorption and solubility value between RMGIC and enhanced RMGI for all the groups. Both materials showed increased water absorption and solubility when immersed in artificial saliva that exhibited a lower pH level and under higher immersion period. Conclusion: Lower pH levels and longer immersion time influence the water absorption and solubility of enhanced RMGI and RMGIC.

Propagasi in vitro tanaman kurma (Phoenix dactylifera L.) pada bioreaktor dengan perendaman sesaat

The cultivation of date palm in Indonesia has increased since the last decade. However, the superior date palm seedlings are still limited and most of them are imported from other countries. The mass supply of superior date palm seedlings can be provided by in vitro propagation in the bioreactor. Therefore, the research was conducted to develop a protocol of date palm in vitro propagation by using Temporary Immersion Bioreactor (TIB). The in vitro propagation was carried out through somatic embryogenesis technique using meristematic tissues isolated from offshoots of date palm female clone cv. Zambli as explants. The explants were sterilized and then cultured to produce embryogenic calli and somatic embryos. Afterwards, somatic embryos germination and plantlets formation were conducted in TIB with treatments of immersion period: 3, 10, and 30 minutes every 6 hours, with 8 replications, The results showed that the optimal somatic embryo germination in TIB was with the immersion period of 30 min every 6 h, resulting in the most formation of shoots and fresh biomass weight increment up to nearly threefold in 6 weeks. Thereafter, plantlets formation in TIB with immersion period of 10 min and 30 min every 6 h exhibited similar performances in producing more plantlets with higher total fresh weight and better vigor than those of 3 min every 6 h. However, there were more rooted plantlets in the TIB with immersion period of 10 min every 6 h. Based on the results, an in vitro propagation protocol via somatic embryogenesis in TIB has been successfully developed for mass propagation of date palm cv. Zambli, which produced plantlets with good vigor and rooting.

Marginal staining of ultra-thin ceramic veneers

The pigmentation of the resin cement at the tooth/ceramic interface compromises the esthetic and longevity of ultra-thin ceramic veneers. Aim: The aim of this study was to evaluate marginal staining of ultra-thin ceramic veneers cemented to intact enamel (non-prepared) and prepared enamel. Methods: Thirty-two (32) permanent central incisors were selected and randomly divided into two groups: intact enamel (IE) and prepared enamel (PE). The ceramic veneers of PE group were bonded to the prepared enamel and the ceramic veneers of IE group were cemented directly onto the intact enamel, with no preparation. Both preparation and cementation were standardized and performed by a single operator. Each group was subdivided into two subgroups (n = 8) with different immersion media - coffee and water. After an immersion period of 10 days, stereomicroscope images were made at 20X magnification of the mesial, distal, cervical and incisal surface of each specimen. Three blinded, trained and calibrated examiners evaluated the images of the resin cement interface of each surface. The data were subjected to Kruskal‑Wallis and Mann‑Whitney statistical analysis. Immersion media and enamel preparation influenced the marginal staining of the tooth/ceramic interface. Results: When immersed in coffee, prepared interfaces presented greater marginal staining than unprepared interfaces. When immersed in water, there was no statistically significant difference between the groups. Conclusion: The cementation of ultra-thin ceramic veneers onto intact enamel is associated with less marginal staining and, consequently, improved esthetics.