• Restorative Dentistry and Endodontics
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• v.39 no.2
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• pp.120-125
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• 2014

Use of an apical plug in management of cases with open apices has gained popularity in recent years. Biodentine, a new calcium silicate-based material has recently been introduced as a dentine substitute, whenever original dentine is damaged. This case report describes single visit apexification in a maxillary central incisor with necrotic pulp and open apex using Biodentine as an apical barrier, and a synthetic collagen material as an internal matrix. Following canal cleaning and shaping, calcium hydroxide was placed as an intracanal medicament for 1 mon. This was followed by placement of small piece of absorbable collagen membrane beyond the root apex to serve as matrix. An apical plug of Biodentine of 5 mm thickness was placed against the matrix using pre-fitted hand pluggers. The remainder of canal was back-filled with thermoplasticized gutta-percha and access cavity was restored with composite resin followed by all-ceramic crown. One year follow-up revealed restored aesthetics and function, absence of clinical signs and symptoms, resolution of periapical rarefaction, and a thin layer of calcific tissue formed apical to the Biodentine barrier. The positive clinical outcome in this case is encouraging for the use of Biodentine as an apical plug in single visit apexification procedures.

• Computers and Concrete
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• v.29 no.4
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• pp.237-246
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• 2022

The concrete quality relies on general factors like preparation technique, uniformity of the compaction, amount and appropriateness of the additives. The current article investigates the impact of a well knows amino acid, L-arginine as an additive on water requirements, setting durations and characterization of various cement samples. Compressive strength tests of reference and L-arginine added cements at age of 2, 7 and 28 days were carried out according to TS-EN 196-1. Samples were blended by incorporating various amounts of L-arginine (25 ppm, 50 ppm and 75 ppm) in the cement water mixture which were tested with Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermo-gravimetric analysis (TG), scanning electron microscopy (SEM) and the energy-dispersive X-ray spectroscopy (EDS) on the 28th day. Results revealed that L-arginine does not affect the setting time, volume expansion of cement and water demands negatively; rather it imparts enhanced sustainability to the samples. It was determined that the highest value belonged to the 75L mortar with an increase of 2.6% compared to the reference sample when the compressive strengths of all mortars were compared on the 28th day. Besides, it has been observed that the development of calcium silicate hydrate or C-S-H gel, calcium hydroxide or CH and other hydrated products are associated with each other. L-arginine definitely has a contribution in the consumption of CH formed in the hydration process.

• Journal of the Korea Concrete Institute
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• v.26 no.3
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• pp.369-375
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• 2014

This study examined the changes of microstructural compositions in cement matrix according to the depth from the surface of a reinforced concrete (RC) column exposed to fire. The RC column was exposed to a standard fire for 180 minutes. After the fire test, core samples passing through the column section were obtained. Using the core samples, the remaining fractions of calcium-silicate-hydrates (C-S-H) and calcium hydroxide in cement matrix at the surface, the depth of 40 mm and 80 mm and the center (175 mm) were examined using thermal gravimetric analysis (TGA) and X-ray diffraction analysis (XRDA). Using nuclear magnetic resonance (NMR) technique, the silicate polymerization of C-S-H in cement matrix was also evaluated. The experimental results indicated that the amount of C-S-H loss at the center of column experiencing the transferred fire temperature of $236^{\circ}C$ has been underestimated as the TGA results showed the highest C-S-H contents are located at the depth of 80 mm, where the transferred fire temperature is $419^{\circ}C$. Moreover, the destruction of silicate connections at the center was observed as similar as that at the depth of 40 mm, where the transferred fire temperature was $618^{\circ}C$. This might be attributed to the temperature changes during cooling time after the fire test was neglected. Due to the relatively low thermal conductivity of concrete, the high temperature, which can affect the change of microstructure in cements, will hold longer at the center of the column than other depth.

• Journal of the korean academy of Pediatric Dentistry
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• v.49 no.4
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• pp.379-391
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• 2022

The current study aimed to compare the pH, solubility value, and ion release capability of premixed mineral trioxide aggregates (MTAs) versus conventional pulp capping materials before and after setting. The following materials were used: resin-modified calcium silicate cement (TheraCal LC^®, TLC), resin-modified calcium hydroxide cement (Ultra-Blend^TM plus, UBP), and 2 kinds of premixed MTA (Endocem MTA^® premixed regular [EMPR] and Well-Root^TM PT [WRP]). The specimens of each material were prepared before and after setting and were immersed in distilled water. The materials' pH and solubility value were assessed. Next, three kinds of ion (calcium, sulfide, and strontium) released by pulp capping materials were evaluated via inductively coupled plasma atomic emission spectrometry. In the after-setting group, the pH of TLC and UBP decreased. However, the pH of the premixed MTAs increased with time. TLC released a higher concentration of strontium ion compared with the other materials. Meanwhile, EMPR released a significantly high concentration of sulfide ion (p < 0.05). In the after-setting group, the 2 kinds of premixed MTAs released a significantly higher concentration of calcium ion compared with the other materials (p < 0.05). In the after-setting group, EMPR had a significantly low solubility value (p < 0.05). The Kruskal-Wallis test, followed by the Mann-Whitney U test with Bonferroni correction, was used in statistical analysis. In conclusion, resin-modified calcium silicate cement, modified calcium hydroxide cement, and the 2 kinds of premixed MTAs had an alkaline pH and low solubility value and they released various concentrations of ions after setting.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.1
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• pp.111-118
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• 2014

The present study concerns the leachability of alkali ions from hardened cement paste in terms of an increase in the pH together with the rate of alkali leaching. To evaluate the influence of mix design on the leaching capacity and rate of alkali, different water-cement ratios (W/C) and binders were used to manufacture paste specimens. The cement paste was made in the form of rectangular bucket where deionised water was subsequently supplied as solvent media. Then the specimen was wrapped in polythene film to avoid contact to atmospheric conditions, which may affect the water chemistry in the bucket. The pH of media was monitored until no further change in the pH value was observed, of which value then used to calculate the leaching capacity and rate. The influence of binder on the pH of solvent is more dominant than that of water to cement ratio: OPC paste produced the highest level of alkali leaching, whilst 30% PFA and 60% GGBS pastes imposed lower level of alkali leaching. After the monitoring of the pH, the inner bucket was ground with an increment of 1.0 mm to measure the leaching influence using the suspension consisting of paste powder and deionised water. It was found that the impact zone for OPC was about 7-8 mm, whilst 30% PFA and 60% GGBS had deeper impact depth of the alkali leaching.

• Korean Journal of Soil Science and Fertilizer
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• v.14 no.4
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• pp.242-249
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• 1982

Effects of lime and ameliolating materials on decreasing available soil cadmium were studied, applying the amendments to Cd pre-and post-treated soils. Soil sttreated with Cd were placed in pots and kept under field moisture condition, summer through winter in 1981. The results of soil analysis made 40 to 60 days after the Cd treatment are as follows ; 1. Greater amount of Cd was extracted by 0.1N-HCl or 2% Citric acid than N-AcNH4 solution. More Cd was dissoluted by 0.1-HCl than 2% Citric acid. No Cd was extracted by pure water. Showing a wide variance in the amount of extractable Cd among treatments (amendments), the $N-AcNH_4$ solution seemed to be the most effective extracting solution of available soil cadmium. 2. Calcium hydroxide was the most effective materials in reducing $N-AcNH_4$ extractable Cd, followed by calcium carbonate and calcium silicate. 3. Superphosphate is also effective in reducing exchangeable cadmium. The reduction seemed to be attributed to the precipitation of cadmium phosphate. 4. The exchangeable cadmium by $N-AcNH_4$ was large in the soil pH range of 6.0 and 6.5, and it decreased as the soil pH became far apart from these values. The decrese of exchangeable Cd at low pH seemed to be related to the increase of $Mn^{+{+}}$ and that at the high pH to the precipitation as Cd-hydroxide.

• The Journal of the Korean dental association
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• v.50 no.3
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• pp.148-154
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• 2012

Mineral trioxide aggregate (MTA) is mainly composed of lime and silica. Its four major phases are tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracaclcium aluminoferrite. MTA has relatively long initial setting time (2h 45m) and various additives can be added to reduce setting time. Compressive strength of MTA increases with time and reaches 100 MPa after 28 days. MTA has high pH of 9-12.5 because of the formation of calcium hydroxide during its hydration reaction. MTA has superior sealing ability to amalgam and IRM when it is used in perforation repair or root end filling. MTA is safe in cytotoxicity and genotoxicity and have potential to promote pulpal and periapical hard tissue formation.

• Advances in concrete construction
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• v.6 no.4
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• pp.345-362
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• 2018

In this paper, mechanical and short-term durability properties of fly ash and slag based geopolymer concretes (FAGPC-SGPC) were investigated. The alkaline solution was prepared with a mixture of sodium silicate solution ($Na_2SiO_3$) and sodium hydroxide solution (NaOH) for geopolymer concretes. Ordinary Portland Cement (OPC) concrete was also produced for comparison. Main objective of the study was to examine the usability of geopolymer concretes instead of the ordinary Portland cement concrete for structural use. In addition to this, this study was aimed to make a contribution to standardization process of the geopolymer concretes in the construction industry. For this purpose; SGPC, FAGPC and OPC specimens were exposed to sulfuric acid ($H_2SO_4$), magnesium sulfate ($MgSO_4$) and sea water (NaCl) solutions with concentrations of 5%, 5% and 3.5%, respectively. Visual inspection and weight change of the specimens were evaluated in terms of durability aspects. For the mechanical aspects; compression, splitting tensile and flexural strength tests were conducted before and after the chemical attacks to investigate the residual mechanical strengths of geopolymer concretes under chemical attacks. Results indicated that SGPC (100% slag) is stronger and durable than the FAGPC due to more stable and strong cross-linked alumina-silicate polymer structure. In addition, FAGPC specimens (100% fly ash) showed better durability resistance than the OPC specimens. However, FAGPC specimens (100% fly ash) demonstrated lower mechanical performance as compared to OPC specimens due to low reactivity of fly ash particles, low amount of calcium and more porous structure. Among the chemical environments, sulfuric acid ($H_2SO_4$) was most dangerous environment for all concrete types.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.1
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• pp.29-36
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• 2017

The purpose of this study is to investigate experimentally the effect of types of alkali-activators and curing conditions on the compressive and tensile behavior of fiber-reinforced cementless composites. Two types of alkali-activators and two curing conditions were determined and density test, compressive strength test, and uniaxial tension test were performed. Test results showed that the cementless composite with sodium silicate showed higher performance in terms of strength, tensile strain capacity, and toughness than that with calcium hydroxide and sodium carbonate. The effect of curing conditions depends on the types of alkali-activators.

• Journal of the Korean Ceramic Society
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• v.25 no.6
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• pp.685-693
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• 1988

From leaching of Korean native halloysite with hot sulfuric acid, active species of siliceous aluminosilicate are obtained as residue, which gives the mole ratio of SiO2/Al2O3 10 and substantially removes most acid-soluble impurities. By dissolving the residue in sodium hydroxide at an ambient temperature sodium silicate solution is prepared, this is used for zeolite synthesis as one of starting materials. In order to prepare zeolite Type 4A thereform, addition of a proper aluminum source is made so that the composition of the reactant materials may be of the following mole ratios : Na2O/SiO2=1.2-1.5, SiO2/Al2O3=1.8-2.0 and H2O/Na2O=34-45 By careful control of ageing time and temperature, subsequent crystal growth is induced into microfine zeolite 4A, which gives optimum particle size distributjion being suitable for detergent builder. The zeolite products thus obtained and highly competitive with those from the use of the refined clay in comparison of their calcium exchange capacity, whiteness and particle size distribution. The present method shows a marginal advantage over the existing procedures requiring neitherseparate purification nor calcinating otherwise necessary for the raw clay ores in use.