Cement Specimens Research Articles

일회용 폐마스크를 활용한 다기능성 복합시멘트의 강도 개선 연구

Recently, the cement development is required with various functions as super-high-rise and multi-functional building structures are receiving a lot of attention around world. Disposable masks have become a necessity of daily life since COVID-19 and the main component of the mask is polypropylene. Polypropylene causes serious second environmental pollution when discharged as household waste. For these reasons, interest in recycling and utilization of disposable waste masks is on the rise. In this study, our purpose is a multi-functional composite cement that can improve compressive strength and delay destruction by mixing mask fibers with cement. Cement specimens were cured by adding 0.0, 0.5, 1.0 and 1.5 wt% of the mask fiber based on the cement weight. The highest maximum load was shown when the mask fiber was added at 0.5 wt%. It was confirmed that cement specimen did not rapidly destruction when the mask fiber was added at 1.0 wt% or more. These research results of this study are expected to have various application fields due to required recycling method for waste masks and the development of multi-functional composite cement required for building structures.

Analysis of nano-particle release from the surface of structural concrete members by laser ablation using soft computing

The paper is concerned with the evaluation of laser-treated cementitious surfaces. It is part of a bigger investigation into the laser cleaning procedure and its impact on the change of the Nano particles of cementitious composites and concrete member structures. Because of the wide range of absorptivity of highly developed surfaces of concrete members and cementitious materials, their reactions to laser irradiation varied significantly. Even while laser could effectively remove the particles from the surface of concrete members, there are usually some residual surface modifications related with mortar removing, fracture development, and glazing (melted mortar). In this study, a large amount of thermal stress is created with low power densities (300 W/cm2) and large spot sizes (50 mm) that promote structural concrete member cracking. By raise of power density, the cement matrix material melts make the thermal ablation mode ineffective. This procedure is also heavily influenced by the beam diameter to aggregate size rate. As a result, due to stable size of aggregate, the procedure is not scalable. In this study, the findings of ablation experiments on cement and concrete member specimens performed with a Yb-fiber laser with a power of 1 kW and a focused beam width of 800 m have been delivered through fiber optic beam delivery. In order to know the influence of substrate composition on ablation ratio and processes, the laser–surface interaction was examined on type I Portland cement with varying amounts of sand or fine silica. The primary objective is to maximize the material removal rate (MRR) and aspect proportion of alumina, stainless steel, and chromium (Cr). The goal of this study is to use an adaptive neural fuzzy inference system (ANFIS) to categorize the multiple input variables for MRR and ratios based on process variables. Scanning speed, annealing temperature, laser power, and laser frequency are all input parameters. The prediction might be crucial in determining the ideal circumstances for micro and Nano architectures of concrete members created by laser ablation. According to the data, annealing power has the greatest impact on aspect ratio, whereas micro structure width has the most effect on MRR. Analysis revealed that contaminants of alumina, stainless steel, and chromium (Cr) were highly segregated into distinct areas of the aerosol's particle size distribution.

Effect of nutrient types on the hydration of cementitious materials with co-cultured bacteria

This study investigated the effect of nutrient types on the hydration of cementitious materials incorporated with co-cultured bacteria. The medium consisted of co-cultured bacteria (Sporosarcina pasteurii and Bacillus thuringiensis), urea, nutrient, and calcium lactate. Different nutrient types were added in the form of a bacterial culture solution or medium solution in the mixing process of cementitious specimens. Thirteen different types of specimens were fabricated with various media, dry-cured for 56 days, and subsequently, isothermal calorimeter analysis, X-ray diffraction analysis, and thermogravimetry analysis were performed to investigate the hydration kinetics and hydrates of the specimens. Finally, compressive strength of the specimens was measured. When bacteria, calcium lactate, and each nutrient were incorporated, as a comparison of compressive strength with the control specimens on the 28thday, 8% compressive strength was increased when TSB was incorporated, but NB and YE were incorporated, the compressive strength decreased by 21% and 22%. The results showed that the incorporation of nutrients and co-cultured bacteria suppressed the hydration of the specimens, whereas the reduction in compressive strength caused by delayed hydration was significantly compensated by CaCO3 amount which was increased by 3.3 times owing to the bio-mineralization of the co-cultured bacteria with TSB.

Effect of Composite or Ceramic Thickness on the Polymerization Hardness of 5 Different Dual-cured Resin Luting Cements

Objective: The aim of the present study was to evaluate the influence of ceramic and composite thickness on polymerization hardness of five different dual-cure resin cements. Materials and Methods: A total of 100 disc-shaped spacer, 10-mm in diameter and five varying thicknesses (1.0mm, 2.0mm, 3.0mm, 4.0mm, 5.0mm) were fabricated from ceramic and composite materials. Dual-cure resin cement specimens with 8-mm diameter were prepared using metal brass mold and activated by light beneath the composite and ceramic disc shaped spacers. A total of 100 specimens of five different dual-cure resins (RelyX, Variolink, NX3, Calibra, Panavia F2.0) were prepared. Knoop hardness of each dual-cure resin cement was measured at five different point using a microhardness device with a 500 gm load, after 1 hr, 1 day, and 1 week polymerization. All data were statistically evaluated using one-way ANOVA. Results: Multivariate analysis of variance revealed significant differences in hardness of specimens dual-cured under composite resin or ceramic spacers and different time intervals (P<.001). Specimens cured through composite resin spacers showed less hardness values than ceramic spacers, with increasing thickness of the spacer. Also increasing the thickness of the composite or ceramic spacers produced a statistically significant decrease in microhardness of the dual-cure cements (P<.05). Conclusions: Hardness values significantly reduced when composite spacers were thicker than 2 mm and ceramic spacers thicker than 3 mm. Dual-cured resin cements are needed to be improved to achieve sufficient degree of hardening under composite and ceramic restorations. Different commercially available brands have different polymerization properties.

Investigating the Mechanical Properties and Durability of Metakaolin-Incorporated Mortar by Different Curing Methods.

In this paper, the traditional, silicate-based Portland cement (PC) was employed as the control to explore the impact of adding varying amounts of metakaolin (MK) on the mechanical properties of cement mortar. In fact, as a mineral admixture, metakaolin (MK) has the ability to significantly improve the early strength and sulfate resistance of cement mortar in traditional, silicate-based Portland cement (PC). In addition to this, the performance of Portland cement mortar is greatly affected by the curing mode. The previous research mainly stays in the intermittent curing and alkaline excitation mode, and there are few studies on the influence of relatively humidity on it. Moreover, the paper investigated the impact of four different curing methods about humidity on the mechanical properties and sulfate resistance. The results show that the best content of metakaolin in Portland cement is 10% (M10), and the best curing method is 95% humidity in the first three days followed by 60% humidity in the later period (3#). Based on previous literature that suggests that adding MK thickens water film layer on the surface of mortar, the mechanism of MK increasing the early strength of cement was analyzed. The compressive strength of the Portland cement containing 10% MK (M10) after 1 day curing is 3.18 times that of pristine PC mortar, and is comparable if PC is cured for three days under the same curing conditions. The traditional PC mortar is highly dependent on the wet curing time, and normally requires a curing time of at least seven days. However, the incorporation of MK can greatly reduce the sensitivity of Portland cement to water; MK cement mortar with only three days wet curing (3#M10) can reach 49.12 MPa after 28 days, which can greatly shorten the otherwise lengthy wet curing time. Lastly, the cement specimens with MK also demonstrated excellent resistance against sulfate corrosion. The work will provide a strong theoretical basis for the early demolding of cement products in construction projects. At the same time, this study can also provide a theoretical reference for the construction of climate drought and saline land areas, which has great reference value.

The Influence of Cement Removal Techniques on In Situ Bacterial Adhesion and Biodegradation at the Marginal Interface of Ceramic Laminates.

This in situ study aimed to analyze the influence of different resin cement removal techniques on bacterial adhesion and biodegradation at the marginal interface of ceramic laminates. Eighty feldspathic ceramic (F) blocks were prepared and cemented onto bovine enamel slabs (7×2.5×2 mm). Excess cement was removed using a microbrush (MBR), a scalpel blade (SCP), or a Teflon spatula (TSP). For the biodegradation analysis, 40 disc-shaped resin cement specimens were prepared (7×1.5 mm) using a Teflon mold. The specimens were randomly allocated into two groups: (1) No finishing procedure (only Mylar strip), and (2) with finishing and polishing procedures using the Jiffy system (Ultradent, South Jordan, UT, USA) (n=20). The in situ phase consisted of using an intraoral palatal device by 20 volunteers for 7 days. Each device contained five cylindrical wells (8×3 mm), where three dental blocks and two cement specimens were included in the wells. Surface roughness (Ra) was measured using a contact profilometer. A micromorphological analysis was performed under a stereomicroscope and a scanning electron microscope. Bacterial adhesion was quantitated based on the number of colony-forming units (CFU/mL) and their biofilm development potential. The cement removal techniques directly affected surface roughness at the marginal interface (p<0.001), and the SCP technique produced higher mean roughness, regardless of the surface area analyzed. Surface polishing protected cement specimens from further biodegradation (p=0.148). There were no differences in CFU counts between the groups after the in situ phase (p=0.96). All specimens showed CFU with a strong ability to develop a biofilm. The techniques used for cement removal increased the surface roughness of ceramic laminates, particularly SCP, but they did not affect bacterial adhesion at the marginal interface. Surface polishing of the resin cement is recommended to mitigate biodegradation.

Experimental study on the shear behavior of frozen cemented sand-structure interface

The shear behavior of the interface between frozen cemented soil and structure is important for analyses of soil-structure interaction and foundation design involving cement grouting and ground freezing. This paper investigated the shear behavior of frozen cemented sand-structure interface. Direct shear experiments were conducted on the frozen sand- and frozen cemented sand-structure interface specimens at various sub-freezing temperatures and normal stresses. Experimental results, including shear stress-displacement curves, the adfreeze and residual strengths, and their differences between the frozen sand- and frozen cemented sand-structure interfaces, were presented and analyzed. The shear stress-displacement relationships of both interfaces display a wave pattern, and the adfreeze and residual strengths of the frozen cemented sand-structure interface were found to decrease significantly when compared with the one without cementation. On average, the adfreeze strength of the frozen cemented sand-structure interface decreases by 47% and the residual strength by 19% compared to the case without cement. As the temperature drops from −2 °C to −14 °C, the peak interface cohesion of the frozen sand case increases by 393%, while that of the frozen cemented sand case rises by 115%. Empirical formulas based on the Mohr-Coulomb model between the strengths and testing parameters, including temperature and normal stress, were proposed for both interfaces. The findings from this study help understand the impact of cement grouting on the shear behavior of frozen sand-structure interface and are significant for practices such as ground construction and foundation engineering when cement grouting is involved in ground freezing.

Mechanical activation of diabase and its effect on the properties and microstructure of Portland cement

Many volcanic rocks with pozzolanic properties are used as additives in cement production. Although diabase is a volcanic rock, it has not been used as an additive material in cement production until now. In this study, pozzolanic reaction ability, mechanical, hydration and microstructure properties were investigated before and after mechanical activation in order to increase the usability of diabase in cement production. Firstly diabase samples were analyzed for chemical, mineralogical compositions and pozzolanic activity. The diabase was first subjected to dry grinding separately from clinker to increase the amorphous structure by decreasing its crystalline structure and mechanical activation was achieved.The pozzolanic activity of the ground diabase gradually increased depending on the grinding time. The effects of 10%, 30% and 50% addition of natural diabase by weight on the characteristics of cement pastes and cement mortars were researched. Zeolite containing cliptonolite mineral was used as a comparison material with diabase. The Blended cement specimens were tested for particle size, setting time, water demand, soundness, heat of hydration, and compressive strength. The compressive strength proportion of the cement mortar samples containing large quantities of natural diabase were lower than that of the Portland control cement at all tested ages up to 28 days, but it was a higher compressive strength than zeolite blended cements. 10%, 30% and 50% diabase blended cements and 10%, 30% and 50% zeolite blended cements give results above the Cem IV 32.5 R standards. 10%, 30% and 50% diabase blended cements have achieved high early compressive strength than zeolite blended cements. 10%, 30% and 50% diabase blended cements have achieved low final compressive strength than zeolite blended cements. In addition, diabase blended cements may produced at approximately 5% lower cost than zeolite blended cements. All results proved that diabase may be a good alternative to new generation mineral additives in producing cement.

Effects of Cement Type, Water-Cement Ratio, Specimen Size, and Curing Time on Concrete Electrical Resistivity

Effects of Cement Type, Water-Cement Ratio, Specimen Size, and Curing Time on Concrete Electrical Resistivity

Effect of light attenuation through veneers on bond strength of adhesives with photoinitiator combinations.

This study aimed to evaluate the effect of light attenuation through ceramic veneers and resin cement on degree of conversion (DC), cohesive strength (CS), and microshear bond strength (μSBS) of experimental adhesive systems. Experimental etch-and-rinse and self-etch adhesives were combined with different ratios of camphorquinone (CQ) and diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (TPO) photoinitiators: CQ-only; 3CQ:1TPO; 1CQ:1TPO; 1CQ:3TPO and TPO-only. Square-shaped ceramic veneer (IPS Empress Esthetic, Ivoclar Vivadent) (n = 10; 10mm long x 10mm wide x 0.5mm thick) and resin cement specimens (Variolink Esthetic LC, Ivoclar Vivadent) (n = 10; 10 mm long x 10 mm wide and 0.3 mm thick) were prepared. Light transmittance of a multiple-peak LED (Bluephase G2, Ivoclar Vivadent) was measured through restorative materials using a spectrometer (n = 5). Adhesive specimens were analyzed for DC, CS, and μSBS by light-curing the adhesive with or without (control) ceramic veneer, and with resin cement fixed to output region of the light-curing tip (n = 10). Data were submitted to ANOVA and Tukey's test (α = 0.05). Total light transmittance through the restorative materials was attenuated, and this attenuation was more evident for the violet spectrum. The DC for the TPO groups in ratios up to 1CQ:1TPO was similar to the control. 1CQ:3TPO showed lower values for CS. μSBS was reduced for all groups with light attenuation, but lower values were observed for 1CQ:3TPO and TPO-only. In conclusion, light transmission was reduced with interposed restorative materials. Adhesives combined with CQ and TPO up to 1CQ:1TPO showed greater cure efficiency and mechanical properties compared with a higher amount of TPO.

Surface Treatment with Silicon-Based Nanoparticles in Portland Cement Specimens Subjected to Physical Sulfate Attack

Surface Treatment with Silicon-Based Nanoparticles in Portland Cement Specimens Subjected to Physical Sulfate Attack

Effects of confinement pressure on the mechanical behavior of an oil well cement paste

Oil well cement paste is a key structural component in wells that should provide mechanical support to the casing and prevent uncontrolled flow of formation fluids along the wellbore and to the environment. Since the annular cement paste is subjected to both hydrostatic pressure and to loads from formation or through the casing, it is important to understand the mechanical behavior and strength of oil well cement pastes under confining conditions. We study cement specimens cored from test sections that were cemented using a full-scale batch mixer. The specimens were tested mechanically without confinement and under 10, 20 and 40 MPa confining pressures using a state of the art triaxial test system. Unconfined samples are found to exhibit linear elastic behavior up to axial strains of approximately 0.2% with an average Young’s modulus of 14.9 GPa and a Poisson ratio of 0.21. At larger strains, the stress–strain response deviates from the initial slope, terminating with a brittle shear failure at axial strains of approximately 0.5%. The corresponding average uniaxial compressive strength is 58 MPa, in good agreement with previously published results. When subjected to confining pressures of 10 MPa or higher, the cement paste accommodated larger strains at a given level of deviatoric stress, and maintained its load-carrying capacity through the entire test cycle. The Young’s modulus for the initial loading phase was found to decrease with increasing confining pressures, and the ultimate deviatoric stress approached approximately 80 MPa, independent of the magnitude of the confining pressures used in this study. The results suggest that the main effect of increasing confining pressure is to increase the sample ductility and the axial strain corresponding to the ultimate deviatoric stress. It is further found that the confined stress–strain behavior of the oil well cement paste can be described by a simple nonlinear constitutive equation. The more ductile and flexible response of well cement under relevant confining pressures is considered to be a positive characteristic of cement as a barrier material for zonal isolation. This study is based on a commercial well cement slurry that is mixed and placed using field equipment. The results are therefore considered novel and unique, and can contribute toward improved knowledge and evaluation of mechanical well cement behavior under realistic, confined conditions.

Mechanical performance, hydration characteristics and microstructures of high volume blast furnace ferronickel slag cement mortar by wet grinding activation

Replacement of cement clinker by industrial wastes has been verified as an effective way to reduce carbon emissions. To realize the application of blast furnace ferronickel slag (BFFS) in high volume in cement mortar, wet grinding was used to improve the activity of BFFS. Three fineness (D50 = 13 μm, 5 μm and 2.5 μm) and three contents (30%, 50% and 70%) of BFFS were investigated comparatively. Isothermal calorimetry, X-ray diffractometer(XRD), Thermal analyzer (TG), Fourier Transform Infrared (FTIR), Mercury injection apparatus (MIP) and Scanning Electron Microscope (SEM) were employed to examine the hydration process and microstructures. The results showed that the pozzolanic behavior and filling effect of BFFS could be improved remarkably by wet-grinding method. The compressive strength of specimens with 50mirc% and 70% BFFS (D50 = 2.5 μm) after curing 28 days could reach 109% and 97% of that of control cement specimens respectively. The results of XRD, TG and FTIR revealed that refined BFFS was involved in pozzolanic reaction at age of 3 days, the effect was more significant with the grinding duration extending. Furthermore, the pore size distribution and the porosity were optimized obviously. Results highlight that wet-grinding treatment of BFFS provided an effective way to improve the early and late age strength of high-volume BFFS cement mortar.

Color stability of a resin nanoceramic after surface treatments, adhesive cementation, and thermal aging

Statement of problemWhether color changes in resin nanoceramic (RNC) restorations can occur because of material and adhesive interface degradation is unclear. PurposeThe purpose of this in vitro study was to evaluate the color of RNCs submitted to surface treatments, cementation, and aging. Material and methodsRNC specimens (N=120) were produced with a thickness of 0.5 mm. The No Treatment-High/Low Translucency (NT-HT/LT) groups did not receive treatments; the Airborne-particle Abrasion-High/Low Translucency (AA-HT/LT) groups were airborne-particle abraded, and the Airborne-particle Abrasion Silane-High/Low Translucency (AASIL-HT/LT) groups received airborne-particle abrasion and a silane agent. Single specimens (n=60) were measured on a spectrophotometer before and after aging (50 000 cycles). The other half was mounted on composite resin bases and measured. The cleaned specimens were cemented (C) on the bases and measured (T0 and T1). ΔE00, ΔL′, ΔC′, and ΔH′ were obtained by using the CIEDE2000 formula and analyzed by using ANOVA and repeated-measures ANOVA. Multiple comparisons were made by using the Tukey HSD test (α=.05). ResultsFor single specimens, the greatest ΔE00 values were observed in the AA-T1-LT resin (5.87). For mounted and cemented conditions, the greatest ΔE00 values were found in the AA-C-T1-LT resin (1.74), and the ΔE00 ranged from 0.75 (NT-OL) to 1.44 (AASIL-C-T1) for the HT resin (P<.001). The mounted and cemented specimens tended toward red and yellow, whereas lighter specimens were observed after cementation. ConclusionsAging affected the color of the RNCs evaluated. The single specimens showed greater color differences than the cemented specimens, reinforcing the importance of the adhesive cement in the optical behavior of thin restorations.

The Effect of Circulating Fluidised Bed Bottom Ash Content on the Mechanical Properties and Drying Shrinkage of Cement-Stabilised Soil.

This study aimed to determine the effect of circulating fluidised bed bottom ash (CFB-BA) content on the mechanical properties and drying shrinkage of cement-stabilised soil. Experiments were performed to study the changes in unconfined compressive strength and expansibility of cement-stabilised soil with different CFB-BA contents and the underlying mechanisms based on microscopic properties. The results show that CFB-BA can effectively increase the unconfined compressive strength of the specimen and reduce the amount of cement in the soil. When the combined content of CFB-BA and cement in the soil was 30%, the unconfined compressive strength of the specimen with C/CFB = 2 after 60 days of curing was 10.138 MPa, which is 1.4 times that of the pure cement specimen. However, the CFB-BA does not significantly improve the strength of the soil and cannot be added alone as a cementing material to the soil. Additionally, swelling tests showed that the addition of CFB-BA to cement-stabilised soil can significantly reduce the drying shrinkage. This research project provides reference values for the application of CFB-BA in cement–soil mixing piles, including compressive strength and the reduction in the shrinkage deformation of specimens.

Consolidated drained behaviour of PVA fibre reinforced cemented Toyoura Sand

ABSTRACT In this study, a series of consolidated drained (CID) compression tests were performed On unreinforced and reinforced cemented Toyoura sand specimens. Specimens were cured for 3, 7, 14, 28, 56 days, with cement contents of 0–3% (dry weight), and different Polyvinyl alcohol (PVA) fibre contents of 0, 0.5, 1, 2, and 3% (weight ratio). Samples were prepared to a target dry density value (e.g. = 1.489 g/cm3) of Toyoura sand using under-compaction moist tamping technique with 10% water content by dry weight of soil. Triaxial compression tests (CID) were carried out at a confining pressure of 100 kPa. The monotonic stress–strain, stiffness, volumetric change behaviour, dilatancy angle, peak strength, and residual strength and brittleness index of the samples were investigated in greater detail. Results show that peak strength increases due to increase in curing duration by approximately 50–700%, and 0–300% in residual strength at 30% axial strain, compared to Toyoura sand. For reinforced cemented specimens there is an increase in volumetric strain with increasing curing duration or in other words, the rate of dilation increases with the increase in curing period. The dilatancy behaviour increases due to the addition of fibres and cement, this dilative behaviour has been attributed to cemented particles forming highly interlocked clusters. Brittleness of the cemented specimens reinforced with 0.5%-1% fibres have been supressed significantly compared to the higher concentrations of fibre (2–3%). Hence, it shows that there might be a threshold fibre concentration range (0.5%-1%), where fibres are considered to be the most effective and beyond this concentration, fibre causes further adverse effects.

Comparison of Silane Heat Treatment by Laser and Various Surface Treatments on Microtensile Bond Strength of Composite Resin/Lithium Disilicate.

In the current study, we evaluated the effects of heat treatment (by Er:YAG or furnace) and various surface treatments on the microtensile bond strength (μTBS) of silanized lithium disilicate ceramic. Seventy lithium disilicate (IPS e. max Press; Ivoclar Vivadent) and composite resin (Tetric N-Ceram; Ivoclar Vivadent) blocks were made and distributed into seven groups (n = 10) at random: S: silanization alone; ALS: airborne particle abrasion (APA) and silanization; SC: APA modified with silica and silanization; SHT1: silanization and heat treatment by Er:YAG; SHT2: silanization and heat treatment performed in the furnace (100 °C, 1 min); HF: etching with HF; and HFS: etching with HF and silanization. Every ceramic specimen was cemented to a composite resin block after surface treatment. Cemented specimens were embedded into acrylic resin and were tested with the μTBS test. Data were analyzed using one-way ANOVA and Tamhane T2 tests (α = 0.05). The SHT1 group had the highest bond of strength compared to the other groups (27.46 MPa). The ALS group had the lowest strength of the groups (15.56 MPa). Between SHT2 and HFS (p = 1), the comparison of the mean µTBS values showed no significant differences. It was concluded that silane heat treatment increased the resin composite–ceramic bond strength; however, within the terms of μTBS, the Er:YAG laser treatment was more successful than other surface treatment applications.

Vat Photopolymerization of Cemented Carbide Specimen.

Numerous studies show that vat photopolymerization enables near-net-shape printing of ceramics and plastics with complex geometries. In this study, vat photopolymerization was investigated for cemented carbide specimens. Custom-developed photosensitive WC-12 Co (wt%) slurries were used for printing green bodies. The samples were examined for defects using quantitative microstructure analysis. A thermogravimetric analysis was performed to develop a debinding program for the green bodies. After sintering, the microstructure and surface roughness were evaluated. As mechanical parameters, Vickers hardness and Palmqvist fracture toughness were considered. A linear shrinkage of 26–27% was determined. The remaining porosity fraction was 9.0%. No free graphite formation, and almost no η-phase formation occurred. WC grain growth was observed. 76% of the WC grains measured were in the suitable size range for metal cutting tool applications. A hardness of 1157 HV10 and a Palmqvist fracture toughness of 12 was achieved. The achieved microstructure exhibits a high porosity fraction and local cracks. As a result, vat photopolymerization can become an alternative forming method for cemented carbide components if the amount of residual porosity and defects can be reduced.

Evaluation of Cement Performance Using Industrial Byproducts Such as Nano MgO and Fly Ash from Greece

The need for environmentally friendly construction materials is growing more and more these days. This paper investigates byproducts from Greece, such as magnesite tailings from Evoia and fly ash from Kardia (Ptolemais), in order to evaluate their suitability as cement additives. For this purpose, the raw materials were tested and studied regarding their mineralogical and chemical components for their morphological characteristics. Different cement specimens of various mixtures of raw materials were produced and tested. These raw materials are considered suitable for cement additives. The effect of nano MgO content seems to have played a more critical role in the physicomechanical performance of produced cement compared to that of the fly ash content. Furthermore, more satisfactory results in the physicomechanical properties of the produced cement gave samples of group II containing 3–4% of nano MgO. Nano MgO content up to 4% seems to have negative influence on the compressive strength of the produced cement, simultaneously reducing its durability. The increase of nano MgO content leads to the increase of the expansion of the produced cement specimens. In the early stage, the expansion rate was intensively larger. With the consumption of nano MgO, the expansion in the later stage gradually slowed down and tended to stabilize.

Polymer-Based Bioactive Luting Agents for Cementation of All-Ceramic Crowns: An SEM, EDX, Microleakage, Fracture Strength, and Color Stability Study.

The aim of the study was to compare microleakage and fracture loads of all ceramic crowns luted with conventional polymer resins and polymeric bioactive cements and to assess the color stability of polymeric bioactive cements. Seventy-five extracted premolar teeth were tested for fracture loads and microleakage in all-ceramic crowns cemented with two types of polymeric bioactive cements and resin cements. In addition, the degree of color change for each cement with coffee was assessed. Thirty maxillary premolar teeth for fracture loads and thirty mandibular premolar teeth for microleakage were prepared; standardized teeth preparations were performed by a single experienced operator. All prepared specimens were randomly distributed to three groups (n = 20) based on the type of cement, Group 1: resin cement (Multilink N); Group 2: polymeric bioactive cement (ACTIVA); Group 3: polymeric bioactive cement (Ceramir). The cementation procedures for all cements (Multilink, ACTIVA, and Ceramir) were performed according to the manufacturers’ instructions. All specimens were aged using thermocycling for 30,000 cycles (5–55 °C, dwell time 30 s). These specimens were tested using the universal testing machine for fracture strength and with a micro-CT for microleakage. For the color stability evaluation, the cement specimens were immersed in coffee and evaluated with a spectrometer. Results: The highest and lowest means for fracture loads were observed in resin cements (49.5 ± 8.85) and Ceramir (39.8 ± 9.16), respectively. Ceramir (2.563 ± 0.71) showed the highest microleakage compared to resin (0.70 ± 0.75) and ACTIVA (0.61 ± 0.56). ACTIVA cements showed comparable fracture loads, microleakage, and stain resistance compared to resin cements.