Synthesis and Characterization of Sol-Gelled Barium Zirconate as Novel MTA Radiopacifiers.

Barium zirconate (BaZrO3, BZO), which exhibits superior mechanical, thermal, and chemical stability, has been widely used in many applications. In dentistry, BZO is used as a radiopacifier in mineral trioxide aggregates (MTAs) for endodontic filling applications. In the present study, BZO was prepared using the sol-gel process, followed by calcination at 700-1000 °C. The calcined BZO powders were investigated using X-ray diffraction and scanning electron microscopy. Thereafter, MTA-like cements with the addition of calcined BZO powder were evaluated to determine the optimal composition based on radiopacity, diametral tensile strength (DTS), and setting times. The experimental results showed that calcined BZO exhibited a majority BZO phase with minor zirconia crystals. The crystallinity, the percentage, and the average crystalline size of BZO increased with the increasing calcination temperature. The optimal MTA-like cement was obtained by adding 20% of the 700 °C-calcined BZO powder. The initial and final setting times were 25 and 32 min, respectively. They were significantly shorter than those (70 and 56 min, respectively) prepared with commercial BZO powder. It exhibited a radiopacity of 3.60 ± 0.22 mmAl and a DTS of 3.02 ± 0.18 MPa. After 28 days of simulated oral environment storage, the radiopacity and DTS decreased to 3.36 ± 0.53 mmAl and 2.84 ± 0.27 MPa, respectively. This suggests that 700 °C-calcined BZO powder has potential as a novel radiopacifier for MTAs.

Investigating the Effect of Selenium Nanoparticles on Mineral Trioxide Aggregates as a Promising Novel Dental Material.

Aim: To enhance mineral trioxide aggregate high plasticity (MTA HP), a commonly used dental calcium silicate cement, by incorporating selenium nanoparticles (SeNPs) known for their antioxidant and anti-inflammatory properties. The objectives included investigating the impact of SeNPs on the setting time and chemical properties of MTA HP. Materials and Methods: We performed a comprehensive study to formulate and profile SeNPs integrated into MTA HP. Diverse concentrations of SeNPs were introduced into MTA HP, and the commencement and culmination of the setting process were gauged employing a Gillmore needle cabinet. The chemical composition was validated using Fourier transform infrared spectroscopy with attenuated total reflectance and X-ray diffraction analysis. Results: The incorporation of SeNPs led to remarkable improvements. Notably, SeNPs positively affected the setting time of MTA HP, with faster setting times corresponding to higher SeNPs concentrations. Chemical analyses confirmed the successful integration of SeNPs with MTA HP. These enhancements make the material may be suitable for dental applications, especially due to its accelerated setting time. Conclusions: MTA HP incorporated with SeNPs represents a significant advancement in dental materials. Its faster setting time, combined with the antioxidant and anti-inflammatory properties of selenium, provides dental professionals with an efficient and time-saving option for complex treatments. This novel nanomaterial holds promise for improving dental procedures and patient outcomes.

Synthesis and Characterisation of Hemihydrate Gypsum-Polyacrylamide Composite: A Novel Inorganic/Organic Cementitious Material.

This study combined inorganic α-hemihydrate gypsum (α-HHG) with organic polyacrylamide (PAM) hydrogel to create a novel α-HHG/PAM composite material. Through this facile composite strategy, this fabricated material exhibited a significantly longer initial setting time and higher mechanical strength compared to α-HHG. The effects of the addition amount and the concentration of PAM precursor solution on the flowability of the α-HHG/PAM composite material slurry, initial setting time, and mechanical properties of the hardened specimens were investigated. The structural characteristics of the composite material were examined using XRD, FE-SEM, and TGA. The results showed that the initial setting time of the α-HHG/PAM composite material was 25.7 min, which is an extension of 127.43% compared to that of α-HHG. The flexural strength and compressive strength of the oven-dried specimens were 23.4 MPa and 58.6 MPa, respectively, representing increases of 34.73% and 84.86% over values for α-HHG. The XRD, FE-SEM, and TGA results all indicated that the hydration of α-HHG in the composite material was incomplete. The incompleteness is caused by the competition between the hydration process of inorganic α-HHG and the gelation process of the acrylamide molecules for water, which hinders some α-HHG from entirely reacting with water. The enhanced mechanical strength of the α-HHG/PAM composite material results from the tight interweaving and integrating of organic and inorganic networks. This study provides a concise and efficient approach to the modification research of hemihydrate gypsum.

The Impact of Nano- and Micro-Silica on the Setting Time and Microhardness of Conventional Glass-Ionomer Cements.

The objective of this study was to investigate the effect of the incorporation of 2, 4 or 6 wt% of amorphous nano- or micro-silica (Aerosil® OX 50 or Aeroperl® 300 Pharma (Evonik Operations GmbH, Essen, Germany), respectively) on the net setting time and microhardness of Ketac™ Molar (3M ESPE, St. Paul, MN, USA) and Fuji IX GP® (GC Corporation, Tokyo, Japan) glass-ionomer cements (GICs) (viz. KM and FIX, respectively). Both silica particles were found to cause a non-linear, dose-dependent reduction in setting time that was within the clinically acceptable limits specified in the relevant international standard (ISO 9917-1:2007). The microhardness of KM was statistically unaffected by blending with 2 or 4 wt% nano-silica at all times, whereas 6 wt% addition decreased and increased the surface hardness at 1 and 21 days, respectively. The incorporation of 4 or 6 wt% nano-silica significantly improved the microhardness of FIX at 1, 14 and 21 days, with no change in this property noted for 2 wt% addition. Micro-silica also tended to enhance the microhardness of FIX, at all concentrations and times, to an extent that became statistically significant for all dosages at 21 days. Conversely, 4 and 6 wt% additions of micro-silica markedly decreased the initial 1-day microhardness of KM, and the 21-day sample blended at 4 wt% was the only specimen that demonstrated a significant increase in this property. Scanning electron microscopy indicated that the nano- and micro-silica particles were well distributed throughout the composite structures of both GICs with no evidence of aggregation or zoning. The specific mechanisms of the interaction of inorganic nanoparticles with the constituents of GICs require further understanding, and a lack of international standardization of the determination of microhardness is problematic in this respect.

Endodontic Radiopacifying Application of Barium Titanate Prepared through a Combination of Mechanical Milling and Heat Treatment.

Mineral trioxide aggregates (MTA) are commonly used as endodontic filling materials but suffer from a long setting time and tooth discoloration. In the present study, the feasibility of using barium titanate (BTO) for discoloration and a calcium chloride (CaCl2) solution to shorten the setting time was investigated. BTO powder was prepared using high-energy ball milling for 3 h, followed by sintering at 700-1300 °C for 2 h. X-ray diffraction was used to examine the crystallinity and crystalline size of the as-milled and heat-treated powders. MTA-like cements were then prepared using 20-40 wt.% BTO as a radiopacifier and solidified using a 0-30% CaCl2 solution. The corresponding radiopacity, diametral tensile strength (DTS), initial and final setting times, and discoloration performance were examined. The experimental results showed that for the BTO powder prepared using a combination of mechanical milling and heat treatment, the crystallinity and crystalline size increased with the increasing sintering temperature. The BTO sintered at 1300 °C (i.e., BTO-13) exhibited the best radiopacity and DTS. The MTA-like cement supplemented with 30% BTO-13 and solidified with a 10% CaCl2 solution exhibited a radiopacity of 3.68 ± 0.24 mmAl and a DTS of 2.54 ± 0.28 MPa, respectively. In the accelerated discoloration examination using UV irradiation, the color difference was less than 1.6 and significantly lower than the clinically perceptible level (3.7). This novel MTA exhibiting a superior color stability, shortened setting time, and excellent biocompatibility has potential for use in endodontic applications.

[Processing properties and viscosities of PMMA bone cements]. / Verarbeitungseigenschaften und Viskositäten von PMMA-Knochenzementen.

Processing properties of PMMA bone cements can be divided into four phases: 1. mixing, 2. waiting, 3. processing and 4. curing. Each of these phases is subject to several external influencing factors, such as temperature and humidity, which must be considered during application. Instructions for use provided by the manufacturers of PMMA bone cements and mixing and application systems contain important information on correct application. The processing properties of PMMA bone cements and possible factors influencing the curing process are of great importance for safe procedures in the operating room. Knowledge of the viscosity and consistency of the PMMA bone cement from the dough phase to complete curing facilitates preparation and application, which in the long term significantly improves the requirements placed on PMMA cements regarding the function and service life of the implant.

Physical-chemical properties and acellular bioactivity of newly prepared nano-tricalcium silicate-58s bioactive glass-based endodontic sealer.

OBJECTIVES: To evaluate the physiochemical properties and apatite-forming ability of a newly prepared nano-tricalcium silicate-58s bioactive glass-based endodontic sealer (C3S-BG-P) and compare its results with the Nishika BG canal sealer and BioRoot™ RCS. METHODS: The physicochemical properties (setting time, flow, solubility, film thickness, and radiopacity) of C3S-BG-P, Nishika BG canal sealer, and BioRoot™ RCS were evaluated in accordance with ANSI/ADA 57/2000 (reaffirmed 2012) and ISO 6876:2012 for root canal sealing materials. The in vitro apatite-forming ability was evaluated after 28 days of immersion of disc-shaped specimens in phosphate-buffered saline (PBS) using field emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. RESULTS: The results of physiochemical tests indicated that all the tested sealers complied with the ADA and ISO standards; however, the solubility of the BioRoot did not meet the two standards. C3S-BG-P revealed significantly superior properties in all physicochemical tests compared to Nishika and BioRoot; however, the solubility of Nishika was significantly lower than that of C3S-BG-P. Furthermore, all tested sealers exhibited apatite precipitation on their surfaces after 28 days of immersion in PBS. CONCLUSIONS: C3S-BG-P had superior physicochemical properties, which mitigated the disadvantages of calcium silicate-based sealers. Moreover, it exhibited apatite precipitation after immersion in PBS. Further in vivo studies utilizing animal models or clinical studies are necessary to support the rationale of the newly developed sealer for clinical application.

Chemomechanical Properties and Biocompatibility of Various Premixed Putty-type Bioactive Ceramic Cements.

INTRODUCTION: This study aimed to evaluate the chemomechanical properties and biocompatibility of recently introduced premixed putty-type bioactive ceramic cements (PPBCs). METHODS: Including ProRoot MTA (PMTA) as a control, BC RRM fast-set putty (BCPT), Well-Root PT (WRPT), One-Fil PT (OFPT), and Endocem MTA premixed (ECPM) were compared to evaluate setting time, radiopacity, pH change, and microhardness. Biocompatibility on human dental pulp cells was compared using CCK-8 assay. Mineralization potential was evaluated using alkaline phosphatase activity, Alizarin Red S (ARS) staining, and quantitative real-time polymerase chain reaction with odontogenic gene marker. For data analysis, 1-way analysis of variance and Tukey's post hoc test were used at the significance level of 95%. RESULTS: Among the PPBCs, BCPT presented the longest (552 ± 27) setting time (minutes) and others showed significantly shorter time than PMTA (334 ± 22) (P < .05). WRPT (6.20 ± 0.54) and OFPT (5.82 ± 0.50) showed significantly higher radiopacity values (mmAl) and others showed similar value compared with PMTA (P > .05). All PPBCs showed high alkaline pH from fresh materials and tended to increase according to time periods from 30 minutes to 12 hours. ECPM showed the highest value of microhardness (81.62 ± 5.90), WRPT showed similar, and others showed lower than PMTA (P < .05). All PPBCs showed biocompatibility in CCK-8 assay. All PPBCs showed similar or better value compared with PMTA in ALP and ARS staining, and ALP and DSPP marker expression (P < .05). CONCLUSIONS: The PPBCs showed clinically acceptable chemomechanical properties and favorable mineralization potential.

Evaluation of Setting Times of Concrete Using Electro-Mechanical Impedance Sensing Technique.

This study presents a novel approach to assessing the setting time of concrete using the electro-mechanical impedance (EMI) sensing technique. The proposed method involves the continuous monitoring of EMI changes by embedding a piezoelectric (PZT) sensor directly in the concrete. A comparative analysis was conducted with the conventional penetration resistance test, which utilizes mortar samples extracted from the concrete. As a result of the experiment, the time deviation rate of the setting time was more than 10% in the penetration resistance test using the mortar sample extracted from the same concrete, whereas the time deviation rate of the setting time was up to 1.77% in the EMI sensing technique using the same concrete specimen. This highlights the effectiveness and potential of the EMI sensing technique for an improved evaluation of concrete setting time.

Effect of incorporation of nano-graphene oxide on physicochemical, mechanical, and biological properties of tricalcium silicate cement.

OBJECTIVE: Evaluation of setting time, compressive strength, pH, calcium ion release, and antibacterial activity of mineral trioxide aggregate (MTA) after modification with three different concentrations of nano-graphene oxide (GO) powder compared to unmodified Biodentine as a commercial control. METHODS: GO powder, unhydrated and hydrated cements were characterized using Environmental Scanning Electron Microscope (ESEM) with Energy Dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Raman Spectroscopy, and Fourier Transform Infrared spectroscopy (FTIR). GO was also analyzed using Scanning Transmission Electron Microscope (STEM) to determine average lateral dimensions. Specimens were prepared and grouped according to the concentration of GO added to Rootdent MTA (control, 1, 3, and 5 wt%) and the material used (MTA and unmodified Biodentine) into five groups. Setting time was evaluated using Gillmore penetrometer (n = 5). Compressive strength was evaluated using universal testing machine (n = 7). pH and calcium ion release were assessed using pH meter and Induced Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) at 1, 7, 14, and 28 days (n = 7). Antibacterial activity was evaluated against Streptococcus mutans using direct contact test (n = 7). One-way and repeated measures ANOVA followed by Tukey's post hoc test were used for data analysis with significance level set at p ≤ 0.05. RESULTS: Addition of GO to MTA reduced both initial and final setting time. GO modified MTA groups and unmodified Biodentine showed significantly increased calcium ion release at 14 and 28 days. All cements showed alkaline pH of the storage media at all tested time intervals. 1 wt% GO recorded the highest compressive strength values in MTA modified groups. The increased concentration of GO from 1 to 5 wt% successively increased antibacterial activity of MTA, with Biodentine showing the lowest significant value. CONCLUSION: Addition of 1 wt% GO can significantly improve the tested properties of tricalcium silicate-based cements without compromising their compressive strength. CLINICAL SIGNIFICANCE: GO is a promising modification for tricalcium silicate cements to improve setting time, compressive strength, and antibacterial activity to provide a variety of materials for different clinical situations. This in turn can reduce the risk of reinfection and allow placement of the final restoration in a single visit.

Effects of White Chicken Eggshell Powder on Compressive Strength, Water Solubility, and Setting Time of Calcium-Enriched Mixture.

Introduction: The present study aimed to evaluate the effects of adding chicken eggshell powder (CESP) to calcium-enriched mixture (CEM) cement on its compressive strength (CS), solubility, and setting time. Materials and Methods: In this study, CESP was added at weight percentages of 3% and 5% to the powder component of the CEM cement. To measure the CS, a total of 36 samples (height, 6 mm; diameter, 4 mm) were tested in a universal testing machine. The setting time was assessed for 18 disk-shaped samples (diameter, 10 mm; height, 1 mm). Additionally, solubility test was performed on 18 samples (diameter, 8 mm; height, 1 mm) after 24 hours, 72 hours, seven days, and 14 days under dehydration conditions by calculating the weight changes; the results were then subjected to a normality test. Next, for the comparison of different test groups, parametric ANOVA test and post-hoc Tukey's multiple comparison test were performed at a significance level of 0.05. Results: The addition of 5% CESP to the CEM cement significantly reduced its setting time and water solubility (P=0.02 and P=0.01, respectively). Moreover, it significantly increased the CS over a 21-day period (P<0.001). Additionally, the addition of 3% CESP also resulted in a significant increase in CS (P<0.001). While 3% CESP reduced setting time and water solubility, the difference was not statistically significant. Conclusion: The findings suggest that the addition of 5% CESP to CEM cement has the potential to improve its sealing ability, durability, and ability to withstand chewing forces in endodontic treatments. These results highlight the relevance of CESP as an additive for cement modifications and indicate its potential clinical implications.

Differences in setting time of calcium silicate-based sealers under different test conditions.

Background/purpose: Recently introduced calcium silicate-based bioceramic (CSBC) sealers require moisture for setting, thus this study aimed to compare the setting times of epoxy resin-and CSBC sealers under different test conditions. Materials and methods: Four CSBC sealers (CeraSeal, EndoSeal TCS, One-Fil, and Well-Root ST) were compared to an epoxy resin-based sealer (AH Plus). Each sealer was placed in a stainless-steel and gypsum molds on a glass slide. Sealer samples (n = 10 per group) were stored in an incubator at 95% humidity and 37 °C. A Gilmore needle with a total weight of 100 g and a 2.0-mm diameter were carefully placed vertically against the sealer, and the setting time was recorded when the needle no longer formed an indentation on the sealer surface. Statistical analysis was performed using two-way analysis of variance and Tukey parametric tests. The level of significance was set at 95%. Results: The setting time of all sealers in gypsum molds was significantly shorter than that in stainless-steel molds (P < 0.05). While AH Plus showed the longest setting time, EndoSeal TCS, One-Fil, and CeraSeal showed the shortest setting times when using gypsum molds among the five sealer types (P < 0.05). Conclusion: The results of this study indicate that CSBC sealers require moisture for setting; a lack of moisture results in a significant delay in setting time. Because the root canals contain moisture, it is necessary to experiment with the setting time of all types of sealers using gypsum molds to determine the biological condition of root canals.

Comprehensive Evaluation of the Performance and Benefits of SSA-GGBS Geopolymer Mortar.

The activity of sewage sludge ash (SSA) is not high; ground granulated blast slag (GGBS) has a high calcium oxide content that can accelerate polymerization rates and exhibit better mechanical performance. In order to improve the engineering application of SSA-GGBS geopolymer, it is necessary to conduct a comprehensive evaluation of its performance and benefits. In this study, the fresh properties, mechanical performance and benefits of geopolymer mortar with different SSA/GGBS, modulus and Na2O contents were studied. Taking the economic and environmental benefits, working performance and mechanical performance of mortar as evaluation indexes, the entropy weight TOPSIS (Technique for Order Performance by Similarity to Ideal Solution) comprehensive evaluation method is used to evaluate the geopolymer mortar with different proportions. The results show that as SSA/GGBS increases, the workability of mortar decreases, the setting time first increases and then decreases, and the compressive strength and flexural strength decrease. By appropriately increasing the modulus, the workability of the mortar decreases and more silicates are introduced, resulting in increased strength in the later stage. By appropriately increasing the Na2O content, the volcanic ash activity of SSA and GGBS is better stimulated, the polymerization reaction is accelerated, and the early strength increases. The highest Ic (integrated cost index, Ctfc28) of geopolymer mortar is 33.95 CNY/m3/MPa, and the lowest is 16.21 CNY/m3/MPa, which is at least 41.57% higher than that of ordinary Portland cement (OPC). The minimum Ie (embodied CO2 index, Ecfc28) is 6.24 kg/m3/MPa, rising up to 14.15 kg/m3/MPa, which is at least 21.39% lower than that of OPC. The optimal mix ratio is a water-cement ratio of 0.4, a cement-sand ratio of 1.0, SSA/GGBS of 2/8, a modulus content of 1.4, and an Na2O content of 10%.

Effects of Mud Content on the Setting Time and Mechanical Properties of Alkali-Activated Slag Mortar.

High mud content in the sand has a negative impact on cement mortar but there is little research on Alkali-activated slag (AAS) mortar. In order to explore the impacts of mud content in the sand on the performance of AAS mortar, this paper used sand that contains silt, clay, and a mixture of silt and clay; tested the setting time of AAS with different mud contents of 0%, 2%, 4%, 6%, 8%, and 10%; and measured the unconfined compressive strength and beam flexural strength of 3 d, 7 d, and 28 d AAS mortar specimens. The microstructure of AAS mortar with different kinds of mud was observed by scanning electron microscope (SEM), the elemental composition of the hydration product was tested by energy dispersive spectroscopy (EDS), and the AAS interaction mechanism with different kinds of mud was analyzed. The main conclusions are: the higher the mud content in the sand, the shorter the initial setting time and the longer the final setting time of AAS, mainly because the mud in the sand affects the hydration process; mud content above 4% causes a rapid decrease in the compressive and flexural strengths of AAS mortar, mainly because the mud affects the hydration process and hinders the bonding of the hydration product with the sand. When there is no mud in the sand, the main hydration product of AAS is dense calcium-alumina-silicate-hydrate (C-A-S-H) gel. When the sand contains silt, the hydration product of AAS is loose C-A-S-H gel. When the sand contains clay, the hydration products of AAS contain C-A-S-H gel and a small amount of sodium-aluminum-silicate-hydrate (N-A-S-H), and needle-like crystals. Loose gel and crystals have a negative effect on the AAS mortar strength.

Characterisation of the Bioactivity and the Solubility of a New Root Canal Sealer.

OBJECTIVES: This study aimed to analyse the effect of using phosphate buffer solution (PBS) on the solubility, pH changes, surface structure, and elemental composition of a new bioceramic Cerafill sealer compared with Endosequence sealer and AH26 resin-based sealer. METHODS: A fresh mixture of each sealer moistened with either deionised water or PBS was subjected to a setting time test. Set discs (n = 10) were submerged in either deionised water or PBS to evaluate pH changes and solubility at 1, 7, 14, 21, and 28 days. Surface characterisation of the sealers was done before and after solubility tests using scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and Fourier transform infrared (FTIR) spectroscopy analyses. RESULTS: An analysis of variance revealed a significant delay in setting of BC-Endosequence (P < .001) with no significant difference when each sealer was moistened with deionised water or PBS (P > .05). Both bioceramic sealers exhibited highly alkaline pH (range, 9.47-10.72). When the sealer was submerged in deionised water, Endosequence exhibited significantly greater solubility, whilst Cerafill and AH26 gained weight. When the sealers were submerged in PBS, both bioceramic sealers gained more weight, with significantly greater values for Endosequence (P < .001). Hydroxyapatite formation was revealed by SEM/EDX and FTIR. CONCLUSIONS: PBS promoted the formation of hydroxyapatite crystals that protect the bioceramic sealers from dissolving.

Properties of Alkali-Activated Slag Cement Activated by Weakly Alkaline Activator.

Sodium sulfate (Na2SO4) and sodium carbonate (Na2CO3) are weakly alkaline activators. Alkali-activated slag (AAS) cement prepared with them shows the special advantages of long setting time and low shrinkage, but it shows slow development of mechanical properties. In the paper, Na2SO4 and Na2CO3 were used as activators and compounded with reactive magnesium oxide (MgO) and calcium hydroxide (Ca(OH)2) to optimize the setting time and mechanical properties. The hydration products and microscopic morphology were also studied using XRD, SEM, and EDS. Furthermore, the production cost and environmental benefits were compared and analyzed. The results show that Ca(OH)2 is the main influencing factor for setting time. It reacts preferentially with Na2CO3 to form CaCO3, which makes AAS paste lose plasticity rapidly and shortens the setting time, and then produces strength. Na2SO4 and Na2CO3 are the main influencing factors for flexural and compressive strength, respectively. Suitably high content is beneficial to promote the development of mechanical strength. The interaction of Na2CO3 and Ca(OH)2 shows a great effect on the initial setting time. High content of reactive MgO can shorten the setting time and increase the mechanical strength at 28 days. There are more crystal phases in hydration products. Considering the setting time and mechanical properties, the composition of activators are: 7% Na2SO4, 4% Na2CO3, 3-5% Ca(OH)2, and 2-4% reactive MgO. Compared with ordinary Portland cement (OPC) and AAS cement activated by sodium hydroxide (NaOH, NH) and water glass (WG) with the same alkali equivalent, the production cost and energy consumption are greatly reduced. Compared with P·O 42.5 of OPC, CO2 emission is reduced by 78.1%. AAS cement activated by weakly alkaline activators shows excellent environmental and economic benefits and good mechanical properties.

Effects of Borax, Sucrose, and Citric Acid on the Setting Time and Mechanical Properties of Alkali-Activated Slag.

The setting time of alkali-activated slag (AAS) binders is extremely short, while traditional retarders of Portland cement may be invalid for AAS. To find an effective retarder with a less negative impact on strength, borax (B), sucrose (S), and citric acid (CA) were selected as potential retarders. The setting time of AAS with different admixtures dosages of 0%, 2%, 4%, 6%, and 8%, and the unconfined compressive strength and beam flexural strength of 3 d, 7 d, and 28 d AAS mortar specimens were tested. The microstructure of AAS with different additives was observed by scanning using an electron microscope (SEM), and the hydration products were analyzed by energy dispersive spectroscopy (EDS), X-ray diffraction analysis (XRD), and thermogravimetric analysis (DT-TGA) to explain the retarding mechanism of AAS with different additives. The results showed that the incorporation of borax and citric acid could effectively prolong the setting time of AAS more than that of sucrose, and the retarding effect is more and more obvious with the increase in borax and citric acid dosages. However, sucrose and citric acid negatively influence AAS's unconfined compressive strength and flexural stress. The negative effect becomes more evident with the increase in sucrose and citric acid dosages. Borax is the most suitable retarder for AAS among the three selected additives. SEM-EDS analysis showed that the incorporation of borax does three things: produces gels, covers the surface of the slag, and slows down the hydration reaction rate.

Effects of Using Aluminum Sulfate as an Accelerator and Acrylic Acid, Aluminum Fluoride, or Alkanolamine as a Regulator in Early Cement Setting.

Aluminum sulfate was employed as the main accelerator in order to explore new non-chloride and alkali-free cement accelerators. Acrylic acid, aluminum fluoride, or alkanolamine were used as regulators to further accelerate cement setting. The setting time, compressive, and flexural strengths in cement early strength progress were detected, and both the cement (raw material) and hydrated mortar were fully characterized. The cement setting experiments revealed that only loading acrylic acid as the regulator would decrease the setting time of cement and increase the compressive and flexural strengths of mortar, but further introduction of aluminum fluoride or alkanolamine improved this process drastically. In the meantime, structural characterizations indicated that the raw material (cement) used in this work was composed of C3S (alite), while hydrated mortar consisted of quartz and C3A (tricalcium aluminate). During this transformation, the coordination polyhedron of Al3+ was changed from a tetrahedron to octahedron. This work puts forward a significant strategy for promoting the activity of aluminum sulfate in cement setting and would contribute to the future design of new non-chloride and alkali-free cement accelerators.

An in vitro study of a custom-made device for thermoregulation of the mixing slab on the setting properties of zinc oxide eugenol impression paste.

Aim: The present study was aimed to investigate the functional relationship between the mixing temperature and properties of a commercially available zinc oxide eugenol impression paste (ZnOE paste). Settings and Design: In-vitro study. Materials and Methods: A custom-made simulated mixing device was indigenously designed to maintain different mixing temperatures, simulating cold, ambient, and hot weather. A commercially available ZnOE paste was mixed according to the manufacturer's instructions in the simulated mixing device at the temperatures ranging from 10°C to 50°C. Initial setting time and consistency were measured according to A. D. A. Specification No. 16 (n = 8). A stainless-steel die having 25, 50, and 75 µm lines was used for surface detail reproduction. Detail reproduction of the stone casts of the impressions was evaluated with a stereomicroscope at 30 magnification (n = 8). The shear bond strength of ZnOE paste to self-cure acrylic tray resin was measured by using the UTM at a crosshead speed of 0.5 mm/min (n = 8). Statistical Analysis Used: Data were analyzed by using one-way analysis of variance (ANOVA) and Tukey's post hoc tests at a confidence interval of 95% (alpha =0.05). Results: Initial setting time, consistency, and detail reproduction of the ZnOE paste were affected by the mixing temperature (P < 0.001). Mixing ZnOE paste at a lower temperature of 10°C and higher temperatures of 40°C and 50°C resulted in shorter initial setting time, thicker consistency, and poor detail reproduction. However, no significant difference was obtained in the shear bond strength among the different mixing temperatures evaluated (P > 0.05). Conclusion: Based on this in vitro study, it is advisable to perform the manipulation of ZnOE paste at a clinical/laboratory temperature of 30°C for optimum performance. The simulated mixing device used in this study can be an alternative for extreme climatic conditions.

Production of sustainable self-consolidating mortar with low environmental impact.

Reusing industrial by-products and agricultural waste as supplementary cementitious materials for producing sustainable concrete is one of the most promising ways to reduce cement production and the detrimental effects of concrete constructions on the environment. However, when it comes to preparing self-consolidating concrete (SCC) and mortar (SCMO) containing such materials in high volume, bleeding, and segregation of their fresh mixture are the crucial factors hindering their large-scale application. In this regard, the main aim of this study is to address such issues by designing sustainable SCMO using ground granulated blast furnace slag (GGBS) in high volume and rice husk ash (RHA) with comparatively lower environmental impact and high quality. To achieve this goal, the workability of fresh mixture and all its three main characteristics, including segregation resistance, passing ability, and filling ability, were evaluated with recently developed empirical apparatuses. For this purpose, 12 mixtures with different compositions were prepared to investigate the fresh properties, compressive strength, setting time, and environmental impact index. The results indicate that there are inextricable links between mixing proportions, strength, and carbon emissions of the mixture. Sustainable SCMO with an embodied-CO2 index lower than 4.5 kg/MPa.m3, good workability, and compressive strength of 49.7 MPa was designed by optimizing cementitious content, while the e-CO2 index of the control mixture was around 8 kg/MPa.m3. The addition of GGBFS and RHA not only decreased the e-CO2 index but also increased the unit cement strength contribution index. The results also indicated that by increasing GGBFS, the fluidity and segregation of the mixture increased while adding RHA increased viscosity and modified bleeding and the segregation index. Moreover, the growth rate of the compressive strength in mixtures containing GGBFS was much higher than that of the control mix at the same age. The promising results of this experimental study indicate that utilization of GGBFS and RHA in SCMO mixture can provide a practical way to reduce the environmental effects of cement production and pave the way for friendly disposal of slag and waste products.