Effects of Printing Angle and Post-Curing Time on the Color and Translucency of 3D-Printed Temporary Restoration.

In resins produced with a 3D printer, the printing parameters affect the properties of the restoration produced. This study examined the effect of the printing angle and post-curing time on the optical properties of temporary restorations. A total of 135 disk-shaped Formlabs temporary resins (10 × 2 mm) were produced at three different printing angles (0, 45, and 90 degrees) and post-cured for three different times (20, 40, and 60 min) (n = 15). Color and translucency measurements were taken for each group with a spectrophotometer (VITA Easyshade V). The ΔE values between printing angles and curing times influence each other. The highest color change was observed in the groups produced with a 90° printing angle. Considering the post-curing times, the highest color change was observed in the groups cured for 40 min. Increasing the curing time from 20 to 40 min decreases the translucency, whereas further increasing the curing time does not significantly affect the translucency. In terms of the impact on the translucency caused by the printing angles, 0° exhibited a lower translucency compared to other printing angles. During the 3D printing of temporary prostheses, both printing angles and post-curing times can affect their optical properties.

Unconfined Compressive Strength of Cement-Stabilized Qiantang River Silty Clay.

Cement-stabilization of weak and soft soils is an efficient way for ground improvement. Traditional Portland cement remains the most popular cementitious material in practice, and thus, a proper dosage design of cement-stabilized soil is of practical interest to meet the sustainable engineering requirements and to remedy environmental concerns. Based on the unconfined compression test of cement-stabilized Qiantang River silty clay, the effects of cement content, mixing moisture content, mixing-water-to-cement ratio, and curing time on the unconfined compressive strength were investigated. The results show that the mixing-water-to-cement ratio can comprehensively characterize the effects of cement content and water content on the unconfined compressive strength of the cement-stabilized clay. A prediction method for the unconfined compressive strength of cement-stabilized Qiantang River silty clay has been proposed with considerations for mixing-water-to-cement ratio and curing time. By comparing the experimental data of the present study with the existing literature data, it is found that there is a unified relationship between the unconfined compressive strength and the mixing-water-to-cement ratio of cement-stabilized Qiantang River silty clay, kaolin, Singapore marine clay, and Bangkok clay under the same curing time. The prediction method recommended by the standard may overestimate the unconfined compressive strength of cement-stabilized Qiantang River silty clay cured for 90 days.

Comprehensive Analysis of Geopolymer Materials: Properties, Environmental Impacts, and Applications.

The advancement of eco-friendly technology in the construction sector has been improving rapidly in the last few years. As a result, multiple building materials were developed, enhanced, and proposed as replacements for some traditional materials. One notable example presents geopolymer as a substitute for ordinary Portland concrete (OPC). The manufacturing process of (OPC) generates CO2 emissions and a high energy demand, both of which contribute to ozone depletion and global warming. The implementation of geopolymer concrete (GPC) technology in the construction sector provides a path to more sustainable growth and a cleaner environment. This is due to geopolymer concrete's ability to reduce environmental pollutants and reduce the construction industry's carbon footprint. This is achieved through its unique composition, which typically involves industrial byproducts like fly ash or slag. These materials, rich in silicon and aluminum, react with alkaline solutions to form a binding gel, bypassing the need for the high-energy clinker production required in OPC. The use of such byproducts not only reduces CO2 emissions but also contributes to waste minimization. Additionally, geopolymer offers extra advantages compared to OPC, including improved mechanical strength, enhanced durability, and good stability in acidic and alkaline settings. Such properties make GPC particularly suitable for a range of construction environments, from industrial applications to infrastructure projects exposed to harsh conditions. This paper comprehensively reviews the different characteristics of geopolymers, which include their composition, compressive strength, durability, and curing methods. Furthermore, the environmental impacts related to the manufacturing of geopolymer materials were evaluated through the life-cycle assessment method. The result demonstrated that geopolymer concrete maintains positive environmental impacts due to the fact that it produces fewer carbon dioxide CO2 emissions compared to OPC concrete during its manufacturing; however, geopolymer concrete had some minor negative environmental impacts, including abiotic depletion, human toxicity, freshwater ecotoxicity, terrestrial ecotoxicity, and acidification. These are important considerations for ongoing research aimed at further improving the sustainability of geopolymer concrete. Moreover, it was determined that silicate content, curing temperature, and the proportion of alkaline solution to binder are the major factors significantly influencing the compressive strength of geopolymer concrete. The advancement of geopolymer technology represents not just a stride toward more sustainable construction practices but also paves the way for innovative approaches in the field of building materials.

Comparative Evaluation of TiO2 Nanoparticle Addition and Postcuring Time on the Flexural Properties and Hardness of Additively Fabricated Denture Base Resins.

Three-dimensionally (3D)-printed fabricated denture bases have shown inferior strength to conventional and subtractively fabricated ones. Several factors could significantly improve the strength of 3D-printed denture base resin, including the addition of nanoparticles and post-curing factors. This study evaluated the effect of TiO2 nanoparticle (TNP) addition and the post-curing time (PCT) on the flexural properties and hardness of three-dimensionally (3D)-printed denture base resins. A total of 360 specimens were fabricated, with 180 specimens from each type of resin. For evaluating the flexural properties, bar-shaped specimens measuring 64 × 10 × 3.3 mm were used, while, for the hardness testing, disc-shaped specimens measuring 15 × 2 mm were employed. The two 3D-printed resins utilized in this study were Asiga (DentaBASE) and NextDent (Vertex Dental B.V). Each resin was modified by adding TNPs at 1% and 2% concentrations, forming two groups and an additional unmodified group. Each group was divided into three subgroups according to the PCT (15, 60, and 90 min). All the specimens were subjected to artificial aging (5000 cycles), followed by testing of the flexural strength and elastic modulus using a universal testing machine, and the hardness using the Vickers hardness test. A three-way ANOVA was used for the data analysis, and a post hoc Tukey's test was used for the pairwise comparisons (α = 0.05). Scanning electron microscopy (SEM) was used for the fracture surface analysis. The addition of the TNPs increased the flexural strength in comparison to the unmodified groups (p < 0.001), while there was no significant difference in the elastic modulus and hardness with the 1% TNP concentration. Among the TNP groups, the 2% TNP concentration significantly decreased the elastic modulus and hardness (p < 0.001). The SEM showed a homogenous distribution of the TNPs, and the more irregular fracture surface displayed ductile fractures. The PCT significantly increased the flexural strength, elastic modulus, and hardness (p < 0.001), and this increase was time-dependent. The three-way ANOVA results revealed a significant difference between the material types, TNP concentrations, and PCT interactions (p < 0.001). Both concentrations of the TNPs increased the flexural strength, while the 2% TNP concentration decreased the elastic modulus and hardness of the 3D-printed nanocomposites. The flexural strength and hardness increased as the PCT increased. The material type, TNP concentration, and PCT are important factors that affect the strength of 3D-printed nanocomposites and could improve their mechanical performance.

Experimental study on time-dependent rheological properties and mechanical performance of cemented fine tailings backfill mixed with polypropylene fiber.

By preparing fine tailings slurry with different mass concentration and fiber content, the rheological parameters of slurry with different fiber content and curing time were tested. In addition, the influence law of fiber content and curing time on compressive strength was analyzed through the prepared fine tailings backfill samples, and the microstructure characteristics of fine tailings backfill were further studied. The results show that when the fiber content is 0.2 ~ 1.2%, the yield stress and plastic viscosity of the slurry increase with the increase of fiber content, and the thixotropy of the slurry also shows the same change characteristics. The bridge effect of fiber makes it easier for forming network structure, which increase the slurry rheology. When the curing time ranges from 0 h to 2.5 h, the increasing of curing time leads to the increasing trend of rheological parameters, and also increases the thixotropy of slurry. However, the increase of rheological parameters will continuously decrease when the curing time exceeds 1 h, indicating that the influence of curing time on yield stress and thixotropy will gradually weaken with the continuous extension of curing time. When the curing age increases from 3 to 56 days, the compressive strength of the fine tailings backfill increases with the curing age, but the increasing range of compressive strength decreases gradually. When the fiber content ranges from 0.2 to 1.2%, the compressive strength of backfill increases first and then decreases with the increase of fiber content, and reaches the maximum value when the fiber content is 0.6%. The extension of curing time reduces the generation of large-scale pore structure, which promotes the formation of more compact microstructure of backfill.

The effect of light curing time and intensity on the bond strength and fracture resistance of orthodontic adhesive.

Background: This study aimed to measure the shear bond strength and compressive strength of orthodontic adhesives at different curing times and intensities. Methods: Ninety extracted human premolars were used. Orthodontic brackets were bonded on the buccal surface of the teeth with orthodontic adhesive light-cured using VRN-VAFU LED curing light at different curing times (1, 3 and 5 seconds) and intensities (1000, 1600 and 2300 mW/cm2 ). A universal testing machine was used to measure the shear bond strength. The ratio of the adhesive remnant and compressive strength of the orthodontic adhesive, at each curing time at the different intensities, were also evaluated. The results were statistically analyzed using one-way analysis of variance followed by Tukey's test. Results: The lowest bond strength values (6.4, 9.9 and 12.6 MPa) were recorded with 1000 mW/ cm2 intensity (at all curing times) in comparison with the other intensities (P<0.05). Increasing the curing time significantly increased the bond strength of the orthodontic brackets (P<0.05), except when the curing time was increased from 3 sec to 5 sec at 1600 mW/cm2 intensity. The highest compressive strength values (130.3, 147.1 and 174 MPa) were recorded at 2300 mW/ cm2 intensity (at all curing times) compared to the other intensities (P<0.05). The highest values of the ratio of the adhesive remnants were recorded at 1000 mW/cm2 intensity (at all curing times) compared to the other intensities (P<0.05). Conclusion: Although, increasing the curing time and\or the curing intensity has a positive effect on the bond strength and compressive strength of the orthodontic adhesive, it might be possible to suggest reducing the curing time of orthodontic adhesive to 1 sec at curing intensity of 2300 mW/cm2.

An In-Vitro Comparison of Shear Bond Strength and Adhesive Remnant Score Between Two Color Change Adhesives in Orthodontic Bonding With Reduced Curing Time Using Different High-Intensity Light Emitting Diode Units.

AIM AND OBJECTIVES: This study aims to determine the effect on shear bond strength (SBS) and adhesive remnant score between two color change adhesives (CCAs) with reduced curing time using different high-intensity light emitting diode (LED) units. MATERIALS AND METHODS: A total of 108 human first maxillary premolar teeth were randomly allocated into three principal groups (n = 36) based on the type of adhesives used. The adhesives include two CCAs: Transbond Plus Color Change Adhesive (3M, St. Paul, MN, USA) and Grengloo (Ormco, Orange, CA, USA), and the conventional tooth-colored adhesive: Transbond XT (3M). Each principal group was further divided into three sub-groups (n = 12 each) based on the curing time and type of high-intensity LED units used for bonding the stainless steel brackets. Woodpecker iLED Light Curing Unit (Guilin Woodpecker Medical Instrument Co., Ltd., Guilin, China) was cured for three and six seconds, and the ELIPAR S10 LED Curing Light (3M) was cured for 20 seconds. Bonding of the brackets was done in a standardized manner following the manufacturers' instructions. All the samples were submerged in distilled water at 370C for 24 hours. SBS testing was performed using an Instron machine, and adhesive residue on the debonded surface was examined and scored using a stereomicroscope. Statistical analysis was conducted using one-way ANOVA and Tukey's post-hoc test. RESULTS:  The results showed significant differences in SBS based on curing time and the type of adhesive resin used. The six seconds curing group exhibited the higher SBS values (15.5 - 22.82 Megapascals [MPa]) followed by the 20 seconds (12.17 - 18.14 MPa) and three seconds (11.31 - 11.74 MPa) groups. Grengloo adhesive demonstrated the highest SBS values among the three types of adhesives. The predominant adhesive remnant scores were 2 and 3. CONCLUSIONS:  Grengloo adhesive demonstrates superior bond strength compared to Transbond Plus and Transbond XT. Both Transbond Plus and Grengloo adhesives experience bond failure within the adhesive layer, regardless of the curing intensity or time.

Impact of a High-Power Light-Emitting Diode Unit With Reduced Curing Times on the Shear Bond Strength of Orthodontic Brackets and Their Adhesive Remnant Index Scores.

AIM AND OBJECTIVES: This study aims to evaluate the curing time minimally required for bonding stainless-steel (SS) brackets using a high-power light-emitting diode (LED) light curing unit (LCU) and examine the debonded enamel surface for adhesive remnant. MATERIALS AND METHODS: Based on the LED LCU and curing time employed, 80 human maxillary first premolar teeth were equally segregated into four groups. Three groups were cured using a high-power LED unit (Guilin Woodpecker Medical Instrument Co., Ltd., Guilin, Guangxi, China) for one, two, and three seconds. The fourth group served as a control and was bonded with another intensive LED unit (Elipar™ S10 LED Curing Light; 3M, Saint Paul, Minnesota, United States) for 20 seconds. Transbond™ XT Light Cure Adhesive (3M, United States) adhesive was used for bonding the SS brackets. All the samples were exposed to shear bond strength (SBS) testing after a 24-hour immersion period in distilled water at 37°C. A stereomicroscope was used to examine and score the adhesive remnant on the debonded surface using a modified adhesive remnant index (ARI). Kruskal-Wallis-ANOVA and post-hoc Mann-Whitney U tests for multiple pairwise comparisons were performed to analyze the data. RESULTS: Time and intensity significantly affected the SBS (P<0.001). A higher SBS value (16.04 megapascals (MPa)) was obtained in the six-second group when compared to the three-second (11.58 MPa), one-second (10.69 MPa), and 20-second control (13 MPa) groups. The ARI was significantly affected by the curing method. CONCLUSIONS: Higher SBSs were recorded for the six-second group using the high-power LED. A greater ARI score is associated with a reduced curing duration and vice versa.

Fracture Load of 3D-Printed Interim Three-Unit Fixed Dental Prostheses: Impact of Printing Orientation and Post-Curing Time.

The fracture resistance of 3-unit interim fixed dental prostheses (IFDPs) fabricated using digital light processing (DLP) additive technology with different printing parameters is neglected. Therefore, this study investigates the effect of different printing orientations and different post-curing times on the fracture resistance of 3-unit IFDPs fabricated from two three-dimensional (3D) printed resins, NextDent, C&B (CB), ASIGA, and DentaTOOTH. A 3-unit dye was scanned, and an IFDP was designed. A total of 300 specimens (150/materials, n = 10) were printed and divided into three groups according to printing orientations (0°, 45°, 90°) per material. Each orientation was subdivided into five groups (n = 10) considering the post-curing time (green state as control, 30, 60, 90, and 120 min). All specimens underwent thermocycling (5000 cycles). Each specimen was fitted onto the die and loaded until fracture using a universal testing machine with a loading rate of 1 m/min. Data were analyzed using ANOVA and post hoc Tukey test (α = 0.05). The result showed that printing orientation had a significant effect on the fracture load for both ASIGA and NextDent materials (p < 0.05). The highest fracture load was recorded with 45° orientation, followed by 0° orientation and 90° orientation showed the lowest values per respective post-curing time. Post-curing time increased the fracture load (p < 0.05). Post-curing time had a positive effect on the fracture load. As the post-curing time increased, the fracture resistance load increased (p < 0.05), with 90 and 120 min showing the highest fracture load. The 0° and 45° printing orientations have a high fracture load for 3D-printed IFDPs, and an increased post-curing time is recommended.

Influence of Mixing Water Content and Curing Time on Bond Strength of Clinker Masonry: The Wrench Test Method.

In the present study, experimental investigations on the influence of mixing water content used for the preparation of mortar mix using factory-made dry-mix mortar dedicated to bricklaying with clinker masonry units are presented, as well as the curing time on flexural bond strength of masonry made of these two materials. The flexural bond strength was tested using the "wrench test" method. The masonry tests specimens were prepared using three volumes of mixing water as follows: 4.0 L (the value recommended by the mortar manufacturer); 4.5 L; and 5 L of tap water per one 25 kg bag of dry pre-mixed mortar. The influence of the mixing water content was analyzed in relation to curing time. All masonry specimens were tested in four series after 9, 14, 21, and 28 days of sample curing. The results showed that the use of 6 and 18% more mixing water than recommended by the manufacturer (4.5 and 5 L per bag) adversely affected flexural bond strength. Moreover, for all three mixing water amounts, it was found that the maximum values of bonding strength were reached after 9 days of curing, which decreased over time. The largest decreases (30-40%) were recorded after 14 days. After 21 days, these values continued to decrease, but more slowly. The final value of the ratio of bond strength to flexural strength of the mortar was similar for all amounts of mixing water and for the 28-day curing time, it oscillated around 0.2.

Conditional Mitigation of Dental-Composite Material-Induced Cytotoxicity by Increasing the Cure Time.

Light-cured composite resins are widely used in dental restorations to fill cavities and fabricate temporary crowns. After curing, the residual monomer is a known to be cytotoxic, but increasing the curing time should improve biocompatibility. However, a biologically optimized cure time has not been determined through systematic experimentation. The objective of this study was to examine the behavior and function of human gingival fibroblasts cultured with flowable and bulk-fill composites cured for different periods of time, while considering the physical location of the cells with regard to the materials. Biological effects were separately evaluated for cells in direct contact with, and in close proximity to, the two composite materials. Curing time varied from the recommended 20 s to 40, 60, and 80 s. Pre-cured, milled-acrylic resin was used as a control. No cell survived and attached to or around the flowable composite, regardless of curing time. Some cells survived and attached close to (but not on) the bulk-fill composite, with survival increasing with a longer curing time, albeit to <20% of the numbers growing on milled acrylic even after 80 s of curing. A few cells (<5% of milled acrylic) survived and attached around the flowable composite after removal of the surface layer, but attachment was not cure-time dependent. Removing the surface layer increased cell survival and attachment around the bulk-fill composite after a 20-s cure, but survival was reduced after an 80-s cure. Dental-composite materials are lethal to contacting fibroblasts, regardless of curing time. However, longer curing times mitigated material cytotoxicity exclusively for bulk-fill composites when the cells were not in direct contact. Removing the surface layer slightly improved biocompatibility for cells in proximity to the materials, but not in proportion to cure time. In conclusion, mitigating the cytotoxicity of composite materials by increasing cure time is conditional on the physical location of cells, the type of material, and the finish of the surface layer. This study provides valuable information for clinical decision making and novel insights into the polymerization behavior of composite materials.

Synergistic effect of activator nature and curing temperature on time-dependent rheological behavior of cemented paste backfill containing alkali-activated slag.

Cemented paste backfill (CPB) that contains alkali-activated slag (AAS) produces more desirable properties and performance (enhanced fluidity, higher strength, lower cost, and limited carbon emission) as compared with CPB made with cement. Significant efforts have been devoted to the study of the effect of the individual factor on the rheology of AAS-CPB. However, the synergistic effect of curing temperature, time, and activator nature is still unclear. Therefore, the current research aims to investigate the time-dependent rheology of AAS-CPB under the combined influence of curing temperature, silica modulus (Ms), and activator concentration (AC). The findings revealed that a higher curing temperature results in a reduction in fluidity and an increase in the thixotropy of CPB. The evolution of rheological parameters of AAS-CPB is more insensitive to the curing temperature as compared to that of OPC-CPB. During the initial 2 h, higher AC can weaken the rheological parameter. However, a more rapid growth rate of rheological properties was observed after 2 h. The rheological parameters of AAS-CPB with higher Ms are always lower than those of AAS-CPB with lower Ms at all temperatures studied. In addition, the discrepancy in the linear correlation between thixotropy and plastic viscosity for OPC-CPBs and AAS-CPBs indicates the different hydration rates of slag and Portland cement. These findings are beneficial in guiding the mix proportion design of AAS-CPB in mines with various underground temperatures.

Effect of different polymerization times on color change, translucency parameter, and surface hardness of bulk-fill resin composites.

Background: Polymerization plays an important role in the optical and mechanical properties resin composite materials. Aim: The current study aimed to evaluate the effect of different polymerization times on the color change, translucency parameter (TP), and surface hardness of resin composites after thermocycling. Materials and Methods: Microhybrid resin composite (Filtek Z250; used in the control group) and bulk-fill resin composites (Filtek One Bulk-Fill Restorative, Tetric EvoCeram Bulk-Fill, and Tetric N-Ceram Bulk-Fill) were used. Each bulk-fill composite was placed as a single layer. Polymerization of the bulk-fill composites in the first group was completed in 20 s, and that in the second group was completed in 40 s (n = 10). Filtek Z250's polymerization was completed with 2 mm (20 s) + 2 mm (20 s). The color change (ΔE00) and translucency parameter (TP00) were calculated using the CIEDE2000 formula. Before and after thermocycling, the TP and surface hardness values were measured. The data were analyzed using one- and two-way analysis of variance, paired-samples t-test, and Tukey's test (P < 0.05). Results: After thermocycling, the ΔE00 values of the resin composite samples were 1.66-2.56. Compared to the control group, the Filtek One Bulk-Fill 20 s group exhibited the lowest color change values. The Filtek Z250 group exhibited lower TP and significantly higher microhardness values than the other bulk-fill resin groups before and after thermocycling (P < 0.05). There were no observed differences in the Tetric N-Ceram and Tetric EvoCeram groups before and after thermocycling. Conclusion: Under the conditions of 10,000 thermal cycles, different curing times did not affect the color change and hardness values of the bulk-fill materials. However, differences were observed among the composite materials. After thermocycling, the surface hardness and TP values decreased in all the resin composites. Depending on the material content, effective results can be obtained from the 20 s polymerization of bulk-fill resin composites.

Effects of microstructure on compressive strength of silica sand-enhanced oil well cement at a wide temperature range.

The influence of microstructure of silica-enhanced cement on the mechanical performance of cement is difficult to describe. In this study, we used the scanning electron microscope and image processing method to investigate the relationship between the complicity of cement microstructure and compressive strength under various temperatures and curing times. Fractal dimension was applied to describe the complicity of silica-enhanced cement. The relationships among compressive strength, fractal dimension, temperature, curing time and pore structure of cement were identified. The results show that curing time directly controls the complicity of microstructure of silica-enhanced cement and compressive strength by altering the pore orientation and macropore ratio in silica-enhanced cement. The curing temperature affects the complicity of cement microstructure and compressive strength indirectly by changing the ratio of micropore and small pore. The fractal dimension of silica-enhanced cement shows good correlation with compressive strength. Pore size distribution is the most important factor that influences the complicity of cement matrix and compressive strength of silica-enhanced cement. When building up the macroscopic mechanical performance model of silica-enhanced cement, we should consider the influence of pore size distribution in cement under different curing temperatures and times on the complicity of cement microstructure.

Fresh, Mechanical, and Durability Behavior of Fly Ash-Based Self Compacted Geopolymer Concrete: Effect of Slag Content and Various Curing Conditions.

This investigation evaluates the influence of various curing conditions and slag inclusion on the fresh, mechanical, and durability properties of self-compacting geopolymer concrete (SCGC) based on fly ash (FA). Curing temperature and curing time have a vital role in the strength and microstructure of geopolymer concrete. Therefore, to begin the research, the impacts of different curing conditions (curing temperature and curing time) and slag content on the compressive strength of FA-based SCGC were examined to determine the optimum curing method. A series of four SCGC mixes with a fixed binder content (450 kg/m3) and an alkaline/binder ratio of 0.5 was designated to conduct a parametric study. FA was replaced with slag at four different substitution percentages, including 0%, 30%, 50%, and 100% of the total weight of the binder. The fresh properties of the produced SCGC specimens were investigated in terms of slump flow diameter, T50 flow time, and L-box height ratio. Additionally, the following mechanical properties of SCGC specimens were investigated: modulus of elasticity and fracture parameters. The water permeability and freezing-thawing resistance were studied to determine the durability behavior of SCGC. In this study, the optimum curing temperature was 85 °C for the duration of 24 h, which provided the maximum compressive strength. The results confirmed that adding slag affected the workability of SCGC mixtures. However, the mechanical characteristics, fracture parameters, and durability performance of SCGC were improved for slag-rich mixtures. When using 50% slag instead of FA, the percentage increase in compressive, flexural, elastic module, and fracture energy test values were about 100%, 43%, 58%, and 55%, respectively, whilst the percentage decrease in water permeability was 65% and the resistance to freeze-thaw test in terms of surface scaling was enhanced by 79%.

A Novel Approach to Non-Destructive Rubber Vulcanization Monitoring by the Transient Radar Method.

Rubber is one of the most used materials in the world; however, raw rubber shows a relatively very low mechanical strength. Therefore, it needs to be cured before its ultimate applicatios. Curing process specifications, such as the curing time and temperature, influence the material properties of the final cured product. The transient radar method (TRM) is introduced as an alternative for vulcanization monitoring in this study. Three polyurethane-rubber samples with different curing times of 2, 4, and 5.5 min were studied by TRM to investigate the feasibility and robustness of the TRM in curing time monitoring. Additionally, the mechanical stiffness of the samples was investigated by using a unidirectional tensile test to investigate the potential correlations between curing time, dielectric permittivity, and stiffness. According to the results, the complex permittivity and stiffness of the samples with 2, 4, and 5.5 min of curing time was 17.33 ± 0.07 - (2.41 ± 0.04)j; 17.09 ± 0.05 - (4.90 ± 0.03)j; 23.60 ± 0.05 - (14.06 ± 0.06)j; and 0.29, 0.35, and 0.38 kPa, respectively. Further statistical analyses showed a correlation coefficient of 0.99 (p = 0.06), 0.80 (p = 0.40), and 0.92 (p = 0.25) between curing time-stiffness, curing time-permittivity (real part), and curing time-permittivity (imaginary part), respectively. The correlation coefficient between curing time and permittivity can show the potential of the TRM system in contact-free vulcanization monitoring, as the impact of vulcanization can be tracked by means of TRM.

Soft computing techniques to predict the compressive strength of green self-compacting concrete incorporating recycled plastic aggregates and industrial waste ashes.

Abstract: Rapid urbanization and industrialization with corresponding economic growth have increased concrete production, leading to resource depletion and environmental pollution. The mentioned problems can be resolved by using recycled aggregates and industrial waste ashes as natural aggregate and cement replacement in concrete production. Incorporating different by-product ashes and recycled plastic (RP) aggregates are viable options to produce sustainable self-compacting concrete (SCC). On the other hand, compressive strength is an essential characteristic among other evaluated properties. As a result, establishing trustworthy models to forecast the compressive strength of SCC is critical to saving cost, time, and energy. Furthermore, it provides valuable instruction for planning building projects and determining the best time to remove the formwork. In this study, four alternative models were suggested to predict the compressive strength of SCC mixes produced by RP aggregates: the artificial neural network (ANN), nonlinear model, linear relationship model, and multi-logistic model. To do so, an extensive set of data consisting of 400 mixtures were extracted and analyzed to develop the models, various mixture proportions and curing times were considered as input variables. To test the effectiveness of the suggested models, several statistical evaluations, including coefficient of determination (R 2), scatter index, root mean squared error (RMSE), mean absolute error (MAE), and Objective (OBJ) value were utilized. Compared to other models, the ANN model performed better to forecast the compressive strength of SCC mixes incorporating RP aggregates. The RMSE, MAE, OBJ, and R 2 values for this model were 5.46 MPa, 2.31 MPa, 4.26 MPa, and 0.973, respectively.

Modeling the compressive strength of eco-friendly self-compacting concrete incorporating ground granulated blast furnace slag using soft computing techniques.

Concern regarding global climate change and its detrimental effects on society demands the building sector, one of the major contributors to global warming. Reducing cement usage is a significant challenge for the concrete industry; achieving this objective can help reduce global carbon dioxide emissions. Replacing the cement in concrete with by-product ashes is a promising approach for reducing the embodied carbon in concrete and improving some of its properties. Among different by-product ashes, ground granulated blast furnace slag (GGBFS) is a viable option to produce sustainable self-compacting concrete (SCC). Compressive strength (CS), on the other hand, is an essential characteristic among other evaluated properties. As a result, establishing trustworthy models to forecast the CS of SCC is critical to saving cost, time, and energy. Furthermore, it provides helpful instruction for planning building projects and determining the best time to remove the formwork. In this study, four alternative models were suggested to predict the CS of SCC mixes produced by GGBFS: the artificial neural network (ANN), nonlinear model (NLR), linear relationship model (LR), and multi-logistic model (MLR). To do so, an extensive set of data consisting of about 200 mixtures were extracted and analyzed to develop the models, and various mixture proportions and curing times were considered input variables. To test the effectiveness of the suggested models, several statistical evaluations including determination coefficient (R2), mean absolute error (MAE), scatter index (SI), root mean squared error (RMSE), and objective (OBJ) value were utilized. In comparison to other models, the ANN model performed better to forecast the CS of SCC mixes incorporating GGBFS. The RMSE, MAE, OBJ, and R2 values for this model were 4.73 MPa, 2.3 MPa, 3.4 MPa, and 0.955, respectively.

3D Woven Textile Structural Polymer Composites: Effect of Resin Processing Parameters on Mechanical Performance.

This work presents the manufacture of polymer composites using 3D woven structures (orthogonal, angle interlock and warp interlock) with glass multifilament tows and epoxy as the resin. The mechanical properties were analyzed by varying the processing parameters, namely, add-on percentage, amount of hardener, curing time, curing temperature and molding pressure, at four different levels during the composite fabrication for three different 3D woven structures. The mechanical properties of composites are affected by resin infusion or resin impregnation. Resin infusion depends on many processing conditions (temperature, pressure, viscosity and molding time), the structure of the reinforcement and the compatibility of the resin with the reinforcement. The samples were tested for tensile strength, tensile modulus, impact resistance and flexural strength. Optimal process parameters were identified for different 3D-woven-structure-based composites for obtaining optimal results for tensile strength, tensile modulus, impact resistance and flexural strength. The tensile strength, elongation at break and tensile modulus were found to be at a maximum for the angle interlock structure among the various 3D woven composites. A composition of 55% matrix (including 12% of hardener added) and 45% fiber were found to be optimal for the tensile and impact performance of 3D woven glass-epoxy composites. A curing temperature of about 140 °C seemed to be optimal for glass-epoxy composites. Increasing the molding pressure up to 12 bar helped with better penetration of the resin, resulting in higher tensile strength, modulus and impact performance. The optimal conditions for the best flexural performance in 3D woven glass-epoxy composites were 12% hardener, 140 °C curing temperature, 900 s curing time and 12 bar molding pressure.

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.