Lower Flexural Strength Research Articles

Alkali leaching and mechanical performance of epoxy resin-reinforced geopolymer composite

Geopolymer material has emerged as a new binder in concrete production, mainly because of the low energy consumption and low greenhouse gas emission compared to Portland cement manufacture. However, low flexural strength and a high tendency to leach alkalis limit the application of this material in the construction field. In this study, a series of fly ash/ground granulated blast furnace slag based geopolymer composites reinforced with different amounts of bisphenol F epoxy resin were produced with an aim to investigate the effect of epoxy resin on alkali leaching and mechanical performance on geopolymer. The results show that the inclusion of a small amount of epoxy resin can significantly enhance the mechanical properties and reduce the total amount of alkali leaching of ambient-cured geopolymer, thus promising the extensive application of geopolymer in the construction industry.

High-flexural-strength of geopolymer composites with self-assembled nanofiber networks

Natural-fiber-reinforced geopolymer composites are environmentally friendly materials that have garnered considerable attention. In practice, the drying shrinkage and uneven dispersion of fibers in geopolymers result in low flexural strength, which limits the use of large-scale composites. In this study, high-flexural strength geopolymer composites with self-assembled nanofiber networks were hybridized using in situ polymerization. Composites with different fiber contents were evaluated via morphology and mechanical strength assessments. A mixed nanofiber and geopolymer solution was created to achieve uniform dispersion, and then the geopolymers were optimized at the nanoscale level using a bottom-up approach to achieve self-assembled nanofiber networks with good interfacial bonding. Due to the water retention properties of the nanofibers and subsequent gel material, the networks facilitated internal curing of the geopolymers, thus preventing drying shrinkage. This ultimately reduced the weight loss and increased the density of the composites. In addition, high flexural strength properties were observed in composites with a fiber content of 0.5%, due to the combination of fiber reinforcement and porosity. Thus, this work introduces new considerations for geopolymer applications.

Improving flexural strength of UHPC with sustainably synthesized graphene oxide

Abstract Ultrahigh-performance concrete (UHPC) has been increasingly employed for infrastructure and building structure, thanks to its excellent durability and exceptional mechanical properties; however, improving its relatively low flexural strength remains a challenging issue. This study presents an experimental investigation on improving the compressive strength and flexural strength of UHPC by employing sustainably synthesized graphene oxide (GO). The content of micro steel fibers (MSFs) for the UHPC ranges from 0.5 to 1.5% by volume of concrete. For each level of MSFs addition, the dosage of GO added is from 0.00 to 0.03% by mass of cement. The results indicate that the electrochemical (EC) method to synthesize GO is greener, safer, and lower in cost for construction industry. And the compressive strength of UHPC is slightly improved, while its flexural strength is significantly increased from 33 to 65%, demonstrating that the incorporation of GO can be an effective measure to enhance the flexural strength of UHPC under standard curing and steam curing. This can be associated with the improvement in bond strength between the MSFs and the matrix contributed by the improved interfacial microstructure, the higher friction increase, and the mechanical interlock at the interface between the MSFs and the bulk matrix, thanks to the addition of GO.

A mechanical strong polymer-cement composite fabricated by in situ polymerization within the cement matrix

Durability and service life of cementitious materials are seriously affected by their low flexural strength and high brittleness. Herein, we developed a novel polymer-modified cementitious composite (PMCC) with enhanced mechanical performances by introducing acrylic acid (AA) and 2-acrylanmido-2-methylpropanesulfonic acid (AMPS) monomers into the cement matrix to form a strong polymer-cement network via in situ polymerization. By optimizing the mass ratio of AA-AMPS copolymer to cement, PMCC with a tunable and enhanced mechanical performance can be achieved. Samples with 3.0 wt% AA-AMPS copolymer exhibited the highest increase of 81.1% in flexural strength while retained adequate compressive strength under the standard curing. The strong chemical interactions between Ca2+ and AA-AMPS copolymer chains that can help form an interwoven polymer-cement network in the cement matrix contributed to this enhanced flexural strength. In fact, drawbacks including large pore size, easy crack, and brittleness can be surmounted effectively via the construction of a polymer-cement network in the cement matrix, then mechanical enhancement can be obtained. This work paves a new way to develop a unique PMCC with high flexural strength via the in situ polymerization of monomers within the cement matrix.

Natural Fibers as an Alternative to Synthetic Fibers in Reinforcement of Geopolymer Matrices: A Comparative Review.

Geopolymer materials have been gaining ground in the civil construction sector not only for having superior physical properties when compared to conventional cement, but also for being less harmful to the environment, since the synthesis of the geopolymer does not release toxic gases or require high energy costs. On the other hand, geopolymer materials like cementitious matrices have low flexural strength and have fragile breakage. To overcome these deficiencies, the insertion of fibers in geopolymeric matrices has been evaluated as a solution. Although most research on this practice focuses on the use of synthetic fibers, the use of natural fibers has been growing and brings as an advantage the possibility of producing an even more ecological material, satisfying the need to create eco-friendly materials that exists today in society. Thus, this paper aimed to, through the evaluation of research available in the literature, understand the behavior of fibers in geopolymer matrices, identify similarities and differences between the performance of geopolymer composites reinforced with natural and synthetic fibers and, understanding that it is possible, point out ways to optimize the performance of these composites.

Mechanical behavior of electrophoretically modified CFRP composites at elevated temperatures: An assessment of the influence of graphene carboxyl bath concentration

AbstractThe study aims at investigating the mechanical behavior of carbon fiber reinforced polymer (CFRP) composites modified with graphene carboxyl at elevated temperature (ET‐110°C) and understanding the effect of electrophoretic deposition bath concentration (0.5 g/L, 1.0 g/L, and 1.5 g/L) on their mechanical behavior at ET. The 1.5 g/L composite has revealed a maximum improvement in energy absorbed before failure of 33.25% at RT and 22.54% at ET for flexural testing and ∼35% at RT for short beam shear testing, over neat CFRP composite. The modified composites have shown an improved flexural strain to failure at both RT and ET, with 1.5 g/L composite exhibiting maximum enhancement of 12.41% at RT and 26.52% at ET over neat composite. However, at ET, modified composites exhibited lower flexural strength and interlaminar shear strength values in comparison to that of neat. Viscoelastic behavior of all composites was studied to understand bath concentration's effect on thermal behavior via dynamic mechanical thermal analysis. Differential scanning calorimetry was employed for governing the glass transition temperature of composites. Fractography of tested samples (both ET and RT) was performed utilizing a scanning electron microscope to determine the prominent failure mode.

Influences of calcium carbonate nanoparticles on the workability and strength of 3D printing cementitious materials containing limestone powder

This paper presents the influences of nano-CaCO3 (NC) on the fresh-state and hardened performances of 3D printing cementitious materials (3DPC) with limestone powder (LS). The LS was added at a rate of 15%, while 0, 1, 2, and 3% NC as a partial replacement for LS. Results show that the addition of NC accelerates the hydration reaction of Portland cement through nucleation. Besides, 15% LS increased the fluidity and vertical displacement but decreased the yield stress and green strength of fresh-state 3DPC. NC improved fresh-state performances of 3DPC significantly thanks to the high specific areas of NC. Mixtures containing 15% LS exhibited lower flexural and compressive strength than that of reference at all ages. However, mixtures containing 14% LS and 1% NC resulted in enhanced strength at all ages compared to mixtures containing 15% LS.

Thermal Power Plant Flue Gas Desulfurization (FGD) Gypsum Waste Particulates Reinforced Injection Molded Flexible Composites

Low density, thermally insulative and moisture resistant flexible polymer composites were developed using Flue Gas Desulfurization (FGD) gypsum waste particulates with Low Density Polyethylene (LDPE) under injection molding technique without any additive or filler modification. The moisture content, particle size, specific gravity, density, pH, electrical conductivity and Fourier-Transform Infrared Spectroscopy (FTIR) analysis of FGD gypsum waste particulates were evaluated together with mineralogical, morphological and elemental analysis by X-Ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy with Energy Dispersive X-Ray Spectroscopy (FESEM-EDS) studies. Developed composites were tested for Density, Water absorption, thermal conductivity and mechanical strength. Density of FGD-LDPE composites varied from 0.91±0.01 to 1.33±0.01 g/cm3 with different concentrations of FGD gypsum filler (10–70 weight %). The water absorption showed 0.69±0.04% for maximum (70 weight %) filler concentration and the corresponding thermal conductivity was found to be minimum (0.3964 W/m/K). The composites were very flexible and exhibited lower tensile strength (6.17±0.05 to 7.15±0.09 MPa), flexural strength (11.25±0.14 MPa) and impact strength (22.70±1.57 KJ/m2) with 50% and 10% filler content. Findings of these results have showed a new path for making flexible composites potentially having applications in sports ground, staircase and instrumentation rooms as a thermal insulation flooring material using FGD waste particulates generated from thermal power plants.

Additively Manufactured Zirconia for Dental Applications.

We aimed to assess the crystallography, microstructure and flexural strength of zirconia-based ceramics made by stereolithography (SLA). Two additively manufactured 3 mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP: LithaCon 3Y 230, Lithoz; 3D Mix zirconia, 3DCeram Sinto) and one alumina-toughened zirconia (ATZ: 3D Mix ATZ, 3DCeram Sinto) were compared to subtractively manufactured 3Y-TZP (control: LAVA Plus, 3M Oral Care). Crystallographic analysis was conducted by X-ray diffraction. Top surfaces and cross-sections of the subsurface microstructure were characterized using scanning electron microscopy (SEM). Biaxial flexural strength was statistically compared using Weibull analysis. The additively and subtractively manufactured zirconia grades revealed a similar phase composition. The residual porosity of the SLA 3Y-TZPs and ATZ was comparable to that of subtractively manufactured 3Y-TZP. Weibull analysis revealed that the additively manufactured LithaCon 3Y 230 (Lithoz) had a significantly lower biaxial flexural strength than 3D Mix ATZ (3D Ceram Sinto). The biaxial flexural strength of the subtractively manufactured LAVA Plus (3M Oral Care) was in between those of the additively manufactured 3Y-TZPs, with the additively manufactured ATZ significantly outperforming the subtractively manufactured 3Y-TZP. Additively manufactured 3Y-TZP showed comparable crystallography, microstructure and flexural strength as the subtractively manufactured zirconia, thus potentially being a good option for dental implants.

Mechanical and durability properties of steel fiber‐reinforced concrete containing coarse recycled concrete aggregate

AbstractThe focus of this study is to investigate the effect of using coarse recycled concrete aggregates (RCAs) as an alternative material to natural coarse aggregate on the fresh, mechanical and durability behavior of concrete reinforced with steel fiber. Eighteen unique concrete mixes with RCA content of 0%, 50%, and 100% and steel fiber content of 0%, 1%, and 2% were prepared, and tests were performed to study slump, density, compressive and splitting tensile strengths, flexural behavior, surface hardness, surface abrasion resistance, water absorption, and sorptivity of each mix. It is shown that concrete containing RCA has a lower unit weight, compressive, splitting tensile and flexural strength, flexural toughness, surface hardness, and abrasion resistance, and a higher water absorption and sorptivity in comparison with conventional concrete. An increased compressive, splitting tensile and flexural strength, flexural toughness, surface hardness, and abrasion resistance, and a decreased water absorption and sorptivity of concrete with an increased steel fiber content from 1% to 2% is less significant compared to those from 0% to 1%. The results also show that, at RCA content of 50%, incorporating 1% steel fiber develops a concrete mix with similar or even better properties compared to unreinforced conventional concrete. At 100% RCA content, incorporating 2% steel fiber develops a concrete mix with similar properties to unreinforced conventional concrete having water to cement ratio of 0.3, but inferior properties to unreinforced conventional concrete having water to cement ratio of 0.5. These findings indicate that recycled aggregate concrete with similar or even better properties compared to concrete with natural aggregate can be developed through properly designing mixes, providing a great avenue toward the production of green construction material for structural applications.

Fabrication and characterization of remineralizing dental composites containing calcium type pre-reacted glass-ionomer (PRG-Ca) fillers

ObjectiveTo fabricate and characterize dental composites with calcium type pre-reacted glass-ionomer (PRG-Ca) fillers. MethodsPRG-Ca fillers were prepared by the reaction of calcium fluoroaluminosilicate glass with polyacrylic acid. Seven dental composites were produced from the same organic matrix (70/30wt% Bis-GMA/TEGDMA), with partial replacement of barium borosilicate (BaBSi) fillers (60wt%) by PRG-Ca fillers (wt%): E0 (0) – control, E1 (10), E2 (20), E3 (30), E4 (40), E5 (50) and E6 (60). Enamel remineralization was evaluated in caries-like enamel lesions induced by S. mutans biofilm using micro-CT. The following properties were characterized: degree of conversion (DC%), roughness (Ra), Knoop hardness (KHN), flexural strength (FS), flexural modulus (FM), water sorption (Wsp), water solubility (Wsl), and translucency (TP). Data were analyzed to one-way ANOVA and Tukey’s HSD test (α=0.05). ResultsAll composites with PRG-Ca induced enamel remineralization. E0 and E1 presented similar and highest DC% than E2=E3=E4=E5=E6. Ra and KHN were not influenced by PRG-Ca fillers (p<0.05). The higher the content of PRG-Ca, the lower FS, FM and TP (p<0.05). Wsp increased linearly with the content of PRG-Ca fillers (p<0.05). E6 presented the highest Wsl (p<0.05), while the Wsl of the other composites were not different from each other (p>0.05). SignificanceIncorporation of 10–40wt.% of PRG-Ca fillers endowed remineralizing potential to dental composites without jeopardizing the overall behavior of their physicochemical properties. Dental composites with PRG-Ca fillers seems to be a good alternative for reinforcing the enamel against caries development.

Flexural Performance and Toughness Characteristics of Geogrid-Reinforced Pervious Concrete with Different Aggregate Sizes.

Pervious concrete is an environmentally friendly paving material to reduce surface runoff in urban construction. However, due to low flexural strength and cracking susceptibility caused by the high porosity, pervious concrete is only used in low-volume traffic roadways and parking lots for current service. This study investigated the permeability, strength, and flexural performance of pervious concrete with different coarse aggregate size, geogrid position, and geogrid layer number. Test results indicate that the geogrid placed at an appropriate position in pervious concrete improved the permeability and compressive strength. Four-point bending tests were conducted in the laboratory to evaluate the flexural performance and toughness characteristics of pervious concrete beam. Meanwhile, this study also proposed a new evaluation method to distinguish the contribution of geogrids and concrete mixture to the flexural toughness of pervious concrete beam at the pre-peak and post-peak stages by two toughness indices. Test results indicate that geogrids improved the flexural strength, deformability, and energy absorption capability of pervious concrete beam. The geogrids placed at both one-third and two-thirds of the heights of pervious concrete beam resulted in the optimum flexural performance. Besides, the small size (5–10 mm) aggregates were conducive to providing high flexural strength for the geogrid-reinforced pervious concrete beam, while the large size (10–15 mm) aggregates played a significant role in obtaining noteworthy post-cracking performance.

Multicriteria performance evaluation of fiber-reinforced cement composites: An environmental perspective

Cement composites have the intrinsic drawback of low flexural strength and crack endurance. Many studies have been conducted to improve the mechanical performance of cement composites by employing commercially available fibers, but less attention has been paid to the environmental impacts associated with these fibers. Therefore, this study aims to evaluate and compare the performance of different fiber reinforced cement composites (FRCCs) based on their mechanical strength, environmental impact potential, and cost. For this purpose, the overall performance of six different fiber (such as Recycled carbon fiber (rCF), Basalt Fiber (BF), Glass fiber (GF), Polypropylene fiber (PPF), Polyvinyl alcohol fiber (PVAF), and Virgin carbon fiber (vCF)) reinforced cement composites were evaluated. Results revealed that the flexural strength of recycled carbon fiber reinforced cement composite (M-rCF) was highest among all other FRCCs. Moreover, depending on the environmental impact category, the lowest impacts were employed by M-rCF and M-PPF. At the same time, the minimum production cost was associated with M-PPF. Therefore, a multicriteria decision technique was employed to evaluate the overall performance of all the FRCCs. Based on the performance score, the FRCCs can be ranked as: M-rCF > M-PPF > M-BF > M-GF > M-PVAF > M-vCF.

3D printing of dental restorations: Mechanical properties of thermoplastic polymer materials

In the seminal field of 3D printing of dental restorations, the time and cost saving manufacturing of removable and fixed dental prostheses from thermoplastic polymer materials employing fused filament fabrication (FFF) is gaining momentum. As of today, the additive manufacturing of the established semi-crystalline polyetheretherketone (PEEK) requires extensive post-processing and lacks precision. In this context, the amorphous polyphenylene sulfone (PPSU) may provide a higher predictability and reliability of the results. The aim of this study was to investigate the mechanical properties of PPSU and PEEK processed by FFF (PPSU1-3D (PPSU Radel) and PPSU2-3D (Ultrason P 3010 NAT)) or extrusion (PPSU1-EX (Radel R-5000 NT) and PEEK-CG (PEEK Juvora)). Three-point flexural strength, two-body wear, and Martens hardness (HM) and indentation modulus (EIT) were tested after aging. One-way ANOVA, the Kruskal-Wallis and the Pearson's and Spearman's correlation tests were computed (α = 0.05).PPSU1-3D and PPSU2-3D showed lower flexural strength values than PPSU1-EX and PEEK-CG. PPSU1-3D showed the highest, and PEEK-CG and PPSU1-EX the lowest height loss. The highest HM and EIT results were observed for PEEK-CG and the lowest for PPSU1-3D. Correlations were observed between all parameters except for the application height.In conclusion, the manufacturing process affected the flexural strength of PPSU, with 3D printed specimens presenting lower values than specimens cut from prefabricated molded material. This finding indicates that the 3D printing parameters employed for the additive manufacturing of PPSU specimens in the present investigation require further optimization. For 3D printed specimens, the quality of the filament showed an impact on the mechanical properties, underlining the importance of adhering to high quality standards during filament fabrication. Extruded PPSU led to comparable results with PEEK for flexural strength and two-body wear, indicating this novel dental restorative material to be a suitable alternative to the established PEEK for the manufacturing of both removable and fixed dental prostheses.

Microstructure and properties of zirconia-alumina composites fabricated via powder injection molding

This study aimed to fabricate zirconia-alumina composites via powder injection molding and investigated the effects of alumina addition on microstructure as well as physical properties of the composites. Zirconia-alumina composites were prepared using polyethylene glycol (PEG) and polyvinyl butyral (PVB) as binders. The powder loading was fixed at 38 vol%, and PEG: PVB binder weight ratio was fixed at 80:20. Alumina content within ceramic component was varied at 0, 10, 20, 30, 40 and 50 vol% to observe the effect of alumina on the composite structures and properties. The injection molding was done at 190℃ followed by water debinding of PEG at 40℃. Thermal debinding of PVB at 450℃ was performed prior to sintering at 1450℃. From the density measurement via Archimedes’ method, the relative density of sintered samples was found to be highest at 10 vol% alumina and gradually lower at higher alumina content. The condition with highest density yielded the highest flexural modulus and flexural strength. XRD indicated that tetragonal zirconia phase coexisted with alumina when alumina was added. Above 20 vol% alumina, monoclinic zirconia was also detected. The increased porosity in samples with high alumina content, as confirmed in SEM morphological observation, correlated with lower flexural strength and lower flexural modulus. The results illustrated the feasibility of powder injection molding in the production of zirconia-alumina composites and the optimum condition in this study was 10 vol% alumina.

Mechanical Reinforcement of Lime Pastes by Electrospun Cellulose Acetate Polymer Fibers

Lime-based composites have been extensively used throughout the years as plasters/renders and jointing mortars in building construction. However, the low flexural strength and tensile ductility of these composite building materials, that are currently still used in the structural and thermal upgrading of existing structures of high cultural and architectural significance, have been a significant drawback. Therefore, researchers have been focusing on the development of novel composites involving the use of additives to enhance the tensile and flexural capacity of lime-based materials. For the first time in this study, naturally-derived polymer fibers produced by electrospinning have been successfully introduced as additives in lime pastes aiming to investigate their effect on the mechanical performance of the end composites. More precisely, the introduction of electrospun cellulose acetate (CA) microfibers within lime pastes resulted to a tremendous improvement of the mechanical properties of the latter. Consequently, the present study paves the pathway towards the use of electrospun fibrous additives in the development of advanced composite lime-based building materials, which is currently an unexplored area.

Fire-resistant cellulose boards from waste newspaper, boric acid salts, and protein binders

Housing construction consumes more materials than any other economic activity, with a total of 40.6 Gt/year. Boards are placed between construction materials to serve as non-load-bearing partitions. Studies have been performed to find alternatives to conventional materials using recycled fibers, agro-industrial waste, and protein binders as raw materials. Here, fire-resistant cellulose boards with low density and adequate flexural strength were produced for use as non-load-bearing partitions using waste newspapers, soy protein, boric acid, and borax. A central composite design was employed to study the influence of the board component percentage on flame retardancy (UL 94 horizontal burning test), density (ASTM D1037–12), and flexural strength (ISO 178–2010). The cellulose boards were characterized by thermal analysis (ASTM E1131–14) and scanning electron microscopy. Fire-resistant cellulose boards were successfully made with low densities (120–170 kg/m3) and flexural strength (0.06–0.64 MPa). The mechanical performance and fire resistance of cellulose boards suggest their suitability for use as building materials. A useful and sustainable construction material with great potential is produced with the valorization of waste materials. Graphic abstract

Correlation of fatigue behavior and dynamic mechanical properties of hybrid composites of polypropylene/short glass fibers/hollow glass beads

Ternary hybrid composites of Polypropylene (PP)/Short Glass Fibers (GF)/Hollow Glass Beads (HGB) were prepared using untreated and aminosilane-treated HGB, compatibilized with maleated-PP, and with varying total and relative GF/HGB contents. Static/short-term flexural strength properties data revealed, through lower flexural strength values, that the presence of untreated HGB particles induces to fiber-polymer interfacial decoupling at much higher extent than in the presence of aminosilane-treated HGB particles. This phenomenon is also evident when evaluating the data from displacement-controlled three-point bending fatigue tests. Monitored up to 106 cycles, the analyzed hybrid composites presented distinct performance relative to their fatigue stress relaxation rate: the lower the matrix-reinforcements’ interfacial adhesion, more pronounced the stress relaxation rate as a function of the number of fatigue cycles. Dynamic Mechanical Thermal Analysis (DMTA) results could successfully reveal the hybrid composites behavior at the microstructural level when they were submitted to both static flexural test and fatigue, depending on the degree of interfacial interactions between the polymer matrix of PP and the hybrid reinforcements of GF and HGB (with and without aminosilane surface treatment).

Effect of metakaolin on the autogenous shrinkage of alkali-activated slag-fly ash paste

The high autogenous shrinkage of alkali-activated materials made from slag and fly ash is recognised as a major drawback with regard to the use as construction materials. In this study, metakaolin was introduced into the alkali-activated slag-fly ash (AASF) paste to mitigate the autogenous shrinkage. The shrinkage mitigation mechanism of metakaolin was explained by studying the influences of metakaolin on the microstructure, shrinkage related properties, and mechanical properties of AASF paste. It was found that adding metakaolin could significantly reduce the chemical and autogenous shrinkage of AASF paste. This shrinkage mitigation is accompanied by a decrease in the alkalinity of AASF paste pore solution, a reduced drop in internal relative humidity, and an increase in porosity of AASF paste. Moreover, the incorporation of metakaolin does not change the type of the reaction products, but greatly delays the formation of the reaction products of AASF paste. The addition of metakaolin, above 5% of the binder, results in lower 28-day compressive and flexural strength of AASF paste.

Cement mortar with enhanced flexural strength and durability-related properties using in situ polymerized interpenetration network

The low flexural strength and high brittleness of cementitious materials impair their service life in building structures. In this study, we developed a new polymer-modified mortar by in situ polymerization of acrylamide (AM) monomers during the cement setting, which enhanced the flexural and durable performances of mortars. The mechanical properties, micro-and-pore structures, hydrated products, interactions between cement hydrates and polyacrylamide (PAM), and durability-related properties of the mortars were investigated comprehensively. Mortars with 5% PAM exhibited the best performance in terms of flexural strength among all the mixtures. The mechanical strength of cement pastes modified by in situ polymerization of AM monomers was significantly superior to those modified by PAM. The chemical interactions between the polymer molecules and cement hydrates together with the formation of polymer films glued the cement hydrates and polymers and resulted in an interpenetrating network structure, which strengthened the flexural strength. Reductions in porosity and calcium hydroxide content and improvement in capillary water absorption were achieved with the addition of PAM. Finally, the chloride resistance was significantly enhanced with the incorporation of PAM.