Shrinkage Of Composites Research Articles

Effect of abaca natural fiber on the setting behavior and autogenous shrinkage of cement composite

In this study, the effects of abaca fibers on the initial hydration and autogenous shrinkage characteristics of cement were investigated with the aim of using natural abaca fibers as construction materials. Abaca fiber content was chosen as the primary experimental variable and was varied from 0 to 0.25, 0.5, 1, and 2% of the weight of cement for testing. To identify the influence of the fibers on the hydration reaction of cement, the heat of hydration, ultrasonic pulse velocity, and setting time were measured. The internal curing effect of abaca fibers was evaluated using thermogravimetry and microstructure analysis by conducting compressive strength and autogenous shrinkage tests. The results indicate that abaca fibers can be used as internal curing agents owing to their high water absorption rate, which results from the cross-sectional characteristics of their hollow bundle-type tubular structure. Abaca fibers are found to be an effective alternative that can mitigate the risk of cracking by reducing the autogenous shrinkage of high-performance cement concrete products.

Thermo-viscoelastic homogenization of 3D woven composites with time-dependent expansion coefficients

Stress relaxation in the viscoelastic matrix influences the evolution of thermal expansion and chemical shrinkage of polymer composites. Its effects are included into a viscoelastic model of the generalized Maxwell type by means of time-dependent thermal expansion and chemical shrinkage coefficients. A homogenization strategy is proposed to obtain these coefficients of the composite from the constituent behaviors, taking into account the viscoelastic effects. The homogenized behavior is validated by full-scale finite element simulations. It reproduces features such as sign changes of the thermal strain rate close to the glass transition temperature and thermal creep effects, which can have an important impact on the residual stress formation in composites, but are not taken into account by classical thermo-elastic homogenization methods.

Effect of pretreated cow dung fiber on mechanical and shrinkage properties of cementitious composites

The proper disposal of cow dung waste has always been a great challenge for the agricultural sector in China and around the world. In this work, the cow dung was processed into a cheap renewable cow dung fiber (CDF) and applied into cementitious composites. The physicochemical properties of raw and alkali pretreated CDF were analyzed by thermogravimetry, Fourier transform infrared spectroscopy, X-ray diffraction, single fiber tensile test and scanning electron microscopy. The strength and autogenous shrinkage of cementitious composites reinforced with the CDF were measured. The results showed that alkali pretreatment dissolved the amorphous components (i.e., hemicellulose and lignin) and enhanced the crystallinity of cellulose. The pretreatment of CDF by 1 mol/L NaOH solution led the 3 d′s compressive and splitting tensile strength of the CDF reinforced cementitious composites to increase by 21.8% and 12.5%, respectively. The presence of CDF, with or without pretreatment enabled to inhibit the development of autogenous shrinkage of cementitious paste. This work is expected to promote an alternative application for the recycling of cow dung waste in sustainable building materials.

Using a professional DSLR camera to measure total shrinkage of resin composites.

This study evaluated the optical method for measuring free total shrinkage using a Digital Single Lens Reflex (DSLR) camera. Eight composites were evaluated, conventional, bulk fill and low-shrinkage: Z100 (3M Oral Care), Gradia Direct Anterior (GC corporation), Spectra Smart (Dentsply), Filtek Z350 XT (3M Oral Care), Aura Bulk Fill (SDI), Vittra APS (FGM), Opus Bulk Fill APS (FGM), and Beautifil II LS (Shofu Inc.). The samples (6 mm diameter and 1.5 mm thick, n = 10) were placed on a polyvinylsiloxane impression material. An image of the uncured sample was captured using a DSLR camera with 105 mm macro lens and a ring flash. Samples were light cured with a 700 mW/cm2 LED light-cure unit for 40s. Post-polymerization images were captured at 2, 10 and 60 min. Projected circumferential areas of the specimens were drawn using the ImageJ software. Volumetric total shrinkage was calculated from the ratio of the areas obtained from pre- and post-curing. Results were analyzed using One-way ANOVA (α = 0.05) and Tukey test. Volumetric total shrinkage values were significantly different among the composite materials (p < .001). The volumetric shrinkage (%) mean and results of Tukey test at 60 min were: Z100: 3.45±0.30 (A); Gradia Direct Anterior: 3.00 ± 0.23 (B); Spectra Smart 2.89 ± 0.35 (B); Filtek Z350 XT: 2.65 ± 0.37 (BC); Aura Bulk Fill: 2.42 ± 0.25 (CD); Vittra APS: 2.14 ± 0.35 (DE); Opus Bulk Fill APS: 1.91 ± 0.24 (E); Beautifil II LS: 1.18 ± 0.16 (F). The optical method using a DSLR camera, was suitable for total shrinkage evaluation and will allow assessment of total shrinkage without the need for specialized equipment.

Study of the influence of using recycled brass fibres from electrical discharge machining process on the physical, thermal and mechanical properties of the resulting mortar

Nowadays, metallic fibre reinforced cementitious composites are widely used on many different construction elements: concrete beds, slabs, precast concrete industry, etc. Fibres reduce the crack generation due to the cementitious composite shrinkage and improves its flexural strength, toughness and durability. If metallic waste materials from the industrial manufacturing sector were used instead of using the commercially available metallic fibres, the energy of both the waste recycling process and the manufacturing of the actual commercial metallic fibres would be saved. This paper studies the use of the waste residual brass fibres generated during the electrical discharge machining process as a reinforcement on mortars. With that in mind, two different fibre types (brass covered steel and recycled brass) on two different mix proportions (0.65% and 1.3% by unit volume of mortar) were added to a self-leveling non-reinforced mortar taken as a reference to evaluate their influence on the physical, thermal and mechanical properties of the resulting mortar. According to the results, for both types of fibres studied, the higher the fibre proportion used, the higher were the density, the thermal conductivity, the flexural strength and the compressive strength.of the resulting mortars. Recycled brass fibres increased the thermal conductivity and decreased the volumetric heat capacity of the resulting mortars more than the steel fibres, which is interesting, for example, on self-levelling mortars used on radiant floor heat exchangers. However, less increase was observed on the mechanical properties of the recycled brass fibre reinforced mortars than that of the steel fibre reinforced mortars, due to the shorter length of the former fibres (5-10 mm for the recycled brass fibres, 13 mm for the steel fibres). Therefore, the parameter that controls the cutting frequency of the waste wire of the electrical discharge machine should be modified to adapt the final fibre length to that of the commercially available fibres.

Influence of Monowave and Polywave LED Unites on G-Aenial Resin Composites’ Polymerization: An In Vitro Study

Objectives: Trimethylbenzoyldiphenylphosphine oxide and phenylpropanedione photoinitiator components in resin composites have been used widely due to their white color. However, it seems that there are some limitations in the required polymerization initiator wavelength. This study aimed to evaluate the polywave and monowave light-activating devices (LEDs) on polymerization and shrinkage strain of two dental composites with different photoinitiator systems. Methods: In this experimental study, 24 samples were prepared in two groups, including G-Aenial A2 and bleach composites. Each group was divided into two subgroups: one cured by monowave LED unit and the other by polywave device. Then shrinkage strain of samples was evaluated using bonded disk technique. Results: Results showed the shrinkage strain of A2 and bleach composites using PW device was significantly greater than MW device. In addition, the A2 composite shrinkage action polymerized with MW device was significantly lower than shrinkage action of A2 and bleach composite using PW machine. Conclusion: The findings of this study revealed that polywave LEDs were more beneficial for the polymerization of resin composites.

Methodology for composite materials shrinkage definition for use in shipbuilding and marine technology

Deformations of steel material in shipbuilding and marine technology applications as a result of mechanical or temperature influences are a well-known problem. However, in the modern shipbuilding industry, the application of alternative materials, especially composite materials, in the structure and for the equipment of the ship is increasingly represented. Consequently, there is a need to determine the deformation and change of characteristics of such composite materials as a result of various mechanical, and especially temperature influences that cause the so-called shrinkage. The basic composite production process involves connecting the matrix with a catalyst and accelerators that create temperature, then the material shrinks by cooling when it can change its dimensions and characteristics. Also, in order to achieve the best possible mechanical properties, composite materials are specially heated and then cooled according to strictly defined processes and curves. The ability to predict the characteristics and parameters of such deformations is important in the context of the application of composite materials. To define such deformations, different methods are used within individual numerical solvers, whose results can differ significantly from each other. Therefore, the authors in this paper present an established methodology for predicting mechanical and temperature deformations, and modelling of composite materials, based on the analysis of analytical methods and numerical solvers with the aim of defining the most accurate numerical solver. By applying the presented methodology, it is expected to raise the level of accuracy and quality of composite materials production as well as to raise the quality of design solutions and efficiency of production procedures during shipbuilding in particular, but also within different marine technology applications and during the product’s life cycle.

Effects of application method on shrinkage vectors and volumetric shrinkage of bulk-fill composites in class-II restorations

ObjectivesUpon initial proximal wall construction, the favorable C-factor of class-II cavities may become unfavorable. This study investigated the application method on bulk-fill resin composite polymerization shrinkage. MethodsOccluso-proximal class-II cavities were prepared in 40 molars and bonded with a self-etch adhesive (Adhese Universal). The study groups varied according to the resin composite application: group-1: bulk application, Tetric EvoCeram Bulk Fill (TBF); group-2: proximal wall construction (TBF) and occlusal cavity filling (TBF); group-3: thin flowable liner layer, Tetric EvoFlow Bulk Fill (TEF) and bulk filling (TBF); group-4: flowable liner (TEF), proximal wall (TBF), occlusal cavity (TBF); and group-5: bulk application, SDR (3 mm) and capping layer (TBF, 1 mm). Each resin composite increment was scanned twice using micro-CT (uncured, cured 40 s) at a resolution of 16 µm. Shrinkage vectors and volumetric polymerization shrinkage were evaluated and statistically analyzed (one-way ANOVA). SEM images were used to investigate the tooth-restoration interface. ResultsShrinkage vectors differed significantly among the groups and were greatest in gp5-fl/SDR (47.6 µm), followed by gp1-TBF (23.8 µm) and least in gp5-fl/SDR+TBF (11.1 µm). Volumetric shrinkage varied significantly with the use of SDR (gp5-fl/SDR: 2.6%) and TEF (gp4-fl/TEF: 2.5%) to TBF (gp4-fl/TEF+wl/TBF: 0.6%) in the incremental application. SignificanceBuilding a proximal resin composite wall yielded smaller shrinkage vectors than the bulk application. Applying a thin flowable liner decreased the shrinkage vectors, even more when building a proximal wall. A thin flowable liner is recommended when building a proximal resin composite wall.

Synthesis of alkali-activated uncalcined Pisha sandstone cement composites

This work reports the utilization of natural Pisha sandstone (PS) as a new precursor to manufacture a novel alkali-activated cement. The rheological properties, compressive strength, drying shrinkage, hydration properties, CO2 emission and energy consumption of the alkali-activated uncalcined Pisha sandstone cement composites (AUPC) were investigated. AUPC mortar containing 1.0 wt% of sodium hexametaphosphate and 0.2 wt% of ligneous calcium sulfonate as plasticizers showed similar rheological properties to those of ordinary Portland cement (OPC) mortar. The compressive strength of AUPC could reach 52.7 MPa after curing at 80 °C for 12 h. The increase of activator concentration (up to 4 mol/L) and the extending of curing time (up to 12 h) significantly increased the hydration of feldspar, montmorillonite and blended slag in AUPC. This resulted in the formation of more low Al/Si ratio aluminosilicate gels, calcium silicate hydrate (C-S-H) gels, and calcium alumina silicate hydrate (C-A-S-H) gels. When the concentration of NaOH and the curing time exceeded 4 mol/L and 12 h respectively, the porosity of AUPC increased, thereby lowering the compressive strength. The 90-day drying shrinkage of the AUPC with 4 mol/L NaOH activator increased from 1.68 to 3.04 mm/m when the water-to-binder ratio increased from 0.25 to 0.45. The total CO2 emissions and energy consumption for producing AUPC were estimated to be much lower than producing OPC.

Modification of the Structure and Properties of Lightweight Cement Composite with PVA Fibers.

This study addresses the application of polyvinyl alcohol (PVA) fibers to improve the performance of lightweight cement composites with pozzolans. Blended cement mixes based on expanded glass granules were modified with PVA fibers (Type A: Ø40 µm, L = 8 mm and Type B: Ø200 µm, L = 12 mm). The following research methods were used to analyse the effect of the fibers on the structure of cement matrix and physical-mechanical properties of lightweight composite: SEM, XRD, DTG, calorimetry tests, and standard test methods of physical and mechanical properties. Results from the tests showed that a denser layer of hydrates was formed around the PVA fiber and the amounts of portlandite, CSH, and CASH formed in the specimens with PVA were found to be higher. PVA fibers of Type A accelerated hydration of the cement paste, slightly increased the compressive strength of the lightweight composite, but had no significant effect on the values of density, ultrasonic pulse velocity and flexural strength. The shrinkage of cement composite was significantly reduced using both types of PVA fiber and both types of PVA fibers increased the fracture energy of lightweight cement composite with expanded granules.

Investigation of mechanical performances and polymerization shrinkage of dual-cured resin composites as core build-up material

This study systematically compared the mechanical performances and polymerization shrinkage of two novel dual-cured resin composites (DCRC) with one conventional packable light-cured resin composite (LCRC) for their application as core build-up material by micro-hardness test, flexural strength test, push-out test, and digital image correlation analysis. The LCRC had a significantly higher micro-hardness (p<0.05) whereas the bond strength demonstrated no difference. The mean values of three materials ranged from 35.16 and 64.82 for the Vickers hardness and from 4.66 MPa to 11.53 MPa for the bond strength. The flexure strength of the three materials was not statistically different from each other. LCRC demonstrated 1.88% of volumetric shrinkage while the two DCRC showed 5.06% and 4.91%, respectively. In general, the DCRC demonstrated a comparable flexural strength and bond strength as the LCRC, however, the significant polymerization shrinkage of DCRC should be emphasized.

Tensile Creep of Cement and Concrete Composites: Monitoring by Means of 2D-Digital Image Correlation

Creep and shrinkage of Cement and Concrete Composites (CCC) are significant properties that need to be considered to use these materials in practice. Many previous scientific studies revealed CCC creep characteristics under sustained compression and shrinkage, using traditional test methods from design standards. Because of the complexity of experimental procedures, CCC creep in tension has not been studied as close. Furthermore, there is no unified standard that proposes applicable testing methods or specific testing apparatus. This study examines the suitability of 2D—Digital Image Correlation (DIC) to observe the creep deformations of specimens under tension. Ordinary Portland cement (OPC) mortar with 1% polyvinyl alcohol (PVA) fibres has been investigated in the research. Compact tension (CT) specimens 150 × 150 × 12 mm (with a notch) were used. Creep deformations under sustained uniaxial tension (applied loading corresponding to 60% of the ultimate strength) were measured. DIC images were captured using an entry/mid-level DSLR camera. Results show that DIC is suitable for studying uniaxial tensile creep of cement and concrete composites. Deformation of specimens in tension was similar to that measured using the conventional method (using surface-attached gauges).

Optimization for Injection Moulding process parameters towards Warpage and Shrinkage of HDPE-PBI composites

Injection moulding is a high-quality process that is preferred in modern manufacturing. Due to the defects in HDPE polymer composites the parameter’s had to be adjusted based on the necessity. Therefore, this study of parameters is to improve the quality characteristics of the injection moulding of HDPE-PBI composite samples. As the composition of HDPE composites varies, the quality aspects that must be controlled are shrinkage and warpage. The parameters that are considered as factors are Melting Temperature (°C), Injection pressure (MPa) and cooling time (sec). Using the Taguchi Optimization method of L9 Orthogonal array, the injection moulding process was performed and found that the injection pressure of 65 MPa and temperature of 180-185 °C showed better results. The influence of parameters was studied through this research using Analysis of Variance (ANNOVA).

Relationships between Flexural and Bonding Properties, Marginal Adaptation, and Polymerization Shrinkage in Flowable Composite Restorations for Dental Application

To evaluate the flexural and bonding properties, marginal adaptation, and polymerization shrinkage in flowable composite restorations and their relationships, four new generation flowable composites, one conventional, and one bulk-fill flowable composite were used in this study. Flexural properties of the composites and shear bond strength to enamel and dentin for flowable restorations were measured immediately and 24 h after polymerization. Marginal adaptation, polymerization shrinkage, and stress were also investigated immediately after polymerization. The flexural properties, and bond strength of the flowable composites to enamel and dentin were much lower immediately after polymerization than at 24 h, regardless of the type of the composite. Polymerization shrinkage and stress varied depending on the material, and bulk-fill flowable composite showed much lower values than the others. The marginal adaptation and polymerization shrinkage of the composites appeared to have a much stronger correlation with a shear bond strength to dentin than to enamel. The weak mechanical properties and bond strengths of flowable composites in the early stage after polymerization must be taken into account when using them in the clinic. In addition, clinicians should be aware that polymerization shrinkage of flowable composites can still lead to the formation of gaps and failure of adaptation to the cavity regardless of the type of composite.

Assessment of the effect of fiber percentage in glass fiber reinforced slag-based geopolymer

ABSTRACT Fibers can increase the ductility of geopolymer materials, acting as reinforcements to improve mechanical properties. These improvements depend on fiber content and quantity. This study evaluates the impacts of different percentages of glass fiber on a GBFS (ground blast furnace slag) geopolymer matrix. The glass fibers were used on the critical length of 20 mm, obtained by pull-out test in previous studies. Percentages of 0.25%, 0.50%, 0.75%, and 1.00% of glass fiber in mass were tested in fresh state, by flow measurement, and in hardened state, by variation of shrinkage, water porosity and response of composites under flexural and compressive load conditions at 7, 14, 28, and 90 days. The mixture resulted in a high porosity geopolymer paste. In addition, an analysis of variance (ANOVA) was performed to evaluate the statistical significance of fibers in compressive strength. The results show that increasing percentages glass fibers, until 0.75%, enhances mechanical properties. Percentage of 1.00% started to show accumulation of branch of multifilament fibers which contribute to higher drying shrinkage. The ANOVA test showed that the percentage of fibers can influence the compressive strength. With the results, the optimum percentage of fibers for his composite mixture was found at 0.75%.

Assessment of polymerization shrinkage of different bulk-fill resin composites

Objectives: This research was designed to evaluate the effect of polymerization shrinkage of different bulk-fill resin composites. Materials & Methods: Ninety extracted molars were prepared as specimens by having a box shape proximal cavity for the restoration of composite resins. The specimens were divided into three main groups (n=30), according to the resin composite materials used (sonic fill, flowable and packable bulk-fill). Profile projector was used for assessment of polymerization shrinkage Results: There is no significant difference between the variables. Sonic fill composite resin has lower polymerization shrinkage than flowable bulk-fill composite and packable bulk-fill composite. The marginal adaptation of sonically activated resin composite is more than the polymerization shrinkage of sonically activated resin composite, while the storage time of sonically activated resin composite is less in bulk-fill .Conclusions: Success of resin composites depends primarily on the degree of polymerization shrinkage as when the shrinkage decrease mostly the post-operative problems decrease.

Improved performance of Bis-GMA dental composites reinforced with surface-modified PAN nanofibers

In the present work, polyacrylonitrile (PAN) nanofibers reinforced dental composites were investigated to achieve the improved interfacial adhesion between the PAN nanofiber and resin matrix using surface modification of nanofibers. PAN nanofibers mat were prepared by electrospinning and then, surface treated with the activated bisphenol A glycidyl methacrylate (Bis-GMA)/triethyleneglycol dimethacrylate (TEGDMA) (50/50 mass ratio) dental resin followed by photo-curing. Also, the treated nanofibers mat was milled into a powder to achieve the uniform distribution of nanofibers in the matrix resin. The reinforced dental composite were prepared by mixing the various mass fraction of the powder (0.5–15 wt%) with the Bis-GMA/TEGDMA dental monomers. The effect of weight ratio of surface-modified nanofibers to blend resin on the chemical structure, morphology, compression and flexural properties, color and polymerization shrinkage of dental composites was evaluated. The results showed that using surface-treated nanofibers with content of 5 wt% enhanced the compression strength, flexural strength, flexural modulus and work of rupture of the resultant dental composite by factors of 23%, 7%, 80%, and 145%, respectively, comparing to the unreinforced neat resin. Also, the polymerization shrinkage reduces by 37%. These significant improved properties of the dental composite could be due to the semi-interpenetration network formation between surface-modified nanofibers and resin matrix and well distribution of nanofibers in the dental resin. Further increasing the nanofiber content led to poor mechanical properties of obtained dental composites. The results also, revealed that the color of resin composite could be whiter using modified PAN nanofibers as the filler.

Improving mechanical and water sorption properties of thermoplastic starch by incorporating chitosan filler

To develop an adequate matrix polymer for agricultural or packaging applications, thermoplastic starch (TPS)/chitosan composites were prepared in a wide composition range either by injection moulding or in an internal mixer followed by compression moulding. Chitosan behaves as filler forming dispersed structure in TPS samples prepared by thermomechanical methods without any additional acid. In the TPS composites chitosan has a considerable reinforcing effect. Regardless of the production methods, the Young's modulus and tensile strength increase significantly. Furthermore, addition of chitosan has a considerable effect on the water sorption of TPS-based composites. Chitosan slightly decreases the maximum water uptake of composites and reduces significantly the water sorption rate especially in the samples prepared by injection moulding. Besides, chitosan can greatly reduce the shrinkage of injection moulded TPS composites and delay the appearance of mould on the surface even at high humidity.

Investigating the Effect of CNTs on Early Age Hydration and Autogenous Shrinkage of Cement Composite

In this study, the effect of carbon nanotubes (CNTs) on the physical properties of cement composites was investigated. The mechanism of the change of autogenous shrinkage of CNTs-reinforced cement composites was also examined. In the experiments, ordinary Portland cement (OPC) and fly ash (FA) were used as binders, and 0.0, 0.1, 0.3, and 0.5% multi-walled CNTs (MWCNTs) were added to fabricate pastes. When the hydration heat was measured through isothermal calorimetry, it was found that CNTs accelerated the early age hydration of the pastes and that the hydration rate increased as the CNT content increased. The compressive strength was the highest when the CNT content was 0.1%. As the CNT content increased, the internal relative humidity (IRH) decreased and autogenous shrinkage showed a decreasing tendency. Through the analysis of the correlation between autogenous shrinkage and IRH, it was confirmed that the reduction in autogenous shrinkage due to the addition of CNTs resulted from the decrease in bulk strain.

Laboratory assessment of early-age durability benefits of a self-healing system to cementitious composites

Shrinkage of cement composites (paste, mortar, grout, or concrete) due to moisture loss during the curing period is a challenge for their durability. In this laboratory study, urea-formaldehyde (UF) microcapsules and polyvinyl alcohol (PVA) microfibres were utilized as a self-healing system to improve the early-age durability of cement mortars by mitigating their total shrinkage during the curing period. Experimental results revealed that the admixed UF microcapsules/PVA microfibres together could mitigate 25% of the total shrinkage during the curing period of 35 days. In addition, this self-healing system could reduce the gas permeability of the mortars by over 75%. The UF microcapsules and PVA microfibres could interfere with the formation of some crystalline hydration products and modify the microstructure of hydrated cement mortar, resulting in slight reductions in the compressive strength (less than 12%) and at some dosages significantly reduced the chloride migration coefficient of the mortars (i.e., 1% 1100+PVA, 2% 700, and 1% 1100). The UF microcapsules mainly affected the pores with a radius between 10 nm and 1000 nm, whereas the PVA microfibers mainly affected the larger pores at the interfacial transition zone.