Increase In Dynamic Modulus Research Articles

Study of Dynamic Modulus of Asphalt Mix after Reinforcement of Sandstone

Sandstone has poor mechanical properties. To facilitate the application of sandstone into asphalt mixtures, sandstone was treated by immersion in sodium silicate solution, and the dynamic modulus after reinforcement was used as a criterion. The results showed that the mechanical properties of the sandstone aggregate treated with sodium silicate were improved, and the dynamic modulus was increased by 18.2%, which will help to reduce rutting. The dynamic modulus and phase angle can be effectively predicted over a wide frequency range using the sigma function and the Kramers–Kronig relationship. Sandstone asphalt mixtures basically conform to linear viscoelasticity, but the phase angle changes are more complicated at high temperatures and do not vary monotonically with frequency. By calculating the rutting coefficient, fatigue coefficient, and DSRFn parameters for performance prediction, it was found that an increase in dynamic modulus resulted in a significant increase in the rutting coefficient but a decrease in the cracking resistance.

Gas CO2 foaming and intermixing in portland cement paste to sequester CO2

In this study, concentrated CO2 gas was used to create foamed cement paste, and concentrated CO2 gas was intermixed in fresh cement paste to produce regular cement paste materials that were not foamed. The potential of both methods to form CaCO3 from calcium ions that would form Ca(OH)2 was investigated. After curing the materials for different ages, the Ca(OH)2 and CaCO3 contents were measured using thermogravimetric analysis; the large void size distributions, dynamic modulus, and compressive strength were tested and compared against Control (no gas added), and N2 foamed and N2 intermixed specimens. A 10% increase in dynamic modulus and compressive strength was measured in CO2 foamed specimens compared to N2 foamed specimens. The increase in mechanical properties was the result of both a narrow void diameter distribution and CaCO3 formation in place of Ca(OH)2. The CO2 foamed cement generation method shows the potential to sequester 0.06 ton of CO2 for every ton of cement which is a CO2 emission reduction of 7.0% of the CO2 production associated with cement production. For the CO2 intermixing method, the void content, compressive strength, and dynamic modulus results were consistent between the Control and CO2 intermixed specimens while the N2 intermixed specimens showed a decrease in compressive strength and dynamic modulus. The CO2 intermixing method showed potential to sequester 0.04 ton of CO2 for every ton of cement or a 4.7% CO2 emission reduction of the total CO2 production associated with cement manufacturing. The reported CO2 emissions are not based on life cycle assessment and do not account for emissions associated with CO2 collection, transportation, and intermixing. The present paper does not investigate the mechanisms of hydration under CO2 intermixing.

Study on performance of geocell-reinforced red clay subgrade

Three comparative treatment plans are used to study the effect of red clay subgrade reinforced with geocell. Multiple subgrade test methods including Benkelman beam, portable falling weight deflectometer, dynamic cone penetrometer and standard vehicle load tests are adopted in the field tests. Test results show that the application of geocell in red clay subgrade can enhance the overall stiffness and strength of the subgrade. The mechanism of geocell in the subgrade is studied. Geocell can provide added confinement to the subgrade soil. Compared with the red clay subgrade without geocell reinforcement, for the red clay subgrade reinforced with 0.1 m-high geocell and 0.05 m-high geocell, the rebound modulus increases by 65% and 33%, the dynamic modulus increases by 69% and 38% and the penetration decreases by 51.7% and 40.4%, respectively. A hard shell layer is formed in the subgrade when it is reinforced with geocell. The geocell-reinforced layer mainly plays the role of stress diffusion. It not only can reduce the additional stress in the subgrade but can also diminish the influence of the depth of the vehicle load.

Hysteretic behaviour of uniaxially thermoformed auxetic foams under 3-point bending low-frequency vibration

The work describes experiments and models related to auxetic (negative Poisson’s ratio) foams subjected to low-frequency and variable amplitude 3-point bending loading. A custom 3-point bending vibration test rig is designed and used to perform the dynamic test of auxetic PU foam beams within low-frequency range (1–20 Hz) and 5 different displacement amplitudes. The auxetic foams tested in this work are manufactured using a simplified and relatively low-cost uniaxially thermoforming compression technique, which leads to the production of foams with transverse isotropic characteristics. Auxetic foam beam samples with two different cutting orientations and different thermoforming compression ratios rc (20–80%) are tested and compared, also with the use of theoretical Euler–Bernoulli-based and finite element models. The dynamic modulus of the foams increases with rc, ranging between 0.5 and 5 MPa, while the dynamic loss factor is marginally affected by the compression ratio, with overall values between 0.2 and 0.3. The auxetic PU foam has a noticeable amplitude-dependent stiffness and loss factors, while the dynamic modulus increases but slightly decreases with the frequency. The dynamic modulus is also 20–40% larger than the quasi-static one, while the dynamic and static loss factors are quite close. A modified Bouc–Wen model is also further developed to capture the amplitude and frequency-dependent properties of the conventional and auxetic foams with different volumetric compression ratios. The model shows a good agreement with the experimental results.

Correlations in rheological behavior between large amplitude oscillatory shear and steady shear flow of silica‐filled star‐shaped styrene‐butadiene rubber compounds: Experiment and simulation

AbstractThe large amplitude oscillatory shear (LAOS) and steady shear behavior of star‐shaped SSBR/silica 60 phr (21 vol%) compounds with various filler surface areas was measured and simulated. An SBR gum and SBR compounds containing four different silicas with surface areas of 55, 135, 160, and 195 m2/g were utilized. Rheological behavior indicated clear correlation with surface area. LAOS tests showed an increase in dynamic moduli, shear stress, and higher order harmonic contributions with surface area. Elastic and viscous Lissajous figures showed significant distortion at intermediate and higher strain amplitudes. Additionally, ratios of third and fifth order stress harmonics to the first stress harmonic (I3/1 and I5/1, respectively) showed a ''bump'' at intermediate strain amplitudes for the three highest surface area compounds. With regards to steady shear, all materials showed strong shear thinning behavior, and an increase in shear viscosity with surface area. The Cox‐Merz rule was shown to be valid for the SBR gum but not for the filled compounds. However, the complex viscosity as a function of shear rate amplitude at various frequencies at high strain amplitudes and the steady shear viscosity as a function of shear rate coincided. This correlation, referred to as the Philippoff approach, has important ramifications for the rubber industry, providing quick data for predicting processing behavior. The Simhambhatla‐Leonov model was successfully employed to simulate rheological behavior for the SBR gum and the lowest surface area silica compound, but the model yielded mixed results for the higher surface area silica compounds.

Modeling of the rheological properties of multinanolayer films in the presence of compatibilized interphase

Rheological behavior of nanolayered films of polyethylene/polyamide 6 (PE/PA6) compatibilized in situ during the coextrusion process has been studied at a temperature between the melting temperatures of PE and PA6. Thanks to the high number of interfaces, a drastic increase in dynamic moduli has been measured when increasing the interphase volume fraction in the films, and a solid-like behavior for the interphase was identified. Different models are compared to capture the complex viscosity of nanolayered films as a function of angular frequency. A model considering interphase and bulk viscosities and a single fitting parameter, namely, the thickness over which the viscosity decreases linearly from the interphase to the bulk one, captures the complex viscosity of all samples. This thickness is comparable to the PE layer thickness up to values about 1 μm before a significant bulk region has to be added to capture the behavior for thicker layers. This suggests that the melt rheology is impacted by the presence of a nanometric interphase over very large (micronic) length scales.

A Nonequilibrium Model for Particle Networking/Jamming and Time-Dependent Dynamic Rheology of Filled Polymers.

We describe an approach for modeling the filler network formation kinetics of particle-reinforced rubbery polymers—commonly called filler flocculation—that was developed by employing parallels between deformation effects in jammed particle systems and the influence of temperature on glass-forming materials. Experimental dynamic viscosity results were obtained concerning the strain-induced particle network breakdown and subsequent time-dependent reformation behavior for uncross-linked elastomers reinforced with carbon black and silica nanoparticles. Using a relaxation time function that depends on both actual dynamic strain amplitude and fictive (structural) strain, the model effectively represented the experimental data for three different levels of dynamic strain down-jump with a single set of parameters. This fictive strain model for filler networking is analogous to the established Tool–Narayanaswamy–Moynihan model for structural relaxation (physical aging) of nonequilibrium glasses. Compared to carbon black, precipitated silica particles without silane surface modification exhibited a greater overall extent of filler networking and showed more self-limiting behavior in terms of network formation kinetics in filled ethylene-propylene-diene rubber (EPDM). The EPDM compounds with silica or carbon black filler were stable during the dynamic shearing and recovery experiments at 160 °C, whereas irreversible dynamic modulus increases were noted when the polymer matrix was styrene-butadiene rubber (SBR), presumably due to branching/cross-linking of SBR in the rheometer. Care must be taken when measuring and interpreting the time-dependent filler networking in unsaturated elastomers at high temperatures.

Effects of Nanomodification by the Silicate Nanoparticles on Characteristics of Basalt Fibre Reinforced Polymer

Composite material represents a complex multi-material structure consisting of coincidence array and reinforcing agent. Basalt continuous fibre and basalt composite material processing technique is one of the present day promising area. With all high characteristics of basalt fibre and basalt made products the ways of it refinement are nowhere near exhausted and one of that ways is nanomodification of the binding agents used in composite production. In this paper quoted the results of the silicate - type nanoparticle retooling influence on mechanical and physical properties of epoxianhydride binding for the purpose of lifting strength and viscoelastic properties of basalt fibre composite. It is found that the appliance of the silicate nanoparticles in epoxianhydride binding between 0.25 to 1 mass. % improve stress-related properties per 10-45%, micro plastics interlaminar shear strength increase by 25-28%, increase of dynamic modulus of elasticity - 30%, mechanical and physical properties of basalt fibre reinforced polymer based on nanomodified binder - 20%. Conducted research efforts show transmission of increased characteristics by nanomodification of epoxianhydride binding onto the characteristics of basalt fibre composite materials.

Disparate dynamic viscoelastic responses of wheat flour doughs coated with different oils for preventing water evaporation during time sweeps and their mechanisms decoupled.

Various non-volatile oils are currently applied in order to prevent water evaporation from exposed surface of dough during oscillatory measurements. A systemic understanding of their effectiveness in controlling water loss and ensuring accuracy of rheological measurements is necessary. In this work, three kinds of coating oils (vaseline, dimethyl silicone oil and low viscosity silicone oil) were selected to minimize water evaporation from dough of 37%, 42% and 47% water content subjected to time sweep tests under oscillatory mode. Evolution patterns of the storage modulus, loss modulus and loss factor with time were followed, and the mechanisms responsible for the response patterns were decoupled. Disparate dynamic viscoelastic responses were found for the same dough coated with different oils. Spontaneous de-structuring of dough combined with thixotropic effect contributed to the decrease of dynamic modulus and increase of the loss factor with time. Dynamic vapor sorption tests showed that water evaporation did occur for the dough even coated with non-volatile oils including vaseline. Water evaporation led to an accelerated increase in dynamic modulus with time, while had a very limited impact on loss factor. Oil invasion only played a minor role in the decrease in dynamic modulus. The measured modulus was actually a sum of the positive and negative contributions. Vaseline was observed as an effective coating oil for rheological measurements of dough, especially with high water content.

Characterizing stress-dependent complex and relaxation moduli of dense graded asphalt mixtures

The objective of this paper is to investigate the stress-dependence of the complex and relaxation moduli of dense graded asphalt mixtures. Complex modulus tests at four different confining pressures were conducted. Then, the stress dependence of the long-term equilibrium modulus of asphalt mixture based on Prony series model was modeled by Uzan model. The Maxwell components of the relaxation modulus were determined by a two-step method. Finally, the stress dependence of the relaxation modulus was quantified by relaxation spectrum of the material. The results show that for the selected dense-graded asphalt mixtures, the dynamic modulus increases, and phase angle decreases with the increasing confining pressures at relatively low reduced loading frequency. However, the stress dependence is insignificant in a relatively high-reduced loading frequency. The Uzan model coefficient of the long-term equilibrium modulus of the relaxation modulus can be determined effectively by the proposed deviatoric stress master curves. To obtain reliable and accurate Maxwell component coefficients, it is recommended that: (a) the measured loss moduli rather than the storage moduli should be used to calculate Maxwell component coefficients if collocation method is utilized, and (b) a log-scaled least squared regression minimization objective should be used as the regression objective for the coefficient determination. The relaxation spectrum of asphalt mixture can be modeled by Gaussian function, where the size of the relaxation spectrum increases but the shape and position of the relaxation spectrum remain unchanged when the confining pressure increases.

Effect of short-term and long-term ageing on dynamic modulus of foamed warm mix asphalt

ABSTRACTThis study investigated the effect of short-term and long-term ageing on the dynamic modulus of foamed warm mix asphalt (WMA) produced by water injection and traditional hot mix asphalt (HMA). Four asphalt binders (PG 64-22, PG 64-28, PG 70-22 and PG 76-22) and one aggregate (limestone NMAS 12.5 mm) were used in the preparation of the laboratory-produced asphalt mixtures. The short-term and long-term ageing of the asphalt mixtures were simulated using AASHTO R 30. The experimental test results showed lower dynamic modulus values for foamed WMA than those obtained for traditional HMA for both short-term and long-term oven-aged specimens. By comparing the dynamic modulus values of the short-term and long-term oven-aged specimens, it was observed that some mixtures, such as those prepared using PG 64-22, had a smaller increase in dynamic modulus for foamed WMA mixtures than traditional HMA mixtures, while a comparable increase in dynamic modulus for both foamed WMA and HMA was observed for other mixtures, such as those prepared using PG 70-22 and PG 76-22. This suggests that the binder type plays a significant role in determining the ageing characteristics of foamed WMA and HMA mixtures.

Thermophysical property and pore structure evolution in stressed and non-stressed neutron irradiated IG-110 nuclear graphite

The nuclear graphite, IG-110, was irradiated with and without a compressive load of 5 MPa at ∼400 °C up to 9.3 × 1025 n/m2 (E > 0.1 MeV). Following irradiation physical properties were studied to compare the effect of graphite irradiation on microstructure developed under compression and in stress-free conditions. Properties included: dimensional change, thermal conductivity, dynamic modulus, and CTE. The effect of stress on open internal porosity was determined through nitrogen adsorption. The IG-110 graphite experienced irradiation-induced creep that is differentiated from irradiation-induced swelling. Irradiation under stress resulted in somewhat greater thermal conductivity and coefficient of thermal expansion. While a significant increase in dynamic modulus occurs, no differentiation between materials irradiated with and without compressive stress was observed. Nitrogen adsorption analysis suggests a difference in pore evolution in the 0.3–40 nm range for graphite irradiated with and without stress, but this evolution is seen to be a small contributor to the overall dimensional change.

An experimental study on the mechanical properties of silty soils under repeated freeze–thaw cycles

In this study, the subgrade fill material from the Nagqu Logistics Center Yard (NLCY) along the Qinghai–Tibet Railway was investigated. And the thaw subsidence properties and dynamic properties were thoroughly analysed in laboratory tests.1)From the determined thaw subsidence properties, the following results were obtained: samples with a higher degree of compactness exhibited heave deformation, whereas those with a lower degree of compactness exhibited compressive deformation after repeated freeze–thaw cycles. However, there is a critical compactness level at which the height of the samples does not change after repeated freeze–thaw cycles. The consolidation effect of the load restrains frost heave deformation; however, the amount of thaw subsidence deformation increases. The thaw subsidence ratio first increases, then decreases and becomes steady after the fifth freeze–thaw cycle as the number of freeze–thaw cycles increases. It is recommended that the thaw subsidence properties of silty soils be assessed after 5–6 freeze–thaw cycles.2)From the determined dynamic properties, the following results were obtained: the dynamic stress vs. strain curves clearly show a nonlinear trend. The dynamic modulus greatly decreases, whereas the damping ratio increases with additional freeze–thaw cycles; and changes level off after the sixth freeze–thaw cycle; the dynamic properties after 6–7 freeze–thaw cycles are suggested for use in designing and calculating indexes. Moreover, the dynamic modulus increases and the damping ratio decreases as the confining pressure and compactness increase.

Dynamic Properties to Evaluate Moisture Sensitivity of Asphalt Mixtures

An experimental measurement of dynamic properties, including dynamic modulus and phase angle, of asphalt mixtures with varying saturation levels of moisture has been carried out in the study. The specimens of asphalt mixture were compacted with three different air void contents and two different levels of moisture saturation. The relaxation modulus expressed by Prony series was estimated from the Prony series expression of dynamic modulus. The purpose of this study is to identify the effect of air voids on dynamic properties that affect and control moisture susceptibility of asphalt mixtures and then compare the stress relaxation behavior of asphalt mixtures between dry and moisture conditioning. The results show that dynamic properties are quite sensitive to temperature and loading frequency in dry and different saturation levels of moisture. Moreover, and the smaller the air voids and saturation level, the greater the increase in dynamic modulus and rate of stress relaxation, indicating better resistance to cracking and less moisture susceptibility.

The influence of thermo-mechanical history on structure development of elastomeric and amorphous glass thermoplastic polyurethanes

In this work, the effect of processing and subsequent thermal treatment on the rheological behavior and microstructure aggregation of two different types of thermoplastic polyurethanes (TPUs) are investigated. Elastomeric TPUs, which are segmented block copolymers composed of alternating soft and hard segments, and amorphous glassy TPU, predominantly composed of hard segments, were subjected to heating/cooling cycles after extrusion. All materials show rheological hystereses after the first thermal cycle; in amorphous glassy TPUs, there is an increase in dynamic moduli but the loss tangent remains unchanged, whereas in the elastomeric TPUs, there are both decreases in dynamic moduli and hystereses in the loss tangent. The changes in molecular weight during the thermal cycle were tracked by gel permeation chromatography and shown not to be responsible for the rheological hystereses. For both elastomeric and amorphous glassy TPUs, fourier transform infrared spectroscopy results indicate that an increase in dynamic moduli, especially G′, is associated with a higher degree of hydrogen bonding. These results combined with X-ray data indicate that upon extrusion the elastomeric TPUs form a network in which hydrogen bonding plays an important role. This structure can be disrupted upon subsequent heating and cooling. POLYM. ENG. SCI., 54:1383–1393, 2014. © 2013 Society of Plastics Engineers

Lyotropic Liquid Crystal Formed in Oleyl Polyoxyethylene Solutions by Adding Different Additives: NaDC, Tween 80, Alkyl Esters

Lyotropic liquid crystalline of oleylpolyoxyethylene(20)(AEO20)/oil/water system was investigated at 25°C. The phase behavior, microstructure, and rheological properties of liquid crystalline were investigated by rheological techniques and polarizingoptical microscopy in the presence of various additives including Tween 80, sodium deoxycholate (NaDC), isoamylacetate, butyl acetate, isopropyl myristate. Diagrams show that cubic phase transforms to hexagonal phase when a shorter chain length oil is applied or NaDC or Tween 80 is added to the system.Flow experiments indicate the shear-thinning properties and a plastic behavior. The turning points of flow curves of the system AEO20 and system AEO20/NaDC were found. The dynamic modulus increase with increase in water content however the tendency is weaken by adding NaDC. Frequency dependence of experimental G ′ and G ′ were fitted using the multiple Maxwell model the cubic LLCs described by three relaxation times while hexagonal LLCs described by 5–8 elements. When AEO20 mixes with Tween 80, the hexagonal have a monotonic decrease distribution of relaxation times without valleys.

Effect of polymer matrix/montmorillonite compatibility on morphology and melt rheology of polypropylene nanocomposites

AbstractIn this study, Ca2+‐montmorillonite (Ca2+‐MMT) and organo‐montmorillonite (OMMT) were modified by three compatibilizers with different degrees of polarity [poly(ethylene glycol) (PEG), alkyl‐PEG, and polypropylene (PP)‐g‐PEG]. PP/MMT nanocomposites were prepared by melt blending and characterized using X‐ray diffraction and transmission electron microscopy. The results showed the degree of dispersion of OMMT in the PP/PP‐g‐PEG/OMMT (PMOM) nanocomposite was considerably higher than those in the PP/PEG/OMMT and PP/alkyl‐PEG/OMMT nanocomposites, which indicated that the dispersion was relative to the compatibility between modified OMMT and PP matrix. Linear viscoelasticity of PP/MMT nanocomposites in melt states was investigated by small amplitude dynamic rheology measurements. With the addition of the modified MMT, the shear viscosities and storage modulus of all the PP/MMT nanocomposites decreased. It can be attributed to the plasticization effect of PEG segments in the three modifiers. This rheological behavior was different from most surfactant modified MMT nanocomposites which typically showed an increase in dynamic modulus and viscosity relative to the polymer matrix. The unusual rheological observations were explained in terms of the compatibility between the polymer matrix and MMT. In addition, the mechanical properties of PP/MMT nanocomposites were improved. A simultaneous increase in the tensile strength and toughness was observed in PP/PMOM nanocomposites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Silks cope with stress by tuning their mechanical properties under load

We compare the nonlinear mechanical properties of silks under load with the quasi-static and isothermal dynamic mechanical properties of nylon as well as human hair. For silk and nylon, the dynamic storage modulus increases with increasing static load, while the quasi-static modulus decreases considerably through yield. However, the modulus of hair decreases irreversibly for both loading conditions. For silk, the increase in storage modulus is only partially reversible after high-loading and is accompanied by a non-recoverable strain. For nylon, the dynamic modulus increase is largely reversible after increased static loading up to a second high stress yield point, where modulus then decreases. Taken together, our data suggest that the dynamic modulus increases with increasing order in the silk and nylon structures under static load, whereas the morphology of hair is gradually degraded under load.

Study of Temperature and UV Wavelength Range Effects on Degradation of Photo-Irradiated Polyethylene Films Using DMA

Plastic bags mostly made of polyethylene (PE) cause pollution as solid waste due to their non-degradability nature. Initiation of a degradative process by enhanced photo-oxidation is a possible method for an accelerated degradation. This paper presents temperature treatment effects on PE films where photodegradation was initiated using ultraviolet (UV) irradiation in the ranges of 200–300 nm and 300–400 nm for 2 hr. Effects of temperature of 40°C and 55°C on non-UV-irradiated and UV-irradiated PE films processed by conventional methods were investigated and evaluated after 50 hr, 150 hr, and 350 hr of temperature exposure. The effects of UV wavelength range irradiation on the degradation were deduced. Measuring the dynamic moduli using a dynamic mechanical analyzer monitored the degradation. The decrease in average storage modulus was 62% with treatment at 55°C, higher than the 16% drop at 40°C for unirradiated samples after 350-hr exposure. Cross-linking in UV-exposed samples, characterized by an increase in dynamic modulus (stiffening), was observed followed by a reduction of storage modulus. Temperature treatment at 55°C together with 300–400-nm UV range irradiation resulted in the largest increase, i.e., 22% after 150 hr, followed by the largest reduction of storage modulus, i.e., 74.6% for a cumulative 350-hr exposure.

THE IMPACT OF MALTODEXTRIN‐BASED FAT MIMETICS ON RHEOLOGICAL AND TEXTURAL CHARACTERISTICS OF EDIBLE VEGETABLE FAT

ABSTRACTThe functionality of two types of maltodextrins as fat mimetics was studied. Vegetable fat was replaced at levels of 16.7, 33.3 and 50% by different aqueous gels of maltodextrin: Pmdx (potato maltodextrin gel) and WMmdx (waxy maize maltodextrin gel). Vegetable fat without the addition of fat mimetics was used as a control sample. Steady shear viscosity, hysteresis and dynamic moduli were measured at semi‐solid conditions (30C), whereas textural measurements were determined in the solid state (20C). Up to 50% fat replacement without much change in firmness could be achieved with WMmdx. However, blends containing Pmdx expressed significant decrease in firmness. Fat replacement caused a strong increase in dynamic moduli, especially with WMmdx. Steady shear viscosity was increased at replacement levels ≥33.3% and to a larger extent with WMmdx. In contrast to Pmdx, incorporation of WMmdx did not affect the steady shear hysteresis of the blends.PRACTICAL APPLICATIONSEdible vegetable fat serves as an ingredient in many foods. In confectionary fat fillings, the vegetable fat is included to control texture and spreadability. Typical confectionary fat filling contains 30–35% fat. Because confectionary products are high in calories, development of reduced fat product with desirable taste and texture is a very challenging task.In this paper the capability of hydrated maltodextrin gel particles to replace certain amounts of fat in different foods was investigated. Therefore, rheological and textural properties of blends consisted of vegetable fat and different type, content and concentration of aqueous maltodextrin gel were determined. Hence, a step toward food products containing water stabilized by small amount of gelling maltodextrin with rheological and textural properties of conventional food product was made.