Reduction In Elastic Modulus Research Articles

Effect of Pile Driving on Ground Vibration in Clay Soil: Numerical and Experimental Study

In this study, peak particle velocity (PPV) values for driving three piles with diameters of 40 cm, 50 cm, and 70 cm in a clayey soil through the impact piling method are investigated by an experimental study and a numerical simulation. An experimental study is carried out on a scale of 1:20 of the operation. Numerical simulation is performed by using an axisymmetric model in PLAXIS 2D finite element software. Properties of the soil and the piles used in the experimental study are obtained from geotechnical tests and employed in the numerical simulation. The model has been verified by comparing the acquired PPV values with those measured in the experimental study. The results show a good agreement between the computed values and the experimental data. Moreover, measured peak particle velocities in the experimental study indicate that an increase in the diameter of the pile can increase the level of ground vibration. Some sensitivity analyses have been performed by numerical modeling to determine the effect of soil and pile properties on the changes of PPV. Also, increase in friction angle of the soil and pile diameter and reduction in elastic modulus of soil will increase the level of ground vibration. The results indicate that the amount of PPV at a distance of 100 cm is about 10.33% of the amount of PPV at a distance of 25 cm from the impact site to the pile with a diameter of 3.5 cm. In addition, this amount of reduction for pile with a diameter of 2.5 and 2 cm is equal to 8.31% and 12.77%, respectively.

Shear performance of fibers-reinforced lightweight aggregate concrete produced with industrial waste ceramsite-Lytag after freeze-thaw action

Freeze-thaw (F-T) is an environmental hazard to concrete, severely reducing the mechanical properties and durability of concrete structures. The quantitative calculation of the shear performance of lightweight aggregate concrete (LWAC) after F-T action remains obscure. This study performed comprehensive research on basalt (BF)- and polyacrylonitrile fiber (PANF)-reinforced LWACs after F-T action, which can provide the basis for durability design. Compared with plain LWAC, specimens with fiber reinforcement showed a lower reduction in the relative dynamic elastic modulus (RDEM) and shear strength, and the shear strength and length-diameter rate of the fibers were the main impact factors. From the tests, 1.0% BF and 1.5% PANF are suggested as optimal for F-T resistance enhancement. Corresponding models are proposed to predict the changing tendencies of the shear strength, peak shear strain and shear modulus of LWACs after F-T cycles, considering the impact fibers and the environmental parameters. A statistically stochastic model was applied to predict the shear stress-strain curves after F-T action, and the calculation results match the test results well. The evaluation criteria in the standard are unsafe for LWAC F-T durability design. The F-T service life evaluation based on strength degradation could be advantageous in terms of the sustainable development of LWACs in an F-T environment.

Evaluating Moisture Damage Using Impact Resonance Test

Abstract Moisture damage in asphalt mixtures has been a major cause for premature failure of asphalt pavements for decades. Although a lot of research has been done and many test methods have been developed to evaluate moisture damage in asphalt mixtures, not much research has been done on the use of nondestructive testing techniques to evaluate moisture damage in asphalt mixtures. The impact resonance (IR) test is a nondestructive test that is used to determine material properties like dynamic elastic modulus. The IR test on asphalt mixtures is done on a thin-disk specimen (150-mm diameter and 25-mm thickness). In this study, the IR test was used to assess moisture damage in asphalt mixtures by determining the resonant frequency of asphalt mixture samples in the unconditioned and moisture conditioned state. The relative reduction (ER) in dynamic elastic modulus was calculated as the ratio of the resonant frequency of conditioned and unconditioned specimens from the IR test, which was used to evaluate moisture damage. Moisture sensitivity of the asphalt mixtures was also determined by the tensile strength ratio (TSR) test. Two different moisture conditioning procedures were used for both the IR test and TSR test—modified AASHTO T 283 (Standard Method of Test for Resistance of Compacted Asphalt Mixtures to Moisture-Induced Damage) and Moisture Induced Stress Tester (MIST) conditioning. Six different mixtures from three different aggregate sources were used in this study. A good correlation was observed between TSR values from the TSR test using both conditioning procedures and the ER values from the IR test using both conditioning procedures for the asphalt mixtures used in this study. This study shows that the IR test can be used to evaluate moisture damage in asphalt mixtures. This study also explored the effects of various parameters such as support condition, impact source, and impact location on the resonant frequency from the IR test.

Strength and thermal shock resistance of fiber‐bonded Si‐Al‐C‐O and Si‐Ti‐C‐O ceramics

AbstractSilicon carbide‐based fiber‐bonded ceramics, obtained from hot pressing of woven silicon carbide fibers, are a cost‐effective alternative to ceramic‐matrix composites due to their ease of fabrication, involving few processing steps, and competitive thermomechanical properties. In this work, we studied the high‐temperature strength and thermal shock resistance of Si‐Al‐C‐O and Si‐Ti‐C‐O fiber‐bonded SiC ceramics obtained from hot pressing of two types of ceramic fibers, by mechanical testing in four‐point bending. The bending strength of Si‐Al‐C‐O‐based fiber‐bonded ceramics at room temperature is ∼250–260 MPa and remains constant with temperature, while the bending strength of Si‐Ti‐C‐O increases slightly from the initial 220 to ∼250 MPa for the highest temperature. Both materials retain up to 90% of their room temperature strength after thermal shocks of 1400°C and show no reduction in elastic moduli. After thermal shock, failure mode is the same as in the case of as‐received materials.

Effect of organic matrix alteration on strain rate dependent mechanical behaviour of cortical bone

The organic matrix phase of bone plays important role in its mechanical performance, especially in the post-yield regime. Also, the organic phase influences loading rate-dependent behaviour of bone which is relevant during the high-speed loading events. Many diseases, as well as aging, affect the matrix phase of bone which causes compromised mechanical properties. Improved understanding of alterations in the organic matrix phase on mechanical response of bone will be helpful in the mitigation of fractures associated with inferior matrix quality. In the present work, effect of alteration in organic matrix of cortical bone on its strain-rate dependent behaviour was investigated. To produce different amounts of collagen denaturation, bovine cortical bones were heated at the temperature of 180 °C and 240 °C. Further, compression testing was performed at quasi-static strain rates of 10−4 s−1 to 10−2 s−1 using a conventional testing machine whereas a modified Split Hopkinson Pressure Bar (SHPB) was used for high strain rate (∼103) testing. Thermal treatment-induced changes in the mineral and organic phases of bone were assessed using X-ray diffraction (XRD) and Fourier-transform infrared-attenuated total reflection (FTIR-ATR) techniques respectively. Compression test results show that thermal treatment of bone up to 180 °C did not affect mechanical properties significantly whereas treating at 240 °C significantly reduced elastic modulus, failure stress and failure strain. Also, thermal denaturation of collagen reduced the strain rate sensitivity of cortical bone at high strain rates. Similar to the compression test observations, nanoindentation results show a significant reduction in elastic modulus and hardness of denatured samples. Further, FTIR results revealed that with the heat treatment of bone, collagen structure undergoes conformational changes at the molecular level. The initial helix structure breakdowns into unordered/random coil structures which subsequently reduced the mechanical competence of bone. The present study provides insight into the effect of organic matrix modification on mechanical behaviour of cortical bone which could be helpful in understanding bone disorders associated with organic matrix phase and development of therapeutic interventions.

Elastic modulus reduction method for stable bearing capacity analysis of dumbbell-shaped CFST arches

The elastic modulus adjustment procedures (EMAPs) can achieve much higher efficiency than incremental nonlinear finite element method (INFEM), however it could not take into account the stability effect on structures. In this paper, the elastic modulus reduction method (EMRM) was presented to estimate the stable bearing capacity of dumbbell-shaped concrete filled steel tube (CFST) arch. Firstly, the homogeneous generalized yield function (HGYF) was developed for dumbbell-shaped CFST members under combined action of axial force and bending moment by means of the fiber model technique, which was employed to determine the stable bearing capacity of these members. Secondly, the HGYF was adopted to define the element bearing ratio so that the EMRM was proposed for evaluating the stable bearing capacity of the dumbbell-shaped CFST arch by strategically reducing the elastic modulus of the highly stressed elements. Finally, results from the INFEM and test data of 3 dumbbell-shaped CFST arches and 30 dumbbell-shaped CFST members were adopted as examples to validate the proposed EMRM and the HGYF, which shows that the stability has a significant influence on the CFST arches and the proposed EMRM achieves higher accuracy and efficiency than the INFEM.

Characteristics of Polymeric Fiber Reinforced Cementitious Composite (PFRCC) under Uniaxial Compression

This study aimed to evaluate the compressive characteristics and toughness of polymeric fiber reinforced cementitious composites (PFRCC). In the experimental program, polyvinyl alcohol (PVA) fibers were used to prepare two groups of PFRCC cylinders with different fiber contents. The main factor considered in this study was the reinforcing index. Several parameters were investigated, i.e. compressive strength, elastic modulus, strain at peak stress, Poisson’s ratio and toughness of PFRCC. The results revealed that there was a reduction in both compressive strength and elastic modulus as the reinforcing index increased, while a significant increase in the strain at peak stress was observed. Moreover, a comparison was made between different methods of toughness estimation and it was found that 7.9 was the best reinforcing index for PVA fibers based on the energy absorption performance and ductility of PFRCC. Furthermore, an empirical model is proposed in this paper to predict the PFRCC-PVA compressive stress-strain curve. The proposed model features new formulas to calculate a number of important coefficients to plot the curve based on the reinforcing index value. Besides that, the model had good convergence compared to the experimental results, with perfect values for both variance and correlation coefficient.

Impact of Sorption-Induced Strain and Effective Stress on the Evolution of Coal Permeability under Different Boundary Conditions

Coalbed methane (CBM) is a relatively common unconventional natural gas, which has great exploitation value. Coal permeability is an important parameter that affects the production and production efficiency of CBM, which is mainly controlled by the sorption expansion/contraction strain and effective stress. To study the seepage characteristics of coal in the process of CBM production, we have used CH4 and CO2 as test gases separately and conducted comparative seepage tests of different gases under constant pore pressure conditions. At the same time, the elastic modulus reduction coefficient Rm has been introduced to characterize the sorption strain of coal, following which the permeability models suitable for different boundary conditions were derived according to the stress–strain relationship. Under the two gases, the new model could not only better reflect the law of coal sorption strain but also better reflect the relationship among effective stress, pore pressure, and coal permeability. Under the conditions of constant pore pressure, coal permeability was mainly controlled by effective stress; with the increase of effective stress, permeability decreased sharply initially and then gradually. Under the conditions of uniaxial strain and constant external stress, with an increase of pore pressure and Rm, the matrix sorption expansion strain increased, resulting in a narrowing of the seepage channel, and Rm indirectly inhibited permeability. At this point, coal permeability was mainly controlled by sorption expansion/contraction strain and effective stress. In addition, compared with other permeability models, the new permeability model possesses higher applicability both in theoretical mechanism and in data matching. The general change trend concerning coal permeability, determined by rebound pressure prb, was consistent with the test results, which further verified the applicability of the model. It is believed that the results of this study could provide a basis for subsequent research on the stress–strain–permeability relationship and for the study of efficient development of CBM.

Thermal rejuvenation of an aged Au-based metallic glass by fast scanning calorimetry

A metallic glass (MG) annealed above its glass-transition temperature T g , and cooled, may show an enthalpy increase Δ H , and other property changes. The extent of this thermal rejuvenation depends on the state of the MG (represented by effective cooling rate Φ i ) and the post-anneal cooling rate Φ c . Previous studies examined effects of (Φ c /Φ i ) up to 10 2 . With a Au-based MG aged for up to 10 years at room temperature, and using fast calorimetry to anneal and then cool at up to 5000 K s −1 , we extend (Φ c /Φ i ) to 10 7 . The rejuvenation is limited by anneal temperature or by Φ c , when, for all MGs, Δ H / T g shows a universal approximate scaling with log(Φ c /Φ i ). We detect decoupling of vitrification from α relaxation, and highlight limitations in the use of fictive temperature to characterize glassy states. Rejuvenation of the Au-based MG decreases its elastic modulus and hardness, extending trends reported for other MGs. • Fast-scanning calorimetry permits extended thermal rejuvenation of a metallic glass. • The cooling-rate ratio giving rejuvenation, 10 2 in earlier work, is extended to 10 7 . • Rejuvenation is in two regimes, limited by anneal temperature or cooling rate. • Thermal rejuvenation gives extended decoupling of vitrification from α relaxation. • Greater cooling-rate ratio extends reductions in elastic modulus and hardness.

The elastic modulus reduction method for upper bound limit analysis of pressure vessels incorporating material strain hardening effect

Pressure vessel is a kind of special equipment which is involved in various industries. Once it is damaged, it will cause great loss to people’s life and property. The traditional elastic modulus reduction method for upper bound limit analysis of pressure vessels adopts the elastic-perfectly plastic material model. This method will result in waste of materials without considering the material strain hardening effect. So the material strain hardening effect is introduced into upper bound limit analysis. Firstly, the equivalent yield strength considering material strain hardening effect is established. Then, the formula of limit load multiplier which is expressed by the equivalent yield strength is derived based on the upper bound theorem. Combined with the strategy for elastic modulus adjustment, the elastic modulus reduction method for upper bound limit analysis of pressure vessels incorporating material strain hardening effect is constructed. The limitation of the elastic-perfectly plastic model for the upper bound analysis method is eliminated by the method proposed in this paper. The result calculated by this method is closer to the true limit load of pressure vessels.

Techniques for Progressive Failure Simulation of Hard Brittle Surrounding Rockmass: Taking the URL Test Tunnel as an Example

Accurate simulation of the failure process of hard brittle surrounding rockmass is very important for the analysis and control of the structural stability in deep underground engineering. In order to simulate the progressive failure process of the hard brittle surrounding rockmass, a continuous discontinuous deformation analysis method that couples the finite element and discrete element is adopted. Taking the URL test tunnel in Canada as an engineering case, the constitutive model of the contact considering the effects of cohesion weakening and friction strengthening is applied, and the 2D approximation to 3D excavation by applying elastic modulus reduction technology is adopted to simulate the range and depth of crack growth of the surrounding rockmass. Then, the comparison between simulated results and on-site monitoring results is performed, which shows good consistency. At the same time, the key factors in the numerical simulation of progressive failure in hard brittle rockmass are identified, including the number of elements, excavation effects, and constitutive models. The results show that the constitutive model determines the basic form of crack propagation, but in order to accurately simulate the progressive propagation of cracks, the number of elements must be sufficient enough and the effects of 3D excavation must be considered. The analysis accurately simulates the progressive failure characteristics of hard brittle surrounding rockmass under high stress, achieving the purpose of reasonably grasping the degree of damage to the surrounding rockmass, and provides technical reference and support on how to accurately simulate the failure of hard brittle surrounding rockmass using the finite discrete element method.

Dependency of hydration and growth conditions on the mechanical properties of oral biofilms

Within the oral cavity, dental biofilms experience dynamic environments, in part due to changes in dietary content, frequency of intake and health conditions. This can impact bacterial diversity and morpho-mechanical properties. While phenotypic properties of oral biofilms are closely related to their composition, these can readily change according to dynamic variations in the growth environment and nutrient availability. Understanding the interlink between phenotypic properties, variable growth conditions, and community characterization is an essential requirement to develop structure–property relationships in oral-biofilms. In this study, the impact of two distinct growth media types with increasing richness on the properties of oral biofilms was assessed through a new combination of in-vitro time-lapse biophysical methods with microbiological assays. Oral biofilms grown in the enriched media composition presented a decrease in their pH, an increase in soluble EPS production, and a severe reduction in bacterial diversity. Additionally, enriched media conditions presented an increase in biofilm volumetric changes (upon hydration) as well as a reduction in elastic modulus upon indentation. With hydration time considered a major factor contributing to changes in biofilm mechanical properties, we have shown that it is less associated than media richness. Future investigations can now use this time-lapse approach, with a clearer focus on the extracellular matrix of oral biofilms dictating their morpho-mechanical properties.

Effective seismic wave velocities and attenuation in partially molten rocks

Significant reduction in mechanical properties, i.e., elastic moduli and seismic wave velocities, as well as enhanced inelastic attenuation is often associated with areas of partially molten rocks. In this paper we suggest a new mechanism responsible for significant reduction of wave velocity and enhanced attenuation. The suggested mechanism considers solid-melt phase transition at thermodynamic equilibrium. Any pressure change, that takes the system out of thermodynamic equilibrium, causes solidification or melting which modifies the heat balance according to the Clausius-Clapeyron equation. The latent heat (sink or source) is transferred away or towards the interface by conductive-advective mechanism, heating or cooling the entire rock mass, and leading to energy loss and dissipation of the mechanical energy and to seismic wave attenuation. We use simplified geometry and derive analytical solutions for wave velocity reduction and attenuation associated with a moving solid-melt interface (Stefan problem). We demonstrate that the latent heat generation due to wave-induced pressure oscillations around thermodynamic equilibrium is an efficient mechanism for energy dissipation and leads to significant reduction in mechanical properties (seismic velocities and attenuation). The highest attenuation occurs when the period of oscillation is close to the heat transfer time-scale associated with the size of melt inclusions. The predicted values are approximately in agreement with large scale seismological observations, showing that seismic waves are mostly attenuated within the shallow parts of Earth's crust and mantle, and are associated with possible presence of melt.

Experimental studies on mechanical and dielectric behavior of Glycerol filled Silicone rubber composites

In this study, Silicone rubber composites are prepared with Glycerol filler in three different volume fractions. The samples developed are subjected to mechanical and dielectric testing. The tensile strength increases first and later decreases with Glycerol loading whereas compression strength decreases with Glycerol loading. Modulus of elasticity in tension and compression both decreases with the increase of Glycerol loading. Dielectric permittivity, dissipation factor and conductivity are increases with the increase of Glycerol loading. The Silicone Rubber (SR) composite with 15% volume of Glycerol filler shown a maximum reduction in modulus of elasticity of 29% (in tension) and 16.8% (in compression), and maximum improvement in the dielectric permittivity of 112% compared to neat silicone rubber. The reduction in modulus of elasticity with an increase in dielectric permittivity with an increase in Glycerol loading suggests that this material is a potential candidate for materials to be used in soft dielectric sensors and actuator applications.

Damage Modeling of Solid Oxide Fuel Cells Accounting for Redox Effects

This paper applies a multiscale mechanistic damage model developed for porous brittle ceramics and implemented in finite element analysis (FEA) packages [1] to study progressive damage in solid oxide fuel cells (SOFC) subjected to thermomechanical loading under operating and shutdown states. The damage model captures the micromechanics of stiffness reduction due to material porosity change and microcracking and integrates the as-obtained stiffness reduction law into a continuum damage mechanics (CDM) formulation for the evolution of microcracks up to fracture. An Eshelby-Mori-Tanaka approach (EMTA) [2-3] is first used to model the ceramic containing pores and aligned microcracks regarded as inclusions with negligible stiffness. The stiffness of the actual porous ceramic is obtained from the EMTA solution averaged over all possible microcrack orientations using an orientation averaging method. The evolution of microcracking damage is described by a CDM formulation derived from our previous model [4]. Apart from the operating and shutdown states, additional damage that may occur due to reduction and re-oxidation (redox cycling) of Ni/YSZ anodes is also studied. The reduction of NiO into Ni leads to changes in volume and porosity of the anode layer that consequently change its physical and thermomechanical properties. The volume change or volumetric “swelling” during redox cycling may affect the structural integrity of the anode and may cause fracture of the electrolyte under high tensile stresses leading to operational failure for SOFCs. In the constitutive relations, volumetric swelling is treated in a similar way to thermal expansion using the models developed in Refs [5-6] for fusion energy ceramic materials. However, while thermal expansion vanishes if temperature change tends to zero, swelling is irreversible and significantly contributes to degrade SOFC stacks during redox cycling.This damage model was implemented in the commercial FEA software ABAQUS© and ANSYS© via user subroutines. First, it has been validated through predictions of strength and stress-strain response for the typical SOFC ceramic materials. Figs 1(a) and 1(b) show the predicted stress-strain responses as a function of temperature for dense NiO/YSZ and Ni/YSZ, respectively. These figures also illustrate the predicted responses at 750°C with prescribed initial values of porosity. The damage model predicts significant reductions in strength and elastic modulus with higher initial porosity and higher temperatures, and the predicted trends are in good agreement with the experimental findings [7-8].Next, the damage model was applied to predict the potential for degradation in a generic planar SOFC stack with large active area cells modeled in ANSYS. Stack models with single and multi-cells were simulated in both co-flow and counter-flow configurations. The thermomechanical loads representing the operating and shutdown conditions were simulated. The realistic thermal gradients that occur in an operating stack were imposed in the models by solving the electrochemistry under various operating conditions using the in-house SOFC multiphysics code (SOFC MP-3D) [9-10]. In addition to the operating and shutdown conditions, a constant temperature redox cycle was also simulated to capture overall cell electrode damage due to volumetric swelling of the Ni/YSZ anode in the anode supported cells. The results from single cell stack models showed little damage at operating and shutdown conditions which could be attributed to enough out-of-plane support for the PEN assembly. The results from the multicell stacks (Fig. 2) showed higher damage in counter-flow configuration. Within the stack, the top cells experienced the highest damage and the middle cells experienced the lowest. Overall, no significant damage that may lead to total failure of the cells was observed in the multicell stack models with the operating conditions considered in this study.

Fault nucleation of tight sandstone by investigation of mechanical, acoustic, and hydraulic responses

To investigate the effect of water on the fracture mechanism and associated acoustic emission (AE) characteristics, triaxial compression experiments were performed on dry and water-saturated tight sandstone specimens sampled from the Sichuan Basin, China. The saturated specimen was precisely controlled by different drainage conditions at the two ends. The detailed spatiotemporal distribution of AE activities and the P-wave velocities were used to examine the initiation and propagation of microcracks, as well as fault nucleation process. There are significant differences in mechanical behavior, P-wave velocity, AE activities, and fault nucleation between the dry and saturated specimens. The mechanical behavior of the saturated specimen is characterized by water weakening, with 10% and 26% reductions in peak strength and elastic modulus, respectively, in comparison with those for the dry specimen. Water enhances inelastic axial deformation and strain softening. The evolution of P-wave velocity is associated with microcracking-induced dilatancy. The decrease in P-wave velocity is suppressed in the saturated specimen, especially at the drained end. Significant attenuation of AE energy is observed in the saturated specimen, resulting into a lower event rate compared with that for the dry specimen. It is shown that the saturated specimen has an extended fault nucleation duration and lower rupture velocity. The precursory phase of dynamic failure can be clearly mapped based on strain softening, accelerating AE event rate, and decreasing b-value, as well as decreasing pore pressure (in undrained condition) or increasing injection rate (in drained condition).

Effects of elevated temperature on epoxy bonded CFRP-to-steel joints in Mode I fracture

This study was undertaken to further knowledge in relation to the effect of elevated temperature on performance of adhesively bonded CFRP-to-steel joints subjected to peel loading. Two epoxy adhesives, Adhesive A and Adhesive B, were assessed with regard to their aging behaviour at two elevated temperatures and for two exposure periods. Adhesive coupon specimens and a modified Mode I fracture test arrangement for use with dissimilar materials was used in the test programme. In total, thirty CFRP-to-steel bonded specimens and thirty adhesive coupons were evaluated. Exposure of coupons of both adhesives to elevated temperatures resulted in a considerable reduction in elastic moduli. Maximum strain of adhesive coupons fabricated with Adhesive A and B experienced an overall average increase of 30% and 39%, respectively, after exposure to elevated temperatures. The maximum failure load of fracture specimens manufactured with Adhesive A and B reduced up to 9% and 12%, respectively, after exposure to elevated temperature. Despite possessing higher strain energy release rate and higher load carrying capacity of fracture specimens manufactured with Adhesive B compared to Adhesive A, the bonding performance of Adhesive B is more affected by elevated temperature and this needs to be noted when using Adhesive B in areas with hot climates.

Selective laser melting of Fe–Al alloys with simultaneous gradients in composition and microstructure

Selective laser melting technique was employed to fabricate a step-wise compositionally graded Fe–Al alloy coupon using the in-situ alloying of blended powders. Microstructural characterization of the fabricated coupons shows a columnar to equiaxed grain structure transition with increasing Al content along the building direction, along which the laser scan speed is increased. In the low Al content regions, the absence of constitutional undercooling (CUC) allows columnar grain growth against the macroscopic thermal gradients, whereas dominance of CUC in high Al regions leads to fully equiaxed and refined microstructures. Nanoindentation studies show a linear increase in hardness and reduction in elastic modulus for Al content up to ~20 at.%; no significant anisotropy in these properties could be seen.

Mitigating the impact of the static and cyclic loading on loose coastal saturated sands utilizing a waterproof and super-fast curing polymer

According to the dramatic increase in construction near loose coastal saturated soils, stabilizing these soils due to saturation conditions has always faced challenges. The main purpose of this investigation is to assess the static and dynamic performance of saturated sand stabilized with polyvinyl acetate powder - as a newly introduced source of polymers which besides helping vegetation grow, owing to its numerous features such as anti-acid, and most importantly waterproof properties and super-fast curing, is superior to its rival, traditional liquid polyvinyl acetate. This paper Analyzes the dynamic properties of soil stabilized based on the results of tensile test crack pattern, microscopic observations of matrix texture, and elasticity modulus of hysteresis loops. Lack of significant change in the strength of samples in saturated and dry conditions indicated waterproofness of polyvinyl acetate powder and revealed a significant rise in the compressive and tensile strength of saturated specimens up to 6% of the polymer. Also, an exponential correlation of unconfined compressive strength (UCS) with direct tensile strength (DTS) was found by data fitting. Also, evaporation tests showed a 7% reduction in evaporation rate with 6% polymer, which can confirm this polymer as a suitable option for improving vegetation. Shear modulus and damping ratio also increased and decreased up to 2% of the polymer, respectively, and by increasing the polymer beyond the 2%, dynamic properties were changed due to the zigzag crack pattern and consequently more ductility of the soil matrix, reduction of elasticity modulus, and increasing the thickness of polymer membranes between soil particles. Ultimately, the research results confirmed polyvinyl acetate powder's efficiency, especially with these tiny amounts, as a potential method for controlling saturated grounds.

Multivariate analysis of effects of microencapsulated phase change materials on mechanical behaviors in light-weight aggregate concrete

In this study, a multivariate analysis of light-weight aggregate concrete embedded by microencapsulated phase change material (MPCM-LWAC) was performed by assessing the effect of water-cement ratio (0.5,0.55, and 0.6), MPCM content (0%, 2.5%, 5.0%, 7.5%, and 10%), curing time (3 d, 7 d, 14 d, and 28 d), as well as MPCM state (liquid and solid state) on the compressive strength, splitting tensile strength, and elasticity modulus. In order to understand the mechanism of the strength change, porosity, SEM images and adiabatic temperature rise of MPCM-LWAC were measured. Results shown that porosity of MPCM-LWAC is linearly proportional to the water-cement ratio, while with the increase of MPCM content, the growth rate of porosity of MPCM-LWAC with the larger water-cement ratio grow more slowly than that of MPCM-LWAC with the lower water-cement ratio, which is contrary to the changes of compressive and splitting tensile strength of MPCM-LWAC. The growth rate of compressive and splitting tensile strength at each age reduces with increasing amount of MPCM, which attributes to the delay in the hardening time of the cement. When MPCM-LWAC samples are subjected to temperature greater than the melting temperature of MPCM, the mechanical behaviors of MPCM-LWAC slightly reduced. The addition of MPCM to LWAC resulted in a linear reduction in elastic modulus. In addition, SEM images showed that no phase change material leakage was found in the damaged specimens.