Compressive Recovery Research Articles

Utilization of sandstone waste in cement mortar for sustainable production of building materials through biomineralization

Sandstone waste generated during stone cutting and processing is a major environmental problem. In this study, different ratios of sandstone powder was utilized as a cement replacement and the mortar specimens were treated with bacteria to enhance the durability properties. With replacement ratio of sandstone powder (10% to 40%), strength loss was observed in all the sandstone-modified mortars. Due to bacterial treatment in CSB10, CSB20, CSB30 and CSB40 specimens, compressive strength was increased by 11%, 12.8%, 17% and 6%, respectively compared to their respective controls. Water absorption rate was significantly reduced and lower sorptivity coefficient was recorded in bacterial treated specimens. In bacterial treated CSB30 specimens, compressive strength recovery (17%) and reduced sorptivity coefficient (0.002) were observed. Present study results suggest that microbial treatment of sandstone modified mortar with a 30% replacement ratio of cement is a possible solution for utilizing stone waste in the construction industry.

Recovery Behavior of the Macro-Cracks in Elevated Temperature-Damaged Concrete after Post-Fire Curing.

Studying the recovery of fire-damaged concrete is of huge economic and environmental significance. The recovery of thermal-induced cracks of fire-damaged concrete leads to the recovery of strength after post-fire curing. To identify the crack recovery behavior of fire-damaged concrete after post-fire curing and its relationship with the recovery of strength, in this study, concrete samples exposed to 400, 600, and 800 °C were treated with the post-fire curing process. The compressive strength recovery was investigated, as well as the crack recovery in terms of the crack length. Moreover, the recovery of the cracks was studied and divided into the categories of mortar cracks and mortar-aggregate interfacial cracks. The results indicate that, after being exposed to high temperatures, the interfacial crack was the main type of crack, and it could clearly be recovered by post-fire curing. The recovery of compressive strength mainly resulted from the recovery of interfacial cracks. The findings of this study can provide practical guidance for the application of post-fire curing to the recovery of fire-damaged concrete structures.

A New Compression and Storage Method for High-Resolution SSP Data Based-on Dictionary Learning

The sound speed profile data of seawater provide an important basis for carrying out underwater acoustic modeling and analysis, sonar performance evaluation, and underwater acoustic assistant decision-making. The data volume of the high-resolution sound speed profile is vast, and the demand for data storage space is high, which severely limits the analysis and application of the high-resolution sound speed profile data in the field of marine acoustics. This paper uses the dictionary learning method to achieve sparse coding of the high-resolution sound speed profile and uses a compressed sparse row method to compress and store the sparse characteristics of the data matrix. The influence of related parameters on the compression rate and recovery data error is analyzed and discussed, as are different scenarios and the difference in compression processing methods. Through comparative experiments, the average error of the sound speed profile data compressed is less than 0.5 m/s, the maximum error is less than 3 m/s, and the data volume is about 10% to 15% of the original data volume. This method significantly reduces the storage capacity of high-resolution sound speed profile data and ensures the accuracy of the data, providing technical support for efficient and convenient access to high-resolution sound speed profiles.

Effects of filament fineness and disc type of drawn textured polyester yarns on carpet resilience and appearance retention performance

The deformation on the carpet texture is generally caused by foot traffic, furniture loading and soiling. The resistance of the carpet to texture distortion depends on the pile yarn characteristic and morphology. In this study, the resilience and appearance retention of carpet samples produced with drawn textured polyester pile yarns which are widely used in the carpet industry, were investigated. In this context, 6 pile yarns were produced with 3 different filament finenesses (3.13, 2.08 and 1.56 dpf) and 2 different disc types (polyurethane and ceramic). The carpet specimens were applied to compression/recovery, dynamic loading, hexapod appearance retention and soiling tests. According to the results, the carpet sample with 2.08 dpf filament fineness and produced by polyurethane disc type showed less thickness loss and better compression recovery results. Hexapod test results showed that the carpet samples with the finest filament had the lowest appearance retention levels. For soiling performance, it was observed that carpet samples with coarser filaments had slightly less staining and disc type had a no significance effect.

Enhanced properties of starch based foams with modified starch/polyester blend as masterbatch

AbstractStarch/PBAT blends were reactively extruded as masterbatch with the addition of tartaric acid (TA) and epoxide chain extender ADR4468 (ADR). The effects of tartaric acid and chain extender on the mechanical properties and structure of starch/PBAT blends were evaluated. The tensile strength of starch/PBAT blends with TA and TA/ADR increased by 31.4% and 85.6%, respectively. Further, starch, plasticizer, and blowing agent were melt extruded with this blend masterbatch, and the effects of masterbatch on the foamability, morphology, and properties of starch foams were investigated. When the masterbatch content was 10 phr, the obtained foam had the lowest apparent density (445.1 kg m−3), and the compressive strength, recovery, and water resistance of the foam were also improved significantly.

Stability and degradation of four agricultural wastes liquefied polyols based polyurethane foams

AbstractBio‐based polyurethane foam has attracted growing attention worldwide due to its advantages of environmental friendliness and wide range of raw materials. However, the stability and degradation ability of the newly prepared foams need to be further explored for their practical application. Four agricultural wastes (XS: oilseed rape straw/OS, rice straw/RS, wheat straw/WS, and corn stover/CS) liquefied polyols were used to replace petroleum polyol for preparing polyurethane foams (XSPU). These bio‐based foams were investigated by Thermogravimetric analysis (TGA), Fourier transformed infrared spectroscopy (FTIR), two dimensional correlate infrared spectroscopy (2D‐COS IR), water immersion test, soil burying test, and compression test to confirm their stability and degradation properties for applications. XSPU foams displayed excellent thermal stability with heating till to 240°C, appeared to change less than 0.3% in dry weight and contain more hydrogen bonds after immersing in water at 20°C for 14 days. The degradability of XSPU foams was significantly higher than that of petroleum polyol‐based PU foam as their soft segments were easier to be decomposed, where the weight loss of XSPU was up to 46.7% after burying in the soil at 23°C and 50% relative humidity for 250 days. The compression recovery ability of these bio‐based foams could reach approximately 98.2% after 1 ~ 3 times of compression test. Generally, XSPU foams displayed excellent thermal stability, stability in water, degradability in soil, and elastic ability, which showed potential application in fields of insulation, degradable plastic, and elastomer.

Tailoring thermal insulation architectures from additive manufacturing

Tailoring thermal transport by structural parameters could result in mechanically fragile and brittle networks. An indispensable goal is to design hierarchical architecture materials that combine thermal and mechanical properties in a continuous and cohesive network. A promising strategy to create such a hierarchical network targets additive manufacturing of hybrid porous voxels at nanoscale. Here we describe the convergence of agile additive manufacturing of porous hybrid voxels to tailor hierarchically and mechanically tunable objects. In one strategy, the uniformly distributed porous silica voxels, which form the basis for the control of thermal transport, are non-covalently interfaced with polymeric networks, yielding hierarchic super-elastic architectures with thermal insulation properties. Another additive strategy for achieving mechanical strength involves the versatile orthogonal surface hybridization of porous silica voxels retains its low thermal conductivity of 19.1 mW m−1 K−1, flexible compressive recovery strain (85%), and tailored mechanical strength from 71.6 kPa to 1.5 MPa. The printed lightweight high-fidelity objects promise thermal aging mitigation for lithium-ion batteries, providing a thermal management pathway using 3D printed silica objects.

Mechanical Properties and Pavement Usability of Modified Asphalt-Based Joint Material of Cement Concrete Pavement

Abstract The virgin-asphalt-based joint materials of cement concrete pavement are subjected to damages because of repeated vehicle load and environmental factors. The styrene-butadiene-styrene (SBS), shape memory polyurethane (PU), and organosilicon (OS) modified asphalt-based joint materials were prepared to improve mechanical properties and pavement usability of virgin-asphalt-based joint materials of cement concrete pavement. The tensile, compressive, shear property, low-temperature ductility, high-temperature fluidity, and elastic recovery performance were tested to select a suitable modifier and confirm its dosage for preparing modified asphalt-based joint material. Results indicate that mechanical properties, ductility, fluidity, and elastic recovery of asphalt joint materials are improved by SBS, PU, and OS modifiers. Especially, the modification effect of PU modifier at the dosage of 8 wt % is most satisfactory, successively followed by OS and SBS. The PU at the dosage of 8 % is proposed to develop a new modified asphalt-based joint material, reducing the failures of joint material and improving the durability of cement concrete pavement.

Evaluation of load-independent microhardness values in Plateau regions of Vanadium substituted Bi-2212 ceramics

This study reveals extensively effect of homovalent V/Bi partial replacement in Bi2.0−xVxSr2.0Ca1.1Cu2.0Oy ceramic matrix (0.00 ≤ x ≤ 0.30) on the key mechanical design performance parameters and load-independent Vickers microhardness parameters in plateau limit region by means of experimental microhardness tests and semi-empiric approaching models. It is found that the vanadium substitution level of x = 0.01 is observed to be optimum amount in the Bi-2212 crystal lattice for refinement of fundamental mechanical properties due to the enhancement in stabilization of durable tetragonal phase, surface residual compressive stress and elastic recovery mechanism. Conversely, from the replacement level of x = 0.01 onwards, the lattice strain field and stress concentration sites enhance significantly depending on the increase of microscopic structural problems, interaction problems between adjacent layers and crack-initiating flaws in Bi-2212 ceramic system. Correspondingly, stress-induced phase transformation begins to play predominant role, and excess vanadium substituted ceramic materials are easily broken at relatively smaller test load. Moreover, the models indicate that every ceramic compound shows standard indentation size effect (ISE) feature due to predominant behavior of elastic recovery in crystal structure. Hence, presence of optimum vanadium ions strengthens typical ISE characteristic behavior. Furthermore, among semi-empirical models the indentation-induced cracking (IIC) model exhibits the highest performance to inspect real microhardness values of Bi2.0−xVxSr2.0Ca1.1Cu2.0Oy ceramic compounds in the plateau limit region.

Coupled sliding–decohesion–compression model for a consistent description of monotonic and fatigue behavior of material interfaces

A thermodynamically consistent model proposed in this work introduces a generative symbolic framework for computational components, which can capture the inelastic behavior of interfaces with 3D kinematics in response to monotonic, cyclic, and fatigue loading histories. It contributes to a long list of existing cohesive zone models by introducing novel forms of potentials for free energy, threshold function, and dissipation to deliver the following model properties: (i) the evolution equations derived from the potentials are linked in such a way that damage develops along with the cumulative measure of plastic sliding, (ii) the convex, continuous, and smooth shape of the threshold function introduced in the effective stress domain enables a general and efficient time integration that automatically handles unloading and reloading, and (iii) the non-associative flow potential includes a scalable degree of coupling between normal and tangential damage evolution. The studies performed in the paper demonstrate that these model ingredients lead to a consistent coverage of arbitrary non-proportional loading scenarios in tangential and normal directions. For monotonic loading, the presented examples illustrate the ability of the model to reproduce the shear dilatancy, pressure sensitivity including the vertex effect, stiffness recovery in compression, and abrasion due to sliding. For cyclic fatigue loading, the studies show that the model reflects the link between the hysteretic behavior and the fatigue damage evolution. This link constitutes the basis for a physically sound description of fatigue degradation along material interfaces. It manifests itself in the presented energy breakdown with distinguished fractions of energy release due to damage and plasticity ascribed to normal and tangential directions. Two calibration and validation examples using pull-out tests exposed to monotonic and cyclic loading are provided to show the applicability of the model for the characterization of the bond between steel bars and concrete. A publicly available implementation using a computer algebra system (CAS) is provided in the form of an interactive Jupyter notebook to document the reproducibility of the results.

Constructing function domains in NiTi shape memory alloys by additive manufacturing

ABSTRACT Additive manufacturing (AM) is an orderly construction process involving track-by-track melt pools, which can modulate three characteristic zones between two adjacent melt pools: the heat-affected zone, transition zone, and cellular grain zone. These three zones constitute a function domain that determines the properties of AM metallic materials. In this study, we constructed a novel ordered function domain by AM of modified Ni50.6Ti49.4 shape memory alloy powder, which was produced by adding uniform Ni nanoparticles into atomised Ni49.6Ti50.4 powder. Interestingly, the three zones of the function domain had the same B2 austenite matrix but inhomogeneous Ni4Ti3 clusters and Ti2Ni nanoprecipitates, which caused different compressive recovery and residual strains in the three zones. The synergetic effect of the three zones generated a stable recovery strain and small hysteresis area in the AMed Ni50.6Ti49.4. Our results provide a novel strategy for modulating the microstructure of NiTi by AM to yield superior properties.

Compressive Wideband Spectrum Sensing and Signal Recovery With Unknown Multipath Channels

We study the problem of joint wideband spectrum sensing and recovery of multi-band signals in a multi-antenna-based sub-Nyquist sampling framework. Specifically, the multi-band signal is composed of a number of uncorrelated narrowband signals spreading over a wide frequency band. Unlike existing works which assume the source signals impinge on the receiver via a line-of-sight (LOS) path, we consider a more practical unknown MIMO channel which results from multipath propagation. A new sub-Nyquist sampling architecture is proposed, where each antenna output passes through two channels, namely, a direct path and a delayed path with a controlled amount of time delay. The signal at each channel is then sampled by a synchronized low-rate analog-to-digital converter (ADC). We utilize the collected data samples to build a set of cross-correlation matrices with different time lags and develop a CANDECOMP/PARAFAC (CP) decomposition-based method to recover the carrier frequencies, power spectra as well as the source signals themselves. Recovery conditions of the proposed method are analyzed, and Cramér-Rao bound (CRB) results for our estimation problem are derived. Simulation results are presented to illustrate the effectiveness of the proposed method.

Chitosan-based thermal insulation compressible foam enhanced with high performance of piezoelectric generation and sensing

A series of chitosan (CS)-konjac glucomannan (KGM) foams with excellent thermal insulation property has been prepared using a directional freezing method, which exhibit high strain recovery, excellent piezoelectric generation and sensing properties. Layered lamellar or honeycomb morphologies in CS-KGM foams attributes a low thermal conductivity coefficient of ca. 0.03 W/(m·K). Bridge-like structure that mainly observed in CS-KGM foams from horizontal freezing endows them with excellent compression recovery performance even after 200 compression cycles. This along with piezoelectricity of CS contributes a long-lasting piezoelectric generation performance, ranging from 0.809 to 2.460 V during compression cycle process. Piezoelectric signals generated from pressing with certain strain and rate, finger taping and hand grasping can be sensed profoundly by CS-KGM. As thus, fully renewable source-based CS-KGM foams with outstanding thermal insulation and piezoelectric performance shows great potential in application as wearable thermal insulation and piezoelectric devices.

Engineering a semi-interpenetrating constructed xylan-based hydrogel with superior compressive strength, resilience, and creep recovery abilities

Recent advances in the area of hydrogel synthesis have been directed to enhance the mechanical properties and biocompatibility, which are critical in their use as functional biomaterials. In this work, a green and facile method is introduced to produce a hydrogel based on xylan, a plant-based heteropolysaccharide, that is shown to successfully form hydrogen-bonded, semi-interpenetrating polymer networks with polyvinyl alcohol. Upon crosslinking with sodium trimetaphosphate, the obtained hydrogels achieved an exceptional compressive strength (up to 84.2 MPa at a fracture strain of 90 %), which surpasses any polysaccharide-based hydrogels reported so far. The hydrogels were further shown to have high degradation temperature (350–370 °C), to be mechanically resilient with a form and creep recovery of 95 % (78 % stress after 1000 cycles under 30 % strain) and 98 % in height, respectively. All materials used in the preparation of the hydrogels were non-toxic and biocompatible, which makes the synthesized hydrogels suitable potential candidates for soft-tissue engineering and biomedical applications.

Diatomite and Na-X zeolite as carriers for bacteria in self-healing cementitious mortars

The use of bacteria in the self-healing process of cementitious composites has been recently widely considered. In this study, diatomite and the Na-X zeolite were proposed as carrier materials impregnated by the Bacillus subtilis endospores. The effect of the impregnation method on a bacterial survival rate (BSR) and cement composites modification method on the strength parameters, was investigated. Additionally, the influence of modification and healing method on the flexural and compressive strength recovery and surface crack repair ratio, was assessed. Test results indicated higher BSR for a vacuum impregnated than immersed samples (up to 31% after 28 days of storage for the impregnated Na-X zeolite). The BSR in the self-healing mortar may be promoted by local pH reduction in the vicinity of carrier particles, especially diatomite (pHPZC = 4.6). Mortars containing medium dissolved in the mixing water showed an increase in the flexural and compressive strength (up to 10.4% and 18.0%, respectively). The addition of bacteria immobilized on the both carrier materials caused a decrease of strength properties (to 16.6%), while the series containing both bacteria and the medium attained the strength properties similar or better than the reference series and the series with carrier materials alone. Series containing bacteria immobilized on carrier material and with medium showed a self-healing ability, which was confirmed by the compressive strength recovery and surface repair ratio of 32.6% and 92.6%, respectively. The increased precipitation of CaCO3 was confirmed by the SEM and EDS analysis.

Effect of CO32- and Ca2+ on self-healing of cementitious materials due to “build-in” carbonation

In this study, the self-healing efficiency of mortar due to “build-in” carbonation was investigated. Sodium carbonate was selected as the healing agent to be carried by porous ceramsites to carry carbonate ions in the mortar as the healing components (HCs). The coating efficiency of the HCs and its effect on the fresh and hardened properties of the mortar were investigated. To investigate the effect of carbonate and calcium ions on formation of carbonates, the healing efficiency of mortars in the presence of an external calcium source only (P), an external carbonate source only (N), and an internal carbonate source combined with an external calcium source (C), was evaluated based on the mechanical property and pore structure by characterization of water absorption, mercury intrusion porosimetry (MIP) and backscattered electron imaging (BSE) measurements. The results showed that the incorporated HCs triggered “build-in” carbonation to heal the cracks. The mechanical regains and water absorption results demonstrated that the incorporated coated HCs significantly improved the self-healing capability of the pre-cracked mortars. The specimen containing 7.5 wt% of HCs showed the maximum compressive strength recovery rate of 1.35 and the greatest value of rate of water absorption was 64%. The MIP results showed a greatest reduction of pores in 100–1800 nm for the self-healing specimens after curing. The BSE results indicated that the main healing product for specimens with HCs was CaCO3. All the results by different measurements are consistent with each other and the best healing efficiency is seen for C, followed by N and P. The availability of carbonate ions is more critical in formation of calcite than the calcium source, particularly when the carbonate ions were provided internally. The optimum HCs dosage and environment for enhancing the self-healing capability of the mortars were 7.5 wt% and a saturated Ca(OH)2 solution, respectively.

MIMO Radar Imaging Based on Two-dimensional Compressive Sensing Recovery Algorithm

Conventional sparse signal recovery-based MIMO radar imaging method rearranges the received two-dimensional (2D) signals into a vector, However, transforming the two dimensional equation to one dimensional equation then solving linear equation based sparse signal recovery problem requires huge memory and computational budget. A two-dimensional compressed sensing MIMO radar imaging algorithm based on improved smooth L0 norm is proposed in this paper. Firstly, a two-dimensional MIMO radar imaging model is established to transform the imaging problem into a sparse optimization problem. Then, the two-dimensional negative exponential function sequence is used as the smoothed function sequence to approximate the L0 norm. The two-dimensional imaging of MIMO radar is realized by cyclic iteration and gradient projection algorithm. Simulation results show that the proposed algorithm has advantages over the traditional compressed sensing algorithms.

Environment-adaptable PAM/PVA Semi-IPN hydrogels reinforced by GO for high electromagnetic shielding performance

In this work, one type of mechanically robust, lithium chloride (LiCl)-containing semi-interpenetrating network (IPN) hydrogel consisting of crosslinked polyacrylamide (PAM) and linear polyvinyl alcohol (PVA) chains and reinforced with graphene oxide (GO) was fabricated, which had excellent anti-dehydration, anti-icing and electromagnetic interference (EMI) shielding performance. The experimental results showed PAM/PVA/GO/LiCl hydrogels had excellent cyclic compression recovery performance. The compressive strength of PAM/PVA (6 wt%)/GO (0.1 wt%)/LiCl (12 mol/1000 g PVA/GO solution) (PAM/PVA 6 /GO 0.1 /LiCl 12 ) hydrogel was almost unchanged after 10 compression cycles at a compressive strain of 70%. The water retention rate of PAM/PVA 6 /GO 0.1 /LiCl 12 hydrogels was nearly 100% under the conditions of 25 °C and 30% RH for 30 h. In addition, the hydrogels had good flexibility even at −50 °C, demonstrating excellent anti-icing properties. The hydrogels exhibited excellent electrical conductivity and EMI shielding performance whose shielding effectiveness was beyond 37.2 dB, showing potential applications in wearable devices, sensors or telecommunications. • Mechanically robust semi-interpenetrating network hydrogels were fabricated. • Excellent anti-dehydration and anti-icing properties of hydrogels were achieved. • PAM/PVA/GO/LiCl hydrogel exhibited excellent EMI shielding performance.

Correlation-based local detection for deceptive interference mitigation in multi-parameter modulated radar

To improve the ability of resisting the deceptive interference for radar, a multi-parameter modulated radar signal is investigated and its compressed sensing model is constructed in this paper. Unlike the traditional frequency modulated continuous wave (FMCW) signal model, the established model has natural advantages in mitigating the deceptive interference due to the agility of multiple signal parameters. Simultaneously, to reduce the impact of the deceptive interference on the target echo, the compressed recovery algorithm combined with the proposed correlation-based local detection is introduced. Before recovering the target echo, the local dictionary matrix is inspected by using the correlation to ensure that the expected echo signal is obtained merely. Simulation results show that the proposed method significantly improves the performance in mitigating the deceptive interference. By coherently integrating the signals over multiple periods, the relative pure range profile or the range-Doppler plane could be acquired. It helps radar system to extract the distance or velocity information in the interference environment.

Study on Autolytic Mechanism and Self-Healing Properties of Autolytic Clinker Microsphere in Alkaline Environment.

In this study, the autolytic clinker microsphere with clinker as core and polyvinyl pyrrolidone (PVP) as coating film was prepared. Pretreatment of clinker with silane coupling agent was firstly processed during the preparation. To investigate the autolytic mechanism, the microstructures of the autolytic clinker microsphere at different curing ages were observed using environmental scanning electron microscopy (ESEM), equipped with an energy dispersive spectrometer (EDS). The autolytic stages were also identified based on the microstructural evolution. The influence of pretreatment degree on autolytic behavior was also studied by measurements of micro-morphology and isothermal calorimetry. Experimental results indicated that the compressive strength recovery of specimens was increased by 15–19% due to the addition of autolytic clinker microspheres. The recovery of compressive strength was also improved with the increase of pH value. The improvements in compressive strength recovery of specimens with microspheres were in the range of 15–19%, 15–31%, 25–36%, and 29–50% with the pH value of 7, 8, 10, and 12, respectively. It was also found that inner damage of cement-based matrix had greater recovery when pre-cracked specimens were cured in alkaline environments.