Strain-hardening Behavior Research Articles

3D auxetic cementitious-polymeric composite structure with compressive strain-hardening behavior

A composite can have properties much better than the components it is made of. This work proposes a three-dimensional auxetic cementitious-polymeric composite structure (3D-ACPC) which incorporates 3D printed polymeric shell with cementitious mortar. Uniaxial compression experiments are performed on the 3D-ACPC to study their quasi-static stress-strain response. Experimental results show that the created composite structure can simultaneously overcome the brittleness of conventional cementitious material and the low compressive strength of 3D printed polymeric cellular shell. Therefore, the 3D-ACPC exhibit compressive strain-hardening behavior ensuring high energy absorption ability. In addition, it is found that structural anisotropy and the shell printing direction have significant impact on the stress-strain response of the 3D-ACPC. Moreover, due to the lightweight cellular structure, the 3D-ACPC shows significantly enhanced specific energy absorption compared to conventional cementitious materials and polymeric cellular materials. To this end, the developed 3D-ACPC has great potential to be used in engineering practice, such as protective structures.

Effects of Graphene Oxide on the Properties of Engineered Cementitious Composites: Multi-Objective Optimization Technique Using RSM

Despite the excellent ductility and energy absorption properties of engineered cementitious composites (ECCs), a low modulus of elasticity and excessive drying shrinkage remain some of its major disadvantages. With the current trend in the application of nanotechnology in cementitious composites research, the effect of graphene oxide (GO) on the properties of ECCs is yet to be fully investigated, despite its promising results in ordinary cement paste, mortar, and concrete. ECCs need extensive material tailoring to provide the required mechanical characteristics and controlled fracture size with strain-hardening behavior. Striking a balance between these crucial hardened aspects of ECC without compromising any desired properties is a challenge. Hence, the main aim of the study reported in this paper is to use the response surface methodology (RSM) multi-objective optimization technique to identify an appropriate GO content via the weight of cement and also the volume fraction of polyvinyl alcohol (PVA) fiber as input variables that positively impact ECCs’ properties. Using RSM’s central composite design (CCD), 13 mixtures of various combinations of the variables (GO: 0.05%, 0.065%, 0.08%; PVA: 1%, 1.5%, 2%) were developed. Six responses were studied, including compressive strength, direct tensile strength, tensile capacity, flexural strength, modulus of elasticity, Poisson’s ratio, and drying shrinkage. Moreover, the microstructural properties of the composites were assessed using field-emission scanning electron microscopy (FESEM) and mercury intrusion porosimetry (MIP). The outcomes revealed that all the properties of ECCs were significantly enhanced by adding an optimum amount of 0.05% GO and 1–1.5% PVA fiber volume fractions. A maximum increase in 30%, 35%, 49%, and 33.9% in the compressive strength, direct tensile strength, flexural strength, and modulus of elasticity, respectively, of the mixes with 0.05% GO addition was recorded. It is demonstrated that the use of 0.05% GO as a nanoscale particle can provide good outputs for the construction industry.

Tensile strain-hardening behavior and related deformation mechanisms of pure titanium at cryogenic temperature

The tensile strain-hardening behavior of pure Ti at 100 K was investigated using X-ray diffraction line-profile analysis and plasticity simulation. The strain hardening was significantly increased at 100 K, compared with that observed at 298 K. Thus, at 100 K, necking was suppressed during tensile testing, which greatly increased material ductility. The remarkable increase in strain hardening at 100 K was attributed to the dominant activation of prismatic <a> slip and the exceptionally increased rate of its activation stress with tensile strain at 100 K. This finding significantly advances the understanding of the strain-hardening behavior of pure Ti at low temperatures, and it can also guide the development of texture-engineering strategies to increase the low-temperature ductility of pure Ti.

Microstructure Characteristics, Mechanical Properties and Strain Hardening Behavior of B2 Intermetallic Compound-Strengthening Fe-16Mn-9Al-0.8C-3Ni Steel Fabricated by Twin-Roll Strip Casting, Cold Rolling and Annealing.

In this study, the Fe-16Mn-9Al-0.8C-3Ni (wt.%) lightweight steel was fabricated by novel twin-roll strip casting technology. The microstructure, tensile properties and strain-hardening behavior of the present steel have been investigated and compared to those of conventionally processed steels with similar chemical compositions. After annealing, a unique gradient microstructure of intermetallic compound (B2)-austenite was obtained along the thickness direction, consisting of granular B2 (average: 430 nm) and fine austenite (average: 1.82 μm) at the surface layer, blocky B2 (average: 1.03 μm) and medium austenite (average: 3.98 μm) at the quarter layer and polygonal B2 (average: 1.94 μm) and coarse austenite (average: 6.13 μm) at the center layer. The cooperative action of B2 pinning dislocation, plane slip and back stress led to stronger strain hardening, among which the strong back stress effect originated from the multistage discontinuous austenite deformation and the mechanical incompatibility between austenite and B2 is believed to be the most important reason, thereby achieving an excellent balance of strength (ultimate tensile strength: 1147 MPa) and ductility (total elongation: 43.2%). This work not only developed a new processing way to fabricate Ni-containing Fe-Mn-Al-C lightweight steel with outstanding mechanical properties, but also provided a potential solution for manufacturing some other metallic materials accompanied by brittle B2 intermetallic.

Toughening additive manufactured Zr-based bulk metallic glass composites by martensite phase transformation

Additive manufacturing technology based on laser powder bed fusion (LPBF) offers a novel approach for fabricating bulk metallic glass (BMG) products without restriction in size and geometry. Nevertheless, the BMGs prepared by LPBF usually suffered from less plasticity and poorer fracture toughness as compared to their cast counterparts due to partial crystallization in heat-affected zones (HAZs). Since crystallization in HAZs is hard to avoid completely in LPBF BMGs, it is desirable to design a suitable alloy system, in which only ductile crystalline phase, instead of brittle intermetallics, is formed in HAZs. This unique structure could effectively increase the toughness/plasticity of the LPBF BMGs. To achieve this goal, a quaternary BMG system with a composition of Zr47.5Cu45.5Al5Co2 is adopted and subjected to LPBF. It is found that nearly a single phase of B2-ZrCu is precipitated in HAZs, while a fully amorphous phase is formed in molten pools (MPs). This B2 phase reinforced BMG composite exhibits excellent mechanical properties with enhanced plasticity and toughness. Furthermore, it is easy to modulate the mechanical properties by altering the amount of the B2 phase via adjusting the laser energy input. Finally, the best combination of strength, plasticity, and notch toughness is obtained in the BMG composite containing 27.4% B2 phase and 72.6% amorphous phase, which exhibits yield strength (σs) of 1423 MPa, plastic strain (εp) of 4.65%, and notch toughness (Kq) of 53.9 MPa m1/2. Furthermore, a notable strain-hardening is also observed. The improvement of plasticity/toughness and appearance of strain-hardening behavior are mainly due to the martensite phase transformation from the B2 phase to the Cm phase during plastic deformation (i.e., the phase transformation-induced plasticity effect). The current work provides a guide for making advanced BMGs and BMG composites by additive manufacturing.

Effects of V Addition on the Deformation Mechanism and Mechanical Properties of Non-Equiatomic CoCrNi Medium-Entropy Alloys.

Equiatomic CoCrNi medium-entropy alloys exhibit superior strength and ductility. In this work, a non-equiatomic CoCrNi alloy with low stacking fault energy was designed, and different fractions of V were added to control the stacking fault energy and lattice distortion. Mechanical properties were evaluated by tensile tests, and deformation microstructures were characterized by transmission electron microscope (TEM). The main deformation mechanisms of CoCrNiV alloy with low V content are dislocation slip, stacking faults, and deformation-induced HCP phase transformation, while the dominant deformation patterns of CoCrNiV alloy with high V contents are dislocation slip and stacking faults. The yield strength increases dramatically when the V content is high, and the strain-hardening behavior changes non-monotonically with increasing the V content. V addition increases the stacking fault energy (SFE) and lattice distortion. The lower strain-hardening rate of 6V alloy than that of 2V alloy is dominated by the SFE. The higher strain-hardening rate of 10V alloy than that of 6V alloy is dominated by the lattice distortion. The effects of V addition on the SFE, lattice distortion, and strain-hardening behavior are discussed.

Lattice discrete particle modeling of the cycling behavior of strain-hardening cementitious composites with and without fiber reinforced polymer grid reinforcement

Strain-hardening cementitious composites (SHCC) has become increasingly prevalent in structural design. Compared to ordinary concrete, SHCC exhibits ultra-high tensile ductility, significant strain-hardening behavior, very fine multi-point cracking, high energy dissipation, and good durability. One robust model for simulating reinforced concrete behavior is the so-called Lattice Discrete Particle Model (LDPM), and specifically LDPM-F which includes the effect of fiber reinforcement. The present cycling constitutive law implemented in LDPM and the cycling fiber-bridging law in LDPM-F though cannot accurately capture the residual tensile plastic strain, loading–unloading path, and energy dissipation of SHCC during cyclic tension. To solve these concerns, the cycling tension–compression constitutive law and the nonlinear cycling fiber-bridging law were reformulated. Further, the new model was used to simulate the cycling tensile behavior of plain concrete, SHCC, and Fiber-Reinforced Polymer (FRP) grid reinforced SHCC (FRP-SHCC). Simulation results show that the multi-point cracking, crack widths, and ultra-high ductility properties are correctly captured by LDPM-F. In addition, LDPM-F with the modified cycling constitutive model can effectively simulate the cycling tension–compression behavior, accurately reproducing the stress–strain relationship, residual plastic strain, and overall dissipated energy. Finally, the simulated failure modes agree well with the actual fracture planes of these materials under cyclic tension.

Strain hardening geopolymer composites with hybrid POM and UHMWPE fibers: Analysis of static mechanical properties, economic benefits, and environmental impact

With unique ultra-high toughness, strain-hardening cementitious composite (SHCC) has attracted considerable attention. However, environmental and economic concerns have hindered its engineering application due to the high consumption of Portland cement and expensive high-performance fibers. To address this issue, geopolymer concrete and polyoxymethylene (POM) fibers are adopted to replace Portland cement and ultrahigh molecular weight polyethylene (UHMWPE) fibers, respectively, to prepare strain-hardening geopolymer composite with hybrid POM and UHMWPE fibers (POM/PE-SHGC). Static mechanical properties, economic benefits, and environmental impact of POM/PE-SHGC with different POM fiber replacement ratios are investigated. Axial compression and tensile tests on POM/PE-SHGC with different POM fiber replacement ratios (0%, 25%, 50%, 75%, 100%) are conducted to investigate the effect of different POM fiber replacement ratios on the static failure mode, tensile crack development, compression behavior, and strain-hardening behavior of POM/PE-SHGC. In addition, Carbon emissions and energy consumption of POM/PE-SHGC were estimated and compared with SHCC. An evaluation method that comprehensively considers environmental and economic benefits and mechanical properties is proposed. The results indicated that under the condition of a total fiber volume fraction of 2%, POM/PE-SHGC with a POM fiber replacement ratios under 75% exhibited good strain-hardening behavior. The compressive strength, ultimate compressive strain, and ultimate tensile strain of POM/PE-SHGC reached a maximum at a POM replacement ratios of 50%, except for a decrease in its tensile strength. Furthermore, the cost, carbon emissions and energy consumption of POM/PE-SHGC was significantly lower than that of SHCC. This study verified the feasibility of producing green, high-performance SHGC and promoted the engineering application of this material.

Crystal plasticity constitutive model and thermodynamics informed creep-fatigue life prediction model for Ni-based single crystal superalloy

Ni-based single crystal superalloys are the main constituent materials for aeroengine turbine blades. They are subjected to extensive in-service plastic deformation and creep-fatigue interaction, which can cause damage and failure and hence limit the turbine blade durability. In this study, a novel crystal plasticity-based constitutive model is proposed to predict the cyclic inelastic deformation of Ni-based single crystal superalloy under creep-fatigue loads, and the key aspects examined include cyclic strain hardening, ratcheting and stress relaxation behavior. The novelty of the model lies in the introduction of a dislocation density parameter in the kinematic hardening rule to describe the evolutionary characteristics of hysteresis loops. The constitutive model is implemented via the crystal plasticity finite element method and the predictions are in good agreement with experimental results. Furthermore, thermodynamic entropy generation is innovatively adopted as an indicator parameter for analysis of Ni-based single crystal creep-fatigue failure, and the corresponding creep and fatigue damage models are developed to evaluate the degree of damage. The half-life concept associated with the steady-state hysteresis loop is employed in the failure model to predict the creep-fatigue life without being limited by the computational efficiency of the crystal plasticity finite element method. The proposed model can well capture the characteristics of Ni-based single crystal creep-fatigue life, and the prediction falls within a scatter band of factor 2.0 compared to experimental results. The proposed creep-fatigue life prediction model is underpinned by deformation and failure mechanisms, which would provide a basis for accurate analysis and robust assessment of Ni-based single crystal superalloy performance and life.

Nonlinear elastic constitutive model of clayey sand reservoirs during depressurization exploitation of natural gas hydrate

Accurate evaluation of the mechanical response of hydrate-bearing reservoirs is a prerequisite for safe and efficient exploitation of natural gas hydrate resources. Therefore, it is necessary to develop a suitable constitutive model and to determine reasonable model parameters for hydrate-bearing sediments (HBSs) during exploitation. In this study, based on the strain-hardening behavior of clayey sand reservoirs published in the previous study, Duncan–Chang model was used as the basic model to establish constitutive models for HBSs during exploitation. The model parameters, initial elastic modulus and ultimate deviatoric stress, were determined by modifying existing formulas and establishing empirical formulas. Four nonlinear elastic constitutive models were proposed by combining the model parameters determined by different methods. Multi-stage and single-stage triaxial test data were used to verify the applicability of the model and determine the optimal model suitable for the sediments under study.

A fundamental understanding of how dislocation densities affect strain hardening behavior in copper single crystalline micropillars

Under mechanical loading, the strain hardening behavior of crystalline face-centered cubic (FCC) metals is of critical importance in determining fracture behavior and overall mechanical performance. While strain hardening is typically accompanied by a decrease in ductility, it can also simultaneously enhance the material's resistance to plastic deformation and improve its load bearing capacity. Hence, we conducted a detailed study using copper (Cu) single-crystal micropillars as a model system to investigate and delineate the relationship between strain hardening and defect behavior. We employed in situ compression in a scanning electron microscope (SEM) and dislocation density-based crystal plasticity (DCP) modeling. The strain hardening rate varied with the compression crystallographic orientation, ranging from negligible values (of approximately 80 MPa) to relatively high hardening rates (of approximately 1150 MPa) for nominal strains of up to 15%. Various analysis methods were applied, including slip trace characterization, electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and transmission Kikuchi diffraction (TKD). These techniques allowed us to identify the distributions of active slip systems, dislocation structures after compression, and correlated internal lattice rotations. Furthermore, the DCP model was developed to specifically understand how serration events are related to dislocation-density evolution or strain bursts, and this was validated with the micropillar experiments. This integrated experimental and modeling investigation offers valuable insights and predictions regarding the evolution of both total and partial dislocations, including Hirth and Lomer junctions, as well as lattice rotations.

Combining 3D textiles and synthetic microfibers for a sustainable strain-hardening behavior in cementitious materials

Concrete and traditional cement have a significant environmental impact. As they will continue to be used abundantly, solutions are necessary to ensure a more sustainable application. The use of metallic reinforcements in cementitious material leads to environmental and durability concerns as well, such as corrosion. A new way of reinforcing cementitious materials is combining 3D textiles with synthetic microfibers. This reinforcement combination, with naturally higher corrosion resistance, can lead to slender, lighter, and more durable structures. The 3D textiles guarantee the loadbearing capacity while the synthetic microfibers limit the crack widths to an acceptable range in which the cracks can be healed through the autogenous healing of the cementitious material. This limits the necessity for maintenance and repair works, increasing the service life of future civil works. Synthetic microfibers, 3D textiles and cementitious matrix synergistically interconnect, leading to a different mechanical performance which needs to be studied. In this paper, the effect of the addition of microfibers to 3D Textile Reinforced Cements (3D TRCs) is investigated, evaluating the influence of the fibers themselves, as well as their content and length. Two types of polypropylene (PP) microfibers with a length of 3 mm and 6 mm are selected. Using four-point bending tests linked with Digital Image Correlation (DIC) monitoring, the strain-hardening behavior, bending behavior and crack formation of 3D TRC specimens with and without added microfibers are investigated. Generally, using 3D textiles, a superior flexural response is already obtained compared to 2D textiles due to the anchorage mechanism of the transversal connections. However, a higher ultimate load and post-cracking stiffness are achieved upon using synthetic microfibers, showing the positive effect of the reinforcement combination. A higher fiber content and longer fiber length amplify this effect. Furthermore, the addition of microfibers generally results in the formation of more and narrower cracks.

Effect of through-thickness microstructure inhomogeneity on mechanical properties and strain hardening behavior in heavy-wall X70 pipeline steels

The ever-increasing demand for oil & gas exploration from land to subsea necessitates using higher-strength and high-ductility heavy-wall thickness pipes, which may increase the microstructural inhomogeneity along the steel plate sections, ultimately impacting the mechanical properties. In this work, the differences in microstructure and mechanical properties between the through-thickness layers of a heavy-wall ferrite/bainite (F/B) dual-phase (DP) X70 pipeline steel plate were studied. The results showed that the size of the ferrite grain and the volume fraction of bainite increased from the surface layer to the mid-thickness layer of the DP X70 pipeline steel plate. The surface and mid-thickness layers had a lower uniform elongation and higher strength and hardness. In comparison, the quarter layer had higher uniform elongation and lower strength and hardness. The refined grain size and the strong {001}<110> texture were responsible for enhanced in strength and hardness. The higher γ-fiber texture at the quarter layer favored the higher plasticity. The analysis results of strain-hardening behaviors based on the modified C-J model showed that the mid-thickness layer had a higher strain-hardening capacity at the beginning of the plastic strain, leading to deformation instability and reduced material plasticity. The surface layer maintained a high hardening exponent even at high plastic strains, which facilitated the deformation properties of the material. The results provide a basis for evaluating the influence of microstructural factors on the strength and plasticity of heavy-wall X70 pipeline steel and the coordination mechanism of micro deformation in DP steels.

New insights into the effects of starch-oleic acid-chlorogenic acid interactions on structural formation by hot-extrusion 3D printing: From perspective of nonlinear rheology

Nonlinear rheology can be used to monitor the molecular chain movement of polymer materials under large strain conditions. In this work, we firstly set up large amplitude oscillatory shear (LAOS) conditions simulating the hot-extrusion 3D printing (HE-3DP) process and attempted to match the structural formation of wheat starch (WS) by starch-oleic acid (OA)-chlorogenic acid (CA) interactions during HE-3DP from perspectives of nonlinear rheology. Results showed that when compared with WS system, the b value and zero-strain nonlinearity (Q0) of WS-OA system increased with OA addition, and it exhibited obvious strain hardening and shear thinning behaviors, which were ascribed to that OA interacted with starch to form single helix and V-type crystalline structure through hydrophobic force, and it obstructed the integrality of gel network. For WS-CA system, the b value and Q0 decreased with CA addition and the shear thickening behavior was increased which could be explained that CA interacted with starch chains through hydrogen bonding following the formation of aggregates structure, thus improving the integrity of network structure. Notably, when compared to above two binary systems, the early emergence of strain thickening and the weakening of strain stiffening for WS-OA-CA system declared that CA contributed to inhibiting the aggregation and assembly of the single helix formed by WS-OA interactions. Overall, this study provided important information for the application of nonlinear rheology in the structure evolution of starch system during HE-3DP.

Type-I to Type-II non-Masing behavior of 304L SS under low cycle fatigue: Material’s internal changes

This study investigates the Type-I and Type-II non-Masing behavior of 304L austenitic stainless steel fatigue tested at room temperature for strain amplitudes ranging from ±0.25% to ±1.0% at a strain rate of 1 × 10-3 s−1. The material exhibited Type-I non-Masing behavior at lower life fractions (≤10%) and Type-II non-Masing behavior at higher life fractions (>10%). Type-I indicates that the master curve construction is possible, but in Type-II, the master curve can not be constructed. Further, low cycle fatigue tests conducted at ±0.25%, ±0.6%, and ±1.0% of strain amplitude were interrupted at life fractions of 8%, 30%, and 50% to investigate the internal material changes. At ±0.6% and ±1.0% of strain amplitude, the martensite content, dislocation density, and local misorientation increased with increasing life fraction, whereas the twins fraction decreased. Low martensite content and internal defects observed at low life fraction (8%) cause a minimal change in the strain-hardening rate behavior at different strain amplitudes, thereby, the Type-I non-Masing behavior. However, at higher life fractions (30% and 50%), high martensite content, high dislocation density, stacking faults, deformation twins, shear bands, dislocation walls, and cells have caused a significant change in the strain-hardening rate behavior, and thus, the Type-II non-Masing behavior.

Microstructure effects on mechanical properties of network-forming polymer systems: An atomistic simulation study

The coupling mechanism of chain entanglement and crosslinking remains unelucidated at the atomic scale. The network-forming dynamics and mechanical properties of pure-entangled matrix (PEM) and crosslinked & entangled matrix (CEM) were explored using all-atomic molecular dynamics simulations. The generation of side chains and local networks significantly affects the mechanical properties. For the PEM, as the reaction degree (r) increased, the dominant factor affecting the mechanical properties of materials changed from the movement of the main chain to entanglement. For the CEM, as r increased, the system first produced a local cross-linked structure and then formed a complete matrix. At extremely large strain, the CEM directly ruptured; the PEM showed a strain-hardening behavior before the final rupture because of the re-distribution of chain entanglements. The PEM and CEM exhibited almost the same elasticity but demonstrated a large difference in viscosity owing to the presence of long side chains in the CEM.

Influences of Corrosion Degree and Uniformity on Bond Strength and Cracking Pattern of Cement Mortar and PVA-ECC

Engineered cementitious composites (ECCs), which have a strain-hardening behavior under tension, is widely used for repairing and retrofitting reinforced concrete structures. In such applications, the performance of the bond between the ECC and corroded rebar is critical for the service life prediction of the repaired structures. In this study, the cracking patterns and bond behavior of polyvinyl alcohol (PVA) ECCs (PVA-ECCs) and cement mortar with uniform and nonuniform corroded steel rebars were studied. It was found that the uniform corrosion–induced cracks were randomly distributed, while the nonuniform corrosion–induced cracks were concentrated perpendicular to the most corroded side. The bond strength of PVA-ECC and mortar specimens was independent of the corrosion method. The bond strength of PVA-ECC and mortar specimens both showed a trend of increasing first and then decreasing with the development of corrosion rate. The threshold corrosion rate for mortar specimens was 0.125%, and the threshold corrosion rate of PVA-ECC specimens was 0.922%.

Evaluating the Impact of Crushing Process on Strength Characteristics and Leachability of Cement-Stabilized Dredged Sediment

Stabilization of dredged sediment and reusing the mixture as a construction material is an effective way to reduce environmental problems and save natural resources. However, the crushing process that occurs during construction may affect the mechanical properties and leachability of the reused stabilized soil, an issue that is less reported. Therefore, consolidated undrained triaxial tests and semi-dynamic leaching tests were conducted on stabilized sediments and recompacted crushed stabilized sediment grains (SG) to evaluate the influence of the crushing process. The results of the triaxial tests showed that the stabilized sediment exhibited strain-softening and brittle behaviors under various confining pressures (100, 200, and 400 kPa), while strain-hardening and ductile behaviors were more obvious in the SG. The reduction in cohesion between stabilized sediment and the SG reflected a loss of cementation bonding during the crushing process. The overall leaching behaviors versus curing time of heavy metals (As, Cr, Cu, Zn, Pb, Ni, and Hg) in stabilized sediment was similar to that of SG. The leaching mechanism indicated a good immobilization of heavy metals in stabilized sediment, while their stability in SG was poorer. The reason for the differences in triaxial strength properties and leachability were mainly attributed to the fact that the strong cementation bonding was destroyed by the crushing process, weakening the soil structure and raising the potential for release of elements.

Tensile properties of slag-based engineered cementitious composites with ground granulated blast-furnace slag

During the last decade, concrete technology has been undergoing rapid development, resulting in a new concept of engineered cementitious composite (ECC) to overcome the brittle behaviour of cement-based materials. ECC is one movement to fully incorporate waste material as an innovation in green material due to excellent toughness and energy absorption capacity, self-healing ability, fire performance, and remain durable under erosion environment. ECC exhibits a strain-hardening behaviour through the formation of micro cracking. This study is focusing on the tensile behaviour of the slag-based ECC. A total of five ECC mixes were designed with different cement to ground granulated blast-furnace slag (GGBS) ratio. Five samples of dog bone and three cylindrical for each mixture were prepared for direct tensile and compression tests. Compared to control samples, there are increments in compressive strength for samples contained 50-60% of GGBS and reductions in compressive strength for samples contained 70-80% of GGBS. The tensile strengths of ECC increase in the rate proportionally to the content of GGBS in ECC mixtures. The failure modes of the ECC cylinder samples including crushing under compressive load and few micro cracks are observed in ECC dog bones.

Characterization of engineering properties of deep-water soils in the South China Sea

The characterization of the geological and geotechnical properties of marine sediments is crucial for the exploration of subsea oil and gas resources. In this study, the engineering properties of deep-water soils recovered from the South China Sea (SCS) were in detail characterized via a series of laboratory tests to explore their physical, mechanical, mineralogical and microstructural behaviors. The results show that the index properties of deep-water soils are characterized by high natural water content, high void ratio, high Atterberg limits, but low density. The sensitivity of these soils is higher than 10, indicating their strong natural structure, which significantly controls the shear behavior and failure model. The intact samples show strain-softening to strain-hardening behavior with an increase in the confining pressure, while reconsolidated samples consistently show strain-hardening phenomenon under any level of confining pressure. The cyclic T-bar penetration tests show a dramatic strength degradation behavior of the intact samples. The compression curves of the intact samples always lie above the remoulded ones, and there is an obvious yielding phenomenon for the intact samples. The deep-water soils exhibit high thixotropy, as proposed by a criterion to evaluate the thixotropic capacity of soils. The mineralogy and microstructure analysis indicate that biogenic silica and an open flocculated structure might be the underlying reasons for the unique physical and mechanical properties of deep-water soils. The findings through this study provide essential parameters for related engineering applications and a deeper insight into understanding the unique properties of deep-water soils.