Research progress on the adaptability of lunar regolith simulant-based composites and lunar base construction methods

The development and utilization of lunar resources are entering a critical stage.Immediate focus is needed on key technologies for in-situ resource utilization(ISRU)and lunar base construction.This paper comparatively analyzes the basic characteristics of lunar regolith samples returned from Chang'e-5(CE-5),Apollo,and Luna missions,focusing on their physical,mechanical,mineral,chemical,and morphological parameters.Given the limited availability of lunar regolith,more than 50 lunar regolith simulants are summarized.The differences between lunar regolith and simulants concerning these parameters are discussed.To facilitate the construction of lunar bases,this article summarizes the advancements in research on construction materials derived from lunar regolith simulants.Based on statistical results,lunar regolith simulant-based composites are classified into 5 types by their strengthening and toughening mechanisms,and a comprehensive analysis of molding methods,preparation conditions,and mechanical properties is conducted.Furthermore,the potential lunar base construction forms are reviewed,and the adaptability of lunar regolith simulant-based composites and lunar base construction methods are proposed.The key demands of lunar bases constructed with lunar regolith-based composites are discussed,including energy demand,in-situ buildability,service performance,and structural availability.This progress contributes to providing essential material and methodological support for future lunar construction.

Improvement of Water Sensitivity of Macro-defect-free Cement Based Composites with Cross Coupling Agent

The enhancement of interface bonding between cement and polymerand the structural reticula- tion of the water-soluble polymer areproposed to minimize the shortening of the mechanical properties ofmacro-de- fect-free(MDF)cement based composites at high relativehumidity. The MDF composites incorporated with vari- ouscross-coupling agents studied experimentally. The results show thatthe MDF composites modified with small amounts of cross-couplingagent had raised mechanical properties, but it is more important thatthe modified MDF composites had a significant increase in waterresistance compared to the original one.

Piezoresistivity in Carbon Fiber Reinforced Cement Based Composites

The results of some interesting investigation on the piezoresistivity of carbon fiber reinforced cement based composites (CFRC) are presented with the prospect of developing a new nondestructive testing method to assess the integrity of the composite. The addition of short carbon fibers to cement-based mortar or concrete improves the structural performance and at the same time significantly decreases the bulk electrical resistivity. This makes CFRC responsive to the smart behavior by measuring the resistance change with uniaxial pressure. The piezoresistivity of CFRC under different stress was studied, at the same time the damage occurring inner specimens was detected by acoustic emission as well. Test results show that there exists a marking pressure dependence of the conductivity in CFRC, in which the so-called negative pressure coefficient of resistive (NPCR) and positive pressure coefficient of resistive (PPCR) are observed under low and high pressure. Under constant pressures, time-dependent resistivity is an outstanding characteristic for the composites, which is defined as resistance creep. The breakdown and rebuild-up process of conductive network under pressure may be responsible for the pressure dependence of resistivity.

Piezoresistive Response Extraction for Smart Cement-based Composites/Sensors

A kind of piezoresistive response extraction method for smart cement-based composites/sensors was proposed.Two kinds of typical piezoresistive cement-based composites/sensors were fabricated by respectively adding carbon nanotubes and nickel powders as conductive fillers into cement paste or cement mortar.The variation in measured electrical resistance of such cement-based composites/sensors was explored without loading and under repeated compressive loading and impulsive loading.The experimental results indicate that the measured electrical resistance of piezoresistive cement-based composites/sensors exhibits a two-stage variation trend of fast increase and steady increase with measurement time without loading,and an irreversible increase after loading.This results from polarization caused by ionic conduction in these composites/sensors.After reaching a plateau,the measured electrical resistance can be divided into an electrical resistance part and an electrical capacity part.The piezoresistive responses of electrical resistance part in measured electrical resistance to loading can be extracted by eliminating the linear electrical capacity part in measured electrical resistance.

Piezoresistivity of Carbon Fiber Graphite Cement-based Composites with CCCW

The electrical conductivity and piezoresistivity of carbon fiber graphite cement-matrix composites（CFGCC） with carbon fiber content（1% by the weight of cement）,graphite powder contents （0%-50% by the weight of cement） and CCCW（cementitious capillary crystalline waterproofing materials,4% by the weight of cement） were studied.The experimental results showed that the relationship between the resistivity of CFGCC and the concentration of graphite powders had typical features of percolation phenomena.The percolation threshold was about 20%.A clear piezoresistive effect was observed in CFGCC with 1wt% of carbon fibers,20wt% or 30wt% of graphite powders under uniaxial compressive tests,indicating that this type of smart composites was a promising candidate for strain sensing.The measured gage factor （defined as the fractional change in resistance per unit strain） of CFGCC with graphite content of 20wt% and 30wt% were 37 and 22,respectively.With the addition of CCCW,the mechanical properties of CFGCC were improved,which benefited CFGCC piezoresistivity of stability.

Modeling and Software Development of the Interfacial Transition Zone of Ellipsoidal Aggregate in Cement-Based Composites

The interfacial transition zone (ITZ) between the aggregates and the bulk paste is the weakest zone of ordinary concrete, which largely determines its mechanical and transporting properties. However, a complete understanding and a quantitative modeling of ITZ are still lacking. Consequently, an integrated modeling and experimental study were conducted. First, the theoretical calculation model of the ITZ volume fraction about the rotary ellipsoidal aggregate particles was established based on the nearest surface function formula. Its calculation programs were written based on Visual Basic 6.0 language and achieved visualization and functionalization. Then, the influencing factors of ITZ volume fraction of the ellipsoidal aggregate particles and the overlapping degree between the ITZ were systematically analyzed. Finally, the calculation models of ITZ volume fraction on actual ellipsoidal aggregate were given, based on cobblestones or pebbles particles with naturally ellipsoidal shape. The results indicate that the calculation model proposed is highly reliable.

Model of Coherent Interface Formation in Cement-Based Composites Containing Polyblend of Poly vinyl Alcohol and Methylcellulose

The texture of interfacial zone between cement paste and quartz in the cement-based composites containing polyvinyl alcohol (PVA), methylcellulose (MC) and their potyblend in an amount of 10 wt % with respect to cement, as well as the texture of dehydrated bodies of PVA, MC, and the potyblend solutions, were investigated with SEM. The network texture of the dehydrated polyblend is confirmed by comparing the texture of dehydrated bodies of PVA and MC. The network texture has restrained the movement of polyblend molecules in the cement mortar but is helpful to forming a coherent interface between cement paste and quartz. The key factor of forming the coherent interface is not the neutralization reaction between H + from hydrolysis of quarts: and OH- from hydration of cement, but the electrostatic attraction and the chemical reaction between polar groups on the polyblend molecule and cations and onions from hydrolysis of quartz and hydration of cement, respectively. The model of the coherent interface formation is that excessive [HSiO3]- and [SiO3]2- onions are bonded with the hydrated cations such as Ca2+ and Al3+ , which is confirmed by the gel containing Ca and Si on the quartz surface.

Effects of temperature on fracture behavior of Al-based in-situ composites reinforced with Mg_2Si and Si particles fabricated by centrifugal casting

An aluminum-based in-situ composites reinforced with Mg2Si and Si particles were produced by centrifugal casting A1-20Si-5Mg alloy. The microstructure of the composites was examined, and the effects of temperature on fracture behavior of the composite were investigated. The results show that the average fraction of primary Si and Mg2Si particles in the composites is as high as 38%, and ultimate tensile strengths （UTS） of the composites first increase then decrease with the increase of test temperature. Microstructures of broken specimens show that both the particle fracture and the interface debonding affect the fracture behavior of the composites, and the interface debonding becomes the dominant fracture mechanism with increasing test temperature. Comparative results indicate that rich particles in the composites and excellent interface strength play great roles in enhancing tensile property by preventing the movement of dislocations.

Study on Modification of Waste Rubber Powder in Cement-Based Composites Mixed with Waste Rubber Powder

In view of the disadvantage that the mechanical properties of cement-based composites can be significantly reduced by incorporating waste rubber powder in situ, the surface modification methods of the original rubber powder by coupling agent KH560, sodium hydroxide, polyvinyl alcohol (PVA), methyl hydroxyethyl cellulose ether (MHEC) and tetraethyl orthosilicate (TEOS) as precursors were adopted respectively. The modification of waste rubber powder was studied by Change rate of mortar strength of cement-based composite mortar mixed with waste rubber powder. The results show that the hybrid modification method using tetraethyl orthosilicate as precursor has better ef-fect. When 5 phr ethyl orthosilicate is added, the compressive strength and flexural strength of cement-based composite mortar can be increased by 31.7% and 28%. Scanning electron microscopy (SEM) results show that the surface of waste rubber powder with good modification effect has many pro-trusions and flake-like porous structures which are beneficial to its bonding with cement-based materials.

Smart Behavior of Carbon Fiber Reinforced Cement-based Composite

The electrical characteristics of cement-based material can be remarkably improved by the addition of short carbon fibers. Carbon fiber reinforced cement composite (CFRC) is an intrinsically smart material that can sense not only the stress and strain, but also the temperature. In this paper, variations of electrical resistivity with external applied load, and relation of thermoelectric force and temperature were investigated. Test results indicated that the electrical signal is related to the increase in the material volume resistivity during crack generation or propagation and the decrease in the resistivity during crack closure. Moreover, it was found that the fiber addition increased the linearity and reversibility of the Seebeck effect in the cement-based materials. The change of electrical characteristics reflects large amount of information of inner damage and temperature differential of composite, which can be used for stress-strain or thermal self-monitoring by embedding it in the concrete structures.

The Influence of Carbon Nanotubes and Nano-Silica Fume on Enhancing the Damping and Mechanical Properties of Cement-Based Materials

This paper conducted experimental studies on the damping and mechanical properties of carbon nanotube-nanosilica-cement composite materials with different carbon nanotube contents. The damping and mechanical properties enhancement mechanisms were analyzed and compared through the porosity structure test, XRD analysis, and scanning electron microscope observation. The results show that the introduction of nanosilica significantly improves the dispersion of carbon nanotubes in the cement matrix. At the same time, the addition of nanosilica not only effectively reduces the critical pore size and average pore size of the cement composite material, but also exhibits good synergistic effects with carbon nanotubes, which can significantly optimize the pore structure. Finally, a rationalization suggestion for the co-doping of nanosilica and carbon nanotubes was given to achieve a significant increase in the flexural strength, compressive strength and loss factor of cement-based materials.

High-Performance and Multifunctional Cement-Based Composite Material

Concrete is a continuously evolving material, and even the definition of high-performance concrete has changed over time. In this paper, high-performance characteristics of concrete material are considered to be those that support the desirable durability, resilience, and sustainability of civil infrastructure that directly impact our quality of life. It is proposed that high-performance material characteristics include tensile ductility, autogenous crack-width control, and material “greenness.” Furthermore, smart functionalities should be aimed at enhancing infrastructure durability, resilience, and sustainability by responding to changes in the surrounding environment of the structure in order to perform desirable functions, thus causing the material to behave in a manner more akin to certain biological materials. Based on recent advances in engineered cementitious composites (ECCs), this paper suggests that concrete embodying such high-performance characteristics and smart multifunctionalities can be designed, and holds the potential to fulfill the expected civil infrastructure needs of the 21st century. Highlights of relevant properties of ECCs are provided, and directions for necessary future research are indicated.

The Smart Behavior of Cement-based Composite Containing Carbon Fibers under Three-point-bending Load

The influences of the fiber volume fraction on the electrical conductivity and the fraction change of electrical resistance under three-point-bending test were discussed.It is found that the relationship beween the electrical conductivity of composites and the fiber volume fraction can be explained by the percolation theory and the change of electrical resistance of specimens reflects to the process of loading.The sensitivity and the response of the change of electrical resistance to the load for specimens with different fiber volume fractions are quite different.which provide an important guide for the manufacture of conductive and intrinsically smart carbon fiber composite.

Effect of Polyaniline/manganese Dioxide Composite on the Thermoelectric Effect of Cement-based Materials

To enhance the thermoelectric effect of cement-based materials,conductive polyaniline(PANI)modified MnO_(2)powder was synthesized and used as a thermoelectric component in the cement composites.The nanostructured PANI was deposited on the surface of the nanorod-shapedα-MnO_(2)particle and the weight ratio of PANI to MnO_(2)was 22.3:77.7 in the composite.The synthesized PANI/MnO_(2)composite was nanostructured according to the SEM image.The test results of the thermoelectric properties proved that the PANI/MnO_(2)composite was effective as the Seebeck coefficient and electrical conductivity values of the cement composites with PANI/MnO_(2)inside were 3-4 orders of magnitude higher than those of pure cement paste and the thermal conductivity values of these cement samples were similar.The obtained maximum figure of merit(ZT)value(2.75×10^(-3))was much larger than that of conductive materials reinforced cement-based composites.The thermoelectric effect of cement composites is mainly enhanced by the increased Seebeck coefficient and electrical conductivity in this work.

Spray Atomized and Codeposited Al-Li Based Metal-matrix Composites Processing and Properties

In spray atomization and codeposition, a molten stream of metal is disintegrated into a fine dispersion of droplets by high velocity gas jets. The resulting semi-solidified droplets are directed towards a substrate where they impact and collect as rapidly solidified splats. Relatively high rates of solidification are achieved as a result of the thinness of the splats and the rapid heat extraction during flight and upon impacting with the substrate. The processing method uses codeposition of the metallic semi-solidified droplets (metallic matrix) with the injected reinforcement ceramic particles. In the present paper, the microstructures, mechanical properties, interfacial properties, thermal stability and aging behaviour of spray atomized and codeposited Al-Li-X MMC's (injected X=SiC, Al2O3) are reported and correlated to the processing conditions.

Effects of the Component and Fiber Gradient Distributions on the Strength of Cement-based Composite Materials

The effects of the component gradient distribution at interface and the fiber gradient distribution on the strength of cement-based materials were studied. The results show that the flexural strength and compressive strength of the mortar and concrete with interface component and fiber gradient distributions are obviously improved. The strengthes of the fiber gradient distributed mortar and concrete (FGDM/C) are higher than those of fiber homogeneously distributed mortar and concrete (FHDM/C). To obtain the same strength, therefore, a smaller fiber volume content in FGDM/C is needed than that in FHDM/C. The results also show that the component gradient distribution of the concrete can be obtained by means of multi-layer vibrating formation.

Multi-scale Modeling of the Effective Chloride Ion Diffusion Coefficient in Cement-based Composite Materials

N-layered spherical inclusions model was used to calculate the effective diffusion coefficient of chloride ion in cement-based materials by using multi-scale method and then to investigate the relationship between the diffusivity and the microstructure of cement-basted materials where the microstructure included the interfacial transition zone （ITZ） between the aggregates and the bulk cement pastes as well as the microstructure of the bulk cement paste itself. For the convenience of applications, the mortar and concrete were considered as a four-phase spherical model, consisting of cement continuous phase, dispersed aggregates phase, interface transition zone and their homogenized effective medium phase. A general effective medium equation was established to calculate the diffusion coefficient of the hardened cement paste by considering the microstructure. During calculation, the tortuosity （n） and constrictivity factors （Ds/Do） of pore in the hardened pastes are n^3.2, Ds/Do=l.Ox 10-4 respectively from the test data. The calculated results using the n-layered spherical inclusions model are in good agreement with the experimental results; The effective diffusion coefficient of ITZ is 12 times that of the bulk cement for mortar and 17 times for concrete due to the difference between particle size distribution and the volume fraction of aggregates in mortar and concrete.

Preparation of Expanded Graphite-based Composites by One Step Impregnation

A new method for preparing expanded graphite-based composites （EGCs） was developed.The obtained samples were characterized by scanning electron microscopy （SEM）,transmission electron microscope （TEM） and nitrogen adsorption.The experimental results indicated that the EGCs was not simply mechanical mixture of EG and activated carbon,instead the activated carbon was coated on the surface of interior and external pores of the EG in the form of thin carbon layer.The thickness of the activated carbon layer was nearly one hundred nanometers by calculation.It was shown that the higher the impregnation ratio and the activation temperature were,the easier the porosity development would be.And the BET surface area and the total pore volume were as high as 1978 m2/g and 0.9917 cm3/g respectively at 350℃ with an impregnation ratio of 0.9.

Microstructure and hardness of Mg-based composites reinforced with Mg_2Si particles

Magnesium powders were mechanically alloyed with SiO2 powder particles having different particle sizes using nigh-energy ball milling techniques under Ar atmosphere for 1 h. The powders were consolidated with cold pressing under 560 MPa. They were then sintered at 550℃ for 45 min under Ar atmosphere. The composites obtained on the Mg-SiO2 system were investigated using the Archimedes principle, a differential scanning calorimeter, X-ray diffraction, optic microscopy, and scanning electron microscopy. For the mechanically alloyed powders, the solid-state reaction of the synthesis of Mg2Si and MgO progressed further during sintering of the materials. The results showed that the strengthening mechanisms were dependent on dispersion hardening of fine Mg2Si and MgO particulates dispersed homogeneously in the matrix. Mg-

SYNTHESIS AND MECHANICAL PROPERTIES OF NiAlBASED COMPOSITES

Mechanical alloying and hot pressing have been applied to prepare fine structured NiAl TiC, NiAl TiB 2 and NiAl γ composites. The formation mechanism, microstructure and compressive properties of these composites have been investigated. In addition, NiAl Cr(Mo) alloys containing different amounts of TiC particulate have been fabricated by hot pressing aided exothermic synthesis(HPES) plus hot isostatic pressing(HIP). Their mechanical properties including Vickers hardness, fracture toughness and compressive strength were tested. Deformation behavior at high temperatures has been studied extensively.