碳纤维水泥基材料的机敏特性研究

水泥基材料是一种高电阻率的惰性材料,通过掺入一定体积含量(0.2 vol%~1.2 vol%)的短切碳纤维,可显著提高其电导率。本文作者研究了碳纤维水泥基材料表观电导特性与其内部微观结构的关系,探讨了电阻率的变化与材料所受外部荷载的关联性。结果表明碳纤维水泥基材料具有实时诊断内部损伤的机敏性:当水泥基材料内部裂纹产生或扩展时,表现为材料电阻率上升;而当水泥基材料内部裂纹闭合时,其电阻率下降。碳纤维水泥基材料的电阻变化与所受荷载呈良好的线形关系;而不含碳纤维的普通水泥基材料在整个受荷过程中,其电导特性则无明显变化。碳纤维水泥基材料电导特性的变化反映了水泥基材料内部损伤状况丰富的信息,根据这一特性可以及时预报水泥基材料内部潜在的损伤状况,有效地防止灾难性的破坏。     

导电功能集料碳纤维水泥基复合材料及其压敏性能

利用石墨粉和粘土基质烧制成导电陶粒,与碳纤维共同组成复合导电相,制备得到导电功能集料碳纤维水泥基复合材料。采用Instron5882材料试验机,动态电阻应变仪和直流稳压电源测试系统研究了其压敏性,发现压应力对其电阻值有显著影响;从开始加载至破坏全过程电阻值变化表现出均匀下降、平衡和迅速上升3阶段;在低加载应力循环下材料电阻变化值与应力有良好相关性,高加载应力循环下因损伤裂纹的不可复原性而使电阻出现不可逆增加;加载速率对电阻变化也有影响,低加载应力时加载速率影响较小,高加载应力时影响较大。     

Nondestructive sensing evaluation of surface modified single-carbon fiber reinforced epoxy composites by electrical resistivity measurement

Nondestructive sensing of a single-carbon fiber reinforced epoxy composites was evaluated by the measurement of electrical resistivity under reversible cyclic loading. For the strain–stress sensing, the strain up to the maximum load of a bare carbon fiber itself is larger than that of carbon fiber composite. As curing temperature increased, apparent modulus up to the maximum load increased and the elapsed time became shorter. Higher residual stress might contribute to the improved interfacial adhesion. The strain up to the maximum load at low temperature was larger than that at higher temperature. The strain of electrodeposition (ED) treated carbon fiber was smaller than that of the untreated carbon fiber composite until the maximum load reached. This could be due to higher apparent modulus of composite based on the improved interfacial shear strength (IFSS). Since the electrical resistivity was responded well quantitatively with various parameters, such as matrix modulus, the fiber surface modification, the electrical resistivity measurement can be a feasible method of nondestructive sensing evaluation for conductive fiber reinforced composites inherently.     

导电水泥基材料的制备及其电阻率测试方法研究

通过试验比较研究了短切碳纤维在水泥基材料中的两种不同分散工艺,利用SEM观察证实了碳纤维水泥基材料的电阻率主要取决于碳纤维的分散程度和所形成的导电网络的搭接状况。针对导电水泥基材料的电阻率测试,比较了两极组合法与四极法的差异。研究结果表明,湿拌法有利于碳纤维的分散,并可在相同的纤维掺量下获得较小的电阻率。与两极组合法相比,四极法可以避免测试过程中的极化现象,并可消除测试电极与碳纤维水泥基材料之间的接触电阻,因而可以作为导电水泥基材电阻率测试的理想方法。     

纳米导电纤维填充天然胶乳复合材料的电性能研究

用纳米导电纤维填充天然乳得复合材料,研究了复合材料的导电性、介电性以及温度对复合材料电阻率的影响。结果表明,随纳米导电纤维填充份数的增加,复合材料的电阻率下降,介常数增大;电阻率对温度的依赖性产大,并且当纳米导昵水在胶乳中形成导电网络时,电阻率和表面电阻率随温度同表现出不同的变化趋势。     

Pitch-matrix composites for electrical,electromagnetic and strain-sensing applications

Pitch-matrix composites for deicing, electromagnetic shielding and strain sensing have been developed by using carbon fiber (discontinuous) and carbon black as electrically conductive fillers. A composite with carbon fiber (5 vol%) as the sole filler is effective for strain sensing, which functions by the electrical resistivity increasing reversibly with tensile strain. A composite with carbon fiber (3.4 vol%) and carbon black (1.5 vol%) is less effective for strain sensing and is lower in tensile strength, modulus and ductility, but it is lower in the electrical resistivity. A composite with carbon black (7 vol%) as the sole filler is very high in resistivity, but exhibits high storage modulus. Either carbon fiber or carbon black as filler increases the storage modulus, decreases the resistivity, renders the ability to provide EMI shielding and increases the softening temperature.     

The performance of stress-sensing smart fiber reinforced composites in moist and sodium chloride environments

The addition of carbon nano-fibers (CNF) to fiber reinforced composites (FRC) based on polyvinyl alcohol fibers can improve the flexural strength of composites. Depending on applied stress, moisture content, and exposure to chloride solutions, the developed CNF composites exhibit specific levels of electrical conductivity. Reported research has demonstrated a strong dependency of electrical response of composite to crack formation in moist and NaCl environments. It was demonstrated that the sensitivity to strain and chloride solution can be enhanced by CNF. The developed technology and smart composite material are scalable for application in nondestructive monitoring of concrete structures that require improved integrity under service loads and stability in harsh environments.     

掺CCCW的碳纤维石墨水泥基复合材料的导电及压阻特性

利用四电极法研究了内掺水泥基渗透结晶防水材料(CCCW)的碳纤维石墨水泥基复合材料试样(40 mm×40 mm×40 mm)的导电特性及其在循环荷载作用下的压阻特性,分析讨论了碳纤维石墨水泥砂浆的体积电阻率及压阻特性随石墨掺量的变化规律。碳纤维和CCCW的掺量分别为水泥质量的1%和4%;石墨掺量分别为水泥质量的0%、10%、20%、30%、40%和50%。结果表明,添加CCCW的碳纤维石墨砂浆试样的体积电阻率随石墨掺量的增加迅速下降,并存在渗滤现象,渗滤阈值为20%左右。在循环荷载作用下,不同石墨掺量试样的电阻和应力存在一定的对应关系。石墨掺量为水泥质量的20%～30%时,碳纤维石墨水泥砂浆试样的体积电阻率与压应力呈现良好的可重复性,电阻值在应力加载时几乎呈线性下降,而卸载时增加。     

超薄预浸料对碳纤维/环氧树脂复合材料导电性能的影响

为了协同提高碳纤维/环氧树脂（CF/EP）复合材料的电性能和力学性能,采用碳纤维丝束展宽、浸润一体化的工艺方法,将12K CF展宽预浸制备成厚度分别为0.02 mm、0.03 mm、0.08 mm、0.10 mm的CF/EP预浸料及其单向层合板,分析测试了微观结构尺度对CF/EP复合材料层合板电阻率、电阻率随温度及在拉伸载荷作用下响应的影响机制。结果表明,随着CF/EP预浸料厚度从0.10 mm减小到0.02 mm,CF/EP复合材料单向层合板中大尺度树脂富集区所占比例明显减小,厚度方向的电阻率从151.3 Ω·cm减小到32.1 Ω·cm,导电性能提高了约5倍;随着温度升高,CF/EP复合材料层合板电阻率逐步下降,厚预浸料层合板沿厚度方向电阻率的下降速率高于薄预浸料层合板;在载荷作用下由CF/EP薄预浸料制成的CF/EP复合材料层合板的电阻率具有较高的稳定性,表明预浸料薄层化有助于提高CF/EP复合材料抵抗载荷作用的能力,从而获得较高的力学性能和电性能。实验结果为CF/EP复合材料结构-功能一体化设计提供了基础。      

粉煤灰／海泡石纤维复合沥青混合料的制备与性能研究

从海泡石纤维和粉煤灰纤维的微观结构特性出发，进行粉煤灰，海泡石复合纤维增强沥青复合材料的制备。通过路用性能试验，研究了海泡石纤维和粉煤灰纤维对沥青混合料性能的影响以及结合机理。结果表明，添加适量海泡石和粉煤灰纤维可以制备性能优良的纤维复合沥青混合料。海泡石纤维对沥青表现极强吸持能力，有效调节沥青与胶浆的含量。粉煤灰纤维在沥青中主要起加固和改善混合料的作用。两种纤维的添加，使沥青混合料的高温变形性、水稳定性、低温抗裂性和抗疲劳性等显著提高。     

Electrical behavior of carbon fiber polymer-matrix composites in the through-thickness direction

The electrical behavior of continuous carbon fiber epoxy-matrix composites in the through-thickness direction was studied by measuring the contact electrical resistivity (DC) of the interlaminar interface in the through-thickness direction. The contact resistivity was found to decrease with increasing curing pressure and to be higher for unidirectional than crossply composites. The lower the contact resistivity, the greater was the extent of direct contact between fibers of adjacent laminae. The activation energy for electrical conduction in the through-thickness direction was found to increase with increasing curing pressure and to be lower for unidirectional than crossply composites. The higher the activation energy, the greater was the residual interlaminar stress. Apparent negative electrical resistance was observed, quantified, and controlled through composite engineering. Its mechanism involves electrons traveling in the unexpected direction relative to the applied voltage gradient, due to backflow across a composite interface. The observation was made in the through-thickness direction of a continuous carbon fiber epoxy-matrix two-lamina composite, such that the fibers in the adjacent laminae were not in the same direction and that the curing pressure during composite fabrication was unusually high (1.4 MPa).     

Electrical crack length measurement and the temperature dependence of the Mode I fracture toughness of carbon fibre reinforced plastics

The conventional optical crack length measurement in fracture toughness testing is unsuitable for tests carried out in a chamber, like temperature tests. An electrical method has therefore been developed which determines the crack length on the basis of a change of electrical resistivity. Compared with optical measurements this method has proved to be very accurate. With this method the Mode I fracture toughness of a carbon fibre reinforced epoxy composite was determined over the temperature range from −55°C to 120°C. It was found that the fracture toughness rises with increasing temperature. At low temperatures the values were constant or increased slightly, with minimum at about 0°C.     

Application of rock wool waste in cement-based composites

This study investigates the properties of cement-based composites with addition of various rock wool wastes. The rock wool wastes are an insulating material. This study used rock wool waste with a cylindrical size distribution ranging from 17 to 250 μm, 30% of which is less than 150 μm. Rock wool waste can be used as a suitable substitute for coarse and fine aggregates, saving on the cost of natural aggregates and minimizing the environmental impact of solid waste disposal. In addition, because the composition of rock wool waste is similar to other pozzolan materials such as fly ash, ground granulated blast-furnace slag (GGBS), and silica fume, it can be considered as a supplementary cementitious material. Experimental results show that partially replacing natural aggregates with rock wool wastes improves the compressive strength, splitting tensile strength, abrasion resistance, absorption, resistance to potential alkali reactivity, resistivity, and chloride-ion penetration of cement-based composites. These improved properties are the result of the dense structure achieved by the filling effect of pozzolanic product. Pozzolanic strength activity index (PSAI) results and scanning electron microscope (SEM) observations confirm these findings. Therefore, rock wool wastes can act as either a cementitious material or inert filler in cement-based composites, depending on the particle size. The critical size appears to be 75 μm.     

碳纳米管增强水泥基复合材料的自收缩及抗裂性能碳纳米管增强水泥基复合材料的自收缩及抗裂性能

水泥基材料的收缩开裂已经成为其破坏的一个主要原因,受到国内外关注,碳纳米管（CNTs）作为一种纳米纤维状材料,可能可以抑制水泥基材料收缩。本文将CNTs放入水中,经过超声处理分散后,形成CNTs分散液,设置不同的CNTs掺量将其掺入到水泥基材料中,通过波纹管实验及圆环试验对该种新型复合材料的自收缩及抗裂性能进行研究。结果表明:CNTs的掺入可以很大程度上抑制水泥基材料的自收缩,最高降低率可到40%以上,且明显提高了水泥基材料的抗裂性能。水灰比的增加会提高CNTs对水泥基材料收缩的抑制效果。当CNTs的掺量为0.1wt%时,可以获得最优效果。同时,CNTs的掺入不仅对水泥基材料自收缩有抑制作用,一定程度上也会抑制水泥基材料的干燥收缩。通过将CNTs掺入到建筑结构关键部分的水泥基材料中,可以提高建筑安全系数。      

Self-healing of mechanical damage of polyethylene/microcapsules electrical insulation composite material

Polyethylene (PE) cable has become an important carrier of the modern power grid due to its excellent electrical insulation performance. However, small damages can inevitably occur during the preparation and operation of the materials, which can distort electric field and trigger discharge, seriously threatening power supply safety. The self-healing of insulation materials by doping microcapsules is a new research innovation. In this paper, the self-healing PE/microcapsules insulation composite material was prepared, and the self-healing behavior of mechanical damage was emphatically analyzed by scratch damage test and crack propagation simulation. The results show that the composite material with 1 wt% microcapsule has better insulation strength. Moreover, the composite material can fill the defective structures, restore local electrical properties, and reverse the deterioration process of the material. The properties of PE/microcapsules composite material are mainly related to the characteristics of the microcapsule itself and the interface introduced by the microcapsules. The properties of the repaired product can directly affect the recovery degree of the damaged area. The stress action during damage can smoothly trigger its self-healing behavior. In conclusion, the PE composite material doped with 1 wt% microcapsules can achieve a good self-healing effect on mechanical damage.

     

Sensing damage in carbon fiber and its polymer-matrix and carbon-matrix composites by electrical resistance measurement

Fatigue damage was sensed in real time in continuous carbon fiber and its polymer-matrix and carbon-matrix composites by electrical resistance measurement in the fiber direction. In a polymer-matrix composite, fiber breakage overshadows fiber damage in causing the resistivity of the composite to increase irreversibly. In a carbon-matrix composite, fiber breakage and matrix cracking caused the resistivity to increase irreversibly, such that these two mechanisms cannot be distinguished. Fatigue damage was detected from 50% of the fatigue life onward for the polymer-matrix composite, and from 0% of the fatigue life onward for the carbon-matrix composite.     

Mechanical properties and durability characteristics of polymer- and cement-based repair materials

This study was conducted to evaluate the mechanical properties and durability characteristics of nine polymer- and cement-based repair mortars. Mechanical properties, such as compressive, tensile and flexural strength, elastic modulus, shrinkage and thermal expansion were studied. The durability characteristics of the repair materials were evaluated by measuring: (i) chloride permeability, (ii) electrical resistivity and (iii) carbonation depth. The mechanical properties of the selected repair mortars did not vary very significantly from each other. The elastic modulus of the polymer-based repair mortars was less than that of the cement-based repair mortars. This will lead to a reduced drying shrinkage cracking in the former repair mortars compared to the latter. The electrical resistivity of polymer-based repair mortars was more than that of cement-based repair mortars. Such a trend was not noted in the chloride permeability data. The chloride permeability in all the repair materials was very low according to ASTM C 1202 criteria. Enhanced carbonation was noted in some of the polymer-based repair mortars.     

Self-sensing piezoresistive cement composite loaded with carbon black particles

Strain sensors can be embedded in civil engineering infrastructures to perform real-time service life monitoring. Here, the sensing capability of piezoresistive cement-based composites loaded with carbon black (CB) particles is investigated. Several composite mixtures, with a CB filler loading up to 10% of binder mass, were mechanically tested under cyclic uniaxial compression, registering variations in electrical resistance as a function of deformation. The results show a reversible piezoresistive behaviour and a quasi-linear relation between the fractional change in resistivity and the compressive strain, in particular for those compositions with higher amount of CB. Gage factors of 30 and 24 were found for compositions containing 7 and 10% of binder mass, respectively. These findings suggest that the CB-cement composites may be a promising active material to monitor compressive strain in civil infrastructures such as concrete bridges and roadways.     

合成纤维种类对水泥基材料干缩开裂形态的影响

研究了相同体积掺量下(均为0.5%),聚丙烯(PP)纤维、尼龙单丝(Nycon RC)纤维和尼龙网状(MultiMesh)纤维对水泥基材料干缩开裂形态的影响.通过圆环法的对比实验,发现纤维表观形状和纤维直径对水泥基材料抗干缩开裂性能和裂缝分布有显著影响.基准水泥基材料呈现单一裂缝破坏模式,而合成纤维水泥基材料呈现了双缝或多缝开裂模式.结合SEM微观测试,分析了合成纤维与水泥基材料的界面性能,探讨了不同纤维种类限制水泥基于缩开裂的作用机理.