Fiber-reinforced Cement Research Articles

Innovative Bridge Deck System Using High-Performance Fiber-Reinforced Cement Composites

This paper details the basis for an innovative concept related to building better and more durable concrete bridge decks. The decks are assumed to be supported by beams of any structural material. The typical deck is made with high-performance, fiber-reinforced cement composites (HPFRCC) and reinforced with only 1 layer of transverse bottom reinforcing bars for positive moment resistance. Thus, reinforcement is as far away as possible from the top surface of the deck and protected from intrusion of corrosive agents. The HPFRCC is designed to: 1) balance part of the negative moment; 2) allow the development of an effective plastic hinge mechanism, with hinges forming at supports and in spans, under ultimate loading; and 3) keep crack widths extremely small under service conditions. A dramatically higher durability is expected. A brief summary of test results and analytical modeling is also provided.

Fiber alignment and property direction dependency of FRC extrudate

This paper studies the phenomenon of fiber alignment during the extrusion process. The fiber alignment is largely dependent on shapes of dies and the compression as well as the shear force generated in the extruder. The fiber alignment orientation, of course, would lead to direction dependency of the tensile properties of fiber-reinforced cement (FRC) extrudates. Such a dependency has been investigated in present study. It is found that when fiber volume ratio is small, say 1% of the glass fiber, the majority of the fiber can be aligned in the extrusion direction. As a result, the tensile strength of the thin plate along the extrusion direction is much higher than that along the transverse direction. When the total fiber volume ratio is increased to 2% or 4%, the fiber volume along the transverse direction is largely increased although the percentage of the fiber aligned along the extrusion direction is still higher. Thus, the tensile strength at a transverse direction can be significantly enhanced. In fact, the tensile strength of the samples along the transverse direction is almost the same as that along the extrusion direction when the fiber volume ratio reaches 2%. Furthermore, the strength of the sample at the extrusion direction does not increase proportionally to the fiber volume ratio. For the comparison purpose, plain sheets without any fibers have been prepared by both casting and extrusion. Mechanical properties of the sheets have also been tested and the test results show that extrusion process and fiber addition do have effects on enhancing the tensile properties. Polymer coating on the surface of the samples has also been used to improve the tensile properties of the extrudates with low fiber volume ratio, which shows some promising results.

Enhancement of aging resistance of glass fiber reinforced cement

Long-term weathering tests revealed that glass fiber-reinforced cement (GFRC) might exhibit tensile strength reduction and ductility loss with aging. The main goal of this research was to assess the effectiveness of polyvinyl alcohol (PVA) powder in enhancing the durability characteristics of GFRC sheets. Accelerated aging was achieved by using low pressure steam curing. The strength and ductility of GFRC sheets were measured by the direct tension test. The test results show that the incorporation of PVA powder into GFRC improves the mechanical behavior and changes the failure mode from brittle to ductile. To investigate the mechanism of the enhancement, the fiber-matrix interface was examined by polarizing optical microscopy and scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDAX). It was found that the addition of the PVA powder results in the deposition of a polymeric film on the fiber surface and thus prevented the accumulation of calcium hydroxide in the interfacial zone. The use of the PVA powder led to a more ductile interfacial microstructure and to better bonding between fiber and matrix, which is believed to be responsible for the tensile property enhancement.

Effects of Pressure on Resistance to Freezing and Thawing of Fiber-Reinforced Cement Board

Effects of Pressure on Resistance to Freezing and Thawing of Fiber-Reinforced Cement Board

The origin of nonlinear current–voltage behavior in fiber-reinforced cement composites

Two distinct slopes (resistances) are obtained in current–voltage ( I– V) plots of discontinuous, conductive fiber-reinforced cement composites. The low-field resistance correlates with the DC resistance ( R DC) of each composite. The high-field resistance correlates with the intermediate frequency cusp resistance ( R cusp) in Nyquist (− Z imag vs. Z real) plots obtained using impedance spectroscopy (IS). A model is developed that is based on passive oxide film formation on copper or steel fiber surfaces at low fields ( I– V) or low frequencies (IS) due to the high pH pore solution of cement paste. With increase of field, leading to film breakdown (active or transpassive corrosion behavior), or increase of frequency, leading to short-circuiting of the passive layer, the fibers act as short-circuiting elements in the composite microstructure, resulting in a decrease in overall resistance.

Incorporation of fibres in geothermal well cements

Fibre-reinforced cements are of potential value in geothermal well cementing jobs due to their ability to withstand higher tensile stresses than conventional cements. Screening tests were performed to evaluate different fibre types with the objective of identifying systems offering the greatest improvement in cement tensile strength. The fibres investigated included steel, stainless steel, carbon, basalt and glass. The baseline cement matrix was standard Class G cement/40% silica flour and variations on this were latex-modification and lightweight formulations incorporating either perlite or microspheres. The fibres that showed the best performance at low volume fraction were 13 mm brass-coated round steel fibres. Steel and carbon microfibres also improved the tensile strength provided the volume fraction was high enough. Thermal and hydraulic properties of cements reinforced with steel fibres were measured and compared with unreinforced mixes. Based on the results, selected fibre types will be used in further property characterization studies and engineering analysis of geothermal wells completed with fibre-reinforced materials.

Using acoustic emission to quantify damage in restrained fiber-reinforced cement mortars

This paper describes the use of acoustic emission (AE) for monitoring early-age cracking in restrained fiber-reinforced mortars. A steel-testing frame was used to prevent the length reduction associated with drying. AE sensors placed on both unrestrained and restrained specimens detected a high degree of activity that may be attributed to surface microcracking caused by moisture gradients that cause the surface to shrink more rapidly than the core. It was found that as the concrete neared the age of visible cracking, the acoustic waves generated in the restrained specimens had a greater amplitude and duration. For this reason, acoustic energy was utilized for these investigations. An increase in acoustic energy was detected before cracks were observed in the restrained specimens. It is believed that the role of fiber reinforcement is twofold. First, fibers arrest cracks thereby preventing unstable crack propagation, and second, they restrain the crack from opening preventing the cracking from becoming visible until a later age.

Laminate of Reformed Bamboo and Extruded Fiber-Reinforced Cementitious Plate

This paper introduces two types of laminates, double-layer reformed bamboo (cross-ply) laminate and fiber-reinforced cementitious (FRC) plate-reformed bamboo laminate. The second laminate is made of reformed bamboo and extruded FRC plates. The reformed bamboo is ductile and tough and has a high tensile strength, while the FRC plate has higher compressive strength. The FRC plate-reformed bamboo laminate fully utilizes the advantages of each component to achieve superior mechanical properties. A series of flexural, impact, and compression after impact (CAI) tests have been conducted to evaluate the performance of both laminates. It is found that the newly developed FRC plate-reformed bamboo laminate has a high flexural strength (up to 96 MPa), excellent impact resistance, good ductility, and outstanding toughness. Hence, it has good potential in engineering applications.

Enhancement of durability of glass fiber-reinforced cement with PVA

Enhancement of durability of glass fiber-reinforced cement with PVA

Influence of Matrix Ductility on Tension-Stiffening Behavior of Steel Reinforced Engineered Cementitious Composites (ECC)

In this paper, the interaction of structural steel reinforcement and high-performance fiber-reinforced cement composites (HPFRCC) in uniaxial tension is examined. The effects of cementitious composite ductility on the steel reinforced composite deformation behavior are experimentally studied and contrasted to normal reinforced concrete (RC). The substitution of brittle concrete with an engineered cementitious composite (ECC), a particular type of HPFRCC with strain hardening and multiple cracking properties, has shown to provide improved load-deformation characteristics in terms of RC tensile strength, deformation mode, and energy absorption. Analysis of the deformation mechanisms suggests that combining steel reinforcement and ECC results in composite action, where unlike in RC or regular FRC, both constituent materials deform compatibly in the postcracking and postyielding deformation process. This deformation compatibility results in a more uniform strain distribution in reinforcement and composite matrix, reduced interfacial bond stress, and controlled damage at relatively large inelastic composite deformations. Research described here focuses on the influence of composite ductility on the deformation behavior of the RC and its effects on the strain distribution in the reinforcement, composite matrix, and interfacial bond.

Enhancement of durability of glass fiber-reinforced cement with PVA

The main thrust of this research was to determine the effectiveness of polyvinyl alcohol (PVA) powder in enhancing the durability of short GFRC materials. Accelerated aging of the materials was achieved through low\|pressure steam curing in a moist chamber. The strength and ductility of GFRC were measured by the direct tension test, which showed that incorporation of PVA powder into GFRC could improve its mechanical behaviour and turn it from brittle to ductile. To investigate the mechanism of the tensile strength enhancement, the fiber\|matrix interface was examined by polarizing optical microscopy and scanning electron microscopy (SEM) with energy dispersive X\|ray analysis (EDAX). It was found that PVA powder tended to migrate to the fiber\|matrix interfacial zone and thus prevented the accumulation of calcium hydroxide in this area. PVA film around the fiber resulted in a more ductile interfacial microstructure and better bonding between fiber and matrix, which should be responsible for enhancing the tensile property and preventing the aging of GFRC. Furthermore, PVA powder reduced the microhardness and brittleness at the interface.

Impact Response of Ultra-High-Strength Fiber-Reinforced Cement Composite

Impact Response of Ultra-High-Strength Fiber-Reinforced Cement Composite

Impedance spectroscopy of fiber-reinforced cement composites

The addition of chopped conductive fibers to cement matrices results in a characteristic “dual-arc” electrical impedance spectrum below the percolation threshold. This behavior can be explained on the basis of a “frequency-switchable fiber coating” model, in which a “coating” (e.g., passive oxide film on steel or charge transfer resistance/double layer on other conductors) insulates the fibers at DC and low AC frequencies, but is shorted out at higher frequencies, where the fibers become short-circuit paths in the composite microstructure. The present work investigates various factors governing the impedance spectra of fiber-reinforced cement composites – fiber aspect ratio, fiber volume fraction, fiber orientation (relative to field direction), and fiber shape. The “gamma” factor (ratio of the low frequency arc diameter to DC resistance) is a useful parameter to characterize the microstructure–property relationships of fiber-reinforced composites.

Regulations will boost European markets for flame retardants

The limitations of the traditional material design approach in driving properties to extreme values and handling multiple design criteria and variables can be overcome by applying the optimization approach. Fiber-reinforced cement based composites based on strong aggregates and exhibiting approximately bilinear fiber pullout behavior are optimized in the present study for a given compressive strength f′c with a view to maximizing their uniaxial tensile strength f′t and fracture energy GF. Relations for the bridging stresses prior to and during fiber pullout are established using fracture mechanics. The mix design leads to nonlinear, single, or multicriterion maximization problems for the objective functions f′t and lch = EGF/f′t2 (characteristic length), subject to an equality constraint on f′c. In this way, optimal values for the microstructural parameters (fracture toughness of paste, length of fiber, and volume fractions and diameters of aggregate and fiber) are obtained.

Pipeline Rehabilitation with Fiber-Reinforced Mortar Lining

This paper introduces an innovative method of in situ water main rehabilitation to solve the metallic pipeline corrosion problem while preventing future lead and lime leaching. The existing main is used as a form, and a thin layer of fiber-reinforced cement mortar lining is applied on the internal surface to form the rehabilitated main. To compare the feasibility of the approach to existing methods of pipe lining, experimental investigations are carried out. The objective is to compare the water quality, pipe friction, and structural strength of pipe sections of the proposed design in contrast to those of existing methods. The results show that the fiber-reinforced lining provides an improved pipeline rehabilitation option, for which the iron content and turbidity of the transported water are much lower than those from other methods. Increased carrying capacity and structural strength, as well as the provision of additional tensile strength for the rehabilitated mains, are also some of the advantages. With this method, a more resilient pipe with protection from water contamination and pipeline corrosion resulted.

Carbon fiber-reinforced cement as a strain-sensing coating

Cement paste containing short carbon fibers was found to be an effective strain-sensing coating. The coating (with fibers) was on either the tension side or the compression side of a cement specimen (without fiber) under flexure. The resistance was measured with surface electrical contacts on either side. The resistance increased reversibly on the tension side upon loading and decreased reversibly on the compression side upon loading. The behavior was similar whether the strain-sensing coating contained silica fume or latex.

Uniaxial compression in carbon fiber-reinforced cement, sensed by electrical resistivity measurement in longitudinal and transverse directions

Uniaxial compression of carbon fiber-reinforced cement pastes in the elastic regime caused reversible decreases in both longitudinal and transverse electrical resistivities. In contrast, uniaxial tension had been previously reported to cause reversible increases in both resistivities. The fractional change in resistivity per unit strain is higher in magnitude for carbon fiber silica fume cement paste than carbon fiber latex cement paste.

Electric polarization in carbon fiber-reinforced cement

Electric polarization induced an increase of the measured electrical resistivity of carbon fiber-reinforced cement paste during resistivity measurement. The effect was diminished by increasing the conductivity of the cement paste through the use of carbon fibers that were more crystalline, the increase of the fiber content, or the use of silica fume instead of latex as an admixture. Intercalation of crystalline fibers further increased the conductivity of the composite, but it increased the extent of polarization. Voltage polarity switching effects were dominated by the polarization of the sample itself when the four-probe method was used, but were dominated by the polarization at the contact–sample interface when the two-probe method was used. Polarization reversal was faster and more complete for the latter.

Enhancing the Seebeck effect in carbon fiber-reinforced cement by using intercalated carbon fibers

The absolute thermoelectric power of carbon fiber-reinforced cement paste was rendered as negative as −17 μV/°C by using bromine-intercalated carbon fibers, which had a high concentration of holes. The corresponding paste with pristine carbon fibers exhibited absolute thermoelectric power as negative as −0.8 μV/°C only.

Role of Interfaces in Controlling Durability of Fiber-Reinforced Cements

Microstructural changes that occur over time around fibers in the cement matrix, leading to an enhanced bond and stiffening of the interfacial transition zone, may result in a reduction in the mechanical properties of the composite. Micromechanical modeling of processes of this kind suggest that such aging trends may occur in microfiber reinforcement but not in macrofiber reinforcement. Degradation in mechanical properties of the composite will show up only when a “pessimum” combination of parameters exist, particularly brittle microfibers in a very dense matrix. Therefore, in the development of new cementitious composites, interfacial effects of this kind should be considered, because aging due to such mechanisms can be demonstrated to occur in practice. Thus, it is not sufficient to assess the durability of cementitious composites by considering only the chemical stability of the fiber in the alkaline cementitious matrix.