Fiber-reinforced Cement Research Articles

Laboratory Testing to Examine Deformations and Moments in Fiber-Reinforced Cement Pipe

Two 381 mm (15 in. nominal) diameter fiber reinforced cement pipes have been tested under embankment loading conditions to study pipe response in both low stiffness, fine grained backfill, and a high stiffness graded granular backfill. Pipe deformations and strains were measured and interpreted to provide insight into the effect of soil backfill on the deformations and moments that develop. Not surprisingly, the use of silty clay backfill resulted in greater pipe deflections while the stiffer granular backfill lead to greater load transfer to the surrounding ground. Calculations using elastic soil-pipe interaction theory were effective in estimating the observed changes in pipe diameter at typical service loads (overburden pressures of 100 kPa, i.e., 14.4 psi in the lower stiffness backfill and 200 kPa, i.e., 28.8 psi in the high stiffness backfill). Measured strain distributions show that the fiber reinforced pipe exhibited ovaling response similar to that seen for flexible and semiflexible pipes. As expected, tensile strains were observed on the outer surface at the springlines and the inner surface at the crown. Strains observed at the haunch were negligible, indicating that the bending moments within the pipe have conventional hourglass distribution, with negligible moments at shoulders and haunches. Differences in strain measured at the inner and outer surfaces were used with the elastic pipe modulus to calculate the experimental bending moments. Comparisons of those experimental bending moments with the bending moment calculated for a rigid pipe indicate that these FRC pipe structures are semirigid so that moments are reduced as a result of support provided by the surrounding soil. A design expression for moment arching factor (MAF or moment divided by the rigid pipe moments) developed in an earlier paper was found to provide reasonable estimates for the experimental moment values. Moment estimated using the design soil moduli of McGrath and MAF provide moment values that are reasonable and conservative relative to those that were observed.

Bond Behavior of Reinforcing Bars in Tensile Strain-Hardening Fiber-Reinforced Cement Composites

Bond between deformed reinforcing bars and concrete induces significant tensile stresses that lead to cracking in concrete due to its weak and brittle nature in tension. Contrary to plain concrete and conventional fiber-reinforced concrete, high-performance fiber-reinforced cement composites (HPFRCC S ) show strain-hardening response under tension and, thus, their use can lead to enhanced bond performance. Pullout-type tests comprising various types of loadings were carried out to investigate the influence of strain-softening and strain-hardening fiber-reinforced cementitious (FRC) composites on the bond strength and the bond stress-slip response of deformed reinforcing bars. Test results showed that the bridging effect provided by fibers in FRC composites after cracking can effectively provide post-clacking tensile capacity to the concrete matrix and limit crack width, thereby leading to enhanced bond resistance. HPFRCC specimens gave the best bond performance in terms of bond strength and stiffness retention capacity, as well as damage-control ability.

Development of Fibre Reinforced Cementitious Composite for Ceiling Application

Natural sponge fibre (Acanthus montanus) was used as reinforcement for ceiling materials in this research work. This fibre, being fairly strong and stiff as well as cheap and plentiful with low energy demand during manufacture, are strong contenders for the reinforcement of cementbased materials. The fibre, whose mass fraction was the variable in this work, was cut down into smaller sizes and mixed with pulverised waste paper, cement and water. The resulting slurry was then poured into rectangular moulds which were compacted until the excess water was expelled and resulting composites became hard. Demoulded samples were left to cure in the open laboratory air for 28 days. Flexural and water absorptivity tests were carried out on the various samples which showed that reinforcement and best mechanical properties were obtained at optimum fibre mass fraction of 4% when compared with the brittle matrix in the absence of reinforcement. These tests confirmed the possible use of sponge fibres as reinforcement in cement matrices for ceiling purposes.

Fracture of fiber-reinforced cement composites: effects of fiber dispersion

Short-fiber reinforcement is commonly used to improve various properties of cement-based materials, including their resistance to shrinkage cracking, post-cracking strength, and toughness. The spatial distribution of fibers within a structural component exhibits local variations that depend on many factors, including the methods of production. Local measures of fiber volume fraction can be much lower than the global average and such regions can act as flaws within the composite material. In addition, fiber orientation is restricted by any near surfaces of the structural component. Such non-uniformities of the fiber distribution can significantly affect fracture behavior and complicate the interpretation of fracture test results. This paper concerns the computational modeling of fiber- reinforced cement composites (FRCC), with attention to the effects of non-uniform fiber distributions. The simulations utilize lattice models of the matrix phase of the composite, based on the Voronoi tessellation of irregularly positioned nodes within the structural domain. A crack band approach provides energy-conserving, mesh-insensitive descriptions of fracture through the irregular lattice. Each fiber is explicitly modeled within the lattice framework. The fiber distributions are synthetically constructed within the structural domain, although experimentally determined fiber positions could be used. Models of simple tensile tests demonstrate a dependence of post-cracking strength and toughness on the spatial distributions of the fibers.

Effects of fibre-reinforced cement composites' ductility on the seismic performance of short coupling beams

The current study examines the effects of the deformation behaviour of cementitious material ductility on the seismic performance of shear-dominant coupling beams. Matrix ductility and reinforcement layouts comprise the main testing variables. Three short coupling beams with two different reinforcement arrangements and matrices are constructed and tested. They are subjected to cyclic loading under a suitable experimental set-up. All specimens are characterised by a shear span–depth ratio of 1·0. The reinforcement layouts consist of a classical scheme and diagonal scheme without confining ties. The effects of cement-based matrix ductility on crack patterns, failure modes, hysteretic characteristics and the ultimate shear load of the coupling beams are examined. The combination of a ductile cement-based matrix and steel reinforcement is found to result in improved energy dissipation capacity, simplification of reinforcement details, and damage-tolerant inelastic deformation behaviour. Test results show that high-performance hybrid fibre-reinforced cement-based composite (HPHFRCC) coupling beams behave better than normal reinforced concrete (RC) control beams. These results are evidenced by the tensile deformation capacity, damage tolerance and tensile strength of HPHFRCC material.

Functionally-graded fiber-reinforced cement composite: Processing, microstructure, and properties

A functionally-graded material system has been developed with a spatially tailored fiber distribution to produce a four-layered, functionally-graded fiber-reinforced cement composite (FGFRCC). Fiber volume fractions were increased linearly from 0% in the compression zone to 2% in the tensile zone so that more fibers were available to carry tensile stress in a bending beam experiment. Extrusion was used to produce single homogeneous layers of constant fiber volume fraction and highly oriented fibers. The FRCC layers with different fiber volume fractions were stacked according to the desired configuration and then pressed to produce an integrated FGFRCC. Polished cross-sections of the FGFRCC were examined using a scanning electron microscope (SEM) to measure the fiber distribution. Flexural tests were carried out to characterize the mechanical behavior and to evaluate the effectiveness of the designed fiber distribution. No delamination between layers was observed in the fractured specimens. Compared to homogeneous FRCC with the same overall fiber volume fraction, the FGFRCC exhibited about 50% higher strength and comparable work of fracture.

Electrical Resistivity, Pulse Velocity, and Compressive Properties of Carbon Fiber-Reinforced Cement Mortar

The electrical resistivity and mechanical properties of carbon fiber-reinforced cement mortar (CFRCM) were investigated. Both cylindrical and prism specimens were used in this investigation to determine the effects of size and shape of specimen on the physical and mechanical properties of the CFRCM systems. Carbon fiber loading was varied up to 6% (w/w), and water-to-cement ratios (w/c) of 0.5 and 1 were used. The specific electrical resistivity of the plain mortar with w/c ratio of 1 (>66,000Ohmm) was reduced to 3,750 and 0.23Ohmm upon increasing the carbon fiber content to 1 and 6% (w/w), respectively. The percolation theory was used to represent the variation of the electrical specific resistivity with fiber content in the cement mortar. Increasing the w/c ratio decreased the strength and toughness of the CFRCM composites. Increasing the fiber content increased the peak strain and toughness, but decreased the Young’s modulus and electrical resistivity of cement mortar composites. Pulse velocity tests showed that the specimen shape also affected the dynamic Young’s modulus, dynamic shear modulus, and the dynamic Poisson’s ratio. The compression strength of the CFRCM was influenced by the w/c ratio and the fiber content. A model was used to predict the compressive stress-strain behavior of different CFRCM systems, and relations between static and dynamic properties have been developed. Empirical relations were developed to relate the specific electrical resistivity to unit weight, Young’s modulus, and pulse velocity.

Safety against formation of through cracks of profiled fibre-reinforced cement sheets for roofing

Loads due to wind, snow or traffic on a roof determine the requirements to the strength and stiffness properties of profiled sheets for roofing. Apart from these loads, locked-in stresses can occur due to differences in temperature and moisture strains in the profiled sheets and the wooden laths supporting the sheets. These tensile and compressive stresses are induced in the sheets if they are firmly fastened to the laths with fastening screws. The purpose of this investigation was to analyse the safety of the profiled sheets in transmitting these loads without the formation of through cracks. The analysis is based on an experimental and a theoretical investigation of the strength and stiffness properties of unexposed profiled fibre-reinforced cement sheets and of sheets that had been exposed on a roof in three years.

Repair of Reinforced Concrete Beams Damaged by Alkali-Silica Reaction

High-performance fiber-reinforced cementitious (FRC) mixtures offer promise as a repair alternative for structures damaged by alkali-aggregate (silica) reaction (ASR). This paper investigates the effects of externally applied U-shaped high-strength FRC jackets on the flexural behavior of ASR-damaged reinforced concrete beams. A series of 13 under-reinforced high-strength concrete rectangular beams were cast, subjected to exposure conditions chosen to generate a rapid increase of ASR damage, repaired, and then tested under four-point loading to determine the effectiveness of the FRC jackets as a method of increasing the beams’ flexural capacity. The overall response of the beams (loaded up to failure); the onset of cracking; and cracking pattern, serviceability, stiffness, and ductility are described. Three types of fibers were used: high-performance polypropylene, hooked-end steel, and brass-coated steel with fiber content ranging from 1 to 2%. Results showed that all repaired beams exhibited a substantial improvement in their flexural behavior compared with the control beams. They regained a large proportion of the control beams’ ultimate load capacity, and showed a typical flexural failure with an increase in the first cracking and service loads. Beams repaired with a mixture of hooked steel and brass-coated steel fibers showed the highest improvement in flexural load capacity, while those repaired with brass-coated steel fibers exhibited the highest improvement in displacement ductility and toughness. An analytical model was developed and shown to be reliable for predicting the ultimate load capacity of the repaired beams. The findings from this study indicate that the proposed repair technique is an effective method for restoring the flexural capacity of ASR-damaged reinforced concrete members.

Effect of Aluminoborate Whiskers on Mechanical Properties of Polycarboxylate Cements

The mechanical properties of polycarboxylate cements containing 20 mass% of four kinds of aluminoborate whiskers with different fiber lengths and diameters were evaluated. Bending strength of the cements increased with increase in fiber length, whereby the strength of the cement with the longest fiber was about two times greater than that of whisker-free cement. The diametral tensile strengths of the four fiber-reinforced cements were also about two times greater than that of whisker-free cement, but which was not dependent on fiber length. Compressive strength was the same or slightly higher than that of whisker-free cement. SEM observation of fractured specimen after diametral compression test showed high affinity between the cement matrix and the whisker.

Effect of Moisture on Piezoresistivity of Carbon Fiber-Reinforced Cement Paste

Piezoresistivity, as exhibited by carbon fiber-reinforced cement-based material, allows a structural material to sense its strain or stress through electrical resistance measurement. This paper addresses the worst scenario associated with the effect of moisture on the piezoresistivity of carbon fiber-reinforced cement paste. This scenario is associated with both water saturation and a fiber content below the percolation threshold. For this scenario relative to the condition after drying at room temperature, the gauge factor (fractional change in resistance per unit strain) is decreased by at least 12% and the variability of the gauge factor with the strain amplitude and with the strain history is increased. These negative effects are attributed to the water at the fiber-matrix interface. The water interferes with the electronic conduction across the interface. Nevertheless, the piezoresistivity remains strong, the signal-to-noise ratio of the resistance remains high, and the relationship between resistivity and strain remains quite linear.

Compressive and Tensile Strength of Natural Fibre-reinforced Cement base Composites

Compressive and Tensile Strength of Natural Fibre-reinforced Cement base Composites

Deformation Capacity and Shear Strength of Fiber-Reinforced Cement Composite Flexural Members Subjected to Displacement Reversals

The behavior of fiber-reinforced cement composite (FRCC) flexural members under large displacement reversals was experimentally evaluated. Emphasis was placed on estimating the displacement capacity and shear strength of members constructed with strain-hardening FRCC materials. Two types of fibers were used: Ultrahigh molecular weight polyethylene fibers and steel hooked fibers in volume fractions ranging between 1.0 and 2.0%. The primary experimental variables were: (1) fiber type and volume fraction; (2) type of cement-based matrix (concrete or mortar); (3) average shear stress demand at flexural yielding; and (4) shear resistance provided through hoops versus total shear demand. All specimens constructed with a strain-hardening FRCC, with or without web reinforcement, exhibited drift capacities of at least 4.0%. A shear stress level of 0.30√fc′[MPa] represented a lower bound for which no shear failure occurred in the strain-hardening FRCC test specimens, regardless of the member inelastic rotation demand. In addition, buckling of longitudinal reinforcement in the strain-hardening FRCC members without web reinforcement was not observed up to plastic hinge rotations of 4.0%.

Strengthening Masonry Arches with Composite Materials

The aim of this study was to compare the effects of strengthening masonry arches using two different composite materials. To this end, an experimental analysis was carried out on models of arches that were first damaged, then strengthened by applying composite material sheets to the surface of the intrados, and last, subjected to a loading process until the point of collapse. One arch was strengthened with carbon fiber-reinforced polymer, the other with glass fiber-reinforced cement matrix. Results collected during the experimental analysis were significant in assessing the capability to support horizontal load, in increasing the collapse load, stiffness, and ductility, and in assessing the different fracture patterns and collapse modes of the arches strengthened with different fiber-reinforced composites. The comparison will be useful for establishing the physical-mechanical and aesthetic compatibilities between the original construction and the strengthening matrix polymeric or cementitious, particularly with reference to the safeguarding of historical buildings.

Piezoresistivity-Based Strain Sensing in Carbon Fiber-Reinforced Cement

For piezoresistivity -based strain sensing using carbon fiber-reinforced cement (152 mm [6 in.] specimens under compression) in the elastic regime, the four-probe method of electrical resistance measurement is more effective than the two-probe method in that it provides gauge factor (fractional change in resistance per unit strain) that is higher and that varies less with the strain amplitude. The two-probe method also suffers from the resistance increasing irreversibly in the first few loading cycles due to minor degradation of the electrical contacts. The use of embedded stainless steel electrical contacts gives more effective strain sensing and slightly lower resistivity than the use of silver paint surface electrical contacts, whether the four-probe method or the two-probe method is used. In case of the four-probe method, the use of embedded steel contacts compared with the use of surface silver paint contacts results in greater linearity and lower noise in the variation of the resistance with strain. In case of the two-probe method, the use of embedded steel contacts compared with the use of surface silver paint contacts results in lower variability of the gauge factor and smaller fractional contribution of the contact resistance to the measured resistance.

Rheology of fiber-reinforced cementitious materials

An improved understanding of the influence of fibers on the rheology of cementitious systems is needed so that fiber reinforcement can be used effectively. However, conventional rheometers are not suitable for testing stiff fiber-reinforced materials. In this study, a parallel plate rheometer that is capable of evaluating the rheology of stiff fiber-reinforced cement paste and mortar systems was designed and built. The governing equations for the rheometer were derived and experimental procedures were developed that yielded reproducible results. A comparative analysis of the custom-built parallel plate rheometer, a commercial rheometer and the values reported in the literature, indicated that the measurements obtained using the rheometer were reasonable. The rheometer was then used to evaluate the rheology of a variety of cement paste systems, including stiff steel fiber-reinforced cement pastes.

Tensile Response and Fracture Process of High-Performance Hybrid Fiber-Reinforced Cement Composites

Five twisted steel fibers (steel cord, SC) are used to improve the post-cracking behavior of cement composites. In addition to these steel cord macrofibers, microfibers are used to enhance the pre- and post-cracking strength and behavior. The three specific hybrid fiber blends pursued in this investigation are SC and polyethylene (PE), SC and polypropylene (PP) as well as SC and polyvinyl alcohol (PVA) fibers. The research results show that SC macrofibers with high ultimate strain, strength and bond stress can bridge the macrocracks in the matrix. Therefore, cement-based composites reinforced with SC fibers exhibit a pseudo-strain hardening in tension as a result of the formation of multiple cracks. The microfibers improved pre-peak mechanical performance, strength, and fracture process by delaying the formation of a macrocrack. The tensile strength, energy consumption capacity and ductility of SC macrofibers and high elastic modulus microfiber PE reinforced cement-based composites are tremendously improved compared to SC macrofibers with lower elastic modulus microfibers PVA and PP.

Mechanical behavior of cement-based materials reinforced with sisal fibers

Fiber-reinforced cement composites were produced in Brazil using blast furnace slag cement reinforced with pulped fibers of sisal originated from agricultural by-products. Thin pads were produced by slurring the raw materials in water, followed by de-watering and pressing stages. Studies of mechanical behavior included observations of stable crack growth behavior under monotonic loading (resistance-curve behavior), followed by scanning electron microscopy (SEM) analysis of the fracture surfaces. Reinforcement with cellulose fibers resulted in improved fracture toughness, even after 9 months in laboratory environment. Microscopic analysis indicated a considerable incidence of crack bridging and fiber pull-out in the composite. The shielding contributions from crack bridging are estimated using a fracture mechanics model, before comparing with the measured resistance-curve behavior.

Affordable, safe housing based on expanded polystyrene (EPS) foam and a cementitious coating

This paper describes an ongoing project to demonstrate an affordable, safe, and energy-efficient housing technology based on expanded polystyrene (EPS) panels with a cementitious coating. The concepts being described are (1) EPS panels embedded with galvanized steel trusses, steel mesh welded or clipped to the protruding points of the trusses and finished with a coating of cement plaster; (2) fiber-reinforced cement board panels and a core of EPS, glued together with high-strength adhesive, dried under high pressure, and connected with cellulose fiber cement board splines; and (3) EPS panels coated with a fiber-reinforced composite. The scope of this project is to model energy flows, analyze costs, simulate seismic forces, test against environmental conditions, and build pilot houses initially in California, Texas and Afghanistan. Results from air quality and energy flow analyses, preliminary cost modeling, structural calculations, and fire testing are reported. The performance goals address seismic safety; energy efficiency in extreme temperatures to reduce fuel use and indoor air quality hazards; affordability and simplicity of construction, as well as ease of expansion for future development; local employment opportunities and small-scale capital investments; and finally, cultural acceptance through education and adaptation to traditional architecture.

Retrofit Using Increased Section Area Method of Artificially Perforated Shear Wall in Existing Wall Dominant Structure

The characteristics relating to high tensile ductility, High Performance Fiber Reinforced Cementitious Composites (HPFRCC) are being so that studied it’ll be adopted in repair and retrofit of buildings. A series of three shear wall specimens were tested under constant axial stress and reversed cyclical lateral loading in order to evaluate the seismic retrofit that had been proposed for the shear wall with the opening. The retrofit involved the use of ECC and MDF, both of which are sprayed through the high pressure pump, over the entire face of the wall. The results indicate that two different types of retrofitting strategies cause the different effects on the strength and ductility of each specimen.