Fiber-reinforced Cement Research Articles

Finite element modelling of the biaxial behaviour of high-performance fibre-reinforced cement composites (HPFRCC) using Concrete Damaged Plasticity

High-performance fibre-reinforced cement or concrete composites (HPFRCC) are increasingly used in structural applications exposed not only to uniaxial but also complex stress states. Current finite...

Development of a new Ultra High Performance Fibre Reinforced Cementitious Composite (UHPFRCC) for impact and blast protection of structures

Ultra High Performance Fibre Reinforced Cementitious Composites (UHPFRCCs) represent a class of cement composites which have superior characteristics in terms of material properties. Their mechanical and fracture behaviour is substantially enhanced compared to other types of concrete. The aim of the specific paper is to present the results of an extended work focused on the development of the first UHPFRCC with the use of constituent materials available in Cyprus. The paper presents results on a broad variety of mechanical properties and the effect of several parameters on the strength development and the rheological characteristics of the produced material. Furthermore, the developed material should have certain properties and specifications, so as to have a sufficient response against blast and impact loading conditions. The optimum mixture has a water–binder ratio equal to 0.16 and volume fraction of steel fibres equal to 6%. The average compressive strength and specific fracture energy obtained for this mixture were around 175MPa and 26000N/m, respectively.

Experimental field investigation of impact and blast load resistance of Ultra High Performance Fibre Reinforced Cementitious Composites (UHPFRCCs)

Ultra High Performance Fibre Reinforced Cementitious Composites (UHPFRCCs) represent a class of cement composites which have superior characteristics in terms of material properties. These materials have, however, a significant increase in cost compared to conventional and even High Performance Concrete and it is therefore appropriate to identify applications which will fully utilise their mechanical properties and performance characteristics. A new class of UHPFRCC material has been developed through the experimental work of a research project entitled “Mix Design, Mechanical Properties and Impact Resistance of UHPFRCCs”, designated UHP-CY. The material is characterised by high compressive strength, high tensile/flexural strength and high-energy absorption capacity. The research work presented in this paper focused on the experimental investigation of the quality and the behaviour of this material in a highly demanding application, such as the impact and blast resistance of structures. The impact resistance of UHP-CY slabs was experimentally verified in a range of real firing shots, using several weapons and projectile types. A purpose-built experimental setup was developed for this work. It was observed that relatively thin slabs made of this material can be an outstanding protective overlay of existing structures, since they can prevent the penetration of strong projectiles without shaped charges. Moreover, these panels can also minimise the damage of retrofitted Reinforced Concrete structures, hit by projectiles with shaped charges. The presence of a high volume fraction (i.e. 6%) of steel fibres in UHP-CY overlays contributes substantially to the control of the back face spalling and fragmentation of the RC walls.

Shear strengthening of reinforced concrete beams with PBO-FRCM composites

The work analyses the functioning of reinforced concrete beams which are shear reinforced with FRCM (Fibre Reinforced Cementitious Matrix) composite mesh on mineral mortar. The analysis of previous tests provides an overview on the efficiency of the related FRP (Fibre Reinforced Polymers) system used for strengthening the beams against shearing forces. The information gathered on the functioning of FRCM strengthened concrete elements show that the key factor in this technology is ensuring appropriate carrying capacity of anchoring of the mesh. The tests were carried out on reinforced concrete beams with different design of lateral reinforcement. The beams differed in terms of the angle of inclination of the reinforcement to the longitudinal axis, as well as in terms of the manner of anchoring the mesh at the top and bottom surface of beams. The destruction mechanisms of beams were analysed and described. Value of deflection measured at the maximum load for all of the beams is significantly greater than the allowable value. The distribution of strains is presented as a function of the load, where the phases of operation in relation to shear of FRCM reinforced beams are visible.

Experimental study of torsional strength of RC beams constructed with HPFRC composite mortar

The torsional performance of reinforced concrete (RC) beam members covered with high-performance fiber-reinforced cementitious (HPFRC) composite mortar was evaluated through pure torsion tests. The HPFRC composite mortar has higher compressive strength and higher split tensile strength than plain concrete. Four beam specimens were constructed for the pure torsion test. Two types of section, and different materials, were used to produce the RC beam specimens. Various types of torsional performance (i.e., first-cracking torque, ultimate torque, and twist angles) were compared experimentally to evaluate the performance of the RC beam specimens. The torque and twist angle at first visible cracking, of the HPFRC composite mortar specimens were greater than those of the others. Therefore, the use of HPFRC composite mortar appears a useful method to enhance the torsional performance of RC-beam members. Moreover, a simple design equation to determine ultimate torque was proposed and tested, for predicting the torsional strength of RC beams with covers of HPFRC composite mortar. The proposed equation performed well.

A qualification method for externally bonded Fibre Reinforced Cementitious Matrix (FRCM) strengthening systems

Fibre Reinforced Cementitious Matrix (FRCM) composites are now widely used for repair and retrofitting existing structures. Guidelines for product qualification are needed to characterize the strengthening systems before they are made available in the market and installed. The paper proposes a procedure that combines the results of direct tensile and shear bond tests to provide engineering design parameters for externally bonded FRCM reinforcements. Due to the possible occurrence of different failure modes, the procedure provides results on the base of the weakest mechanism that takes place. Thanks to its simplicity, the proposed method is suitable for standard product qualification and material assurance purposes. In order to investigate its feasibility, the qualification procedure is applied to different reinforcements comprising basalt, carbon, glass, and steel textiles, bonded with either cement or lime mortars to clay bricks and tuff units.

The Combined Effects of Fiber and Cement-Based Composite Materials

As far as the problems arising in the using of cracking mortar is concerned, a lot of work are done by researchers to improve the performance of cementations material, including adding various fibers into the cement matrix. The crack resistance mechanism of fiber-reinforced cement mortar is studied by scholars through a variety of methods. In this paper, the roles of fiber in fiber reinforced cement-based composite materials and the explanation thereof proposed by domestic and foreign scholars are summarized.

Finite element modelling of the biaxial behaviour of high-performance fibre-reinforced cement composites (HPFRCC) using Concrete Damaged Plasticity

High-performance fibre-reinforced cement or concrete composites (HPFRCC) are increasingly used in structural applications exposed not only to uniaxial but also complex stress states. Current finite element models for these materials have however been only validated for uniaxial stress states, and mostly restricted to cement composites with relatively limited strain hardening capacity in tension. To facilitate the numerical analysis and design of more complex structures, this paper adapts and validates the Concrete Damaged Plasticity (CDP) model for both uni- and biaxial stress states, and for cement composites with a large strain hardening capacity (ratio of failure stress to linear stress limit more than 8). The validation of the numerical model is done by performing laboratory biaxial tension–tension tests under various load cases. For the latter, an adapted cruciform specimen was designed. The strain distribution in the specimen as well as its evolution with increasing load correspond well. As the results show, the adapted CDP model can simulate the nonlinear strain hardening behaviour in tension – different from the linear behaviour in compression – of high-performance cement composites for both uniaxial as well as biaxial stress states. Moreover, failure can be simulated.

Degradation mechanisms of natural fiber in the matrix of cement composites

The degradation mechanisms of natural fiber in the alkaline and mineral-rich environment of cement matrix are investigated. Cement hydration is presented to be a crucial factor in understanding fiber degradation behavior by designing a contrast test to embed sisal fibers in pure and metakaolin modified cement matrices. In addition to durability of sisal fiber-reinforced cement composites determined by means of flexural properties, degradation degree of the embedded fibers is directly evaluated by proposing a novel separation approach. The results indicate that, by reducing alkalinity of pore solution, metakaolin effectively mitigates the deterioration of natural fiber. By combining results of thermogravimetric analysis and microstructure, the alkali degradation process of natural fiber, which consists of hydrolysis of lignin and hemicellulose, stripping of cellulose microfibrils and deterioration of amorphous regions in cellulose chains, is visually presented. Two new concepts of mineralization mechanism, calcium hydroxide (CH)-mineralization and self-mineralization, are also proposed and quantitatively characterized.

Use of Fiber-Reinforced Cements in Masonry Construction and Structural Rehabilitation

The use of fiber reinforcement in traditional concrete mixes has been extensively studied and has been slowly finding its regular use in practice. In contrast, opportunities for the use of fibers in masonry applications and structural rehabilitation projects (masonry and concrete structures) have not been as deeply investigated, where the base matrix may be a weaker cementitious mixture. This paper will summarize the findings of the author’s research over the past 10 years in these particular applications of fiber reinforced cements (FRC). For masonry, considering both mortar and mortar-unit bond characteristics, a 0.5% volume fraction of micro fibers in type N Portland cement lime mortar appear to be a viable recipe for most masonry joint applications both for clay and concrete units. In general, clay units perform better with high water content fiber reinforced mortar (FRM) while concrete masonry units (CMUs) perform better with drier mixtures, so 130% and 110% flow rates should be targeted, respectively. For earth block masonry applications, fibers’ benefits are observed in improving local damage and water pressure resistance. The FRC retrofit technique proposed for the rehabilitation of reinforced concrete two-way slabs has exceeded expectations in terms of capacity increase for a relatively low cost in comparison to the common but expensive fiber reinforced polymer applications. For all of these applications of fiber-reinforced cements, further research with larger data pools would lead to further optimization of fiber type, size, and amount.

Behavior of Steel Fiber-Reinforced Cementitious Mortar and High-Performance Concrete in Triaxial Loading

A study on the behavior of a steel fiber-reinforced cementitious mortar (SFRCM) in a triaxial compression condition and a comparison of results with those of a common high-performance concrete (HPC) is presented. SFRCM with a high compressive strength seems to be a promising material in civil engineering applications. A series of cylindrical specimens of two types of SFRCM with 1% and 2% volume fraction of steel fiber and one type of HPC were prepared and tested under various confining pressures: 0, 5, 10, 15, and 20 MPa (0.72, 1.45, 2.18, and 2.90 ksi). In general, raising the confinement level increases the peak axial stress and the corresponding strain, while on the other hand this causes the specimens to behave more ductile. According to the results, the addition of steel fiber has meaningfully helped increase energy absorption capacity of the specimens. Finally, empirical equations were derived to predict the peak axial stress and the corresponding strain of the tested materials as a function of confining pressure for tested materials.

Strengthening of brick masonry with PVA fiber reinforced cement stucco

This paper presents the behavior of masonry walls externally strengthened by poly vinyl alcohol (PVA) fiber reinforced cement plaster. Tensile weakness of masonry wall is improved by simply applying fiber reinforced cement (FRC) plaster on masonry surface. Strengthening by ductile materials, in order to maintain ductile behavior of masonry to resist shear forces would provide reduction in the crack development and crack width providing delay in failure. FRC was applied to surfaces of the masonry wall as stucco to prevent crack growth under shear effect. An experimental program was performed to study the response of unreinforced and retrofitted masonry walls with externally applied fiber reinforced cement mixture, under shear and compressive loading. The experimental results indicate that retrofitting masonry walls with PVA fiber reinforced cement stucco increases the shear strength of the wall approximately half times in solid and high strength brick walls, 2.5 times in regular brick walls.

Effect of pre-setting pressure applied flexure strength and fracture toughness of new SIFCON + RPC composite during setting phase

Reactive powder concrete (RPC) and Slurry Infiltrated Fiber Concrete (SIFCON) are steel fiber-reinforced cement composites which have superior mechanical properties such as compressive, tensile, shear and flexural strength with extraordinary toughness values. Manufacturing of a new composite material was intended by using superior performance of SIFCON in terms of flexural strength as well as superior performance of RPC in terms of compressive strength. For this reason, fresh SIFCON was filled into the bottom portion of mold by means of specially-designed molds and pre-setting pressure was applied by filling reactive powder concrete on it. For RPC and SIFCON in mold, pre-setting pressure was applied in six different pressures (0, 3, 6, 9, 12, 15MPa). Test results indicated that maximum flexure strength was obtained as 69.70MPa under 15MPa pre-setting pressure. According to control-without pressure, flexure strength was improved by 43.21% with 15MPa pre-setting pressure. Also fracture toughness was increased about 32.03% with 12MPa pre-setting pressure. Prefabricated structural elements can be produced with the composite material, which is built via SIFCON+RPC composite, without needing a steel reinforcement.

Compressive Strength Characteristics of Kenaf Fibre Reinforced Cement Mortar

This paper presents the findings of an investigation on the compressive strength properties of kenaf fiber composite mortar. Water–retted kenaf fibers were used as reinforcement in cement mortar. Fiber contents of 1%, 2% and 3 % (by weight of cement) with varying lengths of 10mm, 20mm and 30mm were used to produce 50mm mortar cubes. The Composite mortars were cured in water for 3, 7, 14, 21, and 28days. A total of 150 mortar cubes were used for the study. Density, water absorption and compressive strength tests were conducted on the composite mortar. Regression analysis was carried out on the compressive strength results using Minitab 15. The results showed that water absorption and density of the composite mortar increased as the volume of fiber and length increased. Compressive strength decreased with increasing fiber volume and length. However, there was increase in compressive strength of between 0.21%-22.3% for composite mortar containing 1-3% volume of fiber with 10mm fiber length. The fitted regression model showed a perfect relationship (R2=84.5%) between compressive strength, fiber volume, fiber length and curing age. Therefore, fiber volume, fiber length and curing are useful predictors of the selected model. Model adequacy test reveals that the fitted regression model is highly adequate. There was no statistically significant difference in the compressive strength of the control samples and those containing 1-3% fiber volumes with fiber length of 10mm.

Comparative electromechanical damage-sensing behaviors of six strain-hardening steel fiber-reinforced cementitious composites under direct tension

This research investigates the electromechanical damage-sensing behavior of strain-hardening steel fiber-reinforced cement composites (SH-SFRCs) with six types of steel fibers (1.5% volume fraction content) within an identical mortar matrix (90MPa). The six types of steel fibers studied are long twisted (T30/0.3), long smooth (S30/0.3), long hooked (H30/0.375), medium twisted (T20/0.2), medium smooth (S19/0.2), and short smooth (S13/0.2) steel fibers. The damage-sensing behavior was evaluated by measuring the changes in the electrical resistance during direct tensile tests. The electrical resistivity of the SH-SFRCs clearly decreased as the tensile strain increased until the post-cracking point, owing to the generation of multiple micro-cracks during strain-hardening. All the SH-SFRCs investigated had nominal gauge factors ranging between 50 and 140; these values are much higher than the commercially conventional gauge factor, which involves metal and is around 2. Both T30/0.3 and T20/0.2 produced the highest gauge factor, i.e., the best damage-sensing capacity, whereas S13/0.2 produced the highest electrical conductivity.

Confined concrete elements with PBO-FRCM composites

The paper summarizes the current knowledge on PBO-FRCM (p-Phenylene Benzobis Oxazole Fibre Reinforced Cementitious Matrix) confined concrete elements that have been acquired on the basis of experimental investigation. The strengthening effectiveness as well as the behavior of PBO-FRCM confined concrete elements have been evaluated. The impact of the intensity of the strengthening on the operational effectiveness of compressed elements have been compared. The analyses have been based on the results of the author’s own investigation as well as on those available in the references. Test results of cylindrical specimens and specimens with square cross-sections were compared. The elements were reinforced with 1–4 layers of horizontally aligned PBO mesh. The compressive strength of non-reinforced concrete determines the effectiveness of the PBO-FRCM strengthening. The best strengthening effects are obtained for lower compressive strengths, at the identical intensiveness of transverse strengthening. The strength of confined concrete elements rises directly proportionally, jointly with the increase in the reinforcement ratio. The PBO-FRCM confined concrete core has limited capabilities of compressibility whereupon the exhaustion of the carrying capacity and the destruction of the element follow. The presence of the strengthening with the PBO mesh affects the longitudinal stiffness and the reduction level of elastic modulus, jointly with the rise in compressive stresses. The information obtained has broadened the knowledge on the subject matter under consideration and has determined the directions of further research work.

Strengthening and long-term monitoring of the structure of an historical church presbytery

The paper presents results of long-term monitoring of structural displacements in the historical presbytery in St. Ann’s Church in Ząbkowice Śląskie (Poland), which was carried out from 2009 to 2013. The monitoring involved periodic HDS 3D (High-Definition Surveying 3D) laser scanning coupled with analysis of the status and scope of conservation work completed.The church was built at the turn of the 14th century. Following a long period of neglect, conservation work was initiated to restore this valuable historical monument. Recognition of the historical value of the building meant that conservation work was preceded with a HDS 3D laser scan of the whole interior of the church. Data from scanning provided geometry information, which formed basis for a numerical analysis (FEM) conducted prior to repair work. It was decided that the oldest and most damaged part of the church – its presbytery – would be monitored in the years following repair work in order to observe conservation effects.Methods used for strengthening and consolidation of cracked brick walls and vaults of the presbytery involved application of steel tie rods, as well as C-FRP (Carbon Fibre Reinforced Polymer) and C-FRCM (Carbon Fibre Reinforced Cementitious Matrix) technologies.

Surface-treated polypropylene fiber for reinforced repair mortar cementitious composites

The effects of surface treatment of polypropylene (PP) fiber on the mechanical and microstructure of fiber-reinforced cementitious (FRC) composites are investigated. Surface treatment of the PP fiber was performed with 3-aminopropyltrimethoxy silane (APS) and methyltriethoxy silane (MTES) in order to improve interaction between PP fiber and matrix. The effects of APS and MTES on the surface of PP fiber are studied by scanning electron microscopy, energy dispersive spectrometer, and Fourier transform infrared spectroscopy. The experiment results indicated that the treatment of PP fiber with APS and MTES can effectively increase the adhesion between fiber and matrix, and an improvement in the flexure and compressive strength of the cementitious composites was found in the samples containing treated PP fiber compared to the samples containing untreated PP fiber. The optimized mechanical properties could be obtained using 1.0% APS (by weight) and 1.0% MTES (by weight)-treated PP fiber at studied conditions, respectively.

팽창재와 수축저감제를 사용한 HPFRCC의 수축 저감 성능

HPFRCC는 물-결합재비 (W/B)가 20%로 상당히 낮고 굵은 골재를 사용하지 않으며, 고분말 혼화재료를 혼입하기 때문에 자기수축이 상당히 크게 발생하여 구조물 적용 시 균열저감대책이 필요하다. 따라서 이 연구에서는 HPFRCC의 수축을 효율적으로 저감시키기 위한 방법으로 수축저감제와 팽창재의 사용을 검토하기 위하여 이들의 단독 또는 병행 혼입률에 따른 역학적 특성과 구속 수축특성을 평가하였다. 구속수축 실험 중에서 링-테스트 (Ring-test)를 통하여 HPFRCC에 사용되는 시멘트에 대하여 중량비로 수축저감제 1%와 팽창재를 7.5%를 병행 사용하였을 경우 압축강도와 인장강도가 크게 저하되지 않으면서도 수축을 가장 효율적으로 저감시킬 수 있는 최적 배합임을 도출하였고 수정된 건조수축 균열실험을 통하여 이를 검증하였다. High-performance fiber-reinforced cement composite (HPFRCC) shows very high autogenous shrinkage, because it contains a low water-to-binder ratio (W/B) of 0.2 and high fineness admixture without coarse aggregate. Thus, it needs a method to decrease the cracking potential. Accordingly, in this study, to effectively reduce the shrinkage of HPFRCC, a total of five different ratios of SRA (1% and 2%), EA (5% and 7.5%), and a combination of SRA and EA (1% and 7.5%) were considered. According to the test results of ring-test, a combination of SRA and EA (1% and 7.5%) showed best performance regarding restrained shrinkage behavior without significant deterioration of compressive and tensile strengths. This was also verified by performing modified drying shrinkage crack test.

Defect Identification and Acceptance of FRP and FRCM Masonry Reinforcement by Infrared Thermography Survey

Masonry structures, both historic and newly built, often need reinforcement interventions to meet new or increased loads or in the case of adjustment against seismic actions. The result of this type of intervention must be verified or tested to ensure the correspondence between what was originally designed and what was realized. In addition to numerous destructive and semi-destructive techniques, infrared thermography (IRT) is a contactless diagnostic technique which can rapidly provide information about the success of such reinforcement interventions, even on masonry structures. In the present work an experimental campaign to evaluate the effectiveness of IRT in identifying different types of defects that can be found on different reinforcement systems (FRP, Fibre-reinforced plastic, or FRCM, Fibre Reinforced Cementitious Matrix) for masonry structures has been performed. A thermographic survey was repeated even after repair works on the defects in order to identify a procedure of acceptance that can also be used on areas subject to total or partial repair.