Fiber-reinforced Cement Research Articles

The effect of different types of fiber on flexure strength and fracture toughness in SIFCON

Abstract Slurry Infiltrated Fiber Concrete (SIFCON) is a special kind of steel fiber-reinforced cement composite which has extraordinary toughness values and surpassing mechanical characteristics like compressive, tensile, shear, and flexural strengths. In this study, steel and polypropylene fibers have been used by mixing in different combinations. 1/1, 1/3 and 2/3 of the beam molds have been filled with these fibers. In the study, the physical and mechanical properties and also the unit strength cost analyses of SIFCON have been examined. The use of the fibers with combinations has caused to an increase in the fiber volume. The highest flexural strength values have been reached with the beam samples completely filled with fiber respectively as 44.02 MPa and 41.23 MPa with the steel fiber at the length of 60 mm and 35 mm and with 60 mm steel and 50 mm polypropylene fiber combination. The combined use of polypropylene fiber and steel fiber has increased the flexural strength and fracture toughness. Consequently; it has been observed that the polypropylene fiber provides significant advantages for the use of SIFCON in terms of unit weight and cost due to the fact that its density and cost are lower when compared to those of the steel fiber.

Shrinkage and Durability Evaluation of Environmental Load-Reducing FRPCM by Using Silicone Oil.

In this study, the shrinkage and durability of environmental load-reducing fiber-reinforced polymer cement mortar (FRPCM) were examined by using silicone oil. The results indicated that the shrinkage can be greatly reduced by adding silicone oil. However, when the silicone oil is added in excess, it affects the strength and durability. Therefore, it is possible to obtain the ECO-FRPCM which gives the effect of reducing the shrinkage and maintaining the strength and durability by adding 3% of silicone oil. From the viewpoint of shrinkage reduction, the use of silicone oil is effective as a substitute for an expansive additive or shrinkage reducing agent used in ECO-FRPCM. Also, by appropriately using silicone oil in combination with an expansive additive or a shrinkage reducing agent, shrinkage can be effectively reduced as compared with the conventional ECO-FRPCM. However, when the silicone oil and the shrinkage reducing agent are used in combination, the shrinkage cannot be efficiently reduced. It is considered that the combination of silicone oil and shrinkage reducing agent influences the mutual shrinkage reduction mechanism, but this needs to be further examined in the future.

The Influence of Crystallization Additives on the Porosity of Polypropylene Fibre-reinforced Cement Mortar

The phenomenon of self-healing cement materials has been described in the professional literature for decades. One self-healing mechanism is based on the presence of crystallization additives in concrete or mortar; when a defect appears in the material, the crystallization additives (CA) are activated, and new crystallization products will fill the pore or crack. The activation of the crystallization additives occurs only under certain conditions. The intensity of crystallization is affected by the nature of the environment within the crack or pores, and in order for the crystallization to occur, the cracks or pores must contain an aqueous solution with sufficient ion content to react with the crystallization additive. This paper discusses the possibility of using crystallization additives to reduce the porosity of cement mortar reinforced with polypropylene (PP) fibres, describes the effect of crystallization additives on the pore structure of cement mortar, and evaluates the influence of the medium on pore size distribution in cement mortar.

Nanocelluloses: Natural-Based Materials for Fiber-Reinforced Cement Composites. A Critical Review.

Nanocelluloses (NCs) are bio-based nano-structurated products that open up new solutions for natural material sciences. Although a high number of papers have described their production, properties, and potential applications in multiple industrial sectors, no review to date has focused on their possible use in cementitious composites, which is the aim of this review. It describes how they could be applied in the manufacturing process as a raw material or an additive. NCs improve mechanical properties (internal bonding strength, modulus of elasticity (MOE), and modulus of rupture (MOR)), alter the rheology of the cement paste, and affect the physical properties of cements/cementitious composites. Additionally, the interactions between NCs and the other components of the fiber cement matrix are analyzed. The final result depends on many factors, such as the NC type, the dosage addition mode, the dispersion, the matrix type, and the curing process. However, all of these factors have not been studied in full so far. This review has also identified a number of unexplored areas of great potential for future research in relation to NC applications for fiber-reinforced cement composites, which will include their use as a surface treatment agent, an anionic flocculant, or an additive for wastewater treatment. Although NCs remain expensive, the market perspective is very promising.

Experimental characterization of fiber-reinforced cementitious mortar under tension

This work focuses on the mechanical characterization of the inorganic matrix used for Fiber-Reinforced Cementitious Matrix (FRCM) composites, nowadays widely used to retrofit existing reinforced concrete and masonry structures. While several works in technical literature investigate the experimental behavior of the whole FRCM composite, few information are available on the mechanical characterization of the mortar, which contains polymers and synthetic fibers in its admixture. However, the knowledge of its behavior in tension, especially after crack formation, is an important feature for the calibration of constitutive models to be adopted in the study of structural elements strengthened with FRCM. To this aim, an experimental program was performed on mortar specimens characterized by different shapes and dimensions, tested under direct tension or three-point-bending. From the performed tests, it was possible to characterize inorganic matrix behavior both in the uncracked stage, through the determination of the elastic parameters (elastic modulus and Poisson’s coefficient), and in the cracked stage. The use of digital image correlation (DIC) technique also allowed the study of the evolution of crack propagation in the specimens. Lastly, a correlation factor between axial and flexural tensile strength is proposed, for both design and numerical modelling purposes.

ИССЛЕДОВАНИЕ СПОСОБОВ РЕМОНТА ЛИЦЕВОЙ КИРПИЧНОЙ КЛАДКИ МНОГОСЛОЙНЫХ СТЕН

This article discusses the methods of repairing the brick facing layer of multilayer walls: repair and restoration of vertical and horizontal expansion joints; use when strengthening repair connections and anchor connections; injection and re-inforcement of cracks; Fibre Reinforced Cementitious Matrix and direct repair of brickwork. The conclusion is made about the importance of choosing the right method of repair and the factors affecting it.

Effect of mineral additions on the microstructure and properties of blended cement matrices for fibre-cement applications

This detailed study of the effect of three mineral additions (limestone, rice husk ash and activated coal mining waste) differing in composition and properties explored the behaviour of blended cements with a 25% replacement ratio. The aim was to select the optimal addition for improving the performance of natural fibre-reinforced cements. The pozzolanic, physical and mechanical properties as well as the pore structure of the blended cement matrices were examined. The findings showed that although rice husk ash is characterised by high pozzolanicity, it had a less favourable effect on the cement than expected, yielding porous, poorly compacted and hence weak matrices. The activated coal mining waste showed better performance, reaching similar strength to control mortar, better pore size refinement and an important reduction in mean pore size of 60% compared to control mortar after 60 days of curing. In light of those findings, this aluminosilicate addition is proposed as the most apt of the three studied for improving the quality of fibre-reinforced cements, keeping in mind that the interaction effect amongst the three mineral additions was not considered in the present work.

The Bond Response of Concrete Brick with Recycled Tire Chip as Partial Replacement of Aggregate Applied in the Non-Structural Masonry Wall

The walls of buildings are made from several types of materials, including red and concrete bricks, glass fiber-reinforced cement, wood and glass. Concrete brick has many advantages. It is relatively cheap, with more economical mortar usage and it has an easier and faster installation. Unfortunately, the main disadvantage of concrete brick is that it is heavier than many other wall building materials. In order to reduce the weight of concrete brick as well as to dispose waste tire safely, the objective of this study is to investigate the mechanical effect of the application of recycled tire as a partial replacement of aggregates in the concrete brick. The application of recycled tire in concrete brick with high volume protects the environment from pollution due to the waste tire. The dimension of concrete brick is 345 mm of length, 90 mm of width and 100 mm of thickness. The recycled tire utilized in the study is in the form of chips with dimensions of 4 mm × 4 mm × 20 mm. The chips are mixed with mortar in order to form the concrete brick. The content of recycled tire chips in concrete brick without superplasticizer is 0, 15, 30, 45 and 60% and with superplasticizer it is 0%, 50%, 55%, 60%, 65%, 70% and 75% by volume. Several types of testing for concrete brick with recycled tire are carried out, focusing on the unit weight, the compressive strength, the flexural strength and the shear strength. It has been found out that concrete brick containing 75% of recycled tire chips reduces the unit weight of concrete brick by ~63% compared to concrete brick without recycled tire chips. Moreover, the highest compressive, flexural and shear strengths are 1.32 N/mm2 for concrete brick with 50% of recycled tire, 0.063 MPa for concrete brick with 55% of recycled tire and 0.064 MPa for concrete brick with recycled tire content of 65%.

Seismic Behavior of High-Performance Fiber-Reinforced Cement Composites Beam-Column Connection with High Damage Tolerance

The purpose of this study is to investigate and evaluate the feasibility of using high-performance fiber-reinforced cement composites (HPFRCC) to satisfy the requirement of transverse reinforcement in beam-column joint under seismic loads. The basic mechanical properties of the HPFRCCs are determined by compression, uniaxial tension, and direct shear tests. Four half-scale exterior beam-column connections are cast and tested under cyclic loads. The cracking patterns, hysteresis behavior, ductility, energy dissipation with damping characteristics and joint shear capacity of the HPFRCC beam-column connections are analyzed, investigated, and compared to the cyclic responses of normal concrete connections designed with/without seismic criteria of ACI. The test results revealed that HPFRCC connections considerably enhances shear and flexural capacity and also improved the deformation and damage tolerance behavior in post-cracking stage comparing to normal concrete connections in ultimate stages. Also, the failure mode of HPFRCC specimens changed from shear mode to flexural mode comparing to the connections without seismic details. Severe damages are observed in normal concrete connection designed without considering seismic criteria. Wide diagonal cracking and damage are observed on the designed NC connections under large cyclic displacement at drift 6%. However, in HPFRCC connections, joint remained intact without any cracks and damage until the test end. This implies that the shear stress requirement can be satisfied without any need to the transverse reinforcement in the HPFRCC joint.

Performance Evaluation of the Fiber-Reinforced Cement Composites Blended with Wheat Straw Ash

Increasing demand for cement in the construction industry is posing a serious threat to the environment. This necessitates the utilization of supplementary cementitious materials such as silica fume, fly ash, rice husk ash, and wheat straw ash as a cement replacement material. Additionally, fiber-reinforced cement composites can be efficiently used in repair and rehabilitation works. In this study, we have investigated the performance of fiber-reinforced cement composites blended with wheat straw ash. Wheat straw ash has been proved to be an effective pozzolanic material. Cement was replaced by 20% (weight) wheat straw ash. Polypropylene fibers were added at a dosage of 0%, 0.5%, 1%, and 2% by weight of cement. Mortar specimens were fabricated and investigated for the compressive, flexure, and indirect tensile strengths, ultrasonic pulse velocity, chloride migration resistance, and carbonation resistance. The results demonstrate that the addition of fibers caused a reduction in the compressive strength, pulse velocity, chloride migration resistance, and carbonation resistance; however, flexure and indirect tensile strengths were significantly enhanced. Moreover, the incorporation of fine size wheat straw ash particles compensated the negative effect of fiber inclusion.

High performance fibre reinforced cementitious composites: Six memos for the XXI century societal and economical challenges of civil engineering

Worldwide increasing consciousness for sustainable use of natural resources has made “overcoming the apparent contradictory requirements of cost and performance effectiveness a challenging task” as well as a major concern. High Performance Fibre Reinforced Cementitious Composites, by providing tailored and multiple functionalized performance can represent an asset for the construction industry to face the challenges imposed by the needs of our continuously and fast evolving society. The paper, moving from a parallel with “Six memos from the next millennium” by Italo Calvino, the author will provide his own perspective on the current state on the topic, trying to highlight the benefits achievable through a reliable and consistent incorporation into a design and construction practice for both new and existing buildings and structures.

Investigation of the usability of high-performance fiber-reinforced cement composites containing high-volume fly ash and nanomaterials as repair mortar

High-performance fiber-reinforced cement composite (HPFRCC) mixtures containing high-volume fly ash and nanomaterials are investigated in this study. In order to determine high early strength and high connection performance between repair mortar produced with HPFRCC containing nanomaterials, high volume fly ash, and concrete which will be repaired, compressive strength, elasticity, and slant shear test were conducted on the samples. The experimental results showed that HPFRCC mixtures containing nanomaterials increased the strength on 1, 3, 7, 28, and 90 days in comparison to control mortars for compressive strength test. Also, the samples containing nanosilica gave the highest compressive strength in all mixtures. In addition, the samples containing nanosilica gave the best result for elasticity modulus, showing similarity to compressive strength test. For the bond strength, deformations were observed on the old concrete in the samples formed from HPFRCC mixtures and old concrete. Expected sloping surface sliding was not occurred.

Using fractal analysis methods in studying mechanisms of deformation and destruction of nano-modified cement concretes

The research results for the mechanism of deformation and destruction of nano-modified fibre-reinforced fine-grained cement concretes are given. Multi-layer polyhedral carbon structures (astralenes) were used as a nano-modifying additive in the formulation of concrete mixtures, which were injected into cement systems together with hard vehicles in the form of basalt micro-fibres. The influence of three types of mineral additives (condensed compacted microsilica, highly active white metakaolin and sulfoaluminate additive 'Penetron Admix') on physical and mechanical properties of dispersive reinforced fine cement concretes under study have been identified. Using the minimal coverage method, quantitative values of critical points have been identified on deformation curves of cement concretes in compression characterising the accumulation moment within fibre-reinforced fine-grained cement concretes for a specific level of micro-defects causing first cracks to occur. It has been found that fibre-reinforced nano-modified fine-grained cement concrete containing highly active white metakaolin as a mineral additive in the amount of 6% of the Portland cement weight has the highest physical and mechanical properties.

Flexural performance of RC columns with FRCC jacketing

A new repair technique consisting on a light jacketing with Fibre Reinforced Cementitious Composites (FRCC) for existing reinforced concrete (RC) buildings has been recently proposed to reduce durability problems of RC members and enhance their capacity. In this work, the effects of FRCC jacketing on the flexural capacity of existing RC columns, with and without a pre-damage, has been evaluated of full-scale specimens under cyclic loading. Digital Imagine Correlation (DIC) was also adopted for understanding the strain distribution in the FRCC jacket. The results shown that the FRCC jacket without a proper anchorage slightly enhanced the flexural capacity of the column. The strengthened column experienced a low damage with respect to control column, but occurrence of premature failures did not allow the achievement of high levels of deformation capacity and ductility.

Direct Tensile Properties of Fiber-Reinforced Cement Based Composites according to the Length and Volume Fraction of Amorphous Metallic Fiber

Direct Tensile Properties of Fiber-Reinforced Cement Based Composites according to the Length and Volume Fraction of Amorphous Metallic Fiber

Sustainable structural rehabilitation and strengthening of the “Ponte delle Grazie” bridge in Faenza, Italy

The “Ponte delle Grazie” is a three span bridge, with a total length of 72 meters, built between 1948 and 1952 in Faenza, Italy. The reinforced concrete main beams of the deck have undergone a strong deterioration over the years. In detail atmospheric agents and chemical aggressions caused a strong deterioration of the concrete, up to the point of making the structure not accessible and at risk of collapse. In fact, the five main beams were heavily damaged, as well as the concrete bearings were strongly compromised. So, an urgent intervention was necessary to save the structure of this historic bridge. A delicate restoration has allowed to remove the deteriorated concrete and to restore the resistant sections with new materials compatible with the old remaining structures. In particular, a specific rehabilitation procedure was studied using fiber-reinforced cement mortar with low elastic modulus, that is shrinkage compensated, in combination with composite materials reinforcements. Without modifying the structural behaviour of the bridge, the deteriorated concrete was restored and reinforced, in a sustainable way, in order to make the structure safe and usable again.

Crack detection of a HPCFRCC thin plate using electrical resistivity method

Electrical resistivity measurement has been used as a test for studying the durability-related properties of cement composites for decades. Applications of electrical resistivity measurement namely health monitoring and crack detection are of great importance for increasing the service life of structures. The former is the capability of cement composite to sense its own strain (piezoresistivity) and the latter is based on the irreversible change of resistivity in the presence of crack. In this study, at first the effect of different fractions of silica fume and carbon fiber on piezoresistivity of cement composites were evaluated by monitoring the variations of resistivity under compression. Secondly, a high performance carbon fiber-reinforced cement composite (HPCFRCC) thin plate specimen was subjected to four-point bending while the variations of resistivity were recorded so that the zone at which the initiation of crack occurs can be detected. Results showed that both compressive strength and water absorption are highly affected by silica fume content while flexural strength slightly changed by increasing silica fume. While the addition of carbon fiber increased water absorption, it marginally affected mechanical strengths. Piezoresistivity test showed the ability of carbon fiber as a functional filler and the facilitated dispersion of fibers in high concentration of silica fume particles. It was confirmed that when carbon fiber content increases to more than 0.4 volumetric percentage, conductivity of specimen substantially increases and required sensitivity from piezoresistivity test is obtained. Crack detection test showed that when cracks are formed the planar surface resistivity of thin plate significantly changes. Thus, the formation and propagation of cracks can be monitored using electrical resistivity measurement in self-sensing cement composites.

Influences of molding processes and different dispersants on the dispersion of chopped carbon fibers in cement matrix

Chopped carbon fiber-reinforced cement composite (CFRC) has become one of the potential smart materials in recent years. The key process of preparing this kind of composite at the early stage is how to disperse carbon fibers evenly into the cement matrix to achieve CFRC composite with good properties. In this study, a three-step mixing process and a six-step mixing process for the preparation of CFRC were suggested, respectively. The fracture morphology was observed by scanning electron microscopy. The influence of mass fractions of three common dispersants methyl cellulose (MC), carboxymethyl cellulose sodium (CMC) and hydroxyethyl cellulose (HEC) on the dispersion of short carbon fibers in water under certain temperature was investigated prior to the manufacture of CFRC. The correlation between mass fraction and viscosity was discussed, and the dispersion effect was assessed from the structure of dispersants and molding process. A hypothetical capsule theory was proposed to reasonably explain the dispersion effect of MC, CMC, and HEC. The experiments showed that pre-dispersion by ultrasonic vibration improved the dispersion of carbon fibers greatly. The dispersivity of carbon fibers was closely related to the category and mass fractions of dispersants. With the same mass fraction of dispersants at a certain temperature, the dispersion effect was in order of HEC > CMC > MC. Meanwhile, when the mass fraction of HEC was between 0.6 and 0.8 wt% by weight of cement and the mass fraction in the aqueous solution was between 1.65 and 1.80 wt%, carbon fibers dispersed most ideally and distributed further uniformly in the cement matrix.

Influence of Fibre Length on the Behaviour of Polypropylene Fibre Reinforced Cement Concrete

Concrete being a mixture of cement, aggregates (fine and coarse) and water, can be used in vast range of applications. It has excellent durability and availability which are its main advantages. Though, concrete is strong in compression it is comparatively weak in tensile loading. Over the years various materials have been used to reinforce concrete to withstand the tensile stresses. Polypropylene fibre is one such fibre which comes in varied sizes, is nowadays being utilized to reinforce concrete. In this study, three PP fibres were used at 0.20%, 0.25% and 0.30% content by weight. The flexural and compressive strengths were determined. Based on the results, it was observed with increase in size of fibre the compressive strength decreased significantly though it was still higher than the controlled sample. The length of PP fibres had significant effect on the compressive strength and flexural strength of concrete. Short PP fibres showed relatively higher compressive strength but lower flexural strength when higher fibre content is used, while long PP fibres achieved lower compressive strength but higher flexural strength than shorter PP fibres. The optimum dosage for both PP fibre sizes was 0.25% at which it achieved increased strength as compared to control sample.

Shear strengthening of reinforced concrete beams with PBO-FRCM composites with anchorage

In this paper results of tests carried out on beams strengthened in shear with PBO-FRCM composites were presented and compared with theoretical calculations according to the ACI549.4R-13 standard. PBO-FRCM (Fibre Reinforced Cementitious Matrix) composites consist of mineral mortar and PBO (p-Phenylene Benzobis Oxazole) composite fibres. The mineral mortar makes them a good alternative to the commonly used FRP composites, especially in structures exposed to high temperatures and in historic buildings. FRCM composites mostly fail due to the debonding (without rupture) of the fibres from the mineral mortar. Proper anchorage should be employed to prevent the premature debonding of the composite and to increase the effectiveness of the FRCM reinforcements. As part of this research tests were carried out on 10 RC T-beams strengthened in shear with PBO-FRCM composites with different anchorage system. The mechanisms of failure of the beams were analysed and described. A theoretical model based on ACI549.4R-13 (the only existing standard for FRCM composites) was described. Shear capacity was calculated on basis of the characteristics of the materials and elements used in the tests. The results of the calculations based on ACI549.4R-13 showed the shear capacity of the T-beams with transverse steel reinforcement and anchored composites to be considerably underestimated. The theoretical model needs to be refined and verified on a larger number of elements. The results and the probable causes of the discrepancies between the experimental results and the analytical ones are discussed.