Fiber-reinforced Cement Research Articles

Dynamic compressive response of high-performance fiber-reinforced cement composites

Composite effect of hybrid fibers with different types containing steel fibers of two different length-diameter ratio, and polymer (PE) fiber was experimentally investigated for high-performance fiber-reinforced cement composites (HPFRCCs). Both of cylindrical cement paste and mortar specimens reinforced with 1.5% vol. hybrid fiber were carried out using a Φ75mm diameter split Hopkinson pressure bar ranged strain rates from 67 s−1 to 219 s−1. A dynamic relationship of compressive stress–strain were tested. Results shows that different fiber reinforcement and strain-rate have a great effect for dynamic behavior of HPFRCCs. The dynamic compressive strength and ultimate strain all generally increase with increasing strain rate. At the similar strain rates, HPFRCCs with larger amount of PE fiber had higher compressive strength. Addition of steel fiber has improved the deformation performance and energy absorption. HPFRCCs with a larger amount of long steel fibers have shown higher dynamic strength.

Commercial and recycled carbon/steel fibers for fiber-reinforced cement mortars with high electrical conductivity

The paper aims to provide a comprehensive study on the compositional optimization of high-conductive multifunctional fiber-reinforced cement mortars (FRCMs). Therefore, the effects of three different fiber types: virgin carbon fibers (VCFs), recycled carbon fibers (RCFs), and brass-plated steel fibers (BSFs), added at a broad range of concentrations, as 0.05%, 0.1%, 0.2%, 0.4%, 0.8%, 1.2%, and 1.6% by volume, on the mechanical, electrical and durability properties of FRCMs have been compared. The results showed that RCFs increase the flexural and tensile splitting strength up to 100%, whereas BSFs improve the compressive strength by 38%. Moreover, the fibers decrease both the capillary water absorption and the drying shrinkage by 39%. Electrical conductivity tests show that RCFs decrease the electrical resistivity of mortars up to one order of magnitude, in addition to a percolation threshold between 0.1 and 0.2 vol%.

Study on in-situ modification of poly-dopamine on glass fibers and its effect on shrinkage performance of cement materials

Cement-based materials are one of the essential construction materials that had been widely used in infrastructure and facilities. However, it experienced shrinkage problems, which led to the cracking of concrete buildings and deterioration of the durability. The incorporation of glass fibers can improve the shrinkage resistance of cement materials by enhancing the interface between cement and fiber. Aiming at improving the shrinkage resistance of cement, in this study, glass fibers were in-situ modified with poly-dopamine in aqueous solution. The effect of dopamine hydrochloride concentration and the pH of the solution were investigated with the optimal condition attained to be 2×10−3 g/ml and 8.5, respectively. Scanning electron microscope (SEM) and X-ray photoelectron spectroscopy analysis (XPS) were utilized for the characterization of as-prepared poly-dopamine modified glass fibers. Subsequently, as-prepared and untreated glass fibers were mixed with cement at varied volume fraction and water-cement ratio for the study of shrinkage performance. The glass fiber-reinforced cement had a lower shrinkage than cement without glass fibers. Compared with the cement without glass fibers, when the water-cement ratio was 0.4 and the volume content of in-situ modified glass fibers of poly-dopamine was 7%, the reduction in 28-day shrinkage of poly-dopamine in-situ modified glass fiber-reinforced cement was large extent, reducing by 42%. The shrinkage resistance performance of in-situ modified glass fibers reinforced cement with poly-dopamine was better than that of untreated glass fibers. In short, this work developed novel approach for in-situ modification of glass fibers and found a new path to improve the shrinkage resistance of cement material.

The effect of the strengthening of AAC masonry walls using FRCM system

This paper describes results from testing the tensile strength of compressed masonry walls strengthened with fiber-reinforced cement matrix [FRCM] system on one side, both sides, or without any strengthening. Test models were prepared from masonry units made of autoclaved aerated concrete SOLBET OPTIMAL 4/600. Walls were built with a ready-mixed mortar for thin layer joints of class M5, without fi lling head joints. PBO fi bre grids embedded in a mineral matrix were used as superfi cial strengthening. Lateral surfaces of masonry walls were strengthened with ready-mixed mortar PBO-MX GOLD MASONRY with embedded grid PBO--MESH GOLD 22/22. Then, the surface layer of ready-mix mortar PBO-MX GOLD MASONRY was applied. The used superfi cial strengthening provided an additional strengthening of the cracked models and their safer behaviour after failure.

Effects of the chemical treatment on coal-fired bottom ash for the utilization in fiber-reinforced cement composites

Around 3 million tons of municipal solid wastes called bottom ash (BA) are produced annually from the coal-fired power plants and it is still much underutilized in Thailand. Hence, the increasing usage of BA in industrial scale is necessary to limit the environmental impacts from landfilling of those by-product. Using of BA in fiber cement (FC) manufacturing seems to be a promising one. However, several negative effects regarding the extremely high water content from the fiber-cement forming process (Hatschek process) and the BA characteristic (the creation of bubble network) need to be eliminated. Both mentioned inferiors significantly reduce the cement hydration mechanism leading to remarkable reductions of set and hardened performances of fiber cement. Therefore, chemical treatment (CT) was introduced to boost up the hydration kinetic and characterized via the relevance of higher heat of hydration. Additionally, scanning electron microscope (SEM) was used to reveal the beneficial effects of treated BA through the microstructures. The results showed the chemically treated BA improve kinetic of hydration reaction was from the modification of BA surface.

Probabilistic damage evolution in masonry strengthened with FRCM subjected to aggressive environment

This paper concerns the applications of advanced Fibre Reinforced Cementitious Matrix (FRCM) systems on existing masonry structures. At the state of the art, it shows that the FRCM-to-masonry bond is affected significantly by substrate properties and environmental conditions. For this purpose, an experimental campaign was realised recreating different experimental scenarios, and the results thereby achieved were critically and comparatively discussed. In particular, specimens constituted of two types of fired-clay bricks (either with a single brick or a running bond masonry) were reinforced with a carbon fibre grid, externally glued by means of a cementitious or a lime-based matrix, and then exposed to salt crystallisation induced by capillarity over several months. Visual observation combined with laser profilometer measurements revealed a progressive deterioration of the surface with material loss and signs of bulging between the composite - masonry interface. Pull-off tests on deteriorated samples confirmed the progressive weakening of the bond in terms of nominal strength. To interpret the amount of data, a novel probabilistic model was proposed, apt to predict possible damaging effects on the surface of reinforced masonry elements.

Analysis of the Versatility of Multi-Linear Softening Functions Applied in the Simulation of Fracture Behaviour of Fibre-Reinforced Cementitious Materials.

Fibre-reinforced cementitious materials (FRC) have become an attractive alternative for structural applications. Among such FRC, steel- and polyolefin fibre-reinforced concrete and glass fibre-reinforced concrete are the most used ones. However, in order to exploit the properties of such materials, structural designers need constitutive relations that accurately reproduce FRC fracture behaviour. This contribution analyses the suitability of multilinear softening functions combined with a cohesive crack approach for reproducing the fracture behaviour of the FRC mentioned earlier. The performed implementation accurately simulated fracture behaviour, while being versatile, robust, and efficient from a numerical point-of-view.

Development and analysis of sponge gourd (Luffa cylindrica L.) fiber-reinforced cement composites

Sponge gourd (Luffa cylindrica L.) fiber-reinforced cement composites were developed and analyzed. Dried sponge gourd fruit’s fibrous vascular system forms a natural 3D network that can reinforce matrices in composite materials, diverting cracks along the complex array of 3D interfaces between the fibers and the cementitious matrix. To avoid fiber deterioration, the cement paste was modified by incorporating pozzolanic materials. The fibers were mechanically characterized by tensile testing of strips of the 3D natural fiber array and of single fibers extracted from the array. The fibers had an average tensile strength of 140 MPa and an average Young’s modulus up to 28 GPa. Image analysis showed that the fiber spatial distribution inside the 3D network was random. The modified cement paste was characterized by its workability (flow table test) and mechanical behavior (compression and three-point bending tests), with average results of 430 mm, 62.7 MPa, and 6.2 MPa, respectively. Under bending, the cement matrix collapsed after the first crack. The sponge gourd-cement composite manufactured with 1 wt% of fibers showed an average flexural strength of 9.2 MPa (approximately 50% greater than the unreinforced matrix). Importantly, the composite also presented a limited deflection-hardening behavior. These results support sponge gourd’s possible use as reinforcement in cement matrix composites.

Permeable Nanomontmorillonite and Fibre Reinforced Cementitious Binders.

Clinker reduction in cementitious binders is of paramount importance today, and nanotechnology has extended permissible limits. In the present study, a reference binder consisting of 60% Portland cement, 20% limestone, 20% fly ash, 3% polyvinyl alcohol (PVA) fibres and 2% superplasticizer is optimized with three different types of nano-montmorillonite (nMt) dispersions; two organomodified ones and an inorganic one at different proportions (0.5% to 4%). Flexural strength, measured on day 7, 28, 56 and 90, was improved after day 28 with the addition of inorganic nMt. Thermal gravimetric analyses carried out on day 7, 28, 56 and 90 coupled with x-ray diffraction (at day 28) showed a distinctively enhanced pozzolanic reaction. Backscattered electron imaging confirmed changes in the microstructure. Late age relative density measurements of the nMt cementitious nanocomposites showed higher values than these of the reference paste, which can be attributed to better particle packing. Mercury intrusion porosimetry measurements give support to the optimal nMt dosage, being 1% by total mass of binder and water impermeability tests (modified with BS EN 492:2012) suggest that inorganic nMt can be a viable option material where permeability constitutes a prerequisite. Suggestions for further activation of the nMt-fibre reinforced cementitious nanocomposites were also made.

Long-term mechanical properties of cellulose fibre-reinforced cement mortar with diatomite

This paper presents a study investigating the long-term mechanical properties of cellulose fibre-reinforced cement mortars incorporating diatomite as a replacement material for quartz sand. Important properties including mass, compressive and flexural strength, sorptivity, water penetration depth and porosity have been rigorously investigated. Significant findings demonstrated that increasing the replacement level of diatomite resulted in a systematic decrease in the final mass of cellulose fibre-reinforced cement mortars and a dramatic increase in both flexural and compressive strength. In the short term, sorptivity, water penetration depth and porosity were enhanced, whereas the pozzolanicity of diatomite provided long-term strength gain over the 6 month period of study. Microstructural development of mortars, confirmed using scanning electron microscopy, revealed a denser, more compact structure in the diatomite specimens, which was consistent with the physical property measurements. This research supports the development of environmentally friendly diatomite-based mortars for construction.

Numerical Modelling of the Tensile Behaviour of BFRCM Strips

This paper aims at investigating the tensile behaviour of basalt fibres on cementitious matrix for the strengthening of masonry structures. The use of Basalt Fibre Reinforced Cementitious Matrix (BFRCM) is favourably considered by the scientific community because it represents a natural composite material with high compatibility with stone and masonry substrate. The study is developed through the generation of Finite Element (FE) models capable of reproducing the tensile behaviour of BFRCM strips with different number of layers of grid. For the scope, the micro-modelling approach is adopted assuming different levels of detail for the simulation of the interface constitutive behaviour. Fibre and substrate are modelled separately and the interface between the two components is simulated by introducing numerical contact properties for reproducing the perfect bond condition, on one hand, and the cohesive tangential slip, on the other hand. The damage of the composite system is investigated using proper damage numerical models at the interface.

On the Use of Digital Image Correlation (DIC) for Evaluating the Tensile Behaviour of BFRCM Strips

Fibre Reinforced Cementitious Matrix (FRCM) composites are becoming largely adopted for retrofitting masonry structures. These materials offer several advantages in comparison to Fibre Reinforced Polymer (FRP) composites, such as good resistance to fire and high temperatures, vapour permeability, possibility to be applied on wet surfaces, higher compatibility with the masonry substrate. However, the tensile behavior of FRCM materials is more complex compared to FRP composites, due to the limited tensile strength of the cement-based matrix. For this reason, FRCM materials require appropriate tensile characterization and, in this context, the use of non-conventional measurement systems, such as the Digital Image Correlation (DIC), can offer numerous advantages. This work presents an experimental study on the application of the DIC technique for the tensile characterization of Basalt Fibre Reinforced Cementitious Matrix (BFRCM) strips. Tensile tests were carried out on three series of specimens reinforced with one, two or three layers of basalt grid in order to investigate the effect of the reinforcement ratio on the tensile response of the composite strips. The test setup and the calibration of the DIC analyses are discussed. It is shown as the DIC allows obtaining detailed information on the tensile response, including the evaluation of the full strain field on the surface of the BFRCM strips and the location of cracks. Results are discussed also in terms of stress-strain curves and failure modes.

Numerical Modelling of the Experimental Response of SRG Systems

Modern repairing and retrofitting methods for existing structures make use of composite materials, consisting of high strength textiles and a matrix, which can be either polymeric or inorganic. These kinds of techniques have been largely applied to masonry structures, since they significantly improve structural performance with a small increase of weight and a minimum invasiveness. However, the application of organic gluing agents on masonry has revealed some well-known drawbacks, which are almost all overcome resorting to inorganic matrixes, namely cement or lime mortars. An entire class of composites is thus identified as TRM (Textile Reinforced Mortars) or FRCM (Fibre Reinforced Cementitious Matrices). Among them, Steel Reinforced Grout (SRG) are characterized by Ultra High Tensile Strength Steel (UHTSS) cords embedded in mortar matrix and their use to improve the structural performance of existing historical masonry buildings is becoming more and more diffused. Qualification tests and acceptance criteria for SRG have just been defined. Nonetheless, numerical simulation of current available test procedures is mandatory to identify peculiar aspects of the response that at a following stage become an integral part of large scale models, when entire reinforced structures or portions need to be analysed. To this end, this work presents the numerical modelling of two different direct tensile tests on SRG systems: the Clamping-grip setup (RILEM Technical Committee 232-TDT 2016) and the Clevis-grip setup (ICC-ES AC434 2016). Numerical models able to replicate experimental tests and catch fundamental differences in their failure mechanisms are present

Post-Cracking B-FRCM Strengthening of a Traditional Anti-Seismic Construction Technique (<i>Casa baraccata</i>): Extensive Experimental Investigations

In the framework of the Mediterranean cultural heritage, the term “fictile tubule” identifies a peculiar type of brick, characterized by a cylindrical shape and a hollow core. Its unique geometry and characteristics rank it among the first hollow clay bricks in history. The large-scale production of fictile tubules allegedly began in the Roman provinces of Northern Africa during the 2nd Century A.D., where they were employed for building vaulted and domed structures without the need of centrings. Over the following Centuries, the construction technique of fictile tubules embedded in mortar was constantly refined and improved. This led to an extensive use of such technique in several buildings - as part of different structural elements (vaults, domes, floors, walls) - all over the Mediterranean area, and especially in Southern Italy. In 1909, after the disastrous earthquake in Messina and Reggio Calabria, Calabrian engineer Pasquale Frezza devised and patented an anti-seismic construction system which evolved the technology of casa baraccata. Frezza’s take on this traditional Calabrian way of erecting buildings involved the use of a specific type of fictile tubule, named carosello, alternated with common bricks in masonry walls, which are then encased in a timber frame. This paper presents an investigation on the structural behavior of Frezza’s evolution of casa baraccata, aimed at its possible revival as a relevant anti-seismic construction technique. Two specimen walls with dimensions equal to 60×60×15 cm3 are built according to Frezza’s patent and experimentally examined through a diagonal compressive test at the Civil Engineering Laboratory of University of Calabria. For the first specimen wall the test is carried out until failure to identify the collapse load. Conversely, for the second specimen wall the test is halted immediately after the formation of the first vertical cracks. The specimen is subsequently repaired using B-FRCM (Basalt Fiber-Reinforced Cementitious Matrix) as reinforcement, and the diagonal compressive test is repeated, this time until failure. The results in terms of collapse load and shear strength for both specimens are then compared and critically discussed, highlighting the increased load-bearing capacity of the wall built according to Frezza’s patent and reinforced with B-FRCM.

Dynamic Mechanical Properties and Fractal Characteristics of Polypropylene Fiber-Reinforced Cement Soil under Impact Loading

This paper aims to study the dynamic mechanical properties, failure patterns, fractal behaviors, and energy dissipation of polypropylene fiber-reinforced cement soil under impact loading. Dynamic compression tests for reinforced cement soil with different polypropylene fiber contents of 0%, 0.4%, 0.8%, and 1.2% were conducted using a 50 mm diameter split Hopkinson pressure bar (SHPB) device. The static and dynamic stress-strain curves, dynamic strength increase factor (DIF), fractal behaviors, and energy dissipation properties of polypropylene fiber-reinforced cement soil were investigated and analyzed. The experimental results indicated that the dynamic strength increase factor (DIF) of cement soil increases firstly and then decreases with the increase of polypropylene fiber content from 0% to 1.2%. The maximum dynamic compressive strength of cement soil was obtained with adding 0.8% polypropylene fiber. With the increase of polypropylene fiber content, the average particle size of cement soil fragments has an increasing trend, whereas the fractal dimension presents a decreasing trend. Besides, the fragmentation degree of cement soil decreases correspondingly with the increase of polypropylene fiber content. The fractal dimension value has a linear relationship with the polypropylene fiber content and a decreasing exponential relationship with the average particle size. The absorbed energy per unit volume of cement soil presents an increasing trend firstly and a decreasing trend subsequently as the polypropylene fiber content increases from 0% to 1.2%. When the fractal dimension of cement soil is kept in the range of 2.04 to 2.15, the absorbed energy per unit volume of cement soil increases first and then decreases. The absorbed energy per unit volume of cement soil has a quadratic parabola relationship with polypropylene fiber content and fractal dimension, respectively. At last, the relationship of the absorbed energy per unit volume, fractal dimension, and polypropylene fiber content can be established, which can be used in the studies of dynamic behaviors and fractal properties of the fiber-reinforced cement soil under impact loading.

Preparation and piezoresistive properties of carbon fiber-reinforced alkali-activated fly ash/slag mortar

In this study, a novel type of conductive mortar was proposed and prepared by alkali-activated fly ash/slag (AAFS) combined with carbon fibers. The workability, mechanical properties, electrical resistivity and piezoresistive properties of carbon fiber-reinforced AAFS (CF-AAFS) mortar were investigated and compared with carbon fiber-reinforced cement mortar (CF-CM). It was found that CF-AAFS exhibited much better workability and significantly higher compressive strength (>66 MPa at 28 days) than CF-CM with the same carbon fiber content. With 0.2 vol% carbon fibers, the electrical resistivity of CF-AAFS mortar decreased from 3313 Ω·cm to 165 Ω·cm at 28 days, reaching the percolation threshold. AAFS mortar with only 0.1 vol% carbon fiber content exhibited good piezoresistivity under both monotonic and cyclic compression. Therefore, CF-AAFS was regarded as a promising material in the use of self-sensing structure in construction.

STRUCTURAL REHABILITATION AND REAL TIME MONITORING OF THE “PONTE DELLE GRAZIE” BRIDGE IN FAENZA, ITALY

Abstract. The “Ponte delle Grazie” is a three spans 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 behavior of the bridge, the deteriorated concrete was restored and reinforced, in a sustainable way, in order to make the structure safe and usable again. After the restoration and reinforcement the bridge capacity satisfy a reduced live load useful for urban traffic. After the restoration and reinforcement the bridge capacity satisfy a reduced live load useful for urban traffic. Even if the structure has returned to be suitable for vehicular traffic, it has been necessary to set up a real-time monitoring system, which monitors the live load and the behavior of the bridge. In detail it is used a system of geophones, that are able to detect the displacement of structures by integrating in time their response. They can provide continuous health monitoring of the bridge by transmitting the data to a remote server.

Long-Lasting Waterproofing Solution for the Subgrade of High-Speed Railway in Cold Region

Abstract A durable waterproofing layer for the subgrade of a high-speed railway is of paramount importance to fight against the decrease of the bearing capacity and maintain the smoothness of the subgrade due to surface water infiltration. This article overviewed the state-of-the-practice waterproofing systems in transportation infrastructure and summarized the functional requirements of the waterproofing layer on a high-speed railway and the technical standards of asphalt concrete waterproofing layers, based on a practice with a test section on the Harbin-Qiqihaer high-speed railway. Field monitoring results of a self-compacted asphalt waterproofing system were presented, and its properties were analyzed with a comparison with the fiber-reinforced cement concrete system. It was concluded that self-compacted asphalt is a long-lasting waterproofing solution for the subgrade of high-speed railways in cold regions.

UHPFRC technology to enhance the performance of existing concrete bridges

‘Structural UHPFRC’ stands for Ultra-High Performance Fibre Reinforced Cementitious Composite material, that is, complemented by reinforcing steel bars forming a R-UHPFRC layer with the goal to enhance the resistance and durability of structural elements in reinforced concrete. This technical paper is intended to serve for the design of enhancement of reinforced concrete bridges. After summarizing the properties of UHPFRC and R-UHPFRC in terms of structural performance, analytical design rules are presented to calculate the increase in structural resistance of structural elements strengthened with a layer of R-UHPFRC. Three applications related to the design and execution of the enhancement of three existing concrete bridges including the three most common cross sections, that is, box girder, multiple beam girder and massive slab, are described with emphasis of conceptual design aspects, main results of design and main features of execution of the UHPFRC work.

Electrode material as a decisive factor in electrical resistivity measurement of cement composites

Electrical resistivity measurement is widely used as a method for characterizing different phases of cement composites and evaluating the self-sensing ability of conductive fiber-reinforced cement composites. Since the electrodes play a significant role in measuring the resistivity that enables us to investigate the properties of cement composites, the parameters related to electrodes including material, layout and fixing style must be determined carefully in order to gain a reliable result. In this study, three different materials were used as electrodes to evaluate and compare the electrical behavior of cement mortars. By qualitatively comparing the results in terms of noise fluctuations, resolution and sensitivity, the desired electrode material was determined. Also the polarization and depolarization zones of the specimens containing different fractions of silica fume were investigated so the effect of silica fume on the measured values can be evaluated. Results showed that brass can be a promising candidate as an electrode due to its low current fluctuations and desirable response period, also electrical polarization and depolarization was influenced by the silica fume replacement percentage.