Comparative flexural behavior of Hybrid Ultra High Performance Fiber Reinforced Concrete with different macro fibers

The flexural performance of four Hybrid (H-) Ultra High Performance Fiber Reinforced Concretes (UHPFRCs) with different macro fibers was investigated according to ASTM standards C1018-97 and C 1609/C 1609M-05. Four macro fibers were long smooth (LS-) steel fiber, two types of hooked (HA- and HB-) steel fibers, and twisted (T-) steel fibers while one type of micro fiber, short smooth (SS-) steel fiber, was blended. The enhancements in modulus of rupture, deflection capacity and energy absorption capacity were different according to the types of macro fiber as the amount of micro fiber blended increased. The order of flexural performance of H-UHPFRC according to the types of macro fiber was as follows: HB- > T- > LS- > HA-fiber. The influence of strain capacity in tension on the flexural performance of H-UHPFRC was also examined. The deflection capacity and the ratio between flexural strength and tensile strength were dependent upon the strain capacity of H-UHPFRC.     

Post-crack (or post-peak) flexural response and toughness of fiber reinforced concrete after exposure to high temperature

Several studies have already reported on the various effects of high temperature on the mechanical properties of fiber reinforced concrete (FRC). Some of these effects include changes in; compressive strength, compression toughness and splitting tensile strength. None of the previous studies have investigated the changes that might occur on the post-crack flexural response and flexural toughness. Post-crack (or peak) response and toughness is considered one of FRC’s key beneficial characteristics – as the purpose of adding fibers is to increase the energy absorption and load carrying capacity after an initial crack. In this study, the flexural toughness test according to ASTM C1018 was carried out on two types of concrete: plain concrete and fiber reinforced concrete with three different types of fiber (steel, polypropylene, and polyethylene) at 0.5% and 1.0% by volume fractions. Prior to the flexural test, the specimens were put in an oven chamber and subjected to high temperatures using the ISO/TR834 standards of: 400 °C, 600 °C and 800 °C. The results showed the typical load–deflection response of FRC was a double-peak response. The first peak represented the properties of concrete matrix and the second peak represented the properties of the fibers used. Under flexural load, instead of dropping (or remaining unchanged), the post-peak load and the toughness were found to increase at lower temperatures (400 °C) and later, decreased as the temperature increased (600 °C and 800 °C). Fiber type and content also played an important role. At a temperature of 400 °C, all FRCs exhibited higher flexural strength and increased post-peak response and toughness. A significant decrease in strength, toughness and load–deflection response was observed with synthetic or plastic FRC (PFRC) when the temperature approached 800 °C. When steel FRC (SFRC) was used, those effects were relatively small. It appears, SFRC has better heat resistance than the PFRC. The density (measured by ultrasonic pulse velocity) was found to decrease more in the PFRC than in the SFRC.     

Mechanical properties of natural fibers reinforced sustainable masonry

This research evaluates the physical and mechanical properties of Portland cement masonry blocks reinforced with lechuguilla natural fibers, that were lightened with 2-l bottles of polyethylene terephthalate.A concrete mix was designed for a target compressive strength of 16 MPa at 28 days, and slump of 70 mm. Masonry concrete blocks with dimensions of 730 × 340 × 130 mm were produced for two different fiber lengths (25 and 50 mm) and with fiber contents of 0.25%, 0.50%, 0.75% and 1.0%.Based on the obtained results, it was found that as the aspect ratio decreases the compressive strength increases and that the use of natural fiber (Vf = 0.5–0.75%) improves masonry post-cracking features, showing a ductile behavior and generating a uniform cracking pattern in the longitudinal sides of the blocks.     

Performance of deteriorated corrugated steel culverts rehabilitated with sprayed-on cementitious liners subjected to surface loads

A variety of alternatives to rehabilitate culverts have been developed over the past decades given their advantages over conventional open-cut culvert replacement. However, the performance of many of these systems has not yet been examined through laboratory testing. The objective of the present paper is to examine the performance of deteriorated steel culverts rehabilitated with spray-on liners when subjected to surface loads. Two 1200 mm diameter corrugated steel pipelines with similar levels of deterioration in the invert-haunch area were buried to a depth of 1200 mm and tested under service load employing a load frame simulating a single axle of a Canadian design truck. The pipelines were then rehabilitated with spray on-cementitious liners (each with a different target thickness). Once rehabilitated, the pipelines were examined again under the service load employing the single axle load frame at 1200 mm of soil cover, and then tested employing a tandem axle load frame at 2100 and 1200 mm of soil cover. During all tests, changes in diameter, curvature and liner strains were monitored. The data obtained indicates that the flexible pipelines responded like semi-rigid structures after rehabilitation. It was also observed that the difference in liner thickness of 30% did influence the response of the pipelines, and that extreme fiber tensions during service loading were 7% and 13% of the tensile strength of the liner materials for the 76 mm and 51 mm liner thicknesses that were specified.     

Improvement of residual compressive strength and spalling resistance of high-strength RC columns subjected to fire

This paper investigates the spalling properties of high-strength concrete in order to improve the residual compressive strength and spalling resistance in specimens subjected to 3 h of unloading fire conditions. This study consists of three series of experiments with eighteen different specimens varying in fiber type and content, finishing material and simultaneous fiber content and lateral confinement. They were fabricated to a 300 × 300 × 600 mm mock-up size. Results of the fire test showed that the control concrete was explosive, while the specimens that contained more than 0.1 vol% of polypropylene (PP) and polyvinylalcohol (PVA) fibers were prevented from spalling. One specimen, finished by a fire endurance spray, exhibited even more severe spalling than the control concrete. The specimen containing 0.1 vol% of PP fiber and using a confining metal fabric at the same time, showed the most effective spalling resistance; in particular, the residual compressive strength ratio was even higher than that of the control concrete before the fire test. It was demonstrated that adding fibers in concrete prevented the spalling occurrence and confining metal fabric around the main bars of concrete specimens can secure the strength of structures during the conditions of elevated temperature.     

Physical and mechanical properties of durable sisal fiber–cement composites

Sisal fiber–cement composites reinforced with long unidirectional aligned fibers were developed and their physical–mechanical behavior was characterized in the present study. Flat and corrugated sheets were cast by a manual lay-out of the fibers in a self-compacted cement matrix and compressed with a pressure of 3 MPa. Direct tensile and bending tests were performed to determine the first crack, post-peak strength and toughness of the composites. Drying shrinkage, capillary water absorption and water tightness tests were performed to characterize the physical properties of the composites. To ensure the composite durability, the ordinary Portland cement matrix was modified by adding metakaolin and calcined waste crushed clay brick to consume the calcium hydroxide generated during Portland cement hydration. The durability of the newly developed composite was determined through accelerated aging conditions using the hot-water immersion test. The developed material presented a multiple cracking behavior under bending, even when subjected to 6 months of hot-water immersion under 60 °C. Scanning Electron Microscopy was used to investigate the micro-structure of the composites before and after aging.     

Effects of steel fiber addition on mechanical properties of concrete and RC beams

C20 and C30 classes of concrete are produced each with addition of Dramix RC-80/0.60-BN type of steel fibers (SFs) at dosages of 0, 30, 60 kg/m³, and their compressive strengths, split tensile strength, moduli of elasticity and toughnesses are measured. Nine reinforced concrete (RC) beams of 300 × 300 × 2000 mm outer dimensions, designed as tension failure and all having the same steel reinforcement, having SFs at dosages of 0, 30, 60 kg/m³ with C20 class concrete, and nine other RC beams of the same peculiarities with C30 class concrete again designed as tension failure and all having the same reinforcement are produced and tested under simple bending. The load versus mid-span deflection relationships of all these RC and steel-fiber-added RC (SFARC) beams under simple bending are recorded. First, the mechanical properties of C20 and C30 classes of concrete with no SFs and with SFs at dosages of 30 and 60 kg/m³ are determined in a comparative way. The flexural behaviours and toughnesses of RC and SFARC beams for C20 and C30 classes of concrete are also determined in a comparative way. The experimentally determined (mid-section load)–(SFs dosage) and (toughness)–(SFs dosage) relationships are given to reveal the quantitative effects of concrete class and SFs dosage on these crucial properties.     

Compressive behavior of circular CFST columns externally reinforced using CFRp composites

Over the last several decades, various approaches to strengthening steel structures through the use of Carbon fibre reinforced polymer (CFRP) composites have been investigated; however, most of the studies have been focused on the steel tubes. This paper presents the feasibility analysis on the application of CFRP composite strips to strengthen the CFST column member under axial loading. CFRP strips having a width of 50 mm were used to confine the columns. The experimental parameters were the spacing between the CFRP strips (20 and 30 mm) and number of CFRP layers (one, two and three layers). All columns were tested under axial compression until failure. The experimental results revealed that bonding of CFRP composites effectively delayed the local buckling of the columns and also reduced the axial deformation by providing a confinement/restraining effect against the elastic deformation at both spacings. The confinement effect provided by CFRP composites was increased with the increase in the number of layers; however, the enhancement in buckling stress was not proportional. The load carrying capacity of the column increased with the application of CFRP strips, by up to 30% compared to the of un-strengthened column. From the test results it is suggested that the application of CFRP strips at a spacing of 20 mm or 30 mm is suitable for strengthening of a CFST circular column member; however, the application of strips at intervals of 30 mm recommended as an economical approach to strengthening compared to the 20 mm spacing. Finally, an analytical equation was proposed to predict the load carrying capacity of the CFRP strengthened CFST column, and the average difference between the calculated and experimental value was only ±5%.     

Laboratory investigation of indirect tensile strength using roofing polyester waste fibers in hot mix asphalt

The vast quantity of waste materials (such as roofing polyester waste fibers) accumulating throughout the world is creating costly disposal problem. The use of these materials was proved to be economical, environmentally sound and effective in increasing the performance properties of the asphalt mixture in recent years. The primary objective of this research was to determine whether homogeneously dispersed roofing waste polyester fibers improve the indirect tensile strength (ITS) and moisture susceptibility properties of asphalt concrete mixtures containing various lengths and percentages of the fiber in various aggregate sources. The experimental design included the use of three aggregate sources, two lengths (0.635 cm (1/4 in.) and 1.270 cm (1/2 in.)) of this fiber, and two fiber contents (0.35% and 0.50% by weight of total mixture). The results of the experiments found that, in general, the addition of the polyester fiber was beneficial in improving the wet tensile strength and tensile strength ratio (TSR) of the modified mixture, increasing the toughness value in both dry and wet conditions, and increasing the void content, the asphalt content, the unit weight, and the Marshall stability.     

Study on the graphite and carbon fiber modified asphalt concrete

The mechanical and electrical properties of graphite and carbon fiber modified asphalt concrete were measured in this paper through the indirect tensile test. The experimental results indicate that the mechanical properties of asphalt mixture are influenced by the addition of conductive component like graphite and carbon fiber, When the graphite content increased from 0 to 22 vol.%, Marshall stability decreased from 12.8 kN to 9.43 kN and residual stability from 91.1% to 87.2%. Rutting dynamic stability decreased from 3318 times/mm to 2619 times/mm. After adding the carbon fiber, when the carbon fiber content increased from 0 to 2 vol.%, their Marshall stability and residual stability increased from 12.8 kN to 13.5 kN and residual stability from 91.1% to 92.7%. Rutting dynamic stability increased from 3318 times/mm to 3403 times/mm. When modified through combination effect of graphite and carbon fiber mixed fillers, the mechanical performance and electrical property were improved greatly, their Marshall stability and residual stability has increased from 9.43 kN to 12.1 kN and residual stability from 87.2% to 89.2%. Rutting dynamic stability increased from 2619 times/mm to 3292 times/mm. Furthermore, the resilient modulus is influenced by the addition of graphite, the value of resilient modulus is as much as that of the original, it is 90% when graphite is 30 vol.% and is 70% when graphite is 45 vol.%. The electrical resistance increases reversibly with increasing tensile strain either under dynamic indirect tensile testing or static indirect tensile testing, graphite and carbon fiber modified asphalt concretes are effective for the self-monitoring of strain. It is foreseen that the strain–stress self monitoring is valuable for weighing, traffic monitoring, border monitoring and structural vibration control.     

Preliminary experimental investigation of the fatigue bond behavior of CFRP confined RC beams

This paper presents the results of the first phase of a study on the effect of the confinement provided by transverse carbon fiber reinforced polymer (CFRP) sheets on the fatigue bond strength of steel reinforcing bars in concrete beams. Reinforced concrete bond-beams 150 × 250 × 2000 mm were tested. The variables examined were the area of the CFRP sheets (none or one U-wrap CFRP sheet), the reinforcing bar diameter (20 or 25 mm) and the load range applied to the specimens. The results showed that increasing the bar diameter increased the fatigue bond strength for the unwrapped beams. The CFRP sheets increased the bond strength of the bond-beams with 20 mm bars. However, for the beams with 25 mm steel bars the failure mode changed from a bond splitting failure for the unwrapped beams to a diagonal shear failure for the CFRP wrapped beams, and there was little increase in fatigue strength. Finally, the bond failure mechanism for repeated loading is described.     

The effect of polypropylene fibers on the properties of fresh and hardened lightweight self-compacting concrete

This paper evaluates the LECA Lightweight Self-Compacting Concrete (LLSCC) manufactured by Nan-Su, of which the Packing Factor (PF) of its design mixing method has been modified and improved.The study analyzes the impact of polypropylene fibers on LLSCC performance at its fresh condition as well as its mechanical properties at the hardened condition.The evaluation of Fiber Reinforced LLSCC (FR-LLSCC) fluidity has been conducted per the standard of second class rating of JSCE, by three categories of flowability, segregation resistance ability and filling ability of fresh concrete.For the mechanical properties of LLSCC, the study has been conducted as follows: compressive strength with elapsed age, splitting tensile strength, elastic modulus and flexural strength, all of which were measured after the sample being cured for 28 days.When self-compacting concretes were lightened to 75% of their normal weight, their fresh properties are affected immensely.Applying 0.3% volume fractions of polypropylene fiber to the LLSCC resulted in 40% reduction in the slump flow (from 720 mm to 430 mm). In general, the rate of slump flow over Super Plasticizer (SP) volume percentage reduced with the use of polypropylene fibers in the FR-LLSC.Polypropylene fibers did not influence the compressive strength and elastic modulus of LLSCC, however applying these fibers at their maximum percentage volume determined through this study, increased the tensile strength by 14.4% in the splitting tensile strength test, and 10.7% in the flexural strength.     

Effect of fiber type and content on bleeding of steel fiber reinforced concrete

In general, the addition of fibers in concrete mix significantly improves many of the engineering properties of concrete. On the other hand, steel fibers reduce the workability of concrete. This paper presents the effect of steel-fiber length (aspect ratio) and content on bleeding of steel fiber reinforced concrete (SFRC). Two different steel fiber types (both is hooked-end) were used at a ratio of 0% (control), 0.3%, 0.64%, 1% and 1.3% by volume. Slump, Ve-Be test, air content and unit weight were determined experimentally. Specimens were poured in the standard moulds and the bleeding water content was measured 30 min, 60 min, 90 min, 120 min, 150 min and 180 min after starting the test. The results indicated that the workability of concrete significantly reduced as the fiber dosage rate increases. This was assessed through standard slump test and Ve-Be consistometer test. The bleeding water content was increased by increase of the fiber volume fraction and fiber aspect ratio according to experimental results. Also, a bleeding coefficient value for SFRC made with and without steel fiber was proposed as a result of this study.     

Behaviour of precast concrete floor slabs exposed to standardised fires

This paper quantifies the thermal movements of 14 simply supported precast reinforced concrete floor slabs of 4.5 m span and 900 mm width exposed to two standardised heating regimes used in fire resistance furnace tests. The tests were designed to show the effect of varying the slab thickness, type of concrete, imposed load, soffit protection and nature of fire exposure on the mid-span flexural deflection and axial movements of the slab ends. Measured deflections showed that during the 90 min design period of fire resistance thermal bowing was dominant and the effect of the 1.5 kN/m² design imposed load was small. The NPD hydrocarbon fire exposure caused a doubling of the flexural deflections achieved using the standard BS 476: Part 8 (now Part 20) fire exposure in the first 20 min of exposure.     

Concrete cover effect on reinforced concrete bars exposed to high temperatures

The mechanical properties of structural reinforcement steel have been investigated after the exposure to high temperatures. Plain steel, reinforcing steel bars embedded into mortar and plain mortar specimens were prepared and exposed to 20, 100, 200, 300, 500, 800 and 950 °C temperature for 3 h individually. The S420 deformed steel bars with diameters of ∅10, ∅16 and ∅20 were used. The mortar was prepared with CEM I 42.5 N cement and fly ash. The tension tests on reinforcements taken from cooled specimens were performed, and the variations in yield strength, ultimate strength and in resilience of three different dimensioned reinforcements were determined. A cover of 25 mm provides protection against high temperatures up to 400 °C. The high temperature exposed plain steel and the steel with 25-mm cover has the same characteristics when the reinforcing steel is exposed to a temperature 250 °C above the exposure temperature of plain steel.     

Structural performance of laminated and unlaminated tempered glass under monotonic transverse loading

A total of thirty six bending tests have been conducted on 1220 × 460 mm sheets of glass, 9.5-, 12.7- and 15.9-mm thick, using slow-rate monotonic loading. Twenty four specimens were laminated on one side using either one or two 0.36-mm thick polyester transparent laminates. The study showed that lamination has significantly changed the failure mode of glass from a catastrophic failure, where fragments of glass shatter in different directions, to one which is still brittle yet safer, as the fractured glass remains fully intact. The average gains in flexural strength, stiffness and strain energy, as a result of lamination, were 20%, 10% and 34%, respectively, while the maximum gains in flexural strength, stiffness and strain energy were 36%, 33% and 52%, respectively. Because of the scatter of data, no specific correlation between the gains and reinforcement ratio (expressed as the ratio of laminate-to-glass thickness) could be established. The load–deflection behaviour of both laminated and unlaminated glass was linear up to failure. No rupture or delamination of the laminates were observed     

Seismic friction base isolation performance using demolished waste in masonry housing

The conversion of large amount of demolished waste into alternate source of building material will contribute not only as a solution to growing waste problem of waste disposal, but also it will conserve the natural resources of other building material and thereby reduce the cost of construction. The present work makes an effort to safe and economic use of recycled mortar as a supplementary material. Conventional and recycled brick prisms were casted with varying percentage of demolished waste added (0%, 10%, 20%, 30%) replacing cement and tested under compression testing machine. As the replacement is increasing, the strength is decreasing. A 1:4 scale single storey brick model was fabricated on shake table for dynamic testing using pure friction isolation system (friction material for coarse dry sand, μ = 0.36). Pure friction isolation technique can be adopted economically in developing countries where low-rise building prevails due to their low cost. The superstructure was separated from the foundation at plinth level, so as to permit sliding of superstructure during severe earthquake. The observed values of acceleration and displacement responses compare fairly with the analytical values of the analytical model except in displacement beyond 2.4 kN. It also concluded that 20% replacement of cement by demolished waste could be safely adopted without endangering the safety of the masonry structures under seismic load.To have an idea that how much energy is dissipated through this isolation, the same model with fixed base was tested and results were compared with the isolated free sliding model and it has been observed that more than 70% energy is dissipated through this pure friction isolation technique. In case of base isolation, no visible cracks were observed up to a table force of 4.25 kN (1300 rpm), whereas for fixed base failure started at 800 rpm and complete bond failure was observed at 1300 rpm.     

Damage to surface structures due to blast vibration

This paper describes effect of blast produced ground vibration on damage potential to residential structures to determine safe levels of ground vibration for the residential structures and other buildings in mining areas. Impacts of 341 blasts detonated at two mines were monitored at the test structures and 1871 blast vibrations signatures were recorded on or near the test structures. Cosmetic cracks in a native brick-mud-cement house were detected at peak particle velocities (PPV) between 51.6 and 56.3 mm/s. The reinforced concrete and cement mortar (RCC) structure experienced cosmetic cracks at PPVs of 68.6–71.3 mm/s at the first floor, whereas at second floor it was detected at PPV levels of 71.2–72.2 mm/s. Minor damage in brick-mud-cement house was recorded at PPV levels of 81.0–89.7 mm/s. The RCC structure at first and second floors experienced minor damage at PPV levels of 104 and 98.3–118 mm/s, respectively. The brick-mud-cement house experienced major damage at PPV level of 99.6–113.0 mm/s, while major damage was recorded in RCC structure on first floor at PPV of 122 mm/s, the second floor at PPV levels of 128.9–161 mm/s. Recommended threshold limits of vibrations for the different type of structures is based on these measurements and observations.     

Effects of crushed glass cullet sizes,casting methods and pozzolanic materials on ASR of concrete blocks

The aim of this study is to investigate the influence of using different particle sizes of recycled glass, casting methods and pozzolanic materials in reducing the expansion due to alkali-silica reaction (ASR) of concrete blocks prepared with the use of crushed glass as fine aggregate. In this work, 25 × 25 × 285 mm mortar bar specimens were prepared using conventional wet-mixed and dry-mixed methods. Except for the control mortar bar, all the specimens were prepared by completely replacing river sand with different particle sizes of recycled glass. In addition, the influence of fly ash (PFA) and metakaolin (MK) content on the reduction of ASR expansion was also investigated. The flexural strength of the mortar bar specimens before and after they had been exposed to 1N NaOH solution was determined to complement the results of ASR expansion test. SEM was performed to examine the microstructure as well as nature of the cement binder-glass interfacial zone. The results reveal that ASR expansion reduced with reducing particle size of glass used. For the same given mix proportion, the dry-mixed method resulted in 44% less expansion when compared with the wet-mixed method. Both PFA and MK were demonstrated to be able to significantly reduce ASR expansion of the concrete glass blocks.     

Asbestos-free technology with new high toughness polypropylene (PP) fibers in air-cured Hatschek process

After almost 70 years of experience in the fiber–cement production in Brazil, Saint-Gobain Brasilit started the non-asbestos production using polyvinyl alcohol (PVA) fiber technology in 2002.Due to PVA costs and availability problems, efforts were done to develop a local high toughness polypropylene (PP) fiber, with improved frictional interface and better dispersion and affinity to Portland Cement matrix.In the last 5 years, more than 1.6 million tons of asbestos-free corrugated and flat sheets have been produced and commercialized representing about 200 million square meters.This paper reviews the alternative fibers for replacing asbestos and the reinforcing model in cement based products. It also presents the Brasilit high toughness polypropylene fibers properties, its manufacturing process and its mechanical performance and improved impact resistance behavior comparing to fiber–cement products available in the Brazilian market.