Glass Fiber Reinforced Polymer (GFRP) materials have proven its efficiency in reinforcing concrete elements. The performance of Glass reinforced concrete columns (GRC columns) under axial loads have ...been studied well experimentally and numerically, While there are a very limited studies about the behavior of reinforced concrete GRC columns when exposed to fire. The weak performance of GFRP bars under fire compared to steel gave a warning about ignoring the fire behavior of GRC columns in fields. The fire performance of square GRC columns has been investigated experimentally and numerically in this study. The experimental program was done by testing nine GRC columns under design fire curve. All columns were tested under constant load during fire. Fire temperature was controlled to follow the design fire curve. Different parameters were investigated in this research; applied load ratio, concrete cover, and column configurations on the fire performance of GRC columns. Fire resistance (FR) of all tested columns were recorded and some recommendations about the FR of GRC columns were developed. The numerical study was conducted using the nonlinear finite element software. 3D-model using ABAQUS program was calibrated to reach the best simulation of GRC columns exposed to design or standard fire curve. The numerical study was done to extend the investigation of the experimental program. The influence of the various parameters have been examined to govern the fire performance of GRC columns. The experimental and numerical studies revealed that the fire resistance of GRC columns is highly affected by the applied load during fire. The difference between FR of GRC columns compared to steel-RC columns (SRC columns) was significant at eccentricity to width ratio greater than or equal to 0.2 and at higher applied load ratios. Spalling has a significant influence on the fire resistance and modes of failure of GRC columns.
•This research focused on analyzing the fire resistance of square concrete columns reinforced with GFRP bars.•The influence of the applied load ratio, concrete cover, and column’s configurations on the fire resistance of GRC-columns.•A numerical evaluation was conducted to study the fire resistance of RC columns reinforced with GFRP bars under fire.•The paper introduces some recommendations about the fire performance of concrete columns reinforced with GFRP bars.
Fire represents one of the significant hazards encountered by civil infrastructures, and thus providing appropriate fire safety measures is a major requirement in a building design for ensuring the ...safety of the occupants. Minimizing fire-induced damage and collapse of structural systems are the primary objectives in the design of concrete structures. An experimental investigation has been carried out to examine the mechanical properties such as compressive, tensile and flexural strengths of concrete exposed to elevated temperature following standard fire curve as per ISO 834. Capacity-based standards have been formulated to predict the residual strength of various grades of concrete exposed to various duration of heating. Stress strain behaviour, elastic modulus, weight loss, spalling and thermal crack pattern of specimens were also investigated. Water–cement ratio and porosity of concrete were found to be the critical factors for strength loss of concrete. A relationship is established between weight loss and strength loss of concrete. Higher grades of concrete were found to have more weight and strength loss than those of lower grades.
•Fire spalling and pore pressure of concrete were investigated under different levels of biaxial compressive stress.•The specimens are more prone to spalling when externally loaded than the unloaded ...specimens.•Fire spalling of concrete occurs due to thermal stress and external biaxial compressive stress, and tensile stresses derived from the vapor pore pressure.•Pore pressure tends to increase with external biaxial compressive stress.•Fire spalling tests should be carried out in loaded conditions.
Explosive spalling of concrete exposed to fire consists in the expulsion of shards from the heated face during rapid heating. The phenomenon can seriously jeopardize the integrity of reinforced concrete structures due to the reduction of the cross-sectional area of the structural elements and even lead to the direct exposure of reinforcing bars to flames. The literature shows that various parameters influence the occurrence of fire spalling, such as heating rate, specimen geometry and boundary conditions, concrete grade, and external loads. In this regard, the present study aims at highlighting the role of external loading in combination with the effects of pore pressure and thermo-mechanical stresses in triggering spalling in normal-strength concrete (fc28days ≈ 45 MPa). Unreinforced concrete slabs (size: 800 × 800 × 100 mm3) were subjected to a standard (ISO 834–1) fire curve under seven different levels of external membrane biaxial compressive load. The experimental results clearly show that compressive loading significantly increases spalling propensity and severity.
The slurry-infiltrated fiber-reinforced cementitious composite (SIFRCCs) material used to show much greater flexural strength and fracture toughness than normal cement concrete. By using these ...performance, the SIFRCCs could be applied for the blast resistant structures such as military purpose structures. However, most gas explosions are accompanied with fire afterward so that these high fracture toughness material needs high temperature resistance simultaneously. The SIFRCCs in this study contains fibers up to 5% by volume fraction. In addition, polymer powder was incorporated into SIFRCCs in order to enhance the fire resistance. The flexural strength and fracture toughness were compare with respected to the variation of polymer powder content, 0%, 0.5%, 1.0% and 1.5%. Powder polymer create capillary pores due to melting and burning when exposure to high temperature and minimize the vapor pressure inside the concrete model and reduces the failure of the concrete model. Specimens were covered with single layer of basalt sheet to study the flexural properties of SIFRCCs with basalt fiber sheet. The flexural strength and toughness of the specimens were investigated before and after the high temperature exposure per ISO 834 standard fire curve.
In case of a fire, the flame can spread from the building through the outer openings to the outside. In such cases, the fire temperature thermal effect determines the façade fibrocement tile thermal ...destruction, while the flammable thermo-insulating systems used for building energy effectiveness ensures it sets on fire. The spread of such a fire becomes uncontrollable and raises an immediate danger to the people inside the building, while such event dynamics delay and make it harder to put out the fire. Extra additive usage in façade fibrocement tiles can raise its resistance to fire temperature effect. Carbon fiber is widely known as a material resistant to the high temperature destructive effect. An investigation was conducted on the influence that carbon fiber has on the properties of autoclaved fiber cement samples. The autoclaved fiber cement samples were made from the raw materials, typical for façade fiber cement plates, produced in an industrial way (using the same proportions). In the samples, carbon fiber was used instead of mix cellulose fiber in 0.5%, 0.75%, 1% proportions. After completing the density research, it was determined that the carbon fiber effect had no general effect on the sample density. Ultrasound speed spreading research showed that the carbon fiber insignificantly makes sample structure denser; however, after the fire temperature effect, sample structure is less dense when using carbon fiber. The results of both these investigations could be within the margin of error. Insignificant sample structure density rise was confirmed with water absorption research, which during the 1% carbon fiber usage case was lower by 4.3%. It was found that up to 1% carbon fiber usage instead of mix cellulose fiber creates a dense structure of autoclaved fiber cement samples, and the carbon fiber in the microstructure influences the mechanical properties of the autoclaved fiber cement samples. After using carbon fiber in ambient temperature, the sample compressive strength and bending strength increased. However, the results of mechanical properties were completely different after experiencing fire temperature effect. Scanning electron microscopy research showed that the bond between the carbon fiber and the cement matrix was not resistant to high temperature effect, due to which the structure of the samples with carbon fiber weakened. Research showed that carbon fiber lowers the mechanical properties of the autoclaved fiber cement samples after high temperature effect. After analyzing the density, ultrasound speed spreading, water absorption, microstructure and macrostructure, compressive strength, and bending strength, the authors determined the main CF usage for AFK dependencies: 1. CF usage up to 1% replacing MCF makes the AFK structure more dense up to 1.5%, and lowers the water absorption up to 4.3%; 2. CF incorporates itself densely into the AFC microstructure; 3. CF usage up to replacing MCF improves the AFK strength properties up to until the fire temperature effect. Compression strength increases up 7.3% while bending strength increases up to 14.9%. 4. AFK hydrate amount on CF surface is lower than on MCF; 5. Fire temperature effect on AFK with CF causes dehydration by removing water vapor from the microstructure, resulting in a lot of microcracks due to stress; 6. The CF and cement matrix contact zone is not resistant to fire temperature effect. SEM experiments were used to determine the CF "self-removing" effect; 7. Due to complex changes happening in the AFK during fire temperature effect, CF usage does not improve strength properties in the microstructure. Compression strength decreases to 66.7% while bending strength decreases to 20% when compared with E samples.
Concrete is a building material having good fire resistance and the resistance depend on many factors including the properties of its constituent materials. Fiber Reinforced Concrete (FRC) apart from ...improving mechanical properties has better fire resistance than conventional concrete. Bond strength of concrete is one of the important properties to be considered by structural engineers while designing reinforced concrete cements. In this research, an experimental investigation has been carried out to determine the effect of fibers on the bond strength of different grades (M20, M30, M40 and M50) of concrete subjected to elevated temperature. Different types of fibers such as Aramid, Basalt, Carbon, Glass and Polypropylene were used in the concrete with a volume proportion of 0.25% to determine the bond strength by pull-out test. Prior to the pull-out test, the specimens were kept in a furnace and subjected to elevated temperatures following standard fire curve as per ISO 834. Based on the test results of the investigations, type of fiber, grade of concrete and duration of heating were found to be the key parameters that affect the bond strength of concrete. The contribution of carbon fiber in enhancing the bond strength was found to be more significant compared to other fibers. An empirical relationship has been developed to predict the bond strength of FRC at a slip of 0.25 mm. This empirical relationship is validated with experimental results.
An investigation was conducted on the influence that industrial metakaolin waste (IMW) has on the properties of autoclaved fiber cement composition (FCC) samples. FCC samples were made from fiber ...cement plate's typical components using the same proportions. In samples, IMW was used instead of cement in 10%, 20%, 30% proportions and in 50%, 100% proportions instead of ground quartz. Differential thermal analysis (DTG), thermogravimetric analysis (TGA), ultrasound pulse velocity (UPV), density, porosity and optical microscope (OM) research methods were used to identify the micro and macrostructure of samples. Mechanical properties were evaluated using flexural and compressive strength research methods. It was established that IMW was used instead of cement in fiber cement composition samples up to 10% and in fiber cement composition samples instead of ground quartz forms density microstructure structure because of Al-rich tobermorite. As a result, the flexural and compressive strength increased. Samples with higher content of IMW instead of cement had unreacted IMW and a less dense microstructure. In this case, flexural and compressive strength decreased. All FCC samples were fired in a standard fire curve (ISO 842) for 30 min. Samples of mechanical properties were established by doing flexural and compressive strength tests, and which results showed the same trends.
The prevention and mitigation of spalling in high-strength concrete (HSC) rely on mixing polypropylene (PP) as an additive reinforcement. The dense internal structures of ultra-high-strength concrete ...(UHSC) result in risks associated with a high thermal stress and high water vapor pressure. Herein, the effects of pore formation and thermal strain on spalling are examined by subjecting fiber-laden UHSC to conditions similar to those under which the ISO-834 standard fire curve was obtained. Evaluation of the initial melting properties of the fibers based on thermogravimetric analysis (TGA) and differential thermal analysis (DTA) demon strated that although nylon fibers exhibit a higher melting point than polypropylene and polyethylene fibers, weight loss occurs below 200 °C. Nylon fibers were effective at reducing spalling in UHSC compared to polypropylene and polyethylene fibers as they rapidly melt, leading to pore formation. We anticipate that these results will serve as references for future studies on the prevention of spalling in fiber-reinforced UHSC.
The article focuses on analyzing changes in the chemical composition of steel samples after the cooling phase. A few distinct types of samples made of St3S steel were heated in an electric resistance ...furnace for 1 h. The temperature in the following minutes of the furnace work was programmed to reflect the standard fire curve defined in the Eurocode in the best possible way. The box-type electric furnace was used. There were three series of samples, and each of them was cooled down in diverse ways: (a) in the water, (b) in the polymer cooling medium AQUA-QUENCH® 320, and (c) in the furnace. After that, the chemical composition of diverse types of samples with various kinds of cooling was checked. This task was realized using a laser elementary analysis microscope with the EA-300 head. The investigation allowed the authors to draw the following conclusions: the electric furnace may be used to simulate an increase in temperature with fire duration according to standard fire curve only in the phase of fully developed fire situation; the EA-300 head for laser elementary analysis allows checking of the chemical composition of investigated elements very quickly (in a few seconds).
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