Explosive Spalling Behavior Research Articles

High-temperature effect on the mechanical behavior of recycled fiber-reinforced concrete containing volcanic pumice powder: An experimental assessment combined with machine learning (ML)-based prediction

The increasing volume of waste generated by various activities has increased interest in using waste to create sustainable construction materials to achieve possible benefits. In addition, using recycled materials to produce fresh concrete is a desirable option because of its low cost, lower landfill space requirement, and the completed concrete quality. Therefore, an experimental inquiry is undertaken to ascertain the impacts of up to 20 wt% cement displaced by Volcanic Pumice Powder (VPP) with the incorporation of 1% and 2% Recycled Nylon Fiber (RNF) on the mechanical properties of concrete composites following room temperature to high-temperature (600 °C) exposure. Fresh concrete characteristics tests were performed, including slump, compacting factor, Kelly ball penetration, and density. The heat resistance of the concrete was then measured by calculating the percentage decrease in weight, the splitting tensile strength, and the compressive strength of the specimens. Heating mainly raised VPP's pozzolanic reactivity and lowered high vapor pressure through melting RNF. Therefore, VPP and RNF-treated concrete had superior mechanical performance than control concrete even when exposed to elevated temperatures. Further, the microstructural modifications brought on by RNF and VPP additions were also explored by deploying Scanning Electron Microscopy (SEM). The use of VPP in concrete led to an improvement in fresh properties, while RNF demonstrated deterioration in the same qualities. Despite this, supervised machine learning techniques are a central focus of this investigation because of their potential to predict concrete characteristics accurately. To predict the fresh and mechanical characteristics of concrete, both the Random Forest (RF) and the K-Nearest Neighbors (KNN) algorithm, along with their ensemble model counterparts, were explored. The outcomes revealed that RNF and VPP considerably improved the concrete's heat resilience and mechanical characteristics and halted the concrete composites' explosive spalling behavior at 600 °C temperatures. To prevent strength loss at high temperatures, it was discovered that adding 1% RNF content to concrete with 10% VPP was the best combination. In addition, the high coefficient correlation (R2) value of the RF and the ensemble model indicates great accuracy in outcome prediction, while the low R2 value of the KNN model indicates that the KNN model is less accurate.

Influence of high temperatures on the mechanical and microstructural properties of hybrid steel-basalt fibers based ultra-high-performance concrete (UHPC)

One of the major problem in ultra-high-performance concrete (UHPC) after exposure to high-temperatures is explosive spalling. Adding a single type of fibers alone is insufficient sometimes for suppressing such spalling, and therefore, hybridization of fibers has been adopted, particularly steel with organic fibers. However, the degradation of organic fibers at ambient and elevated temperatures is a significant challenge in the long term and needs to be addressed. Recently, inorganic basalt fibers have been considered as an alternative to organic fibers due to their better mechanical strength and high-temperature resistance characteristics. In this study, hybridizing steel with basalt fiber is proposed as a potential solution to the aforementioned problem. The spalling behavior, residual compressive strength, microstructure, porosity, hydration kinetics, phase decomposition, and quantification of hydration products were evaluated for hybrid steel-basalt fiber reinforced UHPC after exposure to high-temperatures. The study results indicated that hybrid steel-basalt fiber reinforced UHPC successfully prevented explosive spalling behavior. The use of inorganic mineral basalt fibers offers a promising solution for developing UHPC with superior high-temperature resistance.

Effect of silica fume content in concrete blocks on laser-induced explosive spalling behavior

This experimental study investigated the effect of silica fume mixed in concrete blocks on laser-induced explosion behavior. We used a 5.3 kW fiber laser as a thermal source to induce explosive spalling on a concrete surface blended with and without silica fume. An analytical approach based on the difference in the removal rate and thermal behavior was used to determine the effect of silica fume on laser-induced explosive spalling. A scanner was employed to calculate the laser-scabbled volume of the concrete surface to derive the removal rate. The removal rate of the concrete mixed with silica fume was higher than that of without silica fume. Thermal images acquired during scabbling were used to qualitatively analyze the thermal response of laser-induced explosive spalling on the concrete surface. At the early stage of laser heating, an uneven spatial distribution of surface temperature appeared on the concrete blended with silica fume because of frequent explosive spalling within a small area. By contrast, the spalling frequency was relatively lower in laser-heated concrete without silica fume. Furthermore, we observed that a larger area was removed via a single explosive spalling event owing to its high porosity.

Effects of high temperature and substitution rates of fly ash on the mechanical properties and microstructures of steel-basalt hybrid fibers reinforced cementitious composites

The excellent performance of steel and basalt fiber at room and high temperatures makes steel-basalt hybrid fibers reinforced cementitious composites (SBFRCC) a promising solution for engineering structures with fire risk. In this study, the morphology, explosive spalling behavior, flexural, compressive and splitting tensile strength, and uniaxial tensile properties of SBFRCC with different substitution rates of fly ash after exposure to high temperatures were studied. In addition, the effects of high temperature on the microstructures of SBFRCC were investigated by the scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and X-ray computed tomography (XCT) tests. The results show that the incorporation of steel fiber and basalt fiber can significantly improve the explosive spalling behavior, flexural and splitting tensile strength. After exposure to high temperatures, increasing the substitution rate of fly ash properly can reduce the rate of strength degradation to some extent, but will reduce the compressive strength and increase the explosive spalling rates. The microstructures of SBFRCC become loose and the porosities of SBFRCC increase under the combined effect of the decomposition of hydration products, the melting of fly ash, and the deterioration of steel fiber and basalt fiber.

A Numerical Investigation of Thermal-Induced Explosive Spalling Behavior of a Concrete Material Using Cohesive Interface Model

Thermal-induced spalling is a typical failure behavior of concrete materials exposed to high temperatures. This study uses Abaqus to establish a numerical model of concrete material comprising aggregates and mortar matrix. Cohesive elements considering heat conduction are embedded into this numerical model to simulate the thermal-induced explosive spalling failure process of the concrete material. Simulation results show that the heat gradually transfers from the outer boundaries to the inner areas with increasing temperature. Thermal stresses concentrate in the aggregates-mortar interfaces, where thermal-induced cracks initiate and propagate. The occurrence of thermal-induced cracks reduces the heat conductivity of mortar, reduces thermal stresses and leads to severe spalling failure in the concrete material. This research provides a practical scheme for the numerical simulation of the thermal-induced spalling behavior of concrete materials.

Explosive Spalling Behavior of Single-Sided Heated Concrete According to Compressive Strength and Heating Rate.

In this study, the effects of heating rate and compressive strength on the spalling behavior of single-sided heated ring-restrained concrete with compressive strengths of 60 and 100 MPa were investigated. The vapor pressure and restrained stress inside the concrete were evaluated under fast- and slow-heating conditions. Regardless of the heating rate, the concrete vapor pressure and restrained stress increased as the temperature increased, and it was confirmed that spalling occurred in the 100-MPa concrete. Specifically, it was found that moisture migration and restrained stress inside the concrete varied depending on the heating rate. Under fast heating, moisture clogging and restrained stress occurred across the concrete surface, causing continuous surface spalling for the 100-MPa concrete. Under slow heating, moisture clogging occurred, and restrained stress continuously increased in the deep area of the concrete cross-section owing to the small internal temperature difference, resulting in explosive spalling for the 100-MPa concrete with a dense internal structure. Additionally, while the tensile strength of concrete is reduced by heating, stress in the heated surface direction is generated by restrained stress. The combination of stress in the heated concrete surface and the internal vapor pressure generates spalling. The experimental results confirm that heating rate has a significant influence on moisture migration and restrained stress occurrence inside concrete, which are important factors that determine the type of spalling.

Impact of Elevated Temperatures on the Performance of High-Strength Engineered Cementitious Composite

Engineered cementitious composite (ECC) is a relatively recent construction material with characteristics of high ductility and energy dissipation capacity. Such ductility is fulfilled by adding polymeric fibers, such as polypropylene (PP), polyethylene (PE), and polyvinyl alcohol (PVA) fibers, which would inevitably experience fusion under fire. This paper focuses on the behavior deterioration of postexposure high-strength engineered cementitious composite (HSECC). Color change, surface cracking, and spalling phenomena of HSECC specimens were inspected after specimens exposed to 200°C, 400°C, 600°C, 800°C, and 1,200°C for 1 h. Weight loss, residual compressive/flexural strength, and failure modes of cubes were evaluated correspondingly. Experimental results indicated that the threshold temperature for HSECC to crack is lowered in comparison with ECC of normal strength, whereas explosive spalling behavior could still be prevented effectively with 2.0 vol% PVA fiber. The loss ratio of weight and strength in HSECC was lower than that in ECC, but the failure modes under compression were found to be more catastrophic. HSECC exhibits lower intensity in an X-ray diffraction (XRD) curve than that of ECC. Apparent needle-like channels were observed beyond 400°C, then were gradually filled with reaction products ascribed to the synergistic effect of thermal expansion, volume increase caused by chemical reactions and pore-structure coarsening, and manifested by the results of mercury intrusion porosimetry (MIP).

Behavior Deterioration and Microstructure Change of Polyvinyl Alcohol Fiber-Reinforced Cementitious Composite (PVA-ECC) after Exposure to Elevated Temperatures.

In the case of fire, explosive spalling often occurs in cementitious composites due to dense microstructure and high pore-pressure. Polymer fibers were proved to be effective in mitigating such behavior. However, deterioration of these fiber-reinforced cementitious composites inevitably occurs, which is vital for the prediction of structural performance and prevention of catastrophic disaster. This paper concentrates on the behavior and mechanism of the deterioration of polyvinyl alcohol fiber-reinforced engineered cementitious composite (PVA-ECC) after exposure to elevated temperatures. Surface change, cracking, and spalling behavior of the cubic specimens were observed at room temperature, and after exposure to 200 °C, 400 °C, 600 °C, 800 °C, and 1200 °C. Losses in specimen weight and compressive strength were evaluated. Test results indicated that explosive spalling behavior was effectively prevented with 2.0 vol% polyvinyl alcohol fiber although the strength monotonically decreased with heating temperature. X-ray diffraction curves showed that the calcium hydroxide initially decomposed in the range of 400–600 °C, and finished beyond 600 °C, while calcium silicate hydrate began at around 400 °C and completely decomposed at approximately 800 °C. Micrographs implied a reduction in fiber diameter at 200 °C, exhibiting apparent needle-like channels beyond 400 °C. When the temperature was increased to 600 °C and above, the dents were gradually filled with newly produced substance due to the synergistic effect of thermal expansion, volume expansion of chemical reactions, and pore structure coarsening

Mechanical Properties and Explosive Spalling Behavior of Steel-Fiber-Reinforced Concrete Exposed to High Temperature—A Review

Steel-fiber-reinforced concrete (SFRC) is being increasingly applied to various buildings and civil infrastructure as an advanced cementitious composite. In recent years, the requirements for SFRC in the construction industry have increased. Additionally, the fire resistance of SFRC has attracted attention; therefore, numerous investigations regarding the residual properties of SFRC have been conducted. This paper critically reviews the mechanical properties of SFRC subjected to elevated temperatures, including its residual compressive strength, flexural strength, tensile strength, elastic properties, fracture properties, and stress–strain relationships. The residual mechanical performance of SFRC and the action mechanism of steel fibers are reviewed in detail. Moreover, factors affecting the explosive spalling of concrete at high temperatures as well as the effect of steel fibers on the microstructure of heated concrete are discussed. It is demonstrated that, in general, SFRC exhibits better residual mechanical properties when exposed to elevated temperatures than plain concrete and can prevent the risk of explosive spalling more effectively. The purpose of this literature review is to provide an exhaustive insight into the feasibility of SFRC as a refractory building material; additionally, future research needs are identified.

Numerical simulation of ultra-high-performance fiber-reinforced concrete frame structure under fire action

The research activity in progress and the advancements in concrete technology are leading to an increased use of ultra-high-performance fiber-reinforced concrete (UHPFRC) in structural engineering. UHPFRC is characterized by steel fibers, cement, silica fume, fine sand, superplasticizer, and very low water–cement ratio. UHPFRC is defined as a new material, with unique properties (high ductility, low permeability, very high strength capacity in compression, higher toughness) in comparison with conventional concrete (Buttignol et al, Revista IBRACON de Estruturas e Materiais 10(4):957–971, 2017). This makes it possible to make slender constructions because a smaller cross section can transfer the same force as a larger cross section. However, in case of fire safety design a disadvantageous behavior of UHPC compared to normal-strength concrete is well known and documented. The high packing density of the cement matrix is the main reason for explosive spalling behavior when exposed to fire. In this paper, the numerical simulation using finite-element method has been used to evaluate the behavior of UHPFRC frame structure under fire action. According to results, the three-dimensional finite-element model can be used for calculating the mechanical localized of UHPFRC concrete frame structures subjected to nominal fire curves. The results of numerical analysis under fire action are also compared to the other materials for more understanding the fire resistance between UHPFRC material (with PP fiber, without PP fiber) and high-strength concrete.

Multiphysics Lattice Discrete Particle Model for the simulation of concrete thermal spalling

Explosive thermal spalling behavior during fire exposure is one of the major issues in the design of modern reinforced concrete structures. Previous experience on fire disasters indicates that spalling of concrete can have serious structural and economic consequences and must be taken into account in the design for fire. However, spalling mechanisms and their interaction still remain in dispute in the scientific community. In order to shed some light on this phenomenon, a discrete hygro-thermal model of concrete at high temperature called DTemPor3 is proposed and a full coupling scheme between DTemPor3 and the Lattice Discrete Particle Model (LDPM) is performed. The proposed multi-physical coupled model features the effect of pore pressure and temperature on the mechanical response as well as the impact of cracking on moisture mass transport and heat transfer. Simulations of typical spalling experiments show good agreements with data gathered from the literature for both high-performance concrete and ordinary concrete, demonstrating the accuracy of the proposed approach. Cracking localization is found to significantly impede the local pore pressure build-up due to the increase of pore or crack volume. The numerical simulations demonstrate that the spalling phenomenon can be successfully reproduced, only when the effect of thermal stresses is taken in account along with the effect of pore pressure on crack initiation.

On the explosive spalling behavior of ultra-high performance concrete with and without coarse aggregate exposed to high temperature

Experimental investigations are conducted on the explosive spalling behavior of two types of ultra-high performance concrete (UHPC), i.e., UHPC with coarse aggregate (UHPC-CA) and UHPC without coarse aggregate (UHPC-no-CA) under high temperature slow heating conditions. The influences of polypropylene (PP) fiber and moisture content on the spalling behavior of UHPC are studied. The inner vapor pressure and temperature in the UHPC specimens are measured to analyze the driving force of explosive spalling of UHPC during heating. Results show that UHPC-CA exhibits a slightly better resistance to explosive spalling than UHPC-no-CA and coarse aggregate has a beneficial effect on minimizing the explosive spalling of UHPC. Also, Moisture content of UHPC specimen remarkably affects the explosive spalling behavior of both UHPCs, i.e. the higher the moisture content, the severer the explosive spalling is. Hybrid fibers (steel fiber and PP fiber) significantly improve the resistance to explosive spalling of UHPC and can prevent some UHPC specimens from explosive spalling. These results prove that vapor pressure is the primary driving factor on the explosive spalling of UHPC under the heating conditions in this work. Additionally, layered explosive spalling occurs to both UHPCs. The temperature gradient in UHPC-no-CA is much higher than that in UHPC-CA. Many coarse aggregates without cracking damage peel off from the UHPC-CA matrix. These results indicate that thermal stress is an important factor driving the explosive spalling. However, when the UHPC specimens are fully saturated (100% moisture content), the “pressure releaser” function of PP fiber may not play the most important role in alleviating the explosive spalling in UHPCs.

Effects of elevated temperature on the tensile properties of NS-modified self-consolidating engineered cementitious composites and property optimization using response surface methodology (RSM)

Abstract This paper discusses the influence of elevated temperature on the tensile properties (tensile strength, tensile strain, and energy absorption) and microstructure of nano-silica-modified self-consolidating engineered cementitious composites (NS-modified SC-ECC) mixtures. Response surface methodology (RSM) was utilized to develop a design matrix and predictive models and to perform multi-objective optimization for a matrix of mixtures prepared with polyvinyl alcohol (PVA) fiber at 0.5%, 1%, 1.5%, and 2% volume fractions and NS at 0%, 1%, 2%, 3%, and 4% of the weight of cementitious materials at temperatures of 23 °C, 100 °C, 200 °C, 300 °C, and 400 °C. To investigate the influence of elevated temperature on the certain characteristics of NS-modified SC-ECC mixtures, residual compressive strength, tensile properties, and microstructure properties were assessed at elevated temperatures of up to 400 °C for 1 h. Microstructure was examined using scanning electron microscopy before and after the mixtures had been exposed to elevated temperatures; accessible porosity and pore size distribution with cumulative pore volume were measured using mercury intrusion porosity (MIP) to validate the behaviors of the tensile properties and compressive strength of NS-modified SC-ECC mixtures. The results show that the tensile properties of the NS-modified SC-ECC mixtures improve due to pozzolanic reactivity of NS by utilizing the calcium hydroxide (CH) released from cement hydration to produce more calcium-silicate-hydrate (C-S-H) gel, which refines the fiber-matrix and aggregates-matrix interfacial transition zones (ITZ). The pozzolanic reactivity is further facilitated by temperature curing to produce more C-S-H gel, improving the fiber-matrix interactions at elevated temperatures of up to 200 °C. The PVA fiber improves the elevated temperature behavior of the mixtures and prevents explosive spalling behavior even after the incorporation of 2% NS with a PVA fiber volume of up to 2%. The responses considered in the RSM were tensile strength, tensile strain, and energy absorption. The established models showed high degrees of correlation between the responses and independent variables. Optimized tensile properties could be achieved at 2% PVA fiber volume, 1.3% NS, and a temperature of 125.7 °C. The measured absolute deviations (error) between the experimental data and the theoretical (predicted) models’ results for tensile strength, tensile strain, and energy absorption were 2.83%, 4.4%, and 1.68%, respectively.

RETRACTED: Microstructure and residual properties of green concrete composites incorporating waste carpet fibers and palm oil fuel ash at elevated temperatures

With the increasing amount of waste generation from different processes, there has been a growing interest in the use of waste in producing sustainable building materials to achieve potential benefits. This study investigated the influence of waste polypropylene carpet fibers and palm oil fuel ash (POFA) on the microstructure and residual properties of concrete composites exposed to elevated temperatures. Four mixes containing carpet fibers (0% and 0.5%) and POFA (0% and 20%) were prepared. The specimens were exposed to high temperatures (200, 400, 600 and 800 °C) for 1 h. The fire resistance of the concrete specimens was then measured in terms of mass loss as well as both residual ultrasonic pulse velocity (UPV) and compressive strength. The role of carpet fibers and POFA was investigated through the analysis of the microstructure in terms of scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The results revealed that the addition of waste polypropylene carpet fibers to the concrete matrix significantly enhanced the fire resistance and residual compressive strength in addition to eliminating the explosive spalling behavior of the concrete composites at elevated temperatures. The fire resistance of the concrete mixtures was further enhanced by the inclusion of POFA. The study revealed that the utilization of waste carpet fiber and palm oil fuel ash in the production of sustainable green concrete is feasible both technically and environmentally.

EXPERIMENTAL AND NUMERICAL ANALYSIS OF ULTRA HIGH PERFORMANCE CONCRETE (UHPC) MEMBERS IN CASE OF FIRE

<p>The research activity in progress and the advancements in concrete technology are leading to an increased use of high performance and ultra high performance concrete in structural engineering. Due to its high compressive strength and ductile behavior in combination with steel fibres, UHPC structural members can be designed as slender and light structures compared to standard concrete design. This increasingly leads to the option in architectural design to highlight the bearing capacity of the building without hiding the structural components.</p><p>In case of fire safety design a disadvantageous behavior of UHPC compared to normal strength concrete is well known and documented. The high packing density of the cement matrix is the main reason for explosive spalling behavior when exposed to fire. To avoid spalling, an appropriate amount of polypropylene fibres has to be introduced in the concrete mix design. In addition, slender and light structures are in general more sensitive to fire exposure due to the higher surface to volume ratio.</p><p>In this paper, the analysis of the thermal and mechanical material properties using experimental and numerical methods is presented. The investigations were carried out during the priority program 1182 in the research project “Theoretical and experimental determination of the high temperature behavior of ultra high performance concrete (UHPC)”, funded by the German Research Foundation (DFG), see (Schmidt 2014) and (Hosser et al. 2014).</p>In the project the thermal properties heat conductivity, specific heat capacity and the temperature dependent density as well as the mechanical properties like the temperature dependent stress-strain-relation and thermal expansion were experimentally determined. In addition, the optimum fibre content was determined. The findings of the project were used to develop a material model and checked against experimental results on fire exposed UHPC columns using a FE model.

Fire Resistance of Ultra-High-Strength Concrete: a Review

This paper presents a review of advances in research on fire resistance of high-strength concrete (HSC) and ultra-high-strength concrete (UHSC). Further research needs in the near future on UHSC, especially on reactive powder concrete (RPC), are also discussed. It is commonly recognized that HSC suffers strength loss in a manner basically similar to that of normal strength concrete. But the main problem of HSC is explosive spalling under high temperature, which can be solved by employing either polymer fiber or steel fiber. Since RPC200 is a type of RPC which has been successfully prepared in many counties and is to be applied to engineering practice, fire resistance of RPC200 needs a series of investigations urgently. The objectives of such investigations are to restrain explosive spalling and minimizing spalling probability, so as to ensure satisfactory fire resistance of RPC. It is expected that a research will be carried out on explosive spalling behavior, fracture properties, and micro-structure, to establish a mechanism as well as technical measures for improving fire resistance of RPC.

High temperature resistance of normal strength and autoclaved high strength mortars incorporated polypropylene and steel fibers

The effects of high temperatures up to 900°C on normal strength, water cured and autoclave cured high strength mortars were investigated within the scope of this study. Mechanical properties such as, compressive strength, flexural strength, modulus of elasticity, and weight loss of the specimens were determined. The effect of polypropylene (PP) and steel fibers incorporation on high temperature behavior of high strength mortars were also investigated. Microstructure investigations were also carried out by SEM analyses. Test results indicated that compressive strength of all mixtures increased with increasing temperature up to 300°C. However, above 300°C all specimens showed explosive disintegration except normal strength mortars, and high strength mortars with PP fibers. It seems that, PP fiber inclusion is effective in preventing the explosive spalling behavior of high strength mortars. On the other hand, steel fibers did not improve high temperature resistance. To prevent spalling, minimum PP dosage for autoclave and water cured high strength mortars has been determined as 0.2% and 0.1%, respectively.

Comportamento de secagem e explosão de concretos refratários com diferentes teores de água

O crescimento do consumo de aço e da sua tecnologia de produção tem demandado proporcional desenvolvimento dos refratários, sendo umas das principais exigências o aumento de sua vida útil e a redução do tempo de parada dos equipamentos revestidos por esses materiais. Entre as diversas classes de refratários, os concretos vêm ganhando destaque nos últimos anos, principalmente por apresentarem facilidade de aplicação e reparo. Uma vez que esses materiais são aplicados na forma fluida, problemas no processo de secagem são freqüentemente encontrados na indústria. Assim, alguns trabalhos envolvendo aditivos de secagem têm surgido como forma de reduzir a ocorrência de explosões, sem a necessidade de diminuir drasticamente a taxa de aquecimento do refratário após sua aplicação. Entretanto, informações que relacionem a secagem com variáveis intrínsecas do processamento dos concretos ainda são escassas na literatura. Estudos reportam que a variação na quantidade de água influencia significativamente a reologia, e pode facilitar, por exemplo, a adição de fibras durante a mistura. Neste contexto, este trabalho teve como principal objetivo relacionar o teor de água com o comportamento de secagem e explosão de concretos refratários. Verificou-se que a adição de maior quantidade de água durante a mistura resultou em aumento da permeabilidade e queda na resistência a explosão dos concretos.