Ultra-high Performance Concrete Specimens Research Articles

Enhancing UHPC Tensile Performance Using Polystyrene Beads: Significant Improvements and Mechanisms

This study investigates utilizing spherical polystyrene (PS) beads as artificial flaws to improve ultrahigh-performance concrete (UHPC) tensile performance using a uniaxial tensile test and explains the corresponding mechanisms by analyzing the internal material structure of UHPC specimens with X-ray CT scanning. With a hooked steel fiber volume fraction of 2%, three PS bead dosages were employed to study tensile behavior changes in dog-bone UHPC specimens. A 33.4% increase in ultimate tensile strength and 174.8% increase in ultimate tensile strain were recorded after adding PS beads with a volume fraction of 2%. To explain this improvement, X-ray CT scanning was utilized to investigate the post-test internal material structures of the dog-bone specimens. AVIZO software was used to analyze the CT information. The CT results revealed that PS beads could not only serve as the artificial flaws to increase the cracking behavior of the matrix of UHPC but also significantly optimize the fiber orientation. The PS beads could serve as stirrers during the mixing process to distribute fiber more uniformly. The test results indicate a relationship between fiber orientation and UHPC tensile strength.

Reinforcement Effects on Tensile Behavior of Ultra-High-Performance Concrete (UHPC) with Low Steel Fiber Volume Fractions.

Ultra-high-performance concrete (UHPC) with a low steel fiber volume fraction offers lower material costs than UHPC with typical steel fiber volume fractions, and has the potential to mitigate the ductility degradation of rebar-reinforced UHPC (R-UHPC). This study explores the reinforcement effect on the tensile behavior of UHPC with a low fiber volume fraction with the aim of facilitating more cost-efficient UHPC applications. The axial tensile behavior of 30 UHPC specimens with low fiber volume fractions at different reinforcement ratios was tested through direct tensile tests. The findings indicate that adopting UHPC with a low fiber volume fraction can significantly mitigate the ductility deterioration of rebar-reinforced UHPC (R-UHPC), and both increasing the reinforcement ratio and decreasing the fiber volume fraction contribute to the improvement in ductility. The failure modes of R-UHPC are determined by the ratio of reinforcement ratio and fiber volume fraction, rather than a single parameter, which also means that R-UHPC with different parameters may correspond to different methods to predict tensile load-bearing capacity. For UHPC with a fiber volume fraction low to 0.5%, incorporating steel rebars gives superior multi-crack cracking behavior and excellent capacity to restrict the maximum crack width. Increasing the fiber volume fraction from 0.5% to 1.0% at the same reinforcement ratio will yield little benefit other than an increase in tensile load-bearing capacity.

Steel corrosion process in ultra-high performance concrete monitored by fiber bragg grating sensor

The steel corrosion in Ultra-High Performance Concrete (UHPC) would cause degradation of structural performance or even structural failure. It is an urgent need to monitor and predict the steel corrosion in UHPC, however it is still a tough task. In this paper, Fiber Bragg Grating (FBG) sensors are applied for monitoring the steel corrosion process in UHPC, by combining with steel bar, which is equidistant winding with the sensors, and connected with power supply for accelerating corrosion. The UHPC specimens embedded with steel bars are surrounded by sodium chloride (NaCl) solution, and the steels are artificially corroded with different current densities for investigation. The steel corrosion in Original C60 and Marine Concrete 60 (Marine C60) are applied for comparison. The volume expansion coefficient for monitoring the steel corrosion process, is carried out by FBG sensors, and further comprehensively monitored by three grating sensors. The results suggest that the steel corrosion process in UHPC is slowly with current density lower than 100 μA/cm2, and largely increases with current density higher than 500 μA/cm2, the volume expansion coefficient of corroded steel in UHPC is in range of 2.02–2.62 in this test, which is much different from Original C60 and Marine C60.

On improved microstructure properties of slag-based UHPC incorporating calcium formate and calcium chloride

The study aimed to achieve high strength in slag-based cementless ultra-high performance concrete (UHPC) while investigating the role of calcium formate and calcium chloride as accelerators using advanced characterization and microstructural analysis. The UHPC specimens were evaluated using various techniques, including heat of hydration, thermogravimetric analysis, X-ray diffraction, nuclear magnetic resonance, scanning electron microscopy, and porosity measurements. The results showed that both accelerators improved the UHPC properties, with calcium formate being more effective than calcium chloride, as evidenced by higher heat of hydration, improved microstructure, and lower porosity. Furthermore, the thermodynamic modeling revealed insightful information on the reaction mechanisms with C-(N-)A-S-H and hydrotalcite as the primary hydration products formed in the matrix. Notably, the UHPC specimens with calcium chloride exhibited a very low pH value, which could increase the risk of corrosion in reinforced structures. Therefore, the use of calcium formate as an accelerator can lead to the development of cementless UHPC with superior properties.

A unified tensile constitutive model for mono/hybrid fibre-reinforced ultra-high-performance concrete (UHPC)

Providing a representative and reliable tensile constitutive model for ultra-high-performance concrete (UHPC) has been challenging in the past due to the absence of standardised test methods. In this paper, the authors have proposed a unified constitutive model calibrated to the most commonly used types of steel fibres within the practical range of fibre content. While the novel model serves as the core, a comprehensive experimental program and results are pivotal for validating the model’s effectiveness. In pursuit of this, the recently approved AASHTO standard test method was employed to offer standardised and comprehensive experimental insights into the direct tensile behaviour of mono/hybrid fibre-reinforced UHPC. A set of predictive equations, derived either empirically or from simple mechanics, to predict the key parameters defining the mechanical constitutive law of UHPC material subjected to uniaxial tension are introduced based on experimental findings. The proposed predictive equations and constitutive model exhibited robust predictions of tensile behaviour, aligning well with both the test results and additional independently tested UHPC specimens.

Combined effect of natural fibre and steel fibre on the thermal-mechanical properties of UHPC subjected to high temperature

This research investigates the combined effect of steel and natural fibre on the mechanical properties and spalling resistance of ultra-high performance concrete (UHPC) before and after exposure to elevated temperatures. The effects of two parameters, namely temperature (ambient temperature, 200 °C, 400 °C and 600 °C) and fibre type (solely macro end hooked steel fibre (MHS) and hybrid of micro straight steel fibre (MSS), macro end hooked steel (MHS) fibre and micro jute (MJ) fibre) on the mechanical properties, spalling resistance and mass loss of UHPC were studied.Micrographs from scanning electron microscope (SEM) test were utilized to appraise the steel fibre and jute fibre before and after exposure to elevated temperatures. The test results exhibited that the residual tensile strength and flexural strength were significantly declined after exposure to high temperatures for UHPC specimens reinforced with macro steel fibre only. Moreover, explosive thermal spalling occurred for this group of specimens under 600 °C. Whereas the combined use of jute fibre and micro-macro steel fibre was an effective approach to prevent the explosive thermal spalling under 600 °C and improve the residual tensile strength, flexural strength and toughness of UHPC. Furthermore, preliminary empirical expressions have been developed in this study to predict the residual mechanical properties of UHPC as a function of natural fibre content, steel fibre content and temperature.

Failure mechanism of steel fiber pullout in UHPC affected by alternating cryogenic and elevated variation

This paper investigates the pullout response of straight and hooked-end steel fiber embedded in Ultra-high Performance Concrete (UHPC) subjected to alternating cryogenic (−170 °C) and elevated (200 °C) temperature variation. The temporal evolution of Acoustic Emission (AE) parameters and failure behavior during the pullout process were monitored in situ using the AE test. Additionally, changes in the UHPC microstructure were also evaluated. Results showed that in addition to the UHPC matrices exposed to elevated temperature, the compressive and flexural strength of UHPC matrices subjected to single or multiple cycles were generally higher than those at ambient temperature. Whereas the bond strength/pullout energy of straight fiber increased with a single cycling exposure of UHPC specimens to either cryogenic or elevated temperature, the improvement in the pullout performance of the hooked-end fiber was obtained only after the post-cryogenic thawing of specimens. Moreover, the exposure to an increased number of temperature-variation cycles caused the pullout strength and energy of both fiber groups to gradually decrease. Nonetheless, the pullout performance of the hooked-end fiber was significantly and consistently superior to that of the straight fiber, regardless of the exposure temperature or cycles. The AE test confirmed that the pullout process of both fibers was mainly characterized by tensile failure, with a marginal occurrence of shear failure for the hooked-end fiber. When the UHPC was exposed to various temperatures, the fiber pullout behavior was predominantly influenced by the physical structure of the fibers, thermal deformation proclivity of the matrix, and the competition between mechanisms such as pore moisture phase change, secondary hydration, and the composition of hydrates.

Mechanical Properties and Durability of Sustainable UHPC Using Industrial Waste Residues and Sea/Manufactured Sand

Abstract Considering the continuous development of sustainable development, energy saving, and emission reduction concepts, it is very important to reduce concrete’s cement content in order to improve its environmental impact. Using a reactive admixture to replace part of the cement in ultra-high-performance concrete (UHPC) can effectively improve the overall performance of the concrete and reduce carbon dioxide emissions, which is an important aspect of environmental protection. Here, industrial waste residue (fly ash and slag), sea sand (SS), and manufactured sand (MS) were used to produce UHPC under standard curing conditions to reduce the material cost and make it more environmentally friendly and sustainable. The effects of water–binder ratio, contents of cementitious materials, types of sands, and content of steel fibers on the mechanical performance of UHPC under standard curing were investigated experimentally. In addition, evaluations of the impermeability, chloride, and freeze-thaw resistance of various UHPCs produced were conducted by investigating the effects of various factors on the depth under hydraulic pressure and electric flux of UHPC, as well as the mass loss, relative dynamic modulus of elasticity, flexural strength, and compressive strength of UHPC specimens after freeze-thaw cycles. The obtained experimental results show that the SS-UHPC and MS-UHPC prepared by standard curing exhibit high strength, excellent impermeability, and chloride resistance. The frost-resistant grade of all groups of UHPCs prepared by standard curing was greater than F500 and had excellent freeze–thaw resistance, including those produced with local tap water or artificial seawater. The investigation presented in this paper could contribute to the production of new low-cost and environmentally friendly UHPCs and accelerate the application of UHPC in engineering structures.

Behavior and modeling of FRP grid‐reinforced ultra‐high‐performance concrete under uniaxial tension

AbstractFiber reinforced polymer (FRP) reinforced ultra‐high‐performance concrete (UHPC) structural elements have become increasing popular in research and industry communities. In this paper, uniaxial tension tests were conducted to study the effects of fiber type, fiber length, and fiber content on tensile behavior of FRP grid reinforced UHPC plates (FGRUPs). Additionally, the microstructure analysis of specimens was conducted using scanning electron microscopy. Test results reveal that carbon FRP (CFRP) grid can substantially enhance the tensile performance of UHPC under tension: (1) the FGRUPs exhibit a post‐crack strain‐hardening behavior while the UHPC plates exhibit a post‐crack strain‐softening behavior; (2) the FRP grid enhances the cracking stress of UHPC specimens (except for plates with 1% basalt fibers) and the stiffness of the second segment of the stress–strain curve, and substantially enhances the ultimate tensile stress UHPC specimens. Also, the cost‐effectiveness analysis indicates that plates containing 1% of 12 mm length PE fibers have a highest cost efficiency index. Finally, a modified tensile stress–strain model for FGRUPs is proposed and verified.

Enhancing Sulfate Erosion Resistance in Ultra-High-Performance Concrete through Mix Design Optimization Using the Modified Andreasen and Andersen Method

This study presents an in-depth investigation into optimizing the mix design of ultra-high-performance concrete (UHPC) for enhanced sulfate erosion resistance, utilizing the modified Andreasen and Andersen (MAA) method. By testing the mechanical properties and slump flow of UHPC, it was determined that the optimal W/B = 0.2, and the best volume content of steel fibers is 2%. Through long-term tests lasting 360 days on three groups of UHPC specimens under different curing conditions, their mass loss, compressive strength corrosion resistance coefficient, surface appearance, and erosion layer thickness were tested. The results indicate that under sulfate attack, the mass and compressive strength corrosion resistance coefficients of UHPC specimens showed a trend of first increasing and then decreasing, due to the formation and expansion of ettringite and gypsum. The thickness of the erosion layer increases over time. By 360 days, the internal damage caused by sulfate attack is about twice as severe as it was after 60 days. However, the addition of steel fibers was found to effectively mitigate these effects, reducing mass loss and preserving the structural integrity of UHPC.

Dynamic damage constitutive model for UHPC with nanofillers at high strain rates based on viscoelastic dynamic constitutive model and damage evolution equation

This study established a dynamic damage constitutive model for ultra-high performance concrete (UHPC) with nanofillers, based on a viscoelastic dynamic constitutive model and a damage evolution equation. Ten types of nanofillers, including particle, tube and flake nanofillers, were incorporated to modify UHPC. The split Hopkinson pressure bar was used to obtain the relationship between stress and strain of UHPC specimens at a strain rate of 200/s-800/s. The experimental results indicated that the dynamic compressive strength of UHPC with nanofillers at strain rates of approximately 200/s, 500/s, and 800/s can reach 172.8 MPa, 219.6 MPa, and 275.9 MPa, respectively, reflecting an increase of 85.2 %, 76.5 %, and 53.9 % compared with the blank UHPC. The established dynamic damage constitutive model considered the damage accumulation with strains under dynamic loading. The fitting coefficients of the dynamic damage constitutive model, when compared against experimental results, range from 0.8796 to 0.9963, showing a higher accuracy compared with traditional Zhu-Wang-Tang (ZWT) viscoelastic model, especially at a strain rate of approximately 200/s.

Static and dynamic tensile properties of ultra-high performance concrete (UHPC) reinforced with hybrid sisal fibers

Ultra-high performance concrete (UHPC) is widely applied in concrete structures against impact and explosive loads. To achieve a more eco-friendly and cost-effective UHPC material, mixed plant fibers instead of conventional steel fibers are considered in the present study. UHPC with single and hybrid long and short sisal fibers (12 mm long fibers and 6 mm short fibers) reinforcement (2% fiber content) were prepared and compared against UHPC with no fiber reinforcement. The quasi-static tensile and bending properties of these six types of UHPC specimens were investigated. A split Hopkinson pressure bar test has also been adopted to evaluate the dynamic tensile performance of UHPC specimens under five strain rates, the effect of strain rate has been investigated, and the failure process has been recorded with a high-speed camera. The experimental results showed that the UHPC containing 1% long sisal fibers (12 mm) and 1% short sisal fibers (6 mm) has optimum dynamic mechanical properties. Hybrid sisal fibers are more effective in strengthening UHPC specimens in dynamic tests than in static tests. A synergy effect is also introduced to further characterize the strengthening effect of hybrid sisal fibers. Finally, to more accurately predict the dynamic tensile strength of the specimens under various strain rates, an improved prediction model of the dynamic increase factor for tensile strength is proposed by combining the results of this experiment and previous experimental data.

Study on mechanical properties and microstructure of green ultra-high performance concrete prepared by recycling waste glass powder

Ultra-high performance concrete (UHPC) encounters hindrance in pursing carbon neutrality and extended applications due to the dosage of cementitious materials and high energy consumption. To address this problem, this study utilized WGP to replace placement in the production of UHPC-WGP and invested its impact on workability, mechanical properties, and microstructure. The research results showed that incorporating WGP improved the flowability of UHPC and reduced its early-age mechanical properties but significantly enhanced the later-age mechanical properties. When the WGP content is 20 %, the sample's compressive strength after 28 days increases by 8.6 %. The specimens with 28 days exhibited the highest flexural strength and ultimate deflection, reaching 24.8 MPa and 0.809 mm, respectively, and the UHPC specimens (90 d) demonstrated the lowest total porosity, reduced by 14.6 % compared to the reference group. Furthermore, scanning electron microscopy (SEM) observations revealed that WGP had a good micro-aggregate filling effect and pozzolanic effect improved the microstructure. Finally, low cost and energy consumption characteristics further promote the sustainable application of WGP-based UHPC.

Performance recovery of high-temperature damaged ultra-high-performance concrete under different curing environments

The self-healing capability and susceptibility to salt solution erosion in ultra-high-performance concrete (UHPC) significantly influence the mechanical properties and long-term durability of concrete structures within coastal or underground environments. Acknowledging the intricacies of real-world environments, this study focuses on UHPC that has endured high-temperature damage at 800 °C. The research aims to analyze the property variations within 28 days following exposure to diverse dry and wet conditions, as well as salt solution environments. The findings demonstrate a substantial recovery in both mechanical and transport properties of the high-temperature-damaged UHPC, attributed to its inherent self-healing capability. Among the dry and wet conditions, the optimal performance recovery of UHPC specimens is observed when they are subjected to submerged and immersed environmental conditions. Furthermore, when immersed in a salt solution environment, the beneficial impacts attributed to the self-healing property tend to outweigh the detrimental effects of salt solution erosion. All scenarios exhibit a trend of enhanced properties, with the presence of chloride salts being particularly conducive to the recovery process. However, exposure to a sulfate-rich environment induces deterioration in transport properties and pore structure, resulting in a partial incongruity with the mechanical property results. Microscopic analysis techniques reveal that the primary contributors to enhanced properties encompass a range of hydration products formed due to the interaction between water, salt solutions, and the compromised UHPC. Nevertheless, owing to the intricate nature of the environment, disparities arise in both the type and quantity of hydration products, contributing to variations in the extent of property alterations.

Experimental study of bond behavior between concrete-filled steel tube and UHPC-encased

This paper examines the bond behavior between steel and ultra-high-performance concrete (UHPC) in members made of UHPC-encased concrete-filled steel tubes (CFST). For the push-out test, a total of ten UHPC-encased CFST specimens, eight normal concrete-encased CFST specimens, and two CFST specimens were designed. The specimen parameters considered for variation include steel fiber content, thickness of the steel tube, anchorage length, thickness of outer concrete, and concrete type. Through experimental observation and measured data, the force failure process and crack development pattern of the specimens were observed, and load-slip curves were obtained for the loading end and the free end. A comprehensive analysis was conducted to examine the influence and mechanism of different parameters on the bonding performance of the specimens. Furthermore, an equation was derived to calculate the bonding strength at the interface between the steel tube and the outer concrete. The findings reveal that both UHPC-encased CFST and normal concrete-encased CFST specimens exhibited bond-anchorage failure, with the load-slip curve exhibiting a sudden change at the peak value, indicating a high degree of brittleness. The bond strength between steel and outer UHPC was found to be twice that between steel and core UHPC, and 1.4 times that between steel and outer normal concrete. Increasing the steel fiber content and the thickness of outer concrete within a certain range effectively improved the bonding performance of the specimens. The thickness of the steel tube did not have a significant effect on the bonding performance of UHPC specimens. Additionally, when the anchorage length reached a certain value, further increases did not significantly enhance the bond strength. Moreover, the influence range of the steel tube's anchorage length and outer UHPC on the bonding performance was smaller compared to outer normal concrete.

Estimation of stress–strain constitutive model for ultra-high performance concrete after high temperature with an deep neural network based method

In order to better study and analyze the residual compressive behavior and stress–strain curve relationships of ultra-high performance concrete (UHPC) materials after high temperatures, high-temperature tests and uniaxial compression tests were carried out on 144 specimens in the temperature range of 20 °C-900 °C in this paper. The effects of different curing regimes and cooling regimes on the mechanical properties, apparent characteristic and stress–strain curves of UHPC after experiencing different temperatures were investigated respectively. As the target temperature increased, the stress–strain curves of all UHPC specimens gradually tended to be flatten, the peak point of the curve shifted to the right, the peak strain increased sharply, and the elastic modulus and proportional limits gradually decreased. The compressive strength and modulus of toughness of the UHPC specimens both increased and then decreased as the target temperature increased, with a critical temperature of 300 °C and 500 °C respectively. The Poisson's ratio of the UHPC specimens decreased and then increased as the target temperature increased, with a critical temperature of 500 °C. In addition, based on the experimental results, a Deep Neural Network (DNN) model with four hidden layers and 100 neurons in each layer was constructed to predict the complete residual stress–strain response of UHPC materials after high temperature. The training and validation of the DNN model was completed by pre-processing and segmenting the original dataset with the help of Pytorch deep learning libraries. The DNN model predicts stress–strain curves that are in excellent agreement with the UHPC test curves.

Influence of steel fiber types on residual mechanical properties and explosive spalling of hybrid fiber reinforced ultra-high performance concrete: Optimization and evaluations

To investigate the influence of steel fiber on improving the high-temperature resistance of hybrid fiber-reinforced ultra-high performance concrete (UHPC), four types of UHPC specimens were prepared. The residual strength and fracture energy of all UHPCs were determined after exposure to varying high temperatures, and internal temperature in the specimens were also measured. Additionally, explosive spalling tests were performed on specimens with different moisture contents. The results indicate that the residual mechanical properties of UHPC initially increase and subsequently decrease as the target temperature increases. Notable differences in thermal conductivity were observed among the tested UHPC specimens. As the moisture content of the specimens increased, the likelihood and severity of explosive spalling in the specimens increased. Corrugated high-strength steel fibers, measuring 35 mm in length and 1 mm in diameter, are highly effective at preventing explosive spalling of UHPC, and high-temperature treated recycled steel fiber from tires also exhibits better performance than other two types of steel fiber. High tensile strength of steel fiber and its distinctive corrugated appearance can be the primary contributing factors. Furthermore, two established computational models which demonstrated a significant level of congruence were employed for evaluating explosive spalling and anti-spalling properties of UHPC specimens. This suggests that cracking resistance provided by steel fiber plays an important role in preventing the explosive spalling of UHPC, emphasizing the importance of exploring specific steel fiber based on its appearance and tensile strength.

Performance of pre-cracked beams exposed to corrosion environment cast with ultra-high performance concrete

Ultra-high-performance concrete (UHPC) is a unique type of concrete that has a lot of advantages in the construction sector. There is no risk for reinforced UHPC elements in an aggressive environment or coastal region, unless cracking occurs due to extra-loading or inaccurate structural design. For that, there is a need for this study to be considered. The core concentration of this study is towards understanding the shear behavior of pre-cracked beams cast with UHPC as affected by durability. This program presents materials used to reach the main aim of the present study. 72 specimens were conducted to study UHPC physical and mechanical properties to be compared with traditional normal concrete (NC). Moreover, 10 RC beams were cast to investigate the shear behavior of RC-UHPC beams with dimensions of 100 mm, 150 mm, and 1300 mm. Five non-exposure beams and five exposure beams were corroded by an accelerated corrosion cell, and half the potential cell readings were recorded. Obtained results for specimens provide that; UHPC eliminates deflection with high modulus of elasticity, in chloride penetration test UHPC is 200 times less than NC, and the reduction in bond strength test after corrosion exposure is 66.24 % and 1.69 % for NC and UHPC specimens, respectively. For pre-carking UHPC beams at 80 % of experimental ultimate load; cracking resistance for un-corroded beams exceeds the corroded beams by 250 %. The residual flexural capacities for corroded beams pre-cracking up to 80 % of E.U.L. are 61.6 % and 119 % for NC and UHPC beams, respectively. UHPC is much better than NC in corrosive environments.

Self-healing capability of conventional, high-performance, and Ultra High-Performance Concrete with commercial bacteria characterized by means of water and chloride penetration

This study analyzes the self-healing capability of conventional, High-Performance, and Ultra High-Performance Concrete specimens, incorporating commercial bacteria products that are easily accessible, marketed, and affordable from different sectors. Bacteria were incorporated into different mediums: immobilized in diatomaceous earth and liquid. Specimens were pre-cracked to a range of 50–450 μm cracks and were left to heal for 28 days in 3 different conditions (1) water immersion, 2) one week of water immersion followed by three weeks in a humidity chamber, and 3) humidity chamber. To evaluate the self-healing enhancements of specimens using a bacteria-based healing agent, self-healing efficiency was quantified by optical assessment of crack closure, recovery of water tightness via water permeability testing, and chloride permeability via cracks and matrix. The results show that bacterial agents increased the protection against chloride penetration in cracked and healed specimens of conventional concrete, especially when the specimens were healed in water immersion. Owing to the dense matrix of HPC and UHPC, the chloride penetration in the presence of cracks up to 400 μm can be kept below 10 mm. Crack closure greater than 50% is required in UHPC samples to get a significant healing ratio. The penetration through the cracks is approximately twice that of the matrix penetration in conditions when healing is not enhanced.

Factors influencing pore pressure measurements in concrete during heating and its influence on fire-induced spalling

Measuring pore pressure build-up in concrete during heating is quite challenging due to a number of adverse factors that includes lack of instrumentation, test conditions, and interdependency of factors. This paper presents an experimental program undertaken to investigate different parameters that affect pore pressure measurements. A total of 21 specimens of varying shapes and sizes were made with conventional concrete and ultra-high-performance concrete (UHPC) and were tested under varying heating rates and exposure conditions. Measured results showed that the location of highest peak of pressure inside of the specimen is dependent on the type of concrete being tested and the heating rate used. The pore pressure development in UHPC specimens is fundamentally different than conventional concretes and is highly influenced by the presence of fibers. The complexities associated in measuring the pore pressure can be overcome by adopting certain key measures in the design of future experimental programs.