Strength Of Mixtures Research Articles

Forecasting unconfined compressive strength of calcium sulfoaluminate cement mixtures using ensemble machine learning techniques integrated with shapely-additive explanations

Calcium sulfoaluminate (CSA) cement mixture design is challenging due to the influence of multiple features on its unconfined compressive strength (UCS). Consequently, the relationships between input features and the UCS exhibit non-linear behavior, making it difficult to understand using experimental methods alone. Therefore, for the first time, this study constructed non-linear ensemble machine learning (ML) models on a dataset compiled from experimental literature to accurately predict the UCS of CSA cement mixtures. After applying feature selection techniques, four different ensemble models were built on the modified datasets to predict the UCS. The extreme gradient boosting model built on the dataset modified by the least absolute shrinkage and selection operator method achieved the best prediction accuracy (coefficient of determination; R2 = 0.95) on testing data. Finally, the SHapely Additive exPlanations analysis could interpret the selected ML model both quantitatively and qualitatively, by explaining the independent relationships between each input feature and UCS.

Exploring sulfate optimization techniques in Limestone Calcined Clay Cements (LC3): limitations and insights

This study assessed the feasibility of different methods for sulfate optimization of limestone calcined clay cements (LC3). LC3-based pastes were studied with kaolinite and montmorillonite calcined clays and different gypsum contents. Quartz powder was used in reference systems. The sulfate optimization was done using isothermal calorimetry, compressive strength, thermogravimetric analysis, and chemical shrinkage analysis at different ages. Overall, there is no single best technique to predict sulfate optimization in LC3, carefully combining multiple techniques can assist in more coherent decision-making, such as isothermal calorimetry with compressive strength within 72 h. We recommend the optimum LC3 sulfate content based on criteria established by the decision-maker (academia or industry). Either based on mechanisms and kinetics reactions, phase assemblage, compressive strength, or shrinkage of LC3 mixtures containing different SO3 content. Also, the results of montmorillonite-LC3 systems were satisfactory without accelerated sulfate depletion.

Polyurethane-based composite binder for poroelastic road surface: composition, preparation and properties

To address the high cost and poor water stability of polyurethane (PU) binder used in poroelastic road surface (PERS), a type of PU-based composite binder prepared at room temperature was proposed by using PU as the main ingredient, emulsified asphalt (EA), cement, and defoamer as auxiliary agents. The stabilities of different types of polyurethane-emulsified asphalt (PU-EA) blend systems were investigated and the mix composition of the PU-EA blend system was determined through molecular dynamics (MD) simulations. The interaction mechanisms of all components of the PU-based composite binder were revealed by microscopic measurements through Fourier transform infrared (FTIR) spectroscopy and fluorescence microscopy (FM). The strength and water stability of the PERS mixture bound by the PU-based composite binder were evaluated by the indirect tension (IDT) test and the Cantabro abrasion test. The results showed that the stability of the polyether polyurethane (PEUR)-cationic emulsified asphalt (CEA) blend system was the best, and the potential energy of the PU-EA blend system was the lowest when the PU content was around 50 wt%. Both physical and chemical reactions occurred simultaneously in the polyurethane-emulsified asphalt-cement (PU-EA-C) blend system's components. The calcium silicate hydrate (C-S-H) enhanced the crosslinking gel properties of the PU-EA-C blend system. Cement improved the performance of the PERS mixture in a more efficient way than the PU. When the PU-based composite binder composed of 50 wt% PU, 41 wt% EA, 9 wt% cement, and 0.5 wt% defoamer was used, the water stability and strength performance of PERS mixture were the best. The material cost of the suggested PU-based composite binder was nearly half that of commonly used PU, while the material cost of the PERS mixture was reduced by 25%. These findings would serve as useful references for the promotion and application of PERS pavement.

Study on the shear strength of asphalt mixture by discrete element modeling with coarse aggregate morphology

High shear strength is crucial for asphalt pavements to resist permanent deformation at high temperatures, which is largely determined by the skeletal structure of coarse aggregates. In this study, four size ranges of polyhedral coarse aggregate clumps were built to simulate the morphology and dimensional characteristics of coarse aggregate. Subsequently, virtual triaxial shear tests were simulated using discrete element models. Three gradation types were analyzed to study the effects of aggregate structure, granularity composition, and coarse aggregate modulus on the shear strength of asphalt mixtures. The results show that it is feasible to obtain accurate morphological features of coarse aggregates by controlling the minimum diameter of the filled spheres in a polyhedral coarse aggregate box when constructing a discrete element model. The virtual triaxial shear test model developed in this study can be effectively utilized to simulate the shear mechanical properties of asphalt mixtures under various confining pressures. The numerical simulation results indicate that the cohesion of asphalt mixture AC-13 is the best, while the internal friction angle and shear strength of SMA-13 are the highest. The ranking of factors that affect the cohesion and internal friction can be summarized as: aggregate structure ≫ coarse aggregate modulus > granularity composition, while the order of factors that affect the shear strength is: aggregate structure ≫ granularity composition > coarse aggregate modulus. This indicates that the aggregate structure is crucial for the high-temperature performance of asphalt mixtures. This study addressed the issue of high variability in laboratory test results for macroscopic properties of asphalt mixtures and analyzed the skeleton role of coarse aggregate in asphalt mixtures from a mesoscopic perspective. The findings parameters for explaining the strength mechanism. The discrete element models also facilitate the optimization of asphalt mix design with reduced labor and time consumption on laboratory testing.

Strength and Stiffness Evaluation of a Fiber-Reinforced Cement-Stabilized Fly Ash Stone Dust Aggregate Mixture

The utilization of waste fly ash in road construction is primarily confined to its use in embankment filling or as a stabilizer when combined with lime and cement. Its application in structural pavement layers, such as the base and subbase, faces a challenge due to the high volume of fine particles, which renders it brittle when stabilized. In this study, fly ash was blended with stone dust and aggregated to enhance its gradation. Subsequently, it was stabilized with cement to bolster its strength, rendering it suitable for pavement use. Additionally, polypropylene (PP) fibers were introduced to mitigate the brittleness of the mixture. An extensive experimental investigation was conducted to assess the strength and stiffness properties, including compressive strength, indirect tensile strength, flexural strength, cyclic indirect tensile modulus, and flexural modulus of fiber-reinforced cement-stabilized mixtures of fly ash, stone dust, and aggregate. The experimental results reveal that the addition of PP fibers up to 0.25 wt.% enhances compressive strength, but any further increase in fiber content leads to a reduction in strength. However, indirect tensile strength and flexural strength show improvement, with an increase in fiber percentage up to 0.5 wt.%. It was observed that cement content plays a dominant role in stabilizing these materials. Appropriate relationships have been established between strength and modulus parameters for stabilized mixtures. Based on the strength and stiffness study, a combination of 70% fly ash and 30% stone dust aggregate with 6% cement can be considered for the base layer. Regarding the behavior of indirect tensile strength and flexural strength, an optimum fiber percentage of 0.35% is recommended.

Effect of sustainable/durable composite materials on dynamic performance of aircraft shelters.

Aircraft shelter technology has been evolving over years along with the global technological revolution. They first appeared in the 20th century with the main purpose of protecting parked aircraft. Recently, they are considered a globally important topic in the aerospace field, especially for shielding military aircraft. On the other hand, the civil revolution nowadays is extremely unsustainable. The world is facing vital problems due to the massive consumption of non-renewable resources and pollution of the environment and atmosphere. Sustainability development is not an option anymore; it is the only choice to survive. Therefore, there is a demanding need to push the boundaries of sustainability and go through a green revolution by using Eco-friendly materials and searching for alternatives for non-renewable resources. In this study, sustainable composite materials that are probably used as impact shields in aircraft shelters that are cheaper than typical ones were studied. The applicability of utilizing silica fume and steel slag as partial and full replacements for non-renewable resources in the composite mixture was established. Fiberglass and steel meshes were also implemented as reinforcing elements. The performance enhancement of using such materials in composite mixtures was investigated. Results showed that utilizing silica fume and steel slag enhanced the compressive strength of sustainable composite mixtures by about 9.38%. Similarly, superior dynamic performance was achieved by approximately 800% using different reinforcement techniques.

Investigation on laminar burning velocity measurements of premixed Ethane-Air mixture at higher pressure and temperature conditions

The externally heated diverging channel (EHDC) method was utilized to evaluate the laminar burning velocity (LBV) of premixed ethane-air flames at higher mixture temperature (350-620 K) and pressure (1-5 atm) conditions over different mixture strengths (ϕ = 0.7-1.3). The maximum LBV was noted at ϕ = 1.1 for all pressure and temperature conditions. The inverted parabolic behavior of the temperature exponent was obtained with the minima at ϕ = 1.1. The pressure exponent (β) exhibits a parabolic variation with its maxima at ϕ = 1.0. The current results are further analyzed and compared with the literature measurements, and the comprehensive kinetic model predictions of USC mech II, San Diego mech, and Aramco mech 1.3. The present LBV measurements match well with the kinetic model predictions of Aramco mech 1.3 at most of the mixture and pressure conditions. The present results propose the variation of pressure exponent (β) as a function of temperature ratio, and temperature exponent (α) as a function of pressure ratio for different mixture conditions (ϕ). A revised power-law correlation for α and β variations is also recommended as, Su=Su0Tu/Tu0∝0+∝11-Pu/Pu0)Pu/Pu0β0+β11-Tu/Tu0. The sensitivity analysis indicates the maximum decrement in the positive sensitivity for the chain branching reaction HCO + M ↔ H + CO + M (R30) across all the stated mixture conditions, owing to an increment in the third body effects along with pressure and temperature. The reaction pathway analysis reveals a maximum net reduction in the elemental flux (∼56 %) for the reaction between the species carbon monoxide (CO) and carbon dioxide (CO2) through different reactions, due to a rise in pressure and temperature.

Evaluation of the interface adhesion mechanism between SBS asphalt and aggregates under UV aging through molecular dynamics

The bonding characteristics between asphalt and aggregates have an important role in influencing the strength of asphalt mixtures. To clarify the bonding mechanism at the interface between SBS asphalt and aggregates under UV aging conditions, this research developed molecular models of the interface between SBS asphalt and representative aggregates including quartz (granite), augite (basalt), and calcite (limestone). Subsequently, dynamic simulations were performed on the interface models to assess the adhesive properties. Adhesion work was employed to assess the interfacial adhesion performance between SBS-modified asphalt and various types of aggregates. The results demonstrated that SBS asphalt exhibited significantly higher adhesive work with alkaline aggregates, following the order of limestone > basalt > granite in terms of adhesive strength. The dominant contributor to adhesive work was van der Waals interactions, with electrostatic interactions playing a crucial role in influencing variations in adhesive work among different aggregates. After the aging-induced fracture of SBS materials, there was a noticeable increase in the gap between them and the aggregates, resulting in a significant reduction in the adhesion effectiveness between SBS and aggregates. Aged asphaltene and colloid exhibited heightened polarity, resulting in enhanced electrostatic interactions between asphalt and aggregates, thus reducing adsorption distances and elevating adhesive work. This research provides comprehensive evaluation of the bonding mechanism between asphalt and aggregate under UV aging conditions at the molecular level, and provides guidance for the design of durable asphalt pavements.

Reusing Ceramic Waste as a Fine Aggregate and Supplemental Cementitious Material in the Manufacture of Sustainable Concrete

A viable strategy for promoting sustainable development and a cleaner environment is the reuse of demolition-related ceramic waste and ceramic manufacturing byproducts in the production of concrete. The purpose of this study is to assess the possibilities for using ceramic waste in the production of concrete as a fine aggregate and cementitious material. The effectiveness of concrete mixtures incorporating 20–100% ceramic waste fine (CWF) as a replacement for natural fine aggregate and 10–30% ceramic waste powder (CWP) in place of cement was evaluated. Their influence was assessed with respect to workability, mechanical performance, durability, and elevated temperature resistance. The results were analyzed via energy dispersive x-ray (EDX) and scanning electron microscopy (SEM). The findings illustrated that the increase in the replacement levels of CWP and CWF decreases the concrete workability. The mechanical performance of concrete mixtures is enhanced under compression and flexural tests as the replacement ratios of CWF and CWP increase up to 50% and 10% as replacements of sand and cement, respectively. The increases in compressive and flexural strength were 5.33% and 8.14%, respectively, at age 28 days. The concrete water permeability significantly increases as the CWF replacement ratio increases, and the incorporation of CWP reduces this negative impact. After exposure to 200, 400, 600, and 800 °C, the residual compressive strengths of concrete mixtures incorporating CWF and CWP were up to 95.02%, 89.66%, 74.33%, and 51.34%, respectively, compared to control mixtures, which achieved 84.25%, 76.03%, 59.36%, and 35.84% of their initial strength. Microstructure analysis revealed that combining CWP and CWF significantly improves cement hydration when compared to the reference mixture. Thus, the use of CWF and CWP in the production of masonry mortar might be an economical alternative that would aid in raising the recycling rate of demolition and construction debris and supporting sustainable growth in the building sector.

Optimizing characteristics of high-performance concrete incorporating hybrid polypropylene fibers

The purpose of this investigation is to assess and optimize the impact of hybrid polypropylene fibers (coarse monofilament and staple fibers) on the mechanical characteristics and resistance to elevated temperature of high-performance concrete. Concrete mixtures were designed using central composite design under response surface methodology. Slump test, compressive strength, flexural strength, impact test, elevated temperature resistance and microstructure of concrete were the tests performed. The slump values were slightly decreased with the addition of polypropylene fibers. Concrete mixtures reinforced with hybrid polypropylene fibers have significantly improved in terms of compressive strength and flexural strength ranged from 1.96% to 12% and 14.28% to 41.9%, respectively, at age 56 days compared to control mixture without fibers. The hybridization of 5 kg monofilament and 0.75 kg staple fibers achieved the highest compressive strength (84.6 MPa), flexural strength (14.9 MPa), and the optimum impact resistance at age 56 days. The increase of coarse monofilament fibers significantly improved the spalling resistance performance. The residual compressive strength of mixture containing 5 kg monofilament and 0.75 kg staple fibers up to 63.8% of the initial strength after exposure to 800 C0. Strong relationships were obtained for predicting and optimizing compressive and flexural strength of concrete incorporating hybrid polypropylene fibers.

Photoinitiated chemical vapor deposition (piCVD) of composition tunable, ionically conductive hydrogels on diverse substrates

Ionically conductive hydrogels are finding prominence in a wide range of emerging devices and applications, including biopotential sensors, organic field effect transistors, biomedicine, and soft robotics. Traditionally, these gels are synthesized through solution-phase polymerization or solvent based swelling of a polymer network and then cast in place or adhered to an intended substrate after synthesis. These fabrication approaches place artificial limitations on the accessible chemical composition and ionic conductivity of the gels, and limit deployment of ionically conductive hydrogels in complex platforms. Here we present a modular method to create ionically conductive hydrogels on a variety of rigid, flexible, or filamentary substrates through a photoinitiated chemical vapor deposition (piCVD) process. First, a viscosity tunable precursor mixture of desired ionic composition and strength is created and coated onto a target substrate. Next, an acrylate film is grown directly on these coated substrates via piCVD. Since both the monomer and photoinitiator used during the piCVD process are miscible in the aqueous precursor mixture, polymerization occurs at both the surface of and within the precursor layer. Using this two-step strategy, we isolate a robust composite hydrogel with independently tunable ionic properties and physical structure. This method is compatible with most substrates and results in a conformal, persistent gel coating with excellent rehydration properties. Gels containing a variety of biocompatible salts can be accessed, without concomitant changes in physical structure and morphology. Ionic conductivities can be tuned between 1 × 10−5–0.03 S cm−1 by changing the ionic strength of the precursor mixture. Additionally, we show that the material retains its ion concentration and conductivity after washing. Finally, we deploy this material onto several different substrates and show that through this method the same gel can be manufactured in-place regardless of the intended substrate.

Preparing autoclaved aerated concrete using high-silicon iron tailing

This study aims to prepare autoclaved aerated concrete (HIT-AAC) using high-silicon iron tailing (HIT) as a single siliceous material. The influence of HIT fineness and mix proportion parameters, including the molar calcium to silicon ratio (Ca/Si), the mass ratio of water to solid materials (W/S), and aluminum powder paste dosage, on the properties of HIT-AAC were investigated. The test indices included slurry fluidity, foaming curve of the HIT-AAC mixture, dry density, and mechanical strength of the HIT-AAC block. Furthermore, the hydration products and microstructure of the HIT-AAC sample were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG-DTG), and scanning electron microscopy (SEM). The tested results showed that coarse HIT has adverse effects on the expansion of the HIT-AAC mixture and could not be used for HIT-AAC production. The mechanical strength reached a maximum under the following conditions: HIT-58.3 %, cement-25.8 %, lime-12.9 %, gypsum-3 %, aluminum powder-0.07 %, and W/S-0.5. Microscopic investigation verified the main minerals in HIT-AAC are quartz, tobermorite, hematite, calcite and anhydrite.

Comparative Analysis of the Use of Nanosilica and Fly Ash in Hydraulic Concrete

Context: Nowadays, nanomaterials constitute an innovative alternative for the construction sector. This study evaluates the benefits of adding nanosilica and fly ash to Portland cement concrete in terms of its mechanical strength properties. Methodology: 45 specimens were used to compare the compressive strength and durability of concrete mixtures with nanosilica and fly ash. The specimens were studied after 7, 14, and 21 days to determine their maximum resistance. Results: The addition of small amounts of nanosilica (up to 1%) significantly improved the compressive strength of the concrete. In contrast, a large amount of fly ash (up to 8%) was required for a noticeable effect. Conclusions: Concrete with nanosilica yielded the best results in terms of mechanical strength. The key to improving concrete through nanosilica and fly ash is to reduce the water-to-cement ratio using chemical agents that reduce porosity and increase resistance.

Experimental Study on the Physical and Mechanical Characteristics of Refractory Concrete Using Heat-Treated Steel Slag Coarse Aggregates

The aim of this study is to compare the properties of refractory concrete made with thermally treated and untreated steel slag. Five concrete compositions were prepared and investigated in the present work. The first mixture, referred to as the reference, was formulated using dolomite aggregates, whereas the second and third mixtures were developed by replacing natural coarse aggregate with 50 and 100% by weight of thermally untreated steel slag, respectively. The same replacement ratio (50% and 100%) of thermally treated steel slag was used to produce the fourth and fifth mixtures. Specimens of each specimen were placed in a furnace and heated to 400 °C and 800 °C. The mass loss for all the specimens heated to 400 °C was about 8%, while the reference suffered the maximum mass loss at 800 °C, which was 21.6%. The mixture with a 100% substitution of thermally treated steel slag produced the maximum compressive strength when compared to other mixtures at a temperature of 800 °C. The compressive strength of the M5 mixture was 18 MPa versus 10.87 MPa for the reference mixture. Additionally, optical microscope examination of specimens containing thermally treated steel slag revealed less damage than that observed in mixtures with dolomite.

Combined Influences of Water Content and Coarse Grain Content on Shear Strength of Unsaturated Soil Mixture.

An interlayer existed between the ballast layer and subgrade in the conventional railway substructure. Considering that the shear strength τ of the interlayer soil was influenced by the changes in the ballast grain content and water content, this aspect was explored in the present study. Monotonic triaxial tests were fulfilled, which considered five coarse grain contents fv and three water contents of fine soil wf. The results showed that the growth in fv contributed to an increment in τ of the soil mixture under both saturation and unsaturation. Conversely, in previous studies, the growth of fv induced an increment in τ under saturation, but a decline in that under unsaturation. This was explained by the competing influences of fv and suction ψ: in previous studies, increasing fv induced a decline in the dry density of the fine soil fraction ρd-f, which contributed to a decline in ψ. When the negative influence of declining ψ outweighed the positive influence of the incrementing fv, the τ of the soil mixture decreased. Meanwhile, modelling of the τ-ψ relationship in the soil mixture with varying fv was performed. This proposed model was examined using the test results from both the present and previous studies, which shows its reasonably good performance.

Improvement of pavement engineering properties with calcium carbide residue (CCR) as filler in Stone Mastic Asphalt

Characteristics of pavement material are crucial factors in improving the stability and durability of asphalt pavement due to the poor performance of traditional asphalts. Reusing industrial waste in asphalt concrete production can address these concerns, reduce environmental problems and preserve resources. There have been few studies on the effects of using industrial waste materials on Stone Mastic Asphalt (SMA) properties. This paper examines the impact of Calcium Carbide Residue (CCR) as a filler in SMA. The study evaluates control samples, those with Rock Powder (RP) and Ordinary Portland Cement (OPC) filler, and those with CCR using Marshall stability (MS) and Indirect Tensile Strength (ITSdry and ITSsat) tests. Results show positive effects of CCR and RP on asphalt sample strength. The highest MS, MQ, and TSR values were observed in samples containing CCR80 %+RP20 %. These indices increased 45 %, 35 %, and 51 %, respectively, compared to control samples. The alkaline CCR material forms strong bonds with acidic bitumen, producing asphalt more resistant by 97 % compared to control samples. SMA modified with CCR + RP was also found to be less sensitive to water damage than traditional SMA with RP or OPC filler. The rough texture of CCR may positively affect the strength and durability of asphalt mixtures against moisture damage. Using CCR as a filler in SMA can enhance pavement engineering properties, reduce production costs and environmental problems, and develop sustainable asphalt mixtures for practical application. The main novelty of this research is the use of CCR and RP combination in SMA mixtures.

Adhesive characteristics of novel greener engineered cementitious composite with conventional concrete substrate

Engineered cementitious composite (ECC) is a high-graded advanced construction material that can be used to strengthen and repair structural composites owing to its high mechanical and durability properties. Nevertheless, the ability of ECC to strengthen and repair concrete surfaces depends on the interfacial bond between the conventional concrete (CC) substrate texture and ECC overlay. It ensures sufficient adhesive or bonding ability over a lifetime under various loading and environmental conditions. The present study investigates the bond strength between CC substrate and modified ECC with agro-industrial by-products, such as ground granulated blast furnace slag (GGBS), bagasse ash (BA), and rice husk ash (RHA). The bond strength is determined using three types of tests, namely the slant shear, split cylinder, and split prism tests. A mathematical model has also been developed to predict the bond strength of the different ECC mixtures. The results indicate that incorporating 40% GGBS, 10% BA, and 10% RHA in ECC helps in attaining the maximum interfacial bond strength with cross-hatched textures under all types of testing. According to the ACI standard, ECC with agro-industrial by-products ranging from 10% to 55% achieved the required bond strength in all three tests. Correspondingly, the outcomes of the present research are compared with those obtained from previous studies to gain further insights into various applications, which are highly relatable. Furthermore, the experimental outcomes were strongly correlated with the mathematical modeling with great accuracy.

Investigating the Effect of Experimental Factors on the Performance of Warm Mix Asphalt with Wax Additive using Application of the Taguchi Method

The objective of this study was to assess the impact of experimental factors on the volumetric properties and performance of warm mix asphalt (WMA) with RH-WMA using the Taguchi method. The gradations of the mixtures were based on AC 14, as specified by the Public Works Department of Malaysia. An L16 orthogonal array was employed to design the mixtures, considering three factors: compaction temperatures ranging from 95 to 140°C, RH-WMA contents ranging from 1% to 4%, and asphalt contents ranging from 3.5% to 6.5%. Sixteen mixtures were prepared according to the L16 array. The study focused on investigating several volumetric properties, including bulk-specific gravity, air voids, voids filled with asphalt, and voids in mineral aggregates. Additionally, the strength behavior of the samples was analyzed using the Taguchi method. The resilient modulus and performance of the mixtures were also evaluated. The results of the study indicate that a high RH-WMA content led to a slight decrease in the strength of the asphalt mixture and air voids. However, it increased the voids filled with asphalt (VFA) and resulted in softening of the asphalt mixtures.

Freeze-Thaw resistance and mechanical properties of UHPC reinforced with a lower amount of hybrid fibers

Sustainable development is becoming critical in many industrial fields, including building materials. The rapid development of the construction industry in Kazakhstan requires construction materials having high-quality, low maintenance, and good durability. The main durability issue of construction material associated with Kazakhstan’s severe climate is the volume change of water in concrete caused by the freezing and thawing (F-T) cycles, which threatens the material’s strength and microstructure. Therefore, ultra-high-performance concrete (UHPC), a relatively new material with high compressive and tensile strength and improved microstructural properties, is suggested. Nevertheless, a limited number of researches have been done regarding the F-T resistance of UHPC. This research focuses on the effect of combining two types of fibers (steel and polypropylene (PP) fibers) on the compressive, flexural, and direct tensile strength and F-T resistance of UHPC. Test results indicated higher dosages of PP fiber in UHPC increased strength before exposure to F-T cycles. Adding PP fiber to UHPC led to more prolonged strains for each UHPC mixture. However, adding more steel fibers was beneficial for UHPC exposed to F-T cycles. Although mixtures with high steel fiber dosage presented a more brittle type of failure and lower strain values than mixtures with higher PP fiber dosage, the compressive, flexural, and tensile strength of UHPC mixtures containing higher steel fiber dosages increased after 90F-T cycles. Relative dynamic modulus of elasticity (RDME), which is a common indicator of F-T resistance of concrete, tends to increase for all tested mixtures, with the highest values belonging to ones with higher steel fiber dosage. Hence, it is suggested that UHPC with higher steel fiber dosage is more beneficial in terms of the F-T resistance of UHPC.

Propagation and extinction of premixed H2[sbnd]O2[sbnd]N2 edge-flames

The effects of equivalence ratio (ϕ), global strain rate (σ) and mixture strength on the shapes and propagation rates (Uedge) of premixed edge-flames in H2O2N2 mixtures were investigated experimentally using a counterflow slot-jet apparatus. Results are presented for both single (premixed gas against cold inert gas) and twin (premixed gas against premixed gas) configurations. Both advancing (Uedge > 0) and retreating edge-flames (Uedge < 0) were characterized. Flame images show that for lean mixtures where H2 is the deficient species and thus the effective Lewis number (Leeff) is less than unity, the leading edge-flame has a stronger burning intensity than the trailing strained premixed flame. For mixtures with low ϕ (thus low Leeff) at near-extinction conditions corresponding to sufficiently high or low σ, transitions from continuous to broken structures were observed due to diffusive-thermal instabilities. Such transitions enable flames to survive under conditions where extinction would have occurred without transition. The combined effects of ϕ, adiabatic flame temperature and σ were found to correlate well in terms of the effect of a non-dimensional strain rate (ε) on a scaled propagation rate Ũ.