Variation Of Compressive Strength Research Articles

An experimental characterization of the properties of graphene oxide—Waterborne epoxy resin coating of concrete after chloride erosion

The durability of concrete surfaces is frequently compromised by adverse external factors, such as freeze-thaw cycles and ionic corrosion among others. This study aims to investigate the comparative performance of three concrete coating techniques independently applied uniformly to concrete surfaces, namely the Graphene Oxide—Waterborne Epoxy Resin Coating (GO-WEP) coating and two commercially available WEP coatings (S1, S2). The corrosion resistances of the coatings were evaluated under various conditions: chloride drying-wetting cycles, chloride freeze-thaw cycles, and chloride immersion tests. In this study, the changes in color difference and adhesion of the coating after chloride erosion were studied. And after five drying-wetting cycles, the GO-WEP coating exhibited a color difference value approximately 56 % and 45 % lower compared to S1 and S2 coatings respectively. The S1 and S2 coatings demonstrated adhesive strength below 1.50 MPa after the 3rd and 4th cycles respectively, indicating a loss of protective capabilities. Conversely, the GO-WEP coating maintained adhesive strength greater than 1.50 MPa after five cycles, implying sustained protective capabilities. Following freeze-thaw cycles, the color difference value in GO-WEP was about 16 % and 7 % lower than S1 and S2 coatings respectively. S1 and S2 coatings lost their protective ability after the 4th and 5th cycles respectively, while GO-WEP maintained an adhesive strength greater than 1.50 MPa. Furthermore, following chloride immersion, the GO-WEP coating had a color difference value approximately 20 % and 17 % lower than S1 and S2 respectively. The adhesive strength reduced by 39.7 %, 46.4 %, and 43.1 % for the three coatings respectively, signaling the superior performance of GO-WEP in all tested properties. The surface morphology and compressive strength variations of the coated concrete were also studied. As the experimental cycles progressed, both S1 and S2 coatings suffered noticeable surface damage, while the GO-WEP coating demonstrated no significant changes until the end of the experimental cycles. During the chloride drying-wetting and chloride immersion tests, the concrete specimens showed an increase in strength. Initially, uncoated concrete showed a faster rate of strength increase than coated concrete. However, this rate slowed down and even reversed in later stages. Coated concrete on the other hand, exhibited a steady increase in strength over the experimental cycles, with GO-WEP coated concrete showing the slowest growth rate. In the chloride freeze-thaw cycle test, concrete strength decreased progressively. And by the fifth cycle, the compressive strengths of GO-WEP, S1, and S2 were 31.5 MPa, 30.8 MPa, and 30 MPa, respectively, a 9 %, 6 %, and 3 % improvement over the 29 MPa of uncoated concrete. These findings further reinforce the superior protective effect of the GO-WEP coating on concrete.

Evolution of a Filling Paste Cementitious System and Impact Patterns of Sulfate Mine Water Erosion on Filling Paste Performance.

To assess the impact of sulfate mine water on filling material performance, an accelerated sulfate erosion process was used to analyze the effects of various erosion concentrations, aging periods, and cation types on the macroscopic properties of the filling paste. These properties encompassed apparent phenomena, mass changes, and alterations in the uniaxial compressive strength. Observations revealed sulfate erosion, causing the formation of white substances and salt crystals on specimen surfaces. Initially, all solution-eroded specimens exhibited increased mass and strength. Over time, specimens in 5 and 10% MgSO4 solutions displayed the first signs of decline, while variations in other solutions were relatively small. Increasing the erosion concentration led to greater variations in mass and strength during the initial erosion phase. Specimens in 5 and 10% MgSO4 solutions initially peaked in mass and compressive strength, followed by a decline, while other filling paste specimens continued slow increases. Under equivalent conditions, the MgSO4 solution exhibited stronger erosion than the Na2SO4 solution. Composite erosion by Na2SO4 and MgSO4 involved initial strengthening and gel pore filling, intermediate expansion and crystallization, and late-stage substantial degradation, with MgSO4 exhibiting a more pronounced and complex impact. Gray relational analysis ranked factors affecting mass and uniaxial compressive strength variations as erosion concentration > erosion ion type > erosion aging period. Correlation degrees for factors influencing mass variations were 0.8822, 0.8714, and 0.4754, while for factors influencing uniaxial compressive strength variations, the correlation degrees were 0.8336, 0.7943, and 0.6125, respectively.

Flexural fatigue properties of concrete based on different replacement percentage of natural sand with manufactured sand

Compression and flexural fatigue tests were conducted on concrete specimens with varying strengths under different replacement percentages of natural river sand (R-sand) with manufactured sand (M-sand) at 0%, 30%, 70%, and 100%. The objective was to compare and analyse differences in fatigue damage of concrete across different replacement percentages. Findings were made that when the replacement percentage of M-sand was 30% and 70%, the concrete exhibited higher fatigue life, irrespective of any variations in compressive strength. The fatigue life of concrete with a compressive strength of 30 MPa could be increased by an average of 20%–30% compared to concrete with a compressive strength of 50 MPa, and this increasing trend reached its peak when the replacement percentage of M-sand was in the range of 30%–70%. In order to enhance the prediction of fatigue life for concrete subjected to varying replacement percentages of natural sand with M-sand and to elucidate the evolution process of fatigue damage in M-sand concrete, dynamic strain gauges and DIC methods were employed. This enabled determination of the cycle-varying maximum strain and residual strain during the fatigue process across different replacement percentages. The findings indicate that the addition of M-sand can significantly delay the degradation of dynamic elastic modulus (E), with this effect being enhanced by over 15%. The fatigue damage was defined based on fatigue deformation modulus; therefore, a new fatigue damage model was established. It was observed that this new model improved accuracy by up to 6.1% compared to the traditional fitted model in this test. Finally, the effects of different replacement percentages of natural sand with M-sand on the brittle transition of concrete were analysed at the microscopic level. This analysis involved a combination of microhardness testing and examination of the interfacial transition zone and hydride map of concrete under a scanning electron microscope across different replacement percentages of natural sand with M-sand.

INFLUENCE DU PLASTIQUE RECYCLE DE TYPE POLYPROPYLENE SUR LES CARACTERISTIQUES DU BITUME ET DE LENROBE BITUMINEUX

Asphalt is the most widely used product in the construction of flexible pavements. The purpose of this study is to evaluate the feasibility of incorporating recycled polypropylene plastic into bitumen to obtain modified asphalt to manufacture modified asphalt mixes that offer better properties than conventional asphalt mixes. A type of asphalt mix has been studied, a semi-grained asphalt concrete (SGAC14). Conventional asphalt mixes as well as asphalt mixes containing 2% and 4% of the polypropylene dosages were manufactured. For all the tests carried out, the performance was evaluated according to five criteria: 1) improvement of the rheological properties of the bitumen (ring balls, penetrability, softening point, ductility) 2) suitability for compaction with the gyratory shear press (GCP) 3) Water resistance 4) rutting resistance and 5) the Marshall Trial. The experimental results showed, among other things: an improvement in the rheological properties of the modified bitumen for the respective polypropylene assays of 1%, 2%, 3%, 4% and 5%. For these assays, respectively, penetrability decreased by 29%, 37%, 42%, 74%, and 90% the temperature of beads and rings increased by 0.73%, 2.94%, 5.5%, 6.24% and 9.17% the springback increased by 13.82%, 21.40%, 5.69% and 4.07%. . The modified asphalt mixes with 2% and 4% polypropylene compact better than the reference asphalt at 80 gyrations with respectively 5.5% and 5.1% voids we have 6.1% voids for the reference asphalt. An increase in water resistance for polypropylene dosages at 2% and 4% respectively the latter offer a variation in simple dry compressive strength of 4.84%, 22% and a variation in compressive strength after 7 days of immersion in water of 8.53%, 19.5%. Improved rutting performance of modified asphalt mixes: The SGAC14 class 0 reference asphalt mixes are upgraded to a class 1 and class 2 SGAC0/14 for 2% and 4% polypropylene dosages respectively. Modified asphalt mixes give the best Marshall stability. Overall, the possibility of incorporating polypropylene into SGAC14 type asphalt has been proven.

The Influence of Different Aggregates on the Physico-Mechanical Performance of Alkali-Activated Geopolymer Composites Produced Using Romanian Fly Ash.

In light of the urgent need to develop environmentally friendly materials that, at some point, will allow the reduction of concrete and, consequently, cement consumption-while at the same time allowing the reuse of waste and industrial by-products-alkali-activated fly ash (AAFA) geopolymer composite emerges as a material of great interest. The aim of this study was to investigate the physico-mechanical performance of composites based on AAFA binders and the effect of different types of aggregates on these properties. The experimental results indicate variations in flexural and compressive strength, which are influenced both by the nature and particle size distribution of aggregates and the binder-to-aggregate ratio. The analysis of the samples highlighted changes in porosity, both in distribution and pore size, depending on the nature of the aggregates. This supports the evolution of physico-mechanical performance indicators.

Experimental study of uniaxial compressive mechanical properties of rough jointed rock masses based on 3D printing

Abstract Roughness and inclination are important factors affecting the strength and deformation properties of jointed rock masses. Serrated joint specimens with varying joint roughness coefficient (JRC) and inclination angle were manufactured by 3D printing technique and cement mortar material. Then, uniaxial compression tests were performed for serrated joint specimens. The results show that when inclination angle equals 0° or 90°, the stress–strain curves of serrated joint specimens with various JRC values are basically the same and display a similar variation trend as that of the complete specimen, hence JRC presents a very little impact. When inclination angle varies from 30° to 60°, the stress–strain curves display a significant difference for various JRC values. Both the compressive strength and peak strain increase with the JRC value. With the increase in JRC value, the stress–strain curve exhibits a stress drop point, and with the further increase in JRC value, the stress drop point obviously delays or disappears directly. Variation in uniaxial compressive strength and deformation modulus with inclination angle is approximately U-shape for serrated joint specimens and displays typical anisotropic characteristics. Due to the variation in inclination angles and JRC values, failure modes of serrated joint specimens under uniaxial compression varies from splitting tensile or shear slip failure to compound tensile and shear failure. Rough serrated joint has a strengthening effect on the resistance ability to vertical load, and large roughness can effectively slow down the shear slip failure of jointed rock masses.

Influence of Fly Ash Content on the Durability of Mortar Specimens under Dry/Wet Sulfate Attack.

To investigate the durability of cementitious materials under complex environmental conditions in Xinjiang, this study conducted durability tests on mortar specimens with different fly ash contents under dry/wet sulfate attack conditions, with standard curing and steam curing at 70 °C. The appearance loss and flexural and compressive strength variations in the specimens were analyzed, and an evolution model of the mortar strength under a dry/wet sulfate attack was established. Moreover, XRD and SEM techniques were used to characterize the erosion products and microstructure, and to explore the erosion resistance mechanism of fly ash cementitious materials. The results showed that, after 160 cycles of erosion, the flexural strength of the specimens decreased with the increase in the fly ash content. In the context of steam-cured mortar specimens, throughout the entire erosion period, specimens with a fly ash content of 45% exhibited the highest relative compressive strength. The established strength evolution model had a minimum determination coefficient of 0.879, indicating a good agreement between the model and experimental results. Microscopic research showed that fly ash would undergo a pozzolanic reaction under the action of sulfate and calcium hydroxide, which was beneficial to the improvement of the erosion resistance. As the fly ash content increased, the erosion products of the specimens gradually became dominated by gypsum.

A thermo-hydro-mechanical damage model for lined rock cavern for compressed air energy storage

Large-scale compressed air energy storage (CAES) technology is regarded as an effective way to alleviate the instability of electricity generated from renewable sources such as wind and solar power, which involves the expensive construction of underground caverns to store highly pressurized and high-temperature compressed air. This study documents mechanical behavior and gas permeability of granite under temperature-pressure synchronous cyclic loading, and the response of the surrounding rock to Thermo-Hydro-Mechanical-Damage (THMD) evolution. Firstly, physical experiments were conducted to examine mechanical property and gas permeability evolutions of granite due to temperature-pressure synchronous cyclic loading. Based on these experiments, equations describing the damage evolution of granite were deduced. Subsequently, using these equations in combination with a thermo-hydro-mechanical coupled model of porous media with two-phase fluid flow, a sophisticated computational routine for the thermo-hydro-mechanical-damage analysis of underground gas storage caverns was developed. Lastly, numerical simulations were conducted to study heat transfer, two-phase seepage, and mechanical response of a CAES cavern under operating conditions. Under low to medium pressure and high-temperature synchronous cyclic loading, granite exhibited a significant variation in elastic modulus and compressive strength. Also, its permeability showed a substantial increase due to damage evolution. After two months of operation, prominent heat transfer was observed in the surrounding rock, particularly in the region extending to approximately 10 m from the inner surface of the cavern, exceeding the range of gas leakage diffusion within the cavern. The plastic zone of surrounding rock is distributed above the cavern's roof and below its bottom. Moreover, areas with higher damage are concentrated in the surrounding rock near the cavern's side walls. These findings contributed to our understanding of the behavior of granite in the context of CAES technology and provided valuable insights for the design and operation of gas storage caverns. The development of the THMD model offered a valuable tool for investigating stress and deformation characteristics of the lining and surrounding rock in CAES plants.

Residual mechanical resistance of concrete blocks and laying mortars after high temperatures

AbstractThis paper reports an experimental campaign to evaluate the residual mechanical resistance after high temperatures of two structural masonry components: block and mortar. Residual compressive strength and deformation modulus of four different hollow concrete blocks and two different mortar mixes after heating at high temperatures are investigated. The test method used was the one recommended by RILEM TC 200 for mortars and an adaptation of the same method proposed by Medeiros et al. suitable for the geometry of hollow blocks. Despite the sharp drop in the deformation modulus after heating blocks and mortar, no different behaviours are observed in the deformability of the materials caused by the variables studied. The same cannot be said in relation to the variation of the residual compressive strength of the blocks, which is affected by the variables: initial nominal compressive strength and width of the concrete block. Regarding laying mortars, the results confirmed the small influence of compressive strength on the evolution of residual mechanical strength. The data and analyses reported here on the residual mechanical properties of hollow concrete blocks produced from a concrete mixture of very dry consistency, vibro‐pressed and with normal weight aggregates are relevant, since the data found in the literature generally refer to the wet cast concrete material and in cylindrical bodies.

Composition-property relationships of BP-1 lunar regolith simulant geopolymers for in-situ resource utilization

In-situ resource utilization (ISRU) to construct environmental protection and critical infrastructure is required for long-term human habitation on the Moon and Mars. Analogous to terrestrial construction materials formed from aluminosilicates, i.e., geopolymers, construction materials formed from lunar aluminosilicate regolith are a promising method to create lunar landing pads and habitats. Building on a previous lateral study across multiple regolith simulants, the effects of composition on one specific regolith simulant, Black Point 1 (BP-1), are investigated with the goal of developing relationships between composition and properties. The effects of overall geopolymer composition, activating solution silica and sodium content, and activating solution water content on seven-day compressive strength, strain to fail, and secant modulus are investigated. Decreasing water content has a positive effect on compressive strength and secant modulus of geopolymers formed at ambient-earth conditions, reaching maximum compressive strength at 75 wt% BP-1. Above a compositional limit of Si/H2O = 0.6, differences in Si and Al coordination result in variations in compressive strength with the elemental composition of the geopolymer. At high solids in formulation, the observed trend in compressive strength is nonmonotonic with varying silicon and aluminum content, emphasizing the need for a mechanistic understanding of the relationship between composition and structure for optimization of geopolymer material properties. This study provides a robust set of data for a widely available lunar regolith simulant that can guide further development of processing strategies for lunar ISRU.

Optimization of constituent proportions for compressive strength of sustainable geopolymer concrete: A statistical approach

Geopolymer concrete (GPC) is an environmentally friendly and sustainable concrete produced through the geopolymerization process, involving the combination of alumino silicate materials with alkaline solutions. It has unique advantage of being carbon-negative which helps reduce carbon dioxide levels in the atmosphere. One challenge with making GPC is the significant variation in compressive strength that arises from differences in constituent proportions, specimen ages, andcuring conditions. There is a need to optimize the GPC constituents to achieve the desired compressive strength. To address this issue, a comprehensive dataset comprising 1242 data points from existing literature on fly ash-based GPC (FA-based GPC) was compiled for the purpose of optimizing the constituent proportions of GPC using statistical analysis. Nine independent variables were selected to develop the predictive models for compressive strength using linear (LRA), multilinear (MRA), and non-linear (NRA) regression analyses. The models were assessed using scatter plots between experimental and predicted responses and adopting the performance criteria such as the statistical significance of the model unknowns, R2 values, root mean square error (RMSE), mean absolute error (MAE), and scatter index (SI). LRA revealed that the compressive strength of GPC is not dependent on any single independent variable. Therefore regression analysis with multiple independent variables was conducted. From MRA, ±15 % error for training dataset and (15–20) % error for validating dataset was estimated. The R2, RMSE, MAE, and SI values were found to be 0.8086, 6.11, 5.35, and 0.21. NRA predicted the compressive strength more efficiently because it provides the error ±10 % for both training and validating datasets with R2, RMSE, MAE, SI values of 0.8321, 5.46, 4.77, and 0.19. Further, curing temperature, specimen age, Na2SiO3/NaOH ratio, I/b ratio, and aggregate content were found as the most significant independent variables. The time and cost-effective design mix for FA based GPC can be prepared using the regression models presented in the current work.

Effect of seawater dry-wet cycling on the durability of concrete repair materials

In order to investigate the durability of concrete repair materials in marine environments, this research selected four typical repair materials commonly used on the market to carry out indoor seawater dry and wet cycling tests and real marine environment exposure tests. The research results show that: the compressive strength and abrasion loss variations of these four repair materials under indoor seawater dry-wet cycling are closely related. Among them, magnesium phosphate mortar demonstrates better resistance to seawater erosion in both environments. The chloride ion penetration depth of four repair materials increases with seawater dry and wet cycling time. Its law of change is closely related to the law of change of the most probable pore size inside the material, while the epoxy resin mortar and acrylic-modified mortar have a high depth of chloride ion penetration under the real marine environment due to the microcracks and porous phenomena appearing on the surface of the material. In addition, the results of the tests in the real marine environment differed somewhat from those in the indoor environment, highlighting the need to conduct real marine environment tests. The results provide theoretical support for selecting and evaluating concrete repair materials in the marine environment.

Impact response of nitinol over 300–473 K temperature range

The response of plane-parallel 2 mm thick samples of 47.3Ni-52.7Ti alloy was studied in two series of planar impact tests at temperatures between 300 and 473 K and between 473 and 318 K (heating to 473 K followed by cooling). In two additional series, the samples of 0.4–4 mm thickness were tested at 300 and 338 K (after preheating up to 473 K). In all the tests, the samples were loaded by 1 mm thick copper impactors having velocities equal to 314 ± 2 m/s. The velocity of the rear sample surface was continuously monitored by a laser Doppler velocimeter. It was shown that substantial, by an order of magnitude, variation of Hugoniot elastic limit σHEL and compressive strength Y of the nitinol with temperature are caused by the martensite–austenite transformation and its reversal. The variation of the dynamic tensile (spall) strength σsp of the nitinol along the heating–cooling path was found similar to that of σHEL although the difference between σsp values of austenite and martensite, ∼20%, is much more modest than in the case of σHEL. The test series performed at constant temperatures with samples of different thicknesses allows one to conclude that the plastic deformation in shocked austenite is presumably realized by dislocation motion and multiplication controlled by phonon viscosity. In the shocked martensite, the plastic deformation mechanism at a stress lower than ∼0.3 GPa is likely a thermally activated combination of deformation twinning and slip of kinking dislocations.

The effect of cement replacement with metakaolin and sugarcane bagasse ash as supplementary cementitious materials on the properties of concrete

The use of supplementary cementitious materials in the cement and construction industry is growing rapidly owing to the numerous benefits the application of these materials offers. In this study, the effects of metakaolin (MK) and sugarcane bagasse ash (SCBA) used to partially replace cement on concrete are investigated. The experimental plan was designed using a constant 5% MK and 0-20% SCBA contents by weight. The mix design of 1:2:3 and water-binder (w/b) ratio of 0.5 was employed. Samples prepared were tested at the ages of 7, 14, 28, and 60 days respectively. Concrete workability, water absorption, and densities all showed a decrease with an increase in the percentage of SCBA. The compressive strengths at lower percentages of SCBA (5% and 10%) recorded higher values compared to that of 5% MK and 0% SCBA. An increase in the percentage of SCBA above 10% however led to a decrease in compressive strength. The maximum compressive strength of 22.17N/mm2 was obtained at 60 days in concrete containing 5% MK and 10% SCBA. Both the T-statistics and F-statistics values calculated were statistically significant and exceeded their critical values. This suggests that there is a good relationship between the compressive strength of SCBA and the curing period and that the variation in the curing period and SCBA also causes a variation in the concrete compressive strength. From the results obtained, it is concluded that 5% MK and 10% SCBA can be applied to replace cement for structural concrete production.

Combined effect of fly ash and fiber on spreadability, strength and water permeability of foam concrete

Strength and permeability are the two critical properties of interest for various applications of foam concrete (FC). These properties are well known to be highly dependent on parameters such as density, mix composition and microstructure of FC. Among various measures to enhance the strength and permeation characteristics of FC, incorporation of fly ash and polypropylene fiber has been proven to be effective solutions by various studies. In terms of permeability, though the measurement of air/water permeability has been suggested by various methods, usually such measurements are limited to a pressure of 3 bar. For higher pressures (as recommended in codal provisions) no to limited work is available. In this paper, variation in spreadability, permeability, compressive strength and split tensile strength of FC due to replacement of 50% of sand with Class F fly ash and incorporation of polypropylene fiber is investigated on a systematic basis. For the measurement of permeability at higher pressures (>3 bar), use of novel sealing mechanism using 5 mm thick rubber membrane as sealant with iron spiral cylinder and clamp as casing, is attempted in this work. The present study is first of kind of study using the above-mentioned sealing mechanism for measurement of permeability of FC at higher pressures. Further, only scanty literature is available on permeation behavior of FC with fly ash (as filler) and polypropylene fiber. As per the present findings, particularly in lower density mixes (say density 1000 kg/m3) tested at age of 56 days, replacement of 50% of fine aggregate (by weight) by Class F fly ash results in 114% enhancement in compressive strength and 69% reduction in permeability. In addition, mixes with 0.05% of total solids replaced with polypropylene fiber (by weight) show 25% reduction in compressive strength and 500% increase in permeability in comparison to FC mixes without fly ash and polypropylene fibers. Thirdly, considering mixes with addition of fly ash and polypropylene fibers both, it is found that the effect of fly ash is more predominant from strength perspective than fiber. From permeability perspective however, the fibers control the permeability significantly due to their higher impact on microstructure of FC.

A Review of Physicochemical Stabilization for Improved Engineering Properties of Clays

Severe climatic and environmental conditions warrant the use of stabilization agents in aid of compaction for sustainable improvement in engineering properties of clays. Physicochemical agents are a viable option because they are cost effective, environmentally friendly, and offer improved long-term performance of treated soils. This research developed a fundamental understanding of the clay–water–electrolyte admixtures relations. Based on a comprehensive literature review, the effect of nanomaterials, biopolymers, and geopolymers on the behavior of compacted clays was investigated. It was found that all of these admixtures facilitate the development of an aggregated soil microstructure through unique mechanisms. Biopolymers have the highest water adsorption capacity followed by geopolymers and then by nanomaterials. The effect of admixtures on optimum compaction properties follows a decreasing trend similar to untreated clays (S = 80% ± 20%). The variation of hydraulic conductivity, compression index, and compressive strength are largely within the family of curves identified by typical relationships for compacted clays. These preliminary findings indicate that not all engineering properties are improved to the same level by the different types of physicochemical admixtures. The specific nature of geotechnical engineering (soil type and site conditions) as well as the wide range of admixture types and potential biodegradation of some of the reagents are the major shortcoming of using this class of materials.

Experimental Study on Axial Stress–Strain Behaviour of Steel Fibre-Reinforced Steel Slag Micropowder UHPC

To investigate the toughening effect and stress–strain relationship of steel fibre-reinforced steel slag micropowder ultra-high-performance concrete (UHPC), nine sets of specimens with coarse aggregate and steel fibre contents were prepared for axial compression and elastic modulus tests. This study examines the variations in compressive strength and peak strain of the steel slag micropowder UHPC specimens to determine the corresponding characteristics of the stress–strain relationship. The results indicate that the experimental groups mixed with 1%, 1.5%, and 2% steel fibre increased the peak strain by about 20.3%, 25.3%, and 26.2%, respectively, compared to the non-steel fibre specimens. It can be seen that the toughening effect of UHPC with steel fibre and slag micro powder is good. With a fixed steel fibre content, the compressive strength and peak strain of steel slag micropowder UHPC initially increase and then decrease as the coarse aggregate content increases. The maximum compressive strength is achieved when the steel fibre content is 1.5% and the coarse aggregate content is 20%. A constitutive equation suitable for steel fibre-reinforced steel slag micropowder UHPC was derived through curve fitting based on the experimentally obtained stress–strain curves. The calculated values from the equation show deviations within 10% of the measured values, indicating a good fit. Nonlinear analysis of the entire compression process of prismatic specimens using the finite element method confirms the rationality of the constitutive equation, as the simulated curve closely aligns with the experimental curve. This research findings provide a reference for the engineering application of steel slag micropowder UHPC.

Evaluation of Invasive Herbaceous Plants Utilization for the Production of Pressed Biofuel

The present article focuses on pressed biofuel preparation from invasive herbaceous plants, and the quality indicators and properties were analyzed and determined. Two invasive herbaceous plants were chosen for this research: giant knotweed (Fallopia sachalinensis) and Sosnowsky’s hogweed (Heracleum sosnowskyi). For a control, pine wood biomass was utilized. After harvesting and drying, plant biomass was chopped and milled and later pressed into cylindrical pellets and briquettes. The research results for the pellets’ and briquettes’ physical and elemental properties showed that the density of the pellets (moisture 5–8%) reached 1145.60–1227.47 kg m−3, and the average density of the briquettes reached 615.60–867.31 kg m−3. The determined critical compressive strength of the pellets ranged from 420 N to 676 N, and the briquettes disintegrated under a significantly greater critical force of 783 N to 1219 N. The variation in pellet compressive strength with changes in their moisture content was also investigated. The determined lower caloric value of the pellets varied from 15.9 MJ kg−1 to 18.6 MJ kg−1. Harmful gas emissions during burning of the tested biofuel pellets were also evaluated and determined, and they were sufficiently low and did not exceed the permissible values. Finally, it can be stated that all of the pressed biofuels produced from invasive herbaceous plants met the most important requirements for the quality of pressed solid biofuel and can be used for burning in special boilers.

Durability to chemical attacks and life cycle assessment of alkali-activated binders based on blast furnace slag and sugar cane straw ash

Alkali-activated binder (AAB) is a new material that is being researched as an alternative to the use of Portland cement due to technical and environmental advantages. However, further studies on the durability and environmental impacts of this kind of binder are required to confirm its potential. Therefore, in this work, the durability to chemical attacks and life cycle assessment (LCA) of alkali-activated binders composed of blast furnace slag (BFS) and sugar cane straw ash (SCSA) with BFS/SCSA mass ratios of 100/0 and 75/25 were studied. AAB samples were produced with a solution composed of only NaOH (Na+ concentration of 4 mol kg−1). Portland cement (PC) samples were also produced to compare with AAB samples. For the durability study, the samples were maintained in five different environments to perform durability attacks: sodium sulphate, hydrochloric acid, acetic acid, ammonium chloride, and deionised water. Additionally, unattacked samples were left in a wet room as a reference environment. The compressive strength variation, mass variation, expansion/shrinkage behaviour, visual analysis after application of phenolphthalein, H+ consumption (only for acetic acid, hydrochloric acid and ammonium chloride attacks), thermogravimetric analysis, and powder X-ray diffraction (only for sodium sulphate attack) tests were carried out to analyse the performance of the samples. Results showed that AAB samples presented better resistance to chemical attacks than PC samples based on compressive strength variation for sodium sulphate (−12.1%), hydrochloric acid (−71.8%), acetic acid (−83.7%), and ammonium chloride (−50.1%). The use of SCSA in AAB was more beneficial under sodium sulphate attack (−12.1%). Finally, LCA results showed that the AAB sample with SCSA yielded lower Climate Change impact in kg of equivalent CO2 per kg of produced mortar (0.153 kg CO2-eq). Therefore, the study concludes that using SCSA blended with BFS is a sustainable option to produce AAB.

Residual mechanical properties of recycled aggregate concrete at elevated temperatures

AbstractThis research examines the residual mechanical properties of normal and recycled aggregate concrete when subjected to elevated temperatures. The concrete specimens containing recycled aggregate (0%, 50%, 75%, and 100%) were exposed to different temperatures (25, 200, 400, and 600°C) in a muffle furnace at a heating rate of 10°C/min. The variations in flexural strength, compressive strength, and density were then tested according to ASTM standards. Findings from this investigation indicate that the degradation in the mechanical strength of concrete does not seem to be significantly affected by the increase in the percentage of recycled aggregates. However, a significant and linear decrease in the density was observed at 400°C with an increase in the percentage of recycled aggregates. The degradation of the compressive and flexural strengths of recycled aggregate concrete with increasing temperatures obtained from the experimental analysis was compared with the analytical predictions provided by Eurocode 2. Moreover, simplified equations have been proposed to estimate the degradation of the mechanical properties of recycled aggregate concrete at higher temperatures. The incorporation of recycled aggregates into concrete resulted in satisfactory residual performance.