Replacement Ratio Research Articles

Performance of Molasses Waste as a Cement Replacement to Study Concrete Compressive Strength

To reduce the negative environmental impact of cement production and preserve natural resources, an experimental investigation was conducted to study the performance of concrete specimens at different curing ages and to determine the compressive strength of these specimens by replacing cement with molasses. Experimentation was carried out on the concrete specimens at a temperature range of 25 °C to 30 °C; six specimens were cast for each replacement ratio, except for 0.75% wt. of cement (86.55 g) and 1% wt. of cement (113.6 g), where five samples were considered for each ratio. The average 28-day compressive strength of the conventional concrete specimens came out to be 29 MPa, but increased to 40 MPa with the addition of 0.25% wt. of cement molasses (28.85 g). It was observed that as the percentage of molasses waste in the concrete mix was further increased by replacing the cement, the compressive strength of the concrete specimens increased gradually and then significantly decreased. The findings shed light on the prospect of using molasses waste instead of cement in the concrete mix. Also, it is worth mentioning that about 30% of the cost–benefit was obtained with reference to that of conventional admixtures available in the market for the production of concrete. However, it is notable that a long-term durability study needs to be conducted before making it viable. This work not only addresses a sustainable and innovative method of waste management (SDG12), but also contributes to low carbon emissions (SDG13). The novelty of this work lies in the fact that no such kind of study has been conducted in Pakistan so far, in addition to the very limited international literature available, and, in particular, no evidence on the compressive strength results at higher molasses dosages, i.e., 1% wt. of cement (113.6 g) and 2% wt. of cement (230.8 g).

Polymer Flooding Reduces Emissions and Energy Consumption in the North Sea

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 218231, How Polymer Flooding Reduces CO2 Emissions and Energy Consumption at the Captain Field: An Exergy-Return-on-Exergy-Investment Case Study,” by Tormod Skauge, SPE, and Arne Skauge, SPE, Energy Research Norway, and Nancy Lugo, Ithaca Energy UK, et al. The paper has not been peer reviewed. _ Insights into the energy efficiency and environmental performance of the extraction of heavy oil from the Captain field in the UK sector of the North Sea are gained using life-cycle assessment (LCA), which incorporates the concept of exergy-return-on-exergy-investment (ERoEI). The LCA allows for separation of the process into material and work streams, assessing the effect of each separately. In the complete paper, the authors compare waterflooding (WF) to polymer flooding (PF) as primary extraction strategies. Introduction The Captain field is approximately 145 km northeast of Aberdeen, Scotland. The reservoirs lie at shallow depths of approximately 900 m true vertical depth with correspondingly low temperatures of 31°C and low pressures of 87 bar. A primary challenge is the relatively viscous oil of 40–140 cp. The field was initially developed with long horizontal wells and downhole pumps. Viscous oil implies mobility challenges, however, and water injection could lead to unstable displacement, early water breakthrough, and possible coning issues. After a successful pilot PF at Captain during 2010–2017, a staged enhanced oil recovery (EOR) development approach was adopted in 2016 aiming to extend the pilot polymer-solution-injection scheme to the full field through a phased development. Following the pilot study, the Captain EOR project was split into Stage 1 and Stage 2. The first stage involved drilling of five producers and two EOR injectors by 2022. The second stage included some brownfield modifications across the three Captain installations (two installations and a floating production, storage, and offloading vessel) and a significant expansion in the subsea area. The complete paper concentrates on the expansion in the subsea areas, Areas B and C. The methodology of the study, including the development of simulation cases, LCA, exergy analysis, system boundaries, material and work streams, and CO2 emissions, is detailed in the complete paper. Production Profiles The Stage 2 EOR development evaluates PF for Areas B and C. The baseline is WF with fully produced water reinjection. WF was scheduled to begin in January 2024 and to end in December 2099. The PF case also was slated to begin in January 2024 and to end in 2035 and 2034 for Area B and Area C, respectively. The field is operated on pressure maintenance, and the voidage replacement ratio is kept close to 1.0. This means that the PF injects more liquid than the WF case during the first 5 years of injection when the oil production is higher for PF. After polymer injection ends, the PF case injects less liquid than the WF case. In Area B, water cut is high from the start for the WF case. Because of the high mobility of the water, it fingers through the oil. In contrast, when polymer is injected, the water cut falls to approximately 80% and does not reach the starting value of 94.1% before 7 years, more than 2.5 years after having stopped the polymer injection in this area. The low water cut is the result of production of a large oil bank generated by the improved sweep and mobility reduction of the injected polymer.

Experimental and model evaluation of cyclic compressive performance for RAC-filled BFRP tube composite columns

The mechanical properties of recycled aggregate concrete (RAC) can be significantly enhanced in RAC-filled fiber-reinforced-polymer (FRP) tube composite columns. However, the cyclic compressive behavior of this type of composite columns has been scarcely studied. In this study, a series of cyclic axial compressive tests were conducted on RAC-filled basalt-FRP (BFRP) tube composite columns, and the effects of confinement level (number of BFRP layers) and RA replacement ratio were investigated. The test results indicate that, compared to RAC columns, the compressive capacity and deformability of RAC-filled BFRP tube composite columns increased significantly under cyclic loading. The compressive strength and ultimate strain of BFRP-confined RAC reached 1.42-3.98 times and 2.88-21.53 times those of unconfined RAC, respectively. The compressive strength and ultimate strain under cyclic loading were generally close to those under monotonic loading, with the compressive strength ratios averaging 1.052 and the ultimate strain ratios averaging 1.031. The enhancement efficiency of BFRP confinement increased progressively with increasing confinement level and/or RA replacement ratio. The envelope curves of the cyclic stress-strain curves resembled the stress-strain curves under monotonic loading. The reloading modulus (Ere) and residual modulus (Eun,0) continuously decreased as the unloading strain (εun) increased, while the plastic strain (εpl) increased almost linearly with εun. The values of Ere, Eun,0 and εpl were affected by the confinement level and RA replacement ratio. Finally, typical theoretical models for FRP-confined concrete were used to evaluate the cyclic stress-strain curves of RAC-filled BFRP tube composite columns.

Experimental study on chloride ion permeability of carbonated recycled aggregate concrete considering the effects of multiple factors

The chloride ion permeability is an important index of durability of carbonated recycled aggregate concrete (CRAC), but the resistance to chloride ion permeability of CRAC is affected by many factors and has yet been fully explored, which needs further systematic study. Considering the effects of the replacement ratio of carbonated recycled coarse aggregate (CRCA), the carbonation time of CRAC, the bending load level, the carbonation temperature of CRAC, and the replacement ratio of carbonated recycled fine aggregate (CRFA), the resistance to chloride ion permeability of CRAC was investigated by conducting tests in this paper. The results indicated that, compared with the non-carbonated recycled aggregate concrete (NCRAC), the electric flux of CRAC decreased by 9.14% to 37.34%. An increase in the replacement ratio of CRCA could reduce the resistance to chloride ion permeability of CRAC, while an increase in CRAC carbonation time had a significant effect on improving the resistance to chloride ion permeability. When the replacement ratio of CRCA was 100%, as the carbonation time increased from 0 to 14 days, the maximum reduction in electric flux of CRAC was 31.66%. With the same replacement ratio of CRCA, as the bending load level increased, the decrease in electric flux of CRAC showed an increasing trend compared to that of NCRAC. The resistance to chloride ion permeability of CRAC could be improved with an increase in carbonation temperature. Compared with the CRAC with carbonation temperature of 20 °C, the electric flux of the CRAC with carbonation temperature of 40 °C decreased by 11.03%. When the replacement ratio of CRFA was in the range of 0 to 20%, the resistance to chloride ion permeability of CRAC could be improved by incorporating CRFA, but the improvement effect was not significant. Therefore, compared with the NCRAC, the resistance to chloride ion permeability of CRAC is enhanced, and the research results can provide data support for the engineering application of CRAC.

Research on the Mechanical Properties of Composite Grouting Materials Based on Ordinary Portland–Sulphoaluminate Cement

This study aimed to enhance the mechanical properties of calcium sulfoaluminate cement grouting materials (HCSA) by investigating the effects of ordinary Portland cement (OPC) content, the ratio of quicklime to gypsum, and the dosage of sodium aluminate on the compressive strength of the OPC-CSA composite system. The results indicate that as the OPC content increases, the compressive strength of the blended cement initially increases and then decreases, reaching a maximum at a 60% OPC replacement ratio within the experimental group. The addition of an appropriate amount of OPC to the CSA composite system effectively prevents the regression of compressive strength. With an increase in quicklime content, the compressive strength of the samples at various ages first increases and then decreases, with the optimal ratio of quicklime to gypsum found to be 2:8. Furthermore, sodium aluminate, used as an activator, when increased in dosage, leads to an initial increase followed by a decrease in the compressive strength of OPC-CSA samples, with an optimal incorporation rate of 0.75%, significantly enhancing the strength of the blended cement. In the orthogonal experiments, the dosage of sodium aluminate was identified as the most influential factor affecting the compressive strength of the composite grouting materials.

Global buckling and residual capacities of circular recycled aggregate concrete-filled stainless steel tube (RACFSST) columns after exposure to fire

The post-fire flexural buckling behaviour and capacities of circular recycled aggregate concrete-filled stainless steel tube (RACFSST) columns are studied in this paper, underpinned by testing and numerical modelling. A testing programme was firstly conducted on twelve column specimens designed with three recycled coarse aggregate replacement ratios (0%, 35% and 70%), including nine column specimens after exposure to the ISO 834 standard fire for 15 min, 30 min and 45 min and three reference column specimens at ambient temperature. The test failure modes, load–mid-height lateral deflection curves and failure loads were reported in detail. The influences of heating durations and recycled coarse aggregate replacement ratios on failure loads and mid-height lateral deflections at failure loads of circular RACFSST column specimens were discussed and their lateral deflection distributions were analysed. The testing programme was followed by a numerical modelling programme, where thermal and mechanical finite element models were developed to repeat the experimental results and afterwards used to carry out parametric studies to generate a numerical data pool over a wide range of cross-section dimensions and member lengths. Based on the test and numerical data, the relevant design rules for circular natural aggregate concrete-filled carbon steel tube columns at ambient temperature, as specified in the European code, Australian/New Zealand standard and American specification, were evaluated, using post-fire material properties, for their applicability to circular RACFSST columns after exposure to fire. It was revealed from the evaluation results that the three design codes led to overall acceptable levels of accuracy and consistency in predicting post-fire flexural buckling capacities of circular RACFSST columns, but with some unsafe predictions.

Enhancing thermo-mechanical and moisture properties of 3D-Printed concrete through recycled ultra-fine waste glass powder

This paper presents a novel approach to enhancing 3D printed concrete (3DPC) by incorporating ultra-fine glass powder (UFGP), focusing on its mechanical properties and high-temperature resistance. Investigation like fresh properties, basic physical properties, residual compressive strength after exposure to 400 °C and 800 °C, hygric properties such as water vapor diffusion resistance, liquid water transport, and moisture buffering capacity were performed the observe the effect of UFGP replacement ratio on 3DPC, which demonstrates significant improvements, highlighting the potential of UFGP to elevate 3DPCs’ performance. Results showed significant improvements, particularly with a 20% UFGP mix, which showed the lowest compressive strength loss (9.0% at 400 °C and 53.7% at 800 °C). Additionally, the water vapor diffusion resistance factor for the 20% UFGP mix was measured at 65.03. These results suggest that incorporating UFGP in 3DPC enhances thermal resilience and mechanical properties, offering a solution for high-temperature construction. This study contributes to sustainable construction by emphasizing the importance of mechanical resilience for structural integrity under extreme temperatures.

Self-compacting concrete using molybdenum mineral tailings: materials and mechanical property

Recycling mineral tailings poses significant challenges, but one effective solution is their incorporation into self-compacting concrete (SCC) mixtures. This research explores the material and mechanical properties of SCC by integrating mineral tailings at three different ratios: 10%, 20%, and 30%. The primary aim is to determine the optimal replacement ratio that preserves key characteristics such as flowability and viscosity. To assess the material properties of fresh SCC, we conduct various tests, including rheological, V-funnel, U-box, and air content tests. These evaluations focus on how the addition of mineral tailings at different levels impacts flowability and viscosity. In terms of mechanical performance, we analyze compressive strength relative to the increasing proportion of mineral tailings. The results indicate that higher proportions of mineral tailings negatively affect flowability and viscosity. As a result, the optimal replacement ratio for mineral tailings is identified as up to 20% of the total cement content. These findings suggest that mineral tailings can effectively replace conventional cement, making them a promising option for producing environmentally friendly self-compacting concrete.

Study on the Impact of China’s Pension Insurance System on the Savings Rate of Urban Residents Based on the Preventive Saving Perspective

In the context of population aging, the study of the impact of the pension insurance system on the savings behavior of urban residents can help reduce preventive savings, increase current consumption, and promote the healthy development of the economy. This study constructs a two-period OLG model of the pension insurance system based on the preventive saving perspective using urban panel data of 31 provinces from 2002 to 2021 and conducts empirical analysis through the systematic generalized method of moments. The results show that the pension insurance participation rate was positively correlated with the savings rate, while the pension replacement rate was negatively correlated with the savings rate, and this effect varied significantly across income levels and different levels of aging. Increased participation in high-income areas promoted savings, while increased pension replacement rates in low-income areas reduced savings. The positive correlation between participation rates and savings rates was more pronounced in regions with higher levels of aging, while the opposite was true in regions with lower levels of aging. In addition, the negative correlation between pension replacement ratios and savings rates was particularly pronounced in high-aging regions.

Thermal activation of multi-recycled concrete powder as supplementary cementitious material for repeated and waste-free recycling

Utilizing powder generated during concrete recycling process is considered crucial for achieving complete recycling of concrete waste. However, integrating recycled concrete powder (RCP) often reduces cementitious mixture performance. This study aims to enhance RCP characteristics through thermal activation, facilitating its recycling as cement replacement over multiple recycling cycles. RCPs from three cycles of concrete recycling were heat-treated at 200 °C, 400 °C, 600 °C, and 800 °C for 2 h, and their chemical composition was analyzed before and after treatment. Subsequently, the RCPs replaced cement in mortar by 10 %, 20 %, and 30 %. Various properties of the mortars, such as flow, mechanical strength, water absorption, and drying shrinkage, were tested. The results showed a general decline in mortar properties with increasing RCP replacement ratios and recycling cycles. However, RCPs activated at 600 °C and 800 °C enhanced compressive and flexural strengths by up to 19 % and 16 %, respectively, and enhanced shrinkage resistance by 19 %. Particularly, the three-times RCP activated at 800 °C achieved mechanical performance comparable to standard mortar at 10 % replacement, meeting strength grading requirements per industry standards. This study demonstrates a viable pathway for the repeatable and waste-free recycling of concrete, contributing to more sustainable construction practices.

Physical, Mechanical and Durability Properties of Eco-Friendly Engineered Geopolymer Composites

Engineered geopolymer composite (EGC) is a high-performance material with enhanced mechanical and durability capabilities. Ground granulated blast furnace slag (GGBFS) and silica fume (SF) are common binder materials in producing EGC. However, due to the scarcity and high cost of these materials in some countries, sustainable alternatives are needed. This research focused on producing eco-friendly EGC made of cheaper and more common pozzolanic waste materials that are rich in aluminum and silicon. Rice husk ash (RHA), granite waste powder (GWP), and volcanic pumice powder (VPP) were used as partial substitutions (10–50%) of GGBFS in EGC. The effects of these wastes on workability, unit weight, compressive strength, tensile strength, flexural strength, water absorption, and porosity of EGC were examined. The residual compressive strength of the proposed EGC mixtures at high elevated temperatures (200, 400, and 600 °C) was also evaluated. Additionally, scanning electron microscope (SEM) was employed to analyze the EGC microstructure characteristics. The experimental results demonstrated that replacing GGBFS with RHA and GWP at high replacement ratios decreased EGC workability by up to 23.1% and 30.8%, respectively, while 50% VPP improved EGC workability by up to 38.5%. EGC mixtures made with 30% RHA, 20% GWP, or 10% VPP showed the optimal results in which they exhibited the highest compressive, tensile, and flexural strengths, as well as the highest residual compressive strength when exposed to high elevated temperatures. The water absorption and porosity increased by up to 106.1% and 75.1%, respectively, when using RHA; increased by up to 23.2% and 18.6%, respectively, when using GWP; and decreased by up to 24.7% and 22.6%, respectively, when using VPP in EGC.

Experimental Study on Direct Shear Behavior of New-to-Old Interface for Recycled Aggregate Concrete with Different Replacement Ratios

The large amount of construction waste produced by the construction industry brings severe natural resource consumption and environmental pollution, elevating the awareness of sustainable development. Recycled aggregate concrete, crushed from construction waste, is recognized as an eco-friendly material and the current optimal solution for the environmental problem. The interface shear failure between substrate recycled coarse aggregate concrete (RAC) and overlay natural aggregate concrete becomes vital for structural safety. In order to study the direct shear performance, a total of 19 specimens were designed to carry out the direct shear test with different replacement ratios, interface types and curing ages. The whole process and failure mode were recorded. The relationships between the shear capacity and deformation, ductility, damage evolution, and energy dissipation were evaluated and discussed. The results demonstrate that the RAC component in the interface was the weak line in the shear plane, accelerating the damage evolution. In the early curing stage, the replacement ratio had a slight influence on the shear properties. Increasing the recycled aggregate replacement ratio from 0 to 100% improved the normalized strength ratio by 8.94% and 14.62%, respectively, for curing ages of 3 days and 7 days. A regression equation was proposed to predict the shear strength, accounting for the curing ages. With the increase in the replacement ratio, the ductility and energy dissipation gradually enhanced.

Experimental and numerical evaluation of sustainable application of steel slag as an alternative to gravel in compaction piles

The study investigates the application of steel slag as an innovative material for compaction piles in the stabilization of soft soils, offering an eco-friendly alternative to conventional gravel compaction piles (GCPs). Through a comprehensive series of laboratory tests, field experiments, and numerical simulations, this study evaluated the performance, environmental impact, and long-term behavior of steel slag compaction piles (SSCPs). The key findings revealed that steel slag not only provides immediate soil improvement comparable to gravel but also exhibits significant time-dependent increases in strength and stiffness. Standard Penetration Test (SPT) N-ratios (N1/N0, where N1 = N value after improvement and N0 = N value before improvement) were similar for soils reinforced with SSCPs and GCPs after 0 months, but were about 30 % higher in SSCP-reinforced soils after 3 months. This increase was attributed to the cementation of steel slags, suggesting that the compaction pile with increased stiffness due to cementation acts as a compaction pile with an increased area replacement ratio (α). Environmental assessments confirmed that steel slag meets regulatory standards for soil contamination, positioning it as a sustainable option. Settlement analysis after embankment construction showed reduced and more uniform settlements with SSCPs, suggesting superior load distribution capabilities. Finite element analysis compared the behavior of SSCP-reinforced soils at varying α and stiffness of compaction piles, confirming that the cementation of steel slag produces an effect equivalent to increasing α in uncemented piles, thus enhancing the reinforcement effect.

Experimental and numerical study on the chloride ions penetration in recycled aggregate concrete

Recycled aggregate concrete (RAC) offers a practical solution for improving resource efficiency and reducing environmental impact. Durability degradation in concrete structures is primarily caused by the corrosion of internal reinforcement due to chloride ion penetration. Thus, the resistance of RAC to chloride ion penetration is a crucial durability indicator. This study investigates the effects of recycled coarse aggregate (RCA) and mineral powder on RAC's chloride penetration resistance using rapid chloride ions migration (RCM) tests. Results show that increasing the RCA replacement ratio reduces its resistance to chloride ions penetration. The addition of slag improves resistance to chloride ions of RAC by up to 30 %, while fly ash addition shows an initial increase followed by a decline in resistance to chloride ions penetration of RAC. To address the variability in the spatial distribution and thickness of old mortar within RCA, a two-dimensional random aggregate model incorporating ellipsoids and internal polygons was developed. Five distinct phases were considered in the model: natural aggregate, new motar, old mortar, old interface transition zone (ITZ) between natural aggregate and old mortar, new ITZ between old mortar and new mortar. The model simulated the random placement of aggregates by randomizing geometric shapes, considering factors such as the RCA replacement ratio and particle size. COMSOL software was used to simulate chloride ions penetration in RAC with 30 % RCA, and the simulation model's accuracy was verified through ion chromatography. This study takes into account the random distribution of old mortar on the surfaces of RCA to provide a deeper investigation into chloride transport within RAC.

Exploration of steel slag by lignin and sodium citrate modification for mechanical properties and stability of steel slag-cement cementitious materials

Steel slag is produced globally in huge annual quantities. How to achieve its large-scale utilization is a question that researchers have been exploring. In this work, sodium citrate (SC) was used as a linker to modify Steel slag (SS) with alkali lignin (AL). And steel slag cement cementitious materials (CSS) were prepared with 10% replacement ratio. The effects of AL and SC on CSS were investigated by X-ray diffractometry (XRD), Fourier Transform Infrared Spectroscopy (FT-IR) and Thermo-gravimetric analysis (TG/DTA) etc. The results indicated that AL successfully loaded on the surface of SS. For CSS, as the degree of modification increased, the standard consistency water consumption of CSS decreased from 27% to 23.5%. During the hydration of CSS, its main hydration product was Ca(OH)2, the suitable amounts of AL and SC can stimulate the activity of SS. In addition, SS modification could improve the stability of CSS. The results of Ray's clamp method showed that the addition of AL and SC made the expansion of CSS reduced from 1.5 to 0. The 3 d and 28 d of CSS maximum flexural strengths were 5.42 MPa and 8.61 MPa and the maximum compressive strengths were 22.96 MPa and 49.15 MPa, respectively. This was an increase of 36.67% and 48.27% respectively. Therefore, the combination of AL and SS can not only effectively solve the problem of AL resource utilization, but also is expected to realize the practical application of SS in cement cementitious materials. It has good social and environmental benefits.

Study on the properties and eco-sustainability of early-age carbonation cured cement paste with recycled concrete slurry waste substitution

The reduced early-age properties of cementitious materials substituted recycled concrete slurry waste (RCSW) hinder its utilisation, which can be further improved via early-age carbonation curing with benefits from sequestering the CO2. This study aims to compressively investigate the effectiveness and environmental impact of early carbonation curing on three replacement ratios and three types of treatments of RCSW including sieving, shearing and ball milling with standard curing. In addition to mechanical properties, hydration properties, microstructure characteristics, and carbon sequestration of the treated-RCSW replaced cement paste after different curing methods were investigated and compared. The results showed that, compared to substitution ratios of 30 % and 45 %, cement paste with a 15 % RCSW substitution ratio exhibited higher strength. Furthermore, compared to standard curing, the carbonation curing method effectively improved the early strength and overall performance of the cement paste, with the early strength under carbonation curing at a 15 % RCSW substitution rate being about 89 % higher than that of standard curing. According to economic and environmental calculations, RCSW substitution could effectively reduce carbon dioxide emissions, and the use of carbonised curing methods enabled the cement paste to effectively absorb carbon dioxide.

Ensemble machine learning models for compressive strength and elastic modulus of recycled brick aggregate concrete

This study delivers an in-depth analysis of predicting the compressive strength and elastic modulus of recycled brick aggregate concrete (RBAC). It assembles an extensive database of 633 compression test results and develops five ensemble learning models—random forest (RF), gradient boosting regression trees (GBRT), extreme gradient boosting (XGB), light gradient boosting machine (LGBM) and stacking (St). These models are evaluated against existing empirical formulas with respect to their effectiveness. The findings reveal that machine learning (ML) models outperform existing formulas: for compressive strength prediction, traditional models achieve a maximum determination coefficient R² of 0.38, whereas ML models attain an R² range of 0.91–0.94. For elastic modulus, the highest R² values are 0.44 for traditional models and 0.97 for ML models. Notably, the LGBM and St models excel in predicting compressive strength and elastic modulus, respectively. The study also identifies critical parameters influencing RBAC’s compressive behavior and highlights their impact trends. Remarkably, while the mass-weighted water absorption of coarse aggregates and the replacement ratio of recycled brick aggregates (RBAs) have less impact on compressive strength compared to the effective water-to-cement ratio, they become more influential for elastic modulus. Additionally, the decrease in elastic modulus due to higher RBA replacement ratios or increased mass-weighted water absorption of coarse aggregates exceeds the corresponding reduction in compressive strength. This research not only deepens the understanding of RBAC’s mechanical properties but also provides valuable predictive tools for civil engineering applications.

Performance evaluation of high-performance concrete mixes incorporating recycled steel scale waste as fine aggregates

In this study, steel-scale waste (SSW), a byproduct generated during the manufacturing of steel, was investigated as a potential alternative to natural fine aggregates (sand) for preparing high-performance concrete (HPC). Three grades of sand and SSW with different particle sizes were mixed in varying combinations. Three different compaction techniques (loose, tamped, vibration) were employed. The optimum packing density for both SSW and natural aggregates was achieved using the vibration compaction method. Since the combination of 50 % sand and 50 % SSW exhibited the best packing density for both materials, this bi-grade aggregate mixture was selected for the mix preparation. The mechanical tests (compressive strength, flexural strength) and durability assessment (bulk water sorptivity, rate of water absorption, chloride ion penetration) were performed to achieve the desired objectives. The specimens were exposed to two different curing regimes i.e., normal curing and heat curing at elevated temperature. A significant increase in compressive and flexural strength was observed with the increased content of SSW. A compressive strength as high as 140 MPa was obtained for the HPC mix containing SSW aggregates and steel fibers. The replacement ratio of SSW was optimized to achieve better strength and durability. Experimental results showed that heat curing was more effective than conventional curing methods in improving the performance of the concrete.

Evaluation of Some Uncertainties in the Modeling of Blast Furnace Hydrogen Injection

While blast furnaces remain the dominant ironmaking technology, there is growing interest in using hydrogen to partially replace coke and pulverized coal to reduce CO2 emissions in this hard‐to‐decarbonize process. However, significant discrepancies in modeling the tuyere injection of hydrogen are noted in the literature, which can challenge the scale‐up from modeling predictions and pilot trials to actual blast furnace operations. To address this, the impact of uncertainties in the assumptions of the temperature in the thermal reserve zone and the ratio of H2 and CO utilization on the results of blast furnace process modeling are evaluated using a 1D steady‐state zonal model. The study indicates that variations in the assumed value of thermal reserve zone temperature significantly impact the estimation of optimal hydrogen injection rate, coke replacement ratio, and direct CO2 emissions reductions. In contrast, the same parameters are much less affected by the variations in the assumed value of the proportion between H2 and CO utilization ratios, which, however, affect the top gas composition. A need for further research to determine the range of the difference in temperatures of gas and solid in the thermal reserve zone tolerable for smooth blast furnace operation is highlighted.

Eccentric compression behaviors of iron tailings and recycled aggregate concrete-filled steel tube columns

This paper presents a sustainable method for using iron ore tailings (IOTs) sand and recycled coarse aggregate (RCA) in concrete and concrete-filled steel tube (CFT) columns. The study first examines the impact of RCA replacement ratios (0 %, 50 %, 100 %) on concrete's mechanical properties, finding that both compressive and tensile strengths decrease with higher RCA content due to the negative effects of old interfacial transition zones and adhered cement in RCA. Then, twelve iron tailing and recycled aggregate concrete-filled steel tube (ITRAC-CFT) columns were tested under eccentric compression to assess the effects of varying RCA replacement ratios, eccentricity ratios (0.3, 0.5), and slenderness ratios (12.12, 19.05). Results indicate that RCA ratios have minimal impact on failure modes, ultimate bearing capacity, and stiffness, although ductility increases with higher RCA content. As slenderness ratios increase, the ultimate bearing capacity decreases by 5.3 % and 6.8 % for eccentricities of 0.3 and 0.5, respectively. The study further validates these findings through the finite element method (FEM), showing strong agreement between experimental and predicted results, average value, standard deviation, and coefficient of variation of Nu/NFE were 1.02 %, 0.04, and 3.92 %, respectively. Finally, a comparison with existing design codes (EC4, AISC 360, and GB 50396) reveals that AISC 360 provides the most accurate predictions of the ultimate bearing capacity of ITRAC-CFT columns. The research concludes that the comprehensive use of IOTs sand and RCA in CFT structural concrete is a highly viable and eco-friendly solution, offering potential benefits for sustainable construction practices.