Search

In multispan bridges excited by ground shaking, columns are usually the target ductile members. Although current practice is successful in attaining the no-collapse objective for bridges, columns are usually damaged at displacements associated with this performance level. Minor damage can be repaired, but excessive damage is usually beyond repair. A new design paradigm with minimal damage and repair need is gaining interest. The benefits of such a design can be increased if low-damage technologies are combined with accelerated bridge construction techniques. The main goal of the present study was to develop reinforced concrete bridge columns that are fully precast concrete, low damage, and repairable through component replacement. To achieve the project objectives, 20 repairable precast concrete alternatives were developed and ranked. Subsequently, the top three candidates were designed at 50% scale, constructed at a precast concrete plant, and tested in a laboratory. The precast concrete columns incorporated different exposed fuses, such as stainless steel bars and steel tendons, advanced materials such as ultra-high-performance concrete, a self-centering mechanism, or an accelerated bridge construction socket connection. A reference cast-inplace concrete column was included for comparison. Each precast concrete column was tested twice. It was found that the repair of the precast ultra-high-performance concrete columns with exposed tendons was easy, simple, and quick due to insignificant damage and minimal residual displacements. All precast concrete columns exhibited displacement capacities comparable to or higher than cast-in-place concrete columns. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Architecture & Civil Engineering is the property of Chang'an Daxue Zazhishe and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study evaluates the potential to use shrinkage-reducing admixture (SRA) and pre-saturated lightweight sand (LWS) to shorten the external moist-curing requirement of ultra-high-performance concrete (UHPC), which is critical in some applications where continuous moist-curing is challenging. Key characteristics of UHPC prepared with and without SRA and LWS and under 3 days, 7 days, and continuous moist curing were investigated. Results indicate that the combined incorporation of 1% SRA and 17% LWS can shorten the required moist-curing duration because such a mixture under 3 days of moist curing exhibited low total shrinkage of 360 µε and compressive strength of 135 MPa (19,580 psi) at 56 days, and flexural strength of 18 MPa (2610 psi) at 28 days. This mixture subjected to 3 days of moist curing had a similar hydration degree and 25% lower capillary porosity in paste compared to the Reference UHPC prepared without any SRA and LWS and under continuous moist curing. The incorporation of 17% LWS promoted cement hydration and silica fume pozzolanic reaction to a degree similar to extending the moist-curing duration from 3 to 28 days and offsetting the impact of SRA on reducing cement hydration. The lower capillary porosity in the paste compensated for the porosity induced by porous LWS to secure an acceptable level of total porosity of UHPC. [ABSTRACT FROM AUTHOR]

For continuous steel–concrete composite girder bridges based on the post-combined method, the conventional rectangular group studs contribute to the isolation of the steel girder and the concrete slab before prestressing, leading to the majority of prestress forces being introduced to the concrete slab. However, rectangular-group stud holes cause the prestress forces to be unevenly distributed. In this study, a new type of bellow-sleeved stud (BSS) was developed to mitigate the weakening effects of rectangular group stud holes on the slab. A steel corrugated sleeve with a diameter of 60 mm was employed to cover the stud, which served as an internal formwork to prevent the concrete from bonding with the root of the stud. After prestressing was complete, the steel sleeve was filled with ultra-high-performance concrete (UHPC) to create a reliable combination between the concrete slab and the steel girder. To investigate the shear performance of this new type of connection, eight push-out test specimens were designed, and finite-element models were built. This study drew a comparison between the BSS and the ordinary headed stud (OHS). The research findings suggested that the BSS is subjected to less bending–shear coupling and offers a 4.5% increase in shear strength and a 31.9% increase in shear stiffness compared with the OHS. The study also analyzed the structural parameters influencing the shear performance of the BSS. It is found that the steel sleeve of the BSS has a negative effect on shear performance, but this can be mitigated by infusing high-strength material into the sleeve. Furthermore, the study examined the effect of construction quality on shear performance and suggested that sleeve deviation and grout leakage considerably reduced the shear performance of the BSS. Accordingly, strict control over the construction quality of the BSS is necessary. [ABSTRACT FROM AUTHOR]

To study the eccentric compression mechanical properties of ECC and UHPC filled-in double steel tubular (EUFDST) composite columns, 35 full-scale EUCFDST composite column specimens were designed by ABAQUS software with the slenderness ratio (λ), UHPC cylinder compressive strength (fcu), inner and outer steel tubular strength (fy1, fy2), inner and outer steel tubular thickness (t1, t2), inner and outer steel tubular diameter ratio (Ω), eccentricity (e), and fiber content (γ) as the main parameters. By comparison with the simulation of the existing test, the correctness of the finite element modeling is verified. The parameter analysis of 35 full-scale EUFDST composite columns was carried out to obtain the eccentric load-mid-span deflection curve of the specimens. The failure mechanism, ductility coefficient, and stiffness degradation of the composite columns under different parameters were analyzed, and the section of the composite column was verified to satisfy the plane section assumption. The variation trend of maximum load-bearing capacity and the ductility of composite columns under different parameter conditions was obtained. By introducing the eccentricity correction coefficient and slenderness ratio correction coefficient, the calculation equation of the eccentric maximum load-bearing capacity of EUCFDST composite columns is statistically regressed, which provides a basis for the practical use of these columns. [ABSTRACT FROM AUTHOR]

Due to the extraordinary mechanical properties of ultra-high-performance concrete (UHPC), the shear stirrups in UHPC beams could potentially be eliminated. This study aimed to determine the effect of beam height and steel fiber volume content on the shear behavior of non-stirrup UHPC beams under a larger shear span–depth ratio (up to 2.8). Eight beams were designed and fabricated including six non-stirrup UHPC beams and two comparing stirrup-reinforced normal concrete (NC) beams. The experimental results demonstrated that the steel fiber volume content could be a crucial factor affecting the ductility, cracking strength, and shear capacity of non-stirrup UHPC beams and altering their failure modes. Additionally, the height of the beam had a considerable effect on its shear resistance. French standard formulae were more accurate for the UHPC beams with larger shear span–depth ratios, PCI-2021 formulae greatly overestimated the shear capacity of UHPC beams with larger shear span–depth ratios, and Xu's formulae were more accurate for the steel fiber-reinforced UHPC beams with larger shear span–depth ratios. In summary, French standard formulae were the most suitable formulae for predicting the shear capacity of UHPC beams in this paper. [ABSTRACT FROM AUTHOR]

In bridge reinforcement projects, damaged T-beams are the most common objects for reinforcement, yet the interface bonding and bending performance of UHPC reinforcement on T-beams have hardly been studied. To ensure the reliability and stability of UHPC-strengthened T-beams in practical applications, this study introduced a post-installed rebar bonding technique to efficiently connect T-beams with UHPC layers. Initially, using ABAQUS software [2020 version] for finite element simulation, this study investigated the effects of various post-installed rebar parameters (horizontal spacing, yield strength, diameter, and matrix concrete strength) on the shear performance of the UHPC and RC interface, obtaining the optimal connection parameters. Subsequently, by comparing shear formulas in domestic and international standards, a new UHPC-RC steel bar interface shear strength theoretical formula with 93.6% accuracy was derived. Finally, finite element simulations analyzed the impact of different post-installed reinforcing bar layout forms and longitudinal spacing, as well as UHPC-strengthened location and layer thickness, on the bending performance of damaged T-beams. The results showed a good match between simulation outcomes and experimental results, applicable for further reinforcement analysis of T-beams. When the horizontal spacing of post-installed rebars is 12d, with diameters ranging from 10 mm to 14 mm, their anchoring capability is efficiently utilized. A square form of a post-installed rebar with a longitudinal spacing of 300 mm effectively improves the ultimate bending load capacity of the strengthened beam. The simulation analysis and theoretical results help in the design and application of post-installed steel connections and UHPC-strengthened structures in UHPC-strengthened reinforced concrete T-beam structures. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive study on ultra-high-performance concrete (UHPC) beams without stirrups, where the test data of 487 beams were collected, and an experimental database was established. Four distinct shear strength calculation models for UHPC beams were examined in the study. These models were created from national specification guides. The results indicate that while the code equation is useful for predicting UHPC beam shear capacity, it consistently underestimates actual values, with a mean experimental-to-calculated ratio above 1.5. The database was also used to study the impacts of the compressive strength of UHPC, the shear span-to-depth ratio, the fiber volume fraction, and the reinforcement ratio on the shear strength of UHPC beams. The findings showed that the shear span-to-depth ratio significantly affected the shear load-bearing capacity of UHPC beams. The increase in the compressive strength of UHPC, fiber volume fraction, and reinforcement ratio positively affected the shear strength of UHPC beams to varying degrees. Additionally, there were size effects for beams with a shear span-to-depth ratio of less than 1.5 and an effective depth of more than 300. In addition, coefficients accounting for fiber influence and the shear span-to-depth ratio were incorporated to develop an enhanced formula for UHPC beams. The empirical data from the database tests revealed that the average ratio of the beams' experimental shear capacity to the values predicted by the modified equation is 1.3, with a standard deviation of 0.74. These results suggest that the refined equation offers improved calculation precision and broader applicability. Eventually, a summary of the issues pertaining to the shear performance of UHPC beams and the key future research directions is provided to facilitate a clearer comprehension and awareness of emerging concepts for scholars within the discipline. [ABSTRACT FROM AUTHOR]

Ultra-high-performance concrete (UHPC) is a recently developed material which has attracted considerable attention in the field of civil engineering because of its outstanding characteristics. One of the key factors in concrete design is the compressive strength (CS) of UHPC. As one of the most potent tools in artificial intelligence (AI), machine learning (ML) can accurately predict concrete's mechanical properties. Hyperparameter tuning is crucial in ensuring the prediction model's reliability. However, it is a complex work. The purpose of this study is to optimize the CS prediction method for UHPC. Three ML methods, random forest (RF), support vector machine (SVM), and k-nearest neighbor (KNN), are selected to predict the CS of UHPC. Among them, the RF model demonstrates superior predictive accuracy, with the testing dataset R2 of 0.8506. In addition, three meta-heuristic optimization algorithms, particle swarm optimization (PSO), beetle antenna search (BAS), and snake optimization (SO), are utilized to optimize the prediction model hyperparameters. The R2 values for the testing dataset of SO-RF, PSO-RF, and BAS-RF are 0.9147, 0.8529, and 0.8607, respectively. The results indicate that SO-RF exhibits the highest predictive performance. Furthermore, the importance of input parameters is evaluated, and the findings prove the feasibility of the SO-RF model. This research enriches the prediction method of the CS of UHPC. [ABSTRACT FROM AUTHOR]

Summary: This paper summarizes the literature available on the behavior of concrete‐filled steel tubular (CFST) columns to evaluate the effect of geometrical properties such as shape of cross‐section, diameter‐to‐thickness ratio, and length‐to‐diameter ratio of CFST columns under axial loading. Then, the impact of different material composition for core concrete and encasing material is concluded for columns under axial loading. The performance of CFST is evaluated in terms of failure modes, ductility, stiffness, and axial compressive strength. For encasing tube, carbon steel, stainless steel, and aluminum are studied while for core, various concretes such as Normal (NSC) and high strength concrete (HSC), light weight concrete (LWC), recycled aggregate concrete (RAC), expansive concrete (EC), rubber crumb concrete(RuCC), and steel slag concrete (SSC) are covered for review in this paper. Material limitations as provided by various codes for design of composite structures is also mentioned for both tube and core concrete. Failure modes of concrete‐filled tubular(CFT) columns are most affected by geometric properties columns while materials used for concrete and encasing tube do not cause much difference. Though, ductility, axial compressive strength, and stiffness are affected by both geometric and material properties. [ABSTRACT FROM AUTHOR]

Ultra-high-performance concrete (UHPC) is a cementitious composite combining high-strength concrete matrix and fiber reinforcement. Standing out for its excellent mechanical properties and durability, this material has been widely recognized as a viable choice for highly complex engineering projects. This paper proposes (i) the review of the influence exerted by the constituent materials on the mechanical properties of compressive strength, flexural tensile strength, and elastic modulus of UHPC and (ii) the determination of optimal quantities of the constituent materials based on simplified statistical analyses of the developed database. The data search was restricted to papers that produced UHPC with straight steel fibers at a content of 2% by volume. UHPC mixture models were proposed based on graphical analyses of the relationship of constituent materials versus mechanical properties, aiming to optimize the material's performance for each mechanical property. The results proved to be in accordance with the specifications present in the literature, characterized by high cement consumption, significant presence of fine materials, and low water-to-binder ratio. The divergences identified between the mixtures reflect how the constituent materials uniquely impact each mechanical property of the concrete. In general, fine materials were shown to play a significant role in increasing the compressive strength and flexural tensile strength of UHPC, while water and superplasticizers stood out for their influence on the material's workability. [ABSTRACT FROM AUTHOR]

Breakthrough technology of ultra‐high‐performance concrete (UHPC) introduced in the 1990s exhibits several exceptional mechanical properties that are advantageous in elements of bridge applications. Extensive research has aimed to industrialize UHPC and develop design models. This paper investigates several design models for shear, including a unified approach with that of conventional concrete based on the modified compression field theory (MCFT). An experimental database of UHPC prestressed concrete girders subjected to shear failure is compiled to evaluate model accuracy and a reliability study is conducted to establish appropriate safety factors. The analysis demonstrates that the proposed MCFT‐based model aligns well with experimental results, exhibiting a suitable level of conservatism for design. A reliability assessment of a typical prestressed girder designed according to Canadian Standards Association building and bridge loadings is performed, resulting in a structural reliability evaluation against a target reliability index. The study recommends specific strength reduction and safety factors for design approaches using UHPC. [ABSTRACT FROM AUTHOR]

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

This study investigates the effects of matrix strength on the high‐rate tensile resistance and strain rate sensitivity of strain‐hardening fiber‐reinforced concretes (SHFRCs) under direct tensile loading. Two types of deformed steel fiber, hooked and twisted, were reinforced in two matrices, high‐performance concrete (HPC) with compressive strength of 84 MPa and ultra‐high‐performance concrete (UHPC) with compressive strength of 180 MPa. Additionally, an artificial neural network (ANN) based model was proposed to estimate the strain rate sensitivity of SHFRCs subjected to dynamic direct tensile loading. The results showed that HPC produced relatively lower post cracking strength but much higher strain capacity at a high strain rate than UHPC. Moreover, HPC was found to be more strain rate sensitivity than UHPC. Furthermore, the proposed ANN model was an efficient tool for predicting the strain rate sensitivity of SHFRCs. Based on the sensitivity analysis, the contribution of each influence factor on the final strain rate sensitivity of SHFRCs can be determined. [ABSTRACT FROM AUTHOR]

The flexural behavior of beams strengthened with GFRP bars and high‐performance fiber‐reinforced concrete (HPFRC) was investigated in this paper. The four‐point flexural response of one reference beam and four beams strengthened with high‐performance fiber‐reinforced concrete was investigated by experimental research and theoretical calculation. The experimental and theoretical data (strain, load, etc.) are discussed. Parameters varied included the strengthening scheme (bottom‐side strengthening and three‐side strengthening) and the type of high‐performance fiber‐reinforced concrete (engineered cementitious composite [ECC] and ultra‐high‐performance concrete [UHPC]). The results showed that the cracking load and ultimate load of beams strengthened with UPFRC material were 31.3%–170% and 9.6%–20.7% higher, respectively, relative to the reference beam. Beams with three‐side strengthening (without interfacial debonding) had higher ultimate load, smaller crack width, and better durability relative to beams with bottom‐side strengthening. The UHPC layer was more effective in increasing the ultimate bearing capacity, and ECC strengthening layer was more effective in inhibiting cracking development of beams. Based on the experimental results, a model was proposed to predict the ultimate bearing capacity of beams strengthened with high‐performance fiber‐reinforced concrete, which could provide good agreement between the experimental and predicted results. [ABSTRACT FROM AUTHOR]

This study explores the potential of using fine recycled aggregate (FRA) to replace natural sand in concrete production. The research was divided into two parts. In the first part, natural aggregate's complete fine fraction (0-4mm) was replaced with FRA in conventional concrete for two strength classes. In the second part, individual fine components of high-performance concrete (HPC) were substituted with a similar fraction of fine recycled HPC and concrete aggregate. The physical and mechanical properties of these mixtures with recycled aggregate were evaluated against reference mixtures that contained only natural aggregate, following European standards. Results showed that while most of the concrete and HPC mixtures with recycled aggregate showed slight decreases in properties compared to the reference mixes, the most significant reduction in mechanical properties was observed in the flexural tensile strength of the concrete mixture with FRA, which decreased by over 50 %. The absorption by immersion increased by up to 85 %. The deterioration in properties must be considered during the design stage and only used in applications where it will not affect the functionality of the structures. [ABSTRACT FROM AUTHOR]

As the global population has continued to grow, the costs and environmental issues associated with traditional construction materials like cement and river sand have become increasingly problematic. This research aimed to explore an alternative and ecofriendly approach to traditional building materials. The researchers conducted an experimental program to assess the mechanical properties of the rice husk ash-based concrete at different curing ages 7, 14, 21, and 28 days. Following the mix design, the concrete was produced using water to binder ratio of 0.5. A series of experiments were conducted on both fresh and hardened states to investigate the impact of quarry dust on rice husk ash-based concrete. It was observed from the experimental results that when 40% of the quarry dust was used as a replacement for fine aggregates, the concrete exhibited the highest strength. After 28 days of curing, the compressive strength showed a 0.65% improvement, while the splitting tensile strength displayed a 1.77% enhancement compared to the reference mix. To ensure the reliability of the experimental findings, a statistical analysis was conducted. The study concluded that certain factors, such as quarry dust, curing duration, and rice husk ash, interacted synergistically to influence the compressive and splitting tensile strengths of the concrete. The researchers also proposed equations to predict these strengths based on the aforementioned parameters. [ABSTRACT FROM AUTHOR]

Due to its exceptional qualities, ultra-high-performance concrete (UHPC) has recently become one of the hottest research areas, although the material's significant carbon emissions go against the current development trend. In order to lower the carbon emissions of UHPC, this study suggests a machine learning-based strategy for optimizing the mix proportion of UHPC. To accomplish this, an artificial neural network (ANN) is initially applied to develop a prediction model for the compressive strength and slump flow of UHPC. Then, a genetic algorithm (GA) is employed to reduce the carbon emissions of UHPC while taking into account the strength, slump flow, component content, component proportion, and absolute volume of UHPC as constraint conditions. The outcome is then supported by the results of the experiments. In comparison to the experimental results, the research findings show that the ANN model has excellent prediction accuracy with an error of less than 10%. The carbon emissions of UHPC are decreased to 688 kg/m3 after GA optimization, and the effect of optimization is substantial. The machine learning (ML) model can provide theoretical support for the optimization of various aspects of UHPC. [ABSTRACT FROM AUTHOR]

Lacing reinforcement plays a critical role in the design and performance of reinforced concrete (RC) slabs by distributing the applied loads more evenly across the slab, ensuring that no specific area of the slab is overloaded. In this study, nine slabs, divided into three groups according to the investigated parameters, were meticulously designed and evaluated to study the interplay between the lacing reinforcement and other key parameters. Each slab was crafted for simple support and was subjected to both static and repeated two-point load tests. The lacing reinforcement had an angle of 45° with various tension and lacing steel. The repeated-tested specimens with lacing reinforcement experienced smaller ductility than those of similar static-tested specimens, where the reduction in ductility factor ranged between 8.4% and 22.3% for all specimens. Additionally, the tested slabs were analyzed numerically using the ABAQUS software package. The validated FE test program was used to study the effect of varying the lacing reinforcement ratio, the compressive strength of concrete, and the material types of the tension and lacing reinforcements. The lacing reinforcement becomes more effective in increasing the slab capacity when using the higher compressive strength of concrete. [ABSTRACT FROM AUTHOR]

Sustainable construction becomes a highly key topic in the construction sector owing to its benefits and advantages over economy, environment, and society. This study considers one such application of sustainable construction, rehabilitation of RC beams. Through such rehabilitation, it is possible to extend the life of existing concrete structures. A numerical analysis approach has been framed to study to this phenomenon. Total 10 criteria have been selected to evaluate the rehabilitation material alternatives on RC beams with ultra-high-performance concrete. 9 Alternative materials have been considered for rehabilitation of RC beams. DEMATEL-ANP and PROMETHEE has been used as a methodology in two phases, the first phase used DEMATEL-ANP to analyze the considered criteria and the second phase used PROMETHEE to evaluate the considered alternative materials based on the analyzed criteria. Finally, this study concludes with the effective rehabilitation material for RC beams with ultra-high-performance-concrete. The considered numerical framework can be adopted in various forms of similar or different applications. [ABSTRACT FROM AUTHOR]

This article discusses the strength and ductility of beam-column joints made of Ultra-High-Performance Concrete (UHPC) and Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC). The study examines the impact of these materials on the behavior of the joints and uses computational simulations to analyze their strength and ductility. The results show that UHPFRC joints have superior strength, enhanced ductility, and a unique damage progression pattern. The article also introduces the concept of energy-based ductility and validates the computational analysis with experimental data. Additionally, the document provides a list of references that cover various aspects of concrete structures, which can be useful for researchers and engineers studying the design and performance of these structures. [Extracted from the article]

Waste recovery and environmental protection and the production of low-cost UHPFC are the most trends areas of current researchers. Ultrafine (silica fume) is the basic component of ultra-high-performance fiber concrete (UHPFC), which is very sophisticated and its manufacture is limited by the capacity of some industries. This work, which falls within this context, aims to recover waste (glass, ceramics, and granite) as recycled fillers partially substituted silica fumes in the composition of the UHPFC. The study consists of two parts, the first is to find a formulation based on local materials, the second is to replace the silica fumes by recycled fillers with the percentage of 10% and 20%. The tests carried out on the fresh state mixtures are density, workability and occluded air, and on hardened state are the compressive and flexural tensile strength, sclerometer, ultrasound regarding untreated concrete, and the performance in compressive and tensile strength concerning the concrete heat treated at 90°C, as well as durability parameters (water absorption and chlorides penetrations). The results show that recycled ceramic fillers and 20% of the recycled granite fillers present an acceptable compressive strength, the recycled fillers increase the flexural tensile strength of the UHPFC and the heat treatment improves the mechanical strength. Recycled fillers affect sustainability parameters. [ABSTRACT FROM AUTHOR]

In recent years, bridge safety accidents caused by insufficient shear bearing capacity of bridges have attracted increasing attention. The main causes include internal factors such as insufficient bridge section and deterioration of steel bars, as well as external factors, for example, vehicle load surge and improper maintenance. To address this issue to some degree, this article adopts the method of strengthening RC beams with ultra-high performance concrete (UHPC) and conducts parameter analysis using finite element method, taking into consideration the influence of four parameters: reinforcement material, reinforcement thickness, reinforcement length, and reinforcement form on the shear strengthening characteristics of RC rectangular beams. After obtaining the optimal reinforcement plan through parameter analysis, the author applied the research results to an existing bridge with insufficient shear strength. It then turned out that the shear bearing capacity of the reinforced bridge’s inclined section increased by approximately 27.1%. Simple and fast in construction, this reinforcement method is one of the methods that is effective to increase cross-section reinforcement; besides, it features good economic characteristics and applicability. [ABSTRACT FROM AUTHOR]

Silica fume (SF), an ultra-fine pozzolanic material that is a by-product of industrial processes, is essentially used as mineral filler in the manufacture of ultra-high-performance concrete (UHPC) at a high dosage. However, its high cost can be a significant barrier to UHPC production, particularly in areas where local sources are not available. The aim of this study is to investigate the feasibility of partially replacing SF with two other pozzolanic waste materials, fly ash (FA) and natural pozzolan (NP), for UHPC production. Six different mixes of UHPC were designed, produced and tested initially for workability and compressive strength, considering different constitutions of FA and NP to partially substitute SF. Based on fulfilling the minimum requirements of flow and compressive strength of a UHPC mix, three UHPC mixes, including the control mix with SF alone, were considered for a detailed assessment of their performance in terms of strength, shrinkage, and durability characteristics, including resistance against reinforcement corrosion. Results reveal that both pozzolanic waste materials can be used to replace SF up to 60% to produce UHPC mixes without compromising strength and durability. The outcome of this study would help in reducing the consumption of SF and produce UHPC by utilizing FA and NP as partial replacements of SF when SF is not available locally as a waste material. [ABSTRACT FROM AUTHOR]

The porosity of concrete affects the durability of reinforced concrete structures, wherein high levels of porosity are linked to a shorter service life. Recent works have noted that high porosity levels naturally exist in the aftermath of a fire exposure - especially when concrete is classified as high strength concrete (HSC). To shed more light into this phenomenon, this paper showcases a method for measuring the porosity of HSC under elevated temperatures through scanning electron microscopy (SEM). In this method, SEMbased images were examined to quantify the surface porosity of fire-affected HSC. Detailed image analysis was performed for HSC exposed to various heating durations. The study concludes that the surface porosity obtained via the SEM processing method is in good agreement with that from the SEM-based method (with a minor average difference of 3.8%). As such, the proposed method is expected to be reliable for the porosity analysis of fire-damaged concrete. [ABSTRACT FROM AUTHOR]

The shear bond of interface between concrete and basalt fiber reinforced polymer (BFRP) bars during freeze-thaw (F-T) cycles is crucial for the application of BFRP bar-reinforced concrete structures in cold regions. In this study, 48 groups of pull-out specimens were designed to test the shear bond of the BFRP-concrete interface subjected to F-T cycles. The effects of concrete strength, diameter, and embedment length of BFRP rebar were investigated under numerous F-T cycles. Test results showed that a larger diameter or longer embedment length of BFRP rebar resulted in lower interfacial shear bond behavior, such as interfacial bond strength, initial stiffness, and energy absorption, after the interface goes through F-T cycles. However, higher concrete strength and fewer F-T cycles were beneficial for enhancing the interfacial bond behavior. Subsequently, a three-dimensional (3D) interfacial model based on the finite element method was developed, and the interfacial bond behavior of the specimens was analyzed in-depth. Finally, a degradation bond strength subjected to F-T cycles was predicted by a proposed mechanical model. The predictions were fully consistent with the tested results. The model demonstrated accuracy in describing the shear bond behavior of the interface under numerous F-T cycles. [ABSTRACT FROM AUTHOR]

The acronym "HPGC" refers to "high performance green concrete." This breakthrough is significant because it moves the industry closer to its goal of replacing concrete with eco-friendly alternatives that claim superior mechanical qualities, thereby making concrete a more sustainable building material. When working with metal, a fine powdery dust known as "iron filings" is inevitably created. The purpose of this study was to evaluate the usefulness of iron filings as a fine aggregate in building projects. An experiment was conducted to examine the mechanical iron filings' effects on concrete's characteristics utilised as a supplement to sand. Using a range of sand replacement percentages (0% (control mix), 10% (treatment mix), 20% (treatment mix), and 30% (treatment mix)), the compressive, split-tensile, and flexural strengths of 35 concrete specimens consist of cubes, cylinders, and prisms were tested after 28 days of treatment in water. The findings indicated that the mechanical qualities of HPGC were enhanced when iron filings were used in place of sand, but that the concrete's slump value and workability were diminished. Therefore, only 30% of the sand (fine particles) should be substituted by weight with iron filings in the concrete mix, depending on the desired strength attribute. In this case, the concrete's compressive strength is increased by 13.2%, split-tensile strength by 21.1%, and flexural strength by 49.88%, all by replacing 30% of the sand (fine particles) with iron filings. Therefore, employing iron filings in concrete will help with recycling and waste reduction. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering (17264073) is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The declining availability of natural sand resources and the significant carbon footprint associated with the extensive use of cement are posing severe limitations on the advancement and application of ultra-high-performance concrete (UHPC). In this study, waste tyre-derived recycled crumb rubber particles (CR) were employed to replace quartz sand, and an alkali-activated cementitious material was used to produce waste tyre-alkali-activated UHPC (T-UHPAC). The influence of different CR replacement ratios (0%, 5%, 20%, 35%, 50%) on the tensile and flexural performance of T-UHPAC was investigated, and a predictive model for the stress–strain response considering the CR replacement ratio was established. An optimization method for improving the tensile and flexural performance of T-UHPAC was proposed. The results indicate that the effect of rough-surfaced CR on the interfacial properties of concrete differs from that of smooth quartz sand. A CR replacement ratio exceeding 35% led to a reduction in both the tensile and flexural strengths of UHPAC, while a replacement ratio at or below 20% resulted in a superior tensile and flexural performance of T-UHPAC. The established predictive model for tensile performance accurately forecasts the stress–strain behaviour of T-UHPAC under varying CR replacement ratios, with the accuracy improving as the CR replacement ratio increases. By utilizing CR to replace quartz sand in proportions not exceeding 20%, the production of low-carbon UHPC with exceptional comprehensive mechanical properties is achievable. Moreover, the development of T-UHPAC through the comprehensive utilization of waste tyres presents a promising and innovative approach for the low-carbon and cost-effective production of UHPC, thereby facilitating the sustainable development of natural resources. This research represents a significant step towards the widespread adoption and application of UHPC and thus holds substantial importance. [ABSTRACT FROM AUTHOR]

The objective of this research is to experimentally study the flexural behavior of hybrid reinforced concrete beams. Three test beams, each with dimensions of (2200 X 150 X 240) mm, were fabricated for this purpose. The first beam was constructed using ordinary concrete, while the second beam consisted of two layers of high-strength concrete in the compression zone and normal concrete in the tension zone. The third beam was entirely cast using high-strength concrete. In terms of reinforcement, all beams were equipped with 2φ12 steel bars in the tension zone and 2φ12 steel bars in the compression zone. Additionally, φ12 steel bars were employed to resist shear forces, distributed along the length of the beams with a spacing of 125 mm c/c. Two-point loading was applied to all beams until failure occurred. The results obtained from the experimental tests reveal that the use of hybrid concrete beams enhances the ultimate load capacity by approximately 20.93%. On the other hand, beams constructed entirely from highstrength concrete exhibited an increase in failure load capacity by approximately 28.68%. [ABSTRACT FROM AUTHOR]

The limitations in the available reinforcing methods have accompanied the increasing popularity of 3D Concrete Printing (3DCP). Incorporating steel fibers as reinforcement is a promising approach to overcome these limitations. However, the impact of the printing process on the alignment of these fibers is not well understood. Therefore, the objective of this research is to quantitatively analyze the distribution of steel fiber alignment in 3D printed concrete. To achieve this, digital image analysis was employed to assess the influence of nozzle diameter, print speed, and fiber content on fiber alignment in both moldcast and 3D-printed samples. UHPC matrix without fiber addition and fiber reinforced UHPC composites with brass-coated steel fiber contents of 1.5% and 3% by volume fraction were printed. Furthermore, Material nozzles ranging from 10 mm to 40 mm in size were employed and printing speeds of 15, 25, 35, and 45 mm/s were adjusted. Subsequently, the study examined the implications of fiber alignment on the hardened performance of printed specimens and compared them with conventionally mold-cast samples. The findings of the study demonstrated that increasing the fiber content and using smaller diameter nozzles during the printing procedure led to significant improvements in fiber orientation along the printing direction. As a result, the mechanical performance of the printed samples showed a substantial enhancement compared to the specimens produced through mold casting, primarily due to the improved fiber alignment. [ABSTRACT FROM AUTHOR]

As the modular industry expands, the most widely used building materials are primarily concrete, steel, and wood. However, the use of wood and steel is severely limited compared to concrete for reasons such as durability and economy. To overcome these shortcomings, we aimed to apply ultra-high-performance fiber-reinforced concrete (UHPFRC), which has excellent compressive strength and tensile strength, high durability, and minimal reinforcement with steel fibers. In this study, research was conducted on the development of unit box-type architectural modules using UHPFRC with a compressive strength of 120 MPa and a tensile strength of greater than 7 MPa. Various amounts of steel fibers (Vf = 1.0, 1.5, and 2.0%) were evaluated to determine the optimal mixing ratio of UHPFRC, in which both the durability and mechanical performance were assessed. The compressive strength and tensile strength of UHPFRC were found to be 132 MPa and 10.1 MPa, respectively, while its resistance to chloride penetration averaged 14.47 coulombs, indicating superior durability compared to conventional concrete. To reduce the weight of the unit components of the architectural modular system, both normal concrete (NC) components and UHPFRC were applied. The main variables in the flexural tests were the cross-sectional thickness, steel fiber content, and presence of an insulation material, comprising a total of three variables for evaluating the flexural performance. The application of UHPFRC with a compressive strength of 120 MPa, a cross-sectional thickness of 120 mm, and a 10 mm diameter reinforcement provided a similar performance to that of NC components while reducing concrete usage by 60% compared to NC components. Additionally, structural analysis was performed to prototype the unit box-type modular structure using UHPFRC. The modular structural system developed in this study was found to reduce construction costs by 18.7% compared to traditional steel structural systems. Further research is necessary to address issues such as floor slab vibration and noise, connections, and expansion to multistory buildings for commercialization of modular structures using UHPFRC. [ABSTRACT FROM AUTHOR]

Concrete technologists use different types of additives such as fly ash, slag, natural pozzolans and nanomaterials toenhance concrete performance and durability. However, a detailed explanation of the early-age hydration process and microstructural modification of concrete in the presence of nanomaterials remains to be presented and extensive research is required for strategic modification of cementitious systems. This study focused on the precise monitoring of early-age hydration with the incorporation of nanoalumina (nAl) in tricalcium silicate (C3S) and Portland cement paste and mortar. The dosage of nAl was varied from 1 to 5% (by weight) in C3S and from 0.1 to 1.0% in Portland cement, with a water/cement ratio of 0.4. The hydration studies showed that the nAl increased the cross-linkage in calcium silicate hydrate gel through substitution of aluminium by silicon, which was responsible for the enhancement of the modulus of elasticity (by 40%) with 1.0% nAl) after 7 days of hydration. In summary, the incorporation of nAl modified the concrete microstructure in the initial days of hydration, leading to higher concrete performance and longer service lives of concrete structures. [ABSTRACT FROM AUTHOR]

Fire spalling prediction of fibre-reinforced concrete containing polypropylene (PP) or steel fibre at elevated temperatures is challenging. It is difficult to use conventional methods, such as finite-element modelling and discrete-element modelling, to solve the problem, because of the complicate coupling mechanism of PP and steel fibres in concrete. To this end, two artificial neural network (ANN) models, one (ANN1) based on a concrete mix study and the other (ANN2) based on a compressive strength study, were introduced to assess the resistance of concrete to explosive spalling. Test data (321 and 318 items, respectively) gathered from the literature were utilised to train the proposed models. Twenty-four concrete mixes (96 groups), that is, seven plain concrete mixes, four high performance concrete mixes reinforced with PP fibre, three ultra-high-performance concrete (UHPC) mixes with reinforced PP fibre and ten UHPC mixes reinforced with PP and steel hybrid fibres were designed and tested to validate the accuracy of the models. The study demonstrates that ANN1 and ANN2 can achieve a predictive accuracy of 89.6% and 84.4% for the explosive spalling, respectively, indicating the feasibility of the proposed models for predicting explosive spalling threat of the hybrid fibre-reinforced concrete. [ABSTRACT FROM AUTHOR]

Ultra-high-performance concrete (UHPC) is an advanced cement-based material with excellent mechanical properties and durability. However, with the improvement of UHPC's compressive properties, its insufficient tensile properties have gradually attracted attention. This paper reviews the tensile properties of steel fibers in UHPC. The purpose is to summarize the existing research and to provide guidance for future research. The relevant papers were retrieved through three commonly used experimental methods for UHPC tensile properties (the direct tensile test, flexural test, and splitting test), and classified according to the content, length, type, and combination of the steel fibers. The results show that the direct tensile test can better reflect the true tensile strength of UHPC materials. The tensile properties of UHPC are not only related to the content, shape, length, and hybrids of the steel fibers, but also to the composition of the UHPC matrix, the orientation of the fibers, and the geometric dimensions of the specimen. The improvement of the tensile properties of the steel fiber combinations depends on the effectiveness of the synergy between the fibers. Additionally, digital image correlation (DIC) technology is mainly used for crack propagation in UHPC. The analysis of the post-crack phase of UHPC is facilitated. Theoretical models and empirical formulas for tensile properties can further deepen the understanding of UHPC tensile properties and provide suggestions for future research. [ABSTRACT FROM AUTHOR]

The composite pier, which consists of ultra-high-performance concrete (UHPC) and normal strength concrete (NSC), is a promising option for practical engineering due to its remarkable mechanical performance. However, the cyclic behavior and seismic design mechanism of the composite pier have not been thoroughly investigated. This paper aims to study the cyclic performance of the composite pier by conducting cyclic tests on 10 specimens. The thickness of the UHPC tube, strength of reinforcement, spacing of stirrups, and other parameters are considered. The crack distribution, hysteretic response, and failure modes are observed and analyzed. Results show that the composite pier exhibits good crack-control ability, large bearing capacity, and effective energy dissipation. The expansion of the inner NSC may exacerbate the buckling of the UHPC tube, thus leading to more severe seismic damage. To further investigate the composite pier, a numerical model is established to analyze the optimal thickness of the UHPC tube. The ultimate state of the composite section is taken into consideration, and the upper and lower limits of the height of the compression zone are proposed. Based on the parametric analysis, a recommended range of the UHPC tube thickness is derived. [ABSTRACT FROM AUTHOR]

This paper studies the fresh and mechanical properties of high-strength concrete (HSC) by incorporating recycled concrete aggregates (RCA) of varying sizes and concentrations. The recycled aggregate concrete (RAC) was prepared by partially replacing RCA with natural coarse aggregate (NCA) at 0%, 15%, 30%, and 45%, with aggregate sizes ranging from 5 to 12 and 12–20-mm. Fresh concrete properties, such as slump, Kelly ball, compacting factor, K-slump, and fresh density, were tested to determine the influence of RCA size and concentration. In addition, the mechanical properties were studied through the execution of compressive, split-tensile, and stress-strain tests. The test results revealed that increasing the RCA concentration declines the fresh and hardened properties of HSC. In the fresh concrete experimentation, the 12–20 mm aggregate size RAC mixes exhibited greater workability than the 5–12 mm aggregate mixes. On the contrary, 5–12 mm aggregate mixes RAC had higher compressive and split-tensile strength and a higher modulus of elasticity than 12–20 mm aggregate mixes concrete. When it comes to sustainability, the study found that the smaller size range of RAC produces inferior embodied CO 2 (eCO 2) and provides a cost-effective and sustainable solution for the construction industry. [ABSTRACT FROM AUTHOR]

The advancement in the tensile strength and ductility of plain concrete can minimize the quantity of materials required per unit strength to build eco-friendly structures. This paper compares the compressive and flexural behavior of different strength classes (C20, C30, and C45) of concrete with the varying volume fractions of hooked steel fiber (HSF) considering the application of concrete road. The performance of each strength class was evaluated and compared based on the compressive and tensile testing results. Using the mechanical properties of concrete mixtures; the design thickness, cost, and global warming potential of concrete pavement were calculated and compared between different mixes under the same traffic loadings. The results showed that the maximum utilization of HSF was observed in the high-strength C45, whereas HSF showed comparatively low efficiency in low-strength C20. At 0.25% volume of HSF, low strength C20 concrete showed higher residual strength and flexural toughness than that of the plain high strength C45 concrete. The analysis of design thickness of pavements revealed that low-strength C20 at 0.25–0.5% HSF can provide cost-effective and eco-friendly pavements compared to a plain high strength C45 for the same design loadings. The results of this study provide useful insights on the selection of strength class and concentration of steel fiber for pavement application. [ABSTRACT FROM AUTHOR]

High-performance concrete (HPC) is widely used in infrastructure for its durability and sustainability benefits. However, it faces challenges like autogenous shrinkage, leading to potential cracking and reduced durability. Fiber reinforcement offers a solution by mitigating shrinkage-induced stresses and enhancing concrete durability. In this sense, this study investigates the use of glass microfibers to mitigate autogenous shrinkage and early-age cracking in high-strength self-compacting concrete. Samples were prepared with two water-to-binder ratios (w/b): 0.25 and 0.32; and three glass microfiber contents: 0.20%, 0.25%, and 0.30 vol.%. The concrete mixtures were characterized in the fresh state for slump flow and in the hardened state for compressive strength, static, and dynamic Young's modulus. Unrestrained and restrained shrinkage tests were also conducted in the seven days-age. The findings revealed that glass microfibers reduced the workability in mixtures with lower slump flow values (w/b of 0.25), while less viscous mixtures (w/b of 0.32) exhibited a slight improvement. Compressive strength showed a proportional enhancement with increasing fiber contents in concretes with a w/b ratio of 0.32. A contrasting trend emerged in concretes with a w/b ratio of 0.25, wherein strength diminished as fiber additions increased. The modulus of elasticity improved with fiber additions only in the matrix with a w/b ratio of 0.25, showing no correlation with compressive strength results. In shrinkage tests, the addition of glass microfibers up to specific limits (0.20% for a w/b ratio of 0.25 and 0.25% for w/b of 0.32) demonstrated improvements in controlling concrete deformation in unrestrained shrinkage analyses. Concerning cracking reduction in restrained concrete specimens, the mixtures did not exhibit significant improvements in crack prevention. [ABSTRACT FROM AUTHOR]

A total of five ultra-high-performance concrete (UHPC)-strengthened reinforced concrete (RC) columns and one RC column were built and subjected to eccentric compression testing to examine the force performance of UHPC-strengthened eccentrically compressed plain RC columns. This experimental study examined the crack progression, the damage morphology, the deformation ability, the maximum load-carrying capacity, and the ductile properties of the eccentrically compressed columns. It also investigated the impacts of eccentricity, the reinforcement thickness, and the addition of steel fibers on the effectiveness of reinforcement. The cracking load, peak load, and ductility coefficient of the UHPC-reinforced specimens were increased by 100.28%, 172.30%, and 56.30%, respectively, compared with the RC column at an initial eccentricity of 50 mm. As the eccentricity distance increased, the bearing capacity of the UHPC eccentrically compressed specimens decreased, and the deformation capacity increased. Increasing the steel fiber dosage within the appropriate range decreased the crack width of the specimen. The addition of 2% steel fiber resulted in a 24.8% increase in cracking load, an 8.96% increase in peak load, and a 2.60% increase in ductility coefficient compared to the addition of 1% steel fiber. However, the reinforcing effect of UHPC was weakened under high eccentric pressures. Based on the theory of concrete structure and mechanical principles, the formula for calculating the compressive bearing capacity of RC columns strengthened with high-performance concrete was proposed. The results of calculating the positive section bearing capacity of eccentrically compressed RC columns reinforced with high-performance concrete are in good agreement with the test values. The results of this paper provide an experimental basis and theoretical foundation for the cross-sectional design of UHPC eccentrically compressed columns. [ABSTRACT FROM AUTHOR]

As one of the key factors influencing the hydration process, as well as the microstructure formation and evolution of ultra-highperformance concrete (UHPC), the action mechanism of different curing regimes have been studied to some extent. However, the current knowledge of the underlying mechanisms that control the different effects of different curing regimes is limited. In this study, the composition of hydration products, micromorphology, and migration and evolution of aluminum-phase hydration products of UHPC under three combined curing regimes (standard curing, steam curing + standard curing, and autoclave curing + standard curing) were investigated in depth. Micromorphology observation shows that heat treatment promoted the formation of higher-stiffness hydration products (tobermorite and xonotlite) in UHPC, and the higher the polymerization degree, the higher the Si/Ca ratio of the hydration product. Meanwhile, 29Si and 27Al nuclear magnetic resonance (NMR) spectroscopy shows that specimens with higher strength had higher Al[4]/Si and a lower amount of ettringite and AFm at the early curing stage. The elevated curing temperature reduced the formation of ettringite and AFm and allowed more Al3+ to replace Si4+ into the structure and interlayer of the calcium-(alumino)silicate-hydrate (C-(A)-S-H) gel, which increased the mean chain length (MCL) and polymerization degree of the C-(A)-S-H gel. However, the polymerization effect of Al ions is limited, so the provision of the silicon source to improve the Si/Ca ratio of the system is important. [ABSTRACT FROM AUTHOR]

Ultra-high-performance concrete (UHPC) is considered a sophisticated concrete construction solution for infrastructure and other structures because of its premium mechanical traits and superior durability. Fibers have a special effect on the properties of UHPC, especially as this type of concrete suffers from high autogenous shrinkage due to its high cementitious content, so the properties and volume fraction of fibers are more important in UHPC. This study will describe previous related works on the mechanical behavior of UHPC specimens reinforced with micro- and nanoscale fibers, and compare of the behavior of UHPC reinforced with microfibers to that reinforced with nanofibers. The compressive strength, flexural behavior, and durability aspects of UHPC reinforced with nanoand/or microscale variable types of fibers were studied to highlight the issues and make a new direction for other authors. [ABSTRACT FROM AUTHOR]

The work presented in this paper includes the construction methods and lessons learned from the placement of a non-proprietary ultra-high performance concrete (UHPC) overlay through the rehabilitation of a concrete bridge deck located in Socorro, New Mexico, USA. The selected bridge is a multi-cell, box girder bridge with four spans and a total length of 91.4 m and a width of 16.5 m with two traffic lanes. Rehabilitation of the bridge involved removing the top surface of the existing deck (deteriorated concrete), installing a high-performance deck (HPD) leveling course, and placing a 25 mm UHPC overlay. Sensors were installed in the bridge superstructure (multi-cell box girders, HPD, and overlay) for long-term monitoring. Overlay assessment included physical testing to evaluate the condition of the overlay–substrate bond by chain dragging and direct tension pull-off testing. Conclusions and lessons learned from this investigation serve as a fundamental list of best practices and recommendations for field construction of a non-proprietary UHPC overlay. Recommendations for preparatory tasks including material selection, substrate surface preparation, placement preparation, handling of materials, and UHPC mixing are provided. The recommendations also list best practices concerning the placement of the overlay, curing procedures, and quality assurance testing. Lastly, suggestions are presented for contracts pertaining to UHPC overlay projects. [ABSTRACT FROM AUTHOR]

The main objective of this paper research is a comparative study on the effect of the glass powder (GP) substitute from collected and recycled glass waste, as a fine partial cement replacement on the mechanical performance and durability of high performance concrete (HPC) and ordinary concrete (OC). For this two cement dosing were used of 400 kg/m3 to formulate OC and 450 kg/m3 to formulate HPC, and GP as considered binder like cement and not as fine addition, hence binder represent the sum of cement with GP (L=C+GP) with which will be made our two concretes formulation. Two ratios were used for the Water/Binder (W/B), the first W/B=0.35 for the HPC and the second W/B=0.5 for the OC, this ration is very important to fix the concentration of superplasticizer. A percentage of 10% and 20% substitution of cement CPA without additions noted CEM I 52.5 by the glass powder with fineness of 3600 cm 2/g are used. The evaluation of the compressive strength was followed from 7 to 365 days in order to study the behavior of the GP at different ages affected by the cement dosing and the ratio W/B compared to the reference concrete without GP for the two concretes HPC and OC. At 28 days the strengths of concretes with GP is affected by the replacement of a quantity of cement since the two reference concretes were superior but beyond this age an inverse behavior is noticed such that results obtained at age of 365 days seem to be advantageous in terms of savings in the quantity of cement used by interpreting the compressive strength, and the decrease in quantity of water in the mixtures offers a remarkable difference between the two concretes studied by using 20 % of GP as replacement of cement. [ABSTRACT FROM AUTHOR]

The corrosion of alkaline concrete materials exposed to a sulfuric acid environment is becoming more and more prevalent, and its damage assessment is becoming more and more imperative. This study aims to describe the corroded surfaces of concrete with different strength grades (C30, C50, C80) in sulfuric acid environments in terms of their three-dimensional fractal dimension. Three kinds of concrete with varying strength grades, namely C30, C50, and C80, were immersed in a sulfuric acid solution with pH ≈ 0.85 for four distinct corrosion durations, specifically 0, 28, 56, and 165 days, in accelerated corrosion tests. The 3D laser scanning technique was utilized to capture the 3D coordinates of the surface points of the concrete cylinder before and after corrosion. The fractal dimension of concrete's uneven surface before and after corrosion was computed via the cube covering method, and the mass loss of the concrete specimen was also obtained. The outcomes demonstrate that the three-dimensional fractal dimension provides a new method for characterizing the degree of corrosion deterioration of concrete samples affected by sulfuric acid via laser scanning technology. From the perspective of the appearance, mass loss, and fractal dimension of a rough surface in the sulfuric acid environment at a pH level of approximately 0.85, the degree of the corrosion deterioration of concrete is ranked from high to low as C80 > C50 > C30. These fractal dimensions of the concrete's corroded surfaces with various strength grades increase rapidly in the initial period. However, as the corrosion time progresses, the growth rate of the corroded surface fractal dimension gradually decelerates and tends towards stability, which accords with the law of exponential function. The widespread belief is that the higher the strength grade of concrete, the better its durability; however, this pattern varies in sulfuric acid corrosive environments. Therefore, based on this research, it is recommended that in extremely acidic environments (i.e., very low pH), more attention should be paid to high-strength grades of concrete. [ABSTRACT FROM AUTHOR]

Ultra-high-performance geopolymer concrete (UHPGC) emerges as a sustainable and cost-effective alternative to Portland cement-based UHPC, offering similar mechanical properties while significantly reducing carbon footprint and energy consumption. Research on UHPGC components is extremely scarce. This study focuses on the flexural and crack behavior of UHPGC beams with different steel fiber contents and longitudinal reinforcement ratios. Five UHPGC beams were tested under four-point bending. The test results were evaluated in terms of the failure mode, load–deflection relationship, flexural capacity, ductility, average crack spacing, and short-term flexural stiffness. The results show that all the UHPGC beams failed due to crack localization. Increases in the reinforcement ratio and steel fiber content had favorable effects on the flexural capacity and flexural stiffness. When the reinforcement ratio increased from 1.18% to 2.32%, the flexural capacity and flexural stiffness increased by 60.5% and 12.3%, respectively. As the steel fiber content increased from 1.5% to 2.5%, the flexural capacity and flexural stiffness increased by 4.7% and 4.4%, respectively. Furthermore, the flexural capacity, flexural stiffness, and crack spacing of the UHPGC beams were evaluated using existing methods. The results indicate that the existing methods can effectively predict flexural capacity and flexural stiffness in UHPGC beams but overestimate crack spacing. This study will provide a reference for the structural design of UHPGC. [ABSTRACT FROM AUTHOR]

The design of geopolymer concrete must meet more stringent requirements for the landscape, so understanding and designing geopolymer concrete with a higher compressive strength challenging. In the performance prediction of geopolymer concrete compressive strength, machine learning models have the advantage of being more accurate and faster. However, only a single machine learning model is usually used at present, there are few applications of ensemble learning models, and model optimization processes is lacking. Therefore, this paper proposes to use the Firefly Algorithm (AF) as an optimization tool to perform hyperparameter tuning on Logistic Regression (LR), Multiple Logistic Regression (MLR), decision tree (DT), and Random Forest (RF) models. At the same time, the reliability and efficiency of four integrated learning models were analyzed. The model was used to analyze the influencing factors of geopolymer concrete and determine the strength of their influencing ability. According to the experimental data, the RF-AF model had the lowest RMSE value. The RMSE value of the training set and test set were 4.0364 and 8.7202, respectively. The R value of the training set and test set were 0.9774 and 0.8915, respectively. Therefore, compared with the other three models, RF-AF has a stronger generalization ability and higher prediction accuracy. In addition, the molar concentration of NaOH was the most important influencing factors, and its influence was far greater than the other possible factors including NaOH content. Therefore, it is necessary to pay more attention to NaOH molarity when designing geopolymer concrete. [ABSTRACT FROM AUTHOR]

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

The use of High Strength Concrete is increasing largely nowadays due to its unique properties. The addition of pozzolanic materials such as silica fume and nano-silica as a partial replacement of cement in concrete is considered beneficial as it improves its properties and in the same time reduces the amount of CO2 emitted in the atmosphere during cement manufactory. Adding steel fiber to high strength concrete can improve its ductility, toughness and impact resistance in addition to its strength. The effect of adding silica fume, amorphous nano-silica and steel fibers to the concrete mix on its compressive and splitting tensile strengths was considered in this study at different cementitious contents. Amounts used were 10 % of silica fume and 1 % of nano-silica by weight of cement as partially replacing the same amounts of cement. 2 % of steel fiber by weight of concrete was also used. 500, 600, and 700 kg/m³ cementitious contents were used. SEM micrograph images and EDX spectrum were made on some concrete specimens. Specimens were tested at the age of 28 and 56 days. Concrete prepared with silica fume and nano-silica showed larger compressive and splitting tensile strengths than the control mix. Adding steel fibers resulted in further increase in strength with even larger percentage in the case of tensile strength and this can be related to their ability to control and bridge these cracks. [ABSTRACT FROM AUTHOR]

Grouting defects are an inherent challenge in construction practices, exerting a considerable impact on the operational structural integrity of connections. This investigation employed the impact-echo technique for the detection of grouting anomalies within connections, enhancing its precision through the integration of wavelet packet energy principles for damage identification purposes. A series of grouting completeness assessments were meticulously conducted, taking into account variables such as the divergent material properties of the sleeves and the configuration of adjacent reinforcement. The findings revealed that: (i) the energy distribution for the highstrength concrete cohort predominantly occupied the frequency bands 42, 44, 45, and 47, whereas for other groups, it was concentrated within the 37 to 40 frequency band; (ii) the delineation of empty sleeves was effectively discernible by examining the wavelet packet energy ratios across the spectrum of frequencies, albeit distinguishing between sleeves with 50% and full grouting density proved challenging; and (iii) the wavelet packet energy analysis yielded variable detection outcomes contingent on the material attributes of the sleeves, demonstrating heightened sensitivity when applied to ultrahigh-performance concrete matrices and GFRP-reinforced steel bars. [ABSTRACT FROM AUTHOR]