Conventional Ultra-high Performance Concrete Research Articles

Axial compression behavior of concrete-filled prefabricated aligned steel fiber UHPC tubes

This study presents an innovative composite column system featuring exceptional ductility and versatility, suitable for replacing traditional concrete columns or UHPC composite columns. The composite column, comprised of concrete-filled aligned steel fiber ultra-high performance concrete (UHPC) tubes (ASFUTs), offers superior mechanical properties. Apart from its function as a formwork, the ASFUT provides exceptional rigidity and lateral confinement capabilities, enabling it to withstand substantial axial forces directly. Initially, steel fibers were aligned using an electromagnetic field. Computed Tomography (CT) imaging elucidated an average inclination angle of 16.36° between the fibers and the circumference of ASFUT sections. Compared to conventional UHPC, aligned steel fiber UHPC demonstrates an average 9.1 % increase in compressive strength and an average 129.67 % increase in maximum equivalent tensile. This enhancement can be attributed to the improved fiber bridging effect resulting from the orientation of fibers. Then, the mechanical properties of the concrete-filled ASFUT columns were evaluated by axial compression testing of eight specimens with different fiber contents, shapes, and orientations. The findings indicate that the ASFUTs outperform conventional concrete-filled UHPC tubes, exhibiting notable enhancements across various performance metrics. Specifically, at a fiber volume fraction of 1 %, the concrete-filled ASFUT exhibits a compressive strength, elastic modulus, ductility, and energy dissipation capacity that are 1.12 times, 1.03 times, 1.25 times, and 1.54 times respectively, in comparison to conventional concrete-filled UHPC tubes. Finally, an advanced predictive model for estimating the axial bearing capacity of ASFUT concrete columns was proposed, offering valuable insights for structural design optimization and widespread implementation.

Coarse synthetic fibers (PP and POM) as a replacement to steel fibers in UHPC: Tensile behavior, environmental and economic assessment

Ultra-high performance concrete (UHPC) has excellent compressive strength and ductility. Nevertheless, the extensive utilization of UHPC has been impeded by factors including the exorbitant cost, substantial carbon emissions, and vulnerability to corrosion associated with steel fibers. This study explores an innovative approach by introducing polypropylene fibers (PPF) and polyoxymethylene fibers (POMF) as replacements for steel fibers (SF) in the preparation of hybrid fiber-reinforced ultra-high-performance concrete (HUHPC), with a total fiber content of 3% vol. The influence and mechanism of different PPF/POMF replacement ratios for SF on the flowability, compressive performance, and tensile behavior of HUHPC were investigated. An axial tensile static constitutive model for HUHPC considering the PPF/POMF replacement ratio was established, and a comprehensive environmental benefit assessment index and economic benefit assessment index considering mechanical performance were proposed. The results showed that using PPF and POMF with low modulus as replacements for high-modulus SF significantly improved the flowability of HUHPC. Notwithstanding there is a decrease in compressive and tensile strength of HUHPC resulting from the utilization of low-modulus and low-strength PPF and POMF as substitutes for SF, it modified the axial tensile stress-strain behavior of conventional UHPC and notably improved its tensile toughness. The established axial constitutive model for HUHPC in this study effectively predicted the tensile stress-strain behavior of HUHPC. Importantly, the comprehensive environmental assessment index reveals that HUHPC offers superior environmental and economic benefits compared to traditional UHPC, leading to substantial cost reductions. The development of HUHPC through fiber hybridization presents a promising strategy for the low-carbon and cost-effective production of UHPC, holding significant implications for the broader adoption and application of UHPC.

Local compression capacity of ultra-high performance concrete containing coarse aggregate: Testing and calculation method

The introduction of coarse aggregate (CA) into conventional ultra-high performance concrete (UHPC) can greatly reduce cost and shrinkage without significant sacrifice in strength. Ultra-high performance concrete containing coarse aggregate (UHPC-CA) possesses excellent lightweight characteristics, which is suitable for prestressed concrete structures. Nevertheless, many knowledge need to be explored to promote the engineering application of UHPC-CA structures, including anchorage zone behaviors, effects of key parameters on local bearing capacity, and the lack of reasonable calculating method of UHPC-CA. Thus, 23 groups of UHPC-CA specimens were tested, with varying local area aspect ratio, duct size and concrete compressive strength. The performance of UHPC-CA under the limited area load was analyzed, including feature loads, load-deformation relationships, failure features, cracking patterns and wedge features. Besides, the stress change and damage mechanism of UHPC-CA under the limited area load were investigated by finite element simulation. The results showed that UHPC-CA specimens still followed the wedge cleaving theory. Eventually, a special calculation method for evaluating the local bearing capacity was developed and validated with experimental data and existing normative models.

Development of high performance geopolymer concrete with waste rubber and recycle steel fiber: A study on compressive behavior, carbon emissions and economical performance

Ultra-high performance concrete (UHPC) has good application prospects with its high strength, toughness and good durability performance. However, the high carbon emissions and high cost of its constituent materials are significant factors that limit its development and promotion. This study explores the development of a low-carbon and low-cost rubber modified high performance geopolymer concrete (R-HPGC) using recycled crumb rubber, recycled steel fibers, and low-carbon geopolymer gel. In this study, the compressive experiments of R-HPGC with different rubber volume replacement ratios (0, 5 %, 20 %, 35 %, and 50 %) were conducted to explore the laws and mechanisms of the effect of different rubber volume replacement ratios on the failure mode, compressive strength, deformation, and elastic modulus of R-HPGC. The compressive stress–strain model of R-HPGC considering the rubber replacement ratio were proposed. Meanwhile, a comprehensive evaluation method based on the carbon emission and cost index of concrete per unit strength is proposed to compare the carbon emissions and economical performance of R-HPGC, UHPC and normal concrete (NC). The results show that the compressive behavior of R-HPGC is determined by the mechanical properties and interactions between the mixed aggregates-geopolymer matrix-recycled steel fibers. At a low rubber replacement ratio (≤5 %/≤35 %), the compressive strength of R-HPGC can still reach the standard of ultra-high/high performance concrete (≥120 MPa/≥55 MPa). R-HPGC has a lower comprehensive cost and carbon emission index compared with conventional UHPC. NC has the lowest comprehensive cost index, but its comprehensive carbon emission index is the highest. It is recommended to use a rubber replacement ratio of ≤5 % for R-HPGC, which provides the best compressive mechanical performance, as well as excellent environmental and economical performance. This study provides a low carbon emission, low cost and high performance concrete that can be designed based on a combination of strength, carbon emission and cost.

Properties of local ultra-high-performance concrete with low dosage of polyvinyl alcohol and steel fibre

Ultra-high-performance concrete (UHPC) delivers better durability and mechanical properties than normal-strength concrete. However, conventional UHPC requires heat treatment and a high dosage of high tensile steel fibre to achieve a compressive strength of 120 MPa. The present study was conducted to test a local UHPC with low fibre dosage and without heat treatment by incorporating different polyvinyl alcohol (PVA) fibre and steel fibre. The fibres included in the experimental works were 30 mm PVA macro fibre, 8 mm PVA fibrin and hooked end steel fibre with 35 mm in length. Four series of UHPC were studied, which consist of plain UHPC mix and three fibre-reinforced UHPC mixes. 1% fibre volume was incorporated into all the fibre-reinforced mixes. The mixes were tested for compressive strength, modulus of rupture, drying shrinkage and porosity The UHPC had a compressive strength of more than 120 MPa and modulus of rupture from 8 to 11 MPa. The drying shrinkage of all the UHPCs was less than 255με when cured at 100% relative humidity. The porosity recorded for the UHPC was 2%. Current findings indicated that steel fibre reinforced UHPC performed better than UHPC with PVA fibre in terms of mechanical properties However, UHPC with PVA fibrin performed better in terms of the drying shrinkage. In conclusion, UHPC with more than 120 MPa can be achieved with normal synthetic and steel fibre without special treatment.

Mechanical properties and hydration of ultra-high-performance seawater sea-sand concrete (UHPSSC) with limestone calcined clay cement (LC3)

Ultra-high-performance seawater sea-sand concrete (UHPSSC) has attracted increasing attentions over the past few years as it exhibits exceptional mechanical and durability properties similar to conventional ultra-high-performance concrete (UHPC). Comparing to conventional UHPC, UHPSSC has great advantages when applied in marine engineering, particularly in offshore projects where construction materials are not easily accessible, and the transportation is costly. Nonetheless, current production of UHPSSC still necessitates large amounts of cement due to its low water/binder ratio. The larger demands of cement in manufacturing UHPSSC/UHPC than ordinary concrete can lead to substantial increase in the carbon emission. Therefore, an eco-friendly UHPSSC is developed in this paper by incorporating a promising ternary binder system (LC3) that consists of limestone (LS), calcined clay (metakaolin) and cement. The influence of the metakaolin (MK) dosage on the mechanical, hydration and microstructure properties of UHPSSC is comprehensively studied by carrying out a variety of experiments including mechanical test, isothermal conduction calorimetry test, TGA, XRD, SEM etc. The results showed that the UHPSSC mixed with LC3 exhibited lower early-age compressive strength than the reference mix, but its long-term strength was better than the reference group owing to the formation of more hydrates at the late age by the pozzolanic reaction of MK and the synergistic reaction between LS, MK and cement. Based on this study, the coupled replacement rate of cement by LS and MK could reach up to 40% without strength compromise. Nonetheless, 20% MK and 10% LS appeared to be the optimum substitution rate (total substitution rate of 30%) where the highest long-term strength was achieved. The main exothermic peak and total heat of hydration normalized per binder weight decreased with the increase of MK content level, but the main peak occurred earlier. Moreover, the addition of seawater can promote the hydration, leading to a greater main exothermic peak.

Effect of hybrid industrial and recycled steel fibres on static and dynamic mechanical properties of ultra-high performance concrete

Employing recycled tyre steel (RTS) fibres to replace industrial steel (IS) fibres in ultra-high performance concrete (UHPC) can improve its cost-effectiveness and sustainability. However, the lack of research on dynamic properties of such sustainable UHPC would hinder its application in concrete structures such as protective and defence structures which may experience different dynamic loadings. This paper experimentally investigates the effect of various RTS fibre replacement levels (0.5–2.0% by volume) on the flowability and quasi-static compressive, flexural and tensile strengths of UHPC as well as the dynamic splitting tensile behaviour under various strain rates (4.5–6.5 s−1). The conventional UHPC with 2.0% IS fibre was prepared as the reference. Results indicate that the flowability of UHPC containing RTS fibres is about 5–11% higher than that of reference UHPC. Rising the RTS fibre replacement level up to 1.0% increases the compressive, flexural and tensile strengths while after which, the strengths drop. The dynamic splitting tensile behaviour of all UHPC specimens is sensitive to strain rate in terms of failure pattern, dynamic splitting tensile strength, dynamic increase factor and energy absorption capacity. Using 0.5% RTS fibre to substitute IS fibre can bring the best synergy, leading to the highest dynamic splitting tensile properties of UHPC at a strain rate of approximately 4.5–6.5 s−1. The material cost, embodied carbon and embodied energy of UHPC are reduced by 9–57% in the presence of RTS fibres. The optimal RTS fibre replacement dosage for UHPC is 0.5% considering static mechanical properties, dynamic splitting tensile behaviour, material cost and environmental impact.

Effect of nano-SiO2 on fiber–matrix bond in ultra-high-performance concrete as partial substitution of silica flour

This study investigated the effect of nano-SiO2, which partially substituted silica flour, on the rate-dependent bond behavior of straight steel fibers in ultra-high-performance concrete (UHPC). As much as 0%–50% by weight of the silica flour was replaced with the nano-SiO2. The packing density of the granular particles increased with the nano-SiO2 content up to 15%. However, upon increasing the nano-SiO2 content further, the packing density gradually decreased. A higher packing density was obtained at a replacement ratio of 15% than those of conventional UHPC. The static bond performance of steel fiber in UHPC was improved by adding up to 40% of nano-SiO2. Moreover, the best pullout resistance was observed in UHPC containing 10%–15% nano-SiO2 because of its filling effect and secondary pozzolanic reaction. The equivalent bond strength obtained on adding proper amounts of nano-SiO2 was thus nearly twice that of the plain UHPC. The impact pullout resistance for the UHPC matrix incorporating up to 30% of nano-SiO2 was higher than that for the plain UHPC; however, the best impact pullout resistance was observed at 10%–20% nano-SiO2 contents. A remarkable rate sensitivity of the bond strengths of straight steel fibers in the UHPC matrices was observed. The rate sensitivity of the average bond strength in the plain UHPC decreased on adding nano-SiO2. However, the rate sensitivity of the equivalent bond strength was insignificantly affected by the nano-SiO2 content. Overall, a 10%–15% nano-SiO2 content was considered to be the optimal in terms of the improved static and dynamic bond performances.

RETRACTED: Influence of eco-friendly fine aggregate on macroscopic properties, microstructure and durability of ultra-high performance concrete: A review

Ultra-high performance concrete (UHPC) is considered one of the promising future building material due to its excellent performance. However, it is important to note that the production of quartz sand, the fine aggregate of traditional UHPC, causes several environmental issues, including dust and noise pollution. In addition, excessive use of river sand as a raw material causes a sharp decrease in reserves. Thus, using river sand to prepare UHPC is not a sustainable method. Considering all these undesired impacts, it becomes a necessity for UHPC to meet the increasing demands of environmental sustainability. Another major issue confronting the world is waste disposal. Numerous studies show the feasibility of using industrial by-products, municipal solid waste, and recycled materials as fine aggregates for UHPC. The current work focuses on developing environmentally friendly UHPC using waste instead of quartz sand or river sand. The macroscopic (workability, compressive strength, flexural strength, elastic modulus and shrinkage), microstructural (pore structure, interfacial transition zone), and durability properties of eco-friendly UHPC were comprehensively reviewed. This paper aims to promote the utilization of waste to produce sustainable UHPC and the large-scale use of UHPC worldwide. This development will significantly reduce waste in landfill and decrease the environmental burden of conventional UHPC.

Mechanical and durability performance of ultra-high-performance concrete incorporating SCMs

Production of ultra-high performance concrete (UHPC) requires a high volume of micro silica (MS), called silica fume, that accounts for around 20% to 40% by weight of cement. Using large quantity of MS can impede the use of UHPC in the market due to its high cost and limited resources. This paper evaluates the possibility of producing sustainable UHPC utilizing Supplementary cementitious materials (SCMs) such as Metakaolin (MK), Fly Ash (FA) and Natural Pozzolan (NP) as a partial replacement of MS. The mechanical characteristics such as compressive strength, flexural strength, and fracture toughness and durability performance such as chloride penetrability, water permeability, drying shrinkage, water absorption, electrical resistivity and sulfate resistance were investigated. The results exhibited that a partial replacement of MS with 60% NP, 60% FA and 40% of MK contributed the paramount UHPC mixtures, with satisfactory strength and flowability requirements. The outcomes indicate that the increase in ultra-fine dosages decreases the flowability and increases the strength, as the finer particles perform as a filler between the cement and coarser grains. The UHPC specimens containing FA provided the worthiest results in comparison to other specimens. This study outcome also indicated that the SCMs can be used to develop UHPC with significant improvements in the mechanical and durability performance in comparison with conventional UHPC.

Recycling coral waste into eco-friendly UHPC: Mechanical strength, microstructure, and environmental benefits

On islands far away from the mainland, the raw materials for concrete production are often more difficult to obtain. Converting the coral waste generated during the island construction process into a marine ultra-high performance concrete (UHPC) mixture is an eco-friendly strategy. Coral powder (CP) is used to partially replace cement and silica fume (SF), and its mechanical strength, microstructure and environmental benefits are evaluated. Results show that using a small amount of CP (5%) to replace cement can improve the mechanical properties of UHPC, but the strength of UHPC decreases with the further increase of CP content. From the perspective of nanoindentation test, an appropriate amount of CP refines the pore structure of the UHPC matrix and increases the content of C-S-H, especially the proportion of high-density C-S-H. When 15% of SF is replaced by CP (SF15), the strength of UHPC decreases due to the decrease of C-S-H phase and the deterioration of microstructure. In terms of the width of the interface transition zone, the width of the C5 sample (CP replace 5% cement) is decreased by 16.7% compared with the control group, while the width of the SF15 group is increased by 38.9%. Compared with conventional UHPC, CP-based UHPC has lower carbon emission and non-renewable energy consumption, which effectively utilizes waste and promotes sustainability.

ECO-UHPC with High-Volume Class-F Fly Ash: New Insight into Mechanical and Durability Properties

Ultra-high-performance concrete (UHPC), despite its superior mechanical and durability properties, has a high CO2 footprint owing to its high portland cement content. This drawback can be offset to a notable extent if a high volume of supplementary cementitious materials can be utilized to produce UHPC while maintaining mechanical and durability properties that are comparable to those of conventional UHPC. In this study the effects of high-volume cement replacement by Class-F fly ash (up to 70% by mass) on the mechanical, durability, and microstructure properties of UHPC are investigated, with the aim of encouraging moderate- to low-volume cement use in UHPC (from 600 down to 300 kg/m3). Environmentally friendly-UHPC (ECO-UHPC) mixes, which have CO2 footprint intensities of less than 5 kg/m3/MPa, have been synthesized with different replacements of cement by Class-F fly ash. Results suggest that concretes with ultrahigh strength (>150 MPa) and a strength greater than 100 MPa can be prepared with up to 40% and 70% replacements, respectively, without employing any special curing or fibers. A model has been developed to predict the compressive strength of fly ash–based UHPC from the contents and chemical compositions of its binders. UHPCs made with up to 60% cement replacement by Class-F fly ash exhibit durability properties comparable to that of UHPC without fly ash, in terms of water absorption, initial rate of water absorption, and corrosion risk. The depth of carbonation remains below the detection limit of 0.5 mm, up to 70% replacement.

Towards Ultrahigh Performance Concrete Produced with Aluminum Oxide Nanofibers and Reduced Quantities of Silica Fume.

Ultrahigh performance concrete (UHPC), which is characterized by dense microstructure and strain hardening behavior, provides exceptional durability and a new level of structural response to modern structures. However, the design of the UHPC matrix often requires the use of high quantities of supplementary cementitious materials, such as silica fume, which can significantly increase the cost and elevate the production expenses associated with silica fume handling. This paper demonstrates that a fiber-reinforced composite with properties similar to conventional UHPC can be realized with very low quantities of silica fume, such as 1% by mass of cementitious materials. The proposed UHPC is based on reference Type I cement or Type V Portland cement with very low C3A (<1%) that also complies with Class H oil well cement specification, silica fume, small quantities of Al2O3 nanofibers, and high-density polyethylene or polyvinyl alcohol macro fibers. Previous research has demonstrated that nanofibers act as a seeding agent to promote the formation of compact and nanoreinforced calcium silicate hydrate (C-S-H) clusters within the interparticle and nanofiber spaces, providing a nanoreinforcing effect. This approach produces a denser and stronger matrix. This research expands upon this principle by adding synthetic fibers to ultrahigh strength cement-based composites to form a material with properties approaching that of UHPC. It is indicated that the developed material provides improved strain hardening and compressive strength at the level of 160 MPa.

Micro-chemo-mechanical features of ultra-high performance glass concrete (UHPGC)

The development of Ultra-High Performance Concrete (UHPC) opened new research directions for enhancing the architectural design, sustainability and serviceability of concrete structures. However, the costs and resource intensiveness trigger the need for innovative UHPC mix design incorporating alternative materials, such as post-consumption Glass Powder (GP). This works aims at disclosing the microstructure features of UHPGC, in which the constituents can be partially replaced by different fineness of GP without impacting the long-term strengths. By using the latest NI-QEDS technique (coupling NanoIndentation and Quantitative Energy-Dispersive Spectroscopy), as well as image analysis applied to EDS chemical mappings, it was possible to investigate mechanical properties of the microstructure constituents and their volume fractions. A conventional UHPC microstructure was compared to a similar system with 30% replacement of cement by GP and to another system with 50% replacement of silica fume by Fine GP (FGP). The results showed the key role of GP anhydrous particles contributing to the rigid skeleton of anhydrous inclusions, as well as their bond quality with the surrounding cement paste. The reduction of cement and silica fume was thus possible without impairing the micromechanical properties of the hydrates, by improving the particle packing density in the hardened state. As major conclusion, replacing cement and silica fume with GP and FGP without impairing both micro-scale and macro-scale mechanical properties provides a promising means to reduce the environmental footprint of current UHPC mix design.

Design and preparation of ultra-high performance concrete with low environmental impact

Ultra-high performance concrete (UHPC) is one of the most promising materials to reduce the detrimental effects of building materials on the environment because UHPC requires fewer materials and post-maintenance in comparison with normal concrete. However, the high cost and CO2 emission of UHPC are the major factors influencing its large-scale application in China. This study presents a series of comprehensive methods, including the optimization design of the binder system, utilization of nano-particles and chemical activators as well as heat curing, to prepare UHPC with relatively lower environmental impact. The workability, compressive strength, flexural strength, hydration heat and environmental impact of UHPC were investigated. The results indicate that each of the above methods has a significant effect on the strength and carbon emission of UHPC. UHPC with cement content lower than 200 kg/m3 can be prepared by optimizing its binder system and curing conditions, and its embodied CO2 index is lower than 3 kg/MPa·m3, while the embodied CO2 index of conventional UHPC ranges from 5.5 to 7 kg/MPa·m3. The designed UHPC has a low hydration release heat which may decrease the cracking risk caused by hydration temperature rise. For improving the mechanical strength and the eco-friendliness of UHPC, chemical activating method and heat curing have a synergistic effect.

Mechanical Behavior of UHPC(&lt;i&gt;Ultra High Performance Concrete&lt;/i&gt;) According to Hybrid Use of Steel Fibers

This intends to examine the flexural behavioral characteristics of hybrid UHPC using a mix of steel fibers with different lengths. Three types of fibers are adopted with fixed diameter of 0.2 mm and lengths of 13, 16.3 and 19.5 mm (aspect ratio of 65, 82 and 98, respectively). Comparative analysis of the flexural strength, load bearing capacity, deflection and toughness is performed adopting a mix use of these 3 types of steel fibers with ratio of 2% and 1.5%. The results show that the hybrid use of steel fibers improves significantly the flexural strength and flexural toughness compared to the use of a single type of fiber. When steel fibers with lengths of 16.3 mm and 19.5mm are admixed at a rate of 1% each, UHPC develops a flexural strength larger by 27% (maximum 50%) than conventional UHPC admixed with 2% of steel fiber with length of 13 mm. Moreover, flexural strength similar to that of conventional UHPC is secured when steel fibers with lengths of 16.3 mm and 19.5mm are admixed at respective rates of 0.5% and 1% (total rate of 1.5%).