Properties Of Ultra-high Performance Concrete Research Articles

Mechanical Properties of Ultra-high Performance Concrete Reinforced by Glass Fibers under Accelerated Agin

Ultra-High Performance Concrete (UHPC) is a cementitious composite with fine aggregates and a homogeneous matrix with high compressive strength and excellent durability against aggressive agents. It is common to use short steel fibers in the UHPC. Besides, using steel fibers considerably increases the flexural ductility, durability and energy absorption. Using glass fibers in UHPC is a novel technique which improves its mechanical properties and it has the benefit of being lighter, and cheaper than steel fibers. Furthermore, glass fibers can be used for thin concrete plates for aesthetic purposes. However, glass fibers reinforced concrete is incompatible with the hydration reaction in the alkaline environment of concrete as it can damage glass fibers, so the mechanical properties of the concrete are decreased over long periods. The mechanical properties of UHPC containing glass fibers (GF-UHPC) was investigated under three regimes of normal curing, autoclave curing, and autoclave curing plus being in hot water for 50 days (accelerated aging). Besides, the substitution of silica fume by Metakaolin in GF-UHPC was studied to understand its mechanical properties after thermal curing. The results showed that after accelerated aging, the behavior of specimens become more brittle and the modulus of rupture and toughness indices of all prismatic specimens decreased, the modulus of rupture for samples containing glass fibers was 40% lower than autoclave curing results. However, the compressive strength under accelerated aging increased at least 4% in comparison to the normal curing. Replacement of silica fume with Metakaolin slightly increased the toughness with regard to flexural strength.

Application of nanomaterials in ultra-high performance concrete: A review

AbstractIn the recent decades, traditional concrete poses a great challenge to the modernization of the construction industry because of low tensile strength, poor toughness, and weak resistance to cracking. To overcome these problems, ultra-high performance concrete (UHPC) with superior mechanical properties and durability is developed for broad application prospect in the future engineering construction. However, UHPC is less eco-friendly because it consumes more cement compared with the traditional concrete. The manufacturing of cement produces large amounts of carbon dioxide and therefore leads to the greenhouse effect. Nanomaterials consist of microstructural features that range from 0.1 to 100 nm in size, which exhibit the novel properties different from their bulk counterparts, including filling effect, surface activity, and environmental sustainability. This paper reviews the effect of various nanomaterials used in UHPC to partially replace the cement or as an additive on the microstructures, mechanical properties, and other properties of UHPC. In addition, the limitations and shortcomings of the current research are analyzed and summarized, and development directions are provided for future research on the application of nanomaterials in UHPC.

Investigating the influence of multi-walled carbon nanotubes on the mechanical and damping properties of ultra-high performance concrete

Abstract In this paper, the effects of multiwalled carbon nanotubes (MWCNTs) on the mechanical and damping properties of ultra-high performance concrete (UHPC) were investigated. The results show that the proper amount of MWCNTs can improve mechanical properties as well as the damping properties. For the mechanical properties, the compressive strength and flexural strength of the specimens increased with the increase of MWCNTs content in the range of 0~0.05% (mass ratio to cement). However, when the content of MWCNTs was more than 0.05wt.%, the mechanical properties of UHPC could not be improved continually because too many MWCNTs were difficult to disperse and agglomerated easily in UHPC. Similar laws also have been found for the damping property of UHPC. The loss factor of UHPC increased with the increase of MWCNTs content in the range of 0 ~ 0.05%. The incorporation of MWCNTs would introduce a large number of interfaces into UHPC, the friction and slip between interfaces were the main reasons for the improvement of the damping property of UHPC. However, when the content of MWCNTs was more than 0.05%, it was difficult to disperse effectively. As a result, the overall energy consumption efficiency of MWCNTs was decreased.

Evaluation of the Effect of Exposure Duration and Fiber Content on the Mechanical Properties of Polypropylene Fiber-Reinforced UHPC Exposed to Sustained Elevated Temperature

Abstract This article presents the results of an experimental study conducted to assess the effect of sustained elevated temperature on the mechanical properties of ultrahigh performance concrete (UHPC). UHPC mixtures were prepared with four different dosages of polypropylene (PP) fibers, and each mixture was exposed to a sustained pre-spalling elevated temperature of 300°C for five durations. The experimental data indicate that the used PP fibers were effective in providing sufficient strength and ductility to UHPC mixtures at room temperature. However, the PP fibers ceased to function as reinforcement in UHPC specimens that were exposed to the elevated temperature for 60 minutes. With an increase in the exposure period after melting of the fibers, the specimens exhibited a brittle mode of failure accompanied with an enhancement in the compressive strength and compressive modulus of toughness and a reduction in the modulus of elasticity and flexural strength. The significance of two variables (exposure duration and fiber content) was evaluated, and correlations between the mechanical properties and selected parameters were obtained by conducting a statistical analysis of the experimental data.

Mechanical and fracture properties of ultra-high performance concrete (UHPC) containing waste glass sand as partial replacement material

Recycling of waste glass is an efficient way to protect the environment and save resources. This study evaluated the effective utilizations of glass sand (GS) to replace the quartz sand (QS) in typical ultra-high performance concrete (UHPC) and river sand (RS) in ultra-high performance river sand concrete (UHPRC). Ultra-high performance glass concretes (UHPGC) with different substitution ratios were prepared. The working performances and mechanical properties were evaluated, respectively. Meanwhile, the fracture characteristics of typical UHPC, UHPRC and UHPGC were characterized by acoustic emission (AE) parameters. Results show that the fluidities of typical UHPC and UHPRC are significantly enhanced by the addition of GS. The replacements of QS and RS by GS improve the compressive strengths of UHPC and UHPRC. When the replacement ratio of GS is 75%, the compressive strengths of typical UHPC and UHPRC both reach the maximum. The addition of GS presents no significant effects on flexural and splitting tensile strengths. Moreover, the fracture processes of UHPC, UHPRC and UHPGC under different loading conditions can be favorably characterized by AE amplitude and energy. The scanning electron microscope (SEM) tests of concrete mixes reveal the change trends of mechanical and fracture properties from the microcosmic point of view. The cleaner production of UHPGC realized the recycling of waste glass from landfill, which presents great potential for the future sustainable development of UHPC in bridge structures.

Effect of using mineral admixtures and ceramic wastes as coarse aggregates on properties of ultrahigh-performance concrete

Recent advancements in recycling have transformed nonrenewable resources into partially renewable resources. In line with these advancements, the application of wastes, including ceramics, as substitute aggregate materials for construction has elicited considerable research interest. Ceramic waste aggregates can be used to address complex problems, such as the shortage of materials in construction sites, and reduce environmental wastes. This study aims to investigate the effectiveness of replacing silica fume (SF) and metakaolin (MK) with cement to improve ultrahigh-performance concrete (UHPC) prepared using ceramic wastes as coarse aggregates. Eleven UHPC mixes with 10%, 20% and 30% proportions of either SF or MK were designed. The fresh, physical, mechanical and microstructure properties of these mixes were evaluated, and test results showed that replacing cement with either SF or MK can improve the mechanical and physical properties of UHPC. The use of this waste as construction material will yield substantial technical, economic and environmental benefits, particularly from the perspective of sustainable development. The results showed that replacing SF or MK is effective in improving the strength of UHPC, particularly when the SiO2/CaO ratio was increased to 2.98. The 28-day compressive strength of UHPC with SF increased from 133.1 MPa to 146.6 MPa due to the improved microstructure and denser matrix.

Effect of silica fume and limestone powder on mechanical properties of ultra-high performance concrete

This research aimed to study the effect of Portland cement replacement with silica fume and limestone powder in Ultra High Performance Concrete (UHPC). Nine mix proportions were designed with a constant amount of binder at 1200 kg per cubic meter of concrete. In these mixes, the cement was replaced with silica fume at 10%, 15% and 20% and limestone powder at 15% and 30% by weight of binder. For all mixes, the ratio of water to binder (W/B) and the steel fiber volume fraction were 0.2 and 2% respectively. After the preparation of test specimens and stream curing for 3 days, compressive strength, flexural strength, and length change due to shrinkage of the UHPC mixes were examined. The results showed that the silica fume increases the compressive and flexural strength (at the first peak load) but the limestone decreases. Without the limestone, the 20% silica fume mix provides the maximum average residual strength. However, when either 15% or 30% limestone is admixed, the optimum residual strength occurs at the 15% silica fume. Moreover, it is worth noting that the reducing amount of cement by replacing either with silica fume or limestone powder effectively reduces the shrinkage.

Combined effect of mineral admixtures and fine aggregate on the mechanical properties of ultrahigh performance concrete

The aim of this study was to determine combined effect of mineral admixtures namely fly ash, silica fume as an alternative for cement, and fine aggregate including natural whiter sand (NWS) and finely ground quartz sand as partial replacement of natural river sand (NRS) on the mechanical properties of ultrahigh performance concrete (UHPC) containing steel fiber. Concrete was produced by replacing NRS with 22% upto 100% of NWS consists of particle sizes of 5 to 1800 µm, simultaneously combined with binding materials like fly ash (20, 30 and 40%) and silica fume (5 to 15%) as a substitute for cement in mixtures containing Dramix® 3D steel fiber 65/35 at 100kg/m3, and water curing temperature variation ranging follow ambient temperature from 28-34°C. The results indicated that the NRS was replaced with 100% NWS of 5…1800 µm fraction by weight of NRS, in UHPC containing 20% of fly ash combined with silica fume at the replacement levels of 5 to 15% contributed to improved mechanical properties. Detailed, compressive strength of UHPC obtained values 122, 128, 117, 115.3, and 118.5 MPa respectively. Similar results were also observed for the splitting tensile strength attained at 11.6, 11.9, 11.5, 10.5, 10.2 MPa, respectively, while flexural strength values range between 18.8 to 25.4 MPa. These values higher than compared to that of the NRS reference specimens without containing NWS at 28 days of curing. The achieved experimental results demonstrated that the addition of locally available NWS can be a good substitute for NRS, and therefore, can be effectively used in construction activities, which in turn reduces the depletion on the NRS resources. Furthermore, utilization of by-product materials reduces the carbon footprint of cementitious composites production as well as environmental pollution concerns.

A Review on Raw Materials and Curing Methods Applied in Production of Ultra High Performance Concrete

Ultra high performance concrete (UHPC) refers to cement based materials exhibiting high compressive strength, tensile strength and excellent durability. This paper reviews the raw materials and curing methods currently applied in UHPC manufacturing process. Raw materials, preparation techniques and curing methods have significant influence on properties of UHPC. The use of very high cement content, high strength cement and silica fume may improve the strength and compactness but increase the production cost. The use of high temperature curing leads to denser microstructure and better performance than room temperature curing and water curing do, but obviously limits its application of UHPC. Thus, preparation of UHPC using widely and locally available raw materials such as ordinary Portland cement CEM Type 1 42.5N and common technology such as room temperature curing are trends in production of UHPC.

Ozone treatment on the dispersion of carbon nanotubes in ultra-high performance concrete

This study aimed at investigating the effects of ozone treatment on the dispersion of carbon nanotubes (CNTs) in aqueous solution and the resulting influence on the material properties of ultra-high performance concrete (UHPC). The CNT suspension was fabricated by the ozone treatment and used to produce UHPC/CNT composites. Using spatially-resolved small angle X-ray scattering, the degree of dispersion of CNTs in UHPC matrix was quantitatively evaluated. It was confirmed that the ozone treatment enhanced the dispersion of CNTs in aqueous solution by formulating oxygenic and carboxylic groups on the surfaces of CNTs. Thus, interfacial interaction between the CNTs and UHPC was enhanced, leading to the higher nucleation effect at early ages. Ozone treatment did not significantly modify the hydration mechanism of UHPC. Instead, it provided multiple nucleation sites and double steric repulsion thorough the improved degree of dispersion of CNTs, which resulted in accelerated hydration at early ages and improved compressive strength at later ages.

Multiscale investigation on tensile properties of ultra-high performance concrete with silane coupling agent modified steel fibers

Ultra-high performance concrete (UHPC) is a new generation of cementitious composites that exhibit excellent compressive strength and durability. However, the poor bonding between steel fiber and UHPC matrix usually results in insufficient tensile properties and limits its application. Here, the surface of steel fibers is modified with silane coupling agent (SCA) to enhance fiber/matrix bond. The macroscale workability, flexural and tensile properties of UHPC are investigated. It has been found that SCA modifications contribute to strength enhancement and cracking behavior improvement of UHPC, and its energy absorption capacity increases 13.8%. The microscale characterizations of fiber/matrix interface are conducted through scanning electron microscopy, energy dispersive spectrometer and Fourier transform infrared spectroscopy. The mechanisms behind the enhancement have been revealed and classified into mechanical friction, chemical bonding and physical adhesion. This work provides a green and effective approach for promoting tensile properties and an in-depth understanding of SCA modification mechanisms.

Shear properties of the interface between ultra-high performance concrete and normal strength concrete

Many properties of ultra-high performance concrete (UHPC) are superior to those of normal strength concrete (NSC) - including high strength, toughness, and durability, which makes UHPC a promising repair material for damaged NSC structures. The good bonding and shear resistance of the UHPC-NSC interface may enhance the mechanical properties and ensure the impermeability of repaired concrete structures. Eight sets of interface shear push-out tests were conducted in this study. The shear properties of different UHPC-NSC interface treatments, including shallow chiseling, deep chiseling, interfacial adhesives, rebar exposing, grooving, drilling, and post-installed steel studs, were evaluated and discussed. The results demonstrated that the shear strength of the interface was improved by increasing the concrete strength and surface roughness degree. The ranking of the shear strength of interfacial treatments from the highest to the lowest is as follows: post-installed studs, rebar exposing, high roughness (deep chipping), grooving, low roughness (shallow chipping), and holes drilling. In terms of failure modes, the treatments of chipping, the interfacial adhesive, the exposure of rebar, and the drilling of holes demonstrated brittle interface shear failures, whereas the treatments of grooving and post-installed steel studs showed ductile interface shear failures. Finally, a comprehensive method was proposed to calculate the shear strength of the UHPC-NSC interface, taking several effects into account, including the interface cohesion, mechanical interlocking between concrete and rebars, the UHPC grooved joints, and the dowel action of UHPC. The calculated results were in good agreement with the experimental results, indicating that a reliable prediction of the shear strength of the UHPC-NSC interface could be achieved through the proposed model.

Mechanical Properties of Ultra-High Performance Concrete before and after Exposure to High Temperatures.

Compared with ordinary concrete, ultra-high performance concrete (UHPC) has excellent toughness and better impact resistance. Under high temperatures, the microstructure and mechanical properties of UHPC may seriously deteriorate. As such, we first explored the properties of UHPC with a designed 28-day compressive strength of 120 MPa or higher in the fresh mix phase, and measured its hardened mechanical properties at seven days. The test variables included: the type of cementing material and the mixing ratio (silica ash, ultra-fine silicon powder), the type of fiber (steel fiber, polypropylene fiber), and the fiber content (volume percentage). In addition to the UHPC of the experimental group, pure concrete was used as the control group in the experiment; no fiber or supplementary cementitious materials (silica ash, ultra-fine silicon powder) were added to enable comparison and discussion and analysis. Then, the UHPC-1 specimens of the experimental group were selected for further compressive, flexural, and splitting strength tests and SEM observations after exposure to different target temperatures in an electric furnace. The test results show that at room temperature, the 56-day compressive strength of the UHPC-1 mix was 155.8 MPa, which is higher than the >150 MPa general compressive strength requirement for ultra-high-performance concrete. The residual compressive strength, flexural strength, and splitting strength of the UHPC-1 specimen after exposure to 300, 400, and 500 °C did not decrease significantly, and even increased due to the drying effect of heating. However, when the temperature was 600 °C, spalling occurred, so the residual mechanical strength rapidly declined. SEM observations confirmed that polypropylene fibers melted at high temperatures, thereby forming other channels that helped to reduce the internal vapor pressure of the UHPC and maintain a certain residual strength.

Effects of Steel Slag Powder and Expansive Agent on the Properties of Ultra-High Performance Concrete (UHPC): Based on a Case Study.

In view of the performance requirements of mass ultra-high performance concrete (UHPC) for the Pang Gong bridge steel cable tower in China, the UHPC incorporating of steel slag powder and hybrid expansive agents is optimized and prepared. The effects of steel slag powder and hybrid expansive agents on the hydration characteristics and persistent shrinkage of UHPC are investigated. The results indicate that 15 wt.% steel slag powder and 5 wt.% hybrid expansive agents can effectively reduce the drying shrinkage deformation of UHPC with a slight decrease of strength. Heat flow calorimetry results show that the incorporation of steel slag powder and expansive agents decreases the hydration heat at three days. Moreover, the obtained adiabatic temperature rise of UHPC is 59.5 °C and the total shrinkage value at 180 days is 286 με. The hydration heat release changes of large volume UHPC in the steel-concrete section of cable tower is agreed with the result of adiabatic temperature rise in the laboratory.

Mechanical Properties of Ultra-High Performance Concrete with Partial Utilization of Waste Foundry Sand

Waste foundry sand (WFS) is a ferrous and non-ferrous foundry industry by-product, produced in the amount of approximately 700 thousand tons annually in Poland and it is estimated that only a small percentage of this waste is recycled. The study used WFS to produce ultra-high performance concrete (UHPC) as a partial substitute for quartz sand. It was replaced with WFS levels of 0%, 5%, 10%, and 15% by weight of quartz sand content. The UHPC mixtures were produced and tested to determine the compressive strength, flexural strength, splitting tensile strength as well as the modulus of elasticity at 28, 56, and 112 days. Scanning electron microscope (SEM) analysis was done to identify the presence of various compounds and micro-cracks in UHPC with WFS. The results revealed an increase as well as an insignificant decrease in the mechanical properties up to 5% and 10% WFS replacement, respectively. These studies also prove improvement in the microstructure of UHPC up to a 5% WFS level. In all the tested properties in this work, 5% WFS was found to be an apt substitute for quartz sand.

Effect of natural fibers on thermal spalling resistance of ultra-high performance concrete

It has been established that the addition of synthetic fibers like polypropylene (PP) to ultra-high performance concrete (UHPC) enhances the latter's thermal spalling resistance. The key for this is the thermal mismatch between embedded fibers and matrix as a result of the expansion of PP fibers with temperature. This paper explores the effect of natural fibers (replacing traditional PP fibers) on compressive strength, hot permeability, and spalling resistance of UHPC. Different dosages (3, 5 and 10 kg/m3) of jute fibers are used for this purpose. The findings are critical as they oppose the mechanism of thermal spalling resistance established for synthetic fibers in UHPC. Natural fibers swell by absorbing water (during the casting of UHPC and during their service life) and shrink upon exposure to warm and high temperatures. The deswelling and shrinkage of natural fibers at high temperatures create spaces between fibers and matrix, which could influence permeability at those temperatures. This suggests that percolation of fibers is critical in the case of jute as opposed to PP fibers. It was found that a dosage of 10 kg/m3 of jute fibers is required for eliminating spalling of UHPC as opposed to 3 kg/m3 for PP fibers. Additionally, preliminary efforts are put in to investigate the short-term durability of the samples and changes in properties of UHPC with jute fibers.

Influence of alccofine incorporation on the mechanical behavior of ultra-high performance concrete (UHPC)

The present paper explores the influence of alccofine on the mechanical properties of ultra-high performance concrete. In this study, UHPC is designed as a ternary blend including two types of filler materials namely quartz powder and ground granulated blast furnace slag in combination with alccofine and silica fume separately. An attempt has also been made to reduce the binder quantity by incorporating 6 mm coarse aggregates in to the UHPC mix. A total of 6 UHPC mixtures were designed and studied for their mechanical strength properties such as compressive, split-tensile, flexural strengths and modulus of elasticity at the ages of 7, 28 and 90 days. The experimental results indicated that UHPC mixes blended with alccofine yielded better mechanical performance in comparison to the traditional UHPC. The UHPC mix with cement, alccofine and GGBS as filling powder has yielded maximum strength values of 144.87 MPa, 15.8 MPa and 33.79 MPa for compressive, split-tensile and flexural strengths at 90 days under normal curing conditions. The introduction of coarse aggregates in UHPC has resulted in the overall reduction of mechanical performance of the concrete. Also a statistical tool based on response surface method was used for data analysis to predict compressive strength values from a regression equation and compare them with experimental results to check the validity of obtained experimental values. Based on the findings it can be assumed that alccofine has a possible suitability to act as a supplementary cement material in UHPC.

Experimental and numerical study on static behavior of grouped large-headed studs embedded in UHPC

The static behavior of grouped large-headed studs (d = 30 mm) embedded in ultra-high performance concrete (UHPC) was investigated by conducting push-out tests and numerical analysis. In the push-out test, no splitting cracks were found in the UHPC slab, and the shank failure control the shear capacity, indicating the large-headed stud matches well with the mechanical properties of UHPC. Besides, it is found that the shear resistance of the stud embedded in UHPC is 11.4% higher than that embedded in normal strength concrete, indicating that the shear resistance was improved. Regarding the numerical analysis, the parametric study was conducted to investigate the influence of the concrete strength, aspect ratio of stud, stud diameter, and the spacing of stud in the direction of shear force on the shear performance of the large-headed stud. It is found that the stud diameter and stud spacing have an obvious influence on the shear resistance. Based on the test and numerical analysis results, a formula was established to predict the load-slip relationship. The comparison indicates that the predicted results agree well with the test results. To accurately predict the shear resistance of the stud embedded in UHPC, a design equation for shear strength is proposed. The ratio of the calculation results to the test results is 0.99.

Effects of superabsorbent polymer on interfacial transition zone and mechanical properties of ultra-high performance concrete

In this study, two particle sizes of superabsorbent polymer (SAP) with different contents (0–0.6%) were incorporated in the UHPC samples cured under two regimes: water and steam curing. The interfacial transition zone (ITZ) associated properties, namely compressive strength, flexural strength, and pullout behavior of steel fiber were evaluated. Micro-hardness method and backscattered electron (BSE) imaging examinations were also applied to investigate the underlying mechanisms of SAP performance in UHPC. The results show that the use of SAP densified the ITZ and reduced micro-cracks around the fibers. However, the pores left from SAP impaired the bonding strength and ITZ of UHPC, when high contents and large size of SAP particles were incorporated. Steam curing, though, partly compensated the bond strength loss of fibers caused by the SAP.

Experimental Study on Shear Performance of Cast-In-Place Ultra-High Performance Concrete Structures.

In order to study the direct shear properties of ultra-high performance concrete (UHPC) structures, 15 Z-shaped monolithic placement specimens (MPSs) and 12 Z-shaped waterjet treated specimens (WJTSs) were tested to study the shear behavior and failure modes. The effects of steel fiber shape, steel fiber volume fraction and interface treatment on the direct shear properties of UHPC were investigated. The test results demonstrate that the MPSs were reinforced with steel fibers and underwent ductile failure. The ultimate load of the MPS is about 166.9% of the initial cracking load. However, the WJTSs failed in a typical brittle mode. Increasing the fiber volume fraction significantly improves the shear strength, which can reach 24.72 MPa. The steel fiber type has little effect on the shear strength and ductility, while increasing the length of steel fibers improves its ductility and slightly reduces the shear strength. The direct shear strength of the WJTSs made from 16 mm hooked-type steel fibers can reach 9.15 MPa, which is 2.47 times the direct shear strength of the specimens without fibers. Finally, an interaction formula for the shear and compressive strength was proposed on the basis of the experimental results, to predict the shear load-carrying capacity of the cast-in-place UHPC structures.