Properties Of UHPC Research Articles

Application of the bald search optimization-based regression analysis on properties of UHPC

Application of the bald search optimization-based regression analysis on properties of UHPC

Study of the Effect of Surface-Modified Rubber Particles on the Properties of UHPC Containing Polyoxymethylene Fibers

Study of the Effect of Surface-Modified Rubber Particles on the Properties of UHPC Containing Polyoxymethylene Fibers

Empirical Compression Model of Ultra-High-Performance Concrete Considering the Effect of Cement Hydration on Particle Packing Characteristics.

The mix design of UHPC has always been based on a large number of experiments; in order to reduce the number of repeated experiments, in this study, silica fume (SF), fly ash (FA), and limestone powder (LP) were used as the raw materials to conduct 15 groups of experiments to determine the particle size distribution (PSD) properties of UHPC. A model of multi-component hydration based on the SF, FA, and LP pozzolanic reactions was devised to quantify the rate and total heat release during the hydration process. Additionally, a microscopic pore development model, which was based on the accumulation of hydration products, was established to measure the effect of these products on the particle-packing properties. Utilizing this model, a UHPC strength prediction technique was formulated to precisely forecast the compressive strength based on a restricted experimental data set. The applicability of this prediction method was verified using 15 sets of existing experimental data along with the data collected from 4 research articles. The results show that the prediction method can predict the strength values of different mix proportions with an accuracy rate of over 80%.

Effect of type of mixer on rheological and mechanical behavior of ultra high‐performance concrete

AbstractUltrahigh‐performance concrete (UHPC) is becoming increasingly frequent in several civil construction projects such as industries, buildings, and even infrastructure. The rheological and mechanical behaviors, coupled with durability, are the driving motives for this increase in use over the last few decades. However, the type of mixer used in UHPC production considerably affects the final composites performance due to variations in mixing velocity and the need to disperse particles with low granulometry. This study evaluated the effect of type of mixer in the properties of UHPC in the fresh and hardened states. This study evaluates three types of mixers: planetary vertical axis, horizontal axis, and drum. Results showed that the drum mixer was the least efficient in homogenizing the composite. It showed an average mixing time about 126% longer than planetary vertical or horizontal‐axis mixers to reach the same level of flowability. The composite from the drum mixer also had the most entrained air and void index. The planetary vertical‐axis mixer was the most efficient, with the resulting composite having a potential compression strength of 169.1 MPa, 19.3% higher than the composite from the horizontal‐axis mixer.

Impact of mixing and curing temperatures on fresh and hardened states’ properties of UHPC

New Canadian and American standards for concrete and bridges now provide guidelines for the design, production, curing, material characterization, and installation of ultra-high performance fiber reinforced concretes (named UHPFRC or UHPC) on structures. However, some technical aspects require more research since fundamental knowledge about UHPC is not as complete as for normal strength concretes (NSC). Among these aspects, knowledge on the properties of UHPC produced under field conditions is scarce. The main goal of this work was to evaluate the fresh state properties (slump flow, air content, mass density, hydration heat) and hardened state properties (elastic modulus, Poisson ratio, compressive and flexural strengths) of a UHPC subjected to various mixing temperatures (10, 20, and 30 °C) and curing temperatures (10, 23, and 35 °C) encountered in field conditions. The impact of mixing and curing temperatures on each property is discussed and practical information is provided to help engineers planning UHPC curing duration and formwork stripping.

Electrical and microstructural analysis of UHPC containing short PVA fibers

Steel fibers are the most widely used fibers in making Ultra-high performance concrete. Under extreme weather conditions the embedded steel fibers may be corroded and the risk of serious deterioration will be high. Moreover, while the influence of steel fibers has been thoroughly studied, the addition of synthetic fibers and their effect on properties of UHPC has not completely investigated throughout the years. In this paper, mix proportions containing different volume percentages of PVA fibers were fabricated. Mechanical, electrical and microstructural properties were evaluated. Results showed that unlike steel fibers, chloride diffusion and penetration are reduced by the addition of PVA fibers. Different fractions of cement were replaced with silica fume to determine the optimum value by processing the scanning electron microscope images and Energy Dispersive Spectroscopy analysis. SEM and EDS analysis indicated that a uniform cement paste with a Ca/Si ratio of near 1 which means a harder matrix is obtained when the replacement ratio of silica fume increases.

Analysis of Performance of Local Puzzle Sheet in a Joint Made of UHPC

Nowadays the extraordinary mechanical properties of UHPC can be used for real structures. The exceptionally high bond of reinforcement and UHPC together with significant shortening of lap length are the key features for the simplification of joining of precast elements. The properties of UHPC can be very well used also for providing of subsequent shear connection of composite structures. This paper is focused on analysis of performance of a combined joint where connection of precast elements as well as subsequent composite action between steel and concrete parts of steel-concrete composite structure are carried out in one compact detail. Instead of the traditional headed shear studs there were used local perforated puzzle sheets. More resilient connection of shear sheets to the top flange and a high resistance of UHPC allow for reduction of the extent of shear connectors. In experimental measurements carried out on six beams the behavior of shear connection of conventional monolithic concrete slab with continuous perforated shear sheet and shear connection of precast slab with the joint made of UHPC with local puzzle sheets were compared. During the experiment it has been proven that the performance of the beams with both variants of shear connection is very similar even with the significant reduction of the extent of shear connectors. Numerical analysis which describes the stressing in this detail confirms such behavior.

Preparation of UHPC with Fly Ash Replaced by Rich-Silicon Iron Ore Tailing Powder

In order to raise up the the rate of multipurpose utilization of rich-silicon iron ore tailing (IOTP for short) and the preparation of ultra-high performance concrete(UHPC for short), the influence rules and mechanism of rich-silicon iron ore tailing powder replacing fly ash in UHPC were studied, the influences of different specific surface area and dosage of IOTP replacing fly ash on its strength and liquidity were tested. Moreover, the pore structure and hydration products morphology of UHPC were tested by MIP and SEM methods, respectively. The results show that when fly ash replaced by IOTP, the liquidity of UHPC will be increased. When alternative content of IOTP is less than 10%, proper specific surface area of IOTP can improve the strength and pore structure, it can get the best result when the alternative content is 5% and the specific surface area is 588m2/kg. However, when alternative content of IOTP is 15% or more, all of these properties of UHPC become worse. It proves that IOTP can be used in the preparation of UHPC and improve the properties of UHPC.

Statistical models for mechanical properties of UHPC using response surface methodology

One of the main disadvantages of Ultra High Performance Concrete exists in the large suggested value of UHPC ingredients. The purpose of this study was to find the models mechanical properties which included a 7, 14 and 28-day compressive strength test, a 28-day splitting tensile and modulus of rupture test for Ultra High Performance Concrete, as well as, a study on the interaction and correlation of five variables that includes silica fume amount (SF), cement 42.5 amount, steel fiber amount, superplasticizer amount (SP), and w/c mechanical properties of UHPC. The response surface methodology was analyzed between the variables and responses. The relationships and mathematical models in terms of coded variables were established by ANOVA. The validity of models were checked by experimental values. The offered models are valid for mixes with the fraction proportion of fine aggregate as; 0.70-1.30 cement amount, 0.15-0.30 silica fume, 0.04-0.08 superplasticizer, 0.10-0.20 steel fiber, and 0.18-0.32 water binder ratio.

Impact of Steel Fibers on Workability and Properties of UHPC

This paper is focused on properties of fresh and hardened cement-based composite Ultra-High Performance Concrete with regard to different volume fraction of short brass coated steel fibers BASF MASTERFIBER® 482. Workability of fresh concrete and basic mechanical properties (tensile strength in bending, compressive strength) of hardened UHPC were found out. The workability of fresh concrete was measured by small mortar Haegermann cone. Percentage differences at cost were obtained at hardened concrete, too. The aim of the first experimental part of the research was the impact of volume fraction of steel fibers according to workability of fresh concrete and also according to mechanical properties of hardened UHPC with the same volume fraction of each component of the mixture, only the volume fraction of the steel fibers was different at each mixture. The mixture design of UHPC was changed to maintaining the workability of fresh concrete at the second part of the research. The workability at mixture with dosage of steel fibers of 300 kg/m3 measured by Haegermann cone was around 300 mm. In the framework of grant project GAČR 15-05791S the basic mechanical properties of hardened fine-grained cementitious composite material UHPC at small beams size of 160/40/40 mm and beams size 300/70/70 mm were determined. The aim of the research project was not only the determination of basic mechanical properties for each mixture design but also workability assessment and costs linked with higher amount of the volume fracture of steel fibers.

Design of Experimental Suspended Footbridge with Deck Made of UHPC

This paper deals with the static and dynamic design of experimental footbridge for pedestrians and cyclists in the municipality Lužec nad Vltavou in Czech Republic, Europe. This work aims to familiarize the reader with calculations carried out and the results obtained, describing the static and dynamic properties of proposed footbridge. The construction of footbridge is designed as a suspended structure with prestressed bridge deck consisting of prefabricated UHPC panels and reversed “V” shaped steel pylon with height of approximately 40 meters. The deck is anchored using 24 steel hangers in one row in a steel pylon - 17 ropes in the main span and 7 cables on the other side. Range of the main span is 99.18 meters and the secondary span is 31.9 m. Deck width is 4.5 meters with 3.0 meters passing space. The bridge is designed for the possibility of passage of vehicles weighting up to 3.5 tons. Deck panels are made of UHPC with reinforcement. At the edge of the bridge on the side of the shorter span the bridge deck is firmly connected with abutment and on the other deck it is stored using a pair of sliding bearings. The utilization of the excellent properties of UHPC allows to design a very thin and lightweight construction of the deck, which could not be achieved with the use of normal concrete.

Effect of Nano-Silica Particles on the Fresh Properties of UHPC

Nanotechnology is being used in UHPC for achieving more dense structural packing and better physical and mechanical properties. In this paper, nanosilica particles (0-1wt %) by cement were incorporated in cement pastes and mortars with water-binder ratio of 0.2, and their effect on fresh properties was addressed. The fresh properties of mixtures were investigated by spread, rheology and cohesiveness. In addition, effect of nanosilica on cement hydration was also investigated. The results show that significant increase of yield stress, viscosity and cohesiveness is observed with nanosilica above 0.005 wt% by cement, but nanosilica with content below 0.005% presents an improvement of workability especially with content of 0.002%. Moreover, the addition of nanosilica in cement pastes obviously accelerates the early cement hydration rate, but does not increase the cumulative heat evolution.

The Influence of the Amount of Silica Fume on the Mechanical Property of Ultra-High Performance Concrete

Silica fume constitutes an element of extreme importance in improving the strength and fluidity of UHPC. The adopted amount of silica fume generally is generally exceeding 25% of cement in weight but the influence of this amount on the properties of UHPC is still remaining as a domain to be investigated. Accordingly, this paper investigates the effects of the amount of silica fume on the mechanical characteristics of the fluidity, compressive strength, elastic modulus and flexural strength and on the micro structure of UHPC by means of SEM and MIP. Results revealed that adequate amount of silica fume is improving the fluidity and strength. MIP tests demonstrated that such improvement is brought by the increase of hydrates due to the pozzolan reaction and the effective densification inside concrete due to the filler. It seemed also that similar mechanical characteristics can be obtained for a volumetric ratio to cement ranging between 10 and 25%.

Practical Means for Determination of the Tensile Behavior of Ultra-High Performance Concrete

Abstract Ultra-high performance concrete exhibits sufficient tensile strength and tensile toughness that structurally efficient use of these concretes demands that the tensile capabilities be utilized. A means of determining the tensile properties of UHPC is essential to the expanded use of this advanced construction material. However, no simple, practical test currently exists to determine or verify these properties in a production environment. The ASTM C 496 splitting tensile test method presents a starting point for the development of a practical test procedure, as this test method both is comparatively easy to perform and is well regarded in terms of its ability to create a uniform tensile stress field within a concrete sample. This paper presents an adaptation of this test method that allows for quantitative determination of the tensile cracking strength of UHPC and for qualitative verification of the post-cracking tensile behaviors.