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The goal of the present work is to study the performance of Ultra High Strength Con-crete (UHSC) beams in flexure under static and repeated loads. The main considered variables are the main reinforcement ratios which are (0.0129, 0.0204, and 0.0323), and the method of applying load. For each reinforcement ratio two beams were casted, one of them was tested under four points static load and the other one under repeated load up to failure. The behavioral characteristics of Ultra High Strength Concrete dominantly depends upon its load history, for this purpose experimental investigation of the behavior of (UHSC) beams under load history of repeated cycles is performed as well as that it is compared with the behavior under static load. The average cube compressive strength of the UHSC used in casting the beams was as high as (124 N/mm2). The load deflection curves, first cracks and failure loads, crack pattern, and concrete strain distribution over the depth of the beams were presented.

In general Ultra High Strength Concrete (UHSC) is a new class of concrete that has been developed in recent decades. UHSC is characterized by extraordinary mechanical and durability properties. The UHSC-Matrix is very brittle material behavior. In this research an experimental program consists of twelve square UHSC columns is being carried out to study the behavior of UHSC columns subjected to constant axial load combined with cyclic lateral loading in order to simulate the case of seismic action. The main parameters of this program were: longitudinal reinforcement ratio, percentage of steel fiber, stirrups ratio, axial load level and concrete compressive strength. In this experimental program each specimen represents a column extending on both sides from the beam-column connection to the location of the point of inflection. Particular attention is paid to the effect of each variable on the strength enhancement, stiffness degradation, energy dissipation capacity, curvature ductility and displacement ductility of the tested columns. Valuable conclusions were obtained from the research results. By increasing the concrete compressive strength the column capacity increases accompanied by a decreasing in the ductility aspects, increasing the longitudinal steel ratio from 2% to (3.6% and 4.5%) leading to an increase in the column capacity and ductility aspect of the tested columns. Using steel fiber between (1.33–2.67)% is recommended in UHSC columns in seismic zones. The Egyptian concrete code of practice limits for the columns stirrups is suitable in seismic zones for columns subjected to a low axial load level.

Abstract Feasibility of using copper slag as replacement for quartz sand in the production of Ultra High Strength Concrete (UHSC) is investigated in this research work. Strength and durability performance of Copper Slag incorporated Ultra High Strength Concrete (CS-UHSC) was evaluated. Two type of mix proportions were used to assess the performance, one with untreated copper slag obtained as it is from industry and another with copper slag subjected to mechanical treatment. Mechanical treatment involves the grinding of copper slag to have finer size than the standard size available. Test results indicated that it is possible to produce UHSC of compressive strength more than 150 MPa with 100% untreated copper slag and 200 MPa with 100% treated copper slag as replacement for quartz sand. For complete replacement of quartz sand, reduction in compressive strength was observed with untreated copper slag, whereas an increase in strength behaviour was observed for specimens with treated copper slag. A similar trend was noticed with flexural strength and splitting tensile strength. Superior durability performance was observed in CS-UHSC compared to control UHSC with quartz sand. Thus, it is viable and advantageous to produce UHSC with copper slag as a replacement material for quartz sand. Highlights • Attempt is made to develop Ultra High Strength Concrete (UHSC) with copper slag as aggregate substitute. • Influence of untreated and treated copper slag on strength and durability of UHSC is reported. • Copper slag can be successfully used as aggregate with enhanced mechanical and durability performance. [ABSTRACT FROM AUTHOR]

This paper discusses the feasibility of utilizing sugarcane bagasse ash as a pozzolanic material in the production of Ultra High Strength Concrete (UHSC). Ordinary Portland Cement was replaced with Treated Bagasse Ash (TBA) in this investigation. The replacement dosage varied from 5% to 20% by weight of cement. The effect of bagasse ash on workability, compressive strength, chloride penetration resistance and sorptivity was examined. In addition to this, the effect of different curing regimens on hardened properties of UHSC was carried out. The results proved that it is possible to produce UHSC with cylinder compressive strength more than 160 MPa by incorporating bagasse ash. Optimum replacement ratio of 15% yielded better performance in all the tests, without having any adverse effects on hardened concrete. Convincingly, 20% substitution of sugarcane bagasse ash is good enough for producing UHSC. [ABSTRACT FROM AUTHOR]

Preparation of ultra high strength concrete with manufactured sand is an effective approach to reduce the natural resource depletion and environmental impact of cement concrete industry. In this paper, a new proportion design method was put forward to design ultra high strength concrete with manufactured sand and the microstructure of manufactured sand ultra high strength concrete was observed. Results indicate that the novel method can be applied to design concrete with C120 degree. Ultra high strength concretes prepared with sandstone manufactured sands can have higher strength than those made with river sands. The microstructure of manufactured sand ultra high strength concrete is very dense and the sizes of the hydration products e.g. ettringite, calcium hydroxide and monosulfate Calcium sulfoaluminate hydrates and C-S-H gel become much finer than those in the ordinary concrete. Energy Dispersive Spectrometer result shows that there is no obvious element enrichment at the micro scale of the ultra high strength concrete paste and the hydration products distributes homogeneously. Densely packed and homogenously distributed hydration products with smaller size contribute to the strength of ultra high strength concrete. [ABSTRACT FROM AUTHOR]

In general Ultra High Strength Concrete (UHSC) is a new class of concrete that has been developed in recent decades. UHSC is characterized by extraordinary mechanical and durability properties. The UHSC-Matrix is very brittle material behavior. In this research an experimental program consists of twelve square UHSC columns is being carried out to study the behavior of UHSC columns subjected to constant axial load combined with cyclic lateral loading in order to simulate the case of seismic action. The main parameters of this program were: longitudinal reinforcement ratio, percentage of steel fiber, stirrups ratio, axial load level and concrete compressive strength. In this experimental program each specimen represents a column extending on both sides from the beam-column connection to the location of the point of inflection. Particular attention is paid to the effect of each variable on the strength enhancement, stiffness degradation, energy dissipation capacity, curvature ductility and displacement ductility of the tested columns. Valuable conclusions were obtained from the research results. By increasing the concrete compressive strength the column capacity increases accompanied by a decreasing in the ductility aspects, increasing the longitudinal steel ratio from 2% to (3.6% and 4.5%) leading to an increase in the column capacity and ductility aspect of the tested columns. Using steel fiber between (1.33–2.67)% is recommended in UHSC columns in seismic zones. The Egyptian concrete code of practice limits for the columns stirrups is suitable in seismic zones for columns subjected to a low axial load level. [ABSTRACT FROM AUTHOR]

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This paper presents the results of an investigation carried out on Ultra High Strength Concrete (UHSC) panels subjected to low velocity projectile impact to assess impact resistance. UHSC panel of size 350 × 350 mm and thickness 15 mm is studied under drop weight impact loading for three different pre-determined drop heights ranging from 100 mm to 300 mm. The response of UHSC panel in terms of acceleration vs time is obtained experimentally. Numerical model has been developed to simulate the impact behaviour of UHSC panel. The Brittle cracking model is used to simulate the behaviour of UHSC panel under impact loading and to perform parametric studies by varying the volume fraction of steel fibres. [ABSTRACT FROM AUTHOR]

In this paper, twenty-nine three-point bending beam specimens made of ultra high strength concrete (cube compressive strength of about 125 MPa and cylinder compressive strength of about 105 MPa) incorporating Ultra Fine Ground Granulated Blast-furnace Slag (UFGGBS) were tested. The depths of the beam specimens range from 75 mm to 300 mm. The fracture energy calculated by Hillerborg’s work-of-fracture method, Bazant’s size effect method, and Karihaloo–Nallathambi’s effective crack method, as well as two empirical formulas of Bazant and Becq-Giraudon and of CEB-FIP Model Code 1990 were investigated and compared on the basis of the tested specimens. It was found that the results from the different methods were different from one another. In addition, the authors introduce a nonlinear regression method based on the effective elastic crack model to calculate the fracture energy. It is shown that the proposed method shows good tolerance on the scattered test data, and thus leads to a more consistent fracture energy value. [ABSTRACT FROM AUTHOR]

This paper examines the applicability of relevance vector machine-based regression to predict fracture characteristics and failure load (Pmax) of high strength and ultra high strength concrete beams. Fracture characteristics include fracture energy (GF), critical stress intensity factor (KIC) and critical crack tip opening displacement. Characterization of mix and testing of beams of high strength and ultra high strength concrete have been described briefly. The procedure to compute GF , KIC and CTODC has been outlined. Relevance vector machine is a machine learning technique that uses Bayesian inference to obtain parsimonious solutions for regression and classification. The relevance vector machine has an identical functional form to the support vector machine, but provides probabilistic classification and regression. Relevance vector machine is based on a Bayesian formulation of a linear model with an appropriate prior that results in a sparse representation. Four relevance vector machine models have been developed using MATLAB software for training and prediction of Pmax, KIC, GF and CTODC. Relevance vector machine models have been trained with about 70% of the total 87 datasets and tested with about 30% of the total datasets. It is observed that the predicted values from the relevance vector machine models are in good agreement with those of the experimental values. [ABSTRACT FROM PUBLISHER]

Highlights: [•] A high-strength CBSS is developed with little noise of piezoresistivity. [•] The repeatability and sensitivity of the CBSS has greatly improved by oven drying. [•] Damage of UHSC can be monitored by the CBSS embedded. [•] CBSS can sense strain and stress of the UHSC column up to a stress of 154MPa. [ABSTRACT FROM AUTHOR]

This article presents the details of estimation of fracture parameters for high strength concrete (HSC, HSC1) and ultra high strength concrete (UHSC). Brief details about characterization of ingredients of HSC, HSC1 and UHSC have been provided. Experiments have been carried out on beams made up of HSC, HSC1 and UHSC considering various sizes and notch depths. Fracture characteristics such as size independent fracture energy (Gf), size of fracture process zone (Cf), fracture toughness (KIC) and crack tip opening displacement (CTODc) have been estimated based on the experimental observations. From the studies, it is observed that (i) UHSC has high fracture energy and ductility inspite of having a very low value of Cf; (ii) relatively much more homogeneous than other concretes, because of absence of coarse aggregates and well-graded smaller size particles; (iii) the critical SIF (KIC) values are increasing with increase of beam depth and decreasing with increase of notch depth. Generally, it can be noted that there is significant increase in fracture toughness and CTODc. They are about 7 times in HSC1 and about 10 times in UHSC compared to those in HSC; (iv) for notch-to-depth ratio 0.1, Bazant’s size effect model slightly overestimates the maximum failure loads compared to experimental observations and Karihaloo’s model slightly underestimates the maximum failure loads. For the notch-to-depth ratio ranging from 0.2 to 0.4 for the case of UHSC, it can be observed that, both the size effect models predict more or less similar maximum failure loads compared to corresponding experimental values. [ABSTRACT FROM PUBLISHER]

Highlights: [•] A procedure for constructing bilinear tension softening diagrams of concrete mixes. [•] The tension softening diagram corresponds to the size-independent fracture energy of the mix. [•] Inverse identification based on hinge model. [ABSTRACT FROM AUTHOR]

Abstract: This paper examines the applicability of support vector machine (SVM) based regression to predict fracture characteristics and failure load (P max) of high strength and ultra high strength concrete beams. Characterization of mix and testing of beams of high strength and ultra strength concrete have been described briefly. Methodologies for evaluation of fracture energy, critical stress intensity factor and critical crack tip opening displacement have been outlined. Support Vector Regression (SVR) is the extension of SVMs to solve regression and prediction problems. The main characteristics of SVR includes minimizing the observed training error, attempts to minimize the generalized error bound so as to achieve generalized performance. Four Support Vector Regression (SVR) models have been developed using MATLAB software for training and prediction of fracture characteristics. It is observed that the predicted values from the SVR models are in good agreement with those of the experimental values. [Copyright &y& Elsevier]

An experimental study of the splitting tensile strength and cubic compressive strength of thread-typed steel fiber reinforced ultra high strength concrete (C100) was carried Out. Effects of steel fiber were analyzed on the enhanced toughness and ratio between splitting tensile strength and compressive strength. The dimensions of cubic specimens were 100 mm× 100 mm× 100 mm and steel fibers were added at the volume fractions of 0, 0.50%, 0. 75%, 1.00% and 1. 50%. The research results show that cracks developing path of ultra high strength concrete cubic specimens is more and cracks are scattered, but specimens are not broken, and the compressive toughness is enhanced with an addition of steel fiber. Besides, the compressive strength increases by 10. 6%-15. 5%, splitting strength increases by 38. 2%-91. 9% and ratio between splitting tensile strength and compressive strength is 0. 060 5-0. 084 6, increases by 24. 08%-73. 46% after steel fibers areadded. The prediction models for splitting tensile strength and compressive strength are presented and errors of predicted and measured values are ±1. 79% and ± 17. 84% respectively. Conclusions are drawn that marked brittleness and bad toughness can be overcome by an addition of steel fibers for ultra high strength concrete. [ABSTRACT FROM AUTHOR]

Abstract: Fibre distribution characteristics were evaluated to investigate their effect on the flexural strength of steel fibre-reinforced ultra high strength concrete in conjunction with the direction of placement. For this purpose, an image processing technique developed in this study was employed. Flexural tests were carried out to quantify the effect of fibre distribution characteristics on flexural strength. It was found that the image processing technique developed in this study could quantitatively evaluate the fibre distribution property by the use of the distribution coefficient, the number of fibres in a unit area, the packing density of the fibre image, and fibre orientation. It was also found that the fibre distribution characteristics were dependent on the direction of placing. Fibre distribution characteristics were revealed to strongly affect the ultimate flexural strength, while hardly affecting the first cracking strength. The validity of the current test results was verified through comparison with a theoretical model of flexural strength. [Copyright &y& Elsevier]

• FE-RVE and MFH methods can be used to homogenize elastic modulus across multiscales. • FE-RVE method can be used to obtain local variation of micro fields inside the RVE. • Variation in the homogenized modulus with different particle shapes is negligible. • Various boundary conditions such as PBCs, SUBCs and KUBCs are applied. • Proposed geometry generation algorithm can generate RVEs with high volume fractions. Ultra-High Strength Concrete (UHSC) (greater than 100 MPa) is a mechanically superior material compared with the Normal Strength Concrete (NSC) due to its inherent performance characteristics. Improved modulus of elasticity is one of the key target characteristics in the development of UHSC. Macroscopic response of UHSC is a result of a multitude of phases in different spatial length scales such as mesoscale, microscale, nanoscale etc. and investigating these spatial scales can yield a better understanding about contribution of each heterogenous phases to the macroscopic behaviour of UHSC. In this paper, a new multiscale modelling method including procedures to obtain micro/nano scale properties is proposed to predict the macroscopic elastic modulus using nanoindentation experiments, hydration simulations, Scanning Electron Microscopy (SEM) and Finite Element Representative Volume Element (FE-RVE) modelling. Characterization of nanomechanical properties of the cementitious composite was carried out using nanoindentation, microstructural characterization was performed using scanning electron microscopy, and hydration simulation of the cementitious paste was carried out using Virtual Cement and Concrete Testing Laboratory (VCCTL) software. A five-level multiscale framework is proposed for UHSC and results from these experimental testing and simulations were used as inputs in the proposed framework. A novel algorithm which can model any volume fraction of different phases was developed to generate geometries for RVEs to be used in FE-RVE simulations. Upscaling of elastic modulus using FE-RVE was found to be very accurate, and this method can generate detailed variation of microfields inside the RVE. A parametric study was carried out on how varying inhomogeneities in the RVE, boundary conditions, and the shape of the inhomogeneities would affect the homogenized elastic modulus. Continuum micromechanics models such as Mori-Tanaka method and Self Consistent Scheme were used for the analytical homogenization at each scale for comparison with FE-RVE method. The results of the proposed FE-RVE analysis, the Mean Field Homogenization (MFH) method, and experiment were compared and found to be a very good fit. [ABSTRACT FROM AUTHOR]

Abstract: In this study, pulverized fly ash (FA), pulverized granulated blast furnace slag (PS) and silica fume (SF) were quantitatively studied with the incorporation of Portland cement (PC). PC was replaced with FA or PS at specified ratios. Basalt and quartz powder were used as an aggregate in the mixtures. Three different curing methods (standard, autoclave and steam curing) were applied to the specimens. Test results indicate that high strength concrete can be obtained with high volume mineral admixtures. Compressive strength of these mixtures is over 170MPa. It seems that these mixtures can also be used for reactive powder concrete (RPC) production with some modifications. [Copyright &y& Elsevier]

The fracture behaviour of ultra high strength concrete (UHSC) with axial compressive strength more than 140 MPa is presented in this paper. Based on the wedge splitting tests with six cubical specimens, the fracture behaviour of UHSC with and without coarse aggregates is investigated. The common fracture mechanical parameters such as fracture energy, crack opening displacement (COD), the characteristic length and the fracture toughness by non-linear fracture mechanics (NLFM) theory are experimental determined. Through finite element analysis with suggesting linear and bilinear models for closing force σ(w) vs. crack width with regard to the wedge splitting tests, the relationships between splitting force and COD are simulated and verified with the tested ones. It is concluded that the COD, characteristic length and fracture toughness of UHSC can be improved obviously with the contribution of coarse aggregates. [Copyright &y& Elsevier]

• Development and analysis of 3D numerical mesoscale model is presented. • Realistic aggregate geometric shapes and placing algorithms are discussed. • Cohesive contact can be used successfully to model Interfacial Transition Zone. • Transgranular fracture in UHSC can be observed under static uniaxial compression. • Damage can initiate in any of the three phases and subsequently progress. Ultra High Strength Concrete (UHSC) is a composite material of which the fracture and damage behavior is highly dependent on its constituent phases. Damage and fracture behavior of UHSC is markedly different from the Normal Strength Concrete (NSC) due to its brittle behavior and crushing through the aggregate. This complex behaviour and influence of properties of constituent phases to the mechanical properties of UHSC cannot be understood using conventional testing on materials. To better understand this complex fracture behavior and influence of the phases, a different approach is required. Mesoscale modelling where concrete is modelled as a three-phase material which consists of aggregates, mortar and Interfacial Transition Zone (ITZ), can be considered as a potential method to address these issues. In this paper, development of mesoscale models of concrete using various shapes of aggregates and methods of intersection checks and placing algorithms are presented. Accurate material model selection for the constituent phases and efficient meshing methods are also discussed. Fracture and damage behavior of UHSC under uniaxial compression is investigated using the developed mesoscale models. Transgranular fracture of UHSC under uniaxial compression was modelled successfully and found that the damage initiation can occur in any of the three phases in mesoscale. Effect of various parameters on the damage behavior of UHSC is discussed and the feasibility of using this powerful tool of mesoscale modelling is discussed with the challenges. [ABSTRACT FROM AUTHOR]