High Strength Concrete

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Cast-in-place anchor bolts embedded in plain and steel fibre-reinforced normal-and high-strength concrete members were subjected to monotonic tensile loads. The influence of the concrete member thickness, concrete strength, and the addition of steel fibres to the concrete mixture, on the anchorage capacity and performance was evaluated. The experimental results were evaluated in terms of anchorage capacity, anchorage ductility and stiffness as well as failure mode and geometry. Furthermore, the validity of Concrete Capacity (CC) method for predicting the tensile breakout capacity of anchor bolts in plain and steel fibre-reinforced normal-and high-strength concrete members was evaluated. The anchorage capacity and ductility increased slightly with increasing member thickness, whereas the anchorage stiffness decreased slightly. In contrast to the anchorage ductility, the anchorage capacity and stiffness increased considerably with increasing concrete compressive strength. The anchorage capacity and ductility also increased significantly with the addition of steel fibres to the concrete mixtures. This enhanced capacity and ductility resulted from the improved flexural tensile strength and post-peak cracking behaviour of steel fibre-reinforced concrete. The average ratio of measured strengths to those predicted by the CC method for anchors in plain concrete members was increased from 1.0 to 1.17 with increasing member thickness. In steel fibrereinforced concrete, this ratio varied from 1.29 to 1.51, depending on the member thickness and the concrete strength.

The crack path through composite materials such as concrete depends on the mechanical interaction of inclusions with the cement-based matrix. Fracture energy depends on the deviations of a real crack from an idealized crack plane. Fracture energy and strain softening of normal, high strength, and self-compacting concrete have been determined by means of the wedge splitting test. In applying the numerical model called "numerical concrete" crack formation in normal and high strength concrete is simulated. Characteristic differences of the fracture process can be outlined. Finally results obtained are applied to predict shrinkage cracking under different boundary conditions. Crack formation of high strength concrete has to be seriously controlled in order to achieve the necessary durability of concrete structures.

The authors wish to thank V. Bindignavile and N. Banthia for their insightful discussion and comments. The following response was prepared to address the interesting issues. In their discussion of our paper [1], Bindignavile and Banthia proposed a method to separate Strain Rate Effects from Size Effects. Their suggested method is based upon using the scaling laws and the Buckingham P-theorem to scale down strength, using a suggested dynamic impact factor (DIF) given by the ratio of strength at any strain rate with respect to that at a reference strain rate. This suggested DIF is obtained by comparing different strength values obtained for a fixed size specimen loaded at different strain-rates. This suggested method, however, seems to have some flaws. One must note that the classical scaling laws apply to linear elastic problems and one may not use them for nonlinear problems. As will be shown below, the basic assumption of stress invariance, fundamental to scaling laws and application of the dimensional P-theorem does not hold in fracture analysis. Obviously, this would prevent one from using the method for such application in fracture mechanics problems. Additionally, the method is based on the unsubstantiated assumption of scalability of strain-rate sensitivity for specimens of different sizes, since it is assumed that the ratio of strength to strain-rate should be the same for cylinders of different sizes. Jones [2] used the following procedure to describe the inapplicability of scaling laws to fracture problems: The onset of fast fracture in a member with a crack length B and subjected to a stress S is governed by the relationship SðpBÞ 1=2 ¼ ðEG c Þ 1=2 ; ð1Þ where E is Young's modulus of elasticity and G c is the material toughness, or energy absorbed per unit area of crack.

Abstract— Recent trend in engineering, especially in concrete structure is to develop economical, eco environmental and durable concrete with decreasing or reducing the use of natural material and increasing the use of industrial waste or by products from industries ...

Carbon fiber reinforced polymer (CFRP) laminates were proved as very effective method for either repairing or strengthening of used structures. However, the literature has no enough information about the behavior of RC continuous (two-span) T-section beams strengthened with CFRP laminates, especially in hogging moment zone. This paper examines the effect of CFRP laminates lengths, used for strengthening of the hogging moment zone, upon the behavior of such beams, to determine the optimum strengthening length.3-D theoretical models using the Finite Element (FE) Package ANSYS are used. Very good agreement was found between both proposed FE models and previous experimental research used for the verification of the FE model. Finally, redistribution of moments, energy dissipation and ductility of such beams are examined. It can be concluded that changing the strengthening CFRP length in the hogging moment zone is very effective upon the overall behavior of T-section continuous beams and ...

Behavior and failure mechanisms of circular HSC columns reinforced with CFRP bars and spirals under eccentric loads are presented. The performance of CFRP bars in compression is assessed. A detailed sectional analysis for predicting the axial force and bending moment at different load eccentricity is introduced. The P-M interaction diagrams encompassing different parameters are developed.

The available research has evidenced that discrete steel fibers can increase significantly the shear resistance of High Strength Concrete (HSC) structural elements when High Strength Fiber Reinforced Concrete (HSFRC) is designed in such way that fiber reinforcing mechanisms are optimized. In general, the increase of the concrete compressive strength is associated to an increase of its compactness, resulting benefits in terms of durability, but a strong concern emerges related to the integrity of this material, since it fails in a too brittle mode when submitted to high temperatures. To contribute for the knowledge about the benefits provided by discrete steel fibers when added to HSC applied to laminar structures, an experimental program composed of slab strips submitted to shear loading configuration was carried out. Uniaxial compression tests with cylinders of 150 mm diameter and 300 mm height, and bending tests with 600×150×150 mm3 beams were executed to assess the compression an...

The aim of this study is to assess the effectiveness of alkali-activated
fly ash-based geopolymer mortar. The experimental program comprises two main phases. Firstly, the study examines the impact of various mix
composition and process parameters on the compressive strength of the
geopolymer mortar. Mix composition parameters include sodium
hydroxide concentration and aggregate to binder ratio, while process
parameters involve curing temperature. Compressive strength tests are
supplemented with advanced analytical techniques such as X-ray
diffractometry (XRD) and Scanning Electron Microscopy (SEM).
Secondly, the resistance of the geopolymer mortar against carbonation is
evaluated. The investigation focuses on the influence of aggregate to binder ratio and curing temperature on the carbonation depth of the mortar. Carbonation depth is a measure of carbonation. Additionally, XRD and SEM testing support the carbonation tests. The study reveals that the
compressive strength of the geopolymer mortar increases with higher
concentrations of NaOH, ranging from 8M to 14M. An aggregate to binder
ratio of 2:1 is found to optimize compressive strength at 28 days. The
enhanced strength is attributed to mineral formations like zeolite and
sodalite, as confirmed by XRD tests. Moreover, mortars with higher
porosity exhibit greater susceptibility to carbonation. Changes in pore
solution chemistry, as evidenced by XRD tests, contribute to mortar
carbonation. Despite these findings, long-term performance analysis of
geopolymer mortar under carbonation remains unexplored due to time
constraints, warranting further investigation beyond the current study's
scope.

An anisotropic elasto-damage model for predicting the response of concrete subject to montonic and fatigue loading is presented in this study. The model utilizes a concrete appropriate damage-effect tensor M in constructing the constitutive equations. The concept of multiple bounding surfaces is used, with a varying size limit fracture surface defining fatigue loading in contrast to a fixed size limit fracture surface for monotonic loading. The model after calibration is shown to predict the monotonic, compressive uniaxial stress-strain path for concretes of various strengths as well as S-N curves depicting the fatigue response of concrete.

Equations to characterize the anchorage strength of headed bars were developed, incorporating key factors affecting anchorage strength: concrete compressive strength; embedment length; bar diameter; spacing between the bars; and confining reinforcement parallel to the headed bars. Results from tests of 138 exterior beam-column joints, 64 without and 74 with confining reinforcement within the joint region, were used to develop the equations. Concrete compressive strengths ranged from 4050 to 16,030 psi (27.9 to 110.6 MPa) and bar stresses at failure ranged from 33,100 to 153,160 psi (228 to 1056 MPa). The bearing area of the headed bars ranged from 3.8 to 9.5 times the area of the bar. Some headed bars contained obstructions adjacent to the head that exceeded the dimensions permitted for HA heads in ACI 318-14 and ASTM A970-13a but are now permitted by ASTM A970-18. The test results show that headed bar anchorage strength is proportional to the concrete compressive strength raised to the power 0.24. The contribution of confining reinforcement is proportional to the area of confining reinforcement parallel to the headed bar within eight to 10 bar diameters of the headed bar. Headed bars with obstructions larger than those permitted in ACI 318-14 that meet the provisions in ASTM A970-18 exhibit anchorage strengths that are similar to those that meet the provisions in ACI 318-14.

A The current environmental problem is regarding to CO2 gas emissions from cement production and the presence of hazardous material waste (B3) from steel production. One solution for that problem is by applying slag cement as a substitute for type I portland cement in concrete mix to create a high quality concrete that is environmentally friendly with a high durability and initial strength. This research aimed to compare a high quality concrete made from slag cement and a high quality concrete with conventional mixture. The slag cement used was obtained from PT. Indocement Indonesia. It is coupled with the use of Master Ease 3029 superplasticizer. The results showed that from the samples of concrete of 3, 7, 14, 28, 56 and 90 days of age, the maximum absorption value of normal concrete occurs at the age of 90 days with acid water curing of 1.57%. While the maximum absorption value of slag cement concrete occurs at the same age with acid water curing of 1.50%. The curing of normal co...

High-strength concrete (HSC) is highly applicable to the construction of heavy structures. However, shear strength (Ss) determination of HSC is a crucial concern for structure designers and decision makers. The current research proposes the novel models based on the combination of adaptive neuro-fuzzy inference system (ANFIS) with several meta-heuristic optimization algorithms, including ant colony optimizer (ACO), differential evolution (DE), genetic algorithm (GA), and particle swarm optimization (PSO), to predict the Ss of HSC slender beam. The proposed models were constructed using several input combinations incorporating several related dimensional parameters such as effective depth of beam (d), shear span (a), maximum size of aggregate (ag), compressive strength of concrete (fc), and percentage of tension reinforcement (ρ). To assess the impact of the non-homogeneity of the dataset on the prediction result accuracy, two possible modeling scenarios, (i) non-processed (initial) ...

This article analyzes by means of fracture mechanics the current splitting-test standards for concrete. The cohesive crack model, which has shown its utility in modeling the fracture of concrete and other cementitious materials, has been used to assess the effect of the specimen size, the specimen shape and the width of the load-bearing strips on the conventional splitting tensile strength, f st. The results show that, within the ranges recommended in the standards, the values of the splitting tensile strength can differ by up to 40%, and, consequently, f st can hardly be assumed to be a material property. Empirical formulae for concretes with different compressive strength (10 ± 80 MPa) and maximum aggregate size (8 ± 32 mm) have been used to show that f st is nearly specimen independent only for certain compositions, such as highstrength concretes, or when the aggregate size is under 16 mm. New closed-form expressions for f st are given in this paper to incorporate the effect of material properties, and some recommendations are drawn to minimize the influence of the width of the load-bearing strips.

An over reinforced beam is characterized by an excessive ratio  of steel reinforcement to concrete, beyond the optimal balance required for structural efficiency. This assignment delves into the intricacies of over reinforced beams, examining their definition, distinguishing features, comparison with other types of beams, implications on structural behavior and safety, and practical examples with calculations. we aim to deepen our understanding of how over reinforcement influences the behavior of reinforced concrete beams, guiding us in designing structures that adhere to both theoretical principles and practical considerations.Over-reinforced beam sections are reinforced concrete beams where the concrete
failure strain is attained before the steel yield strain is reached. The steel in the tension zone won't give up much before the concrete achieves its maximum strain of 0.0035 if the over-reinforced beam is designed and loaded to its maximum capacity.Due to insufficient yielding of the steel, the beam does not deflect or split and does not provide significant forewarning before failure.

The compressive strength of core concrete is affected by many parameters and one of them is the strength of the concrete, which affects the strength of the core compressive strength. This is achieved by using correction factors present in several standards such as ASTM C 42/C 42M-04, but this standard was not considered for high and very high strength concrete (HSC). In this study, a beam of (1x 4x 0.2) m constructed with 100 MPa target strength for core samples. Four different core diameters (25-50-75-100) mm and for each diameter different core length-diameter ratios(λ=l/d) (2-1.75-1.5-1.0) were extracted from the beam for assessing the strength in both casting directions. The relationship between the strength of concrete with respect to reference samples and different cores size with different slenderness ratio, length to diameter (λ) were investigated. The Ultrasonic Pulse Velocity (UPV) was conducted for all samples and the relationship between UPV and strength of cores were de...

The objective of this work is to calculate the compressive strength, ultrasound pulse velocity (UPV), relative dynamic modulus of elasticity (RDME) and porosity induced into concrete during freezing and thawing. Freeze-thaw durability of concrete is of great importance to hydraulic structures in cold areas. In this paper, freezing of pore solution in concrete exposed to a freeze-thaw cycle is studied by following the change of concrete some mechanical and physical properties with freezing temperatures. The effects of pumice aggregate (PA) ratios on the high strength concrete (HSC) properties were studied at 28 days. PA replacements of fine aggregate (0-2 mm) were used: 10%, 20%, and 30%. The properties examined included compressive strength, UPV and RDME properties of HSC. Results showed that compressive strength, UPV and RDME of samples were decreased with increase in PA ratios. Test results revealed that HSC was still durable after 100, 200 and 300 cycles of freezing and thawing in accordance with ASTM C666. After 300 cycles, HSC showed a reduction in compressive strength between 6% and 21%, and reduction in RDME up to 16%. For 300 cycles, the porosity was increased up to 12% for HSC with PA. In this paper, feed-forward artificial neural networks (ANNs) techniques are used to model the relative change in compressive strength and relative change in UPV in cyclic thermal loading. Then genetic algorithms are applied in order to determine optimum mix proportions subjected to 300 thermal cycling.

Blast furnace slag aggregates (BFSA) were used to produce high-strength concretes (HSC). These concretes were made with total cementitious material content of 460-610 kg/m 3. Different water/cement ratios (0.30, 0.35, 0.40, 0.45 and 0.50) were used to carry out 7-and 28-day compressive strength and other properties. Silica fume and a superplasticizer were used to improve BFSA concretes. Slump was kept constant throughout this study. Ten percent silica fume was added as a replacement for ordinary portland cement (OPC) in order to obtain HSC. The silica fume was used as highly effective micro-filler and pozzolanic admixture. Superplasticizer at dosages of 2%, 1.5%, 1%, 0.5% and 0% by OPC weight for 0.30, 0.35, 0.40, 0.45 and 0.50 w/c ratios, respectively, were adopted. Results showed that compressive strength of BFSA concretes were approximately 60-80% higher than traditional (control) concretes for different w/c ratios. These concretes also had low absorption and high splitting tensile strength values. It is concluded that BFSA, in combination with other supplementary cementitious materials, can be utilized in making high strength concretes.

In this study, the concrete-steel bond strength of concrete filled cylindrical steel tubes has been experimentally investigated. 22 short, high strength and normal concrete filled circular steel tubes were tested. Push-out test was carried out as the common method to evaluate the bond carrying capacity. Four different concrete mixes were used in preparing the specimens. The steel tubes were welded type with the nominal inside diameters of 3, 4, 6 and 8 inches. According to the test results bond strength increases with reduction of the w/c ratio of concrete mixes. The high strength to normal concrete bond strength ratio increases with the diameter of steel tubes. The bond strength decreases for higher diameters in both normal and high strength concrete specimens.

In this study, the concrete-steel bond strength of concrete filled cylindrical steel tubes has been experimentally investigated. 22 short, high strength and normal concrete filled circular steel tubes were tested. Push-out test was carried out as the common method to evaluate the bond carrying capacity. Four different concrete mixes were used in preparing the specimens. The steel tubes were welded type with the nominal inside diameters of 3, 4, 6 and 8 inches. According to the test results bond strength increases with reduction of the w/c ratio of concrete mixes. The high strength to normal concrete bond strength ratio increases with the diameter of steel tubes. The bond strength decreases for higher diameters in both normal and high strength concrete specimens.

This paper discusses the behaviour, design and analysis of high strength reinforced concrete (HSC) deep beams regarding the neutral axis variation. The study of this structural element is motivated by the lack of a clear procedure for the design of these structural elements, which have many useful applications such as in foundations, in offshore structures, in tall buildings and in bridges. It should be noted however, that the design of these structural elements is not covered sufficiently by the existing codes of practices. For example, the British code BS8110 explicitly states that, for design of deep beams, reference should be made to specialist literature. Other codes such as the ACI, the draft Euro code EC/2, the Canadian code and the CIRIA guide No.2b present some design guidelines based on empirical analysis. The present research consists of six HSC deep beams designed and casted with self compacted concrete (SCC). The main goal of this research is to study the stress-strain distribution along the beam section at mid-span and discuss the variation of the neutral axis within the depth. Sufficient horizontal and vertical web reinforcement are used to ensure tensile reinforcement yielding before shear failure. It was decided to keep the beam's length, depth and thickness constant while varying the tensile reinforcement percentage. Strain gauges have been attached on the concrete surface, on the tensile reinforcement and on the horizontal and vertical web bars to monitor the strains, both in concrete and in the different reinforcement bars. The data show clearly that the distribution of strains, and hence of stresses, in the deep beams studied

Short steel fiber concrete (SF) tensile strength is dependent on fibers distributions and orientations inside the material. In the present investigation numerically are simulating (using FEM) all fibers motions in fresh concrete during the process of filling the mold by SF. Flow modeling was executed for Newton’s and viscous Bingham’s liquids. Potential weakest internal zone (is the place with undesirable fibers orientations and spatial distributions –the place of future macrocrack), from the point of view future load bearing capacity under four point bending conditions was recognized. Structural SF fracture model was created; material fracture process was modeled, based on single fiber pull-out laws, which were determined experimentally (for straight fibers, fibers with end hooks, and corrugated fibers).

Nowadays, practicing ‘industrial ecology’ for sustainable industrial development is a common practice in the engineering field. This practice promotes recycling by-product waste of one industry by substituting/replacing them for the virgin raw material of another industry, thereby reducing the environmental impact of both. One of those by-product wastes is bottom ash, which produced from coal-fired power plant that faces an increasing production up to hundred and thousand tones over the continents. Previously, a significant amount of research has been conducted in order to explore the potential use of bottom ash in the production of concrete and mortar. Most of the research focused on its potential use as fine aggregate replacing natural sand, and exploring its beneficial properties in enhancing the properties of concrete and mortar. This present paper reviews the literature related to the properties of fresh and hardened concrete incorporating bottom ash as a partial or total repla...

The paper gives a short description of mechanism for creep and shrinkage of concrete accorting to Europen Normative Eurocode 2. It is focused on effect of relative humidity and cement class on creep and shrinkage parameters calculated for slender reinforced concrete columns. Two main methods will be presented, the method based on nominal stiffness and the method based on nominal curvature for calculation of slender columns. Columns with rectangular section with uniform distribution of the reinforcement are studied and some parameters like relative humidity of enviroment and cement class will be changed in order to study the influence of creep and shrinkage in second order effects. The resultants are given in tables and graphs. Keywords—Creep, shrinkage, relative humidity, slenderness, bending stiffnes, Eurocode 2

Equations to characterize the anchorage strength of headed bars were developed, incorporating key factors affecting anchorage strength: concrete compressive strength; embedment length; bar diameter; spacing between the bars; and confining reinforcement parallel to the headed bars. Results from tests of 138 exterior beam-column joints, 64 without and 74 with confining reinforcement within the joint region, were used to develop the equations. Concrete compressive strengths ranged from 4050 to 16,030 psi (27.9 to 110.6 MPa) and bar stresses at failure ranged from 33,100 to 153,160 psi (228 to 1056 MPa). The bearing area of the headed bars ranged from 3.8 to 9.5 times the area of the bar. Some headed bars contained obstructions adjacent to the head that exceeded the dimensions permitted for HA heads in ACI 318-14 and ASTM A970-13a but are now permitted by ASTM A970-18. The test results show that headed bar anchorage strength is proportional to the concrete compressive strength raised to the power 0.24. The contribution of confining reinforcement is proportional to the area of confining reinforcement parallel to the headed bar within eight to 10 bar diameters of the headed bar. Headed bars with obstructions larger than those permitted in ACI 318-14 that meet the provisions in ASTM A970-18 exhibit anchorage strengths that are similar to those that meet the provisions in ACI 318-14.

The theory of truss analogy has undergone
significant changes over time and eventually turned to the
strut-and-tie model (STM) method. The elements of STM,
which are strut, tie, and node, play a significant role in the
design and analysis of Discontinuity-region (D-region).
Each element requires assigning particular dimensions in
STM to yield accurate analysis results. STM has been
modified in many aspects in prior research, but the
determination of the width of the strut has yet to be further
explored and researched. This research aims to evaluate the
determination of the width of the strut in RC deep beams
by going through effective compressive stress of the strut
produced by statics point load. In other words, the effect of
the width of the strut on the failure load of RC deep beams
is the main objective. Hence, the failure of the elements of
STM, which are strut, tie, and node, is considered, and
particularly, a comparison is drawn between the tie and the
strut to detect which one fails earlier and controls the
failure of RC deep beam when changing the width of the
strut. The width of the strut varies within a range according
to the prior experimental investigations, and this range is
used in this research with six width increments. The
research is confined to analyzing D-regions in RC deep
beams of ordinary concrete subjected to a three-point
bending test configuration. The control of failure of RC
beams is seen to swing from the strut to the tie when the
width of the strut is at the fourth width incremental. This
indicates that the sequence of failure of elements of STM
swings from one to another, depending on the width of the
strut. It is recommended to use both STM and Finite
Element Method (FEM) verified with prior experimental
results to identify a correct load trajectory and strut
dimensions. Classifying deep beams into four groups
according to their shear span-to-effective depth ratio in the
range of zero to two is crucial for the identification of the
width of the strut, as the spread of compressive stresses
over the length of the strut significantly changes depending
on this ratio.

This paper presents the results of the experimental study for the un-heated and fire damaged reinforced concrete square columns confined with a single layer of Carbon Fiber Reinforced Polymer (CFRP) jacket. A total of four un-heated reinforced concrete square columns, two unconfined control specimens and two CFRP confined square columns were tested under axial compression. The experimental data of the four fire damaged reinforced concrete square columns, two unconfined fire damaged control specimens and two CFRP confined fire damaged square columns tested under axial compression were selected from the already published research study. The results of the experimental tested data of un-heated reinforced concrete square columns were compared with the published data of the fire damaged reinforced concrete square columns in terms of confined compressive strength and the gain in axial load bearing capacity. The results showed that a single layer of CFRP jacket is more effective for enhanc...

Bi-materials (D) Fracture properties (C) Thermal treatment (A) Mechanical properties (C) This study investigates the effect of thermal cycles on the fracture properties of the cement-based bimaterials. Sixty eight cubes were exposed to a varied number of 24-hour thermal cycles ranging from 0 to 90 and subsequently were tested in a wedge splitting configuration. The mechanical and fracture properties of normal strength and high strength concretes are substantially improved after 30 thermal cycles, but less so after 90 thermal cycles both in isolation and when bonded to an ultra high-performance fibre-reinforced cement-based composite.

Detailed observations are presented on the evaluation of the residual properties of high strength concrete specimens after exposure to high temperatures. The variables considered were fiber reinforcement consisting of steel or polypropylene microfibers and two different specimen sizes. Both heat treated and undamaged (no heat treatment) specimens were tested by conducting three-point bending experiments at ambient conditions approximately one month after exposure to the high temperature. Residual strength and post-peak response were monitored using a closed-loop load frame, and the damage zone was observed with optical and acoustic techniques. Electronic speckle interferometry provided high resolution measurements of the displacement field due to the development of fracture. The size and shape of the localized damage zone were identified through the acoustic emission due to pre-peak microcracking, one of the significant factors influencing the strength of quasi-brittle materials.

The experimental investigation is mainly focused on the development of cost effective high strength concrete containing high volume fly ash. Fly ash is a byproduct of coal fired electric power station. The current annual worldwide production of coal ash is estimated about 700 million tonne. Fly ash is a beneficial mineral admixture for concrete. It influences many properties of concrete in both fresh and hardened state concrete. Utilization of waste materials in cement and concrete industry reduces the environmental problems; also utilization reduces the amount of solid waste, green house gas emissions associated with Portland clinker production and conserves existing natural resources. Due to increase in demand for cement, there is a need of alternate material. Since fly ash is pozzolanic in nature, it can act as partial replacement material for Portland cement. In this study, keeping the binder content as constant and replacing cement with fly ash upto 60%, the mechanical behavior...

The optimization of composite materials such as concrete deals with the problem of selecting the values of several variables which determine composition, compressive stress, workability and cost etc. This study presents multi-objective optimization (MOO) of high-strength concretes (HSCs). One of the main problems in the optimization of HSCs is to obtain mathematical equations that represents concrete characteristic in terms of its constitutions. In order to solve this problem, a two step approach is used in this study. In the first step, the prediction of HSCs parameters is performed by using regression analysis, neural networks and Gen Expression Programming (GEP). The output of the first step is the equations that can be used to predict HSCs properties (i.e. compressive stress, cost and workability). In order to derive these equations the data set which contains many different mix proportions of HSCs is gathered from the literature. In the second step, a MOO model is developed by making use of the equations developed in the first step. The resulting MOO model is solved by using a Genetic Algorithm (GA). GA employs weighted and hierarchical method in order to handle multiple objectives. The performances of the prediction and optimization methods are also compared in the paper.

The prediction of the actual ultimate capacity of confined concrete columns requires partial confinement utilization under eccentric loading. This is attributed to the reduction in compression zone compared to columns under pure axial compression. Modern codes and standards are introducing the need to perform extreme event analysis under static loads. There has been a number of studies that focused on the analysis and testing of concentric columns. On the other hand, the augmentation of compressive strength due to partial confinement has not been treated before. The higher eccentricity causes smaller confined concrete region in compression yielding smaller increase in strength of concrete. Accordingly, the ultimate eccentric confined strength is gradually reduced from the fully confined value f cc (at zero eccentricity) to the unconfined value f 0 c (at infinite eccentricity) as a function of the ratio of compression area to total area of each eccentricity. This approach is used to implement an adaptive Mander model for analyzing eccentrically loaded columns. Generalization of the 3D moment of area approach is implemented based on proportional loading, fiber model and the secant stiffness approach, in an incremental-iterative numerical procedure to achieve the equilibrium path of P-e and M-u response up to failure. This numerical analysis is adapted to assess the confining effect in rectangular columns confined with conventional lateral steel. This analysis is validated against experimental data found in the literature showing good correlation to the partial confinement model while rendering the full confinement treatment unsafe.

Results of an experimental program on the anchorage strength of headed reinforcing bars are presented. Two hundred and two exterior beam-column joint specimens with concrete compressive strengths ranging from 3960 to 16,030 psi (27.3 to 110.6 MPa) were tested under monotonic loading. Key parameters included concrete compressive strength, embedment length, bar size, head size, spacing between headed bars, and confining reinforcement within the joint region. Bar stresses at failure ranged from 26,100 to 153,200 psi (180 to 1057 MPa). Specimens exhibited concrete breakout, side-face blowout, or a combination of the two failure modes, with concrete breakout being the dominant failure mode. A comparison of bar stress at anchorage failure with the stress calculated based on ACI 318-14 shows that ACI 318-14 provides a very conservative estimate of anchorage strength for No. 5 (No. 16) bars and low concrete compressive strengths. The estimate becomes progressively less conservative with increasing bar size and concrete compressive strength.

Headed bars are often used to anchor reinforcing steel as a means of reducing congestion where member geometry precludes adequate anchorage with a straight bar. Currently, limited data on the behavior of headed bars are available, with no data on high-strength steel or high-strength concrete. Due to a lack of information, current design provisions for development length of headed reinforcing bars in ACI 318-14 limit the yield strength of headed reinforcing steel to 60,000 psi and the concrete compressive strength for calculating development length to 6,000 psi. Current design provisions for developing headed bars in ACI 349-13, which are based on ACI 318-08, apply the same limits on the material strengths (60,000 psi and 6,000 psi, respectively, for headed bars and concrete). These limits restrict the use of headed bars and prevent the full benefits of higher-strength reinforcing steel and concrete from being realized. The purpose of this study was to establish the primary factors that affect the development length of headed bars and to develop new design guidelines for development length that allow higher strength steel and concrete to be utilized. A total of 233 specimens were tested, with four specimen types used to evaluate heads across a variety of applications. Two hundred two beamcolumn joint specimens, 10 beam specimens with headed bars anchored near the support in regions that are known as compression-compression-tension (CCT nodes, 15 shallow embedment specimens (each containing one to three headed bars for a total of 32 tests), and 6 splice specimens were evaluated. No. 5, No. 6, No. 8, and No. 11 bars were evaluated to cover the range of headed bar sizes commonly used in practice. Concrete compressive strengths ranged from 3,960 to 16,030 psi. A range of headed bar sizes, with net bearing areas between 3.8 and 14.9 times the area of the bar, were also investigated. Some of these heads had obstructions larger than allowed under current Code requirements. In addition, the amount of confining reinforcement, number of heads in a specimen, spacing between heads, and embedment length were evaluated in this study. The results of this study show that provisions in ACI 318-14 and ACI 349-13 do not accurately account for the effect of bar size, compressive strength, or the spacing of headed bars in a joint. The effect of concrete compressive strength on the development length of headed bars is accurately represented by concrete strength raised to the 0.25 power, not the 0.5 power currently used in the ACI provisions. Confining reinforcement increases the anchorage strength of headed ii bars in proportion to the amount of confining reinforcement per headed bar being developed. Headed bars with obstructions not meeting the Class HA head requirements of ASTM A970 (heads permitted by ACI 318-14 and ACI 349-13) perform similarly to HA heads, provided the unobstructed bearing area of the head is at least 4.5 times the area of the bar. Headed bars exhibit a reduction in capacity for values of center-to-center spacing less than eight bar diameters. These results are used to develop descriptive equations for anchorage strength that cover a broad range of material strengths and member properties. The equations are used to formulate design provisions for development length that safely allow for the use of headed reinforcing bars for steels with yield strengths up to 120,000 psi and concretes with compressive strengths up to 16,000 psi. Adoption of the proposed provisions will significantly improve the constructability and economy of nuclear power plants and other building structures.

Equations to characterize the anchorage strength of headed bars were developed, incorporating key factors affecting anchorage strength: concrete compressive strength; embedment length; bar diameter; spacing between the bars; and confining reinforcement parallel to the headed bars. Results from tests of 138 exterior beam-column joints, 64 without and 74 with confining reinforcement within the joint region, were used to develop the equations. Concrete compressive strengths ranged from 4050 to 16,030 psi (27.9 to 110.6 MPa) and bar stresses at failure ranged from 33,100 to 153,160 psi (228 to 1056 MPa). The bearing area of the headed bars ranged from 3.8 to 9.5 times the area of the bar. Some headed bars contained obstructions adjacent to the head that exceeded the dimensions permitted for HA heads in ACI 318-14 and ASTM A970-13a but are now permitted by ASTM A970-18. The test results show that headed bar anchorage strength is proportional to the concrete compressive strength raised to the power 0.24. The contribution of confining reinforcement is proportional to the area of confining reinforcement parallel to the headed bar within eight to 10 bar diameters of the headed bar. Headed bars with obstructions larger than those permitted in ACI 318-14 that meet the provisions in ASTM A970-18 exhibit anchorage strengths that are similar to those that meet the provisions in ACI 318-14.

Bu calismada mermer, granit ve andezitin kendiliginden yerlesen betonda agrega olarak kullanilabilirligi arastirilmistir. Bu amacla sahit olarak kalker kokenli agrega ile uretilen kendiliginden yerlesen beton tasariminda %25, %50 ve %75 oranlarinda mermer, granit ve andezit agregasi kullanilmistir (uc farkli cimento dozajinda 350, 400 ve 450 kg/m3 ). Uretilen beton numuneleri uzerinde taze halde cokme yayilma deneyi ile sertlesmis halde basinc mukavemeti ve yarmada cekme mukavemeti deneyleri gerceklestirilmistir. Sonuc olarak incelenen agregalarin beton uzerindeki performansinin kullanim orani ve cimento dozajina bagli olarak degistigi, taze beton ozellikleri uzerinde olumsuz etkisi olmasina ragmen, dusuk oranlarda kullanildiginda basinc mukavemetinde olumlu etkiler ortaya koydugu sonucuna ulasilmistir.

The paper examines the properties of ®ve dierent types of repair materials, including conventional cementitious, polymer and polymer-modi®ed repair mortars. Assessment was carried out on the basis of the engineering properties (compressive strength, tensile strength and modulus of elasticity), pore structure (porosity and pore size distribution), transport properties (permeability and diusion) and shrinkage. These properties were measured up to the age of 28 days after curing in a hot-dry environment. The epoxy resin repair mortar showed superior strength and transport characteristics with a very ®ne pore structure; however, its modulus of elasticity was remarkably low when compared with that of normal-and high-strength concretes. A hot-dry curing environment adversely aects the shrinkage and performance-related properties of conventional repair mortars; however, small improvements could be achieved by the use of mineral admixtures (¯y ash and silica fume). The paper discusses also the dierent testing techniques which could be used to assess the potential performance of concrete repair mortars.

The prediction of the actual ultimate capacity of confined concrete columns requires partial confinement utilization under eccentric loading. This is attributed to the reduction in compression zone compared to columns under pure axial compression. Modern codes and standards are introducing the need to perform extreme event analysis under static loads. There has been a number of studies that focused on the analysis and testing of concentric columns. On the other hand, the augmentation of compressive strength due to partial confinement has not been treated before. The higher eccentricity causes smaller confined concrete region in compression yielding smaller increase in strength of concrete. Accordingly, the ultimate eccentric confined strength is gradually reduced from the fully confined value f cc (at zero eccentricity) to the unconfined value f 0 c (at infinite eccentricity) as a function of the ratio of compression area to total area of each eccentricity. This approach is used to implement an adaptive Mander model for analyzing eccentrically loaded columns. Generalization of the 3D moment of area approach is implemented based on proportional loading, fiber model and the secant stiffness approach, in an incremental-iterative numerical procedure to achieve the equilibrium path of P-e and M-u response up to failure. This numerical analysis is adapted to assess the confining effect in rectangular columns confined with conventional lateral steel. This analysis is validated against experimental data found in the literature showing good correlation to the partial confinement model while rendering the full confinement treatment unsafe.

The goal of this study is to gather a High Strength Concrete (HSC) composite reinforced by silica fume and superplasticizers. Specimens are Cured by water and tested after aging time of 3, 7, 28 days. Specimens are cubes of 150 and 200 mm and 150x300mm cylinder. The aim is to get mean strength of 80- 85 MPa, and determination of physical properties of the materials used, which are basic components of the High Strength Concrete (HSC) composites. After designing mix proportions, according to design requirements some adjustments were done. Both fresh and hardened properties of the specimens were tested under standard condition (curing schemes, setting time, comp.str. etc). Compressive strength test results were gathered and compared with the requirements.

High Strength Self Compacting Concrete adalah salah satu inovasi beton dengan keunggulan memiliki workability dan mutu beton yang tinggi. Fly ash dapat digunakan sebagai filler atau bahan pengganti semen. Pengujian yang dilakukan adalah pengujian slump yang meliputi slump flow test, l box test dan v funnel test serta pengujian kuat tekan dengan waktu curing 14 hari untuk persentase 1%, 5%, 15% dan 20% dan waktu curing 28 hari untuk persentase 1%. Benda uji berbentuk silinder dengan dimensi 100 mm dan 200 mm. Dari hasil penelitian diperoleh penggunaan fly ash persentase 1% memenuhi syarat untuk Self Compacting Concrete menurut EFNARC dengan nilai slump flow test 700 mm dan memenuhi syarat untuk High Strength Concrete dengan nilai kuat tekan rata-rata 70,61 MPa pada curing 14 hari. Kemudian dilakukan penelitian lanjut menggunakan persentase 1% untuk memperoleh nilai slump pada ketiga pengujian slump serta nilai kuat tekan pada 28 hari. Sehingga diperoleh nilai slump flow test 719 mm, l box test 1 cm dan v funnel 19,99 detik dengan kuat tekan rata-rata 41,52 MPa pada 14 hari dan 44,36 MPa pada 28 hari. Penggunaan fly ash sebagai filler dengan persentase 1% mereduksi biaya produksi sebesar 0,81% terhadap biaya produksi HSSCC tanpa filler fly ash.

Concrete with a design strength of 100 to 150 N/mm 2 made using low-heat portland cement and silica fume (LSF) was subjected to thermal histories with different maximum temperatures (Tmax) to examine their autogenous shrinkage properties. The autogenous shrinkage properties were found to significantly change when Tmax exceeded 45 to 60�C. Comparing these results with past studies using portland cement, the authors clarified the autogenous shrinkage properties of LSF concrete and proposed a technique for their prediction by modifying conventional equations. Furthermore, the applicability of the proposed method was verified.