bluuebunny/crossref_metadata_2025 huggingface dataset:
Bond strength at high temperatures
Authors: Diederichs U. , Schneider U.
Published: October 2009

Synopsis

This paper deals with the bond strength of steel and concrete at high temperatures because, although bond strength is of major importance in the determination of the behaviour of concrete structures in fire, there is no detailed information available on this problem. For this reason a test apparatus was developed which enabled pull-out experiments to be carried out on cylindrical concrete specimens with short embedment lengths. During the tests the slip at the non-loaded end of the concrete specimen and the pull-out force were reassured. In the temperature range 20 to 800°C the pull-out system enabled two different types of experiment to be carried out: force–slip measurements at thermal steady state and at non-steady state conditions. In these experiments normal-weight concrete made with Portland cement and siliceous aggregate and three different types of reinforcing steel (ribbed steel bars, plain round bars and deformed prestressing bars) were used. Differences between the results for the different types were noted, especially between the ribbed steel and plain round steel bars.
Relationships between permeability and pore structure of hardened cement paste
Authors: Nyame B. K. , Illston J. M.
Published: October 2009

Synopsis

A description is given of a steady-state method of measuring the permeability of hardened cement paste. The method takes advantage of the applied hydrostatic pressure in sealing truncated conical disc specimens at hydraulic gradients up to 150000. Relationships between saturated permeability and pore structure parameters, as determined by drying at 105°C and mercury intrusion porosimetry, are presented for hardened cement pastes of differing water/cement ratios and times of hydration. It was found that there is no unique relationship between permeability and porosity, though well defined trends were evident for the effect upon permeability of time of hydration at constant water/cement ratio. Similar trends were found between permeability and surface area at constant time of hydration. A broad-banded relationship was evident between permeability and hydraulic radius for all the grouped results. Reasonably close agreement was found between the structural parameter from hydraulic radius theory and the permeability, though with some discrepancies at low permeabilities.
Extended model for estimating the strength-developing capacity of Portland cement
Authors: Popovics Sándor
Published: October 2009

Synopsis

This paper presents a new formula for estimating the strength-developing capacity of Portland cement. This formula was obtained by the extension of a so-called exponential cement model published earlier for relative strengths. This extension is in two directions: (1) the strengths are expressed in stress units, such as N/mm2, instead ofpercentages; and (2) this new model reproduces the effect of cement fineness upon the strength development in addition to the compound composition and age of testing. Compressive and tensile strengths obtained on standard ASTM Ottawasand mortar specimens illustrate the validity of the new formula.
Static and cyclic response of reinforced concrete beams repaired by resin injection
Authors: Hewlett P. C. , Morgan J. G. D.
Published: October 2009

Synopsis

This paper covers laboratory testing, both static and cyclic (reversed loading), of reinforced concrete beams aimed at establishing the repair capability and consequences of synthetic resin injection. Beams designed to fail both in tension and in shear were tested to failure, repaired and re-tested. Unidirectional and reversed loading sequencies were applied. The purpose of cyclic loading was to establish the effect of an interposed resin layer within cracked concrete, resulting from ‘wedging’ and possible resin fatigue. The work has established that, if cracks are accessible to the resin (i.e.not less than 0·1 mm wide), failed beams can be reinstated to load-deflection and ultimate load behaviour at least as good as those of the unfailed beam. If; however, bond between reinforcement and concrete has been destroyed, or the reinforcement extended beyond its elastic limit, total reinstatement is doubtful. Extensive shear cracking can be reinstated totally and beams failed in this way are both stiffer and stronger than originally. Within the limits of this test programme, resin within a crack has no deleterious effect upon repaired beam’s behaviour under reversed loading.
The behaviour of reinforced concrete flanged beams with stiffeners
Authors: Subedi N. K.
Published: October 2009

Synopsis

The modes of failure and the ultimate strength of deep reinforced concrete flanged beams with stiffeners can be predicted. The major contributions to the ultimate strength come from the strength of the web and the main reinforcement. A simple method is proposed for the analysis of reinforced concrete flanged beams with stiffeners. Results from micro-concrete model tests and also tests carried out at the Polytechnic of Central London and Concordia University, Canada, are compared with the proposed method of analysis.
Portland–pfa cement: a comparison between intergrinding and blending
Authors: Monk Michael
Published: October 2009

Synopsis

Portland–pfa (pulverized-fuel ash) cements containing 20-40% (by weight) pfa have been prepared in the laboratory both by intergrinding the ashes with clinker and by blending with cement. The ashes were obtained from four base-load stations and the cements and clinker from two UK cement works. Cement properties have been assessed according to BS 4550 and scanning electron microscopy was used to examine the effects of grinding upon the pfa particles. The work has shown that intergrinding leads to an improvement in the water-reducing properties ofcoarse pfas and also in their pozzolanic activity as indicated by compressive strength development at later ages. Setting times have been found to be essentially the same for blended and interground cements, both being considerably longer than for typical ordinary Portland cements. The results of the work on laboratory-prepared cements have been confirmed on factory-produced cements. Thus the results of this investigation indicate that, provided pfas are chemically acceptable, they can be used for Portland-pfa cement manufacture by intergrinding irrespective of their coarseness.
Further responses of the bond in reinforced concrete to high temperatures
Authors: Royles R. , Morley P. D.
Published: October 2009

Synopsis

Tests were carried out to examine the effects of heat treatment upon the bond between concrete and steel by using direct displacement measurements and monitoring acoustic emission. A description of the experimental set-up has been given previously and, as before, it was used to test cylindrical pull-out specimens with an actual embedment length of 32 mm. The variables considered were type of bar (plain anddeformed bars of 16 mm diameter) and the effect of load cycling (for the deformed bar only) upon the bond after it has been subjected to heat treatment. The acoustic emission equipment was incorporated into the system to assess its validity in this type of testing and was used in all three of the different test situations investigated.
Measuring long-term strains in concrete by microcomputer
Authors: Hirst M. J. S.
Published: October 2009

Synopsis

A new low-cost computer interface has been developed for acoustic strain gauges. The interface will operate and read up to four gauges and brings the benefits of computer control and results processing to these robust gauges. All control programming uses standard BASIC commands. To complement the interface, a program has been developed which effectively turns the computer into a complete datalogger for acoustic strain gauges. Operational modes range from immediate display of strains to long-term monitoring of the gauges under clock control.
Simpler nodal forces for yield-line analysis of reinforced concrete slabs
Authors: Johnarry Tonye
Published: October 2009

Synopsis

An alternative scheme for nodal forces for equilibrium analysis of yield patterns is investigated. The principal features of the scheme include defining the forces in terms of: (a) the key(yie1d) moment referred to the axes of rotation: (b) the angles between the yield lines and the axes of rotation: (c) the normal moments only stated in (a), leaving out completely explicit twisting moment terms. The scheme is not another form of the work method, but leab to solutions which match those obtained by the work method. In some cases of slabs with holes, exact solutions have been found where the work method (or the existing equilibrium method) has been unable to lead directly to such results.
Properties of concrete made with crushed concrete as coarse aggregate
Authors: Sri Ravindrarajah R. , Tam C. T.
Published: October 2009

Synopsis

Effects of using recycled concrete of different qualities as coarse aggregate upon the strength and deformation of concrete are reported. Tests on the aggregates showed that the recycled concrete aggregates have lower specific gravity and higher absorption capacity than the original crushed granite aggregate. The resistance to mechanical actions such as impact, crushing and abrasion for the recycled concrete aggregates is also lower. The effects of using recycled concrete aggregates instead of natural aggregates in concrete are: reduction in compressive strength up to 25%; reduction in modulus of elasticity up to 30%; improvement in damping capacity up to 30%; and higher amounts of drying shrinkage and creep. Available methods of predicting the modulus of elasticity on the basis of compressive strength for conventional concrete overestimate the modulus of elasticity for recycled-aggregate concretes.
The effect of vibration on the rheological properties of fresh concrete
Authors: Tattersall G. H. , Baker P. H.
Published: October 2009

Synopsis

Using a set-up in which the bowl of a two-point workability test apparatus was mounted on an electro-magnetic vibrating table, measurements were made on unvibrated fresh concrete and on the same samples under vibration. It was shown that when vibration is applied the flow properties of fresh concrete are no longer represented by the simple linear Bingham model but approximate to those of a power law pseudoplastic with zero yield value. At very low shear rates behaviour approximates to that of a Newtonian fluid and, subject to the exceeding of a small threshold condition, fluidity decreases as a simple exponential function of the maximum velocity of vibration.
Water sorptivity of mortars and concretes: a review
Authors: Hall C.
Published: October 2009

The sorptivity is an easily measured material property which characterizes the tendency of a porous material to absorb and transmit water by capillarity. Its theoretical basis in unsaturated flow theory is reviewed, together with methods of measurement suitable for cement-based materials. Available data on mortars and concretes are included. The dependence of the sorptivity on initial water content, temperature and fluid properties is also described. Other test methods (the initial surface absorption, the Figg water absorption and the Covercrete absorption tests) are discussed in terms of the sorptivity.
Near surface characteristics of concrete: intrinsic permeability
Authors: Dhir R. K. , Hewlett P. C. , Chan Y. N.
Published: October 2009

The measurement of the intrinsic permeability of concrete is described. The tests developed are rapid and reliable. It is shown that the intrinsic permeability of concrete can be characterised using the air permeability test. Hydraulic permeability data can also be derived if required. The permeability of concrete in the surface layer (that comprising the cover to reinforcement) is greatly affected by both the water/cement ratio and curing. Concrete quality should not be estimated from strength data alone.
Steel in concrete: Part I A review of the electrochemical and thermodynamic aspects
Authors: Sagoe-Crentsil K. K. , Glasser F. P.
Published: October 2009

The electrochemical and thermodynamic factors influencing the stability of steel reinforcements in concrete are reviewed on the basis of prevailing conditions during the states of passivity, passivity breakdown and the onset of active corrosion. Details of reaction mechanisms characteristic of each of the states are outlined and the areas requiring further studies are defined. The resistivity of the concrete cover—both at the steel/concrete interface and of the bulk concrete matrix—and bulk humidity levels appear in general to be most significant. Special emphasis is given to intermediate humidity levels since these are encountered by normal structuresand they also represent a rather active thermodynamic regime regarding the durability of concrete reinforcements. Factors discussed in connection with the intermediate humidity regime are: (l) the availability of O2, (2) the chloride ion efect and (3) carbonation.
A simple pull-out test for in situ determination of early strength of concrete
Authors: Jaegermann C.
Published: October 2009

The aim of the work reported was to develop a simple non-destructive testing method for monitoring strength development between 5 MPa and 15 MPa for form stripping in industrialized building. Existing test methods are briefy reviewed and requirements for the test summarized. A simple pull-out test has been developed using wood-screws, which can be inserted in critical areas of the element during casting. In a laboratory investigation the deflect of different variables on the pull-out load-standard cube strength relationship was examined. These included cement content, water/cement ratio, slump, mode of compaction and accelerated heat curing. Evaluation of test results indicates low dependence of the proposed method on mix proportions, and suggests reasonable repeatability. Further tests are proposed to refine the method for various field applications.
Determination of crack location, type and orientation ina concrete structures by acoustic emission
Authors: Ohtsu Masayasu , Shigeishi Mitsuhiro , Iwase Hiroyuki , Koyanagit Wataru
Published: October 2009

Elastic waves emitted by microfracturing are called acoustic emission (AE). Recently AE techniques have been extensively applied to concrete engineering as a non–destructive testing (NDT) method. A key aspect of AE is that the nucleation of internal cracks is directly detected by a surface observation. In conventional AE techniques, such AE parameters as event count (activity), amplitude, energy and spectra are correlated with the failure process of materials. Thus, AE characteristics are utilized for NDT. The AE source (crack) is also located by employing a multichannel (more than 5) AE detecting and recording system. In this Paper an advanced AE analysis procedure is proposed. In addition to crack locations, crack types and crack orientations are determined from AE relative amplitudes of the first motions. The procedure classifies cracks into tensile cracks and shear cracks. Based on information of the crack type, the crack orientation is determined; this is the direction of crack opening in the case of tensile cracks, and the direction of sliding motion in the case of shear cracks. The proposed procedure is applied to a pull-out test of an anchor–bolt from a concrete block and a cylinder–tensile test. In the pull out test the opening directions of the tensile cracks is perpendicular to the failure surface, while the directions of sliding motion of the shear cracks are parallel to the failure surface. In the cylinder–tensile test the opening directions of the tensile cracks are perpendicular to the loading direction and all sources are located near the final plane. The proposed procedure is therefore able to determine the microcrack kinematics generated in concrete.
Behaviour of concrete spirally confined by fibreglass filaments
Authors: Ahmad S. H. , Khaloot A. R. , Irshaid A.
Published: October 2009

Results are presented on the strength and deformation capacity of concrete transversely reinforced with fibreglass filaments (wires). A total of 33 cylinders confined with fibreglass wires were tested to obtain complete stress–strain curves in compression. The wires were 80% glass and 20% polyester resin matrix, and had a tensile strength of 300 ksi (2070 MPa). Based on the experimental data, an analytical equation was developed to predict the stress–strain curves of plain and fibreglass wire–confined concrete. The two constants in the equation were calibrated from the observed test results, so that only the strength of concrete was required to generate the stress–strain response of plain concrete, and the strength of plain concrete and the spacing of the fibreglass wires were required to generate the complete stress–strain response of fibreglass–confined concrete. Results of this study are compared with those reported for concrete confined transversely by steel reinforcement.
Short-term and time-dependent design rules for slender RC columns of circular cross-section
Authors: Bradford M. A.
Published: October 2009

A numerical method of analysis developed elsewhere by the Author which can be used to analyse the short-term and time-dependent behaviour of slender RC columns of circular cross-section under constant eccentricity, is described briefly. The method is used to investigate the accuracy of the design of circular columns implicit in the Australian Standard AS3600-1988. The code method is shown to be comparitively inaccurate for circular columns, and a design procedure for both short and long-term loading that may be readily implemented, is proposed.
Concrete research in the UK
Authors: Narayanan R. S.
Published: October 2009

It may seem curious for a practising engineer to be writing a guest editorial in the Magazine of Concrete Research. If this is thought to be unusual, in some ways it sums up the attitude to research in the UK. However, research should not be regarded as an indolent activity for the gratification of a few academics. Any industry which does not concern itself actively with research is bound to become moribund. In my terms, research is not purely confined to academic ivory towards, but rather it encapsulates every part of the industry, including materials, design, construction, maintenance, repair, and also the effective management and control of these processes.
Alkali-reactivity of greywacke aggregates in Maentwrog Dam (North Wales)
Authors: Blackwell B. Q. , Pettifer K.
Published: October 2009

Greywacke as a rock group has been implicated in promoting alkali–aggregate reaction (AAR) in a number of structures throughout the world. The Maentwrog Dam is believed to be the first major case recorded in the U K. Petrographic examination of concrete cores taken from the dam showed that the structure is affected by AAR, notwithstanding any other contributory causes of distress. SEM examination revealed three main AAR gel types having morphological, situational and chemical characteristics consistent with those in flint aggregate concrete promoting the alkali–silica reaction. X-ray diffraction studies showed that matrix phyllosilicates did not exhibit exfoliations diagnostic of the controversial alkali–silicate mechanism, corroborating the petrographic examination evidence that an alkali–silica mechanism is the most likely explanation for distress. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies showed that the microcrystalline quartz, acting as a matrix cement in the rock, has local dislocation densities of 1014 m−2, and this is believed to be the reactive constituent. Similarities between the Maentwrog greywacke and a Canadian greywacke, which has promoted AAR in the Malay Falls Dam (Nova Scotia), are shown. This confirms that greywackes are vulnerable to the alkali–silica reaction rather than alkali–silicate reactions.
Probabilistic model for material behaviour analysis and appraisement of concrete structures
Authors: Rossi P. , Wu X.
Published: October 2009

Description of the nonlinear behaviour of materials and structures is often deterministic and the obtained results (ultimate loads, load-displacement response, patterns of cracking, etc.) are generally supposed to be correct. The purpose of this Paper is to show that these results can be debated and that the deterministic models are insufficient if a more accurate approach of safety is required. The Paper shows how a model on a probabilis- tic basis can improve the quality of the numerical simulation of the loading of concrete specimens.It shows also that a stochastic approach can give very important information on the problem of the localization of cracks in a heterogeneous material like concrete.
Long-term strains measured in reinforced concrete building
Authors: Parrott L. J.
Published: October 2009

Strains measured over a period of 17 years are reported for a reinforced concrete building. Vibrating wire strain gauges were embedded in the ribs and beams of the first floor of a three-storey telephone exchange in south-west England. Groups of gauges were located at mid-span of two 170 mm thick ribs, at mid-span of a 470 mm thick beam, and near the support column and edge beam of the 470 mm thick beam. Gauges in each group were positioned at different depths in the direction of the expected stress and transversely, so that shrinkage and load-induced strains could be calculated. Concrete temperatures and relative humidities were measured so that allowance could be made for the small variations of thermal strain and changes in drying conditions. Elastic modulus, weight loss and strain measurements were undertaken on site-stored and laboratory-stored prisms cast from the in situ concrete. n e embedded vibrating wire strain gauges enabled the strains to be measured sensitively and reliably over the 17 year period of observation. It took about 10 years for drying shrinkage to reach approximate equilibrium, but some additional shrinkage was then observed owing to change in use of the building. There was only approximate agreement between the measured shrinkage strains and those estimted from British Standard BS 81l0: Part 2: 1985. The normal pattern of flexural strains in the floor was superimposed by a tensile strain component that seemed to arise from the restraint of drying shrinkage.
An experimental study of the behaviour of sleeved bolt connections in precast concrete frames
Authors: Mohamed S. A. M. , Jolly C. K.
Published: October 2009

Sleeved bolt beam-to-column connections have been used in the precast concrete industry for many years. They have advantages over other jointing methods in component production, quality control, transportation and assembly. However, there is at present limited information concerning their detailed structural behaviour under shear loading. The study reported in this paper was undertaken to elucidate the behaviour of such joints under symmetrical vertical loading. Two series of full-scale tests were preformed on sample columns for which the column geometry and bolt arrangements conformed with successful commercial practice. The first series of tests was used to investigate the influence of bolt density on the ultimate load, failure mode and stiffness of such connections. The second test series showed the influence of varying concrete strength and the effectiveness of the confining reinforcement. Full details of these test programmes are given. The finite element modelling technique was used to develop three-dimensional models which were calibrated against the test observations. These models subsequently provided complete stress and deformation distributions within the joint components at intervals up to the ultimate load, and are the subject of another paper.
A model for stress—strain relationship of spirally confined normal and high-strength concrete columns
Authors: El-Dash K. M. , Ahmad S. H.
Published: October 2009

An analytical model is developed to predict the complete stress–strain relationship of normal and high-strength concrete subject to uniaxial compressive loading and confined by transverse reinforcement. The confinement pressure is assumed to be uniform within the core of the column. The internal force equilibrium, the properties of the materials, and the geometry of the section are used to evaluate the pressure. The model utilizes a single fractional equation which satisfies realistic behaviour of the ascending portion, the peak point, and the post-peak descending portion of the stress–strain relationship. The predictions of the model and the available experimental results are compared over a range of concrete strengths. The model shows good predictive capability and is applicable for a wide range of variables such as the diameter of the circular section, the pitch, diameter and yield stress of the spiral, and the volumetric ratio of lateral reinforcement.
The combined influence of chemical and mineral admixtures on the alkali—silica reaction
Authors: Li Z. , Mu B. , Peng J.
Published: October 2009

The tests in accordance with the ASTM C227 (mortar bar test) have been carried out to investigate the effects of calcium nitrite (CN), fly ash, microsilica and their combination on the alkali—silica reaction (ASR). The chemically combined water, X-ray diffraction and compressive strength of each batch of specimens were also measured to explore the mechanism of these effects. The results show that both mineral admixtures and the CN solution have positive effects in preventing ASR expansion. It is found that the addition of a CN solution in this experiment has additional effects, being favourable for strength development.
Scale effects in uniaxially compressed concrete specimens
Authors: Carpinteri A. , Ferro G. , Monetto I.
Published: October 2009

The experimental nominal strength varies with specimen size. Such a phenomenon was investigated earlier by Griffith and Weibull. Recently, several models have been proposed to predict strength reduction with size increase in concrete structures. Confirmation was given of the proposed size effect laws, based on the extensive experimental data that can be found in the literature. Direct tension, splitting, bending, shear and torsion tests have been mainly considered. In particular, direct tension and bending have been recently analysed by Carpinteri et al. On the other hand, the compressive behaviour of concrete, being very complex, has been disregarded. In this paper, which can be considered as the continuation of the two previous ones published in this journal, where the multifractal scaling law was used to explain the scale effects on flexural and tensile strength, scale effects on the compressive strength of concrete specimens are analysed. The failure mode of compressed concrete specimens can be considered as resulting from local tensile mechanisms, or from a combination of tensile and shear mechanisms, according to the specimen geometry. It is thus possible to interpret some experimental investigations reported in the literature through the multifractal scaling law as well as the Bazant’s size effect law, where a tensile failure mechanism is assumed. A comparison between the two best-fit methods is presented. From the interpretation of the experimental results, a criterion to determine the specimen dimension minimizing the size effects is also proposed.
Tensile properties of fibre-reinforced very high strength DSP mortar
Authors: Jamal Shannag M. , Hansen Will
Published: October 2009

This paper reports on the tensile behaviour of fibre-reinforced densified small particle (FR-DSP) cement containing high volume fractions of steel fibres (more than 2%) and main reinforcement (1–3%) in direct tension. Approximately 30 tensile plate specimens were made. Parameters investigated include a very high strength cement-based matrix with a compressive strength of more than 150 MPa, fibre volume fraction within the matrix, and main reinforcement ratio. It is shown that incorporating large volume fractions of steel fibres (more than 2% by volume) in DSP composite results in a dramatic increase in matrix tensile strength (up to 100%). Adding a minimum of 1% main reinforcement (by volume) near the specimens' edges retards the initiation of cracks induced by edge effects and thus results in a further increase in ductility and tensile strength. It is shown that DSP composites can exhibit tensile strengths up to 25 MPa at peak strains ranging from 0·2% to 0·4%.
Influence of electrochemical chloride extraction on the bond between steel and concrete
Authors: Buenfeld N. R. , Broomfield J. P.
Published: October 2009

Laboratory tests were undertaken to assess the effect of electrochemical chloride extraction (ECE) on the bond strength of plain reinforcing steel in concrete. Specimens were cured/stored for 3 months prior to ECE and were then treated at a current density of between 0·02 and 0·75 A/m2 of reinforcement area for periods of up to 32 weeks. Chloride-free specimens showed a small gradual increase in bond strength after ECE. Prior to ECE, specimens containing chloride (1·5% by weight of cement) had higher bond strength than chloride-free specimens, due to corrosion. This enhanced bond strength was largely eliminated by 2 weeks of ECE, due to dissolution of corrosion products, although these specimens also then showed a slight increase in bond strength after further treatment. Tests carried out 10 min, 24 h and 28 days after ECE suggest that bond strength reduces during ECE. Variations in bond strength are considered with regard to the processes occurring during ECE, and the practical implications of these findings are discussed.
Factors affecting the efficiency of repair to propped and unpropped bridge beams
Authors: Mangat P. S. , O'Flaherty F. J.
Published: October 2009

This paper presents the results of laboratory and field investigations of bridge beams repaired both under propped and unpropped conditions. In the laboratory, beams were repaired using hand-applied repairs. Repairs to beams in two highway bridges were carried out using both hand-applied and flowing repairs. The repair materials used were commercial products of wide-ranging properties (shrinkage, creep and elastic modulus). Both low stiffness repair materials of elastic modulus, Erm, less than the substrate Esub, and high stiffness repair materials (Erm > Esub) were used. The repairs were applied in the tensile zone of the beams. Strain distributions in the different phases of repair patches were monitored under service loading for a period of up to 240 weeks. The results show that high structural efficiency is achieved with repairs having Erm > Esub, other properties (shrinkage and creep) being within reasonable limits. Such repairs are less prone to restrained shrinkage cracking and show a capacity for load redistribution into the repair patch. Low stiffness repairs (Erm < Esub), on the other hand, are prone to restrained shrinkage cracking and are ineffective in load-sharing with the substrate. Repairs to propped flexural members developed erratic and non-uniform load distribution in the different phases upon reapplication of load. Composite action between the repair patch and the substrate results in cracking in the repair patch, rendering the repairs structurally inefficient.
Stability of reference electrodes embedded in concrete: a statistical evaluation
Authors: Proverbio E.
Published: October 2009

Embeddable reference electrodes are essential in monitoring corrosion status of reinforcing steel in concrete structures when a continuous remote control of potential or surveys of sites difficult to access are required. Due to unavoidable potential fluctuations the comparison between different types of reference electrodes and their long term stability cannot be performed without a statistical approach to data analysis. An effort in this sense, with interesting results, has been made as reported in this paper. Three different embeddable reference electrodes were tested in two different concrete mixtures, a low resistivity and a high resistivity concrete. In spite of a wide data scatter a statistically significant distinction in the behaviour of different embeddable reference electrodes has been evidenced.
Spatial distribution of steel fibres in sprayed and cast concrete
Authors: Robins P. J. , Austin S. A. , Jones P. A.
Published: October 2009

Research has investigated the fracture of steel fibre reinforced sprayed concrete under flexural load with the aim of developing a stress-profile model to predict flexural behaviour in the form of a load–deflection response. This paper reports the work associated with establishing the number, distribution and geometry of the fibres bridging a typical cracked section of both sprayed and cast steel fibre reinforced concrete beams. X-ray photographic analysis and manual counting techniques are described. The simple X-ray technique developed is shown to be capable of determining the probability distribution associated with fibre embedment length and fibre orientation occurring across a cracked beam section. The results showed that there was little difference between casting (using table vibration) and spraying (wet process) on the resulting fibre orientation distribution properties. The fibre distribution data obtained can be used, in combination with fibre pull-out data, to model the tensile stress-profile of a beam specimen under flexural load. Hence, these data form a key part of a stress-profile model approach for predicting flexural behaviour – an essential requirement of a much needed design rationale for steel fibre reinforced concrete.
Aggregate distribution in concrete with wall effect
Authors: Zheng J. J. , Li C. Q. , Jones M. R.
Published: October 2009

In view of the importance of aggregate density to the mechanical properties of concrete, it is necessary to determine the aggregate density at any point in concrete or any cross-section of a concrete element. Once the aggregate density is known, some other mechanical properties of the concrete can be determined based on the theory of micro-mechanics. This paper attempts to simulate aggregate distribution in plain concrete taking into account of wall effect. Based on the study of the characteristics of the simulated aggregate distributions, a model of aggregate density is developed and its statistics are derived. Simulation results show that the average aggregate density of concrete in both two and three dimensions converges asymptotically to a constant when the number of simulations tends to infinity. Using mathematical regression, the aggregate density as a function of distance from the boundary and the thickness of the boundary layers can be expressed analytically in terms of the aggregate area or volume fraction of the concrete. The experimental verification of the developed model of aggregate density is also presented in the paper.
Jacketing of reinforced concrete columns subjected to axial load
Authors: Ong K. C. G. , Kog Y. C. , Yu C. H. , Sreekanth A. P. V.
Published: October 2009

This paper investigates the suitability of two existing confined concrete models, based on the concept of an effectively confined concrete core, to predict the behaviour of jacketed reinforced concrete columns when subjected to axial loads. Two types of jacketing with reinforced concrete (RC) were studied: full-length and partial jacketing. Consideration is also given to variations in the properties of the different concretes used in the jacket and the original column. Existing experimental data show that jacketing of RC columns using reinforced concrete enhances the axial load-carrying capacity, strain at peak axial load and post-peak ductility. However, conventional methods of analysis underestimate both the peak axial load and the corresponding strain. The two models were used to predict the entire load–strain relation of jacketed RC columns subjected to axial loading. The predictions agree well with available test results. For columns subjected to patch jacketing with only one set of stirrups, the predicted peak loads showed good agreement with experimental results. However, the corresponding strains were overestimated by as much as 20%.
Mesomechanical model for concrete. Part I: model development
Authors: Zhu W. C. , Teng J. G. , Tang C. A.
Published: October 2009

A damage mechanics-based numerical model for simulating the fracture process of concrete is presented. The model is based on knowledge of heterogeneity of concrete at the meso-level, in which the concrete is assumed to be a three-phase composite made up of the cement matrix phase, the aggregate phase and the matrix–aggregate interface phase. The constitutive law of each phase is defined on the basis of elastic damage mechanics, the finite element method is employed as the basic stress analysis tool, and the maximum tensile strain criterion and the Mohr–Coulomb criterion are adopted as damage thresholds. A simple method analogous to the smeared crack method is used for tracing the crack propagation process and for capturing the interaction of multiple cracks. Based on this model, a numerical simulation program, named Concrete Fracture Process Analysis (CFPA), was developed. The influences of various parameters of the model on its performance, including the Weibull distribution parameters, constitutive parameters and the number of elements are discussed in detail. Issues in the realistic simulation of concrete behaviour are also examined. Results from numerical simulations of concrete specimens under a variety of loading conditions using CFPA are presented in the companion paper.
FE analysis of RC shear walls subject to cyclic loading
Authors: Kwak H.-G. , Kim D.-Y.
Published: October 2009

This paper describes an extension of a numerical model that was developed to simulate the non-linear behaviour of reinforced concrete (RC) structures subject to monotonic in-plane shear, and introduced in the companion paper. The extended model is intended to effectively simulate the behaviour of RC structures under cyclic loadings. While maintaining all the basic assumptions adopted in defining the constitutive relations of concrete under monotonic loading, a hysteretic stress–strain relation of concrete, which crosses the tension–compression region, is defined. In addition, unlike previous simplified hysteretic stress–strain relations, curved unloading and reloading branches inferred from the stress–strain relation of steel considering the Bauschinger effect are used. Modifications of the stress–strain relation of concrete and steel are also introduced to reflect a pinching effect depending on the shear span ratio, and to represent an average stress distribution in a cracked RC element, respectively. Finally, correlation studies between analytical results and experimental studies are conducted to establish the validity of the proposed model.
Durability characteristics of controlled low-strength materials containing recycled bottom ash
Authors: Won J.-P. , Lee Y.-S. , Park C.-G. , Park H.-G.
Published: October 2009

The main intent of this research is to determine the feasibility of utilising recycled bottom ash as a controlled low-strength material (CLSM). A comprehensive study of bottom ash in CLSM and mixture proportions indicates that this type of bottom ash is a suitable ingredient in CLSM. The durability characteristics of CLSM manufactured with bottom ash under various physical and chemical deterioration conditions were investigated. Long-term compressive strength tests, water permeability tests, repeated freezing and thawing cycle tests, and repeated wetting–drying cycle tests were conducted. Results show that by mixing CLSM with bottom ash, acceptable CLSM material can be developed.
Self-compacting lightweight aggregate concrete: design and experimental study
Authors: Andiç-çakır ö. , Yoğurtcu E. , Yazıcı Ş. , Ramyar K.
Published: October 2009

This study focuses on the production of self-compacted lightweight structural concrete. For this purpose, lightweight concrete was produced by replacing normal aggregate with pumice aggregate obtained from the Kayseri region. Three series of mixtures were prepared to obtain the proper self-compacting lightweight concrete (SCLC) mixture. The D series included normal-weight, self-compacting concrete (SCC) mixtures and the H series included SCLC mixtures having 100% lightweight coarse aggregate and different air contents. Fresh concrete test results obtained from these mixtures were used as a basis for the T series containing different amounts of lightweight and normal-weight coarse aggregate. Some mechanical and fresh concrete properties were obtained from the T series. It was found that the loss of strength owing to lightweight aggregate addition is higher than the decrease of unit weight of the mixture. Furthermore, the decrease in flexural tensile strength owing to addition of lightweight aggregate is less than the reduction in compressive strength and splitting tensile strength. The percentage of entrained air and paste content are important factors to avoid segregation problems in lightweight SCC mixtures. There is a good relationship between 28-day compressive strength and unit weight data obtained from the H and T series.
Approximate expressions for the simulated response of slender longitudinal reinforcement in monotonic compression
Authors: Gil-Martín L. M. , Hernández-Montes E. , Aschheim M. , Pantazopoulou S. J.
Published: October 2009

Detailed non-linear three-dimensional (3D) finite-element analyses of the behaviour of reinforcing bars in compression were conducted for different slenderness ratios and for two different nominal strengths of steel. An equivalent engineering stress–strain response is determined for the bars, based on results obtained in natural coordinates. Approximate expressions to represent the equivalent engineering stress–strain response were fitted to the computed results. The approximate expressions are intended for use in moment–curvature analyses of reinforced concrete sections, where the contribution of the reinforcement is considered in the monotonic response of the cross-section, in cases where spalling of cover concrete allows the reinforcement to buckle. An example of moment–curvature analysis is carried out using the stress–strain relationship presented in this paper.
Deterioration of concrete joints under low-intensity, high-cycle loading
Authors: Austin S. , Arnold S. , Fleming P. , Robins P.
Published: October 2009

This paper reports on the results from a series of laboratory tests assessing the rate of deterioration for concrete cracks and joints under low-intensity, high-cycle loading, typical of that found in industrial flooring, external hardstandings and rigid pavements. The testing incorporated a variety of crack geometries, reinforcement types, reinforcement quantities and load magnitudes for over 80 half-scale prism specimens. The data presented demonstrates that joint/crack failure contains four distinct phases of deterioration, each controlled by a different mechanism of material degradation. ‘V'-shaped cracks were found to produce a higher load transfer than the equivalent surface width parallel crack, with the incorporation of A142 fabric and steel fibres significantly reducing differential displacement and crack face deterioration. The data has enabled serviceability limits to be established for each of the material parameters tested, keeping differential displacement within acceptable levels and preventing the onset of failure.
Hydraulic model studies for the Ghazi-Barotha hydropower project, Pakistan
Authors: Ackers J. C. , Ashraf Akhtar M.
Published: October 2009

The $2200 million Ghazi-Barotha hydro-power project—one of the largest currently under construction worldwide and expected to be completed in about 2002—will have a peak generating capacity of 1450 MW and provide an estimated annual energy output of 6600 GWh. Its main components are a gated barrage and flow diversion structure on the Indus River at Ghazi, about 7 km downstream of Tarbela dam a 52 km long power channel with a discharge capacity of 1600 m3/s, bypassing a relatively steep reach of river, including Attock Gorge a five-unit powerhouse, discharging back to the Indus at Barotha via a 2 km long tailrace an ‘emergency’ spillway providing a bypass to the powerhouse two ‘headponds’ upstream of the power intake, to provide sufficient daily storage to support diurnal ‘peaking’ of the units.

The project has a number of interesting hydraulic features, many of which were developed with the aid of about a dozen physical model studies. This paper includes a brief description of the project, outlining the role of most of the model studies and then describes two of them in greater depth.
Flood disasters: lessons from the past—worries for the future
Authors: Berz Gerhard
Published: October 2009

Flood disasters account for about a third of all natural disasters throughout the world (by number and economic losses) and are responsible for more than half of the fatalities. Trend analyses reveal that major flood disasters and the losses generated by them have increased drastically in recent years. Co-operation between the state, the affected population and the insurance industry assumes a key role with regard to the flood hazard. Scientists, engineers and insurers must work together in formulating their requirements and shaping them in such a way that politicians can derive clearly recognizable policy options (e.g. land use restrictions) from them. Another important aspect is stepping up the efforts being made towards curbing climate change, which will otherwise exacerbate the risk in the future.
Regression and dimensional analysis in coastal engineering: some pitfalls
Authors: Hedges T. S.
Published: October 2009

Most civil engineers are familiar with the concept of regression analysis. Fewer seem aware of the importance of model specification which includes defining the correct functional form of the regression equation. Furthermore, most engineers appear to equate regression with the process of minimising the sum of the squares of the differences between the measured values and the values predicted by the equation fitted to the data. But providing a least-squares fit to the data is only one of several possibilities. While its popularity is easily understood, the process suffers from the disadvantage that it is not robust: it is sensitive to the presence of outlying data points. The alternative regression procedure of minimising the absolute deviations of the fitted equation from the data is better in this respect. The paper focuses on linear regression analysis, particularly as it is used in conjunction with dimensional analysis, in the field of coastal engineering. However, the issues raised with regard to linear regression are equally relevant to non-linear regression. The reader is also reminded of the hazards of spurious correlation and examples are given both of poor and good model specification.
Shoreline management plans: a national review and engineering perspective
Authors: Cooper N. J. , Barber P. C. , Bray M. J. , Carter D. J.
Published: October 2009

Shoreline management plans were introduced by the Government in England and Wales in the early 1990s as a means of enabling large-scale and longer-term planning of risks to people and the developed and natural environments from coastal flooding and erosion. This paper presents results from a national review of the first-generation shoreline management plans, commissioned by the (then) Ministry of Agriculture, Fisheries and Food (MAFF), which critically assessed the methods used during their preparation and implementation and the type, detail and format of output generated. Particular focus is given in the paper to: (a) client-side project management and the procurement of consultants; (b) the nature of assessment of coastal defences; (c) the identification and adoption of strategic coastal defence options such as ‘hold’, ‘retreat’ or ‘advance’ the existing line of defence and ‘do nothing’; and (d) the levels of economic assessment contained within the Plans. The general strengths and weaknesses of shoreline management plans are presented, together with future recommendations that, when adopted, will enable the quality of shoreline management planning to continue to improve.