bluuebunny/crossref_metadata_2025 huggingface dataset:
Flexural tests of steel-concrete-steel sandwiches
Authors: Solomon S. K. , Smith D. W. , Cusens A. R.
Published: October 2009

Synopsis

In order to reduce the weight of roadway slab on medium- and long-span composite bridges, a possible alternative in the form of a steel-concrete-steel sandwich has been appraised. This consists of a concrete core, precast or otherwise, to which is attached reinforcement in the form of flat steel plates by means of epoxy resin adhesive. Specimens of the order of 100 mm thick were tested statically over a span of 1·8 m, and carried loads equivalent to wheels of the HB vehicle with an adequate safety margin. Accepted design procedures gave reasonable prediction of the ultimate loads.
Damage and energy dissipation in cement pastes in compression
Authors: Spooner D. C. , Pomeroy C. D. , Dougill J. W.
Published: October 2009

Synopsis

A study is reported of the energy dissipated in damage and in damping when cement paste prisms are loaded in uniaxial compression. Damage, characterized both by change in initial elastic modulus during sequential loading-unloading cycles and by the energy dissipated in damage, is detected at axial strains as low as 500 to 600 × 10−6 As the axial strain increases, the initial elastic modulus falls and the energy dissipated in damage gradually increases. Volumetric strain measurements indicate that the mechanism of fracture in cement paste in uniaxial compression is basically the same as in concrete: the formation of cracks introduces a dilating effect in opposition to the normal reduction in volume of the specimen under load. Whereas energy is only dissipated in damage during the first loading over a given strain range, it can be repeatedly dissipated by the damping process. The experimental data on cement pastes indicate that the energy dissipated in damping depends uniquely upon the strain range undergone by the specimen but that it is independent of the degree of damage in the specimen.
Crack initiation in plain concrete
Authors: Walsh P. F.
Published: October 2009

Synopsis

At the tip of a sharp crack or re-entrant notch, the stresses calculated by a simple elastic analysis become infinite. Consequently, maximum-stress or -strain failure criteria and stress-concentration factors cannot be used to predict failure at such points. The linear elastic fracture mechanics theory can, however, be applied. In the paper, a brief treatment of the application of this theory to sharp cracks in concrete beams is presented and the effect of beam size is particularly examined. The same basic technique is applied to re-entrant notches. Experimental evidence of the validity of the approach is given. Theoretical results are included which allow these test data to be extended to a wide range of notch conjigurations. It is expected that this work will have considerable importance for the problem of crack initiation at corners of openings in walls etc.
An assessment of the commercial prospects for fibre- and polymer-modified concretes
Authors: Pomeroy C. D.
Published: October 2009

Synopsis

The principal effects of fibres of various types and of polymers upon the properties of Portland cement pastes, mortars and concretes are discussed briefly, and possible applications are suggested in which the special properties of the modified cement-based materials may be exploited commercially. It is concluded that structural reinforced and prestressed concretes are unlikely to be replaced by fibre or polymer concretes. It is more likely that the viable applications will exploit properties, in either the fresh or the hardened states, that are peculiar to the particular fibres or polymers incorporated in the matrix. It is also suggested that sufficient research has already been undertaken to provide data on the effects of fibres and polymers upon concrete properties and that the major effort should now be directed to the development of saleable products rather than the acquisition of additional basic information.
The expanded hysteresis loop method for measuring the damping properties of concrete
Authors: Ashbee R. A. , Heritage C. A. R. , Jordan R. W.
Published: October 2009

Synopsis

A method of measuring the damping properties of concrete is described wherein the stress-strain or load-deflection hysteresis loop is electronically modified to make it easier to examine the loop or measure its area. The logarithmic decrement for concrete is typically about 0·05 (ranging from 0·03 to 0·15) giving a length: breadth ratio for the hysteresis loop of about 100:1. This is too elongated a figure to measure accurately or to study for loop characteristics. The electronic treatment is first to make the loop upright (i.e. parallel to the load axis) and then to amplify the width in the direction of deflection. Accuracy depends upon stable, accurate amplification, but this is not difficult for the structural frequencies of interest (< 5 Hz). The experimental techniques include the use of a very stiff, servo-controlled test machine to obtain accurate stress levels, frequency, waveform of loading, etc. and steel reference specimens are tested to eliminate machine errors. The method is claimed to be a significant step forward in the study of damping and is applicable to other hysteresis systems where the two parameters can be measured electrically.
Influence of aggregate volume concentration upon the workability of concrete and some predictions from the viscosity—elasticity analogy
Authors: Hobbs D. W.
Published: October 2009

Synopsis

A simple theoretical approach is used to obtain rheological equations for concrete. It is assumed that the cement-paste phase approximates to either a Newtonian fluid or a Bingham body. The approach used predicts that changes in aggregate volume concentration give rise to large changes in fluid viscosity yield value and plastic viscosity. It is shown indirectly by using the viscosity—elasticity analogy that the resulting equations are in good agreement with experimental results on concrete.
The ultimate moment of resistance of unbonded partially prestressed reinforced concrete beams
Authors: Tam A. , Pannell F. N.
Published: October 2009

Synopsis

Existing theories for the ultimate moment of resistance of partially prestressed unbonded concrete beams are unsatisfactory on two counts—either they are too tedious to be used (involving lengthy iterations at times) or they fail to take into consideration the span/depth ratio, which is an important factor. After reporting the results of tests on eight such beams, the paper puts forward a revised theory leading to a simple design method for the ultimate load analysis of beams of this kind. It is shown that the theory gives an accurate prediction of the ultimate strength of the test beams.
Marine floating concrete made with polystyrene expanded beads
Authors: Bagon C. , Frondistou-Yannas S.
Published: October 2009

Synopsis

The performance of concrete containing expanded polystyrene beads was studied in the context of marine floating structures and compared with that of concrete containing perlite, the latter being an ultra-lightweight aggregate used for marine applications. It was found that, for an equal density of about 80% that of sea water, polystyrene concrete has a compressive strength that is 50% higher, a modulus of elasticity 100% higher, and a modulus of rupture 25% higher than those of perlite concrete. Furthermore, polystyrene concrete is much more resistant to sulphate solutions than perlite concrete even though it is less resistant than normal-weight concrete.
The strength of restrained reinforced concrete columns—a new approach
Authors: Butler Donald J.
Published: October 2009

Synopsis

The aim of the work described in this paper is to present a new approximate method for estimating the strength of reinforced concrete columns in rigid framed structures. The method employs a deteriorating stiffness stability concept combined with a modified use of the conventional short-column moment-thrust interaction diagram. When compared with ‘exact’ computer-based solutions, the method is shown to predict failure loads very accurately (mean = 99%, coefficient of variation =4%) over a broad range of significant design parameters. The scope of the work is limited to symmetrical single-curvature, no-sway cases at this time, but the results obtained suggest that the method, when properly modified, can provide a good basis for treating more general problems as well.
A comparison of creep, elasticity and strength of concrete in tension and in compression
Authors: Brooks J. J. , Neville A. M.
Published: October 2009

Synopsis

A method of manufacturing a bobbin-shaped specimen for testing concrete in direct tension is described. Direct tensile strength is related to tensile and compressive strengths as determined by standard tests and their changes with age are described. Data on the modulus of elasticity in compression and in tension at two exposure conditions are given, and the influence of age upon creep and creep recovery is established. The differences in behaviour of strength, modulus of elasticity, creep and creep recovery are discussed by considering the effects of load and storage environment upon the adsorbed water of the cement paste, and the suggested creep mechanism is a combination of the seepage and viscous shear theories.
A low-cost creep rig for concrete
Authors: Cridland L. , Bakoss S. L. , Burfitt A. J.
Published: October 2009

Synopsis

A low-cost creep rig based on a commercially available flexible-diaphragm jack (flat jack) was developed by the authors. It was designed for creep tests on 380 × 130 × 130 mm specimens at a maximum load of 170 kN. A portable hydraulic hand pump is used with the flat jack to apply the load. Thirty rigs of this type have been used, six of them for continuing tests over a period of three years. The paper describes the methods used to calibrate the jack and shows that the rig is capable of maintaining a constant load to the accuracy required by the Australian Standard.
Predicting long-term creep and shrinkage from short-term tests
Authors: Brooks J. J. , Neville A. M.
Published: October 2009

Synopsis

On the basis of experimental results from creep and shrinkage tests lasting five years and data from other investigators, it is proposed that long-term deformations can be predicted within reasonable limits of accuracy from values measured at 28 days. The expressions given are sensibly independent of a wide range of the independent variables which affect creep and shrinkage of concrete.
The Behaviour of Bamboo-Reinforced Concrete Columns Subjected to Eccentric Loads
Authors: Cook D. J. , Pama R. P. , Singh R. V.
Published: October 2009

SYNOPSIS

Experimental and theoretical investigations to determine the characteristics of bamboo-reinforced concrete columns subjected to uniaxial and biaxial loads are described. Studies to establish the mechanical properties of the bamboo related to its use as a reinforcement are also described. Data on the behaviour of twenty-four columns, viz nine bamboo-reinforced concrete cotumns and nine unreinforced columns subjected to uniaxial load and six bamboo-reinforced concrete columns subjected to biaxial load, are given. The applicability of accepted methods for the prediction of the ultimate load of reinforced concrete columns subjected to uniaxial and biaxial loads is described and it is shown that, when cognizance is taken of the characteristics of bamboo, behaviour can be predicted with reasonable accuracy.
Osmosis as a cause of blistering of in situ resin flooring on wet concrete
Authors: Warlow W. J. , Pye P. W.
Published: October 2009

SYNOPSIS

Excessive water in concrete affects many flooring materials and leads to their early failure. In many cases the floorings are badly blistered, each blister containing an aqueous solution under compression. This paper suggests that the pressures that arise are most likely to result from osmosis. From theoretical considerations, concrete may be expected to act as a semi-permeable membrane. In a simple experiment, hardened cement paste and mortar were shown to act as such a membrane in an osmotic cell. The proposed mechanism helps to explain failures of flooring involving liquid pressures that could not have been generated by an external agency. A better understanding of the distribution and concentration of soluble salts in concrete is necessary to reduce the possibility of osmotic flow. As it is not possible to predict when conditions may lead to the formation of an active osmotic cell, as many sources of extraneous moisture as possible should be eliminated. On ground floors, therefore, the provision of a damp-proof membrane is essential to prevent ingress of ground moisture.
Computer experiments on slender beam—columns of reinforced concrete
Authors: Constantinescu Dan R. , Illston John M.
Published: October 2009

SYNOPSIS

A computer model is described which determines the behaviour under load of slender concrete beam—columns of uniform rectangular symmetrically reinforced cross-section. The various modes of deflection and failure are presented for both short-term and sustained load and the predicted results compared favourably with the results of laboratory tests. Computer experiments are reported in which the effects of various structural and material parameters are investigated. The parameters include the distribution of moment along the member, slenderness, the ratio of reinforcement, the cover to the steel, the design strengths of steel and concrete and the magnitude of concrete creep. The empirical CEB/FIP proposals for estimating the strength of slender members are corroborated by the results of the computer experiments.
The evaluation of resin systems for concrete repair
Authors: Tabor L. J.
Published: October 2009

SYNOPSIS

Although resins have been used for repairing concrete for many years, there is still a lack of convincing data about their performance in this role. This is largely due to the absence of a suitable test for evaluating the repair techniques. Details are given of a test which realistically appraises the effectiveness of the injection of resin into cracks, the repair of damaged concrete with resin mortars and the use of resin primers with fresh concrete. The test piece is a rectangular prism with either a diagonal repaired crack or a scarf joint between the original concrete and the repair material. It is subjected to compressive test and compared directly with an undamaged concrete prism of similar dimensions. Thus the repair is subjected to a high degree of shear and is appraised in the same simple terms of cube or prism strength with which the engineer assesses the quality of his original concrete.
An analysis of the ultimate strength of lapped joints of compression reinforcement
Authors: Cairns John
Published: October 2009

Synopsis

Bond failure of ribbed reinforcing bars generally takes place by splitting of the surrounding concrete cover, unless heavy confining reinforcement is present. The bond action of the bars must therefore exert a radial bursting force on the concrete cover, and so the ultimate strength of a lapped joint may be calculated by equating the bursting force produced by bond to the ultimate confining force on the lapped bars provided by the member. In this paper, expressions are derived for the relationship between the stress developed in a lapped bar and the resultant bursting force and they show that this depends mainly upon the strength of the concrete in the member and the deformation characteristics of the bar. The contribution made by bearing of the ends of lapped bars to the ultimate strength of compression laps is also evaluated. Values of lap strength calculated from the analysis are shown to be in good agreement with results obtained from tests on lapped joints in reinforced concrete columns.
Studies on prestressed concrete hollow beams in combined torsion and bending
Authors: Rangan B. V. , Hall A. S.
Published: October 2009

Synopsis

The results are reported of tests on fifteen hollow prestressed concrete beams tested in combined torsion and bending. The main variables are the wall thickness and the torquelmoment ratio. Equations are given for both the cracking strength and the ultimate strength.
Cracking of concrete cover along anchored deformed reinforcing bars
Authors: Tepfers Ralejs
Published: October 2009

Synopsis

The state of stress in the concrete due to bond forces from deformed reinforcing bars is analysed. For determination of the cracking resistance of the concrete cover, a concrete ring model is used. The stresses are calculated for an elastic stage, a plastic stage, and an elastic stage with internal ring cracks. The appearance of the concrete cover cracks along the deformed bars in the bond zones for normal cover thickness can be determined by using the mean of the values obtained for the two last stages. The partly cracked elastic stage gives cracking loads just on the safe side.
Interaction of casting and mould surfaces in slip-form technology
Authors: Reichverger Z.
Published: October 2009

Synopsis

Friction and adhesion between concrete and form surfaces during the first hours of contact determine the shifting process in slip-form technology and are also of interest in processes involving immediate stripping and in the transportation of ready-mixed concrete. Experimental data are presented on the behaviour of hardening mortar (as a part of concrete obviously coming in contact with mould surfaces) with different mould materials in terms of friction and normal and tangential adhesion, including the aspect of surface cleanliness. These results make it possible to determine the forces required for overcoming adhesion in normal and tangential shifting of the form, and to recommend facing or coating agents for slip-form panels. The results, obtained in small laboratory tests, were then checked by casting 0·15 × l·0 × 2·5 m wall panels in a part of a slip-form.
Biaxial strees–strain relationships for concrete
Authors: Tasuji M. Ebrahim , Nilson Arthur H. , Slate Floyd O.
Published: October 2009

Synopsis

On the basis of experimental results reported more fully elsewhere, a stress-strain relationship is proposed for plain concrete that is applicable to all combinations of biaxial tension and compression. The proposed equation accounts for both non-linear and orthotropic behaviour of concrete. Also based on experimental results, a biaxial ultimate strength criterion is proposed for concrete in the form of a failure stress envelope. The proposed equations are given in a form such that they may be incorporated readily in plane-stress analysis of reinforced concrete using the finite-element approach.
Punching shear strength of concrete slabs subjected to in-plane biaxial tension
Authors: Johnson R. P. , Arnaouti C.
Published: October 2009

Synopsis

It has been found in three tests that in-plane biaxial tensile strains up to 0·0017 cause no reduction in the strength in punching shear of a reinforced concrete slab 90 mm thick. The test results are compared with the predictions of the recent Bridge Code (BS 5400) and of plastic theory.
Thermoluminescence test for fire-damaged concrete
Authors: Placido Francis
Published: October 2009

Synopsis

A new test of fire damage in concrete is proposed based on the technique of thermoluminescence. The thermoluminescence signal remaining in samples of sand extracted from concrete structures is shown to be an indicator of probable fire damage in concrete exposed to temperatures in the range of300°–500°C. The thermoluminescence test is shown to be easy to apply, to require only small samples and to be a more objective test than those in current use where reinstatement is being considered. An important feature of the proposed test is that it is sensitive to the thermal exposure experienced by the concrete rather than just the maximum temperature reached.
Results of a ‘round robin’ thermal conductivity test organized on behalf of the British Standards Institution
Authors: Spooner D. C.
Published: October 2009

Synopsis

A ‘round robin’ series of thermal conductivity tests has been carried out under the auspices of BSI subcommittee RHE 9/2. Three sets of pre-conditioned specimens were circulated to a number oflaboratories with an interest in thermal conductivity testing of masonry materials. The only measurements made at each laboratory were of the dimensions, weights and thermal conductivity of the specimens. Consequently, the results only reflect those sources of variability, specimen preparation and conditioning being deliberately excluded. The measurements of thermal conductivity reported by the laboratories vary quite considerably and, it is suggested, the causes of the variations need further study.
Reinforcement stresses in a reinforced concrete beam–column connection
Authors: Allwood R. J.
Published: October 2009

Synopsis

The stresses in the tensile reinforcement of a beam passing through a wide column have been measured in a model experiment and compared with those expected by practising engineers and those obtained from finite element analyses.
Effect of cover upon the stress–strain properties of concrete confined in steel binders
Authors: Gangadharam D. , Reddy K. Nagi
Published: October 2009

Synopsis

Cover to the stirrups in reinforced concrete structures is one of the important parameters in the theory of confined concrete, On the basis of experimental results, a new term ‘effective confinement index’ is introduced. The expressions for increase in maximum stress and the corresponding strain in terms of effective confinement index are given. Theory is developed to obtain the stress–strain curve of total condtere with confined core and unconfined cover. The experimental and analytical stress–strain curves are compare. Also the maximum stresses and the corresponding strains of shell concrete are compared with the results obtained by the theory of sargin et al.
The strength of the concrete in composite reinforced concrete beams in hogging bending
Authors: Taylor R. , Al-Najmi A. Q. S.
Published: October 2009

Synopsis

The concrete in the compression Zone of a composite reinforced concrete beam loaded in hogging bending is subjected to a complex multi-axial stress system which enables it to withstand much higher longitudinal stresses and strains than is possible in normal reinforced concrete. This paper attempts to assess the ultimate average compressive stresses attained in such beams, the results indicating stresses of the order of three times those in normal reinforced concrete. Hypotheses explaining the confining forces are suggested.
The effect of pulverized-fuel ash upon the workability of cement paste and concrete
Authors: Hobbs D. W.
Published: October 2009

Synopsis

It is assumed that cement paste approximates to a Bingham fluid. It is shown that this assumption leads to predictions which are in general agreement with reported workability data obtained on concretes in which different ratios of ordinary Portland cement to pulverized-fuel ash were used.
Optimal limit state design with unbonded prestressing tendons
Authors: Marro Piero
Published: October 2009

Synopsis

This paper explores the theoretical behaviour of concrete structures prestressed by means of unbonded tendons according to the CEB-FIP ‘Model Code for concrete structures’. The subject matter is dealt with analytically. The study comprises two parts: the first deals with sections containing unbonded prestressing steel only, the second investigates structures having traditional bonded reinforcement in addition to unbonded tendons. In both cases, diagrams and tables have been provided to facilitate optimal design. To make the scope of the investigation as general as possible, the calculated values have been obtained, or at least presented, in non-dimensional terms. A detailed design example is given in the Appendix.
The conduction of electricity through concrete
Authors: Whittington H. W. , McCarter J. , Forde M. C.
Published: October 2009

Synopsis

This paper examines the relationship between mix proportions, electrical properties of the constituents of concrete and the over-all electrical resistivity for concrete. The mechanisms for the conduction of electricity through the heterogeneous medium of concrete are discussed and an electrical model is proposed. Analysis from a purely theoretical standpoint is also described and the values of electrical resistivity obtained experimentally are shown to compare favourably with the theoretical model.
Discussion: The alkali2–silica reaction2—a model for predicting expansion m mortar
Authors: Hobbs D. W.
Published: October 2009

Synopsis

Data are presented which illustrate the influence that reactive aggregate content, mix proportions and cement alkali content have upon the time to cracking and upon the subsequent expansion of mortar specimens stored in water at 20° C. It is shown that an assumption that the alkali-silica reaction is a two-stage process leads to predictions which are in general agreement with the observed expansion behaviour of mortars.
Concrete coating for submarine pipelines
Authors: Palmer A. C.
Published: October 2009

Synopsis

A submarine pipeline is usually externally coated with reinforced concrete, the function of which is to protect the corrosion coating against impact damage, and give the pipe additional weight to stabilize it on the sea bed. There are unusual requirements in design and application technology. The paper examines the current state of knowledge and practice and the development of more stringent specifications as a result of North Sea experience. It goes on to consider research needs, among them rational design methods and the development of coating concrete with improved resistance to impact, abrasion and bending.
Flexural tests of steel-concrete open sandwiches
Authors: Ong K. C. G. , Mays G. C. , Cusens A. R.
Published: October 2009

Synopsis

A potential method for reducing the weight of the roadway deck on medium- to long-span composite bridges is to use an open steel-concrete sandwich. This consists of a concrete core which is cast against a steel plate, the necessary shear connection being provided by epoxy resin adhesive. Open sandwich beams and slabs constructed in this manner have been appraised by testing over spans of 1·8 and 0·9 m, respectively. Then carried loads equivalent to wheels of an HB vehicle with an adequate safety margin, and current designprocedures generally underestimated both theirflexuraland shear strengths.
FRP-encased concrete as a structural material
Authors: Fardis Michael N. , Khalili Homayoun H.
Published: October 2009

Synopsis

Plastics reinforced with continuous glass fibres have outstanding tensile strength in the fibre direction and excellent corrosion resistance, but are characterized by low modulus and low compressive strength. It is proposed to develop composite members in which a prefabricated FRP (fibreglass-reinforced-plastic) casing is used initially as the form to cast plain concrete, and thereafter to confine the concrete, act as tensile reinforcement and provide corrosion protection. Significant cost savings are possible with the proposed combination of materials, especially in exposed structures, such as bridges. An experimental investigation of FRP-encased concrete cylinders in axial compression and of rectangular FRP-encased beams in bending is presented. The results demonstrate the excellent strength and ductility characteristics of FRP-encased members. The behaviour of circular FRP-encased concrete beam-columns is described also, in terms of analytically obtained moment-axial-load and ductility-axial-load interaction diagrams and moment-curvature relations. The weathering characteristics and the fire resistance of the FRP are discussed, and measures to improve these environmental properties are reviewed.
Long-term deflections of reinforced concrete beams
Authors: Bakoss S. L. , Gilbert R. I. , Faulkes K. A. , Pulmano V. A.
Published: October 2009

Synopsis

Long-term static load tests were carried out on simply supported and continuous reinforced concrete beams at the N.S.W. Institute of Technology, Sydney, Australia. The instantaneous and time-dependent beam deflections were recorded, together with the time-varying strain distributions at selected cross-sections and the redistribution of bending moments due to creep and shrinkage. In this paper, the measured beam deflections are compared with values predicted by British and American design code methods and by finite element methods. The creep and shrinkage properties used in the predictions were obtained from test specimens and were also calculated in accordance with CP 110:1972, AS 1481–1978, ACI 209:1971 and the CEB–FIP 1978 Model Code. For the samples of concretes examined, the applicability of these predictive methods is discussed.
The effect of pfa upon alkali-aggregate
Authors: Gaze M. E. , Nixon P. J.
Published: October 2009

Synopsis

The effect of pulverized-fuel ash (pfa) upon the expansion of mortar bars containing Beltane opal and stored at 38°C has been investigated. The alkali level in the mortar bars was kept constant in order to eliminate the effects of alkali dilution by the pfa. The expansion was found to be reduced ut all levels of pfa substitution and when 20 and 30% pfa was present there was very little expansion at all. The reduction in expansion when the alkali level is reduced was also demonstrated in a parallel series of experiments.
The dependence of punching resistance upon the geometry of the failure surface
Authors: Regan P. E.
Published: October 2009

Synopsis

Punching tests were made on forty concrete slabs with the distances between loads and supports short enough for the shapes of the failure surfaces to be defined by specimen geometry. The results obtained are used to derive a simple empirical expression for punching strength in terms of the geometry of the failure cone. The empirical expression is shown to be similar to the results of a plastic analysis and the relationship of the results to the design of more normal slabs is discussed briefly.
Impact behaviour of prestressed concrete beams in flexure
Authors: Hughes B. P. , Mahmood A. T.
Published: October 2009

Synopsis

Predicting the impact performance of prestressed concrete beams can be greatly facilitated if the energy absorption under impact is related to the energy absorption under static loading. Model beam tests are described which investigate the deformational behaviours under static and impact loads and the total work done bring a member to the same limiting damage or deflection due to either type of load. Design charts, based the model test results, suitable for predicting the performance of beams subjected to flexural impact loads then presented.
Creep and shrinkage in a lightweight-aggregate concrete
Authors: Arnaouti C. , Sangakkara S. R.
Published: October 2009

Synopsis

A model is presented for the determination of the creep and shrinkage of a large reinforced concrete structure from the shrinkage data of a small plain concrete prism. The method is based on the linear relationship between drying creep and concurrent shrinkage and the relationship between drying shrinkage and the exposed area to volume ratio of a concrete specimen. This model was developed to obtain time-dependent properties of concrete slabs for the non-linear finite element analysis of restrained concrete slabs. Results obtained from the creep and shrinkage model and conclusions are also presented.
The influence of lateral pressure upon anchorage bond
Authors: Robins P. J. , Standish I. G.
Published: October 2009

Synopsis

This paper examines the effect of lateral pressure upon the anchorage bond behaviour of both plain and deformed reinforcing bars in lightweight-aggregate concrete. Two common bond tests, the cube pull-out and the semi-beam tests, were modified that lateral pressures could be applied to the bond specimens. The major variables studied were the magnitude of the lateral pressure, the bar diameter. the length of embedment and the concrete strength. The results of over 200 bond tests show that for plain bars the application of lateral pressure can result in an increase in pull-out load of over 250%, whilst for deformed bars of similar size the corresponding increase is about 75%. The different bond mechanisms for plain and deformed bars were highlighted by the failure modes of the bond specimens; this difference in behaviour is rejected in the theoretical work by a frictional bond strength criterion for plain bars and a splitting or shearing criterion f or deformed bars.
Superplasticized flowing concrete: strength and deformation properties
Authors: Dhir Ravindra K. , Yap Andrew W. F.
Published: October 2009

Synopsis

This is the third and final paper from a wide-ranging investigation undertaken into superplasticized high workability concrete. The properties described are those of strictly flowing concrete in the hardened state and include: compressive strength, drying shrinkage, thermal expansion, elastic deformation, creep, creep recovery and post-creep-recovery elastic deformation and strength. It is shown that flowing concretes made with superplasticizers of categories A and B exhibit similar properties. In comparison with the corresponding normal concrete, flowing concrete, for a given strength, is likely to require a slightly higher cement content, it exhibits higher shrinkage, slightly higher elastic modulus and lower creep, whilst its creep recovery and post-creep-recovery elastic deformation and strength properties are generally comparable. With regard to the various mix, curing and testing parameters considered, both normal and flowing concretes appear to respond in a similar manner for the properties studied.
Uniaxial tensile fatigue failure of concrete under constant-amplitude and programme loading
Authors: Cornelissen H.A.W. , Reinhardt H.W.
Published: October 2009

Synopsis

Uniaxial repeated-tension and tension-compression tests on plain concrete are described. The results are presented as S—N diagrams and in the form of a modified Goodman diagram. Stress reversals appeared to reduce life significantly. By a statistical treatment, the influence of scatter in the static strength upon the fatigue results was ascertained. To avoid the effect of this scatter, cyclic creep rate was evaluated to predict life more accurately in constant-amplitude tests as well as in programme loading tests. With this procedure for programme loadings, no significant sequence effect of the loading blocks was observed in the resulting Miner sums. Miner's number M = 1 proved to be a safe failure criterion in general.
Effect of specimen and crack sizes, water/cement ratio and coarse aggregate texture upon fracture toughness of concrete
Authors: Nallathambi P. , Karihaloo B. L. , Heaton B. S.
Published: October 2009

Synopsis

Tests were performed on cement mortar and concrete beams, in two stages, with a view to studying the influence of several specimen and mix variables upon the fracture behaviour of concrete. On the basis of the results from the first stage of tests, in which a single water/cement ratio and type of coarse aggregate were used, a simple formula was established to estimate the fracture toughness of concrete in terms of specimen dimensions, maximum aggregate size and notch depth, together with the mix compressive strength and modulus of elasticity (determined from separate standard cylinder tests). It was found to predict, with sufficient accuracy, the results from the second stage of tests in which, besides variation of the type of coarse aggregate and water/cement ratio, some of the specimen sizes were outside the range used in the first series.
Physical characterization of UK pulverized-fuel ashes for use in concrete
Authors: Dhir Ravindra K. , Jones M. Roderick , Munday John G. L. , Hubbards Frederick H
Published: October 2009

Synopsis

The characteristics of pfa to BS 3892:Part I and their possible effects upon concrete are examined by using supplies from 26 sources in the UK. Fineness identified as giving an over-all measure of ash quality and is used to propose a four-part classification to provide a realistic basis for ash utilization in concrete.
Transient thermal strain of concrete: literature review, conditions within specimen and behaviour of individual constituents
Authors: Khoury Gabriel A. , Grainger Brian N. , Sullivan Patrick J. E.
Published: October 2009

Synopsis

This is the first of three papers presenting the results of an investigation into the effect of material and environmental factors upon the transient thermal strain behaviour of concrete during the first heat cycle under load to 600°C. A literature review of transient thermal creep of concrete is presented. It reveals inadequate understanding of this subject for temperatures above 100°C and a lack of data for conditions pertinent to the analysis of concrete structures during first-time heating. This paper also presents results of preliminary work forming background information for the analysis of the transient thermal strain behaviour of unsealed concrete specimens. The complex temperature, moisture and thermal stress conditions developing during thermal transients in concrete test specimens have, therefore, been investigated experimentally and/or theoretically. The ‘structural’ effects and modification of material behaviour caused by these conditions have consequently been minimized by appropriate design of experiment. Characteristics of the individual aggregate and cement paste constituents have been determined by dilatometry, DTA and TGA tests which showed aggregate thermal stability to be a critical factor.
Application of the highly stressed volume approach to correlated results from different tensile tests of concrete
Authors: Torrent R. J. , Brooks J. J.
Published: October 2009

Synopsis

The highly stressed volume (HSV) approach is considered for relating tensile strength of concrete as determined by a range of test methods and a range of loading configurations with various sizes of specimen. The paper demonstrates that the approach explains the effect of specimen size of geometrically similar specimens upon tensile strength as determined by a given method. However, the HSV approach alone does not correlate the different values of tensile strength as yielded by various methods of test.
Strain of concrete during first heating to 600°C under load
Authors: Khoury Gabriel A. , Grainger Brian N. , Sullivan Patrick J. E.
Published: October 2009

Synopsis

This is the second of three papers presenting the results of an investigation into the transient thermal strain behaviour of concrete during the first heat cycle to 600°C under load. The results during first heating to 600°C under uniaxial compressive load of eight different unsealed concrete andcement paste mixes are presented. The thermal strains were shown to consistof ‘free’ and ‘load-induced’ components which possessed different and distinct properties. The free thermal strains of the unloaded concretes were dominated by the thermal expansion of the constituent aggregate, whilst the load-induced thermal strains (LITS) were identical for temperatures up to about 450°C, irrespective of type of aggregate used, provided certain criteria were met. A ‘master’ LITS curve therefore existed which represented LITS of Portland-cement-based concretes in general. Also LITS was not significantly influenced by the age of the concrete (1 and 9 years) or the initial moisture condition (moist and air-dry). These findings could considerably simplify the analysis of heated concrete structures, particularly since only two strain components are required. Replicate tests were performed to provide a statistical basis for analysis of the results. The effect of aggregate restraint was determined by comparing results from concrete and cement paste specimens. In addition to ‘material’ factors, the effects upon free and load-induced thermal strain of the following ‘environmental’ parameters were examined: temperature level, initial moisture conditioning, preheating, rate of heating and stress level.
Punching shear of steel-concrete open sandwich slabs
Authors: Ong K. C. G. , Mansur M. A.
Published: October 2009

Synopsis

An experimental programme was conducted on simply supported, two-way epoxy-bondedsteel-concrete open sandwich slabs under a central patch load. The major parameters of the study were the method of surface preparation for the steel plate, size of patch load, grade of concrete and thickness of concrete topping. The results of twelve slabs tested in this programme are presented and discussed. On the basis of the test data, a modijication to the existing plastic theory for conventional reinforced concrete is suggested for the design of open sandwich slabs against punching shear failure.
The effect of phenol upon concrete
Authors: Smith M. A.
Published: October 2009

Synopsis

Phenols are common contaminants of sites used for coal carbonization (e.g. for town gas manufacture, coking plants and tar works). Phenol itself (C6H5OH is reported to be detrimental to concrete, but no quantitative data are available. The paper describes the results up to two years of a series of tests carried out on 100 mm cubes immersed in phenol solutions of varying concentrations. It is concluded that concentrations of phenol as low as 0·2% by volume have an adverse efect upon the developmen of the compressive strength of concrete and that concentrations as low as 0·1 % may be detrimental. Concentrations of phenols of this order may sometimes be encountered onsites used for coal carbonization.
Strength gain and calcium hydroxide depletion in hardened cement pastes containing fly ash
Authors: Marsh B. K. , Day R. L. , Bonnery D. G.
Published: October 2009

Synopsis

Hardened cement paste specimens, with and without partial replacement of the cement by fly ash, were cured f o r various ages up to one year at temperatures 20-80°C. Compressive strength, calcium hydroxide content and porosity, by mercury intrusion porosimetry, were measured as curing proceeded. Results indicate that elevated curing temperature accelerates the pozzolanic reaction to a greater extent than the normal hydration reactions of Portland cement. When elevated temperatures are used, the strength of fly ash pastes may surpass that of plain pastes at early ages. Strength degradation was observed in pastes cured at the higher temperatures; this degradation was more pronounced in the plain pastes.

Consumption of calcium hydroxide with no corresponding gain in strength, or with a reduction in strength, was observed for ash-pastes cured at 50°C and above. Changes in mercury porosity, on the other hand, correlate well with changes in strength during the early strength-gain periods and also during the later strength-degradation periods.
Strain of concrete during first cooling from 600°C under load
Authors: Khoury Gabriel A. , Grainger Brian N. , Sullivan Patrick J. E.
Published: October 2009

Synopsis

This is the third of three papers presenting the results of an investigation into the transient thermal strain behaviour of concrete during the first heat cycle to 600°C under load. The strains measured during the first cooling of concrete from 600°C are presented here, together with the results of residual compressive strength and elastic modulus tests. These are analysed with reference to the complete thermal cycle and constituent materials property data already given in the two previous papers. Strains during first cooling were primarily influenced by the thermal strain of the coarse aggregate and were unaffected by initial moisture content (as-cast, air-dry or pre-dried at 105°C), heating rate (0·2 or 1°C/min) or concrete age (1 year or 9 years). The applied load level did not affect the cooling strains of concretes with the more thermally stable aggregates of basalt or sintered pulverized-fuel ash, or the siliceous gravel concrete despite the extensive cracking it suffered during heating. This indicated the absence of transient creep during cooling and also the insignificance of any thermal stress effects for the specimen size and cooling rates used, The thermal expansion of limestone aggregate during heating contained an irreversible component which created sufficient differential cooling strain between cement paste and aggregate to cause cracking on cooling. The degree of cracking reduced with increasing levels of applied compressive load (0–30% of the initial unheated strength). The residual strain results represent the sum of all irrecoverable contractions and expansions, during the thermal cycle. These include shrinkage and load-induced thermal strain (LITS) during first heating and the effects of any cracking on cooling. From this work, the residual contractions of the loaded specimens can be successfully predicted by a simple superposition of all irrecoverable strains developed during the thermal cycle. The effect of temperature upon elasticity was dependent upon whether or not the concrete was loaded during the thermal treatment. For loaded concretes tested hot after a heating-cooling-heating cycle, the elastic strain response changed little between 100°C and 600°C compared with the free thermal strain (FTS) and LITS. For concretes tested cold after heating under load but cooling unloaded, the elastic strains increased with temperature level. Residual compressive strength of all the concretes was a function of the load level during the thermal cycle. The residual strength of specimens initially heated at 0.2°C/min was less than that of specimens heated at 1.0°C/min. This indicated that longer time at temperature was more influential than possible structural' effects due to spatial temperature variations in the specimens during heating.
Anchorage of welded wire fabric used as shear reinforcement in beams
Authors: Mansur M. A. , Lee C. K. , Lee S. L.
Published: October 2009

Synopsis

In this paper, welded wire fabric bent into a U shape is considered as web reinforcement in beams, the necessary anchorage at its open ends being furnished by welded cross wires. About 70 pull-out tests were made to investigate the influence of various parameters that affect the anchorage. Four simply supported over-hanging beams were also tested to evaluate the upper anchorage located in the tension and compression zones of the beam and to study their cracking behaviour and ultimate strength. Test results indicate that welded cross wires can provide adequate anchorage if certain restrictions on the relative size and spacing of these wires are followed, and the beams can attain the desired shear capacity. The use of deformed welded wire fabric signlficantly improves the cracking characteristics of a beam by comparison with an equivalent amount of smooth welded wire fabric.
Anchorage zones in prestressed concrete members
Authors: Fenwick R. C. , Lee S. C.
Published: October 2009

Synopsis

In an anchorage zone of a post-tensioned concrete member tensile stresses are induced in different localities. The way in which these arise is briefly discussed. A series of simple anchorage zone tests is reported, in which the forces resisted by reinforcement placed to resist bursting tensile forces were monitored. The test results together with a series of finite analyses show that once a bursting crack forms the resultant loss of transverse stlflness in the member leads to a decrease in the magnitude of the bursting force and a change in its location. A method of assessing the magnitude of this force once a crack has formed is presented.
Indirect and non-destructive methods for assessing abrasion resistance of concrete
Authors: Sadezadeh Massud , Kettle Roger
Published: October 2009

Synopsis

Three non-destructive test methods have been investigated to determine their suitability as indirect methods for assessing the abrasion resistance of concrete slabs. The ultrasonic pulse velocity technique was not found to be sufficiently sensitive to variation in the concrete mix design. The surface hardness method, using the Schmidt rebound hammer, was found to be partially sensitive to factors which are known to influence the abrasion resistance of concrete. The initial surface absorption method was found to be very sensitive to these factors and was closely related to abrasion resistance of concrete as determined by an accelerated abrasion test.