bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of loading history upon the compressive properties of concrete
Authors: Cook D. J. , Chindaprasirt P.
Published: October 2009

Synopsis

The influence of sustained and cyclic load histories upon the compressive properties of concrete, mortar and paste are reported. It is shown that the effects of a sustained load produce asmall increase in strength and a relatively large increase in stifiess, whereas cyclic loading results in a small decrease in strength and a relatively large decrease in stifiess. Both load histories decrease the strain at peak stress on reloading. It is proposed that sustained loads result in redistribution of stress concentrations in the cement paste and consolidation in the gel. Cyclic loads, on the other hand, produce limited microcracking. The hypothesis is supported by the substantially greater damage observed in the specimens subjected to a cyclic load and the higher specific creep, which other researchers have shown to be largely irrecoverable.
Bond stress along lapped reinforcing bars
Authors: Tepfers Ralejs
Published: October 2009

Synopsis

The state of stress along a lapped splice in reinforced concrete can be determined by using the modulus of displacement theory. The theory is based on actual displacement or local deformations in the bond zone near the surface of the reinforcement. The stresses along the anchorage length can also be estimated with moment cracks taken into account. Special attention must be paid to cracks in the cover along the reinforcement. In practice, however, the simpler equations with the concrete acting just as an adhesive between the lapped bars gives reasonable results. By using this theory, formulae can also be evaluated for other types of bond anchorage.
Assessing the strength of in situ Portland cement concrete by internal fracture tests
Authors: Chabowski A. J. , Bryden-Smith D. W.
Published: October 2009

Synopsis

The results of a programme of about 1500 internal fructure tests performed on ordinary Portland cement concrete to assess its compressive strength are reported. The influence of the type and size of uggregate upon the test results is examined as well as the effect of precompression of the concrete. The variability of the data was assessed statistically to derive relationships between the results of internal fructure tests, i.e. the indicated maximum torques and cube strength US a basis for estimating the compressive strength of in situ concrete. Considerations affecting the use of internal fracture tests as a means of assessing the strength of concrete in structures in service are briefly discussed.
The flexural strength of concrete blockwork
Authors: de Vekey R. C. , West H. W. H.
Published: October 2009

Synopsis

The results of a large number of flexural strength tests on wallettes (small masonry panels for testing) made with a range of commercially available concrete blocks are reported. The relationships between the performance of the wallettes and several properties of the block were investigated as a possible basis for a table of characteristic flexural strength values in BS 5628: Part 1: 1978, ‘the Code of Practice for Structural use of masonry’. In general, the basis chosen, compressive strength, and the levels set in the Code are satisfactory but the margins of safety may be lower for masonry made with some types of blocks and for thicker walls. Interim results for full-size walls are also given which confirm the trends indicated by the tests on wallettes.
Analysis of fresh concrete: determination of cement content by the Rapid Analysis Machine
Authors: Dhir Ravindra K. , Munday John G. L. , Ho Nyok Yong
Published: October 2009

Synopsis

The effects of several practical aspects of Rapid Analysis Machine (RAM) testing of freshly mixed concrete for its cement content are described. It is demonstrated that the RAM is capable of giving sufficiently reliable results, provided it is properly maintained throughout and used with care by a trained person. The repeatability of the RAM results was found to be better than that of results from the current BS 1881 test for analysis of fresh concrete. The RAM results are also less variable than the conventional 28 day strength results.
Bending–torsion interaction for concrete beams reinforced with steel fibres
Authors: Mansur M. A.
Published: October 2009

Synopsis

Results from an experimental investigation on steel-fibre-reinforced concrete beams under combined bending and torsion are presented, the principal variables being depth of beam and torsion to moment ratio. On the basis of the observed skew-bending mechanism of torsional failure, equations are derived for ultimate torque. The test results are then compared with the theoretical predictions. The proposed method gives good predictions of the ultimate torque and interaction behaviour of beams under combined bending and torsion.
The anchorage capacity of reinforcing bars at normal and high temperatures
Authors: Hertz Kristian
Published: October 2009

Synopsis

The anchorage failure of reinforcing bars is analysed, and it is shown that two modes of failures are possible: splitting or bond failure. It is concluded that the anchorage capacity cannot be estimated by means of a standard specimen, since splitting failure is dependent upon the geometry of the cross-section. A simple method for calculating the resistance to splitting is proposed, and a test method for determining the bond strength is presented. Test results are shown from a series of 280 specimens exposed to various maximum temperatures, and a relation between the bond strength and the ultimate limit stress of concrete under plane strain conditions is indicated. The influence of high temperatures upon the anchorage resistance is explained, and the theory is illustrated by examples.
Some properties of concrete containing sintered domestic refuse as a coarse aggregate
Authors: Wainwright P. J. , Boni S. P. K.
Published: October 2009

Synopsis

An artificia1 aggregate has been produced by pelletizing and firing the residues collected from incinerators used to burn domestic refuse. Tests on concretes made with this material as a coarse aggregate have been carried out forperiods of up to 4% years. The properties tested include compressive and tensile strength, modulus of elasticity, shrinkage and creep. The results so far obtained would appear to indicate that, under laboratory conditions, the material performs in a satisfactory manner. Although the material is not commercially available at the moment, it may be possible to produce it at a cost which would make it no more expensive than many lightweight aggregates currently on the market.
Tests on superplasticizing admixtures for concrete
Authors: Roberts M. H. , Adderson B. W.
Published: October 2009

Synopsis

The performance in concrete of nine commercial superplasticizing admixtures has been examined by using a particular test procedure to evaluate their performance and to provide comparative data on their effects. All the superplasticizers were observed to have an appreciable fluidifying action in fresh concrete so that, under appropriate conditions, they either considerably improved its workability at normal water content or permitted a water reduction of at least 10% to be made while maintaining normal workability. For very-high-workability concrete deficient in fine material, or with exceptionally high additions of superplasticizer, excessive bleeding and segregation of the fresh concrete occurred, resulting in its rejection. Some superplasticizers also tended to increase the air content of concrete and/or to have a retarding influence upon its setting and hardening characteristics; these effects produced a reduction in compressive strength in some circumstances. For water-reduced superplasticized concretes with air contents below 3%, the compressive strength values obtained at ages from 7 days to 2 years exceeded those to be expected from water reduction alone. Concretes containing super-plasticizers and with appropriate entrained air contents showed a high resistance to freezing-and-thawing actions under wet conditions.
The electrical response characteristics of setting cement paste
Authors: McCarter W. J. , Curran P. N.
Published: October 2009

Synopsis

The objective of the work presented in this paper is to investigate the changes in the electrical properties of cement paste during the first 24 hours after gauging with water. It is demonstrated that the electrical response characteristics of setting cement paste can be used as an effective means of studying the progress of cement hydration and for monitoring structuralchanges occurring within the paste
Radial temperature distributions within solid concrete cylinders under transient thermal states
Authors: Khoury Gabriel A. , Sullivan Patrick J. E. , Grainger Brian N.
Published: October 2009

Synopsis

Radial temperature gradients develop within typical concrete test cylinders during heating and can introduce structural effects which distort the material strain response of the concrete. Analytical solution of the Fourier equation, assuming infinite specimen length and invariable material properties, indicates that the maximum radial temperature difference (ΔT) obtained during heating at constant rates is directly proportional to the rate of heating and the square of the radius, and inversely related to the thermal diffusivity. A finite difference solution for a specimen heated on all sides confirms these relationships and indicates that the temperature at the centre is unaffected by end heating for a specimen length/diameter ratio greater than 1–1·5 during heating at 1°C/min. This is confirmed experimentally for gravel and lightweight concrete specimens. The effect of variations in thermal diffusively is to cause two peaks in the ΔT versus surface temperature relationship at about 160°C and 550°C corresponding to the processes of moisture loss and dissociation of Ca(OH)2 respectively. A weighted average temperature was calculated which suggests that the most suitable location to place a thermocouple to measure the average specimen temperature is at 58% of the radius. Radial temperature dlfferentials can be minimized by reducing the rate of heating and particularly the radius of the specimen. They can also be estimated by a simple relationship which, if used in conjunction with the specific test technique reported here, can provide an evaluation of the thermal diffusivity of materials.
Fracture toughness testing by means of the compact compression test specimen
Authors: Barr B. I. G. , Sabir B. B.
Published: October 2009

Synopsis

The paper describes an experimental and numerical study of the compact compression test specimen for determining the fracture toughness of concrete. A range of cubes and prisms was used in the study and the best results were achieved by means of the double-notched 100 mm and 150 mm cubes. The fracture toughness of the concrete used in the study was 0·5 MN/m3/2 and the results were shown to be independent of the test specimen geometry.
New technique for determining the electrical resistivity of concrete
Authors: Hughes B. P. , Soleit A. K. O. , Brierley R. W.
Published: October 2009

Synopsis

An improved method for measuring the electrical resistivity of concrete has been developed which eliminates difficulties due to polarization efsects and capacitive reactance. Typical results for fresh and hardened concrete obtained with the proposed technique are also presented and compared with results using more conventional techniques
Mathematical models for dowel action under monotonic and cyclic conditions
Authors: Vintzēleou E. N. , Tassios T. P.
Published: October 2009

Synopsis

On the basis of physical models describing the behaviour of dowels embedded in concrete, formulae for the prediction of dowel strength under monotonic actions are derived. In addition, formulae for calculating transverse displacements corresponding to the dowel strength are given. Theoretical values of dowel strength calculated according to equations given in this paper are compared with experimental dowel strengths reported in the literature. It is found that the proposed formulae give good predictions for both failure mechanisms (concrete crushing and yield of the bar or concrete splitting). Additionally, a formalistic model for full displacement reversals, based on the results of an experimental programme, is proposed.
Durability tests on building mortars — effect of sand grading
Authors: Harrison W. H.
Published: October 2009

Synopsis

Results are reported on a laboratory investigation into the properties and performance of mortar under simulated severe exposure, Six different sands varying from very coarse to very fine were used in OPC mortars plasticised either with lime or an air-entraining agent. Test specimens were produced by laying mortar between either wet or dry bricks and then removing the mortar bed after 24 hours. The properties of the fresh and the hardened mortar were measured.

In the new durability test small pieces cut from the mortar bed were subjected to 25 wet/dry cycles. Freeze/thaw was introduced to the cycle for some of the specimens and some were subjected to wetting with sulphate solution. The results show the effect of sand grading and brick suction on the properties of the mortar and its durability. Mortars subject to little or no suction from the bricks when layed showed poorer strength and lower durability than those subject to suction. The sulphate resistance did not appear to be related to the grading of the sand used in the mortar although for many of the mixes the strength and frost resistance was reduced with the more finely graded sands.
Symmetric punching of reinforced concrete slabs
Authors: Regan P. E.
Published: October 2009

Synopsis

The paper reports punching tests on 28 reinforced concrete slabs. The tests were divided into five series primarily concerned with the effects of the arrangement of flexural reinforcement, absolute size or depth, concrete strength and ratio of reinforcement, boundary restraint and the size of the loaded area. The results are compared with the predictions of four Codes of Practice-BS 8110, CP 110, ACI 318-83 and the CEB-FIP Model Code. In regard to BS 8110 it is demonstrated that the Code generally gives a small scatter of the ratio of calculated and experimental strengths, although its method of defining the ratio of flexural reinforcement is inferior to that of CP 110. It is also shown that BS 8110 does not achieve the level of safety intended in the definition of characteristic strength. If the ddefinition of the ratio of reinforcement were improved, the intended level of safety could be attained by a 10% reduction in either the basic shear stress or the size factor ξS.
Effect of exposure time and rates of heating and cooling on residual strength of heated concrete
Authors: Mohamedbhai G. T. G.
Published: October 2009

Synopsis

The paper describes tests on 100 mm concrete cubes heated to temperatures in the range of 200–800°C to determine the effect of varying time of exposure and rates of heating and cooling on the residual compressive strength of concrete. These variables were found to have a significant effect on concrete heated to the lower range of temperatures but their effect became less pronounced at high temperatures. Almost all the loss of compressive strength occurred within two hours of exposure to the maximum temperature. Pulse velocity measurements did not predict the residual strengths accurately and appeared to be more indicative of the levels of temperature to which the concrete had been exposed.
Relationship between strength and volumetric composition of moist-cured cellular concrete
Authors: Tam C. T. , Lim T. Y. , Sri Ravindrarajah R. , Lee S. L.
Published: October 2009

Synopsis

The effect of the volumetric composition of cellular concrete, particularly water and air voids, on its compressive strength has been demonstrated to follow Feret's general formula. The increase in strength at all ages with a corresponding increase in water/cement ratio (opposite to that of mortar mixes) as obtained in the experiment has been shown to be consistent with Feret's formula. The inclusion of the degree of hydration in the modified form of Power's gel/space ratio further improves the correlation with strength when this is taken as the parameter.
An investigation of the pozzolanicity and hydraulic reactivity of a high-lime fly ash
Authors: Papayianni Joanna
Published: October 2009

Synopsis

Lignite fly ashes (LFA) often have self-cementing as well as pozzolanic properties, due to their high lime content. LFA is compatible with Portlandcement and can replace a significant percentage of cement in concrete in order to save energy and reduce costs.

The properties of LFA, ground to highlight its hydraulic properties, have been investigated by means of strength and other tests on mortars and pastes, with various levels of replacement of OPC by LFA. Analysis by X-ray diffraction, differential thermal analysis-thermogravimetry and electron microscope-selected area electron diffraction methods indicated that the strength of OPC/LFA mortars is due to compounds of C-S-H gel formed by the reaction of free lime with silica, and from the hydration of dicalcium silicate which may exist in LFA. The early strength is attributed to hydrated calcium aluminate compounds and ettringite.
A simplified non-linear analysis of concrete frames
Authors: Pulmano V. A. , Bakoss S. L. , Shin Y. S.
Published: October 2009

Synopsis

This paper presents a simplified method for the analysis of reinforced concrete frames subjected to sustained service loads. The finite element model used takes into account the non-linearities due to cracking and the time-dependent effects due to creep and shrinkage. It is based on methods widely used by designers at present to analyse short-term linear behaviour. The method is suitable for implementation on microcomputers for applications in the design of medium-rise reinforced concrete frames. Predictions of the behaviour of laboratory-tested frames are shown to be in good agreement with measured values.
The relationship between permeability coefficients for concrete obtained using liquid and gas
Authors: Bamforth P. B.
Published: October 2009

Synopsis

Tests have been carried out on four concretes to measure their permeability coeficient using both water and nitrogen. In every case the gas permeability was significantly higher than the water permeability, the dlference increasing as the permeability reduced. The theory of gas slippage, first reported in 1875 and subsequently studied in relation to oil sands in 1941, has been identified as a major reason for the recorded differences betweeri the water and gas permeability coefficients for concrete. An equation relating water and gas permeability has been derived for mature, sealed-cured concrete, which takes into account the mean absolute pressure used for gas permeability measurement. This can be used to adjust gas permeability results to give a reasonable approximation of the intrinsic permeability of the concrete.
Punching shear tests on steel-fibre-reinforced micro-concrete slabs
Authors: Narayanan R. , Darwish I. Y. S.
Published: October 2009

Synopsis

Investigations of the behaviour and strength characteristics of steel-Jihre-reinforced micro-concrete slabs subjected to punching shear are presented and discussed. A total of 12 simply-supported square slabs were tested. The parameters varied were the volume fraction of the fibres, the amount of tensile reinforcement and the concrete strength. The test results confirm that an increase infibre content improved the shear strength of the slabs; the position of the critical shear perimeter around the loaded area was also influenced by the fibre content. Based on these tests, a design method is suggested for evaluating the punching shear strength of fibre-reinforced concrete slabs. The predictions obtained bythe suggested method are shown to be satisfactory by comparing them with the values observed in the tests carried out by the authors and previous investigators.
A theory of transfer bond resistance of deformed reinforcing bars in concrete under lateral pressure
Authors: Navaratnarajah V. , Speare P. R. S.
Published: October 2009

Synopsis

The basic bond mechanism for reinforcing bars in concrete under external pressure is considered and an existing partly cracked elastic theory for bond resistance is extended to cover both uniform and non-uniform distributions of external pressure.

Results obtained from this theory are compared with experimental results at various stages of bond failure. The prediction of pull-out force at 0·1 mm free-end slip is found to be satisfactory.
Shear strength of lightweight aggregate concrete beams: design to BS 8l10
Authors: Clarke J. L.
Published: October 2009

Synopsis

Provisions for the use of structural lightweight aggregate concrete are included in British codes of practice but limitations are applied to the design values that may be used. This paper is concerned with the strength in shear, which is limited in the codes to 80% of that for normal-weight concrete of the same compressive strength. The paper reviews the published test data and describes a series of tests on beams, both with and without shear reinforcement. On the basis of the review and the tests it is concluded that the code provisions are unnecessarily conservative.
Analysis of aggregate interlock behaviour at cracks in reinforced concrete
Authors: Soroushian Parviz , Obaseki Kienuwa , Choi Ki-Bong
Published: October 2009

Synopsis

Analytical methods have been developed for predicting the resistance provided by aggregate interlock against sliding-shear deformations at cracks in reinforced concrete. These methods are shown to be capable of predicting test results with a reasonable accuracy, and they are used for an analytical study of the influence on aggregate interlock behaviour of the initial crack width, concrete compressive strength, maximum aggregate size, and the restraint provided against opening. The relative significance of aggregate interlock compared to the dowel action of reinforcing bars in resisting the sliding-shear action across cracks in reinforced concrete was also assessed analytically.
A comparative study of fracture parameters in notched concrete beams
Authors: Alexander M. G. , Blight G. E.
Published: October 2009

Synopsis

The paper compares a number of fracture parameters, both linear and non-linear, obtained from the results of tests carried out on notched concrete beams with depths varying from 100 to 800mm. The parameters were critically investigated, for their ability to describe concrete fracture. The concept of a ‘fracture process’ is introduced. The type of, fracture process as well as the existence of an extensive microcracked zone ahead of the main crack critically affect values of the measured parameters. It was concluded that none of the existing parameters are entirely satisfactory, due primarily to a lack of true size-independence in the relationships. Parameters must he linked to fracture processes, which, together with the presence of the microcracked zone, implies that ultimately a number of non-linear parameters will suit the concrete fracture problem best.
Heat release characteristics of concrete containing ground granulated slag in simulated large pours
Authors: Coole M. J.
Published: October 2009

Synopsis

Simulated large pour studies in which ground granulated blast furnace slags from three European sources were blended with OPC have shown that both the peak temperature and the time to reach this temperature are strongly injhenced by slag source. With a reactive slag and a moderate level of OPC replacement (20–40%) the temperature rise at the centre of a large pour may be higher than that at the centre of an equivalent OPC pour.

Five levels of slag replacement were investigated in concrete with a cement content of 315 kg/m3. The compressive strengths of concrete cubes cast from the same mix and stored under matched curing conditions were also determined.

Results obtained with concrete under variable loss, semi-adiabatic conditions were compared with those obtained with pastes under isothermal conditions at a single temperature of 20°C. The isothermal results are of little value in predicting behaviour in large pours and can be quite misleading.

It therefore follows that care should be taken when selecting a slag source and a slag level for large concrete pours. Reliance should not be placed on published results obtained with other slags or on isothermal calorimetry carried out at 20°C only.
SRPC and modified concretes subjected to severe sulphuric acid attack
Authors: Fattuhi N. I. , Hughes B. P.
Published: October 2009

Synopsis

Mortar and concrete cubes have been immersed in a channel containing a 3% solution of continuously flowing sulphuric acid. The cementitious materials examined were: ordinary Portland cement containing polyvinyl alcohol (PVA) and pulverized-fuel ash; sulphate-resisting Portland cement, and a proprietary dense mortar. The change in weight with time of each cube was measured for up to 81 days. The effect of the PVA was to preserve the integrity of the cubes, and possibly slow down the rate of acid attack. The rate of acid attack on the SRPC concretes was similar to that on OPC concretes. The dense mortar had much improved resistance to sulphuric acid attack, and the improvement was enhanced with increased volume fraction of aggregate.
A new gas permeameter for measuring the permeability of mortar and concrete
Authors: Cabrera J. G. , Lynsdale C. J.
Published: October 2009

Synopsis

A permeability cell for measuring the permeability of mortar and concrete to gas is described. The problems encountered and overcome during the development of the cell are discussed. The cell is designed to test 25 mm diameter mortar samples but can also be used for 50mm diameter concrete specimens. Specimens of heights between 10 and 50mm can be tested.

Measurements using the new cell are highly repeatable and reproducible. The cell is very sensitive to the influence of water/cement ratio, age and replacement of cement by pulverized-fuel ash. It can be used to obtain permeability profiles through the depth of a concrete element in order to evaluate the influence of different curing conditions or curing compounds.
Model to predict cracking in fibre reinforced concrete due to restrained shrinkage
Authors: Grzybowski M. , Shah S. P.
Published: October 2009

Many parameters govern the performance of fibre reinforced concrete subjected to restrained shrinkage. These include the potential extent of shrinkage, the degree of restraint, time-dependent constitutive properties of concrete, fibre parameters and bond characteristics of the fibre–matrix interface. An analytical model is proposed which incorporates many of the key parameters and enables progressive cracking development to be predicted in fibre reinforced concrete subjected to restrained shrinkage. The theoretical background is outlined, followed by a comparison of the model prediction with two sets of data.
Influence of mix proportions, plasticizers and superplasticizers on creep and drying shrinkage of concrete
Authors: Brooks J. J.
Published: October 2009

The influence of plasticizing and superplasticizing admixtures on long-term deformations of concrete is reassessed. An approximate method is proposed to allow for changes in mix proportions when the admixtures are used as water and cement reducers, so that the influence on deformations is isolated from the influence of water/cement ratio and cement paste content. For five types of admixture, there is a general increase in both creep and shrinkage of between 3% and 130%, but limited data and variability indicate no conclusive differences between types of admixture or between types of deformation. In the absence of specific test data, it is suggested that, for admixture flowing concrete, deformation should be increased by 20%. For other applications of admixtures involving changes in mix composition, deformation can be estimated by the proposed method.
Preliminary field studies of rates of dissolution of hydrated cement
Authors: James A. N.
Published: October 2009

Studies have been made of dissolution kinetics of Portland cement concrete from a masonry dam in service since 1886. Finely ground samples washed free of excess lime and alkalis were used to measure rates of release of calcium and silica into water having a pH of 5·7 and low total hardness. A dissolution rate constant for a second-order process of between 1·0 × kg−6 m4 s−1 and 1·6 × kg−1 m4 S−1 was determined at 21°C. Preliminary results suggest that it is feasible to use quantitative methods of designing hydraulic concrete structures against deterioration by aggressive water, Previously described design procedures to accommodate soluble minerals in foundations of hydraulic structures, may also be used for concrete, mortars and grouts in aggressive environments. The preliminary data need to be extended to validate the proposal, and recommendations are made for that purpose.
Electromagnetic screening by reinforced concrete
Authors: Battilana J. A.
Published: October 2009

The reduction of unwanted emissions from electronic equipment is of interest, both to limit interference suffered by neighbouring apparatus, and to prevent unauthorized reception of sensitive information. In many cases, the properties of standard building materials can be exploited to provide adequate screening at low cost. An experimental and theoretical study has been made of the screening offered by reinforced concrete buildings. The measured attenuation was found to be within the range suggested by calculation based on the properties of concrete and a simple theory of the effect of the reinforcing bars. A t frequencies below 1 GHz, the screening is determined primarily by the spacing of the reinforcing bars. At higher frequencies, the moisture content of the concrete is the important factor. Normal levels of reinforcement provide a useful degree of screening at frequencies below a few hundred megahertz. If screening at higher frequencies is important, then additional measures will be necessary.
Strain and bond stress distributions in tension lap joints in reinforced concrete
Authors: Judge R. C. B. , Scott R. H. , Gill P. A. T.
Published: October 2009

Fifteen reinforced concrete tension specimens were tested, each reinforced with a pair of lapped rods. Longitudinal reinforcement strain distributuions were measured using electrical resistance strain gauges installed within the reinforcement, and strain concentration gauges were used to obtain very detailed information at the ends of some rods. Thirteen of the specimens were loaded incrementally to study short-term effects and the other two were used for a preliminary investigation of sustained loadings. Results show the changing nature of the strain distributions, first as transverse cracks were developed and subsequently as lap failure was approached. The test results have been compared with the theoretical work of Tepfers. Peak and mean bond stresses at the formation of each crack were calculated and compared and bond stress distributions at lap failure are discussed.
The statistical distribution of the drying shrinkage of concrete using Monte Carlo simulation
Authors: Al-Sugair F. H. , Almudaiheem J. A.
Published: October 2009

The drying shrinkage of concrete is one of the most important quantities to be estimated for concrete members and has therefore received considerable attention; however, most of the existing drying shrinkage prediction models do not give an estimate of the variability associated with the model. In this Paper, the modelling uncertainty of the drying shrinkage is predicted in addition to its mean value. In predicting the drying shrinkage, the codified Ross equation has been used. The uncertainty is predicted from the uncertainty of the variables used in the equation. Monte Carlo simulation is used to predict the statistical distribution of the drying shrinkage of concrete. The model and simulation is applied to several sets of data found in the literature. In general, the model predicts the mean value and the variance of the drying shrinkage successfully. In addition, the model is easily implemented and requires relatively little effort and information. It was found that the log-normal distribution accurately describes the statistical distribution of the drying shrinkage of concrete.
A comparison of the properties of OPC, PFA and ggbs concretes in reinforced concrete tank walls of slender section
Authors: Thomas M. D. A. , Osborne G. J. , Matthewst J. D. , Cripwell J. B.
Published: October 2009

This Paper compares the properties of cores taken from the walls (250 mm thick) of a 2·5 year old reinforced concrete tank constructed using ordinary Portland cement (OPC), pulverized fuel ash (PFA) and ground granulated blastfurnace slag (gghs) concretes of equal strength grade. Measurements taken during and shortly after construction showed the PFA and ggbs to be beneficial in terms of reducing hydration temperatures and the amount of secondary steel required to control thermal and shrinkage cracking. Ultrasonic pulse velocity measurements carried out on the tank walls before coring showed no significant difference between the three concretes, and laboratory tests on cores showed them to have comparable compressive and tensile strengths. The PFA and ggbs concretes showed greater carbonation depths than the OPC concrete, although the PFA concrete was significantly less permeable to both gas and liquid. These results are discussed with reference to pore structure measurements, which show the PFA concrete to have a coarser pore structure than the OPC concrete close to the surface—at depth the situation is reversed. Generally, the results show the three concretes to have very similar properties, suggesting that the early-age benefits observed for concretes containing PFA and ggbs can be achieved in slender concrete elements without compromising strength and durability requirements.
Modification of the two-point workability apparatus
Authors: Wallevik O. H. , Gjørv O. E.
Published: October 2009

There were two main problems with the original two-point workability test apparatus—segregation of the concrete during testing, and difficulties in operating the equipment. Based on the modification of the apparatus described in this Paper, it appears that reliable rheological information on fresh concrete properties can be obtained; also, the susceptibility of the mix to concrete segregation can be quantified.
Punching shear resistance of lightweight aggregate concrete slabs
Authors: Clarke J. L. , Birjandi F. K.
Published: October 2009

Provisions for the use of structural lightweight aggregate concrete are included in British codes of practice, but limitations are applied as to the design values that may be used. This Paper is concerned with the strength in shear of slabs subjected to punching, which is limited in the codes to 80% of that for normal-weight concrete of the same compressive strength. Tests on slabs made with five different lightweight aggregates are described; on the basis of the results it is concluded that the code provisions are unnecessarily conservative.
Field measurements for early-age strains in concrete walls
Authors: Anson M. , Rowilson P. M.
Published: October 2009

Temperature changes and in-plane movements at early age in 12 reinforced concrete walls are reported. Between 14 and 37 vibrating wire strain gauges were placed in eleven of the walls. Temperatures were monitored at each gauge location. Gauges were placed mid-way through the wall thickness. In-plane residual (‘restrained’) strains were deduced from restraints applied to free in-plane movement of the cooling concrete in various parts of the wall. Restraint to free movement is provided externally by previously cast elements such as a wall foundation, combined with internal effects arising from the considerable variation in peak temperatures from place to place in a wall. At their tops, it is found that walls are in compression after cooling. In other parts, the tension is not usually very high, although a restraint factor of 0·5 to free horizontal movement is approached locally in some walls and a high diagonal strain > 200 microstrains was estimated in two of the walls.
Flow simulation of fresh concrete subjected to vibration
Authors: Mori H. , Tanigawa Y.
Published: October 2009

It is very important to estimate the flow and deformation behaviour of fresh concrete at the stages of mixing, transporting, placing, consolidating etc. to obtain good performance of concrete works. However, analytical methods to predict the behaviour of fresh concrete are not well established, and there are few theoretical studies to clarify the properties of fresh concrete subjected to vibration1,2
The rheology of fresh mortar
Authors: Banfill P. F. G.
Published: October 2009

The effects of mixing procedure, testing procedure and relative proportions of constituent materials on the rheology of fresh mortar, as measured by the ViscoCorder, have been studied. Mortar shows structural breakdown, and the flow curve of the broken down material conforms to the Bingham model. The yield value and plastic viscosity vary with composition in a similar way to that shown by fresh concrete: tests with the instrument on model concrete (i.e. with no coarse aggregate) could be useful in predicting the behaviour of fresh concrete.
Absorption of water and chloride into concrete
Authors: McCarter W. J. , Ezirim H. , Emerson M.
Published: October 2009

The theory of unsaturated flow in porous materials has been applied to the study of water penetration into concrete. This theory predicts the classical relationship between the cumulative volume of water absorbed and the square root of the elapsed time. In this Paper data are presented on both the volume of water absorbed and the depth of penetration of water, for a range of concrete mixes, as a function of time.
Modified DOE mix design method for high volume fly ash concretes and controlled low strength concretes
Authors: Hansen T. C.
Published: October 2009

On the basis of some fundamental principles for the design of fly ash concrete mixes,1,2 the Author proposes a number of modifications and extensions of the British DOE method for the ‘Design of normal concrete mixes’. The suggested modifications make it possible to extend use of the DOE method to design of wet lean concretes and controlled low strength materials (CLSM). The properties of both these types of concrete are con-siderably improved by the addition of high volumes of fly ash, but it requires some skill to design high volume fly ash concretes in a logical manner, so that they do show the optimum properties both in the fresh and the hardened state.
Elastic modulus and strength of hollow concrete block masonry with reference to the effect of lateral ties
Authors: Khalaf F. M. , Hendry A. W. , Fairbairn D. R.
Published: October 2009

This paper presents the results of an experimental investigation to derive a formula for the short-term static modulus of elasticity Em of unfilled andfilled concrete blockwork masonry. The formula is based on the modulus of elasticity of each individual material used in the construction of blockwork masonry. The effects of using lateral ties as reinforcement on the behaviour, ductility and strength of concrete blockwork masonry are also investigated.
Chloride ingress measurements and corrosion potential mapping study of a 24-year-old reinforced concrete jetty structure in a tropical marine environment
Authors: Liam K. C. , Roy S. K. , North wood D. O.
Published: October 2009

A corrosion survey was made of a 24-year-old reinforced concrete jetty structure in Woodlands, in the northern part of Singapore. This particular jetty structure was selected for the field survey since it was already showing signs of reinforcement corrosion and deterioration. Two piles which were located near the stairs (and were easily accessible) were surveyed in detail. The survey covered the mean tidal zone, the upper tidal zone at 0·8 m above the mean tide level, and the splash zone at 1·3m above the mean tide level. The principal test methods used in the survey were chloride profile analysis and corrosion potential mapping. A general visual and de lamination survey was also carried out. The chloride content in the concrete increased with height above the mean tide level. Chloride diffusion coefficient values, which were calculated from the chloride profile measurmounts, ranged from 2·13 × 10-8 cm2/s athe mean tidal zone to 5·50 × 10 8 cm2/s at the splash zone. The upper tidal and splash zones, i.e. those with the highest chloride content, were found to be most susceptible to corrosion. The corrosion potential measurement was reasonably consistent and reliable method for monitoring and assessing the level of rebar corrosion.
Carbonation of fly ash concrete
Authors: Thomas M. D. A. , Matthews J. D.
Published: October 2009

The carbonation of fly ash concrete is reported, with particular emphasis on the role of curing. Concretes with nominal strength grades C25, C35 and C45 and a range of fly ash levels (0–50%) were exposed to various treatments during the first 28 days; i.e. different moist curing periods anda range of ambient temperatures and relative humidities after curing. After28 days the concretes were stored either internally or externally (sheltered) and the rate of carbonation was monitored. The results emphasize the importance of adequate curing for concrete durability, irrespective of the presence of fly ash. In some cases increasing the initial curing period from 1to 7 days had the effect of reducing carbonation by 50%. Concretes with up to 30% fly ash carbonated to a similar or slightly greater degree compared with OPC concretes of the same strength grade. However, concretes containing 50% fly ash carbonated at significantly greater rates. A graphical model is presented which allows prediction of the carbonation rate to be made from a knowledge of the concrete mix (strength grade and fly ash content), degree of curing, ambient conditions during and after casting, and type of exposure.
Ductility and plastic design of RC sway frames
Authors: Scholz H.
Published: October 2009

Ductility in plastically designed RC sway frames is examined. Simple member slenderness rules are derived for frames subjected to combined or vertical load. The method is intended as a first assessment of the ductility problem, before a more rigorous elastic–plastic analysis is undertaken. The recommendations are illustrated by way of a numerical example.
Ductility of low-rise structural walls
Authors: Mo Y. L. , Shiau Wen-Chang
Published: October 2009

Based on equilibrium and compatibility conditions, as well as a stress–strain relationship for softened concrete, a truss model theory is derived to predict the strengthand behaviour of low-rise reinforced concrete shear walk m e theoretical prediction was compared to the tests of twenty- four shear walls and was found to be applicable throughout the loading history. The effects of material properties (including steel yielding stress and concrete compressive strength) and reinforcement ratio on the ductility of low-risestructural walls was firther studied using numerical experimentation. It was found from this study that the ductility factor of four can be reached when the steel yielding stress, the concrete compressive strength and the reinforcement ratio are 280 N/mm2, 56 N/mm2 and 0·0025, respectively.
Effect of first-storey shearwalls with Teflon sliders on earthquake-resistant buildings
Authors: Mo Y. L. , Chang Y. F.
Published: October 2009

A practical system for earthquake-resistant building design is described. The system utilizes Teflon sliders at the top of the first-storey reinforced concrete framed shearwalls to carry a portion of the superstructure. The earthquake forces are basically resisted by the first-storey reinforced concrete framed shearwalls, and energy dissipation is provided by the first-storey ductile columns and by the Teflon sliders. Utilizing this concept the seismic response characteristics of a multistorey frame are analysed and discussed.
Estimating the potential strength of concrete with prior load history
Authors: Yip W. K.
Published: October 2009

Recommended procedures in evaluating the results of concrete core testing to establish the estimated in situ cube strength or estimated potential strength of concrete are given in standards and guidance documents. Many factors have been considered to determine their combined influence in the interpretation of the conversion process, from a core strength to an equivalent moulded cube strength. Nonetheless, it is recognized that further research is required to determine the effects of other influencing factors. This experimental investigation examines the effects of different degrees of simulated uniaxial compressive load history within prismatic concrete specimen on the strength of cores drilled in the direction of the load history from different locations of the specimen. The results show that the strength of a core drilled from such parent concrete may be as much as 31·7% lower than that of a similar size core drilled from similar parent concrete which has no prior load history.
Carbonation of concrete containing pfa
Authors: Hobbs D. W.
Published: October 2009

Depths of carbonation at an age of 8·3 years are reported for concretes prepared using one Portland cement and for companion concretes in which 35% by mass of the Portland cement was replaced by one or other of two types of pfa. It is shown that the depth of carbonation in Portland/pfa concretes is similar to that in Portland cement concretes of similar 28-day compressive strength.
Methods for studying corrosion in reinforced concrete
Authors: Rodríguez P. , Ramírez E. , González J. A.
Published: October 2009

This Paper reviews available techniques for monitoring steel corrosion in reinforced concrete. Electrochemical techniques are by far the most suitable for this purpose, and meet most of the requirements. me responses of direct and alternating current corrosion monitoring methods for steel–concrete systems are compared under two extreme conditions, i.e. steel being corroded in the active state and in the passive state. Most practical situations will belong to one of these or be intermediate to them. Results of polarization resistance measurements (taken by applying a potential step, a current step and small-amplitude cyclovoltammetry), a coulostatic method and electrochemical impedance spectroscopy are reported. It is shown that metal polarization resistance in particular, and electrochemical methods in general, can provide fast and reliable information on the corrosion rate of steel in concrete, suflciently accurate to distinguish between acceptable and unacceptable conditions in most scientific and technical applications.
The effectiveness of PFA in reducing the risk of cracking due to ASR in concretes containing cristobalite
Authors: Hobbs D. W.
Published: October 2009

Expansion results up to an age of 42 months are reported that were obtained in tests carried out at 20°C to determine the effective alkali release from pulverized fuel ash (PFA) in concretes of normal cement content containing cristobalite as the reactive constituent in the aggregate. It is shown that at an alkali content of about 3 kg/m3 the effectiveness of PFA in reducing the risk of expansion due to alkali-silica reaction depends on: (a) the alkali content of the Portland cement; (b) the proportion of the Portland cement replaced; (c) the total alkali content of the PFA. Examples are cited from the literature of affected field concretes that broadly fit the deductions made from this study.
A distribution function for the fatigue life of concrete
Authors: Yang D.
Published: October 2009

The fatigue life distribution of concrete under repeated loading with random excitation is scattered. Thus it is desirable to use an uncertainty measure such as probability in the analysis of concrete fatigue life. This Paper, based on a fatigue damage mechanism analysis, considers the fatigue damage development process of concrete to be a Markov process. A new distribution function is given for the damage at a given time which can also predict the life distribution if the critical damage is given. By comparison with test results, it is shown that this new distribution is sufficiently flexible to fit test data.