bluuebunny/crossref_metadata_2025 huggingface dataset:
Precise shape grading of coarse aggregate
Authors: O'Flannery L. J. , O'Mahony M. M.
Published: October 2009

The objective of the research described here was to derive dimensional parameters to provide a unique descriptive fingerprint for any sample of coarse-aggregate particles. The practical component of the work focused on devising a quick and accurate field test capable of yielding values for the descriptive parameters to enable a coarse-aggregate sample to be quantitatively appraise. The aim of the paper is to propose this test as a means of ensuring quality control of coarse-aggregate shape. The parameters used were derived from first principles and applied to realistic particle shapes using simple mathematical models. Standard specifications were analysed to identity finite limits of acceptance for specific applications. These limits were then converted into precise terms of reference for the parameters. Extensive laboratory tests were performed on coarse-aggregate samples using the innovative test regime. The results show that such a system can be useful in providing information about an aggregate.
An empirical model for predicting the mechanical properties of confined concrete
Authors: Vintzileou E. , Malliri P.
Published: October 2009

This paper presents an empirical model for the calculation of the main characteristics of concrete confined by means of hoops or spirals. The model included in CEB-FIP Model Code 1990 was initially used as a basis, its validity was checked against experimental results provided by 17 researchers for more than 300 specimens. Since the comparison showed that the model fails to predict accurately, especially the strain at strength and the ultimate strain of confined concrete, modified formulae are proposed taking into account additional parameters which affect the characteristics of confined concrete, for example unconfined concrete strength. The comparison between experimental values of strength and strains and those predicted using the modified empirical model proves to be satisfactory. The relatively large scatter associated mainly with strain values, as well as the reliability of the available experimental results, is discussed.
Load capacity of slender reinforced concrete walls governed by flexural cracking strength of concrete
Authors: Sanjayan J. G.
Published: October 2009

This paper demonstrates, using experimental results and theoretical derivations, that some reinforced concrete walls may be able to carry much higher loads if the flexural cracking strength is considered in the calculation. The paper presents a theoretical derivation of a formula for estimating the axial load capacities of reinforced concrete walls subjected to eccentric axial loads as well as uniform lateral loads. A simplified, approximate version of the formula is also presented. The formula is based on the assumption that the failure of the walls is controlled by the flexural cracking strength of concrete. The paper also describes an experimental programme and reports test results for four reinforced concrete walls with varying amounts of reinforcements of varying type, namely, mesh (fabric), bar and steel fibre reinforcement. The test results show that the amount and type of reinforcement do not have any influence on the load capacity of the walls but only have an effect on the ductility of the walls. Comparisons are made with the formula and other commonly used methods of estimation. The formula estimations are much closer to the test results than the other methods for the type of walls tested.
Shake table tests on small-scale low-rise structural walls with various sections
Authors: Mo Y. L. , Lee Y. C.
Published: October 2009

Five shake table tests on small-scale low-rise structural walls were performed. The walls were made with different sections, namely I, T, L, Z and C shapes, to study the effect of section shape on the mechanical behaviour of such walls. It was found from the tests that the wall with a Z shape suffered a premature failure owing to the additional out-of-plane forces; therefore, low-rise structural walls with a section of Z shape are not recommended for use. On the other hand, when the experimental primary curves of such walls are used to predict the dynamic response, the hysteretic loops of such walls can be predicted with acceptable accuracy.
Performance of very-high-strength concrete subjected to short-term repeated loading
Authors: Taher S. E.-D. F. , Fawzy T. M.
Published: October 2009

The effect of short-term repeated loading on very-high-strength concrete prisms of various sizes has been experimentally investigated. Concrete batches made of local materials were cast using different types of coarse aggregate. The level of cyclic preloading was altered and the corresponding influences on the ultimate strength, strain and modulus of elasticity were monitored. The effect of changing the number of cycles at a certain preloading level was investigated. For certain loading levels the number of cycles to failure was observed. The size of the specimens tested was noted to have a significant effect on the stress–strain parameters. Behavioural modelling using the concepts of continuous damage mechanics was conducted. On the basis of the experimentally observed behaviour, a mathematical expression for the damage variable was derived. Simulation by the proposed damage model captured most of the salient features of the response such as the effect of cyclic preloading at different levels, the number of cycles to failure in fatigue tests and the stress–strain curves.
Controlling the quality of fresh concrete—a new approach
Authors: Chidiac S. E. , Maadani O. , Razaqpur A. G. , Mailvaganam N. P.
Published: October 2009

Traditionally, the slump test has been used to measure concrete consistency. However, many researchers contend that the slump alone is not a sufficient measure of consistency and that other quantifiable rheological properties such as shear yield stress and plastic viscosity are more representative and should be considered. A SLump Rate Machine (SLRM) was adapted and calibrated, to consistently measure the plastic properties for a number of concrete mixes, namely slump rate and slump flow. Furthermore, a theoretical model was developed to correlate the slump flow and slump rate with the shear yield stress and plastic viscosity of fresh concrete, respectively. Employing the SLRM and the theoretical model has resulted in an efficient new approach to adequately predict the rheological behaviour of fresh concrete as well as to provide reasonably accurate values for shear yield stress and plastic viscosity.
High-strain-rate tensile behaviour of concrete
Authors: Cadoni E. , Labibes K. , Berra M. , Giangrasso M. , Albertini C.
Published: October 2009

In order to study the dynamic behaviour of concrete, a wide programme of research has been carried out at the Joint Research Centre, Ispra site by means of the Hopkinson bar bundle. The aim of this study was to produce new data on some debated basic subjects of industrial importance, such as the behaviour of plain concrete at strain rates corresponding to those provoked by quasi-static, earthquake and impact loading. In this paper the high-strain-rate tensile behaviour of plain concrete is described.
Durability of reinforced concrete sewer pipeline over 23 years
Authors: Blight G. E. , Alexander M. G.
Published: October 2009

A reinforced concrete sewer pipeline in Johannesburg, South Africa, is exposed to the weather where it crosses three dry valleys over a series of pipe bridges. In 1975, a year after commissioning the sewer in May 1974, it was discovered that the pipes were cracking, that the cracking was spreading on each affected pipe, and that more and more pipes were being affected. A programme of field measurements soon established that the cracking resulted from restrained thermal bending. Pipes were insulated experimentally and it was shown that the thermal bending could be very much reduced by this means. It was therefore decided to permanently insulate the pipes on all three pipe bridges. Twenty-three years later in 1998, poor people living in shack settlements near the pipe bridges began to steal the aluminium sheeting protecting the insulation and also removed the insulation, thus exposing the pipes to the elements once more. This provided an opportunity to inspect the condition of the pipes and to assess the long-term efficacy of the insulation. It was found that the pipes had been almost perfectly protected by the insulation and it was decided to reinsulate them immediately, using an equivalent insulation system that it is hoped will not be so susceptible to theft.
Influence of elevated temperature on axially loaded expansive cement grout borehole plug sealing performance
Authors: Akgün H. , Daemen J. J. K.
Published: October 2009

The strength of expansive cement grout borehole plugs cast in rock cylinders is investigated theoretically and experimentally as a function of curing and testing temperature of the plugged rock cylinder and of borehole size. The distributions of thermally induced stresses and displacements, shear stresses along the plug–rock interface due to an axial stress applied to the plug, and resultant interfacial shear stresses due to a combination of uniform elevated temperature and axial load are studied and analysed. Conservative in this analysis is the assumption of elastic behaviour and the fact that the strength tests were conducted after a cement grout curing period of only eight days. Details on experimental procedure regarding sample curing conditions, experimental apparatus and sample loading are presented. The axial strength decreases with increasing curing and testing temperature and with increasing plug radius. The results of the theoretical analysis lead to a recommendation to design plugs with a length-to-radius ratio of at least 8 in order to reduce the thermal shear stresses at the plug–rock interface to acceptable levels.
Behaviour of high-strength concrete with dolomitic aggregate at high temperatures
Authors: Janotka I. , Nürnbergerová T. , Nad L.
Published: October 2009

Tests were carried out on concrete with normal Portland cement, silica fume and dolomitic aggregate subjected to temperatures of 20–800°C to determine the effect of temperature on the phase composition and pore structure development, and physico-mechanical properties of concrete specimens. It is shown that the reduction in hydrate phase volume is connected with the pore structure coarsening manifested by the evident growth in pore median radius and total porosity values. Damage to the structural integrity of concrete is markedly influenced by the level of temperature elevation. This process is described by a three-stage model which incorporates deductions made from this study and those cited from the literature of similarly affected concretes.
Seismic behaviour of reinforced concrete columns
Authors: Mo Y. L. , Wang S. J.
Published: October 2009

To expedite the fabrication of reinforcement cages of columns, a new configuration of transverse reinforcement with four C-shape ties for columns was proposed. In this paper, to evaluate the effect of such a configuration on the seismic performance of the column, nine reinforced concrete columns with a cross-section of 400 × 400 mm were tested. It was found from the test results that the new configuration of transverse reinforcement has better seismic performance than that usually used in design. The models for the stress–strain relationship of confined concrete found in the literature were also examined by the tests. It was found that the model of Mander et al. provides the best predictions.
Rates of carbonation and reinforcement corrosion in high alumina cement concrete
Authors: Dunster A. M. , Bigland D. J. , Holton I. R.
Published: October 2009

High alumina cement (HAC) concrete was used extensively in the UK from the 1950s to the early 1970s in the manufacture of precast, prestressed concrete beams. Long-term durability problems have now begun to affect these elements, the most important of which is reinforcement corrosion due to carbonation of the cover concrete. A ten-year programme of research, funded by the DETR, was initiated at the Building Research Establishment in 1993 to provide data on the rates and mechanisms which control carbonation and reinforcement corrosion in HAC concrete. This paper reviews data obtained over 5 years. Carbonation depths and rates for the HAC concretes studied were found to be influenced by water/cement ratio, curing and exposure conditions, in a similar manner to Portland cement (PC) concretes. The carbonation rates appeared to be the same as those for PC concretes with 28-day compressive strength properties similar to the fully converted (minimum) strength of the HAC concrete. The majority of the steel in specimens exposed in natural conditions was still in uncarbonated concrete after five years' exposure. The risk of reinforcement corrosion in these specimens was therefore low. However, electrochemical measurements taken on fully carbonated specimens illustrate the strong relationship between the availability of moisture, concrete resistance and the rate of corrosion.
Proposed changes to flexural design in BS 8110 to allow over-reinforced sections to fail in a ductile manner
Authors: Ziara M. M. , Haldane D. , Hood S.
Published: October 2009

The provisions for flexural design contained in BS 8110 have been reviewed in the context of introducing improvements in the level of ductility that can be achieved in structural concrete sections. Increased ductility will lead to corresponding enhancements in the flexural behaviour of members. Accordingly, changes to the present approach to flexural design in this code have been put forward. Design equations have been developed and compared to those present in the code. The proposed approach permits a section to be designed regardless of its longitudinal reinforcement ratio and also allows the amount of stirrups required to achieve the increased level of ductility to be determined. A test programme comprising 21 beams has been carried out to investigate the validity of the proposed design approach. The test results have confirmed the validity of the proposed approach. All of the beams exhibited enhanced flexural behaviour even though their longitudinal reinforcement ratios were significantly in excess of the maximum limit allowed in the code.
Evaluation of thermal crack by a probabilistic model using the tensile strain capacity
Authors: Lu H. R. , Swaddiwudhipong S. , Wee T. H.
Published: October 2009

Tensile strain capacity is defined as the maximum tensile strain that concrete can withstand without a continuous crack forming. The present study shows that the tensile strain capacity of concrete is a relatively constant value and it is virtually unaffected by mix proportions, curing age and compressive strength. This result is consistent with the fact that the same value of tensile strain capacity can be used to evaluate thermal cracking of concrete of different mix proportions. The phenomenon of occurrence of a crack inherently contains a large number of indefinite factors and it is proper to use the concept of probability for evaluation. The probabilistic model based on strain is proposed in this paper. Over 200 uniaxial tension tests were conducted to study the relationship between the tensile strain capacity and the number of failed specimens. From the experimental results, the relationship between the probability of occurrence of a crack and the restrained tensile strain is established in the model. The results from the experiment of thermal cracking of a cyclinder agreed reasonably well with the proposed model.
The hardening behaviour of cementitious materials
Authors: Abyaneh M. Y. , Keedwell M. J. , Leppard C. , Claisse P. A.
Published: October 2009

Data from tests on samples of lime-pulverised fuel ash (PFA), lime–gypsum–PFA and cement–PFA mixtures have been analysed. In the case of the lime–PFA mixture, three phases of strength gain were identified, as follows. Phase 1—a rapid initial gain in strength, followed by an induction phase during which little or no strength gain was recorded. After an induction period this was followed by: phase 2—a further period of rapid strength gain; and phase 3—a period of slow gain in strength. A strengthening model based on the interlacing of fibrous growth forms is considered for the phase 3 stage of strengthening which is validated by scanning electron microscope work. It is shown that additional strength resulting from the additions of gypsum at 20°C is due to the phase 3 strengthening stage.
An elastic model to quantify the effect of moisture on the mechanical properties of concrete at the time of test
Authors: Guo J. S. , Waldron P.
Published: October 2009

This paper describes the detailed development of a mathematical model for determining the effect of moisture on the mechanical properties of concrete at the time of test. Based on the theory of elasticity, it focuses on the stress distribution around spherical cavities in concrete filled with different types of inclusions. Results obtained from the mathematical model have assisted in interpreting a number of experimental phenomena that have been the subject of long-term controversy. In particular the model explains why compressive strength tests yield higher measured values for dry concrete specimens than for otherwise identical wet specimens, while the measured values of static modulus exhibit the opposite effect. It also provides an explanation as to why measured tensile strength values obtained from direct tension, tensile splitting or torsion tests are largely independent of moisture content. The model provides an analytical tool for studying the interdependence between the mechanical properties of concrete and its moisture content. It also yields essential input for the computational simulation of the behaviour of concrete structures that are subjected to large changes of moisture condition. Moreover, it provides a method for analysing the stresses at the surface of any type of inclusion but particularly for cavities filled with incompressible liquids under any stress field.
Toughness and tortuosity of polypropylene fibre reinforced concrete
Authors: Sabir B. B.
Published: October 2009

This paper gives the results of an investigation in which the fracture toughness and fracture energy of concrete were determined using notched specimens prepared from standard cubes used for compressive strength tests. The test samples were made from concretes containing several levels of silica fume as partial cement replacements and a range of polypropylene fibre contents. Several notch geometrics were investigated and the tests revealed no significant influence on the fracture toughness by the size of the notches. Significant increases in the fracture toughness were obtained when the cement was replaced by 15% silica fume. The fracture toughness was found to be largely unaffected by the polypropylene fibres. The laboratory tests are augmented by finite element analysis and the investigation enabled an assessment of the tortuosity of the fracture surface to be made. The tortuosity was found to decrease with increase in the silica fume content. This is considered to be due to the enhanced composite action between the aggregates and the hardened cement paste caused by the reduction in the thickness of the interfacial zone effected by the silica fume. The tortuosity also decreased with increasing notch size. This is due to the presence of a greater proportion of coarse aggregates being encountered by the advancing crack in the case of the specimens with shorter notches. The polypropylene fibres were found to be effective in controlling the fracture after first crack. The ductility imparted to the matrix by the fibres was assessed using a toughness index determined from the area under the load-displacement curve obtained from the tests. Significant increases in the toughness indices of all concretes examined were obtained by additions of small amounts of fibre.
The influence of the permeability of concrete cover on reinforcement corrosion
Authors: Williamson S. J. , Clark L. A.
Published: October 2009

Surface permeability tests were performed on near-surface concrete, which was either directly over or remote from reinforcing bars. Test specimens were 150 mm concrete cubes with either 8 mm or 16 mm diameter bars placed in either the corner or the side faces of the specimens. Permeability of cover concrete over a bar was found to be greater than that remote from a bar. Cover to maximum aggregate size ratio was identified as the most important variable in the identification of the point when there will be no significant difference between the permeability of cover concrete over a bar and that remote from a bar. Aggregate size, bar location, method of compaction and cover thickness were also found to influence near-surface concrete permeability.
Study of water movement in concrete
Authors: Wong S. F. , Wee T. H. , Swaddiwudhipong S. , Lee S. L.
Published: October 2009

An investigation on the movement of water in 100% Portland cement concretes is presented. The water diffusion and sorptivity tests, together with the accelerated water permeability test, are performed to determine the transport parameters that characterise the mechanisms of water diffusion, sorptivity and permeability in concrete respectively. The effects of pore humidity, ambient temperature, environmental relative humidity, applied hydrostatic pressure gradient and water-cement ratio are also explored. The results obtained from the tests on water diffusion, sorptivity and permeability show good agreement with those reported in the literature. The study of water movement has practical implications on the prediction of transport and distribution of aggressive chemical agents in concrete, as well as on the development of rational and quantitative durability assessment for concrete structures exposed to different climatic and environmental conditions.
The extraction of pore fluid from concrete using a heavy liquid extraction method
Authors: Cromie J. A. , Abu-Tair A. I. , Lyness J. F. , McFarland B.
Published: October 2009

Concrete has an intricate pore structure comprising pores and voids. The pore fluid is held within the pore structure of the concrete and provides the transport mechanism for aggressive ions, such as chloride ions. Pore fluid analysis is the most representative and accurate method of analysis for the investigation of ion ingress, ion egress and related phenomena. The micro-techniques necessary for evaluating the ion concentrations contained in the small amounts of fluid obtained are well established. The traditional method for the extraction of concrete pore fluid involves crushing the concrete at high tri-axial pressures (> 400 N/mm2) in specially constructed pore fluid expression devices. A novel method devised at the University of Ulster is presented and discussed.
Punching shear of slabs: crack size and size effects
Authors: Marzouk H. , Osman M. , Hussein A.
Published: October 2009

Fictitious crack model assumptions and equilibrium equations were used to develop a numerical model in order to predict the punching load and the deformations of reinforced concrete slabs. Concrete strength, aggregate type, reinforcement ratio as well as the fracture strength properties were taken into account in developing the new model. In spite of the low tensile strength of concrete, it has considerable fracture energy, therefore the fracture process zone in front of a growing crack can contribute to the flexural concrete strength. The proposed model adopted the fictitious crack model principles. The three equilibrium equations were used on a radial segment of the slab and the effect of crack size and size effect were incorporated in the formulation. The model results were compared with the experimental results and currently available shear design formulae to investigate the effect of the fracture properties on the predicted punching load. The model provided consistent and improved results compared to the existing codes.
Slab deflections in the Cardington in-situ concrete frame building
Authors: Vollum R. L. , Moss R. M. , Hossain T. R.
Published: October 2009

This article presents data on the deflection of the flat slabs in the Cardington in-situ concrete building. The effects of concrete tensile strength and reinforcement on long-term deflection are discussed. A coefficient K is proposed to compare cracking induced at striking, construction of subsequent slabs and service loading. Deflections of the Cardington slabs are shown to be almost linearly related to the minimum value of K. An effective concrete strength is proposed for use in deflection calculations to account for the effect of construction loading.
A mix constituent proportioning method for concrete containing ternary combinations of cements
Authors: Jones M. R. , Magee B. J.
Published: October 2009

This article reports a laboratory experimental programme that investigated the performance of concrete made with ternary combinations of Portland cement (PC) with pulverised fuel ash (PEA), granulated blastfurnace slag (GBS) and silica fume (SF), with the aim of developing a simple concrete mix constituent proportioning method. The test mixes used combinations of these cements that conformed to ENV 197-1. All mixes used gravel aggregated mixes and a superplasticiser to achieve slump class S2 (60–90 mm) to provide characteristic cube strengths from 20 to 60 N/mm2. Standard cube strengths were measured up to 180 days. Recommendations are made for the optimum PC replacement level to achieve the highest cube strength at 28 and 180 days for mixes both with and without silica fume. The data have been generalised and fitted to the familiar format of the BRE Design of Normal Mixes to allow the proportioning of the concrete mix constituents. A visual from of the mix design method has been adopted such that the combinations of cements that can be used to achieve particular characteristic cube strengths are simple to identify.
Analysis of reinforced concrete beams strengthened by external unbonded bars
Authors: Cairns J. , Rafeeqi S. F. A.
Published: October 2009

The article outlines a novel strengthening technique for reinforced concrete beams using external unbonded reinforcement. The advantages of the method lie in speed and simplicity of installation. The article provides a general description of structural behaviour of beams strengthened using the technique, supported by a numerical model to represent the behaviour of strengthened beams. A set of seven laboratory tests on reinforced concrete beams strengthened using the technique are reported, results compared with those of two reference specimens, and the model validated using test data. It is shown that good efficiencies can be achieved when strengthening lightly reinforced beam sections, but that with more heavily reinforced sections only limited strength enhancements are attainable.
Modelling of heated concrete
Authors: Khoury G. A. , Majorana C. E. , Pesavento F. , Schrefler B. A.
Published: October 2009

This paper presents the basic principles and details of the physical, mathematical and numerical models forming the main structure of the numerical analysis of the thermal, hydrol and mechanical behaviour of normal, high-performance and ultra-high performance concrete structures subjected to heating. A fully coupled non-linear formulation is designed to predict the behaviour and potential for spalling, of heated concrete structures for fire and nuclear reactor applications. Concrete is considered as a multiphase material consisting of a solid phase, two gas phases and three water phases. The physical model is described with emphasis being placed upon the real processes occurring in concrete during heated based on tests carried out in several major laboratories around Europe as part of the wider HITECO research programme. Examples of preliminary outputs are presented in the form of isoline diagrams compared with those obtained from experiment.
Combined deterioration of concrete subjected to loading, freeze—thaw cycles and chloride salt attack
Authors: Mu R. , Miao C. , Luo X. , Sun W.
Published: October 2009

This article discusses the combined deterioration of concrete with different strength grades when subjected to three-point bending loading, freeze–thaw cycles and chloride salt attack. Test results show that concrete tested in chloride salt solution scaled much more severely than in fresh water. Weight loss in chloride salt solution was twice that in water. However, dynamic modulus of elasticity (DME) of concrete in chloride salt solution dropped more slowly than that in water due to decline in freezing point as a result of chloride salt. It is also shown that the degradation process of concrete simultaneously exposed to loading, freeze–thaw cycles and chloride salt attack was significantly accelerated. The higher the stress ratio, the less the freeze–thaw cycles that concrete could bear and consequently the shorter the service life.
Steel fibre reinforced concrete: a contribution to the evaluation of the limit of proportionality
Authors: Indelicato F.
Published: October 2009

Two methods for the estimate of the characteristic values of the limits of proportionality of a steel fibre reinforced concrete, ffctk,fl are compared: a method derived directly from the classical ISO method for the determination of a statistical tolerance interval and another proposed by RILEM TC 162-TDF Committee. This is done by comparing the results obtained on 200 samples of size n = 15 and 200 samples of size n = 10, all extracted in a random manner from the same normal distribution of the values of the limit of proportionality, LOP. It is concluded that according to the ISO method, the confidence level is 95% with a 5% risk of overestimate, as generally accepted by the standards, while with the proposed RILEM method, the confidence level of the estimate (1 − α) turns out to be only 80% and hence implies a 20% risk of overestimate.
Limitations and realistic application of equivalent load methods in pre-stressed concrete structures
Authors: Oh B. H. , Jeon S. J.
Published: October 2009

The purpose of this paper is to investigate several important methods of obtaining the equivalent loads in pre-stressed concrete structures, and to compare the advantages and limitations of each method. The methods devised in this study include the use of curvature of tendon, characteristics of primary moment, self-equilibrium condition and linear segments approximation of tendon. Several important numerical examples, including simple and continuous beams, are presented to show the differences among the methods. It is shown that the equivalent loading system is not uniquely determined depending on the approach adopted to calculate the equivalent loads, which results in different section forces even from the same pre-stressed concrete structure. The self-equilibrium conditions of the equivalent loading system are discussed, which indicates that some parasitic reactions may arise by some approximate equivalent loads even for the determinate structures. The present study indicates that the equivalent load method can be applied to various types of pre-stressed concrete members in a rational and efficient manner by carefully obtaining the equivalent loads.
Long-term sharing of load between steel and concrete in the walls of cylindrical reinforced concrete silos
Authors: Blight G. E.
Published: October 2009

When designing reinforced concrete silos, it is common to assume that the concrete carries no tension and that hoop tension in the silo wall is carried entirely by the hoop reinforcing. In fact, the concrete may carry a considerable proportion of the hoop tension when the silo is filled for the first time, and the sharing of load between steel and concrete may persist through many years of continuous service, with repeated filling and emptying of the silo. The paper presents four case histories of strain measurements made on reinforced concrete silos that illustrate the long-term sharing of load between steel and concrete in silo walls during service.
Non-linear finite-element analysis of thin shell SFRC structures
Authors: Zhu E. C. , Guan Z. W. , Shen S. Z.
Published: October 2009

Although thin shell concrete structures have been widely used in modern construction, buckling and cracking are still major problems for such structures. By introducing steel fibre reinforcement, such shells are of better structural behaviour due to improvement in concrete properties by steel fibres. However, there are few studies on non-linear finite-element analysis of SFRC shells. In this paper, a new constitutive model of SFRC suitable for finite-element analysis was established. A computer program taking both geometrical and material non-linearity into account was developed. Some concrete and SFRC shells were analysed with the program. An SFRC cylindrical shell was tested to make further validation of the finite-element modelling. Reasonably good correlation between the numerical and experimental results was obtained.
Behaviour and the controlling factor of delayed ettringite formation in shrinkage-compensating massive concrete
Authors: Yan P. , Peng J. , Qin X.
Published: October 2009

The longitudinal variance of confined shrinkage-compensating concrete was investigated under different curing conditions. A delayed ettringite formation (DEF) was observed in the specimen cured with temperature match conditioning (TMC), simulating the situation in the core of massive concrete. DEF induced the loss of expansion efficiency at the early age and then delayed the expansion at the later age in shrinkage-compensating concrete. Both behaviours are detrimental to the long-term performance of shrinkage-compensating concrete. Environmental humidity was identified as the dominating factor in controlling the occurrence of the detrimental delayed expansion induced by DEF in shrinkage-compensating massive concrete.
Seismic behaviour of structural walls with specific details
Authors: Han S. W. , Oh Y.-H. , Lee L.-H.
Published: October 2009

Bearing wall systems have been commonly used for low to mid-rise buildings particularly in low to moderate seismic zones. This study investigates the seismic performance of bearing walls with rectangular sectional shape and specific details of reinforcements. Such details have been developed for 10- to 15-storey apartment buildings in Korea, and used most commonly in apartment building construction. To investigate seismic behaviour of such walls, experimental tests were carried out. Structural behaviour is expressed in terms of ductility, deformation, and strength capacities. For this purpose, three full-scale test specimens were constructed having different shear-span ratios (2 and 3). The test results of this study are compared with those of other researchers. By this comparison, seismic performance of the walls with specific details is discussed. Also this study compares the response modification factor (R) for the bearing wall systems in different seismic design provisions.
Relative moisture movement through recycled aggregate concrete
Authors: Padmini A. K. , Ramamurthy K. , Mathews M. S.
Published: October 2009

This paper discusses the relative permeation characteristics (volume of voids and water absorption (ASTM C642-97) and sorption) of three strengths of concrete with (i) three maximum sizes of fresh granite aggregates (parent concrete), (ii) recycled concrete aggregates derived from each of three strengths of parent concrete, and (iii) two types of crushed brick aggregates. For a given strength, the volume of voids, water absorption and sorptivity of recycled aggregate concrete (i) reduces with increase in maximum size of aggregate used, (ii) increases with increase in strength of parent concrete from which the recycled aggregate is derived, and (iii) is higher for brick aggregate concrete than for concrete produced with crushed concrete aggregate. The variation in volume of voids, water absorption and sorptivity between parent concrete and recycled aggregate concrete reduces with increase in strength of concrete.
Behaviour of large concrete specimens in uniaxial tension
Authors: Li Q. , Duan Y. , Wang G.
Published: October 2009

The behaviour of large size concrete specimens (250 × 250 × 500 mm) in uniaxial tension has been studied. The complete tensile stress–strain response of the concrete was acquired through a limited experimental programme. The experimental programme comprised testing three different mix categories. A relationship between the tensile and nominal compressive strengths of large size concrete specimens was established. Accordingly, the uniaxial tensile strength of the concrete can be predicted by the expression [Formula: see text], where f′t and f′c are the tensile and nominal compressive strengths respectively. In comparison with the expressions for small size concrete specimens (150 × 150 × 300 mm), this expression predicts lower tensile strength for large size specimens (250 × 250 × 500 mm). In addition, the axial stress–crack width curves, fracture energy and brittleness of the concretes are also obtained based on the stress–deformation curves. It was found that the fracture energy and brittleness are both dependent on the tensile strength and the maximum aggregate size of the concrete.
Numerical simulation of strength envelope and fracture patterns of concrete under biaxial loading
Authors: Zhu W. C. , Teng J. G. , Tang C. A.
Published: October 2009

A numerical model that can simulate the fracture process of plain concrete under variety of plane stress conditions is introduced and used to simulate the fracture patterns of concrete specimens subjected to different combinations of biaxial loadings. In this numerical model, the concrete is assumed to be a three-phase composite composed of matrices, aggregates and interfaces between them. The finite element program is employed as the basic stress analysis tool when the elastic damage mechanics is used to describe the constitutive law of meso-level element and the maximum tensile strain criterion and Mohr-Coulomb criterion are utilised as damage threshold. The numerical simulation predicts well the strength envelope and cracking patterns of concrete specimens under different biaxial loading conditions.
Fractal fragmentation theory for shape effects of quasi-brittle materials in compression
Authors: Carpinteri A. , Pugno N.
Published: October 2009

The influence of the slenderness (shape effects) of a specimen in compression and of the friction between it and the loading platens on the dissipated energy density and on the compressive strength (strain-softening response) is theoretically and experimentally analysed. The energy dissipated during the process is assumed to be proportional to the area of the free surface of the fragments created under compression. A very general law, describing the energy dissipation in natural as well as in man-made fragmentation phenomena, is herein presented, obtaining, as particular cases, the classical comminution laws (Surface, Volume and Third Comminution theories). As a consequence, the dissipated energy density and the strength for a structural element under compression are obtained, by varying its slenderness under different boundary friction conditions. Finally, a comparison between experimental data and theoretical predictions on shape effects is presented. The influences of the specimen slenderness and friction on dissipated energy density and compressive strength are captured by the proposed model in a satisfactory way.
Fibre-optic sensors and smart composites for concrete applications
Authors: Lau K.-T.
Published: October 2009

Many extensive researches in the area of utilising fibre-reinforced plastic (FRP) materials for retrofitting and repairing existing damaged concrete structures have increasingly been made in recent years. The FRP can improve the overall flexural and compressive properties of the structures by using externally bonded FRP sheets. The conventional non-destructive inspection technologies such as strain gauge, and acoustic emission become inappropriate for structures after being repaired by externally bonded FRP materials. Optical fibre sensors have attracted considerable interest recently as non-destructive structural health monitoring devices for infrastructure elements. This paper gives a brief discussion of the principles of the fibre-optic technology for concrete structure assessment and its potential use in future engineering applications. Due to the increasing use of the FRP in most civil infrastructure elements, the conceptual idea of ‘smart composites’, which can be used as reinforcements as well as real-time structural health monitoring devices for concrete structures, is also discussed.
A direct method for deep beams with web reinforcement
Authors: Tan K. H. , Tang C. Y. , Tong K.
Published: October 2009

This paper takes account of the effect of web reinforcement, be it in vertical, horizontal, inclined or orthogonal configurations. This is because test results have indicated that the contribution of web reinforcement to shear strength is indeed significant and should not be ignored. An original and rational strut-and-tie model for the tensile contribution of both reinforcement and concrete is proposed, which takes account of their influence on the principal tensile stress. The proposed model is verified against three case studies of a total of 116 beams. Generally, the predictions are not only accurate and consistent in each case study, but also conservative.
Influence of constituents of concrete on its tensile strength and shear carrying capacity
Authors: Desai Satish
Published: October 2009

Research in concrete technology has served the interests of durability, competitiveness and sustainability of concrete construction through development of mix design. Work in this field is mainly aimed at making efficient use of aggregate and developing binders with optimum cement content and industrial by-products as binder components, for example, pulverised fuel ash and ground granulated blast furnace slag. Compared with the traditional Portland cement concrete, concrete elements made with such mixes are expected to have enhanced durability that is attributable to improvement in their microstructure, reduction in voids and increase in resistance to ingress of moisture, gases, etc. This paper examines whether such attributes of different concretes could also improve their engineering properties, e.g. increase in the ratio of flexural tensile strength to compressive strength, better bond between steel and concrete and, in the end, enhanced shear capacity. It is also proposed to examine whether flexural tensile strength should be used as a parameter in the design rules to obtain realistic estimates of shear capacity, in place of the compressive strength. This approach could promote the use of modern mix design techniques and it may have some positive influence on economy of concrete construction, particularly flat slabs, where depth of a concrete member is often governed by contribution of concrete to the shear capacity.
A routine method for measuring bond stress, steel strain and slip in reinforced concrete beams at service loads
Authors: Kankam C. K.
Published: October 2009

This paper presents a technique designed to give routine measurements of the average bond stress, average steel strain and total slip of a reinforcing bar relative to its surrounding concrete, between cracks in the constant moment region of concrete beams at their service loads. Tests were conducted on double pull-out concrete prisms reinforced with steel bars that had been fitted with transverse anchor bars at their centre. The major variables considered in the study that generally influence bond stress were type and size of bar, concrete strength and loading history. The method provides data to establish a relationship between the average bond stress, maximum steel stress and the total slip of the reinforcing bar. Equations have been derived on the basis of a linear distribution of the strain in the steel bar for the computation of average bond stress and average steel strain that are required for a rational calculation of crack width and deflections of structural concrete members.
Homogenisation of concrete in a batch plant: the influence of mixing time and method on the introduction of mineral admixtures
Authors: Vandanjon P.-O. , de Larrard F. , Dehousse B. , Villain G. , Maillot R. , Laplante P.
Published: October 2009

This paper presents a study conducted on the effects of mixing within a batch plant operation for ‘building industry’ type concretes containing mineral admixtures (fly ash, limestone filler or blast-furnace slag). The primary objective of this study was to evaluate the technical bases of French standard XP P 18-305, which stipulates that the mixing time of these concretes is to be increased whenever a mineral admixture is introduced, as opposed to the admixture being mixed with Portland cement to create a blended cement. Testing was carried out in a semi-industrial plant at a 1:1 scale; various techniques were employed both to evaluate the homogeneity of the batches and to characterise the performance of the materials produced. Results suggest a slight advantage in homogeneity in favour of the blended cements, yet this advantage at the scale of the completed structure is not necessarily significant. Moreover, the feasibility of concretes with a binder consisting of at least two-thirds blast-furnace slag, added into the mixer under typical batch plant operations, has been confirmed. The paper concludes with a few research directions in the area of concrete mixing.
In situ measurement of the intrinsic permeability of concrete
Authors: Claisse P. A. , Ganjian E. , Adham T. A.
Published: October 2009

In this paper test methods that could be used on in situ concrete are used to obtain values for the permeability of concrete. The permeability is of interest because it significantly affects the ability of the concrete to prevent corrosion of embedded reinforcement. The important feature of the tests in this paper is that they yield values for permeability that are expressed in fundamental units and therefore have a better foundation in materials science than tests which only yield comparative data. The two in situ tests used are a new vacuum–air test using drilled holes 1 and a surface absorption test. Results from these tests are compared with direct measurements of permeability obtained in a high pressure through flow cell. The results show strong correlations but some differences in absolute values are noted.
Performance of concrete mixes with OPC–PFA blends
Authors: Dias W. P. S. , Nanayakkara S. M. A. , Ekneligoda T. C.
Published: October 2009

This paper describes a comprehensive programme of testing for strength, durability (sorptivity, carbonation, drying shrinkage, sulphate attack and chloride ingress) and fresh-state properties (slump, slump loss, setting time, temperature rise and plastic shrinkage) of grade 25 and 35 concretes, where the ordinary Portland cement (OPC) binder was replaced with 15% and 25% of pulverised fuel ash (PFA). Three types of OPC–PFA mixes, designated ‘safe’, ‘workable’ and ‘economical’, were investigated. In general, the results from the PFA mixes were similar to or better than the OPC control mixes. The charge passed in the indirect chloride ion penetration test and the heat of hydration temperature rise were considerably reduced in the PFA mixes. They were however more susceptible to plastic shrinkage cracking. It was also found that the strength ratio between PFA mixes and OPC controls was slightly greater at 3 days than at 7 days, after which this ratio increased again, as expected.