bluuebunny/crossref_metadata_2025 huggingface dataset:
The strength development of silica fume concrete and its prediction under varying temperature conditions
Authors: Wen H. X. , Bagheri A. R. , Plum D. R.
Published: October 2009

The strength development of three silica fume concrete (SFC) mixes under the changing temperature conditions in a newly cast lining of a mine shaft has been investigated. A temperature matched curing rig has been improved for simulating different temperature regimes. The strength predictions of the SFC under changing temperature regimes show good agreement with test results, but adjustment of the empirical activation energy at high temperatures is necessary. The relationship between early-age splitting and cube compressive strength has been examined and was found to be different from that for conventional concrete due to the two-stage pattern of strength development of the silica fume plus superplasticizer concrete. Mixes involving two forms of silica fume, namely densified and commercially slurrified, are tested, and no notable dlfference has been found.
Steel in concrete: Part II Electron microscopy analysis
Authors: Glasser F. P. , Sagoe-Crentsil K. K.
Published: October 2009

The microstructure, crystallinity and the chemical and mineralogical constitutions of corrosion products formed under exposure of a steel-reinforced concrete fence post to normal atmospheric conditions have been investigated by analytical electron microscopy techniques. A bi-layered structure is observed comprised of a dense inner spinel phase (Fe3O4,/γ-Fe2O3,) in epitaxial orientation to the steel substrate and a relatively porous outer layer of mainly χ-FeOOH. A weak but apparent band showing a relatively elevated chloride concentration, rims the inner corrosion layer. The permeation through the corrosion layer of the products of cement hydration is indicated by the detection of nodules of Ca(OH)2, crystals at the steel reaction boundary. The mechanism of reinforced steel corrosion is thus evaluated on the basis 0fthese.finding.s and with special reference to the role of chloro-complexes and the modes of Eh, and pH buffering actions in the composite steel-corrosion product-cement system.
Membrane curing of concrete: water vapour permeability of curing membranes
Authors: Dhir R. K. , Levitt M. , Wang J.
Published: October 2009

This Paper describes the developmental work undertaken to enable the measurement of the water vapour permeability of a curing membrane and shows that a single-cell transmission test method which is inexpensive, versatile andeasy to operate can be usede effectively for this purpose. The water vapour permeability of a curing menzbrane determines that mernbrane's intrinsic moisture retention characteristic and is shown to provide a more reliable peyformance indicator for membrane curing of concrete than the commonlJ1 used curing efficiency index, which is an empirical and relative value that depends on a particular test method and measuring system.
A study of four waterproofing systems for concrete
Authors: Blight G. E.
Published: October 2009

As part of a study of possible mitigatory measures for concrete structures damaged by alkali–aggregate reaction, four treatments for waterproofing concrete (two coatings and two pore liner penetrants), have been compared. Tests were performed both on small specimens in the laboratory and on full–size structures in the field. It was found that none of the systems waterproofed concrete completely, but that three of them initially reduced the rate of water penetration, particularly under field conditions. Following initial tests, the laboratory specimens were exposed to the weather for four years, after which time the earlier tests were repeated. The effectiveness of the treatments applied in the field was also reassessed after four years. On the laboratory specimens, all treatments had apparently become more effective. In the field, the treatments had evidently retained moisture in the concrete, i.e. they had done precisely the opposite of what is required of a waterproofing system.
Effect of Ca(OH)2 on alkali–silica reaction
Authors: Wang H. , Gillott J. E.
Published: October 2009

Nevada opal was employed as a standard material to test the effect of Ca(OH)2 on alkali–silica reaction. It was found that when opal was present in various alkaline systems, their reactivity and expansivity were altered significantly. When opal was mixed with Ca(OH)2 at a mole ratio of C/S = 0·1 it showed very little reaction; when opal was mixed with NaOH at a mole ratio of N:S = 0·2 it was severely attacked and the reaction products were highly hygroscopic and expansive. Opal mixed with both calcium and sodium hydroxides at the above mole ratios was also severely attacked; however the reaction products showed no swelling capacity and their ability to sorb water was less than that of the products of opal–NaOH reaction.
Nature of compression strength in concrete
Authors: Penttala V. E.
Published: October 2009

A compression strength theory for concrete based on the capillary porosity of binder paste in concrete and the intrinsic tensional strength of the CSH gel is presented. The capillary pores were modelled as spheres of equal radius and the tensional stress peak on the surface of the voids was calculated using a FEM program. The intrinsic tensional strength of the binder was determined from gas evolution curves of the binder paste by thermogravimetric means. To validitate the theory, eleven different test concretes with compression strength values from 25 to 135 MPa were produced. As binders, five different Portland cement types with and without silica fume were used. The testing ages of the concretes were 28 and 365 days. The porosities of the test concretes were measured by mercury porosimetry, and the microporosity of the hardened binder paste by nitrogen adsorption. The correlation coefficient R-squared between the test results and the results of the theory was 0·941.
Tensile and flexural strength of cement mortar subjected to non-uniform self-stress
Authors: Tazawa E. , Miyazawa S.
Published: October 2009

In order to generate non-uniform self-stress that is different in area of working zone, the partial surface provided by controlling the coating area of mortar beams was exposed to drying conditions. The distribution of self-stress was experimentally determined by measuring the variation in strain when a part of the specimen was cut or notched. The beams were uniaxially or flexurally loaded, and the ultimate load was experimentally determined. The elastic strain due to self-stress was superposed on the strain due to the external load, then the stress distribution was determined from a simplified stress-strain curve in which tension softening was taken into consideration. The values of ultimate load which were calculated from the stress distribution showed good agreement with the observed ones.
Support reaction and its implication for orthotropy in the yield-line method
Authors: Johnarry T
Published: October 2009

The yield-line method is widely used for the analysis and design of reinforced concrete slabs. The distribution of support reaction has hitherto not been found, and hera method for the compatible reaction is described. The solution for the reaction and the attendant bending moments over the yield-lines also lead to the solution for the hithertounsolved problem of the degree of orthotropy in the slabs.
Creep recovery of plain concrete and its mathematical modelling
Authors: Yue L. L. , Taerwe L.
Published: October 2009

In order to study creep recovery of plain concrete, an extensive series of creep tests was carried out on normal-strength concrete and high-strength concrete. The main aspects studied are the influence of preloaded stress level, loading age and unloading age on creep recovery. Test results obtained on high-strength concrete and normal-strength concrete are compared, from which the influence of concrete strength on creep recovery is obtained. The experimental results have confirmed that creep recovery is linearly related to the preloaded stress level, and they reveal that both loading age and unloading age have significant influences on creep recovery. However, concrete strength has little influence on creep recovery. Based on the test results, a formula to predict creep recovery has been obtained by making use of an optimization technique.
Torsional behaviour of precast concrete edge beams and connections
Authors: Elliott K. S. , Davies G. , Adlparvar R. M.
Published: October 2009

This Paper examines the effect of connections on the torsional behaviour of precast concrete edge beams in temporary and permanent condition in precast concrete buildings. Two types of connection are considered: the end connection to columns, and the connection between the beam and the precast floor units. In both cases the site-placed concrete gives some measure of composite action. 600 mm deep and 300 mm wide L-shaped edge beams with the rigid end condition failed in torsion where there was twisting of the beam, accompanied by large rotations and yielding of shear reinforcement. Torsional capacities exceeded the AC 1318 and BS 8110 ultimate design values by factors of l·43 and 2·51, respectively. When edge beams with real column connections were subjected to the same loading, failure occurred in the joints unless there was a top connection. When the same beams were tested compositely with hollow-cored slab there was no torsional failure in the beam. This represented the permanent condition in a precast frame. There are two factors which contribute to the elimination of torsion in precast edge beams: a self-equilibrating horizontal propping force provided by the slab, and a reduction in the eccentricity of slab loading. the design recommendations are that edge beams need not be reinforced agains torsion, provided that the beam contains the minimum area of stirrups, that hollow-cored flooring with a bearing of 75 mm is used, and that tie reinforcement is provided between the edge beam and slab. The in situ concrete should be at least grade 25 N/mm2.
Simulation tank to aid interpretation of radar results on concrete
Authors: Bungey J. H. , Millard S. G. , Shaw M. R.
Published: October 2009

Subsurface scanning impulse radar has grown in popularity in recent years, especially for the location of reinforcing bars and voids within concrete. The interpretation of results is often subjective and based on previous experience. However, there is a lack of detailed published data from systematic studies to assess objectively the capabilities of radar. The propagation and reflection of radar signals are governed by the dielectric constantsand conductivities of the materials involved. A simulation tank has been developed which utilizes an oil-water emulsion which may be modified to match both the dielectric and conductivity properties of a range of concretes. This enables a wide selection of features to be modelled in the laboratory, either singly or in combination, to provide characteristic responses. Initial attention has been concentrated on the presence of reinforcing bars and air voids, with results compared with those from laboratory and on-site concrete specimens. The development and capabilities of the approach are described, and illustrated by some typical results. These are found to resemble closely those obtained on concrete, and there is considerable scope for usage of this facility to aid the understanding and interpretation of results from concrete elements in the field.
Deflection and ductility of continuous RC beams
Authors: Scholz H.
Published: October 2009

Recent research work by the Author in the fields of deflection and ductility of reinforced concrete beams has shown that in design-oriented procedures both these aspects can be controlled through effective depth-linked requirements. The present study compares the required effective depth to meet a specified deflection limit with the effective depth satisfying a given ductility capacity. Domains are identified that are governed by deflection or by ductility limitations. It has been concluded that many practical continuous beams that meet the usual deflection limits are also satisfactory in regard to ductility. Thus the need to examine ductility falls away in many instances. A numerical example is used to illustrate the findings of this study.
Straw pulp waste liquor as a water-reducing admixture
Authors: Chang D. Y. , Chan Sammy Y. N.
Published: October 2009

This paper discusses the production and properties of a new water-reducing admixture produced from alkaline treated straw pulp waste liquor. The development of the new material could help to eliminate the environmentally polluting black waste liquor of paper pulp, and also provides a low-cost by-product that can be wideldx-4 used in the construction industry. It could have important social and economic benefits. The new water-reducing admixture is produced by evaporation and sulphonation of the alkaline treated black straw pulp waste liquor. It gives a water reduction of over 8%, and the compressive strength of concrete could be increased by over 10%. n admixture complies with the relevant Chinese National Standard. Trial tests show that this type of water-reducing admixture can be further modified to become a high-range water reducer by use of a modifying agent.
Horizontal web steel as shear reinforcement
Authors: Desai S. B.
Published: October 2009

This paper concerns the enhancement of shear resistance of reinforced concrete members using horizontal web steel. Based on a test programme, a design rule is proposed for enhancement of shear resistance of a reinforced concrete member when horizontal web steel is provided at the centre of the cross-section. This rule could be used in conjunction with any design method where the shear resistance of a section is obtained by adding the individual contributions of concrete and the web reinforcement. For members exposed to fire, there are potential benefits in providing central bars as shear reinforcement.
A new technique for measuring the air permeability of near-surface concrete
Authors: Dhir R. K. , Hewlett P. C. , Byars E. A. , Shaaban I. G.
Published: October 2009

A non-destructive, rapid test capable of measuring the air permeability of in situ concrete is described. The technique is based on the application of a hard vacuum to the concrete surface. The rate of pressure recovery is recorded after the vacuum line is disconnected. The experimental results lead to an exponential pressure–time relationship similar to that obtained from analytical solution of Darcy’s equation. The air permeability of concrete can be simply expressed in terms of a vacuum decay parameter, but minor changes in the application of the test make it possible to determine the air permeability of concrete in situ. The test results are sensitive to changes in the parameters that affect the pore structure of concrete, including water–cement ratio, curing conditions, cement content, air content and plasticizing admixtures.
Relationship between the rheology of unvibrated fresh concrete and its flow under vibration in a vertical pipe apparatus
Authors: Banfill P. F. G. , Yongmo Xu , Domone P. L. J.
Published: October 2009

Ten different concretes have been tested under vibration using a vertical pipe apparatus. The fluidity of the vibrated concrete, determined from the rate of efflux from the pipe, is controlled by the peak velocity of the vibration and influenced by the rheology of the unvibrated concrete. Fluidity is proportional to peak vibrational velocity up to a critical level, above which it increases no further. The critical velocity is proportional to the yield value of the unvibrated concrete, and the peak fluidity is inversely proportional to the plastic viscosity of the unvibrated concrete.
Towards the design of reinforced concrete eccentric beam—column joints
Authors: Vollum R. L. , Newman J. B.
Published: October 2009

The authors have previously proposed a simplified method for the design of external beam—column joints. This paper extends that work to joints in which one of the beams is eccentric to the column. Such connections occur in practice owing to architectural and geometrical constraints. Results are presented for tests on ten specimens in which one of the two beams framing into the column was eccentric to the column. The authors are unaware of any previous tests on such specimens. The tests were designed to investigate the effects of eccentricity and reinforcement detailing on connection strength, cracking and deformation. The tests showed that such connections can be used in practice providing that the torsional capacity of the joint is not exceeded. An analytical model is developed for predicting the strength of such connections and preliminary design recommendations are made. The work is also relevant to the case of joints where the beam is wider than the column.
Effect of high–intensity sustained triaxial stresses on the mechanical properties of plain concrete
Authors: Taliercio A. L. F. , Berra M. , Pandolfi A.
Published: October 2009

An experimental research programme was carried out to investigate the effects of high–intensity prolonged triaxial stresses on the strength and stiffness properties of concrete. The specimens tested were subjected to constant stresses equal to 90 or 95% of the failure stress deviator under monotonic loading in different deviatoric planes. The stiffness properties of the specimens were evaluated at different time intervals. The decrease in shear modulus was taken as a measure of the creep–induced damage. The specimens which did not fail at constant stress within five days were unloaded and monotonically reloaded to failure. For the specimens tested at the lower stress, damage tends to stabilize after the early stage at constant load, whereas, for the tests performed at the higher stress, damage seems to keep on increasing for the entire duration of the creep test. The strength of the specimens surviving the creep tests was found to increase moderately with respect to the control samples, with the failure envelope of the material being dependent on the hydrostatic creep stress.
The importance of gas permeability in addition to the compressive strength of concrete
Authors: Abbas A. , Carcasses M. , Ollivier J. P.
Published: October 2009

The permeability to gases of cementitious materials is one of the major contenders for becoming a standard parameter for the quantification of the durability of these materials. This coefficient is thought to be closely related to the compressive strength. It is shown systematically here, by conducting permeability studies as a function of the degree of saturation of concrete on two sets of concrete compositions having the same compressive strength (100 MPa and 25 MPa), that entirely different gas permeability values may exist for different mix compositions which have the same compressive strength. These measurements were carried out on 5 cm thick, 15 cm dia. specimens by using a CEMBUREAU permeameter and oxygen as the percolating fluid. The results emphasize the fact that the 28 day compressive strength alone cannot be a criterion of the durability of concrete unless it is coupled with the quantification of the resistance to the entrance of aggressive chemicals.
A theoretical refinement of Branson's effective-moment-of-inertia equation
Authors: Gohnert M. , Xue P. Y.
Published: October 2009

Branson's effective-moment-of-inertia equation is semi-empirical. The exponent m was derived from 58 beam tests performed by himself. As with all empirical work, the equations are potentially limited to the sample of data from which the equations were derived. For this reason, a theoretical form of the exponent m has been developed to allow a more generic application of the theory. An alternative moment-of-inertia equation is also given which is equivalent to the theoretical version of Branson's equation, but simpler in form. To validate the proposed theory, a series of tests were done to illustrate the accuracy of the equation.
A model for the bond between concrete and reinforcement
Authors: Lundgren Karin , Gylltoft Kent
Published: October 2009

The bond mechanism between deformed bars and concrete is known to be influenced by a number of parameters, such as the strength of the surrounding structure, the presence of splitting cracks and yielding of the reinforcement. However, when reinforced concrete structures are analysed with finite element models, it is quite common to assume that the bond stress depends solely on the slip. A new model has been developed, which is specially suited for detailed three-dimensional analyses. In this new model, the splitting stresses of the bond action are included, and the bond stress depends not only on the slip, but also on the radial deformation between the reinforcement bar and the concrete. Bar pull-out tests with various geometries and with both monotonic and cyclic loading have been analysed. The results show that the new model is capable of predicting splitting failures and the loss of bond if the reinforcement is yielding, as well as dealing with cyclic loading in a physically reasonable way.
Study on the reuse of returned concrete
Authors: Okawa Y. , Yamamiya H. , Nishibayashi S.
Published: October 2009

A method to reuse concrete that has been returned from the job site either entirely or partially unused is studied. By adding a stabilizer to returned unused and returned concrete to cease cement hydration, leaving it in a fresh concrete state for a long time, and then adding an activator the following day to produce R-concrete, the concrete can be reused in the same manner as ordinary concrete. By adding a superplasticizer to the concrete to obtain sufficient consistency with slump of 22 cm, an 18 cm slump can be obtained the next day. The properties of R-concrete, such as compressive strength, freeze resistance and change in length are equivalent to ordinary concrete. The longer the setting time of the returned unused concrete, the longer the setting time of R-concrete made by adding stabilizer to it. On the other hand, R-concrete made by mixing returned concrete with new concrete exhibits an equal setting time to ordinary concrete.
Zeolite ceramsite cellular concrete
Authors: Feng N.-Q. , Xing F. , Leng F.-G.
Published: October 2009

When the natural zeolite ceramsite (NZC) is added to cellular concrete, using the natural-zeolite powder as a gas carrier, natural-zeolite ceramsite cellular concrete is formed. It is a new type of concrete. Its compressive strength at 28 days is 12–14 MPa, while its density is 900–1000 kg/m3. It has a double capillary structure of cellular concrete and ceramsite. The NZC absorbs water and its capillaries are full of water when the concrete is mixed. But after concrete hardening, the capillaries in the NZC undergo ‘self-vaccumization’ owing to dehydration, so that the adhesion between the ceramsite and cellular concrete is increased.
Residual fracture properties of normal- and high-strength concrete subject to elevated temperatures
Authors: Zhang B. , Bicanic N. , Pearce C. J. , Balabanic G.
Published: October 2009

The effects of elevated temperatures (Tm), related to the exposure period (th) and the curing age (ta), on the residual fracture properties of normal-strength concrete (NSC) and high-strength concrete (HSC) were investigated by conducting three-point bending tests on 87 notched preheated beams. Most beams were exposed to temperatures between 100°C and 600°C for 12 h at 14 days, while some NSC beams were heated either for various exposure periods up to 168 h at 14 days or for 12 h at 7, 28 and 90 days. The weight loss (ω) was also monitored. The measured residual properties included the energy parameter (fracture energy GF), a number of strength parameters (compressive strength fcu, tensile strength f′t and modulus of rupture fr), stiffness parameters (Young's modulus Ec and Poisson's ratio νc) and the brittleness parameter (the characteristic length lch). ω increased with Tm and th but decreased with ta. There existed a transition point for ω at 200°C which could mark a distinction between physical and chemical processes. GF increased with Tm and ω up to 300°C and then decreased. GF also increased with th at lower temperatures but decreased at higher temperatures, and increased with ta as well; fcu, f′t and fr did not change very much with Tm up to 200°C and decreased thereafter. A longer th had an intensifying effect on all strengths at lower temperatures but a damaging effect at higher temperatures. All strength parameters increased with ta. Ec and νc decreased continuously with Tm, th and ω. Ec increased whereas νc decreased with ta. The concrete became less brittle with increasing Tm, th and ω or with decreasing ta. In this study, all fracture parameters tended to become stable at 90 days. Finally, a linear relationship between GF and fcu existed not only for room temperature but also for higher temperatures.
Chloride transference numbers in steady-state migration tests
Authors: Castellote M. , Andrade C. , Alonso C.
Published: October 2009

The present paper is part of a series to study the different basic aspects of migration experiments. In it, chloride transference numbers are used to find the optimal testing conditions. First, the evolution of transference number values of chlorides a steady-state experiment is studied. Then, the meaning of the maximum, which appears when the anodic chloride transport number is calculated, is interpreted. The experimental data from two series of experiments (NaCl and steel electrodes, using finite and infinite sources, and CuCl2 and copper electrodes) with different Cl− concentrations (0·05, 0·1, 0·2, 0·5 and 1 M) are fitted to a Gauss modified exponential equation, which has enabled us to obtain the coulombs corresponding to the mentioned maximum and to determine the better conditions to perform a steady-state migration test: it seems that they are 1 M NaCl as catholyte solution and steel electrodes. Also, some terms have been added to the nomenclature of transference numbers previously proposed by the authors.
A new classification system for fire-damaged concrete based on the strain energy dissipated in a hysteresis loop
Authors: Nassif A. Y.
Published: October 2009

This paper reports on experimental research into further developing the stiffness damage test (SDT) as a quantitative tool to be used in assessing fire-damaged concrete. The research programme reported here aimed at establishing the correlation between the strain energy dissipated in a hysteresis loop, performed on fire-damaged concrete core, and the post-firing residual stiffness characteristics. The dependency of such correlation on the level and mechanism of damage was investigated by involving five test variables, namely: maximum temperature of exposure, method of cooling, duration of thermal exposure, grade of concrete and type of aggregate used. The investigation involved approximately 180 concrete cores (75 mm in diameter × 175 mm long) which were extracted from river gravel and limestone aggregate concrete blocks. The cores were subjected to various heating and cooling regimes in the temperature range 217–470°C. The extent of fire damage was assessed using the SDT for determining the characteristics of quasi-static low-stress load–unload cycles. The strain energy dissipated in a hysteresis loop was adopted as a dimensionless damage index (DI) by dividing it by the stress range. Both the DI and the residual plastic strain were found to correlate well with the percentage residual initial and chord moduli. Such strong correlation is used to introduce a new classification system for the level of fire damage in concrete. A DI of 5 is associated with a 24% reduction of the chord modulus while a DI of 20 is associated with a 66% loss of the chord modulus. The coefficient of variation, which is used as a repeatability indicator, of the SDT parameters was found to be within acceptable limits. The correlation between the maximum temperature of exposure and the residual stiffness characteristics was also established. It is evident that the residual stiffness of fire-damaged concrete is not a sole function of the maximum temperature of exposure. The method of cooling, duration of exposure, and type and grade of the fire-affected concrete materials are major determinants in the extent of damage.
High-pressure foam method for the fracture and stripping of concrete structures
Authors: Young C. , Otuonye F. , Jia J.
Published: October 2009

A controlled foam injection (CFI) method has been developed, tested and demonstrated to have capabilities to fracture and strip reinforced concrete structures such as pavements and bridge decks. The method uses a high-pressure foam to initiate and propagate fractures in concrete structures. In contrast to methods using explosives to fracture and break concrete or rock, the CFI method does not generate ground vibrations or airblast. The foam components are biodegradable and environmentally benign. The CFI method can be used for demolition work or the repair and rehabilitation of degraded concrete structures.
Softening behaviour of concrete prisms under eccentric compressive forces
Authors: Debernardi P. G. , Taliano M.
Published: October 2009

The behaviour of reinforced concrete elements has been analysed by means of tests on prisms subjected to normal forces with different degrees of eccentricity. The tests were performed in strain-controlled conditions until failure. Along the fibres running parallel to the axis of the specimen, stress–strain curves are seen to be homogeneous before peak load is reached, whereas the deformations measured in the softening branch are more scattered and are found to depend on gauge length due to strain localisation within the compressive zone. This behaviour is also verified for specimens subjected to centred compression and makes it difficult to define the stress–strain plot in the softening branch. By assuming a σ–ε constitutive law based on the deformation measured over a predetermined gauge length in centred compression tests, the results of tests conducted with eccentric loads were compared to those obtained under the commonly accepted assumption of plane section remaining plane and the possibility of stress integration. In this case, all specimens were of the same size and the measurements were performed over the same gauge length. The maximum loads obtained experimentally for each test were seen to be higher than the theoretical loads and to increase in percentage with increasing eccentricity. Since increasing eccentricity corresponds to a decrease in the size of the compression zone, it can be inferred that the scale effect on the compressive strength of concrete is a function of the height of the compression zone.
Effect of moisture content of highly porous bottom ash on properties of concrete mixture and hardened concrete
Authors: Nisnevich M. , Sirotin G. , Dvoskin L. , Eshel Y.
Published: October 2009

Research for advantageous utilisation of bottom ash presently formed at thermal power stations by using pulverised coal combustion is being conducted at The Research Institute of The College of Judea and Samaria (Ariel, Israel). It proves the effectiveness of comprehensive use of highly porous bottom ash as aggregate and fly ash as additive for production of lightweight concrete. Proportions, properties and conditions of producing normal weight concrete-comprised fly ash were considered by a number of experiments. However, the problem of using highly porous aggregates with fly ash as an additive is inadequately studied and elucidated in technical publications. One of the main features of these concrete mixtures is a high content of water, resulting in two conditions: (a) absorption of water by highly porous bottom ash particles; and (b) bonding the water to the fine fly ash particles. The goal of this research was to study the proportions and properties of the considered concretes. The research was concentrated on evaluating the effect of moisture content of the bottom ash on the lightweight concrete strength and the concrete mixture proportions. The actual problem depends on using water to sluice off the bottom ash from the furnaces and hydraulic transport at present power stations.
Moment redistribution in continuous profiled steel–concrete composite slabs
Authors: Lee L. H. , Quek S. T. , Ang K. K.
Published: October 2009

The moment redistribution behaviour of continuous cold-formed profiled steel deck and concrete composite slab was studied both experimentally and numerically. An experimental programme consisting of three two-span continuous composite slabs was performed. The experimental results indicated that the composite slabs have adequate ductility for redistributing moments, and the ultimate capacity of continuous composite slabs can be increased significantly. The short-term deflection at the increased service load satisfies the serviceability criteria. A numerical procedure to determine the negative to positive moment redistribution capacity and the corresponding deflection at serviceability for profiled steel–concrete composite slab was validated using the experimental results.
Estimation of torsional crack width for concrete structural members
Authors: Park Sun-Kyu , Ko Won-Jun , Kim Hyeong-Yeol
Published: October 2009

This paper deals with the estimation of crack width for the concrete structural members under pure torsion. An analytical method is proposed to estimate the torsional crack width for the reinforced concrete members. The proposed method utilises the conventional crack theory and can take into account the bond-slip between the reinforcement and concrete. The stresses induced in the reinforcement and concrete under torsion are obtained by using the space truss theory. An analytical equation for the estimation of the maximum crack width is formulated as a function of the mean bond stress. The validity, accuracy, and efficiency of the proposed method are established by comparing the results of present study with the experimental data as well as the results obtained from the analytical study. The results of analysis presented in this paper indicate that the proposed method can be effectively used to estimate the torsional crack width of the concrete structural members under torsion.
Vapour phase application of hydrophobic coatings to cement-based materials
Authors: Chowdhury A. , Gillies A. , McDonald P. J. , Mulheron M.
Published: October 2009

A new method of applying hydrophobic coatings to cement-based materials based on exposure to the treatment vapour is proposed. The method is demonstrated for the application of monomeric alkyl (isobutyl) alkoxy silane to cement paste and mortar samples manufactured and cured under a variety of conditions. The efficacy of the treatment is compared to conventional flood coating using magnetic resonance imaging (specifically SPRITE) to monitor the time dependent uptake of water into treated samples. It is concluded that the method as proposed is of significant benefit for some of the samples.
Strength impairment of concrete mixed in hot weather: relation to porosity of bulk fresh concrete paste and maturity
Authors: Mouret M. , Bascoul A. , Escadeillas G.
Published: October 2009

Normal-strength concrete mixed in summer can be less strong than the annual average. One cause of these variations is the effect on concrete strength of the temperature of the constituents. Concretes were cast at different temperatures because of different temperatures of the constituents. The slump value, which is the criterion for acceptance on the building site, was kept constant whatever the initial temperature may be, either by the addition of water or by the use of a plasticiser at the end of mixing. Concretes were cured for 24 h under either the conditions specified in the French standard for manufacturing control or simulated hot weather conditions, and then stored in water at 20°C up to the time of test. Compressive strength was determined at 1, 7 and 28 day ages on 11 × 22 cm cylinders. The results show that the decrease in strength is dependent on the combined effective water and air content of the bulk paste of fresh concrete, and on the maturity of the concrete, which is influenced by its temperature history. By combining two classical relations: strength and design factors (Feret's relation) and strength and maturity (Arrhenius Law), decreases in strength could be analysed for any mixing and curing conditions.
A compressive strength model for roller-compacted concrete with fly ash
Authors: Tangtermsirikul S. , Kaewkhluab T. , Jitvutikrai P.
Published: October 2009

Roller-compacted concrete (RCC) is typically used in the construction of dams and road pavements since it provides substantial benefits over conventional concrete for the construction of such structures such as faster construction, lower costs of construction and materials, etc. Incorporating fly ash into RCC can further reduce cost of materials and enhance the concrete performances. Recently, a huge fly ash RCC dam (Tha Dan Dam) project was started in Thailand. This utilises the largest the volume of RCC in the world at 5 million m3. However, one of the main problems concerns the mix proportion of RCC with fly ash. This paper presents a model for predicting compressive strength of RCC with fly ash in order to minimise the process of trial mixing. The model was formulated based on quantities of concrete ingredients, chemical compositions and physical properties of cement and fly ash. It was found that at room temperature of 28 ± 3°C the proposed model could be used to predict compressive strength of the tested mixtures of roller-compacted concrete with fly ash designed for dams and road pavements at the ages between 3 and 91 days with satisfactory accuracy.
Effects of a fine smoothing mortar layer in the prevention of chemical floor covering deterioration
Authors: Räsänen V. , Eronen J. , Wirtanen L. , Penttala V.
Published: October 2009

This paper examines how a fine smoothing mortar (FSM) layer affects the moisture state and performance of covered concrete slabs, and discusses ion and pore water transport through the FSM layer from the concrete slab to the adhesive and overlaying floor covering materials. Similarly, changes in the pH value of the FSM due to ageing and moisture content are also discussed. In order to obtain a fast floor covering time and to ensure that the moisture content under the floor covering does not impair quality, a thin FSM layer should be installed fairly soon after casting and after necessary curing it should be allowed to dry uncovered for few days to several weeks. It has been confirmed that a low-alkali smoothing mortar layer can hinder the destruction of adhesives and floor covering materials caused by high moisture content, alkalinity and high OH− ion contents in the pore water of concrete. However, where the mortar layer has cracked, it has also been found that the performance and quality of the covering material can be reduced even when a low-alkali smoothing mortar layer is used. Cracks in the smoothing mortar layer can cause moisture and reactive ions to penetrate the adhesives and floor covering layers. The destruction of some adhesives can take place also in a low pH and high RH environment, and the adhesion between concrete and the FSM layer can be lost due to high pH at the concrete surface.
Properties of volcanic scoria based lightweight concrete
Authors: Hossain K. M. A.
Published: October 2009

The results of investigations on the suitability of using volcanic scoria (VS) as coarse aggregate in lightweight concrete production are reported. Tests were conducted on concrete by replacing 0–100% of coarse crushed gravel aggregate by volume. The physical properties of volcanic scoria were critically reviewed to evaluate the possible influence on both the fresh and hardened state of concrete. The properties of VS concrete using different percentages of VS aggregate were evaluated by conducting a comprehensive series of tests on workability, strength, drying shrinkage, surface absorption and water permeability. It is concluded that the VS concrete has sufficient strength and adequate density to be accepted as structural lightweight concrete. However, compared with the control concrete, the VS concrete has a lower modulus of elasticity, and higher permeability and initial surface absorption.
Equivalent gas permeability of concrete samples subjected to drying
Authors: Verdier J. , Carcassès M.
Published: October 2009

The aim of this work is to give an equivalent gas permeability in order to estimate the associated flow through a concrete specimen exposed to drying, for example with a non-uniform moisture distribution inside (equivalent to a saturation profile), and related to the apparent permeability value, calculated for the same dry sample. The chain of reasoning to obtain this permeability for a given drying situation requires estimation of the water content profile via a model of drying, and of the relative permeability (determined for a given constant moisture content in concrete) over the entire saturation field. The method is based on a finite element idealisation of the sample thickness by a discrete approach in one dimension. It is the analogy between Darcy's law and Ohm's law that allows the local relative permeability to be likened to a local conductivity. Then the existing relation between conductivity and conductance leads to the determination of an equivalent conductance that is transformed into an equivalent conductivity. Thus the equivalent permeability that is calculated on the basis of this modelling is representative of a real in-situ phenomenon. This approach allows a more precise estimation of the flow rate variation in structures subjected to pressure increase as, for instance, in security tests of nuclear containment vessels.
Mesomechanical model for concrete. Part II: applications
Authors: Teng J. G. , Zhu W. C. , Tang C. A.
Published: October 2009

In Part I of the study reported in the companion paper, a mesomechanical model for concrete was formulated, and the roles of various parameters of the model were examined in detail. In this paper, results from numerical simulations obtained using the computer program CFPA (Concrete Fracture Process Analysis) employing the mesomechanical model presented in the companion paper are presented. These simulations cover a variety of loading conditions including uniaxial compression, uniaxial tension, indirect tension, shear and biaxial loading, and an fibre-reinforced polymer-to-concrete bond test. The results show that the CFPA program can successfully simulate the entire fracture process of concrete, including the initiation, propagation and coalescence of cracks, localisation of deformation and stress redistribution.
FE analysis of RC shear walls subject to monotonic loading
Authors: Kwak H.-G. , Kim D.-Y.
Published: October 2009

This paper describes the implementation of an orthotropic concrete model in a non-linear finite-element analysis of reinforced concrete structures subject to monotonic in-plane shear. Based on the force equilibria, compatibility conditions, and bond stress–slip relationship between the reinforcement and the surrounding concrete, a criterion for considering the tension-stiffening effect is proposed, using the concept of average stresses and strains. The material behaviour of concrete is described by an orthotropic constitutive relation, focusing on the tension–compression region with tension-stiffening and compression-softening effects defining the equivalent uniaxial stress–strain relation in the axes of orthotropy. The behaviour of cracked concrete is described by a system of orthogonal cracks, which follows the principal strain directions and rotates according to the loading history. Finally, correlation studies between analytical results and available experimental data are conducted to assess the validity of the proposed models.
Impact of optimal longitudinal reinforcement on the curvature ductility capacity of reinforced concrete column sections
Authors: Hernández-Montes E. , Aschheim M. , Gil-Martín L. M.
Published: October 2009

The traditional practice of providing symmetric reinforcement in column cross-sections has been shown to be non-optimal for columns subjected to non-symmetric design loads. An approach for determining a continuum of acceptable combinations of reinforcement by means of a reinforcement sizing diagram (RSD) has been described recently. This approach allows the minimum (or optimal) reinforcement of a cross-section to be determined based on strength considerations. This paper compares the curvature ductility capacity of cross-sections designed with optimal reinforcement to that obtained for cross-sections having symmetric reinforcement, for discrete values of axial load between 0% and 65% of Agfck, where Ag is the gross section area and fck is the concrete compressive strength. Unconfined concrete and confined concrete behaviour are considered, with the latter based on the Mander model, for confinement satisfying the requirements of ACI-318-02 for high seismic zones. The use of non-symmetric longitudinal reinforcement is determined to cause small to moderate changes in the computed curvature ductility capacities relative to the values computed for conventionally reinforced columns.
Bond of high-strength concrete under monotonic pull-out loading
Authors: Alavi-Fard M. , Marzouk H.
Published: October 2009

An experimental investigation was conducted on high-strength concrete specimens to examine the bond strength characteristics under monotonic loading. The range of compressive strengths tested was between 70 and 95 MPa. The influences of load history, confining reinforcement, bar diameter, concrete strength, reinforcement spacing and rate of pull out were investigated experimentally. The internal concrete strains close to the contact surface and also the steel strain were measured. The test set-up, load application, instrumentation and measurement, and test procedure were designed to measure strains and deformations. Several specimens with reinforcement bar diameters of 20, 25 and 35 mm were tested. The test results revealed that the bond strength of high-strength concrete is higher than the corresponding normal strength concrete. However, the bond behaviour of high-strength concrete is more brittle in comparison with normal strength concrete. The concrete strains were measured around the steel reinforcement. Concrete strain measurements are useful to identify the internal crack pattern and to predict possible failure modes. The area under the curve of the bond stress–slip curve can define the bond energy. The bond energy is related to ductility and can be used along with the bond strength in evaluating the bond behaviour of high-strength concrete.
Shear strength of reinforced recycled concrete beams without stirrups
Authors: Fathifazl G. , Razaqpur A.G. , Isgor O.Burkan , Abbas A. , Fournier B. , Foo S.
Published: October 2009

A new method of mixture proportioning is used for investigating the shear performance of reinforced concrete (RC) beams made with coarse recycled concrete aggregate (RCA). In this method, RCA is treated as a two-phase material comprising mortar and natural aggregate therefore to proportion the concrete mixture with RCA, the relative amount and properties of each phase are considered separately. Using the new mix proportioning method, several beams were designed and tested to study the effect of a number of parameters including the shear span-to-depth ratio and beam size on the serviceability and strength of RCA concrete beams without shear reinforcement. For each beam its load–deflection curve, shear deformations, diagonal cracking load, crack pattern, ultimate shear strength and failure mode were determined. The results showed that the shear performance of RC beams made with RCA can be comparable, or even superior, to that of beams made entirely with natural aggregates at both serviceability and ultimate limit states, provided the proposed mixture proportioning method is used. Furthermore, the simplified methods of ACI and CSA standards as well as Eurocode 2 were found applicable to all reinforced RCA-concrete beams.