bluuebunny/crossref_metadata_2025 huggingface dataset:
Bond behaviour of low-strength concrete
Authors: Mohamed A. Z. , Clark L. A.
Published: October 2009

Appraisals of existing buildings have shown that concrete with strength much lower than the minimum values specified in design codes can be encountered. In this Paper the results are presented of twelve series of bond tests covering plain and deformed bars with a concrete of mean strength ∼ 5 N/mm2. Other variables are the presence of links and the cover/diameter ratio. The flexural tensile strength of the low-strength concrete is found to be low when compared with the relationships usually adopted in UK design codes for normal-strength concretes. However, the splitting tensile strength is related to compressive strength in a similar manner to normal-strength concrete, and bond strength results show that the BS 8110 bond equations can generally be safely used for the assessment of low-strength concrete with deformed bars, but are optimistic for plain bars.
Stability and plastic design of RC sway frames
Authors: Scholz H.
Published: October 2009

This Paper addresses stabiliq aspects in plastic analysis and the design of reinforced concrete sway frames. Simple slenderness rules are developed to control-in-plane overall frame buckling and member buckling. A numerical example and various comparisons are used to justify the proposals and to illustrate the simpliciq of the method in practical design.
Deleterious alkali–silica reactivity in the laboratory and under field conditions
Authors: Hobbs D. W.
Published: October 2009

Expansion test results are reported for concretes made with a range of original alkali contents and prepared a number of UK aggregates containing chert and flint. The concretes were subject to three exposure regimes: moist storage at 38°C, moist storage at 20°C, and external exposure. The current age of exposure for some of the concrete prisms stored at 20°C and some of the concrete blocks stored externally is 4·5 years. It is shown that original alkali contents above about 5·0 kg/m3 are necessary for deleterious expansion to result from alkali–silica reaction, and that concretes stored externally which have exhibited abnormal expansion within 4 years gave expansions in excess of 0·2% when stored moist at 38°C for one year. A model is presented which may enable the expansion behaviour of a number of the concretes tested under field conditions to be broadly predicted from the expansion measurements made in controlled tests on same concretes.
Bond strength tests for ribbed bars in lightweight aggregate concrete
Authors: Clarke J. L. , Birjandi F. K.
Published: October 2009

This Paper outlines a project to study the bond characteristics of ribbed reinforcement in structural lightweight aggregate concrete, using aggregates available in the UK. Because there are different methods of determining bond, three approaches were considered in this investigation, but the majority of the programme used the test method developed at the BCA. The Standard BSI and RILEM methods are discussed briefly in an appendix.
Response of prestressed concrete continuous beams to static loads
Authors: Mo Y. L. , Chien C. F.
Published: October 2009

The inelastic response of statically indeterminate reinforced concrete frames can be predicted by the trilinear theory reported recently. In this Paper the trilinear theory is further developed to include prestressed concrete continuous beams. This generalized theory predicts the inelastic response of 15·24 m long continuous prestressed concrete test beams with acceptable accuracy.
Development of a non-destructive test to quantify damage in deteriorated concrete
Authors: Chrisp T. M. , Waldron P. , Wood J. G. M.
Published: October 2009

A non-destructive test to quantify the degree of deterioration in concrete is described. Developed originally for the assessment of concrete damaged by Alkaki–Aggregate Reaction, the test has potential as a technique to measure the degree of internal damage caused by other actions such as thermal cycling, fire and impact loading. To date, the test has been applied to approximately 1000 core specimens from concrete displaying varying degrees of deterioration, and it appears to be robust and repeatable. In the test a sensitive compressometer is used to measure strain during cycles of compressive load applied at a slow strain rate by a servo-controlled machine. Data are recorded and processed automatically on a microcomputer. Subsequent calculation of hysteresis and stiffness permits a number of damage parameters to be established for each specimen. Early results indicate a strong correlation between these parameters and the degree and nature of the observed damage.
Response of box tubes to dynamically applied torsions
Authors: Mo Y. L. , Yang R. Y.
Published: October 2009

Based on equilibrium and compatibility conditions, as well as a stress—strain relationship for softened concrete, a truss model theory for reinforced/prestressed concrete box tubes subjected to static torsions was applied to determine the torque–twist relationship as the primy curve for the purpose of dynamic analysis. In this Paper, the inelastic response of reinforced/prestressed concrete box tubes to dynamically applied torsions is predicted using the primary curve obtained by the truss model theory, the hysteresis loops model proposed for shearwalls and the linear acceleration step-by-step method. Furthermore, the algorithm is described, and a numerical example is given.
A study of carbonation-induced corrosion
Authors: Parrott L. J.
Published: October 2009

This study is concerned with measurements of corrosion in steel rods embedded at 4, 8, 12 and 20 mm from the exposed surface of concrete dried and carbonated uniaxially for 0·4, l·5 and 4 years. Corrosion was stimulated by exposing all specimens to a moist environment for a prescribed period prior to extraction and cleaning of the rods for gravimetric corrosion measurements. Corrosion was mainly controlled by the unneutralized remainder, i.e. the depth of reinforcement cover minus the depth of carbonation. Corrosion increased as the unneutralized remainder reduced from about +5 mm to −10 mm. The relationship between corrosion and the unneutralized remainder was not significantly affected by the depth of cover, the water/cement ratio, the period of curing or the exposure conditions during carbonation. However, corrosion seemed to be increased when there was 50% ground granulated blast-furnace slug in the cement; in contrast 30% pulverizedfuel ash or 5% ground limestone had little effect.
A comparative study of models for confinement of concrete by circular spirals
Authors: Ahmad Shuaib H. , Mallare Melchor P.
Published: October 2009

A number of analytical models have been proposed for predicting the stress-strain curves of spirally confined concrete. In this Paper the analytical models available in the literature for confinement of concrete by circular spirals are studied, and their predictions are compared with experimental results reported in the literature. It is concluded that none of the analytical models could accurately predict the stress-strain curves for the full range of experimental data considered in this study. Most of the models were able to predict the peak strength but failed to predict satisfactorily the associated strain and the stress-strain curves. The stress-strain predictions of some of the models were adequate for low- and medium- strength concretes, but the models demonstrated poor prediction for higher strength (f′c< > 42 MPa) concretes. Some of the models predicted the stress-strain curves better for concrete confined with lower amounts of spiral confinement (ρps > < 0·01) than for concrete confined with higher amounts of spiral confinement (ρps < > 0·01). The predictions of the iterative model of Ahmad and Shah were generally in closest agreement with the experimental results. Since this model utilizes the multiaxial properties of concrete and employs an interaction between the dilation characteristics of the concrete core and the spiral confinement, it appears to be the most suited to the accommodation of parameters influencing the stress-strain response of spirally confined concrete.
In-plane stiffness of reinforced concrete slabs under compressive membrane action
Authors: Eyre J. R. , Kemp K. O.
Published: October 2009

The ultimate load capacity of reinforced concrete slabs laterally restrained at their perimeter supports is very sensitive to the in-plane stiffness of the surrounds and of the slab itself An examination of previous experimental work suggests that the assumption of an elastic full depth of element, which is frequently used for the slab self-stiffness in the theoretical load prediction of compressive membrane slabs, is an overestimate. In a programme of experimental work on elements under combined bending moment and axial force reflecting the stress states at fixed stages during yield of a one-way spanning slab, the axial stiffness was shown to be dependent upon the stress state and considerably less than the full depth stiffness.
Shear strength of reinforced high strength concrete beam without web reinforcement
Authors: Jin-Keun Kim , Yon-Dong Park
Published: October 2009

Twenty singly reinforced high strength concrete beams without web reinforcement were tested to investigate their behaviour and to determine their ultimate shear capacities. Test variables were longitudinal steel ratio (ρ), shear span to depth ratio (a/d) and effective depth (d). The cylinder compressive strength (f′c) of concrete used in this study was 53·7MPa. One type of reinforcing bar with yield strength of 477MPa was used. All beams were loaded with two equal concentrated loads. Test results were analysed and compared with the strengths predicted by BS 8110 equation, ACI code equation, CEB–FIP model code equation, Zsutty's equation and Bazant's equation. With regard to the results, the CEB–FIP model code equation predicts shear strength of test beams relatively well, whereas BS 8110 equation is excessively conservative for most test beams and the ACI code equation gives unsafe results for beams with d of 915 mm. It was shown that the effects of ρ and a/d on the shear strength of beams are not significantly influenced by the concrete strength. Within the scope of this study, there was no clear difference in size effect with increasing compressive strength of concrete.
Influence of chloride ions on sulphate deterioration in plain and blended cements
Authors: Al-Amoudi O. S. B. , Rasheeduzzafar  , Maslehuddin M. , Abduljauwad S. N.
Published: October 2009

This investigation was carried out to elucidate the role of chloride ions in sulphate attack in plain and blended cements. Paste and mortar specimens made with Type I and Type I cements as well as with Type I cement blended with fly ash, silica fume and blastfurnace slag (BFS) were exposed to four sulphate and/or chloride environments for a period of two years. The performance of these cements was evaluated through visual inspection and measurement of reduction in compressive strength. X-ray diffraction and scanning electron microscopic techniques were used to study the sulphate attack mechanisms in plain and blended cements in both the presence and the absence of chloride ions. Results indicate that sulphate deterioration in plain cements was mitigated by the presence of chloride ions, whereas in blended cements, particularly those made with silica fume and BFS, the beneficial effect of chloride was only marginal. This is attributed to the Mg-oriented sulphate attack which was more operative in blended cements. In contrast to the gypsum and ettringite-oriented sulphate attacks, this type of attack was not inhibited in the presence of chloride ions.
The suitability of cores in predicting the behaviour of structural members suffering from ASR
Authors: Jones A. E. K. , Clark L. A. , Amasaki S.
Published: October 2009

The use of cores to predict the expansion of structures with alkali-silica reaction (ASR) has been questioned elsewhere. In this Paper the use of the mechanical properties of cores to predict the structural behaviour of such structures is also questioned. Laboratory data on the influence of restraint to ASR expansion on the mechanical properties of ASR-affected concrete, and on ultrasonic pulse velocities of columns before and after coring is presented. The results are discussed in relation to the prediction of concrete properties in ASR-affected structures.
Use of the coulostatic method for measuring corrosion rates of embedded metal in concrete
Authors: Rodrí P. , González J. A.
Published: October 2009

Corrosion at the steel-mortar interface in reinforced concrete structures was studied by use of the coulostatic method. The corrosion rate and double-layer capacitance thus obtained were consistent with those provided by other, more common electrochemical methods. The coulostatic method provides more reliable data for corrosion in the passive state as a result of the measuring electrode being perturbed to a much lesser extent than with the other methods.
Behaviour of biaxially loaded square and L-shaped slender reinforced concrete columns
Authors: Taso W. H. , Hsu C.-T. T.
Published: October 2009

This Paper presents an experimental and analytical investigation of the strength and deformation behaviour of biaxially loaded slender and tied columns with squure and L-shaped cross-sections. Both ascending and descending branches of the loud–deformation curves are explored. The proposed computer analysis predicts well the experimental datu of eight L-shaped and six square slender columns.
PFA concrete: chloride-induced reinforcement corrosion
Authors: Dhir R. K. , Jones M. R. , McCarthy M. J.
Published: October 2009

The Paper describes a study undertaken to determine the effect of PFA on reinforcement corrosion due to chlorides in concrete. The results indicate that the time to corrosion initiation when PFA is included is greatly increased, but that the quantity of chlorides causing this does not differ significantly between PFA and OPC concretes. After a given period of exposure, the concentration of chlorides at the surface of the reinforcement and the resulting corrosion intensity were lower in PFA concrete. A relationship between corrosion rate, water-soluble chloride content and coeficient of chloride diffusion has been developed, suggesting that the ability of the binder system to limit chloride migration is an important factor influencing the corrosion process. From this a means is proposed of evaluating corrosion risk in concrete under chloride attack.
Complete stress — strain behaviour of high-strength concrete under compression
Authors: Hsu L. S. , Hsu C.-T. T.
Published: October 2009

A series of compression tests were conducted on 3 × 6 in (76·2 × 152·4 mm) cylindrical specimens using a modified testing method that gave the complete stress–strain behaviour for high-strength concrete with or without tie confinements. Empirical equations are proposed to represent the complete stress–strain relationships of unconfined and confined high-strength concretes with compressive strength exceeding 10 kip/in2 (69 MPa). Various parameters were studied and their relationships were experimentally determined. me proposed empirical stress–strain equations are compared with actual cylinder tests under axial compression, and are found to agree well.
Strength and carbonation of autoclaved lime – sand concrete with aggregate superfine sand as
Authors: Wu L. , Peng X. , Yang J.
Published: October 2009

Lime–sand concrete is a new type of free-cement concrete that has good physical–mechanical properties and durability. It is difficult to use superfine sand as an aggregate to produce high-quality lime–sand concrete without suitable production techniques. In this study, the influence of the autoclaving schedules, water–solid ratio and calcium–silicate ratio on the compressive strength, bending strength, splitting tensile strength and carbonation depth of autoclaved lime–sand concrete with superfine sand as aggregate was experimentally investigated. The results show that water–solid ratio has as great an influence on the strength and carbonation depth of lime–sand concrete as on those of Portland cement concrete. There is a suitable autoclaving schedule for each given mix proportion, and a suitable calcium–silicate ratio for each autoclaving schedule.
Creep and shrinkage effects in prestressed beams
Authors: Sritharan S. , Fenwick R. C.
Published: October 2009

The results of a series of tests on prestressed concrete beams show that the addition of longitudinal passive reinforcement can have some adverse effects on the behaviour under serviceability conditions. These arise from the restraint that reinforcement provides to creep and shrinkage deformations in the concrete. High compression stresses can be induced in the longitudinal passive reinforcement by creep and shrinkage in the concrete, while in prestressed reinforcement the initial prestress tensile stresses are reduced by these actions. As a result, when the initial flexural cracks form, longitudinal passive reinforcement may sustain significant compressive stress. Experimental observations are compared with predictions from three methods of analysis. A modified form of the effective modulus method, suitable for use in a design office, was found to give predictions comparable in accuracy to the more sophisticated methods.
Alkali – carbonate reaction: significance of chemical and mineral admixtures
Authors: Wang H. , Gillott J. E.
Published: October 2009

This Paper deals with the effect of admixtures on the expansion of concrete prisms caused by alkali-carbonate reaction (ACR). The alkali-reactive aggregates were dolomitic limestones from the Pittsburg quarry, Kingston, ON. Admixtures used included accelerators, retarders, an SNF-type superplasticizer (modified sulphonated naphthalene formaldehyde condensate), an air-entraining agent (AEA) and several Li and Ba compounds. The effect of 9% Ca(OH)2 and of 20% silica fume (SF), and the combined effect of both these materials, was also investigated. Expansions smaller than those of controls were shown by prisms containing the accelerators, the retarders, SF, the Li salts at early ages and two of the three Ba salts. Some increases in expansion were shown by prisms containing Ca(OH)2, the superplasticizer, one Li salt and one Ba compound. The AEA had no significant effect on expansion. The effect of admixtures on the expansion of prisms caused by ACR was often different from that of similar admixtures on the expansion of prisms caused by alkali–silica reaction.
Specific heat and thermal diffusivity of hardening concrete
Authors: De Schutter G. , Taerwe L.
Published: October 2009

This paper focuses on the evolution of the thermal characteristics of early-age concrete as a function of the state of the hardening process. A literature review is presented, together with new test results obtained by means of improved test methods: For the determination of the specific heat of cement paste during hardening and of the thermal diffusivity of hardening concrete, test methods are developed based on existing methods. The specific heat is determined for hardening cement paste samples made with blastfurnace slag cement. It is concluded that the specific heat and thermal diffusivity decreases linearly with the degree of hydration.
Application of the layering method on large concrete pours
Authors: Loo Y. H. , Peterson J. S. , Swaddiwudhipong S. , Tam C. T.
Published: October 2009

In large concrete constructions, differences in temperature develop within the concrete mass as a result of slow dissipation of heat of hydration, causing thermal stresses and possibly early cracking of concrete. In some instances, cooling of concrete has been used successfully to reduce the temperature difference, although in hot weather it may be difficult and costly to cool large volumes of concrete. This paper proposes a new layering method in which only the central portion of concrete is cooled for the reduction of temperature differences. The results of computer simulations involving the application of this layering method are presented.
Properties of concrete in the cover zone: developments in monitoring techniques
Authors: McCarter W. J. , Emerson M. , Ezirim H.
Published: October 2009

The work presented in this paper forms part of a wider research programme being undertaken on water and ionic movement within the cover region of structural concrete and the evaluation of the properties that, ultimately, determine durability. The developments in monitoring techniques employed in the testing programme are detailed, with particular emphasis on the application of electrical methods. Data are presented that highlight the testing methods and the interpretation of the results. Examples are given of other uses of the data to provide additional information on the electrical and physical properties of concrete, and on its moisture state. In particular, it is shown that it is possible to determine such factors as rates and depths of water penetration, degree of saturation and porosity of the concrete cover, and the resistivity of the concrete at the level of the reinforcement.
Prediction of final concrete strength in hot climates
Authors: Jalali S. , Abyaneh M. Y.
Published: October 2009

The strength of concrete at long curing times, i.e. final strength, is adversely affected in hot climates. The final strength is known to decrease with increasing curing temperature even when the effects of other related factors, such as dessication due to high curing temperature, are precluded. Physical and chemical causes have been suggested for this phenomenon. Physical causes are believed to be due to the large differences in volumetric expansion of concrete constituents with temperature. According to this theory, the large increase in volume of air and water with high temperatures creates internal stresses in the curing concrete. If the tensile strength of concrete is not sufficient to withstand these internal stresses, porosity increases and microcracks are formed, resulting in the loss of final strength. Other researchers have suggested chemical causes for the loss of final strength of concrete cured at high temperatures, i. e. that the chemical composition of the hydrates is affected by the curing temperature, the microstructure of hydrates is partially changed by the effect of temperature, and the degree of hydration at long curing times is affected by curing temperature. This paper suggests that the temperature dependence of final strength, as well as other phenomena in concrete strength gain, can be explained adequately if the hydration of cement is assumed to follow the nucleation and diffusional growth processes. Then, the direction of final strength change with temperature can be successfully explained by the general concepts of chemical equilibrium. For practical purposes it is important to predict quantitatively the dependence of the final strength on temperature. Based on principles of thermodynamics a linear relationship between the natural logarithm of strength and the reciprocal of curing temperature is suggested. The available data for concrete strength and some results obtained for lime–fly ash mixtures have been used to verify the suggested relationship.
Biaxially loaded slender high-strength reinforced concrete columns with and without steel fibres
Authors: Hsu C.-T. T. , Hsu L. S. M. , Tsao W.-H.
Published: October 2009

This paper explores the load-deformation behaviour of plain andjbrous high-strength reinforced concrete slender columns from zero load until failure. The proposed empirical stress-strain equations given here for high-strength and high-strength steel fibre concretes were used as material properties to modify the computer programs of biaxially loaded slender columns previously developed. The new computer program can evaluate the complete biaxial load-deflection and moment-curvature relation-ships of slender columns. A total of nine high-strength and five high-strength steel fibre reinforced concrete columns were tested to compare their experimental load-deformation results with the analytical values derived from theoretical studies. Agreement was satisfactory for both ascending and descending branches of the load- deformation curves.
A probabilistic model of fracture in concrete and size effects on fracture toughness
Authors: Xu S. , Barr B.
Published: October 2009

Assuming the weakest link concept, a probabilistic model of fracture in concrete structures has been developed in terms of the critical stress intensity factors. The probabilistic model, which is expressed in the form of the Weibull distribution, has been compared with a range of experimental results in the literature. The results predicted by the formula are in good agreement with the values reported in the literature for four test specimen geometries – compact tension specimens, notched three-point bend specimens, wedge splitting specimens and compact compression specimens. The results presented in the paper have been applied to predict the fracture in large concrete dams and the results compare favourably with observed cracking.
Strain softening of concrete in compression under different end constraints
Authors: Choi S. , Thienel K.-C. , Shah S. P.
Published: October 2009

Strain softening of concrete in compression is not just a materials behaviour; it depends also on structural properties. Factors affecting the softening behaviour of concrete, such as concrete strength, gauge length, feedback signal, the length of specimen, shear resistance provided by the loading platens, the rotation of the spherical loading platen, and the stiffness of the testing machine, were examined. The influence of these factors on peak stress, peak strain, strain softening behaviour and failure localization are described and discussed.
Factors influencing compressive strength of concrete masonry prisms
Authors: Khalaf F. M.
Published: October 2009

This paper presents the results of an experimental investigation on blockwork masonry prisms to study the effect on their compressive strength and behaviour of the following factors: (a) concrete infill and mortar strengths; (b) specimen height-to-thickness ratio; (c) specimen length-to-thickness ratio; (d) mortar joint thickness; (e) bond between the block and concrete infill.
Study of compressive strength characteristics of coral aggregate concrete
Authors: Arumugam R. A. , Ramamurthy K.
Published: October 2009

Coral islands are tiny and are scattered in deep seas throughout the world, hundreds of kilometres away from the mainland. For construction activities in these islands, coral shingles and coral sand are the main locally available materials. A review indicates that only a few investigations have been undertaken on the properties of coral aggregates and concrete made with them. This paper discusses the results of a systematic investigation of the physical, chemical and mechanical properties of coral shingles and coral sand. Their suitability a3 aggregate for concrete making has been studied through comparison with the results of tests on conventional crushed granite aggregate and river sand. The workability, density and compressive strength characteristics of different nominal mixes of conventional aggregate concrete and coral concrete with various water-cement ratios have been compared and discussed.
Experimental investigation on the triaxial fatigue behaviour of plain concrete
Authors: Taliercio A. L. F. , Gobbi E.
Published: October 2009

An experimental research programme was carried out with the aim of investigating the effects of cyclic triaxial loading upon the mechanical behaviour of concrete. A triaxial press was used, capable of applying on cylindrical specimens an axial load and a confining pressure cyclically varying in time according to independent programs. Cycles (at 1 Hz) were characterized by different (a) mean stress, (b) amplitude, (c) ratio r of the mean confining pressure to the mean axial stress and (d) phase angle between loads. Some uniaxial cyclic tests were also performed. Those specimens that did not fail within about 400 000 cycles were monotonically tested to failure in uniaxial compression. Despite their scatter, the results obtained qualitatively show that: (a) other test parameters being constant, fatigue life is usually shorter in tests in phase opposition rather than in phase coincidence; (b) as the cycle amplitude increases, fatigue life decreases (mainly in tests in phase opposition); (c) fatigue life increases as the mean confinement increases; (d) a strong correlation exists between ‘Secondary creep rate’ and fatigue life, irrespective of the ratio between mean stresses; (e) all specimens submitted to post-cyclic failure tests exhibited a decrease in elastic modulus in proportion to the increase in r during cycles; the specimens submitted to uniaxial cycles experienced an increase in static strength in comparison with the virgin ones.
In-situ strength testing of high strength concrete
Authors: Price W. F. , Hynes J. P.
Published: October 2009

High strength concrete is being used increasingly in major civil engineering and building projects. Measurement of the in-situ strength is often required as a means of determining early age strength development and form work stripping times, or, for verifying structural performance. A number of techniques for the estimation of the in-situ strength of high strength concrete have been examined. The use of temperature matched cured test cubes was found to give the closest correlation with in-situ strength although ultrasonic pulse velocity measurements and pull-out tests were useful techniques. One aspect of testing high strength concrete that emerged as significant, was the need to base calibration or correlation curves on specimens sealed against moisture ingress or moisture loss. rather than on water-cured specimens. Two high strength concrete mixes incorporating different aggregate types (with mean 28 day cube strengths of 90 MPa and 100 MPa) were investigated in large-scale test items. A comparison of maturi measurements, UPV and pull-out tests is given together with discussion of the nature of in-situ strength development in high strength concrete.
The tensile strain capacity of concrete
Authors: Tasdemir M. A. , Lydon F. D. , Barr B. I. G.
Published: October 2009

The importance of understanding the behaviour of concrete in tension is noted and the major role of tensile properties in the fracture of concrete is examined. Some applications of a tensile strain criterion are discussed together with major influential factors. It is shown that the tensile strain capacity under direct tension can be predicted, from the tensile strength and the static modulus of elasticity and that the relation is virtually independent of mix composition, age, specimen size and testing technique, provided that un notched specimens are used. Prediction is not so good with notched specimens and it is concluded that the former are more reliable for design purposes.
Micro crack characterization in concrete under uniaxial tension
Authors: Li Zongjin
Published: October 2009

The microcrack properties in concrete and low volume short fibre reinforced concrete under uniaxial tension have been characterized using an acoustic emission (AE) technique. To obtain overall information on micro cracking, a newly developed test method is used to ensure stable measurement of post-peak response. The phenomena of micro cracking localization are investigated by interpreting the locations of AE event sources. It is, found that localization does exist and starts before peak load. The AE activities are further investigated using a quantitative analysis technique. The 2-D moment tensor representation of each event, assumed to be a point source, is deduced. By interpreting the behaviour of the dipole, forces, the orientation, and the movement of micro cracks are inferred. The results show that the behaviour of a micro crack might be different from the behaviour of a macroscopic crack.
Techniques for determining some microstructural parameters in glass reinforced cement
Authors: Kakemi, M. , Hannant D. J. , Mulheron M.
Published: October 2009

Two important parameters which control the fracture behaviour of glass fibres in cement composites, whether they contain one fibre type or are hybrids of two fibre types, are the perimeter of the glass strands in contact with hydrated cement and the way in which glass filaments fracture in multi filament strands. In scanning electron microscopy (SEM) observations, much improved images were obtained by detecting back scattered electrons rather than secondary electrons. This improvement gave good contrast between the fibre strands and the matrix, hence the perimeter of the glass strands could be determined using an image analyser. The progression of filament fracture within a strand was examined using two techniques, acid dissolution and light transmission through the filaments. These techniques showed that strands tend to fail progressively in hybrid composites containing glass and polypropylene fibres and that glass fracture continues to occur after the peak load has been reached.
Mechanisms of the influence of externally supplied NaCl on the expansion of mortars containing reactive aggregate
Authors: Kawamura M. , Takeuchi K. , Sugiyama A
Published: October 2009

Translation from Proceedings of JSCE, 25, No. 502, 1994

This study aims at revealing the mechanisms of the influence of NaCl externally supplied on the expansion of mortars due to the alkali–silica reaction. In reactive aggregate-bearing mortars with relatively low alkali contents, the promotion of their expansions in 1 M NaCl solution at 38°C was caused by a rise of OH− ion concentration in the pore solution. The increase in OH− ion concentration in the pore solution in mortars was responsible for the intrusion of Cl− ions into mortars containing a reactive aggregate. In reactive aggregate-bearing mortars with a relatively large amount of added NaOH, at least a part of unusually large expansions of the mortars was caused by the delayed formation of ettringite during the immersion in NaCl solution.
Estimating the alkali contribution from fly ash to expansion due to alkali—aggregate reaction in concrete
Authors: Thomas M. D. A. , Blackwell B. Q. , Nixon P. J.
Published: October 2009

This paper reports the findings from an investigation to determine the ‘effective’ alkali contribution from jly ash to the expansion of concrete containing natural reactive UK aggregates. Concrete prism expansion tests were carried out using flint/chert sand (from three different sources), a crushed siltstone and a crushed siliceous limestone; results are also reported for a gre-vwacke aggregate. Fly ash from three commercial sources was used. The results demonstrate that the ‘efective’ alkali contribution from the fly ash, estimated from expansion results, varies depending on the level of replacement and nature of the reactive aggregate. With moderately reactive aggregates, such as flint, 25% fly ash was found to be effective in preventing cracking, regardless of the OPC alkali content. However, with more reactive aggregates (i.e. aggregates that react at lower alkali levels), Fly ash concrete expanded at lower OPC alkali contents than control specimens, indicating an ‘efective’ alkali contribution from the fly ash. Higher levels of fly ash are required to prevent cracking with these aggregates. Effective alkali ‘contributions’ (from fly ash) determined for a particular aggregate are not applicable to concrete containing other reactive aggregates, and specifications need to be cognizant of the need for higher ash replacement levels with more reactive aggregates.
Field studies of fly ash concrete structures containing reactive aggregates
Authors: Thomas M. D. A.
Published: October 2009

The paper presents the, findings, from field studies of fly ash concrete structures containing reactive (alkali-silica) aggregates. Data is presented from a number of hydraulic structures in Wales and Ontario constructed using geologically similar greywacke-argillite aggregates. All the structures without ash showed evidence of damage due to ASR: indeed reaction with this aggregate has led to replacement of structures in both areas. Reaction may occur at alkali levels significantly below 3 kg/m3 Na2Oe, and has been, found in a structure with a measured [available] alkali content of less than 25 kg/m3 Na20e, However; the, fly ash concrete structures are in excellent condition after more than 25 years service despite having higher alkali contents than many of the damaged structures; the Lower Notch Dam was actually constructed using a high alkali cement (> 1·0% Na20e). Microstructural and pore solution analysis showed that much of the alkali in the fly ash concrete was [bound] in the CSII and not available to the pore solution for ASR. Published findings related to the McPherson Test Road and Hanshin Expressway are reviewed; these structures have been cited as examples of ASR in fly ash concrete structures. Based on the available data, recent claims that fly ash actually [contributed] to the failure of these structures are repudiated. In fact, fly ash was found to be effective in controlling expansion in the McPherson Test Road, the cracking observed in fly ash concrete being attributed to drying shrinkage. Details regarding the use of ash in the Hanshin Expressway are not adequately reported, however, it would appear that 18% fly ash was not effective in completely suppressing expansion in this structure. This is not surprising in view of the moderate level of ash and excessive alkali content of the concrete (up to 0·33% Na20e). The balance of, field performance data sustains the concept of using Class F fly ash to control expansion due to ASR in concrete, provided the material is used at sufficient levels of replacement. Further control of the alkalis, from other sources would appear to be a prudent precaution even when the concrete contains fry ash. It is surprising that many specifications have adopted the advice, from accelerated laboratory tests and penalize fly ash by assigning an [alkali contribution] (e.g. one-sixth the total alkali or all of the ASTM C312 [available] alkali) to the material which may often preclude its use. Such advice appears to contradict the more cogent argument from the field where Class F fly ash has been successfully used for many decades with no reported incidences of ASR in structures containing sufficient levels of ash.
Sequential examination of slowly expanding alkali-reactive aggregates in accelerated mortar bar testing
Authors: Wigum B. J. , French W. J.
Published: October 2009

The NBRI mortar bar test, now adopted with slight modification as ASTM C1260-94, has been used to study the sequential development of alkali-aggregate reactions jor certain slow/late expanding types of reactive rocks. The work presented here is concerned with the expansion produced by mylonites. meta-argillite, meta-greywacke, granite, limestone and silica glass. At different stages in the test, the situation at the reaction site and the formation of the gel reaction products have been investigated using both optical and scanning electron microscopes. The composition of the gel reaction products and the amount of mobilized silica have also been measured. The accelerated test method appears to echo the alkali-aggregate reactions occurring in, field concrete. The different rock types show different rates of expansion, and two different reaction styles are observed at the reaction sites. One of these two phenomena involves dissolution of quartz along grain boundaries and the other involves crack generation within the aggregate. The process of cracking and the amount of cracking appear to be the main, factors governing the amount of expansion produced by the reaction. No correlation was, found between the amount of alkali-silicate gel produced as the reaction product and the expansion of the mortar bar.
Workability retention of high strength/superplasticized concrete
Authors: Chan S. Y. N. , Feng N. Q. , Tsang M. K. C.
Published: October 2009

One of the methods of producing high strength concrete (HSC) is by reducing the water/cement (w/c) ratio to achieve a compressive cylinder strength of over 41 N/mm2 as defined by the American Concrete Institute or over 60 N/mm2 as stipulated by FIP/CEB. The consequent low workability is then overcome by adding superplasticizer to achieve a specified workability, preferably without segregation, set retardation or excessive air entrainment. For a given workability, the lower the w/c ratio, the higher is the superplasticizer dosage requirement. However, there is a practical upper limit on the dosage of superplasticizer because of its cost, the reduced plasticizing efficiency above an optimum dosage level, and the risk of loss of strength caused by segregation and heavy air entrainment, as well as possible retardation in setting and hardening. For superplasticized concrete, the rapid loss of workability presents a major technical problem for in situ construction using conventional pumping and casting methods. The present1y adopted repeated dosing method imposes manpower, quality control and cost penalties as well as the risk of superplasticizer over-dosing. This paper studies the slump loss behaviour of HSC incorporating a variety of superplasticizers. To retain the workability of HSC, a recently developed and patented admixture, carrier fluidifying agent (CFA) was used in a series of concrete mixes. It was found that CFA maintained the workability of HSC mixes for a period of up to 2 hours. The effects of CFA on the setting, hardening, air content and compressive strength development of the concrete were also studied and no adverse effect was observed. Laboratory trials using a repeated dosing method were also carried out, and apart from being labour intensive, this method was found to be less effective and more expensive.
Damage accumulation on deformed steel bar to concrete interaction detected by acoustic emission technique
Authors: Balázs C. U. , Grosse C. U. , Koch R. , Reinhardt H. W.
Published: October 2009

Acoustic emission (AE) signals and relative displacements were simultaneously recorded on pull-out specimens subjected to monotonic, cyclic and long-term loads. The bond length was twice the rib spacing. Most of the signals were observed during an increase in load or applying the cyclic load, however, signals were recorded during cycling and under constant load as well. The AE signal patterns were compared by applying the coherence spectrum analysis based on Fourier transforms of the signals. The internal damage accumulation, defined as the cumulative AE amplitudes, showed similar tendencies to the slip development both under cyclic and long-term loads.
Effects of loading frequency and stress reversal on fatigue life of plain concrete
Authors: Zhang B. , Phillips D. V. , Wu K.
Published: October 2009

The effects of loading frequency and stress reversal on the fatigue properties of concrete were investigated by conducting flexural fatigue tests on plain concrete beams. A new fatigue equation based on the classical Aas-Jakobsen S—N equation is proposed which contains the above effects. This equation agrees well with previous experimental results and proves to be suitable for some other loading states other than bending.
Bond and splitting in bar pull-out: behavioural laws and concrete cover role
Authors: Gambarova P. G. , Rosati G. P.
Published: October 2009

Concrete splitting originating at the interface of longitudinal rebars is a tricky aspect of R/C structures, since the ensuing loss of bond may cause the premature activation of one of the major failure mechanisms. Consequently, the study of bond after concrete splitting, leading to the formulation of suitable behavioural laws, is still needed, and constitutes the objective of this paper, in order to quantify the loss of bond efficiency in terms of peak strength, initial stiffness, friction and bond-confinement interaction. Within this context, the authors try to give a systematic answer, starting from the results obtained in Milan in the late 1980s and early 1990s, by testing three series of specimens, reinforced with a single ribbed bar (Ø 14, 18 and 24 mm) and characterized by a preformed splitting crack, whose width was controlled during each pull-out test. In the last part of the paper, the bondconfinement law proposed by the authors is introduced into a recently developed limit analysis model, which considers the concrete embedding of the bar as an elastic-plastic fracturing material, and some plots of bond strength plotted against concrete cover are given, for different values of the transverse pressure. Although transverse pressure is always beneficial, bond strength exhibits an upper bound, since high pressures lead to bond collapse in shear, owing to the shearing off of the concrete keys between bar ribs.
Effect of curing on water permeability of concretes prepared with normal Portland cement and with slag and silica fume
Authors: Khatri R. P. , Sirivivatnanon V. , Kin yu Lam
Published: October 2009

The effect of curing on the coefficient of permeability of concretes was studied. Concretes, grades 35 and 40, were prepared from a normal Portland cement and from a high slag blended cement. The effect of the addition of silica fume to both of these binders was also studied. The water permeability of various concretes was measured using the constant flow method. The coefficient of permeability was evaluated for concretes subjected to three types of curing: samples were continuously moist cured for 7 or 28 days, or were subjected to 28 days of intermittent curing. Twenty-eight days of intermittent curing was found to be as effective in reducing permeability as 7 days of continuous moist curing. Twenty-eight days of continuous moist curing gave the lowest coefficient of permeability. The addition of silica fume to normal Portland cement considerably reduced the permeability, and concretes prepared with high slag blended cement had lower permeability than did those prepared with normal Portland cement.
Statistics for concrete and steel quality in Saudi Arabia
Authors: Arafah A. M.
Published: October 2009

This paper presents the results of an experimental programme designed to develop probabilistic models for the compressive strength of concrete and the yield strength of reinforcing steel produced in Saudi Arabia, as a first step towards the development of a national design code for reinforced concrete buildings. A total of 955 concrete samples and 434 samples of steel bars were randomly collected from construction sites for strength testing. The results indicate that ready mixed concrete is well modelled by the normal distributions, whereas site mixed concrete is well represented by the log-normal distribution with a low mean/nominal ratio and a high coefficient of variation. Variation in the yield strength of reinforcing steel is modelled by the normal distribution, with a high mean/nominal ratio. The models are verified by the χ2 and Kolmogorov-Smirnov goodness offit tests at the 5% significance level. The models developed in this paper are useful for predicting the performance of structural elements and assessing their reliability levels. They are also essential for calculating resistance factors for a limiting state design code.
Effect of spandrel beams on strength and behaviour of column-slab connections
Authors: EI-Sheikh A.
Published: October 2009

Spandrel beams are commonly used to strengthen the connections between slabs and edge columns in flat slab structures. The present study uses experimental and analytical means to improve understanding of the behaviour of these connections, especially when spandrel beams are used. The parameters considered are the spandrel beam size and reinforcement ratio, the width of the inside column slab interface, and the type of straining actions to be transferred through the connection. The efficiency of using a slab extension (beyond column outer face) instead of a spandrel beam is also studied. Based on the failure mechanism observed during the tests, a new analytical method to predict the strength of edge column-slab connections is suggested. A second analytical method is also developed while being based on a simplified failure surface. The accuracy and reliability of both methods are thoroughly assessed in this study.