bluuebunny/crossref_metadata_2025 huggingface dataset:
Deleterious expansion of concrete due to alkali-silica reaction: influence of pfa and slag
Authors: Hobbs D. W.
Published: October 2009

Synopsis

The literature dealing with the effectiveness of partial replacement of a high-alkali cement by pulverized-fuel ash (pfa) and ground granulated blast furnace slag (slag) in preventing deleterious expansion due to the alkali–silica reaction (ASR) when a reactive aggregate is used is reviewed, and results are reported of recent tests carried out on concrete at C&CA. It is shown that the effectiveness of pfa's and slags in preventing deleterious expansion due to ASR varies widely and that the use of some pfa's and slags may not reduce the risk of deleterious expansion.
Hollow concrete blocks with enhanced structural efficiency and a compatible grout
Authors: Shrive N. G. , Jessop E. L.
Published: October 2009

Synopsis

Concrete blocks with two hollow cores are commonly used in load-bearing walls. Many variations on this basic type of unit are produced. However, the typical geometry and mortaring practices employed tend to cause such units to fail at much lower stresses than the strength of the concrete from which they are made.

When the causes of failure in both hollow and grouted concrete masonry are examined, three criteria can be established which should improve the loadbearing capabilities of concrete blocks. Blocks and grout were manufactured to conform with these criteria and expected strength improvements were observed.

A new concrete block ‘system’ has been devised with a more efficient load-bearing capability and a number of additional attributes. The system is 19% lighter and 19% stronger than ‘standard’ masonry, is also more versatile and requires fewer site materials than conventional masonry.
An activation energy approach for the temperature dependence of basic creep of hardened cement paste
Authors: Dias W. P. S. , Khoury G. A. , Sullivan P. J. E.
Published: October 2009

Synopsis

Arrhenius rate theory is used to describe the temperature dependence of basic creep of hardened cement paste, within certain temperature limits. The time shift principle is coupled with this Arrhenius temperature dependence to obtain an overall power law relationship between creep strain and equivalent time (which accounts for both temperature and time dependence). This enables the formulation of an extrapolation technique for basic creep strains in situations where there are time or temperature constraints on experimentation. Two distinct values of activation energy corresponding to two different temperature ranges, are used to arrive at possible creep mechanisms that would operate in each of these ranges.
Shear and moment capacity of reinforced steel-fibre-concrete beams
Authors: Lim T. Y. , Paramasivam P. , Lee S. L.
Published: October 2009

Synopsis

An analytical approach for predicting the shear and moment capacity of reinforced steel-fibre-concrete (RSFC) beams is proposed. Recent plasticity analyses for shear capacity of reinforced concrete beams are extended to RSFC beams by including the contribution of the fibres. Moment capacity is derived using the usual sectional analysis and fully plasticized stress blocks and forces. By establishing relevant capacities for a given beam loaded over a range of span/depth ratios, the capacity and governing mode of failure can be predicted. The observed failure loads and modes of failure for 22 test beams agree well with the predictions. Data presented in the literature are also analysed and compared. The present approach allows for direct comparison between the efectiveness of stirrups and fibres as shear reinforcement. The results suggest that fibres can replace stirrups partially or wholly as long as parity in the shear reinforcement factor is maintained.
Oil-pressure measurement in the two-point workability apparatus
Authors: Wimpenny D. E. , Ellis C.
Published: October 2009

Synopsis

Large fluctuations in the oil pressure within the twopoint apparatus during concrete testing make any reading of the pressure gauge open to operator bias. This paper details the fitting and use of a pressure transducer system capable of measuring, recording and analysing the oil pressure. Results obtained using the pressure gauge and the pressure transducer indicate that operator experience in Combination with mix workability has some influence upon the accuracy of the gauge readings, and this underlines the substantial benefits of the proposed system.
Recycled concrete as fine and coarse aggregates in concrete
Authors: Sri Ravindrarajah R. , Loo Y. H. , Tam C. T.
Published: October 2009

Synopsis

The effects of using crushed concrete as coarse and fine aggregates upon strength and deformation of concrete are reported. The properties of recycled aggregates differ from those of natural aggregates due to the presence of a considerable proportion of mortar attached natural aggregate and loose mortar. For a medium strength concrete, the results show that strength and modulus of elasticity are reduced by about 10% and 35%, respectively, whereas drying shrinkage is nearly doubled when recycled aggregates are used instead of natural aggregates in comparable mixes. The efect of recycledfine aggregate on the deformational properties is less than that of coarse aggregate. Fresh concrete properties are only marginally affected by the use of recycled aggregates.
The resistance of stainless steel partly embedded in concrete to corrosion by seawater
Authors: Flint G. N. , Cox R. N.
Published: October 2009

Synopsis

The corrosion resistance of Type 316 stainless steel, partly embedded in concrete, partly exposed to stagnant seawater and partly exposed to flowing seawater, has been determined over various periods up to about 12; years duration. The exposure tests were carried out in full immersion and tidal conditions, on specially designed concrete blocks. Mild steel specimens were also tested for comparison. Corrosion of exposed stainless steel was localized, not extensive, and affected neither the strength nor ductility of the specimens. Contrary to expectation, crevice corrosion occurred on only one of the 42 test specimens, and only after 12½ years total immersion.

It is considered that the alkalinity of the concrete was responsible for minimizing corrosion on both embedded and external areas of stainless steel. Ordinary Portland cement concrete gave more protection to the stainless steel than did sulphate-resisting Portland cement concrete due, it is thought, to the higher cement content of the former and consequent greater reserve of alkalinity. The higher proportion of tricalcium aluminate in the OPC concrete and its known effect in complexing chloride ions and delaying their ingress into concrete was also considered to be of great significance.
Settlement of fresh concrete—an effective stress model
Authors: Clear C. A. , Bonner D. G.
Published: October 2009

Synopsis

The settlement of fresh concrete under load is examined both theoretically and experimentally. It is shown that settlement depends on the effective stress to which the intergranular structure is subjected, and that the settlement has two major components. One of these is immediate settlement due to compression of the pore fluid and the intergranular structure in response to applied load. The other is consolidation settlement created by the dissipation of pore water with time which gradually transfers load from the pore water onto the intergranular structure. A reduction in consolidation settlement will reduce the risk of settlement cracking and void formation around reinforcing bars. For discrete cycles of loading, such as placing of concrete in layers, a direct measure of consolidation settlement as a proportion of total settlement is given by a pore water pressure coefficient.
Grouted and dowelled jointed precast concrete columns: behaviour in combined bending and compression
Authors: Kuttab A. , Dougill J. W.
Published: October 2009

Synopsis

Tests are described on the behaviour of grouted and dowelled jointed precast columns under combined bending and axial load. Only part of the longitudinal steel is used for dowel action so that the axial load capacity needs to be enhanced in the region of the joint. This is done by the use of additional links in each of the units comprising the jointed column. The jointed column had load capacities similar to those expected for monolithic columns but the failure zone was localized. As a consequence, when overall behaviour is determined by failure at the joint, it can be expected that a jointed column will be more brittle than a monolithic column.
Effect of sodium chloride and sodium hydroxide from the surrounding solution on alkali-silica reaction in mortars containing fly ash
Authors: Kawamura Mitsunori , Takemoto Kunio , Terashima Nagamasa
Published: October 2009

Synopsis

It is known that sodium chloride from the surrounding solution promotes the expansive alkali-silica reaction in cementitious materials, and that the incorporation of pozzolanic materials suppresses the expansion caused by the intrusion of alkali salts. However, the mechanisms responsible for these phenomena are not fully understood. In this paper, substantial differences in expansion behaviour between mortars(made with a high-alkali OPC, nine fly ashes at replacement levels of 0, 10, 20 and 30%, and Beltane opal fine aggregate) immersed in I N NaOH and I N NaCl solutions are discussed, taking account of the composition of the pore solutions extracted from the mortars. Mechanisms for the initiation and acceleration of the alkali-silica expansion in mortars exposed to the NaCl solution are also discussed.
Delayed analysis of fresh concrete for cement and water content by freezing
Authors: Clear C. A.
Published: October 2009

Synopsis

Using a domestic chest,freezer, samples of fresh concrete can befrozen and stored, for at least 28 days and then tested for cement and water content by standard, fresh analysis methods. This technique, for delaying, fresh analysis is useful us it provides the option of checking the mix proportions of concrete supplied to construction sites which do not have suitable test equipment immediately available. Frozen 8 kg samples of fresh concrete for cement content analysis must be thawed before they can be tested using the Rapid Analysis Machine. Thawing i s readily achieved by mixing each frozen sample with 2·5 li of hand hot water, for about 10min. Samples for water content analysis do not require any extra preparation before testing, as they can be dried to constant weight from their,frozen state using a suitable microwave oven.
Creep and drying shrinkage of concrete blockwork
Authors: Brooks J. J. , Abdullah C. S.
Published: October 2009

Blockwork walls and piers constructed from dense aggregate concrete blocks exhibit creep and shrinkage behaviour which is similar to that of concrete with respect to the geometry of the cross-section. Deformations are greater in walls than in piers and they can be quantified by composite modelling of the block and mortar phases of the blockwork. It is important to simulate the rate of moisture diffusion in each phase so that unbedded specimens have the same ratio of volume to exposed surface area as the blockwork. Experimental verification is given for creep, vertical shrinkage and horizontal shrinkage over a period of six months.
On the mechanism of steel corrosion in concrete: the role of oxygen diffusion
Authors: Gonzalez J. A. , Molina A. , Otero E. , López W.
Published: October 2009

The generally accepted view of the corrosion of steel embedded in concrete assumes that the reduction of oxygen supports the overall process of corrosion in this medium. The results presented in this Paper show that under certain circumstances the corrosion rate may be high, even though the supply of oxygen is small or negligible. Therefore, the corrosion mechanism appears to require the existence of some cathodic process which does not require oxygen diffusion. The existence of crevices at the steel/concrete interface affording relatively low pH environments, is presented as a possible explanation for the high corrosion rates of steel in concrete without oxygen. The existence of crevices is ensured by the heterogeneity of concrete.
Variation of creep Poisson's ratio with stress in concrete under short-term uniaxial compression
Authors: Loo Y. H. , Base G. D.
Published: October 2009

An experimental study of creep Poisson’s ratio, the ratio of transverse creep to axial creep, for sustained load durations of up to 31 min, revealed that its variation with stress occurred in three stages. It was found that creep Poisson’s ratio remained fairly constant and close to the elastic Poisson’s ratio at stresses below 50% of the compressive strength. Above this stress level, creep Poisson’s ratio generally increased with stress but decreased with time under sustained loading, until a threshold stress was exceeded. Beyond this threshold stress, creep Poisson’s ratio was found to be greater than 0·5 and increasing with time. At this third stage, it was shown that the volume of concrete increased with time at increasing rates. This third stage is therefore the stage of dilating creep which will inevitably lead to eventual creep fracture. The threshold stress, which was found to be about 79 to 89% of the compressive strength in this study, was therefore established as the strength of concrete under sustained loading, or simply, the creep strength.
Measurement of the compressive impact strength of concrete using a thin loadcell
Authors: Perry S. H. , Bischoff P. H.
Published: October 2009

This Paper describes a method developed to measure the uniaxial stress-strain response of concrete loaded in compression at the high strain rates which occur during hard impact. Concrete cylinders, nominally 100 mm in diameter and 250 mm long, were impacted with a drop hammer, and transient measurements were recorded with electrical resistance strain gauges used in conjunction with a novel loadcell; the latter incorporating manganin pressure gauges. Particular attention is given to problems encountered with stress measurement when dynamic stress waves are present within the concrete specimen, especially when stress and strain are not measured at the same location.
Effect of chloride in mix ingredients on sulphate resistance of concrete
Authors: Harrison W. H.
Published: October 2009

The sulphate resistance of concretes containing various levels of chloride introduced in the mixing water was assessed by immersion in sodium sulphate and magnesium sulphate solutions. Mortar and concrete cubes were made using ordinary Portland cement (OPC) and sulphate-resisting Portland cement (SRPC) with chloride contents of 0–4·5%; the chloride was introduced in a salt of either sodium or calcium. Deterioration was monitored by comparing the strength of cubes in sulphate solutions with that of similar cubes stored in water over a period of 7 years for concrete and of 1 year for mortar. The 100 mm concrete cubes (which were also assessed visually at 3 and 7 years) were made with two levels of cement content (225 and 335 kg/m3). A 1:3 cement/sand mix was used for the 12·5 mm mortar cubes. The results over 1 year for the mortar cubes showed that chloride had either a negligible or a generally beneficial effect on the resistance to sulphate attack for both OPC and SRPC. A similar overall trend was observed for the concrete cubes after 7 years, with the apparent exception of some concretes containing calcium chloride and immersed in strong sulphate solutions, for which sulphate resistance was considerably reduced.
Size effect in concrete specimens with dissimilar initial cracks
Authors: Kim Jin-Keun
Published: October 2009

In most structural members with initial cracks (or initial notches), strength tends to decrease as the member size increases: a phenomenon known as size effect. In contrast to other structural materials (wood, steel etc.), concrete shows the size effect with or without initial crack. Published experimental results indicate that even a large concrete member without initial crack resists some stress, contrary to Bazant’s size effect law. In this study, the size effect for concrete with dissimilar initial cracks is discussed on the basis of non-linear fracture mechanics, and prediction models are proposed for splitting tensile strength, shear strength and uniaxial compressive strength tests. The models are derived using regression analyses, with extensive experimental data relating to specimens of various sizes; it is felt that they perform much better than Bazant model, particularly for very large specimens.
Within-test variability of some non-destructive methods for concrete strength determination
Authors: Leshchinsky A. M. , Leshchinsky M. Yu. , Goncharova A. S.
Published: October 2009

Experimental investigations of within-test variability of non-destructive methods to determine concrete strength are reported. Rebound, indentation, ultrasonic (with direct and surface transmissions) and shearing rib methods were among those studied.
Review of recent research on alkali-activated concrete in China
Authors: Wang Shao-dong
Published: October 2009

Alkali-activated slag cementing materials were invented over 30 years ago. Alkali-activated slag concrete has many advantages over ordinary concrete, such as high strength, low production cost and good durability. However, its application has not been widespread, apart from trials in the USSR, because some problems persist. After five years of systematic study of this fascinating material, a good prospect for its application has been discerned. The main purpose of this Paper is to contribute to the continuing study of alkali-activated slag concrete by sharing some experiences of both success and failure, so as to forestall unnecessarily repetitive research work.
Concrete durability: estimation of chloride concentration during design life
Authors: Dhir R. K. , Jones M. R. , Ahmed H. E. H.
Published: October 2009

Values of the coefficient of chloride diffusion D, as measured by the classical diffusion test and by a penetration test, are compared. It is shown that D cannot be determined reliably from penetration tests. Two sets of nomograms are developed for the design of concrete structures in chloride environments. The proposed nomograms can cope with a wide range of concrete variables: a basis is provided for their extension to include parameters not studied in the present investigation.
Application of expert systems technology in the design of durable concrete
Authors: Wilkins A. J. , Elgy J.
Published: October 2009

This Paper describes work undertaken to explore the possible application of expert system technology to the domain of concrete durability design. The potential usefulness of expert systems in general and in this area is discussed. The information for the domain was obtained from BRE digests and concrete experts. Following BRE digests, the domain was divided into separate modules covering sulphate attack, alkali-aggregate reaction, steel corrosion and mix design. A prototype (DEX) was developed, incorporating modules covering each of the sub-domains. The modules were linked into an overall system capable of producing concrete mix designs incorporating the advice held in the BRE documents. Many potential implementation problems are solved within DEX by the use of a hypertext system to provide user support. The use of hypertext techniques is proposed both as a useful expert system development aid and as a supplementary form of publishing BRE digests and similar standards documents.
Mix details and material behaviour of polystyrene aggregate concrete
Authors: Perry S. H. , Bischoff P. H. , Yamura K.
Published: October 2009

Polystyrene aggregate concrete is one of many lightweight, low strength materials with good energy-absorbing characteristics. However, due to poor workability and a susceptibility to segregation, quality control is difficult during manufacture. This Paper describes the procedures adopted for the mix design and casting of concretes containing 40, 50 and 60 vol.-% (corresponding to specific densities of 0·8, 1·0 and 1·2 respectively) of beaded polystyrene aggregate. Strength and density were controlled by varying the mix proportions. Stress-strain relationships are given, and the compressive strength is shown to vary approximately linearly with density. Modifications to Pauw's equation for the determination of Young's modulus are considered.
PFA concrete: near surface absorption properties
Authors: Dhir R. K. , Byars E. A.
Published: October 2009

Water absorption properties of concrete made with ordinary (OPC) and rapid–hardening Portland cement ( RHPC), and both cements blended with pulverized fuel ash ( PFA), were studied for a design strength range of 25–70 N/mm2 at ages of 28 and 180 days, and with a number of curing conditions of varying relative humidity and temperature. It was found that with standard curing in water at 23°C, PFA enhanced the quality of concrete as judged by absorption properties. RHPC/PFA blends performed better than OPC alone, but blends with OPC gave better results than RHPC. Air curing greatly increased absorption, but this was no worse for PFA concrete than OPC or RHPC concrete. PFA concrete responded better than OPC concrete to curing temperature. The optimum PFA content varied with concrete type, curing regime and age.
Strength and ductility of steel fibre reinforced concrete under bearing pressure
Authors: Soroushian P. , Bayasif Z.
Published: October 2009

An experimental programme is presented on the behaviour of plain and steel fibre concretes under the action of bearing stresses. The effect is assessed of the inclusion of fibres in the top layer of a concrete block under the bearing area, as opposed to full-depth fibre reinforcement of the block. The effectiveness of dowel bars under the bearing area in increasing the bearing load carrying capacity of concrete and fibre reinforced concrete is investigated. The specimen's configuration is selected to simulate the pressure of columns on footings.
Time-dependent behaviour of simply-supported steel-concrete composite beams
Authors: Bradford M. A. , Gilbert R. I.
Published: October 2009

A theoretical and experimental study of the time-dependent behaviour of composite steel-concrete structural members has been undertaken at the University of New South Wales. As part of the experimental investigation, long-term static load tests were carried out on four simply-supported composite steel-concrete beams. The deformations were monitored for a period of about 250 days, as were the creep and shrinkage characteristics of concrete specimens under the same ambient conditions as the test beams. Pushout tests were also conducted on the headed studs used as shear connectors in the test specimens, and slip deformations and slip strains were recorded for two different connector densities. In this Paper transverse deflexions are shown to agree well with a design proposal presented elsewhere. The experimental results presented here provide benchmark data for the calibration of more complex theoretical treatments that incorporate creep, shrinkage and connector slip.
Concrete dynamic modulus: influence of drying and rewetting
Authors: Almudaiheem J. A. , Al-Sugair F. H.
Published: October 2009

The dynamic modulus of elasticity of concrete is an important variable. The dynamic modulus in itself is not used in design; however, its importance is derived from the fact that it can be measured quite accurately using non-destructive tests, and it has been successfully correlated with other strength variables. Measurement of the dynamic modulus non-destructively allows the monitoring of the concrete strength in situ and in laboratory specimens with very small statistical variability. In this study, the effect of drying in several environmental conditions on the dynamic modulus of concrete containing superplasticizers (SPs) is investigated. SPs are used frequently in concrete casting, especially in hot arid climates, to compensate for the loss of workability due to water evaporation. In addition, after the concrete has been dried for some time the effect of rewetting the specimens on the dynamic modulus is investigated. Specimens with and without superplasticizers are cast and cured then dried in temperatures ranging from room temperature to 100°C grade, with the relative humidity kept at around 20%. The dynamic modulus of the concrete is monitored over time via two non-destructive techniques. The first is the resonant frequency method which gives quite accurate results for the dynamic modulus, and the second is the pulse velocity method which is popular but less accurate. A comparison is made between the values obtained by the two methods.
Investigation of reinforced concrete frame behaviour—theory and tests
Authors: Mo Y. L.
Published: October 2009

The nonlinear behaviour of reinforced concrete frames with sidesway is governed by two efects: first the nonlinearity of materials due to cracking and the plastic behaviour of materials, and second the nonlinearity of geometry caused by the second-order deformation. These two efects may interact, and the whole phenomenon is known as the nonlinearity of geometry and materials. Reinforced concrete frames are frequently used to resist wind or earthquake forces. These forces will accentuate the complexity of the frame behaviour because of the continuous change of the shape of the bending moment diagram. The change of moment diagram will in turn afect the magnitude of the cumulative plastic rotations. A trilinear theory was devised to predict theoretically the moment-load curves of reinforced concrete frames throughout the loading history. This method utilized the trilinear moment-curvature curve for critical sections, as well as the principle of virtual work to express the compatibility condition and to find deflections. The theoretical prediction was checked by experiments with nine small-scale reinforced concrete frames. The materials for these frames were found to be acceptable, as reported in the companion Paper. The comparison indicates that both the theory and the tests are in good agreement throughout the loading history.
Response of reinforced high-strength concrete beam–column joints under load reversals
Authors: Ha G.-J. , Kim J.-K. , Chung L.
Published: October 2009

With the increasing use of high-rise reinforced concrete structures, high-strength materials, smaller member sections and larger reinforcing bars should be employed. Therefore, the stress resistance capacity of a joint is also required to be increased over other parts of a structure. The application of high-strength concrete has progressively increased in many structures, and it has now been used in many parts of the world. Previous research1–3 has shown that the behaviour of a reinforced high-strength concrete structure subjected to monotonic or earthquake-type loading is significantly different from that of a reinforced normal-concrete structure. It tends to be brittle when overloaded to failure, and to show a more sudden appearance of microcracking. Lack of ductility in concrete members raises serious concerns for structural safety. The behaviour of reinforced high-strength concrete members and joints must be accurately assessed before high-strength concrete can be used with confidence in reinforced concrete frame structures. The objective of this experimental research was to study the behaviour of reinforced high-strength concrete beam–column joints, and to develop a new approach for the design of such joints in high-rise reinforced concrete buildings.
Capillary absorption of water in hardened cement pastes treated with silicic esters or alkylalkoxysiloxane
Authors: Atzeni C. , Massidda L. , Sanna U.
Published: October 2009

By diminishing the ability of cementitious materials to absorb water by capillarity, their durability can be enhanced. The results are presented of impregnating hardened cement pastes prepared with various w/c ratios with silicic esters (deposition of silica gel within the pores) and alkylalkoxysiloxane formation of siloxane films on the pore surface). The changes brought about in sorptivity are discussed according to some extensions of Darcy's equation.
Direct tension tests on notched and un-notched plain concrete specimens
Authors: Phillips D. V. , Binsheng Zhang
Published: October 2009

Direct tension tests were conducted on plain concrete specimens in a stiff loading frame which allowed complete stress-deformation relations to be obtained. The suitability of the specimen shape and the testing apparatus was verified by finite-element analysis. The behaviours of notched and un-notched specimens with different water-cement ratios were examined and compared. Piecewise linear and exponential stress-deformation relations are proposed and interpreted physically. Relationships between fracture parameters fracture energy and brittleness indices) and basic strength properties are also presented.
Deflection of lightweight aggregate concrete beams
Authors: Birjandi F. K. , Clarke J. L.
Published: October 2009

This Paper is concerned with the study of the deflection of structural lightweight aggregate concrete beams over a period of six months using two types of lightweight aggregate available in the UK. The beams were centrally loaded under a constant load over the specified period and the deflections along their length were measured at regular intervals. The aim was to cover the likely range of density of structural lightweight aggregate concrete, and to compare the results with those of normal weight concrete and also with their estimated values calculated according to the requirements in BS 8110: Part 2.
Material and environmental factors influencing the compressive strength of unsealed cement paste and concrete at high temperatures
Authors: Sarshar R. , Khoury G. A.
Published: October 2009

Results of uniaxial compressive strength measurements taken on 1210 unsealed cement paste and concrete specimens heated to temperatures up to 600°C are reported; they show that both material and environmental factors have a significant influence during the heat cycle and afer cooling. The best results were obtained using firebrick aggregate and a cement blend containing 65 % slag replacement of OPC by weight. At 600°C the “hot” compressive strength of this material was 85% of the value measured before heating.
Preconditioning in situ concrete for permeation testing Part 1: Initial surface absorption
Authors: Dhir R. K. , Shaaban I. G. , Claisse P. A. , Byars E. A.
Published: October 2009

A new method for testing concrete using the initial surface absorption test (ISAT) has been developed for site use. It is based on applying a vacuum to an ISAT cap placed on the concrete surface until drying is achieved. The progress of the drying is monitored by placing indicating silica gel desiccant in the ISAT cap and observing the colour change. The method is quick, simple and practical for in situ applications. Results of comparisons with the existing in situ method in BS 1881 show that the new method is potentially more capable of producing reliable and reproducible measurements, and therefore will allow better comparison of in situ and laboratory-obtained data.
PFA concrete: influence of simulated in situ curing on elasto-plastic load response
Authors: Dhir R. K , Jones M. R.
Published: October 2009

A study comparing the elasto-plastic load response of OPC and PFA concretes was undertaken using temperaturematched curing (TMC) to simulate in situ conditions. For a given strength, the concrete type and curing regime had no sign$cant effect on the modulus of elasticity. However, PFA concrete showed a more ductile failure than the corresponding OPC concrete. In addition, higher plastic strain energies for the PFA concretes indicated better postfailure toughness than that of the OPC concretes.
Analysis of concrete hollow block masonry prisms under eccentric compression
Authors: Ramamurthy K. , Ganesan T. P.
Published: October 2009

This Paper discusses the analysis of concrete hollow block masonry (HBM) prisms in running bond with difflerent block geometries under eccentric compression. Hollow blocks of unsymmetrical cross-sections with different percentages of solid area have been evoloved. Their behaviours in masonry prisms under eccentric compression have been compared with that of a conventional block with symmetrical cross-section, using a special-purpose three-dimensional elastic finite-element analysis program, developed adopting eight-noded isoparametric solid elements. The potential increase in the capacity of masonry with blocks of unsymmetrical sections is evaluated. The need to determine the enhancement in the capacity of masonry with hollow blocks of symmetrical and unsymmetrical cross-sections over the capacity of that with solid blocks, through systematic experimental investigations, is emphasized.
New guidelines for cold weather concreting
Authors: Edmeades R. M. , Day R. I.
Published: October 2009

For more than 30 years the Cement and Concrete Association publication Winter concreting has provided practical guidance on whether or not concreting operations should proceed when freezing weather is forecast. However, the basic guidance curves do not adequately cover contemporary strength grades of concrete, or the use of composite cements, and modern Portland cements tend to differ from those produced when the curves were derived. To remedy this deficiency, the original Bergström model describing the thermal behaviour of newly cast concrete has been adapted for computerization and applied to mix designs in current use. Strength development and heat of hydration measurements were also carried out in order to produce new guidance curves covering 30, 40 and 50 N/m2 strength grades, and concretes made with: OPC; 70:30 OPC:PFA; and 40:60 OPC:GGBS. Discrepancies between the new and old curves are attributed mainly to the different maturity functions employed in the calculations.
Durability indicators of OPC concretes subject to wick action
Authors: Dias W. P. S.
Published: October 2009

Durability indicators for six OPC concrete mixes were obtained from wick action testing on concrete cylinders placed in water and a sodium chloride solution of concentration similar to sea water. Although 49 weeks of exposure to wick action in the salt solution was not sufficient to cause appreciable deterioration in the concretes, indirect durability indicators such as moisture transport phenomena and chloride ingress measurements were used to distinguish between the different concrete mixes. Increases in the water:cement ratio from 0·4, through 0·6, to 0·8 caused significant reductions in durability properties. An increase in cement content from 400 to 600 kg/m3 also impaired durability. However, the inclusion of 0·6% (by volume) chopped coir fibre to the control mix (w/c = 0·4, cement content = 400kg/m3) reduced durability only marginally. On the other hand, the inclusion of ultrafine gneissic quarry dust as a partial fine aggregate replacement in the control mix improved the durability indicators somewhat.
Experimental investigation of behaviour of anchorage zones
Authors: Ibell T. J. , Burgoyne C. J.
Published: October 2009

This Paper is the first of three on the behaviour of anchorage zones for prestressed concrete. Details of an experimental investigation carried out to determine the behaviour of concrete prisms strip-loaded through rigid steel plates are presented. This loading arrangement represents the transfer of force from tendon to concrete at the anchorage of a prestressed concrete structure. The results of several tests have shown that present design methods of anchorage zones are generally very conservative, which leads to an excessive quantity of steel reinforcement in this highly stressed region, that can lead to poor-quality compaction. It has been found, however, that the spreading of such steel over depths greater than those presently used could perhaps relieve this congestion with little loss in strength of the anchorage. Out-of-plane failures during strip-loading tests were also encountered. Proof must therefore be obtained that such third-direction failure cannot occur in practice if planar failure of the anchorage has been assumed during analysis.
Fracture energy of lime–sand concrete and application of the acoustic emission technique
Authors: Wu L. , Peng X. , Chu Q. , Bai G. , Yang J.
Published: October 2009

The linear localization technique known as the acoustic emission technique was appliedto the investigation of crack initiation and propagation in lime–sand concrete. The results showed that all parts of the tested lime–sand concrete specimens were damaged to some extent during the fracture process. The fracture energy and specific fracture energy were measured by use of the Instron 1346 materials testing machine. On the basis of the experimental results, the influence of autoclaving schedules, calcium–silicate ratio and water–solid ratio on fracture energy and specific fracture energy of this concrete was researched.
Service-load tests on profiled composite and reinforced concrete beams
Authors: Uy B. , Bradford M. A.
Published: October 2009

Tests are reported on two profiled composite steel-concrete beams and two reinforced concrete beams of the same flexural strength as the projiled beams under service loads. The beams were monitored under sustained loading for a period of approximately 250 days. Time-dependent deflections and strains in the beams were measured over this period, as werethe creep coeflcients and shrinkage strains of companion specimens. lhe results show thatthe time-dependent deformations of the profled composite steel-concrete beams are significantly less than those of the reinforced concrete beams. The test results are intended toprovide benchmark data for validating theoretical predictions of the deformations of profiled composite beams under service-load conditions.
Shear strength of reinforced lightweight concrete beams of normal and high strength concrete
Authors: Ahamad Shuaib H. , Xie Yuliang , Yu Tiejun
Published: October 2009

An experimental investigation was conducted to study the ultimate shear strength and the load-deformation characteristics of shear critical reinforced lightweight concrete beams of normal as well as high strength concrete. A total of 15 shear critical reinforced concrete beams without and with shear (web) reinforcement were tested in a ‘stiff’ testing facility and complete load–midspan deflection curves including the post-peak portion were obtained. The experimental variables were the concrete compressive strength, shear span to depth ratio (a/d) and the amount of shear reinforcement. Concrete cylinder strength (f'c) was varied between 30·5 MPa (4430 psi) and 89·3 MPa (12950 psi). The shear span to depth ratio was varied between 1 and 4 and the shear reinforcement ratio (γw) was varied between 0 and 0·784 percent.

For the range of variables tested, the results indicate that the predicted ultimate shear capacities in accordance with the ACI Code and the BS 8110 Code provide an adequate margin of safety when compared with the observed values for normal as well as high strength lightweight concrete beams using dlflerent types of lightweight aggregates such as stalite, lytag, pellite and pumice. Furthermore, the results indicate that the restriction imposed by the BS 81 10 Code on the strength of concrete not to exceed 40 MPa for shear strength computations may be overly restrictive. The presence of shear (web) reinforcement improves the post-peak deformation characteristics of reinforced lightweight concrete beams of normal as well as high strength concrete.
A model of plastic shrinkage
Authors: Radocea A.
Published: October 2009

The proposed model of plastic shrinkage is based on the idea that the capillary pressure in a saturated mixture, exposed to drying, depends on the geometry of the spaces between the solid particles near the surface of evaporation and the difference between the amount of evaporated water and the amount of water transferred from inside the mixture to the surface. The geometry of the pores at the surface and the factors affecting the amount of water transferred to the surface are studied by investigating the development of capillary pressure in three groups of materials with different behaviour when mixing with water: fine sand beds, silica fume and fly ash slurries, and cement pastes. It is shown that the total relative deformation of a sample depends on the rate of evaporation and the development of capillary pressure. Furthermore, the capillary pressure is a function of the water loss, the pore structure near the surface, the thickness of the sample and the modulus of plastic shrinkage.
A simple treatment to distinguish alkali—silica gel from delayed ettringite formations in concrete
Authors: Marusin S. L.
Published: October 2009

Alkali-silica gels or formations of late-developing Sample preparation and visual ettringite (delayed ettringite formation (DEF)) that fill examination sockets around aggregate particles may sometimes be observed by an optical microscope on unpolished or polished sawn concrete surfaces only as a ‘gel’ or as dark circles around the aggregate particles. They may thus be indistinguishable from each other. It has been found that the preparation of an unpolished or polished sawn concrete surface by carbon deposition (for SEM work) allows alkali-silica gel reaction and DEF to be distinguished by the nuked eye. However, X-ray elemental analysis recommended to confirm the visual observation.
Strength and ductility enhancement in high-strength confined concrete
Authors: Issa M. A. , Toban H.
Published: October 2009

Twenty-five prismatic concrete specimens with 125 × 125 mm (5 × 5 in) square cross-section and 400 mm (16 in) height made with normal-weight high-strength concrete were tested under quasi-static axial compressive loading to investigate the effect of various parameters on the strength and deformation characteristics of confined high-strength concrete. 20 specimens were confined by circular and square continuous spirals and provided with a protective concrete cover. This transverse reinforcement alone provided confinement for the concrete specimen, i. e. there was no longitudinal reinforcement. In addition to the confined specimen, five plain concrete specimens were tested to assess the actual characteristics of the unconfined concrete. The main parameters considered were compressive strength of the concrete and the amount and yield strength of the transverse steel. The primary purpose of the confinement was to increase the maximum strength, corresponding strain and toughness of the confined high strength concrete. It was observed that the characteristics of the confining steel influenced the behaviour of the confined concrete.
A carbonation prediction model for accelerated carbonation testing of concrete
Authors: Loo Y. H. , Chin M. S. , Tam C. T. , Ong K. C. G.
Published: October 2009

This Paper reports an experimental investigation to establish the influence of ambient CO2, concentration, exposure temperature and curing duration on the rate of carbonation in concrete. The test specimens were concrete cylinders 100 mm in diameter and 200 mm high. Of the parameters investigated, the standard 28-day compressive strength f28 was found to be effectively representative of the concrete quality in several carbonation models proposed. Index test results, i.e. water absorption and sorptivity, were also incorporated to depict the effects of the surface property of concrete. The proposed models agreed well with the experimental data.
Rotation capacity of structural concrete members
Authors: Riva P. , Cohn M. Z.
Published: October 2009

A plastic rotation capacity expression based on a realistic non-linear analysis model is derived for structural concrete members. Effects of section shape, compression reinforcement and bending moment distribution are considered. A set of diagrams enables the plastic rotation capacity of rectangular, T and I structural concrete members under linear, sagging, and hogging bending moments to be determined. Use of these diagrams enables the compatibility requirement of critical sections of structural concrete continuous beams under either concentrated or distributed loads to be checked. Comparison with available plastic rotation formulations shows that neglecting the influences of the loading distribution and of ratios between contraflexure point distance and the section depth may lead to non-conservative results. It is found that for lightly reinforced sections (steel failure) plastic rotation capacities increase, while for highly reinforced sections (concrete failure) plastic rotation capacities decrease, with increasing reinforcement index values.
Prediction of free chloride concentration in concrete using routine inspection data
Authors: Mangat P. S. , Molloy B. T.
Published: October 2009

This Paper presents a wide range of experimental data on chloride Concentrations in the pore fluid (free chloride contents) of various mixes of concrete. The results show that Fick's second law for unidirectional diffusion into a semi-infinite medium is valid for free chloride penetration into concrete. The values of diffusion coeficient Dc, decrease with time and it is shown, on the basis of substantial experimental data, that diffusion coefficients of free chloride penetration Dfc and acid-soluble chloride penetration Dac can be correlated over a wide experimental range. The Paper derives expressions based on Fick's second law of diffusion which can be used to predict long-term concentrations of free chloride in concrete using data obtained in a routine inspection of a concrete structure. These data include acid-soluble chloride concentrations in concrete cores and the chloride concentration of the solution to which concrete is exposed. The free chloride concentration profiles across the depth of concrete derived using these procedures show fairly good agreement with long-term experimental data. Since the pore fluid in concrete provides the electrolyte for reinforcement corrosion, the procedures derived in the Paper will be valuable in the setting up of accurate practical procedures for assessment of corrosion in concrete.
Potential effects of electrochemical desalination of concrete on alkali – silica reaction
Authors: Page C. L. , Yu S. W.
Published: October 2009

The recent development of an electrochemical method of chloride removal (desalination) for the treatment of corrosion of reinforcing steel in chloride-contaminated concrete offers the prospect of an effective repair strategy for certain types of structure that have been exposed to chloride ingress from the environment. As with any novel remedial technique, however, it is necessary to examine potentially detrimental side-effects. This Paper presents preliminary results of an investigation into one such phenomenon, namely cathodically stimulated alkali-silica reaction (ASR) in the concrete interfacial zone adjacent to the embedded steel. It is shown that for concrete specimens containing potentially reactive siliceous aggregates in cementitious matrices of bulk alkalinity below the threshold levels required to induce expansive ASR, local expansion and cracking in the vicinity of steel cathodes may be caused by the application of current densities in the range 1–8 A/m2 for periods of 4–12 weeks and subsequent moist storage. The relationship between the ultimate expansion of the concrete and the total charge passed through it during electrochemical treatment is complex and suggests a novel form of ‘pessimum’ behaviour. The discovery of this effect has important practical consequences, affecting the range of appropriate treatment conditions and testing regimes for diagnosis of ASR-susceptible concrete when electro-chemical desalination is being considered.