bluuebunny/crossref_metadata_2025_split huggingface dataset:
Response of the Bond in Reinforced Concrete to High Temperatures
Authors: Morley P. D. , Royles R. 
Published: October 2009

Synopsis The effect of high temperutures upon the bond between the steel und concrete in reinforced concrete was examined over a temperature range of 20–750°C. The concrete mix was constant throughout und 16 mm deformed reinforcing bar (Tor bar) was used in most tests. Various parameters were examined including different test conditions and depths of cover. The four test conditions used were: (l) stressed during heating (a steady-state bond stress of 3·70 N/mm2 was applied) and loaded to failure when hot, (2) stressed during heating and loaded to failure when cooled, (3) no applied stress during heating and loaded to failure when hot, and (4) no stress during heating and loaded to failure when cooled. Four different depths of concrete cover (25, 32, 46 und 55 mm) were l for the stressed/residual test condition, but only tht 55 mm cover was used with the other three test conditions. The effect of heat upon the compressive und tensile strength of the concrete was also considered, together with its effect upon the bond performance. Some 16 mm plain bar specimens were used in the tensile strength studies. Introduction When a reinforced concrete structure has been involved in a fire. it is often possible for it to remain standing, because of the good fire-resisting properties of the concrete. This means that. in dealing with such a situation. a choice can be made between reconstruction and reinstatement. Often reinstatement can be the quicker and cheaper alternative. However, before a decision can be made, it is necessar/10 establish whether or not the damaged structure is suitable for such treatment. To do this, its residual capacity for structural performance must be assessed, which requires knowledge of the properties of steel and concrete, and of the bond between them at temperatures experienced in fires.
Mechanisms of ‘shear’ failure
Authors: Kotsovos Michael D. 
Published: October 2009

Synopsis It is postulated that the various modes of diagonal failure exhibited byreinforced concrete beams under increasing load are associated with the multiaxial stress conditions that exist in the region of the path along which the compressive force is transmitted from support to support. This concept leads to a comprehensive description of the causes and mechanisms of diagonal failure which, in contrast with currently accepted concepts, is compatible with published experimental information. It is shown that, although current ‘shear’ design procedures may guard against diagonal failure within the shear span, they may lead to a ‘brittle’ type of failure outside this span which does not give adequate warning of impending structural collapse.
Durability of cement sheets reinforced with fibrillated polypropylene networks
Authors: Hannant D. J. 
Published: October 2009

Synopsis The durability of cement sheets reinforced with fibrillated polypropylene networks is examined in terms of the effects upon the tensile stress–strain curve of three years of natural weathering or of a similar period of indoor storage. It is shown that three years of exposure has little effect upon the strengths of the networks, but that increases in the strength and elastic modulus of the matrix in the naturally weathered specimens alter some features of the stress–strain curve in comparison with similar material stored indoors.
Properties of ultra-high-strength concrete containing a superplasticizer
Authors: Brooks J. J. , Wainwright P. J. 
Published: October 2009

Synopsis Tests have been undertaken over a period of one year to compare the time-dependent properties of high-cement-content (500–730 kg/m3) concretes with and without a superplasticizing admixture. For mixes containing the superplasticizer. there was an improvement in strength and modulus of elasticity and a decrease in shrinkage, but there were increases in creep and swelling. The process of microcracking is postulated to be a contributing factor in shrinkage and in creep under drying conditions.
Apparatus for measuring the transient thermal strain behaviour of unsealed concrete under constant load for temperatures up to 700°C
Authors: Sullivan Patrick J. E. , Khoury Gabriel A. , Grainger Brian N. 
Published: October 2009

Synopsis Apparatus was designed for the strain measurement of unsealed cylindrical concrete specimens under transient thermal states. This subject has received in sufficient attention to date arld is of interest io prestressed concrete nuclear reactor pressure vessel and fire applications. To simplify analysis of results, the imposed conditions includean arrangement for applying constant uniaxial compressive load and an automatic temperature control system which ensures as linear a rate of heating as possible and minimizes axial temperature differentials along the specimen. A strain measuring device was designed which produced accurate results under transient thermal states.
Torsion in plain and prestressed concrete beams containing polypropylene fibres
Authors: Narayanan R. , Kareem-Palanjian A. S. 
Published: October 2009

Synopsis Torsion tests on 23 plain and prestressed concrete beams containing polypropylene fibres are presented and discussed. The addition of these fibres to concrete is shown to improve the post-peak ductility, though there is no change in the ultimatc torsional capacity of the beams tested. A simple method of predicting the ultimate torsional capacity of these beams from a knowledge of the cube strength and the applied prestress is proposed; by comparison with the experimentally observed strengths, the method is shown to yield satisfactory predictions.
Comparisons between closed-loop and straight metal fibres inconcrete
Authors: Taylor Michael A. 
Published: October 2009

Synopsis Concretes containing closed-loop fibres and conventional straight fibresare compared for workability, bond strength, compressive strength, tensile strength, flexural strength and toughness. The concept of spacing is treated briefly. Tests indicate that all fibres have little effect until after significant cracking occurs. After cracking, closed loops offer much better integrity than straight fibres. Closed-loop fibres reduce the variability ofboth compressive and tensile strengths.
Shear transfer across cracks in reinforced concrete due to aggregate interlock and to dowel action
Authors: Millard S. G. , Johnson R. P. 
Published: October 2009

Synopsis Tensile cracking of reinforced concrete plate elements results in a significant reduction in the in-plane shear stiffness and strength. Shear can be transmitted across the cracks either by interlocking of the aggregate particles protruding from each face or by shearing of the reinforcement crossing the cracks. Tests of a new type are devised to study these mechanisms independently and the results are compared with several theoretical models. It is concluded that the aggregate mechanism results from a combination of crushing and overriding of the crack faces and can be predicted if the normal stiffness that restrains crack widening is known. The initial shear stiffness and ultimate shear strength due to dowel action are successfully predicted from theoretical models and an exponential curve is used to describe the intermediate behaviour.
Some preliminary test data on cement–pfa–anhydrite mixes
Authors: Hyde A. F. L. 
Published: October 2009

Synopsis Cement-stabilized pfa is commonly used as a load-bearing fill for civil engineering purposes. Anhydrite is often used for similar purposes in the mining industry. A series of compressive strength tests were carried out on combinations of these three materials to determine their potential as moderate to high-strength fills. The tests were carried out on 38mm dia. by 75mm long specimens prepared by static compaction techniques. Attempts to stabilize pfa using anhydrite showed little potential for increasing the load-bearing capacity of pfa. However, a study of the combination of cement and anhydrite in the stabilization of pfa showed these two materials to be complementary in increasing the compressive strength of compacted stabilized pfa compared with using just cement or just anhydrite as the stabilizing agent. The 14, 28 and 56 day strengths of cement-bound pfa were more than doubled by the replacement of 1·4% cement by weight with 10% anhydrite by weight. The addition of higher proportions of anhydrite could decrease this enhanced strength or give only a marginal increase. Long-term tests after a curing period of one year showed no apparent deterioration in strength.
A modification of the Tattersall two-point test apparatus for measuring concrete workability
Authors: Cabrera J. G. , Hopkins C. J. 
Published: October 2009

Synopsis This paper describes a mod2Jication of the Tattersall two-point test apparatus for measuring concrete workability. The modified apparatus is easier to operate, giving a full and permanent record of what happens during the test and eliminating operator bias, which exists in the present oil-pressure measuring system.
Improvements to the Figg method for determining the air permeability of concrete
Authors: Cather R. , Figg J. W. , Marsden A. F. , O'Brien T. P. 
Published: October 2009

Synopsis Modifications to the Figg method for in situ determination of the air permeability of concrete are recommended. These are the use of a hole size of 10mm diameter × 40 mm deep with a silicone rubber plug 20 mm from the surface and a digital solid-state manometer. The time, in seconds, taken for a pressure change from 55 to 50 kN/m2below atmospheric is taken as a measure of the air permeability. A table of protective quality of cementitious materials is tentatively proposed.
Shear strength of smooth unreinforced construction joints
Authors: Clark L. A. , Gill B. S. 
Published: October 2009

Synopsis The results of 60 tests on smooth unreinforced construction joints in concrete prisms are presented. Each specimen was subjected to loading which induced combined direct and shear stresses at the joint. It was found that shear was transmitted by a combination of ‘cohesion’ and ‘friction’. A slight dependence of the shear strength upon the age ofthe first pour of concrete at the time of the second pour was found. A relation for the shear strength of a smooth unreinforced construction joint is proposed as a function of concrete compressive strength and the associated direct stress at the joint.
Applications of diffusion theory to permeability tests on concrete Part I: Depth of water penetration into concrete and coefficient of permeability
Authors: Vuorinen Jukka 
Published: October 2009

Synopsis The paper describes an application of diffusion theory to the penetration of water under pressure into concrete. The resulting second-order differential equation is non-linear, because the water-storage capacity of the open pores in concrete depends upon the counterpressure arising. Numerical computer analysis of the permeability equation leads to a formula for calculating the coefficient of permeability when the values of the test parameters and the depth of water penetration are known. The application of the final formula to a series of laboratory test results shows that there is a fairly good correlation between the values of the coefficient of permeability so calculated and those based on direct measurement of water flow through a concrete specimen.
Applications of diffusion theory to permeability tests on concrete Part II: Pressure-saturation test on concrete and coefficient of permeability
Authors: Vuorinen Jukka 
Published: October 2009

Synopsis In addition to the conventional permeability tests, the coefficient of permeability of concrete can be found through interpretation of observations made during the pressure-saturation test. An opportunity for this offers itself in the application of diffusion theory to the mathematical model of this test. After explaining this procedure, the paper compares the results with those obtained by a method in which the depth of water penetration into concrete is measured. Although the correlation can be considered satisfactory from the practical point of view, it seems that the mathematical model used does not in all respects represent the complicated phenomenon of water outflow from a saturated concrete specimen.
A study of toughness indices
Authors: Barr B. I. G. , Hasso E. B. D. 
Published: October 2009

Synopsis The paper reviews various methods of evaluating the toughness of fibre-reinforced concrete materials by means of toughness indices and discusses in detail the use of various multiples of jirst-crack defection to define toughness indices. A new toughness index is proposed, based on the load–deflection curves obtained up to twice the defection at first cracking. The index is given by the ratio of two areas under the load–deflection curve and is expressed as a percentage which varies from zero for plain concrete, through 67% for an elastic-plastic material, to a theoretical maximum value of 100% for an extremely tough material. Both modulus-of-rupture and notched-beam test specimens were used in the study. Although only one geometry is reported and only Duoform steel fibre was used in the study, the method described is potentially applicable to all geometries and types of fibre. The proposed toughness index is shown to be independent of the notch depths used in the geometry reported and has well defined maximum and minimum values. It also has a large range, which should make it suitable to distinguish between various types and amounts of fibre.
Pore structure and permeability of hardened cement paste
Authors: Hughes D. C. 
Published: October 2009

Synopsis A review of the literature on flow through porous media suggests that the permeabilityof hardened cement paste should be related to pore size distribution, pore conductance, tortuosity and isotropy. It is likely that these factors do not exhibit a unique value. Tests were made on OPC and OPC/pfa pastes cured for I, 4 and 12 weeks in Ca(OH)2, solution. The permeability of both types was similar for those pastes cured for 4 and 12 weeks at 35°C, whilst after one week's curing the OPC/pfa paste was sign$cantly the more permeable. Pore size distribution was determined by using a two-stage mercuryintrusion technique. A simple model, based upon Poiseuille's formula, was developed and shown to yield a reasonable correlation with the experimental determination of permeability for the OPC pastes and on SRPCpaste cured for 4 weeks. The correlation was not so goodfor the OPC/pfa pastes, probably as a consequence of structural damage during mercury intrusion in such pastes.
Core point-load test for steel-fibre-reinforced concrete
Authors: Robins P. J. , Austin S. A. 
Published: October 2009

Synopsis The point-load test, more commonly used in geotechnical practice, is evaluated for application in concrete testing as a potential method for estimating the strength of steel-fibre-reinforced concrete. Both diametral and axial test configurations are investigated and the effect of load direction in relation to fibre orientation is explained. Whilst the diametral test is suitable for measuring the strength of random three-dimensionally orientated fibre concrete, the axial test is shown to be more appropriate for assessing the properties of an anisotropic material such as sprayed steel-fibre concrete.
The effect of a Pfa with a high total alkali content on pore solution composition and alkali silica reaction
Authors: Nixon P J , Page C L , Bollinghaus R , Canham I 
Published: October 2009

Synopsis The effectiveness of a pfa with a high total alkali content in suppressing expansion caused by alkali silica reaction has been investigated using concrete specimens containing flint sand. The observed behaviour has been related to the effect of the pfa on pore solution composition. With such a slowly reacting aggregate, typical of those found in concrete affected by ASR in the UK, 20 or 30% of the pfa stopped any deleterious expansion. The effect of the pfa on the pore solution depended on the age and the alkalinity of the cement. At 28 days there was a net contribution to the alkalinity of moderate or high alkali cement pastes but at longer ages the pfa reduced the alkalinity below that produced by dilution with an inert material. In very low lkali cement pastes however there was a net contribution to the alkalinity at all ages up to one year.
Post heat exposure behaviour of reinforced concrete beams
Authors: Khan M. R. , Royles R 
Published: October 2009

Synopsis Consideration is given to the behaviour of reinforced concrete beams after subjection to elevated temperatures in the range 20 to 800°C. Prismatic concrete beams reinforced with plain mild steel and tor bars were cast using the same concrete mix and water: cement ratio. Each beam was heated to a particular temperature and held at that level for one hour prior to coolingfreely in air to ambient temperature and then testing to failure under four point loading. Temperature distributions within the beam sections were monitored during the heating cycle, and bond-slip as well as load-deflection responses were examined in the residual heat treated condition. Crack pattern development was studied arising from both thermal and loading effects and the influence of bar type and grouping were examined.
Determination of specimen-size independent fracture toughness of plain concrete
Authors: Nallathambi P. , Karihaloo B. L. 
Published: October 2009

Synopsis Simple analytical expressions are proposed for determining the critical stress intensity factor Kc, and the critical energy release rate Gc, of plain concretes in three-point bending. These expressions take into account the slow crack growth preceding fracture and the complex state of stress existing at a propagating crack front. The fracture toughness so determined is shown to be essentially independent of the test specimen dimensions and to depend only on the mix variables. It is also argued that unlike Kc, or Gc, the fracture energy GF of plain concretes is strongly dependent on the test specimen dimensions. It is therefore advisable to express the fracture toughness of plain concretes through the specimen-size independent parameters Kc, or Gc.
A method for determining the relative permeability of concrete using gas
Authors: Martin G. R. 
Published: October 2009

Synopsis This paper describes a method of measuring the relative permeability of concrete specimens to gases by passing nitrogen through them. The specimen is a 100 mm cube sealed on two opposite faces and with a central 6 mm hole running between them. Nitrogen from a sealed reservoir at a standard initial pressure is passed into the hole. The reservoir pressure is automatically recorded at suitable intervals, and the rate at which it falls is a measure of the permeability. The test has been shown to be quick and simple to carry out, and to have good repeatability provided specimens are allowed to dry suflciently before testing. The apparatus has also been used to pass CO2 through a specimen, causing its permeability to fall as a result of carbonation. Suggestions for future work to make use of the method are given.
Development of mechanical properties of ordinary Portland and Oilwell B cement grouts
Authors: Domone P. L. , Thurairatnam H. 
Published: October 2009

Synopsis The compressive strength and dynamic elastic modulus of ordinary Portland cement (OPC) grouts typical of those used for structural connections in steel jacket offshore platforms has been measured. The main aim of these tests has been to provide baseline data for grout selection and development. Variables tested include water/cement ratio (0·3 to 0·5). OPC and Oilwell B cement, fresh and sea-water for mixing, curing temperatures of 8 and 20°C and the incorporation of superplasticisers. Properties have been measured at ages of I day to 1 year. OPC grouts show a significantly more rapid development of properties at early ages than Oilwell B cement grouts, but the differences are minimal after 7–28 days. Other variables have expected effects on the grout properties. Good correlations of both strength and modulus with ultrasonic pulse velocity have been obtained, and hence greater use can be made of this non-destructive test in future work. Values of dynamic Poisson's ratio calculated from the other properties show a dependence on both strength and water/cement ratio.
Equilibrium element analysis of plain concrete and steel-concrete composite cylinders subjected to external pressure
Authors: Choate P. R. , Montague P. 
Published: October 2009

Synopsis An equilibrium element method is derived for the axisymmetric analysis of the mid-length region of thick- walled cylinders of non-linear material construction. The method is used to examine the behaviour of plain concrete and steel-concrete composite cylinders subjected to externalfluid loading. The incremental form of a nonlinear elasticity model is adopted for the concrete and the steel is described be elasto-plasticity.
Relaxation of concrete and its relation to creep under uniaxial cyclic compression at various frequencies
Authors: Brooks J. J. , Forsyth P. 
Published: October 2009

Synopsis Following an earlier creep investigation, relaxation of five-day cyclic compressive stress under constant cyclic strain is reported for frequencies ranging from 1 cycle per day to 1·2 Hz. As with creep, relaxation has to be defined carefully because of the shape of the stress–strain curve. On the other hand, in contrast with creep, there is no increase in relaxation from a frequency of 30 cycles per hour to 1·2 Hz. Relaxation under a cyclic strain can be related to creep but the established methods of estimating stress from strain require modification. Using a modified Effective Modulus approach, the full stress cycle after relaxation can be predicted from static creep.
Reinforced concrete deep beams some test results
Authors: Subedi N. K. , Vardy Alan E. , Kubotat N 
Published: October 2009

Synopsis thirteen simply supported reinforced concrete deep beams with span/depth ratios of 1,2 and 3 are loaded to failure. The percentage of main reinforcement varies from 0·22 to 1·16 and three modes of failure are reported, namely flexure, diagonal splitting and local crushing. Detailed experimental evidence including some strain measurements is presented to enable the development of the failure mechanism to be monitored. The failure loads are compared with values predicted by CIRIA Guide 2, which is shown to be safe provided that failure is by diagonal splitting (the commonest case in practice). It is argued that a need exists for design recommendations for deep beams with larger span/depth ratios than those covered by the Guide.
Non-linear moisture profiles and shrinkage in concrete members
Authors: Terrill J. M. , Richardson M. , Selby A. R. 
Published: October 2009

Synopsis A simple approach to the measurement of moisture variations in concrete prisms is used to produce profiles such as might occur in a waterproofed bridge deck slab. The method relies on segmentation of a number of companion blocks containing crack initiators. Shrinkage/weight loss curves are produced for small concrete cylinders with varied curing times. Cylinders cured for less than about four weeks show a bi-linear relation between shrinkage and weight loss, with little shrinkage due to early moisture loss and more rapid shrinkage with later losses. Combination of non-linear moisture profiles with the shrinkage/weight loss relations into a numerical analysis allows tentative estimates of axial shrinkage, curvature and self-equilibrating stresses in a cracked or uncracked reinforced concrete section with or without allowance for creep.