bluuebunny/crossref_metadata_2025_split huggingface dataset:
The estimation of the strength of concrete made with lightweight aggregate
Authors: Shirayama Kazuhisa 
Published: July 2012

Summary In an earlier paper the author proposed an experimental formula for estimating the compressive strength of lightweight aggregate concrete by an extension of Abram's water/cement ratio theory. The present paper describes compressive strength tests performed on concrete made with expanded clay aggregate produced in Norway which show good agreement with the formula. The relations between cube strength and cylinder strength and modulus of elasticity are discussed, and a Table of mix proportions for this lightweight aggregate concrete is proposed.
Variations in concrete proportions due to side vacuum treatment
Authors: Buchan A. R. , Hawkes J. M. 
Published: July 2012

Summary A technique for the analysis of fresh concrete into its constituent parts was perfected. Tests using this technique were made on concrete which had been subjected to side vacuum treatment to determine the effect of: the duration of treatment; the application of vibration; variations in the initial water/cement and aggregate/cement ratios; redistribution of the water content after treatment. The results indicate that: treatment causes migration of the finer particles (sand and cement) towards the processed face (this is increased if the concrete is vibrated); as the initial water/cement ratio increases, the movement of sand and cement. increases, but raising the aggregate/cement ratio decreases the movement of sand; immediately after treatment the water content is non-uniform, with a minimum value at the vacuum face, but gradual redistribution occurs after treatment stops.
Test on a prestressed concrete hollow-box bridge deck
Authors: Gifford F. W. 
Published: July 2012

Summary Hollow-box pre-tensioned beams laid side by side and held together transversely by prestress or other means are advocated for bridge decks of spans from 30 up to about 90 ft. A detailed account is given of tests on a one-third scale model of a 30 ft span. Comparisons, both general and with reference to tests by the Cement and Concrete Association, are made with the type of deck comprising inverted T beams transversely reinforced and completed with in situ concrete above.
Further studies of pore size distribution in mortars
Authors: Kroone B. , Crook D. N. 
Published: July 2012

Summary The method of mercury penetration was used to study the influence of variations in the sandi cement and waterlcement ratios on the pore size distributions of mortars, down to pore sizes of 0·01μ; diameter. It was found that the total volume of the pores with diameters greater than 5μ; increased as the sandi cement ratio increased, but decreased as the waterlcement ratio increased, within the limits of the experiments. It was also found that the cross-section of the pores became more irregular as the sand content increased. and that at low waterlcemem ratios an increase of the water/cement ratio tended to produce pores of more regular cross-section.
Strength tests on scaled-down concretes suitable for models, with a note on mix design
Authors: Johnson R. Paul 
Published: July 2012

Summary The paper describes procedures for testing the strength of “scaled-down” concrete mixes suitable for models of concrete structures. The effects of the scale of mix and the size of test specimen on the magnitude and scatter of the results are given in detail. It is concluded that tests on 1½ in. diameter cylinders 3 in. long give a satisfactory measure of the strength of concrete made with aggregate passing a 3/16 in. sieve. Mix design curves are given for a limited range of mixes of medium workability.
The rotation of reinforced concrete plastic hinges at ultimate load
Authors: Chan W. W. L. 
Published: July 2012

Summary On the basis of the simplified ultimate load theory which assumes elastic members spanning between plastic hinges, the procedure for checking required rotations caused by moment redistribution and rotation capacities of plastic hinges is outlined, and the influences of strength of concrete, compression and tension reinforcement, and form of loading on hinge rotations are discussed. In particular, it is shown that compression steel, which significantly affects flexural rigidity in structural members, as well as concentrated rotations at plastic hinges, provides a convenient means of adjusting deformations in ultimate load design. From a study of test results from 54 beams and 13 struts, the paper shows that the methods and parameters that are recommended in the recently published report on “Ultimate load design of concrete structures” for the computing of plastic hinge rotations are safe and statistically acceptable.
The deformation of a rectangular slab stiffened by beams under transverse loads
Authors: Severn R. T. 
Published: July 2012

Summary A rectangular slab spans between simple supports and is stiffened by beams of uniform cross-section (Figure 1). Complete composite action is assumed to exist between the slab and the beams. Each panel of the slab can carry point loads, acting at any point of the panel, and a uniformly distributed transverse load, and the beams carry loads which are either uniformly distributed along their lengths or are concentrated so as to act as point loads. The magnitudes of the loads carried by each panel and by each beam will generally not be the same. It is assumed that the transverse deflexion of the structure and the stress function that describes forces in the plane of the slab are governed by independent biharmonic equations. To these equations series solutions are taken and the coefficients which they contain are determined by satisfying the conditions of compatibility and continuity at the slab-beam junctions. The results of experiments with models are described and brief details are given of computer programmes which may be used to carry out the computations involved.
A lower bound solution to the collapse of an orthotropically reinforced slab on simple supports
Authors: Kemp K. O. 
Published: July 2012

Summary Although upper bounds to the collapse loads of simply supported, orthotropically reinforced concrete slabs can be readily calculated by application of the yield-line theory, corresponding lower bound solutions which must satisfy equilibrium and the yield criterion at all points in the slab are not yet available. A lower bound solution to the collapse of a simply supported, rectangular slab, orthotropically reinforced and carrying a uniformly distributed load is developed. It is based on one originally proposed by Sawczuk(4) but the distribution of twisting moments has been modified to just produce positive yield moments at all points in the slab and negative yield moments at the corners. The lower bound collapse loads calculated for a range of coefficients of orthotropy μ, and ratio of width to length of slab λ, agree extremely closely with the upper bound values derived from the yield-line theory. The yield lines, however, are quite different and are found to be an infinite set of curves in the lower bound solution. Finally, the solution is used to determine the extent of negative reinforcement required in the corners of the slab and the loads transmitted to the supporting edges.
Thermal stresses in reinforced concrete slabs
Authors: Hannant D. J. , Pell P. S. 
Published: July 2012

Summary A description is given of an experimental and theoretical investigation into the stresses induced in steel and concrete in reinforced concrete slabs subjected to high temperatures and thermal gradients. It is shown that the observed stresses in the steel are dependent on time and previous temperature cycling of the slabs. Initially, the stresses in the steel were in close agreement with the values derived from the elastic analysis but as shrinkage and creep increased, with time and temperature, large losses of tensile stress were measured until, in several cases, the steel developed compression even while the thermal gradients were considerable. The main cause of the loss of tensile stress in the steel was attributed to the increased rate of concrete shrinkage at temperatures near or above 100°C, with secondary effects due to creep and reduction in the expansion coefficient. Design recommendations are made which enable the final equilibrium stresses to be determined within fairly wide limits and it is shown that the final steel stresses are likely to bear little relation to the stresses calculated from an elastic analysis alone.
General relation between mix proportion and cement content of concrete
Authors: Popovics Sándor 
Published: July 2012

Summary Semi-empirical equations are presented for the relation between cement content and mix proportion of concrete. Other variables are the consistence, specific gravities of cement and mineral aggregates, grading of aggregate, and air content. The paper shows equations for the case in which only one material is used as mineral aggregate (equations 1–4), and for the more general case in which a blend of two materials is used (equations 5–8). The form of the equations is relatively simple considering the large number of variables involved. The values calculated from the equations are compared with results of experiments performed by various research workers, and it is shown that there is good agreement between calculated and experimental values.
The flexural rigidity of reinforced concrete
Authors: Everard K. A. 
Published: July 2012

Summary By assuming that for short tests the stress at a-particular point in a reinforced concrete beam may be identified with a particular strain, a general non-linear theory of bending is proposed. The case of parabolic stress distribution in a rectangular beam is examined in detail and expressions describing the moment-curvature relations for various parameters are obtained. These expressions can be used to calculate the angles of discontinuity which may be developed in a reinforced concrete section at moments up to the ultimate.
The thermal conductivity of concrete
Authors: Campbell-Allen D. , Thorne C. P. 
Published: July 2012

Summary A simple theory is developed which gives the thermal conductivity of concrete in terms of the thermal conductivity of its constituents. The predictions of this theory concerning the variation of the thermal conductivity of concrete with moisture content have been tested by experiment and have been found correct; this experimental work covers the effect of moisture content on the thermal conductivity of concrete made with three different aggregates, namely, dolerite, haematite and barytes.
The materials testing laboratory of the Cement and Concrete Association
Authors: McIntosh J. D. 
Published: July 2012

Summary A new laboratory for research on the engineering properties of concrete and its constituent materials has been erected for the Cement and Concrete Association at its research station at Wexham Springs to re-house various departments which had been operating in temporary accommodation. The paper describes the measures taken to deal with problems applicable to all buildings of this type. Air-conditioning of many of the rooms influenced the siting, planning and method of construction of the building. Particular problems included reducing nuisance from the dust and noise of many operations, preventing the spreading of shock and vibration to the rest of the structure, planning a convenient flow pattern for routine operations while allowing adequate versatility for other techniques, and filtering “live” cement from liquid waste. Although all the desirable refinements were not included at the time of erection, provision was made, where possible, for them to be incorporated later.
A note on the effect of frequency on the behaviour of fresh concrete during vibration
Authors: Green H. , Roberts A. B. 
Published: July 2012

Summary The behaviour offresh concrete during vibration varies with thefrequency of the vibration applied. For each mix there is a particular frequency at which a drastic change in the acceleration of the mould and the mix takes place during vibration with constant power input. The strongest concrete is produced at this frequency of vibration.
The effect of grout properties on the structural behaviour of post-tensioned concrete beams
Authors: Geddes J. D. , Soroka I. 
Published: July 2012

Summary The effect of grout properties on the structural behaviour of 18 post-tensioned prestressed concrete beams was investigated. The beams were 6 × 10 in. in cross-section and 10 ft long with an average concrete compressive strength of approximately 8,500 lb/in2. In each beam the prestressing cable consisted of eight 0·2 in. smooth high-tensile wires having a nominal eccentricity of 2 in. All the beams were identical but the properties of the grouts were varied over a wide range. The fluidity (immersion test) varied between 4 and 85 s, the bleeding (“tin-can” method) varied between 0 and 16·9%, the volume change (“tin-can” method) varied between 18 % sedimentation and 11·1 % expansion, and the cylinder compressive strength at 21 days varied between 2,100 and 4,300 lb/in2 Air-entraining agents, plasticizers and expanding agents were used in some of the grouts. At 28 days the beams were tested to failure by two-point symmetrical loading and the following factors were determined: the ultimate strength; the ratio of steel stress at failure to its ultimate tensile strength (λ); the pattern of cracking (number, spacing and width of cracks). Evaluation of the results clearly suggests that the structural behaviour of grouted post-tensioned prestressed concrete beams subjected to bending is not significantly affected by extreme variations in the properties of the injected grouts.
Resin-bonded glass-fibre tendons for prestressed concrete
Authors: Somes N. F. 
Published: July 2012

Summary The high strength and low modulus of elasticity of resin-bonded glass-fibre tendons have prompted consideration of their use in prestressed concrete. The paper describes development work carried out with this material and reports on the testing of eight prestressed beams. Failure loads show agreement with those calculated by the strain compatibility method. Considerable difficulty was encountered in developing a satisfactory anchorage. The use of the correct stress at tensioning and the avoidance of surface damage at casting are shown to be very important, and bond and transmission characteristics were found to be similar to those of steel wire of the same diameter. Bondedfibre tendons may successfully be employed in prestressed units if their initial anchoring stress does not exceed 0·45 of the short-term strength.
A new method of proportioning stirrups in reinforced concrete beams
Authors: Taylor R. 
Published: July 2012

Summary A possible basis from which to elaborate an empirical design method for proportioning stirrups in reinforced concrete beams is developed from a consideration of the actual behaviour of a beam under load and the designer's need for simplicity. Empirical values of the design factors involved are suggested. Reference is made to the results of tests on beams in which the shear reinforcement was designed in accordance with the proposals.
The effect of curing conditions on the physical properties of concrete
Authors: Elvery R. H. , Evans E. P. 
Published: July 2012

Summary An investigation has been carried out to study the effect of different curing conditions on certain physical properties of concrete. The conditions ranged from a temperature a little above freezing to that of high-pressure steam, and included normal and tropical temperatures. The properties measured included crushing strength, dynamic and static moduli, ultrasonic pulse velocity and modulus of rupture.
Determining the thickness of concrete pavements by mechanical waves: directed-beam method
Authors: Bradfield G. , Gatfield E. N. 
Published: July 2012

Summary The device described forms a compact and convenient means of determining the thickness of concrete roads and pavements (and of similar rock-like materials) to an accuracy of a few per cent; this can probably be improved upon by refinements discussed. An interesting outcome of the development is that it appears to be possible to measure accurately the velocity of irrotational waves propagating on or just below the surface of the specimen. The paper mentions possible applications to mining, the measurement of Poisson's ratio and crack detection.
Researches into the complete stress-strain curve for concrete
Authors: Barnard P. R. 
Published: July 2012

Summary This paper describes two series of tests on concrete specimens for the purpose of determining the complete stress-strain relation in uniaxial compression, including the falling branch. In the second series, lateral as well as longitudinal strains were measured which showed that initial tension cracking occurs locally within the gauge length and that portions of this length may be uncracked at maximum load on the specimen. The results included in the paper demonstrate the ability of concrete to undergo very large changes in length without ceasing to carry load.
The measurement of particle elongation and flakiness: a critical discussion of British Standard and other methods
Authors: Lees G. 
Published: July 2012

Summary The author has given reasons elsewhere for recommending a more careful study of particle shape in engineering aggregates. Measurements of flakiness and elongation have long been considered important, but methods of determining these qualities both by direct measurement and by means of gauges are in need of some revision. This paper points to some of the difficulties and fallacies concerned and suggests means to overcome them.
Yield criterion for initially isotropic reinforced slab
Authors: Kwiecinski M. W. 
Published: July 2012

Summary This paper deals with the problem of formulating a yield criterion for quasi-isotropic reinforced slabs. The possibility of the kinking of reinforcement bars on the open fracture line is taken into account and a detailed analysis of yield moment on the plastic hinge is made. Both the “square” yield criterion and the criterion for perfect kinking of reinforcement prove limiting cases of the proposed partial-kinking theory. Values of plastic moments obtained from this criterion are more optimistic than those obtained by Johansen's criterion. The proposed theory enables one to describe analytically the results of some former experimental investigations which have shown that the ultimate moment in an initially isotropic slab is not independent of the plastic hinge inclination.
The action of ammonium salts on concrete
Authors: Lea F. M. 
Published: July 2012

Summary Results are reported on the action of 5% solutions of ammonium salts on a Portland, a Portland-pozzolana, and a high alumina cement concrete. Ammonium chloride and nitrate solutions had a strong leaching action, acting as dilute acids owing to loss of ammonia by reaction with lime. Strengths of concrete cubes with all three cements fell by at least a half in four years without outward signs of deterioration. Analysis of the specimens showed large reductions in the lime content of the cements. In the action of ammonium sulphate on Portland cement, the expansion caused by formation of calcium sulpho-aluminate is dominant. High alumina cement was unaffected by ammonium sulphate.
Some tests on the yield criterion for a reinforced concrete slab
Authors: Kwiecinski M. W. 
Published: July 2012

Summary This paper describes experimental work to verify the yield criterion for an isotropically reinforced concrete slab based on the concept of kinking of reinforcement bars across a fracture line. Sixteen model slabs with various arrangements of reinforcement were tested in one-way bending and experimental results have been compared with theoretical predictions. It appears that the concept of kinking is well confirmed although more tests on the behaviour of a fracture line arbitrarily inclined to the direction of the bars seem desirable.
Developments in apparatus for recording load-strain curves of concrete beams loaded in flexure
Authors: Hanks B. J. 
Published: July 2012

Summary A technique has been developed at the Road Research Laboratory for automatically recording the load-strain curves in flexural tests of concrete beams at the standard rate of loading specified in B.S. 1881. The new technique almost completely eliminates the noise and electrical pick-up associated with the resistance strain gauges previously used, and overcomes the undesirable drying-out of the concrete beams resulting from the employment of epoxy resin adhesives to attach the resistance strain gauges. Strains were measured by an inductive transducer combined with an oscillator and ademodulator, the output of which drives the Yinput of an X- Y plotter. The load applied to the specimen is measured by the distortion of a large spring with a travel of 4 in. A linear potentiometer attached to the spring is fed with a direct supply of 500 m V. The output from this potentiometer drives the X input of the X- Y recorder. The apparatus takes only about five minutes to prepare and thus expedites the work of testing concrete beams.
Cube tests and the uniaxial compressive strength of concrete
Authors: Hughes B. P. , Bahramian B. 
Published: July 2012

Summary The cube is undoubtedly the most convenient specimen to use when large numbers of crushing tests are required for concrete control purposes. The cylinder, or prism, on the other hand can give a much better estimate of the uniaxial compressive strength of concrete. The recent tendency has been to favour the adoption of the cylinder as the standard specimen, despite its shortcomings regarding convenience. The paper shows that variable differences can occur between the cube crushing strength and the uniaxial compressive strength, and then indicates how these differences can be greatly minimized by a suitable modification of the testing technique. This simple modification to the cube test enables the uniaxial strength to be determined very readily. The extremely convenient cube specimen can therefore now be used for uniaxial compressive strength determinations as well as for normal control purposes. The continued use of the cube as the standard form of test specimen is therefore recommended.
A method of studying the effect of vibratory stress, including fatigue, on concrete in flexure
Authors: Gatfield E. N. 
Published: July 2012

Summary The method and apparatus enable vibratory flexural stresses of magnitudes comparable with those used in conventional quasi-static tests to be applied to concrete beams. The beam is mounted horizontally on rigid supports and is vibrated inflexure by a moving-coil vibrator coupled to the upper face of the beam at the centre. The frequency of resonance and the strain in the beam at the centre of the top face are measured and, in normal operation, the driving current is adjusted to maintain a constant value of strain whilst changes of frequency with time are observed. A decrease in frequency indicates a decrease in the dynamic Young's modulus of elasticity of the concrete, and is associated with a development of micro-cracks in the concrete. The cracks which form at sufficiently high levels of strain fatigue have been observed by a photo-elastic technique before the appearance of visible cracks. Strains between 60 and 120 × 10−6 ultimately led to fatigue of the concretes tested. Stress-strain relationships were derived from curves relating resonant frequency with magnitude of strain, and were found to be approximately linear for un-fatigued specimens and markedly non-linear for specimens which had become fatigued.