bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comments on an indirect tensile test on concrete cylinders
Authors: Wright P. J. F. 
Published: July 2012

Summary A test which originated in Brazil for determining the tensile strength of concrete involves applying a compressive load to opposite generators of a cylindrical specimen. The specimenfaiL~ in tension along the diametral plane containing the load. Experiments with this teot have shown that: (1) Packing strips of relatively soft material are necessary between the specimen and the platens of the testing machine. Plywood strips ½ in. wide and ⅛ in. thick are satisfactory for the purpose, but the material and dimensions of the strips have little effect, provided they can conform to small irregularities in the surface of the specimen. (2) Cylinders 6 in. in diameter by 6 in. long may be usedfor concrete containing aggregate up to ¾ in. maximum size. Longer specimens may tend to give more uniform results, while smaller specimens may give higher average values. (3) The new test gives results higher than those given by a direct tensile test, but lower than the modulus of rupture of beams. It tends to give more uniform results than the direct tension or transverse test, but less uniform results than a compression test on cubes.
An alinement chart for the evaluation of the dynamic modulus of elasticity and Poisson's ratio for concrete
Authors: King W. H. , Lee I. D. G. 
Published: July 2012

Summary The report describes the method of construction and use of an alinement chart for the solution of the dynamic modulus of elasticity and Poisson's ratio from observations obtained in the electrodynamic test for longitudinal resonant frequency and the test for ultrasonic pulse velocity of concrete specimens.
The influence of size of concrete test cubes on me all strength and standard deviation
Authors: Neville A. M. 
Published: July 2012

Summary It is suggested that the mean strength and the standard deviation of a sample of concrete cubes are functions of the cube size. The results of tests on over 300 cubes of three sizes are given, and from the statistical analysis of these results it is concluded that the smaller 2·78 in. cubes have a significantly higher mean strength and higher standard deviation than the larger 5 in. and 6 in. cubes. From these results, it is suggested that the standard deviation obtained from standard 2·78 in. mortar cubes gives an excessive estimate of the effect of the variation in cement quality as compared with the results obtained from 6 in. or 4 ill. concrete cubes.
The use of cements of different fineness in soil-cement mixtures
Authors: Clare K. E. , Farrar D. M. 
Published: July 2012

Summary A study of the literature has shown that increasing the fineness of the cement in mortar and concrete mixes results in an increase in their strength at early ages. This paper describes tests to determine whether a similar effect is obtained with mixtures of soil and cement, so that if possible a reduction could be made in the proportion of cement used in soil stabilization by using a cement of greater fineness than the commercial varieties now employed. That fraction of a sample of ordinary Portland cement that passed the B.S. No. 300 sieve was added to a silty clay and test specimens were prepared. The 7-day unconfined compressive strength obtained was found to be 140% of the strength obtained when the whole cement was used. Taking the compressive strength at 7 days as the criterion, this suggests that if 10% of ordinary Portland cement was normally required to stabilize this soil, 7% of the fine-grained cement should prove equally satisfactory. In further tests, a cement clinker was ground to three different degrees of fineness in a laboratory ball mill, the coarsest being equivalent to ordinary Portland cement. The 7-day compressive strength obtained when the finest cement (specific surface = 5,800 cm2/g) was added to the silty clay was 125% of the strength obtained when the coarsest cement (specific surface = 2,900 cm2/g) was used. The corresponding increase for mixtures of sand and cement was 120%. Chemical analysis showed that the removal of the coarse grains in an ordinary Portland cement increased the proportion of sulphur trioxide present. In a third series of experiments, the compressive strength of a cement-stabilized silty clay obtained with a cement of given fineness was found to increase when the proportion of gypsum added to the cement was increased to a certain optimum value, but the increase was not as large as that obtained in the previous experiments by sieving cement. It is believed that fineness, sulphur trioxide content and possibly also the particle-size distribution can affect the strength obtained with a given cement, and further experiments are needed to determine the combination of fineness and sulphur trioxide content required to obtain a cement of maximum strength from clinker processed in a given way.
The composition of the ferrite phase in Portland cement
Authors: Midgley H. G. 
Published: July 2012

Summary A study of the composition of the ferrite phase present in commercial Portland cements has been made using powder X-ray diffraction techniques. From the results of an examination of thirty-one different samples, the most frequently occurring composition lies between 4CaO.Al2O3.Fe2O3 and 6CaO.Al2O3.2Fe2O3.
The early shrinkage characteristics of hand-placed concrete
Authors: Shacklock B. W. 
Published: July 2012

Summary The shrinkage characteristics of fresh concrete from 10 to 15 minutes up to 2 or more days after mixing have been examined for a variety of mixes suitable for compaction by hand. The apparatus used for these tests, which is still in the prototype stage of design, is described briefly. Under drying conditions, apparent expansion of the concrete, thought to be caused primarily by settlement of the specimen in the apparatus, occurs immediately after placing up to a time between 1½ and 4½ hours after mixing; by this time the concrete has stiffened sufficiently not to flow. Shrinkage, varying between 1 × 10−4 and 13 × 10−4 takes place during the next 6 to 8 hours; there is then little further movement for a day or more. Concrete kept under water shows a greater apparent expansion, and no early shrinkage. For mixes of approximately constant workability, the amount of early shrinkage under drying conditions appears to increase as the richness of the mix increases (with corresponding changes in the water/cement ratio), and it also increases as the amount of bleeding within the concrete decreases.
The effects of the properties of coarse aggregates on the workability of concrete
Authors: Kaplan M. F. 
Published: July 2012

Summary It is well known that different types of aggregate produce different degrees of workability when used in concrete of given mix proportions and water/cement ratio. A rounded aggregate will, for example, give concrete of higher workability than all angular aggregate. Thirteen coarse aggregates were investigated to determine the effects of their shape, surface texture and water absorptive capacity on the workability of concrete. An attempt has also been made to assess these effects quantitatively. The main conclusions were as follows. (1) Changes in the angularity of coarse aggregates have a greater effect on the workability of concrete than changes in the flakiness of the aggregates. Increased angularity and/or flakiness leads to a reduction in the workability of concrete. (2) Although there was a wide variation in the surface textures of the aggregates, no correlation was found between this property and the workability of concrete. (3) The differences in the capacities of the aggregates to absorb water were insufficient to produce significant changes in the compacting factor. No correlation was, therefore, found between this property and concrete workability. This does not rule out the possibility that highly porous aggregates when used in a dry condition will affect the workability of concrete.
The staining of concrete by pyrite
Authors: Midgley H. G. 
Published: July 2012

Summary Concretes and mortars made with some Thames river gravels have, in recent years, been suffering from brown staining. This has been traced to the mineral pyrite, FeS2; not all specimens of the mineral are reactive and it is possible to distinguish between the two types, reactive and unreactive by a simple test: on immersion of the suspect pebble or grain in lime water, the reactive forms will produce a brown precipitate within a few minutes while the unreactive form is stable. It appears that the reactivity is associated with the “defect” structure of the mineral, the unreactive forms being “stabilized” by ions of some metal impurity.
Electrical curing of concrete
Authors: McIntosh J. D. 
Published: July 2012

Summary: The effects of a number of variables on the compressive strength of concrete, heated by an alternating electric current passing through it, have been examined and tests made at refrigeration temperatures with a view to relaying small areas of the floors of cold storage chambers. A constant voltage was applied to the concrete so that the temperature increased quickly to a maximum (somewhat below the boiling point of water) and then gradually decreased; no control of the current was required. The relationship between the compressive strengths of treated concrete and the same mix cured normally has been examined in detail; it was found to vary with the maximum temperature and the time of treatment. Analysis of temperature and resistance measurements showed that the rise in temperature to the maximum was directly proportional to the rate of heating per unit volume of concrete. The possibility of employing the principle of electrical curing for accelerated compressive strength tests is discussed briefly, and the application of the method to the repair of the floors of cold storage chambers is outlined.
The prediction of temperatures in mass concrete by numerical computation
Authors: Ross A. D. , Bray J. W. 
Published: July 2012

Summary: The effects in mass structure$ of the chemical generation of heat in the concrete are briefly reviewed. Some reference is made to the practical techniques designed to reduce steep temperature gradients and hence to control cracking due to thermal causes. There remains, however, the problem of predicting temperatures in a mass of concrete of known thermal properties which is placed under specified conditions. Formal mathematics can give solutions only in the simplest cases but the number of influential factors in practice necessitates the employment of approximate step-by-step methods of numerical calculation. The method proposed by Schmidt for the uni-dimensional flow of heat is outlined and illustrated by a numerical solution for the case of a mass, initially at a high uniform temperature, which loses heat from two parallel boundaries a finite distance apart. The treatment of a similar mass in which there is generation of heat is then considered and graphical solutions for these simple cases are also presented. It is shown that a more elegant computational technique can be achieved when heat is generated by lowering the boundary temperature and, further, that the numerical working can be reduced by a simple modification of the tabular method of setting out the calculations. The utility of these devices is illustrated by application to the same example for comparison with the original solution. The method is then extended to two and three dimensions for which the appropriate values of a non-dimensional number connecting dijjusivity space and time intervals are established. To illustrate the power of the step-by-step calculation, the numerical results of a simple two-dimensional problem are compared with the rigorous mathematical solution and show excellent agreement. It is shown that the method can readily be applied to more complex cases. A solution is presented for the case of two lifts of concrete placed at different times on an underlying rock base which has a thermal capacity but no heat generation. In an appendix the accuracy obtainable by these numerical solutions is discussed.
Ultimate strength of pre-tensioned I beams in combined bending and shear
Authors: Sethunarayanan Rm. 
Published: July 2012

Summary This paper summarizes conclusions drawn from tests on pre-tensioned I beams without web reinforcement. The factors that govern the ultimate strength of such beams in combined bending and shear, and their influence on the mode offailure, cracking, and the ultimate load are studied. A simple theoretical analysis is presented for evaluating the ultimate strength of I beams failing by crushing of the web. The theoretical expression is compared with the test results of the author and of other workers and shown to result in a fairly safe and reasonably accurate estimate of the ultimate load. An empirical equation is suggested to determine the inclined cracking load and the collapse load for diagonal tension failures.
The determination of the compressive stress-strain properties of concrete in flexure
Authors: Smith R. G. 
Published: July 2012

Summary A description is given of an apparatus for the determination of the compressive stress-strain properties of concrete in flexure, based on the principle developed by the Portland Cement Association, The apparatus can be used in a standard universal testing machine with little or no modification. The relatively small size of the test specimen is convenient and economical, especially when materials for models are being tested. A theoretical analysis is developed which enables the distribution of the stress in the concrete to be determined across the section without reference to the magnitude of the strain. If a value is assumed/or the strain at any one stage of loading, the theoretical strains at all other stages may be determined. Comparison is made between the theoretical strains and the experimental strains obtained during a test on a concrete prism.
Microscopic point measuring: a quantitative petrographic method of determining the Ca(OH)2 content of the cement paste of concrete
Authors: Larsen Gunnar 
Published: July 2012

Summary Studies of deteriorated concrete have led to the development of a new quantitative petrographic method of investigation, which has been called the “point measuring” method. In this, the Ca(OH)2 content of the cement paste is measured at a number of points in thin sections by means of a polarizing microscope fitted with-a micrometer eye-piece. The main advantage of this method over the “traditional” methods is that it provides information on both the average value of the Ca(OH)2 content and its variation in the paste.
The moisture movement of natural aggregate and its effect on concrete
Authors: Snowdon L. C. , Edwards A. G. 
Published: July 2012

Summary This paper summarizes the background and development of the work carried out at the Scottish Lahoratory of the Building Research Station on the quality of concrete prepared from various aggregates. It establishes that many natural crushed rock and gravel aggregates undergo changes of volume, to a greater or lesser extent, as they take up or lose water, and shows how this characteristic influences the shrinkage and durability of concrete in which they are incorporated.
Relations between strength and age for soil-cement, with particular reference to the prediction of later strengths from earlier strengths
Authors: Grimer F. J. , Krawczyk J. 
Published: July 2012

Summary The relations between strength and age were determined for four soils stabilized with cement for a range of cement contents, moisture contents and cement consignments. Two methods of predicting the 7- and 28-day strengths of cement-stabilized soil from the 1- and 2-day strengths were examined: prediction using a mean ratio of later to earlier strength; prediction by graphical extrapolation from 1- and 2-day strengths. It was concluded that, with both methods, determinations of early strength would provide a satisfactory estimate of later strengths for many soils, and that stabilization works might often be controlled more effectively by an early strength than by a 7-day strength.
Tests on beams with sustained loading
Authors: Hajnal-Kónyi K. 
Published: July 2012

Summary Six pairs of concrete beams, each containing one beam reinforced with mild steel (M.S.) and one with Tentor steel (H.T.), with spanldepth ratios (L/d) of 20, 30 and 40, and all designed for the same bending moment, were kept under the full design load for 4¾ years. During this period the deflexions increased to 3·14–3·94 times the original. All the beams became unserviceable, although their factor of safety against failure was over 3. The test results were compared with deftexions calculated by various methods. The ratio of the cross-sectional areas of the reinforcement was M.S./H.T. = 1·70, but the average ratio of the maximum deflexions was only H.T./M.S. = 1·14. The average depth of the neutral axis increased considerably. The tests proved that the limiting slenderness ratios in CP 114(1957), Clause 309a, Table 13 are excessive if a substantial proportion of the design superimposed load is to be supported for a long period. It is suggested that Table 13 in the Code should be revised and that the limiting slenderness ratio should vary with the stress in both the steel and the concrete.
Determining the thickness of concrete pavements by mechanical waves: diverging-beam method
Authors: Bradfield G. , Woodroffe E. P. H. 
Published: July 2012

Summary By using large composite blocks of piezoelectric material, e.g. barium titanate, as separate transmitting and receiving transducers, it has been found possible to employ an echo technique for determining the thickness of concrete pavements (from about 4 in. to 18 in.) without a knowledge of the velocity of the mechanical waves in the concrete being assumed. The separation of the transducers sited on the top surface was varied and a series of travel times was measured. From these it was possible to deduce the thickness to an accuracy of about ±10% and, during the same analysis, to derive the velocity of the longitudinal waves in the concrete to an accuracy slightly better than ±10%. The presence of the subsoil support below the concrete slab caused no adverse effect.
An investigation into a hypothetical deformation and failure mechanism for concrete
Authors: Anson M. 
Published: July 2012

Summary Measurements were made of the deformations of materials, consisting of a hard component within a softer matrix, in order to test the assumption of “thrustring effect” used in the derivation of the lattice analogy for concrete. This effect is found to be present together with “internal restraint”. Poisson's ratio was measured for a variety of mixes, and this enables lattice proportions to represent the mixes to be selected. The lattice model is extended into three dimensions and reasonable agreement is obtained between the lattice and actual concrete behaviour for the cases considered.
The elastic-plastic behaviour of prestressed concrete frames
Authors: Pietrzykowski J. 
Published: July 2012

Summary This report summarizes the results of an investigation into the behaviour and ultimate strength of a post-tensioned, prestressed concrete frame under transverse load. The aim of the investigation was the partial verification of the recommendations made by the Research Committee of the Institution of Civil Engineers (Proceedings of the Institution of Civil Engineers. Vol. 21. February 1962. pp. 399–442) concerning the methods for designing statically indeterminate structures. Three frames were tested; the deflexions and strains due to bending were measured at selected points. The experimental results show a considerable measure of agreement with the theoretical conclusions forming the basis of the recommendations and it is considered that the method recommended can, in spite of the laboriousness involved, serve as a useful tool in the designing of statically indeterminate prestressed structures.
Some tests on the effect of edge restraint on punching shear in reinforced concrete slabs
Authors: Taylor R. , Hayes B. 
Published: July 2012

Summary The results of tests on 22 plain and reinforced concrete square slahs failing in punching shear are reported. The effect of horizontal restraint on strength in punching shear was obtained by testing pairs of slabs. One of each pair was simply supported along its edges; the other was similarly supported hut confined within a surrounding steel frame. The increase in strength due to the restraining frame variedfrom zero to 60%, the extent of increase depending on the state of flexural cracking in the simply supported slabs at failure.
Some experiences with a commercial compression testing machine
Authors: Atherton M. J. 
Published: July 2012

Summary The unsatisfactory behaviour of a commercial compression testing machine led to an investigation into the cause of variation in testing, which in turn led to the discovery that the removal of polar grease lubricating the ball-seat controlling the top platen of the machine reduced variation to one-third of previous values while increasing the mean strength of a group of specimens without the calibration of the machine being changed. The reasons for this behaviour are discussed and a recommendation given that polar greases should not be used to lubricate ball-seats in compression testing machines.
Prestressed concrete beams under a sustained temperature crossfall
Authors: Ross A. D. , England G. L. , Suan R. H. 
Published: July 2012

Summary The paper briefly discusses the time-dependent effects of thermal stressing of prestressed concrete beams with reference to long sustained temperature crossfalls. Certain principles and assumptions are presented and an iterative numerical method is introduced to allow for creep in the calculation of the variation with time of stresses, strains and displacements. The results of tests on heated simply supported and continuous prestressed beams are compared with the predictions of the theory. The measure of agreement shows that the method can indicate the magnitude of the severe time-dependent effects with reasonable accuracy. Finally, it is demonstrated in general terms that under a prolonged temperature crossfall, a prestressed concrete beam will, in general, reach a stable stress distribution. This distribution can be calculated without reference to the elastic modulus and coefficient of expansion of the concrete. The limiting stresses thus calculated have been verified in various examples by the iterative analysis described earlier. These steady-state stresses are useful in that they form a limit to the range of possible stresses, and they can be calculated directly without iteration.
Reducing the shear reinforcement in reinforced concrete beams and slabs
Authors: Leondardt F. 
Published: July 2012

Summary The shear tests reported in the present paper were carried out in Stuttgart from 1961 to 1963. The mechanism of failure at ultimate shear load is explained in terms of the truss analogy, and the ratio between the width of the compression flange and the thickness of the web is shown to have a considerable influence on the inclination of the top chord and of the diagonal struts of the truss and, consequently, on the tensile forces in the web. From the results, a simple method for reducing the shear reinforcement is derived. For short beams with a slenderness ratio l/d < 8 or for concentrated loads close to the supports, a further reduction in shear coverage is possible. The determination of the points for cut-off and bent-up bars must be adapted to the variations in the compression members of the truss. The tests showed clearly that stirrups are preferable to bent-up bars for shear reinforcement, particularly if high-tensile steel is used.