bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crystallographic research on the hydration of Portland cement. A first report on investigations in progress
Authors: Bernal J. D. , Jeffery J. W. , Taylor H. F. W. 
Published: July 2012

Summary The results of investigations carried out at Birkbeck College since 1948 are described. (a) Anhydrous cement compounds. The crystal structure of tricalcium silicate (C3S) has been determined. The crystal is built from Ca++, (SiO.)4-, and O-- ions; co-ordination of the Ca ions by oxygen is unsymmetrical. In atite, the form present in cement, some Si is replaced by AI, and Mg ions are present in otherwise vacant sites. Possible relationships between structure and cementing properties are discussed. (b) Hydration Products. At room temperature, action of water on C3S can yield, under appropriate conditions, either of two compounds, calcium silicate hydrates (I) and (II). These differ in composition but are closely related in structure. The first has been detected in a sandtime block, and one of them, probably the second, is present in set C3S pastes. Direct detection of the hydrated compounds in set cement has so far been hindered by experimental difficulties, but it is probable that one or other of these substances is present. Hydrothermal reactions in the CaO-SiO2H2O system have been studied; it is probable that steam curing of cement at 100°C does not yield silicate hydration products very different from those formed at room temperature, but that at 180°, basically different compounds may be produced. Calcium silicate hydrate (I) has a layer structure, in which entry or removal of water molecules, due to changes in temperature and/or humidity alters the inter-layer spacing. The layers themselves are elongated in one direction, giving rise to a fibrous structure. These facts may explain the cementing power of the substance, and may also account for the volume changes observed in set cement.
Tests of properties of fresh concrete
Authors: Bergström Sven G. 
Published: July 2012

Summary A description is given of a deformability meter for studying the properties of fresh concrete which has been evolved at the Swedish Cement and Concrete Research Institute. Examples are adduced to demonstrate the effects produced by varying mixes and by the admixture of resins. The test results afford information on the tendency to segregation and the workability of the concrete. This information permits certain qualitative forecasts regarding the properties of hardened concrete.
The design of reinforced concrete beams of large initial curvature
Authors: Wright W. 
Published: July 2012

Summary When the initial curvature of a reinforced concrete section is large in comparison with its depth, the stress can no longer be assumed to increase linearly outwards from the “gravity”* axis and, as a result, the neutral axis is displaced towards the centre of curvature. In this paper the appropriate equations for balanced design are derived and design charts for pure bending are given for one set of values of the permissible stresses and modular ratio.
The design and use of a demountable mechanical strain gauge for concrete structures
Authors: Morice P. B. , Base G. D 
Published: July 2012

Summary This paper describes the principle, design and use of a form of demountable mechanical strain gauge which has been found particularly useful for determining strains in concrete structures. The instrument which uses a lever and dial gauge is cheap to make and use, and is located on 8 in. gauge lengths which are formed by pairs of punched and drilled steel discs glued to the concrete surface. With practice, 200 strains per hour may be measured with an accuracy of about ±5 × 10−6 under most laboratory test conditions. Even greater accuracy has been obtained using the gauge in its ideal horizontal position and with the readings lying within a small range on the dial. In development tests of this kind 90 per cent of measured strains were within ±3 × 10−6 of the mean. Tests on various locating discs show that normal, drilled mild steel discs give the best results.
Curing temperature, age and strength of concrete
Authors: Bergström Sven G. 
Published: July 2012

Summary The effects of curing temperature and age on the strength of concrete can be expressed in terms of a single parameter given by the product of age and temperature, as has been suggested by Nurse.(1)*· and Saul.(2) In this parameter, the temperature is reckoned from — l0°C, which seems to be a reasonable value of the lowest temperature at which any appreciable increase in strength can take place. In the present paper, the correctness of this assumption is verified by means of check calculations made on previously known test series and on some new Swedish tests. It is to be noted, however, that special precautions must be taken to protect the concrete from freezing during the initial period after placing, and that the humidity of the ambient air must be taken into account. Moreover, the deterioration of concrete subjected to repeated freezing and thawing must be studied as a separate problem.
Creep tests on prestressing steel
Authors: Gifford F. W. 
Published: July 2012

Summary Details are given of tests on 0·2 in. diameter prestressing steel maintained under approximately constant strain, in order to determine the relaxation of stress at various initial loads, including the effect of initial overstressing. A special testing technique was developed facilitating a simple but sensitive method of measuring the force in the wires, which were of a sufficient length to give a good average value of the effect of creep.
Effect of various factors on the flexural strength of concrete test beams
Authors: Nielsen Knud E. C. 
Published: July 2012

Summary The paper describes bend tests on plain concrete beams carried out by the author at the Swedish Cement and Concrete Research Institute, Stockholm (the CBI), as part of their research programme. The test results are here used as a basis for an analysis of the effect of various factors on the flexural strength of concrete test beams. The reported results of previous workers in this field are summarized and discussed. These are so presented as to provide additional data for an analysis of the applicability of various theories of the effect of dimensions of the test specimen. The paper closes with some practical considerations which should be taken into account when determining the flexural strength of plain concrete beams.
The workability of vibrated concrete
Authors: Plowman J. M. 
Published: July 2012

Summary The paper describes a method of comparing the workability of mixes of low water content by measuring the power required to vibrate them under standard conditions. A relationship between the number of gaps in a grading and the average power demand is obtained from energy-time curves for various mixes and types of grading. An example illustrates the use of this relationship in calculating the weight of concrete which can be vibrated on a table under given conditions.
Statistical methods in concrete research
Authors: Wright P. J. F. 
Published: July 2012

Summary The application of statistical methods has helped greatly in planning and interpreting concrete research at the Road Research Laboratory and, as no statistical text-book deals specifically with the problems of concrete technology, this paper aims to bring such methods to the attention of research workers elsewhere. The assessment of variation in test results is discussed and some useful statistical processes are introduced. These include a test for the difference between two sets of results, the method of analysing the causes of variation in test data and the fitting of equations to experimentally determined relationships between two variables. An appendix gives a method for fitting a Gaussian distribution to a series of test results. A subsequent paper will deal with the design of experiments in concrete research.
Heat of hydration in concrete
Authors: Rastrup Erik 
Published: July 2012

Summary The paper traces the development of a function between time and temperature, which makes it possible to refer the process of hardening of concrete at varying temperature to hardening at constant temperature. It is further shown that it is possible to predetermine the temperature of concrete during hardening when properties of concrete, sizes and shape of the specimen, insulation and external temperature are known. The time temperature function can also be applied to the development of strength. The validity of the theory is demonstrated by the results of tests upon 27 American and 3 Danish cements.
An investigation of the erosive effect on concrete of soft water of low pH value
Authors: Halstead P. E. 
Published: July 2012

Summary An investigation is described in which the effect of soft moorland water on concrete has been studied by tests on 4 in. concrete cubes. Cubes were immersed in moorland water or tap water for periods of up to four years and were then weighed and crushed to determine their compressive strength. After immersion in soft water, all types of concrete lost strength and weight to an extent which increased as the immersion was prolonged. Cubes made of Portland cement concrete of very high strength or high alumina cement concrete lost about one-third of their strength after four years' immersion. Cubes of concrete of all other types, irrespectire of strength or kind of cement used, lost about half their strength after four years' immersion. Concrete containing entrained air behaved similarly, but concrete painted with bitumen maintained its strength whilst the coating was intact.
An investigation into methods of carrying out accelerated freezing and thawing tests on concrete
Authors: Wright P. J. F. , Gregory J. M. 
Published: July 2012

Summary It was noted in earlier investigations that accelerated freezing and thawing tests on concrete carried out using a continuously refrigerated room produced results more rapidly than similar tests using a cabinet-type refrigerator, although in each case the specimens reached the same limiting temperatures of about 5° and 60°F. Attempts have therefore been made to modify the technique so that results can be obtained more rapidly in the refrigerator. The tests show that damage occurs more rapidly when specimens are frozen immersed in water than when frozen in air, although the rate offreezing is lower. This suggests that evaporation of water from the surface of the specimens before freezing may mitigate the damage by reducing the stresses developed near the surface when the water freezes. Little was gained by the use of a brine bath surrounding the water-immersed specimens. Measurements of the temperatures of the specimens during freezing and thawing suggest that two cycles per day could be carried out successfully in the refrigerator in place of the one cycle per day formerly used.
An energy approximation to the solution of a corner-supported rectangular slab
Authors: Morice P. B. 
Published: July 2012

Summary The Rayleigh-Ritz method is used to obtain an approximate solution to the problem of the de flexion of a rectangular flat slab supported only at its four corners and loaded with either an arbitrarily positioned point load or uniformly distributed load. The assumed functional approximation does not completely satisfy the stress-free boundary condition, yet despite this experimental results show reasonable agreement with the predicted values in the case of single concentrated loads on two steel plates.
A vibration method for measuring the thickness of concrete road slabs in situ
Authors: Jones R. 
Published: July 2012

Summary A method has been devised for determining the thickness of concrete road slabs by measuring, at the surface of the slab, the velocity of propagation of vibrations at audio and ultrasonic frequencies. A vibration generator acting vertically on the surface of the slab produces vibrations of known frequency which are detected by a pick-up. The pick-up is moved progressively away from the generator and positions are noted at which the vibrations at the generator and pick-up are in phase. The distance between successive positions gives the wavelength (λ) of the vibrations; the velocity of propagation is determined from the product of the wavelength and frequency. In the frequency range from 1,000 c/s to 4,000 c/s, the vibrations are identified asffexural waves and their velocity (V) depends upon the frequency, the thickness (T), and the elastic constants of the concrete slab. At frequencies above 50 kc/s, the velocity is constant, and the propagation becomes sensibly independent of the frequency and the thickness of the slab, i.e. it is then the Rayleigh wave velocity (VR) of surface waves in the concrete. From the theoretical analysis, a graph is prepared giving the variation of V/VR with the quantity πT/λ, and this enables the thickness of the slab to be calculated from the experimental results. Tests have been made on slabs of thicknesses varying from 4 to 9 in., some slabs being laid directly on the subgrade and some on prepared bases of soil cement and hoggin. The results have generally been satisfactory and, in many cases, the dimensions of cores drilled from the slabs have agreed with the calculated values of thickness to within ±10 per cent.
Some tests on the effect of time on transmission length in pre-tensioned concrete
Authors: Base G. D. 
Published: July 2012

Summary A certain amount of work already published has indicated that the transmission length in pre-tensioned concrete increases very considerably with time. Evans reports a transmission length increase for 0·08 in. diameter high-tensile steel wire from 58 diameters to 125 diameters in two and a half years, with most of the increase taking place in the first month after transfer. A Swiss report also quotes figures showing an eventual doubling of the transmission length at transfer for wire of 2 and 3 mm diameter. Recent work by the Cement and Concrete Association on 0·2 in. diameter smooth wire indicates no such increase in transmission length, there being little movement, over several months, of the point at which maximum concrete strains were reached in the units tested.
The sleeve pump for semi-solids
Authors: Ede A. N. 
Published: July 2012

Summary A pumping cycle has been designed for unsaturated fragmentary materials which makes use of the pumped material jammed in a tubular sleeve as a piston for forcing forward further material in an outlet barrel. The return stroke of the sleeve is made at rapid acceleration, releasing the material in the forward position and resetting the sleeve for a further cycle. Preliminary performance figures are given, and the means of application to pumping concrete is indicated.
The investigation of the quality of thick concrete by ultrasonic pulse propagation
Authors: Cawkell A. E. 
Published: July 2012

Summary The velocity of ultrasonic pulses through concrete is measured by an oscillograph timing technique. The relation between velocity and concrete quality has been described els ewhere. To increase the rangge—about 8 ft through good quality concrete with the standard instrument (type UCT)—higher power, and low frequency sharply directional magnetostriction tranducers were used. Practical details of the tests are described, and it is considered that 20 ft is the maximum path length possible with this method. Further developments are discussed.
The effects of age and water/cement ratio upon the relation between ultrasonic pulse velocity and compressive strength of concrete
Authors: Kaplan M. F. 
Published: July 2012

Summary Experiments have been made on concretes with varying aggregate/cement and water/cement ratios, with the main object of ascertaining the effects of changes in age and water/cement ratio upon the relation between ultrasonic pulse velocity and the compressive strength of concrete. It was found that the ratio of changes in pulse velocity and compressive strength due to a change in water/cement ratio is not generally the same as that due to a change in age. Because of this, the relation between pulse velocity and compressive strength cannot be expected to be independent of age and water/cement ratio. It appears, however, that, for compressive strengths up to about 4,000 lb/in2, the relation may for practical purposes be regarded as being so. For concrete of the same aggregate)cement ratio, it was found that low pulse velocity at an early age predicts low strength at later ages.
Synthetic compounds related to tobermorite: an electron-microscope, X-ray, and dehydration study
Authors: Gard J. A. , Howison J. W. , Taylor H. F. W. 
Published: July 2012

Summary Tobermorite-like preparations with Ca/Si ratios in the range 0·8–1·4 have been synthesized at room temperature and hydrothermally, and a systematic study has been made using the methods indicated in the title. The results are compatible with the existence of three phases: tobermorite (5CaO.6SiO2.5H2O), CSH(I) (0·8–1·33 CaO.SiO2.aq.), and CSH(II) (1·5–2·0 CaO.SiO2.aq.). CSH(II) may have a layer structure in which one surface of each layer is composed of hydroxyl groups, analogous in some respects to the hydrated form of the clay mineral, halloysite. The evidence of the electron microscope gives some clues to possible mechanisms of conversion of CSH(I) and CSH(II) into tobermorite.
A co-ordinated approach to the shrinkage testing of concretes and mortars
Authors: Fulton F. S. 
Published: July 2012

Summary Investigations into the shrinkage of concretes and mortars are seldom sufficiently comprehensive. In consequence, the results are often related to one particular factor which is regarded as having a major influence on shrinkage. In this paper a theory is developed which correlates fairly well with observed results, and which draws attention to the various factors which should be studied in any fundamental investigation into shrinkage. An empirical formula is also put forward which correlates well with accepted shrinkage values. It is suggested that, for any aggregate or combination of aggregates, a shrinkage index may be determined empirically which permits an evaluation of the shrinkage potentialities of mixes made with such aggregates, and which may be used to predict the shrinkages of comparable mixes. Finally it is pointed out that the interpretation of shrinkage test results presents considerable difficulty.
Relation between the change of water content and the consistence of fresh concrete
Authors: Popovics Sándor 
Published: July 2012

Summary The assumption that a change of consistence in a concrete mix that is due solely to a change of water content is independent of the composition of the mix (type of cement, cement content, original water content, original water/cement ratio, air content, grading and maximum size of aggregate) is tested and shown to be valid within wide limits. This assumption is called “assumption of independence” and its use in the prediction of consistence is called “k procedure”. In the appraisal of this assumption, it is first proven mathematically that the assumption of independence is identical with the assumption that the consistence of concrete is a parabolic function of the water content, and the degree of the parabola is independent of the composition. Then it is shown that for six methods of measuring consistence the experimental results substantiate the existence of such a parabolic relation within wide limits. A parabolic formula for the k thinning factor is derived, and its numerical forms for six methods of measuring consistence are presented. It is shown for various cases that the use of the k factor in the prediction of consistence is simple and the calculated results are in accordance with experimental data.
A simple technique for recording load-strain curves for concrete beams loaded in flexure
Authors: Trott J. J. 
Published: July 2012

Summary A method is described for automatically recording load versus strain using a commercial X-Y plotter. Typical curves are given showing the results obtained with pavement-quality concrete and with lean concrete. The modulus of elasticity of the lean concrete was derived from the tangent to the load-strain curve at the origin and was found to be less than that obtained by resonance tests. A reasonable correlation was found between the elastic modulus and the strains at which micro-cracking was assumed to begin.
The distribution of pressure in a model silo containing cement
Authors: Lenczner D. 
Published: July 2012

Summary This paper, which is an extract from a wider field of investigation of the pressure distribution in a model silo containing different materials, at rest and during flow, describes tests with cement at rest. The results are compared with some of the better-known theories on silos. The main conclusions are that the pressure distribution on the silo base with cement at rest is not uniform hut decreases from the centre outwards, that Janssen's fundamental assumptions when applied to cement are wrong, and that laky's theory over-estimates the load carried by the silo walls whereas, for silos of proportions commonly met in practice, Airy's theory gives quite satisfactory results.
Relation between phase composition, over-all porosity and strength of hardened lime-pozzolana pastes
Authors: Jambor Jaromir 
Published: July 2012

Summary By means of X-ray analysis, differential and gravimetric thermal analysis, electron microscopy, and chemical analysis, the main hydration products of 22 pastes made from lime and various pozzolanic materials and hardened in water for 400 days were found to be calcium hydro-silicates of the tobermorite group (approximate formula C0·8-1·1.S.H0·9-1·5) and Strätling's compound, C2ASH11. A formula is developed giving the compressive strength of the pastes in terms of the volume of the hydration products produced.
Some aspects of methods for measuring consistence
Authors: Popovics Sándor 
Published: July 2012

Summary A brief, general description is presented of the K-procedure for the prediction of consistence. From this, a thinning factor K is developed for the standard compacting factor test. Numerical values of K are presented for practical application. An example illustrates the use of Tables for the estimation of water quantity which is needed for a given value of the compacting factor. The equations presented show good agreement with test results obtained by several investigators. Finally, the virtues of the standard slump test are demonstrated.
The lateral stiffness and strength required to ensure membrane action at the ultimate load of a reinforced concrete slab-and-beam floor
Authors: Park R. 
Published: July 2012

Summary The lateral stiffness and strength required of supporting beams and exterior panels of continuous reinforced concrete slab-and-beam floors in order to ensure membrane action in the panels at ultimate load is considered. It is shown that tie reinforcement may be required in the supporting beams to carry the membrane forces. Tests on twenty small-scale mortar models of idealized nine-panel slab-and-beam floors with the interior panel uniformly loaded are described. The tests illustrated the modes of failure of exterior panels with insufficient reinforcement to resist the reactire forces due to the membrane action of the interior panel. The ultimate loads of interior panels of the slabs with adequately reinforced exterior panels showed good agreement with theory derived previously (which included the effect of axial strains in the panel and lateral movement of the edges due to extension of the tie steel) once the concrete had cracked.