bluuebunny/crossref_metadata_2025 huggingface dataset:
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.
The influence of amplitude and frequency in the compaction of concrete by table vibration
Authors: Cusens A. R.
Published: July 2012

Summary

This paper describes experimental work on the compaction of concrete by table vibration. The cases of castings of small depth and those of greater depth are separated and guiding principles suggested for each. The effects of rotational instability and the injfuence of the mould are considered.
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.
A note on the mechanism of diagonal cracking in reinforced concrete beams without shear reinforcement
Authors: Taylor R.
Published: July 2012

Summary

An hypothesis is made concerning the mechanism of diagonal cracking in reinforced concrete beams without shear reinforcement; a test on a beam with pre-formed flexural cracks appears to support the hypothesis. The implications of such a mechanism of diagonal cracking are 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.
A new photoelastic material for use in problems concerning reinforced concrete
Authors: Bignell V. F. , Smalley V. , Roberts N. P.
Published: July 2012

Summary

A new photoelastic material has been developed for use in the analysis of problems concerning reinforced concrete. The material is a modified epoxy resin and has been reinforced and loaded. Crack patterns and photoelastic patterns have been examined.
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.
Some tests on the effect of yield lines on the behaviour of reinforced concrete T beams
Authors: Taylor R. , Hayes B. , Wallin R. C.
Published: July 2012

Summary

An exploratory series of tests on three reinforced concrete T beams was made to determine the effect of longitudinal cracking in the flange. The tests indicated that the strength of a reinforced concrete T beam is unlikely to be greatly affected by such cracking.
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.
The shear strength of pre-tensioned I beams with unreinforced webs
Authors: Arthur P. D.
Published: July 2012

Summary

This paper presents the results of two-point loading shear tests on 50 pre-tensioned concrete I beams without web reinforcement. Although many of the beams carried a shear load greater than the cracking shear load, the amount of the excess could not be predicted, and it is concluded that failure should be considered to have occurred when the web is cracked in shear. An expression is developed for the diagonal cracking shear force. Test results already published are shown to give satisfactory agreement with this expression, and comparisons are made, for specific cases, between the ultimate shear load predicted by it and by other design equations and code rules.
The deformation of concrete and micro-concrete in compression and tension with particular reference to aggregate size
Authors: Hughes B. P. , Chapman G. P.
Published: July 2012

Summary

The effects of varying the type and size of the aggregate on the stress-strain characteristics of concrete and micro-concrete in compression and tension are described. By applying new experimental techniques, it has been shown that the use of a larger and rounder aggregate yields a concrete which attains a lower maximum strength at a correspondingly smaller deformation.
Some experiments on concrete cubes with non-plane surfaces
Authors: Westley J. W.
Published: July 2012

Summary

After the return of some cube moulds from site early in 1965 and their absorption into the general laboratory stock of moulds, excessive variations were found in the strength of some specimens made from carefully controlled concrete mixes. At the same time cubes coming into the laboratory for testing showed surfaces that were excessively convex and it was found that some of the cube moulds being returned from site were very worn and had surfaces which varied from plane by up to 0·025 in. Several cube moulds were examined and measurements taken to select those with surface variations between 0·001 and 0·015 in. from plane. Cubes were cast in these moulds and, after curing for 7 and 28 days, measured for surface planeness and tested for compressive strength. The results indicate that a 0·010 in. total variation from the plane in the surfaces of a concrete cube can cause a reduction in compressive strength of up to 15 %.
The use of the fineness modulus for the grading evaluation of aggregrates for concrete
Authors: Popovics Sándor
Published: July 2012

Summary

Experimental evidence is used to show that, despite certain weaknesses, the fineness modulus method is applicable within wide practical limits. Then aspects of the fineness modulus and the specific surface not generally known are discussed. These include two mathematical expressionsfor thefineness modulus as afunction of the particle size distribution, which show that the fineness modulus is a measure of the (logarithmic) average particle size of the grading. This, in turn, provides a new interpretation for the relationship between the grading and workability. Similar mathematical expressions are presentedfor the specific surface, and they show that this is also a measure of an average particle size. Specifically, it represents the reciprocal value of the ‘harmonic’ average particle size. However, experimental evidence suggests it is inferior to the fineness modulus where aggregates for concrete are concerned. A further item is the ‘D-m-s method’ in which the fineness modulus and specific surface are both used for grading evaluation, to combine the advantages of the two methods. Finally, an analogy is used in an attempt to explain why the logarithmic average particle size is the parameter which is the most suitable for the grading evalulation of concrete aggregate.
A laboratory test for determining the angularity of aggregate
Authors: Hughes B. P. , Bahramian B.
Published: July 2012

Summary

A convenient and reliable test has been developed for determining the angularity of aggregates. An examination of the existing methods indicated that the determination of the volume of voids in the aggregate when placed in a standard way was the most promising. Two methods, referred to as the flow-rate test and loose bulk density test, were investigated in detail. The latter test was found to be the most satisfactory and can be used in modified forms for both coarse and fine aggregates. It gives satisfactory results for both spheres and natural aggregates.
The influence of CaSO4.2H2O upon the hydration character of 3CaO.Al2O3
Authors: Feldman R. F. , Ramachandran V. S.
Published: July 2012

Summary

This paper presents a quantitative interpretation of results of differential thermal analysis of hydration reactions at 2, 12,23 and 52°C of 3CaO.Al2O3 mixed with 0, 0·25, 2·5, 10 or 20% gypsum, and compares these with length changes obtained from the hydration of compacts of these mixtures. Estimates of the relative reaction rates from d.t.a. peak areas and measurement of length change during these reactions showed marked agreement, although interpretation had to be made with caution. It was concluded that the formation of ettringite (high sulpho-aluminate) had no direct effect upon reaction rate, but that the reactivitv of 3CaO.Al2O3 was reduced by the sorption of (SO4)2− ions on active sites of its surface. Gypsum reduces the rate of conversion of the hexagonal hydro-aluminates to the cubic hexahydrate, probably also by sorption of (SO4)2− ions, and thus is a second mechanism by which they can retard the normal hydration of 3CaO.Al2O3. The degree to which a given addition of gypsum retards the hydration of 3CaO.Al2O3 at a particular temperature is affected by a balance between (1) the concentration of (SO4)2− ions on and around the surface of the 3CaO.Al2O3; (2) the rate of reaction of (SO4)2− ions with the hexagonal hydro-aluminates; (3) the thickness of the hexagonal hydro-aluminate layer around the 3CaO.Al2O3 grain. Reactions at the various temperatures are discllssed in terms of the above parameters.
The influence of testing machine characteristics upon the cube and cylinder strength of concrete
Authors: Sigvaldason O. T.
Published: July 2012

Summary

Although the compression test on cubes and cylinders is used very extensively as a measure of the general quality of concrete, there has been increasing evidence to show that such tests are not as reproducible as has normally been assumed. There are large differences in the strengths obtained from different testing machines, and often a considerable scatter in strengths from one machine. In a series of tests, the influence of such characteristics as spherical seating behaviour, misalinement, homogeneity of specimen, longitudinal stiffness and platen restraint on the strength of cubes and cylinders has been examined. Depending upon the behaviour of the spherical seating, differences of about 6% may be obtained with accurately centred specimens. If such specimens are also misalined, this difference becomes even larger, as enormous reductions in strength are observed with effectively pinned seatings. Cube and cylinder strengths are affected quite differently by the method of end loading, the cylinder/cube strength ratio being lowest when both ends are fixed. Longitudinal stiffness of the machine does not affect strength. Platen restraint, however, has a very significant influence, particularly if the end-blocks are small.
Analysis of tobermorite by the silicate-derivative technique
Authors: Lentz Charles W.
Published: July 2012

Summary

A specimen of natural tobermorite from Crestmore, California, was studied by a new extraction technique. This investigation revealed that tobermorite can be resolved into two fractions. One of them is a soluble species and the other insoluble. The infra-red spectrum of the soluble polysilicate derived from tobermorite is not identical with the infra-red spectrum of the soluble polysilicate derived from a Portland cement paste. The insoluble derivative has the same morphology as the original tobermorite.
Kinematical compatibility problems in yield-line theory
Authors: Janas M.
Published: July 2012

Summary

An attempt is made to classify assumptions made in yield-line theory in connexion with the upper-bound theorem of limit analysis. Both classical theory and theory taking into consideration membrane forces are examined for reinforced concrete slabs. The complete set of generalized stresses and strain rates is considered, and compatibility conditions imposed by the associated flow law are discussed, including those for the configuration of yield lines and for internal compatibility of the cross-section. In the case of Johansen's yield-line theory, the general type of fan pattern generated from the envelope line is considered, and some statical restrictions applied in the upper-bound technique are discussed. Considerations are limited to the case of isotropy, unless otherwise specified, but conclusions can be more or less directly extended to the case of orthotropic slabs.
Some factors affecting the compressive strength of concrete
Authors: Hughes B. P. , Bahramian B.
Published: July 2012

Summary

Abrams's law of compressive strength versus water/cement ratio is well known and many investigators have studied the possible effects of other factors, such as cement content and sand concentration, upon concrete strength. In particular, the British and American literature is often at variance concerning these secondary effects so that a primary aim of the present paper is to reconcile these conflicting views. Any considerations of secondary effects require a very clear definition of what is meant by ‘compressive strength’ and ‘water/cement ratio’. Furthermore, different aggregates can give significantly different results. These considerations are illustrated by presenting data for curves relating compressive strength and water/cement ratio for three distinct criteria for compressive strength and two types of coarse aggregate. The paper then re-examines the effects of varying both the cement content and the sand concentration, for a given water/cement ratio, upon the compressive strength. It is shown that the effects of these secondary factors are in general fairly small and that rational explanations can be given for the often conflicting conclusions obtained by earlier investigators.
Parabolic velaroidal shells
Authors: Chronowicz A. , Dennison A. C.
Published: July 2012

Summary

This paper presents a solution to the differential membrane equation of parabolic velaroidal shells in which a finite polynomial stress function is used. The method of determining stresses and deflexions from the Vlasov-Marguerre differential equations for the bending of such shells by using finite difference techniques is also indicated. Tests conducted on a cement mortar model shell are described and the results are compared with those obtained theoretically.
Creep stability and buckling strength of concrete columns
Authors: Bažant Z. P.
Published: July 2012

Summary

A solution is given for the long-term deflexions of a reinforced concrete column with an initial curvature according to a general theory of linear creep. This is used to produce solutions: (1) according to the Arutyunyan-Maslov theory (using an incomplete gamma function); (2) according to the approximate Dischinger-Whitney law; (3) by the use of an effective deformation modulus. It is shown that, whilst critical long-term loads may be calculated, these are very sensitive to inaccuracies in the creep theory and that it is more convenient to consider the long-term buckling strength of a column. A practical method of analysis is presented in which the long-term buckling strength is assessed by calculating the short-term buckling strength but using a reduced elastic modulus. Graphs are presented to aid analysis.
Allowing for membrane action in the plastic analysis of rectangular reinforced concrete slabs
Authors: Hayes B.
Published: July 2012

Summary

The existing methods for allowing for membrane action in predicting the plastic behaviour of reinforced concrete slabs are reviewed and their limitations outlined. A new equilibrium method is presented and compared with the existing methods. Comparison of the theoretical predictions of the met/1Od with the results obtained/rom tests on model reinforced concrete slabs shows good agreement.
The strengths of cements reinforced with glass fibres
Authors: Grimer F. J. , Ali M. A.
Published: July 2012

Synopsis

Fibrous composite materials utilizing ceramic fibres and inorganic cements offer a potential source of new lightweight, strong and durable materials. Commercial glass fibres now available are not durable in an alkaline medium of the kind present in most hydrating cements; a new alkali-resistant glass has been developed at the Building Research Station to surmount this difficulty. Because this has renewed interest in the subject, and to provide a yardstick for the effectiveness of the new glass, composites made with commercially available glass fibres and various inorganic binders were studied to find suitable methods of fabrication and to establish the behaviour of the material. This paper describes the influence of type of matrix, age and glass content upon the impact, tensile and bending strengths of composites fabricated by a simple spray-suction technique. On the basis of the properties developed before chemical interaction between glass and cement becomes dominant, it can be foreseen that, given a durable glass, the composites will have pronounced advantages over existing sheet materials in respect of impact strength, bending strength and resistance to cracking. As supplies of alkali-resistant fibre become available, the programme will be repeated with this material.
An experimental investigation of the flexural rigidity of T beams for frame design
Authors: Krishnamoorthy C. S. , Yu C. W.
Published: July 2012

Synopsis

Tests conducted on eight T beams subjected to negative moments at the ends and positive moment near midspan are described. The moment-curvature relationships for various sections and the distribution of flexural rigidity, EI, along the beam are discussed. A simplified design procedure is suggested to determine the equivalent EI value for T beams to be used in the limit design of reinforced concrete frames.
A dilatometer for measuring the volume changes of concrete under load
Authors: Spponer D. C.
Published: July 2012

Synopsis

A new apparatus is described which enables the change in volume of cement paste or concrete specimens under load to be monitored continuously. It relies upon the displacement of water from one bellows containing the specimen under load into another, unrestrained bellows. The difference between the magnitudes of the movements of the bellows is proportional to the volumetric strain. The results are shown to be in good general agreement with other volumetric strain measurements. The apparatus has some advantages over current methods.
Model tests to determine the influence of support stiffness upon the distribution of pile loads on an eight-pile cap
Authors: Clarke J. L. , Taylor H. P. J.
Published: July 2012

Synopsis

Tests were carried out on three models, to scales of 1:4, 1:15 and 1:38, of a large pile cap spanning eight piles. The smallest model was tested to determine the effect of the cracking of the pile cap and of varying pile stiffnesses upon the distribution of the applied load between the piles. The results of the tests are presented and are compared with the results of the tests at the larger scales. The use of very small models is shown to be of great value in amplifying the results of more expensive large-scale tests.
A note on an aspect of the variability of deflections
Authors: Beeby A. W.
Published: July 2012

Synopsis

The only property of the concrete normally known to the designer at the calculation stage of a design is its specified characteristic strength. This paper considers the consequence of this fact for the reliability of deflection calculations by investigating the uncertainties introduced by the essential assumption that there are unique relationships between cube strength and modulus of elasticity and between cube strength and tensile strength. It is shown that, for members having low percentages of reinforcement, the likely range of differences attributable to this assumption can be very large under service loads. Some philosophical questions concerning the relationship between ‘research’ and ‘design’ formulae are also raised.
Characteristics and prediction of creep of a saturated mortar under variable temperature
Authors: Illston J. M. , Sanders P. D.
Published: July 2012

Synopsis

In a previous paper it was shown that four strain components can be identified when concrete, stored in an environment with a varying temperature, is subjected to a sustained load. They are: (a) elastic strain; (b) delayed elastic strain; (c) transitional thermal creep; (d) flow. Each component is, in some sense, related to temperature, and the first part of this paper is devoted to the development of explicit functions for each of the components in terms of temperature and time. In particular, it is shown that all the time-dependent strains can be generated from a single curve in which flow is plotted against weighted maturity. The expressions are used in the second part of the paper to predict the strains in mortar tubes under torsional loading, when subjected to severe regimes of temperature change. The predictions show reasonable agreement with experimental results, and a simplified method of prediction, for use in practice, is also demonstrated.
Oxodegradable plastics: degradation, environmental impact and recycling
Authors: Thomas Noreen L. , Clarke Jane , McLauchlin Andrew R. , Patrick Stuart G.
Published: July 2012

This paper summarises the results of a study to assess the environmental impact of oxo-degradable plastics. These plastics are mainly based on polyethylene and contain additives that cause the plastic to undergo oxidative degradation by a process accelerated by light and/or heat. The approach used in the study has been to review the published research on oxo-degradable plastics, assess other literature available in the public domain, and also to engage with stakeholders throughout the life cycle of the product. The main purpose of the study was to assess what happens at the end of life of the plastics and whether this has a beneficial effect. The study concluded that incorporating additives into petroleum-based plastics to accelerate their degradation does not improve their environmental impact and potentially gives rise to certain negative effects. In particular there is concern that these plastics are neither suitable for conventional recycling methods, due to the presence of degradation accelerators, nor suitable for composting, due to the lack of biodegradability. There is also concern about the fate of oxo-degradable plastic fragments in the environment.
Impact of cattle grazing on the occupancy of a cryptic, threatened rail
Authors: Richmond Orien M. W. , Tecklin Jerry , Beissinger Steven R.
Published: July 2012

Impacts of livestock grazing in arid and semiarid environments are often concentrated in and around wetlands where animals congregate for water, cooler temperatures, and green forage. We assessed the impacts of winter–spring (November–May) cattle grazing on marsh vegetation cover and occupancy of a highly secretive marsh bird that relies on dense vegetation cover, the California Black Rail (Laterallus jamaicensiscoturniculus), in the northern Sierra Nevada foothills of California, USA. Using detection–nondetection data collected during repeated call playback surveys at grazed vs. ungrazed marshes and a “random changes in occupancy” parameterization of a multi‐season occupancy model, we examined relationships between occupancy and habitat covariates, while accounting for imperfect detection. Marsh vegetation cover was significantly lower at grazed marshes than at ungrazed marshes during the grazing season in 2007 but not in 2008. Winter–spring grazing had little effect on Black Rail occupancy at irrigated marshes. However, at nonirrigated marshes fed by natural springs and streams, grazed sites had lower occupancy than ungrazed sites. Black Rail occupancy was positively associated with marsh area, irrigation as a water source, and summer vegetation cover, and negatively associated with marsh isolation. Residual dry matter (RDM), a commonly used metric of grazing intensity, was significantly associated with summer marsh vegetation cover at grazed sites but not spring cover. Direct monitoring of marsh vegetation cover, particularly at natural spring‐ or stream‐fed marshes, is recommended to prevent negative impacts to rails from overgrazing.
Native predators reduce harvest of reindeer by Sámi pastoralists
Authors: Hobbs N. Thompson , Andrén Henrik , Persson Jens , Aronsson Malin , Chapron Guillaume
Published: July 2012

Contemporary efforts to protect biological diversity recognize the importance of sustaining traditional human livelihoods, particularly uses of the land that are compatible with intact landscapes and ecologically complete food webs. However, these efforts often confront conflicting goals. For example, conserving native predators may harm pastoralist economies because predators consume domestic livestock that sustain people. This potential conflict must be reconciled by policy, but such reconciliation requires a firm understanding of the effects of predators on the prey used by people. We used a long‐term, large‐scale database and Bayesian models to estimate the impacts of lynx (Lynx lynx), wolverine (Gulo gulo), and brown bear (Ursus arctos) on harvest of semi‐domesticated reindeer (Rangifer tarandus) by Sámi pastoralists in Sweden. The average annual harvest of reindeer averaged 25% of the population (95% credible interval = 19, 31). Annual harvest declined by 96.6 (31, 155) reindeer for each lynx family group (the surveyed segment of the lynx population) in a management unit and by 94.3 (20, 160) for each wolverine reproduction (the surveyed segment of the wolverine population). We failed to detect effects of predation by brown bear. The mechanism for effects of predation on harvest was reduced population growth rate. The rate of increase of reindeer populations declined with increasing abundance of lynx and wolverine. The density of reindeer, latitude, and weather indexed by the North Atlantic Oscillation also influenced reindeer population growth rate. We conclude that there is a biological basis for compensating the Sámi reindeer herders for predation on reindeer.
Inferior Alveolar Neurosensory Deficiency Associated With Placement of Dental Implants
Authors: Givol Navot , Peleg Oren , Yarom Noam , Blinder Daniella , Lazarovici Towy Sorel
Published: July 2012

Background: This study reports and analyzes a large series of patients with neurosensory deficiency related to the placement of dental implants (DIs) and resulting in liability claims (LCs).

Methods: From 1998 to 2009, there were 92 LCs related to persistent altered sensation post DI placements in Israel. Patients’ demographics, year and source of LCs, interval between the procedure that resulted in a neurosensory deficiency and the LC, qualifications of the surgeon, preoperative imaging modality, DI length, available alveolar bone for DI placement, placement site, timing of DI placement (immediately after tooth extraction or after socket healing), and treatment after the diagnosis of neurosensory deficiency were recorded and analyzed.

Results: There were 21 cases during the first 5 years of the study (mean 4.2/year) and 63 cases (mean 12.6/year) over the following 5 years. Thirty LCs were issued during the second postoperative year and 15 LCs after >5 years. Most LCs (76%) involved procedures that were planned and performed according to radiographs and 24% after computed tomography. Sixty‐five percent of the LCs were performed by general dental practitioners and 35% by specialists. More than one DI was performed during the surgical procedure that resulted in a neurosensory deficiency in 73 LCs (79.3%), and the DI was >10 mm in 55 (59.8%) cases.

Conclusions: LCs for DIs that result in a neurosensory deficiency pose a legal risk to the practitioner long after the injury has occurred.
Comparison of Current US Risk Strategy to Screen for Hepatitis C Virus With a Hypothetical Targeted Birth Cohort Strategy
Authors: Tomaszewski Kenneth J. , Deniz Baris , Tomanovich Peter , Graham Camilla S.
Published: July 2012

Objectives. We compared the theoretical performance of a 1-time, birth cohort strategy with the currently recommended risk strategy for screening for hepatitis C virus (HCV) infection, which is undetected in an estimated 75% of 4 million affected people in the United States.

Methods. We applied current American Association for the Study of Liver Disease risk screening guidelines and a targeted birth cohort strategy to National Health and Nutrition Examination Survey data from 2003 to 2006 to estimate their performance in identifying HCV cases.

Results. Risk guidelines would recommend testing 25% of the US population aged 20 years or older and, if fully implemented, identify 82% of the projected HCV-exposed population. A targeted birth cohort (1946–1964) strategy would test 45% of the same population and identify 76% of the projected HCV population.

Conclusions. In this ideal-world simulation, birth year and risk screening had similar theoretical performances for predicting HCV infection. However, actual implementation of risk screening has not achieved its theoretical performance, and birth cohort screening might increase HCV testing rates.
The Return of Rainbow Diet Pills
Authors: Cohen Pieter A. , Goday Alberto , Swann John P.
Published: July 2012

The US Food and Drug Administration (FDA) has recently warned consumers about the risks of weight loss supplements adulterated with multiple pharmaceutical agents. Some of these supplements combine potent anorectics, such as amphetamines derivatives, with benzodiazepines, beta-blockers, and other medications to suppress the anorectics’ adverse effects. These weight loss supplements represent the most recent generation of rainbow diet pills, named for their bright and varied colors, which date back more than 70 years. Beginning in the 1940s, several US pharmaceutical firms aggressively promoted rainbow pills to physicians and patients. By the 1960s the pills had caused dozens of deaths before the FDA began removing them from the US market. We used a variety of original resources to trace these deadly pills from their origins in the United States to their popularity in Spain and Brazil to their reintroduction to the United States as weight loss dietary supplements.
Improving State Health Policy Assessment: An Agenda for Measurement and Analysis
Authors: Macinko James , Silver Diana
Published: July 2012

We examine the scope of inquiry into the measurement and assessment of the state public health policy environment. We argue that there are gains to be made by looking systematically at policies both within and across health domains. We draw from the public health and public policy literature to develop the concepts of interdomain and intradomain policy comprehensiveness and illustrate how these concepts can be used to enhance surveillance of the current public health policy environment, improve understanding of the adoption of new policies, and enhance evaluations of the impact of such policies on health outcomes.
Effects of Aging and Education on False Memory
Authors: Lee Yuh-Shiow , Lee Chia-Lin , Yang Hua-Te
Published: July 2012

This study examined the effects of aging and education on participants' false memory for words that were not presented. Three age groups of participants with either a high or low education level were asked to study lists of semantically related words. Both age and education were found to affect veridical and false memory, as indicated in the recall and recognition of the studied word and nonstudied lures. A low education level had a negative effect on memory performance for both young and middle-aged adults. Older adults with a high level of education had a higher level of false memory than those with a lower education level. The results of this study are discussed in terms of the importance of education on false memory and mechanisms that create false memory of words in older adults.