bluuebunny/crossref_metadata_2025 huggingface dataset:
The workability of concrete
Authors: Murdock L. J.
Published: July 2012

Summary

An analysis is made of a large number of tests for workability as measured by the compacting factor, in order to determine how workability is related to the grading and shape of aggregate, the mix proportions and the water/cement ratio.

An index is developed which takes account of the influence of particle size on workability, and largely overcomes the limitations of the fineness modulus and surface area coefficients. Similarly, an angularity index is introduced which is based on a test on the aggregate and is shown to take account of its shape.

The relation between workability and mix proportions is assessed. It is established that a proportion of the water, equivalent to a water/cement ratio of about 0·25, is required to wet the cement, and that any additional water may be regarded as available to make the mix workable.

An approximate relation is given for the calculation of compacting factors, and a worked example illustrates the use of this relation for mix design.
The lateral buckling of slender reinforced concrete beams
Authors: Siev A.
Published: July 2012

Summary

The paper gives a brief summary of the theory of buckling for homogeneous materials, with special reference to reinforced concrete, account being taken of variations in shape and in loading. The method involves the determination of the flexural and torsional rigidities in the uncracked, cracked elastic, and cracked plastic states.

Tests were made on two series of beams: six of rectangular section (1 ½ × 16 in.), andfour inverted L beams.

It is concluded that the spanlwidth ratio is not the only factor affecting buckling; the widthlheight ratio and the percentage of reinforcement and its distribution are of equal importance.
A new machine for the fatigue testing of reinforced concrete beams, and some preliminary results
Authors: Larnach W. J.
Published: July 2012

Summary

The paper describes the construction and operation of an hydraulically operated fatigue machine of 5 tons capacity for tests in bending or compression. The machine proved capable of long periods of service with the minimum of attention.

A series of fatigue tests in bending on normally reinforced concrete beams indicated that high proportions of the static failing load could be applied as many as 300,000 times without significantly altering the ultimate strength of the beams.
Reinforced concrete joints between prestressed concrete members
Authors: Reeves J. S. , Morice P. B.
Published: July 2012

Summary

The practice has developed in recent years of constructing statically indeterminate prestressed concrete structures by applying connecting restraints to two or more statically determinate prestressed concrete members. The present paper discusses a joint that may be used to convert two or more simply supported prestressed concrete beams into a continuous beam by joining them together over the supports. This joint utilizes unprestressed continuity steel contained within the crosssection of the continuous beam.

Alternative designs for such a joint are proposed and examined for suitability in fulfilling the necessary functions. Some remarks are added on the design of composite continuous beams.

Tests are reported on five two-span composite beams each made from two post-tensioned, grouted beams. The ratio of the ultimate moments of resistance of the critical sections was varied. The tests demonstrated the essentially satisfactory nature of the proposed joint.
Tests on a one-tenth scale model of a hyperbolic paraboloid shell roof
Authors: Jones L. L.
Published: July 2012

Summary

Tests which have been carried out on a one-tenth scale model of a hyperbolic paraboloid shell roof have given data from which the tie-bar force, corner reactions, deflexion and stress distribution of the actual structure have been calculated.

In the interior of the shell, the stresses calculated are in good agreement with those calculated by the membrane theory. Near the edge beams both the forces and the moments increase rapidly; since, however, the edges of the shell were thickened, the maximum stresses in the structure under a working load of 60 lb/ft2 were only 250 lb/in2 compression and 100 lb/in2 tension. At this load the maximum deflexion would be 0·5 in. The tie-bar force measured was only two-thirds of that predicted by the membrane theory, and equilibrium conditions revealed that the lower corners were carrying approximately 0·4 and the higher corners 0·1 of the total load.

The model shell had a load factor of at least 5.
Some tests on the durability of concrete mixes of similar compressive strength
Authors: Keene P. W.
Published: July 2012

Summary

The practice of specifying that concrete should have a certain minimum strength has recently become more general, and this, together with the increased use of vibration as a method of compacting concrete on site, has often led to the use of leaner mixes of lower workability. However, although their compressive strength may be similar, little is known about the durability of these mixes compared with that of richer, more workable mixes suitable for hand-compaction.

A series of tests has therefore been carried out on mixes made with different cements, of varying degrees of workability, having aggregate/cement ratios ranging from 4·0 to 7·5 by weight, all with an average compressive strength of about 4,500 lb/in2 at 28 days.

The durability of the concrete was assessed by measuring the change in weight and in compressive strength of cubes immersed in sulphate solution and the change in weight of, and in ultrasonic pulse velocity through, cubes subjected to repeated cycles of freezing and thawing. In addition, tests were carried out for absorption, drying shrinkage, and moisture movement.

It was found that the leaner mixes of lower workability tended to have a slightly greater resistance to alternate freezing and thawing, lower absorption, and less drying shrinkage and moisture movement. No difference was observed between the leaner and richer mixes in resistance to sulphate attack.

It is concluded that the durability of fully compacted medium-strength concrete of low workability is not affected adversely by the use of aggregate/cement ratios of up to 7·5 by weight.
The design and construction of a device for recording small displacements
Authors: James P. R.
Published: July 2012

Summary

The paper describes the design and construction of an electro-mechanical device for remote, continuous recording of displacements of the order of one millimetre.
The effect of air-entrainment on the shrinkage of concrete stored in laboratory air
Authors: Keene P. W.
Published: July 2012

Summary

Tests are described comparing the shrinkage of air-entrained concrete with that of concrete of similar workability and strength but without entrained air.

Changes in length of 3 × 3 × 10 in. prisms were measured by means of a micrometer screw gauge. Some specimens were cured in moist air for the first 7 days before being transferred to the air of the laboratory; the others were stored throughout in the air of the laboratory. Some time after the specimens had reached maximum shrinkage they were measured for moisture movement.

The conclusions drawn from the results of the tests are that the shrinkage of concrete of medium strength and workability is not significantly affected by air-entrainment, but with or without entrained air the shrinkage is greater for concrete cured in moist air for the first 7 days than for concrete allowed to dry immediately.
A demountable inductive strain gauge
Authors: Reynolds G. C.
Published: July 2012

Summary

The paper describes a demountable strain gauge, with a gauge length of 50 mm, or just under two inches, suitable for measuring strains of 10−5.
Studies of pore size distribution in mortars
Authors: Kroone B. , Crook D. N.
Published: July 2012

Summary

Pore size distributions of mortars cured by hydration, carbonation, and under atmospheric conditions were measured down to pore sizes of 0·01μ diameter by the method of mercury penetration. It was found that hydration decreased the volume of the larger pores and that carbonation decreased the volume of the intermediate size pores but increased the volume of pores exceeding 5μ in diameter.

The main effect of curing in carbon dioxide was evident after 1 day, but equilibrium during hydration was reached in about 12 days. The pore size distribution was not greatly affected by curing under atmospheric conditions. The larger pore sizes (>5μ) appeared to be affected by the extent to which the samples were compacted in moulding.

The volume of pores between ∞ and 0·01μ as determined by mercury penetration is, for mortars with low cement/water ratios, considerably less than the total porosity determined by saturation with water. This points to the existence of capillaries of diameters of 0·01μ and less, or of cavities with entrances of these diameters in set cement, as deduced by Powers, Copeland and Mann from permeability data.
The behaviour and ultimate strength of prestressed concrete hollow beams under combined bending and torsion
Authors: Swamy Narayan
Published: July 2012

Summary

This paper summarizes the results of an investigation into the behaviour and ultimate strength of post-tensioned prestressed concrete hollow beams under combined bending and torsion. Twenty-four full-size beams were tested with ratios of bending moment to twisting moment varying from pure bending to pure torsion. The size and shape of the hollow, and the shear reinforcement were varied. The deflexions and strains due to bending and torsion were measured at selected points. With low ratios of bending moment to twisting moment, a primary torsion failure occurred and with high ratios a primary bending failure resulted. Between these two types of failure, there is a transition from cleavage to crushing failure. The presence of small amounts of torsion decreased the bending strength, whereas the addition of small quantities of bending increased, within certain limits, the torsional strength.

The experimental results show that the customary failure theories do not give satisfactory results for all stress combinations, and that they cannot adequately explain the failure conditions. It is suggested that any failure criteria must be based on the tensile and compressive strength of concrete and that more test data are necessary before a simplified design approach can be proposed.
Dynamic loading of prestressed concrete beams
Authors: Oladapo I. O.
Published: July 2012

Summary

The paper describes experiments to compare the behaviour of prestressed, post-tensioned concrete beams under dynamic loading with that under static loading. The total loading time was reduced from 10 min for the static loading to 0·05 s for the dynamic. This change in the rate of loading produced significant increases in the cracking strength of the concrete and in the ultimate moment of the beam. It was found that under dynamic loading prestressed concrete considerably increased its capacity for sustaining elastic deformation and for absorbing energy by inelastic deformation.
The deformation of a rectangular slab with free edges under transverse loads
Authors: Severn R. T.
Published: July 2012

Summary

The Rayleigh-Ritz energy method is used to obtain an approximation to the deflected shape of a flat slab which is loaded transversely and which is supported either on columns (Part 1), or on an elastic foundation (Part 2) for which the upthrust at any point is directly proportional to the displacement at that point. Computer programmes (Ferranti Pegasus) are briefly described by use of which solutions can be obtained in about four minutes.
The triaxial testing of fresh concrete
Authors: Ritchie A. G. B.
Published: July 2012

Summary

The workability of a stable concrete mix can be subdivided into the properties of compactability and mobility. The report describes the development of a triaxial test to assist in the expression of mobility in fundamental physical units.
Redistribution of moments in two-span prestressed concrete beams
Authors: Mallick S. K.
Published: July 2012

Summary

The results of experimental and analytical studies on the redistribution of moments in 21 beams tested to destruction under certain arrangements of concentrated loads are presented. For most of the beams, the results differed from those computed by Guyon's method. An extension of this method has been proposed by taking into consideration the concentration of curvature at the plastic hinges. Close agreement was found between the experimental and the calculated results based on the modified procedure.
The strains under constant stress of cast and sawn concrete specimens compared
Authors: Davies R. D.
Published: July 2012

Summary

Experiments to compare the strains under constant stress of concrete specimens cast to size and supposedly identical specimens sawn from the interior of larger pieces are described. No important difference was found.
The influence of transverse prestress on the strength of prestressed concrete bridge slabs
Authors: Cusens A. R. , Abbasi A. F.
Published: July 2012

Summary

The paper describes the results of tests on eight square prestressed concrete slabs having unbonded wires. The ratio of transverse prestress to longitudinal prestress (γi,) was varied hetween 0 and 100%. A system of wheel loads based on AASHO specifications was used and it was found that, for the upper range of values of γi ultimate loads were considerably in excess of those predicted by the use of yield-line theory. It is suggested that at least part of this increased load capacity could be utilized if a suitable design criterion were adopted.
The effect of the type of aggregate on the diagonal cracking of reinforced concrete beams
Authors: Taylor R. , Brewer R. S.
Published: July 2012

Summary

Comparative rests are reported on reinforced concrete beams without shear reinforcement made with different types of aggregate: two types of lightweight aggregate and one gravel aggregate were used. Other variables were the concrete strength and the type of reinforcement. The principal results of the tests were as follows.

(1) For concretes of similar cube strength, the average diagonal cracking loads of the beams made with lightlveight aggregate were lower than those of the beams made with gravel aggregate.

(2) The average diagonal cracking loads of beams reinforced with ordinary mild-steel were higher than those of the corresponding beams reinforced wirh an equivalent area of cold-worked deformed hars.

(3) The diagonal cracking load increased with increasing concrete strength, the rate of increase heing similar for all three types of concrete.
The suitability of a lightweight aggregate (Aglite) for structural concrete
Authors: Evans R. H. , Dongre A. V.
Published: July 2012

Summary

This paper gives the results of tests on Aglite concrete to establish its tensile and compressive strengths, its absorption and permeability characteristics, and the behaviour and ultimate strength of reinforced beams in shear and flexure. Throughout the work, the values obtained were compared with those for a gravel concrete having the same 28-day compressive strength.
The ultimate flexural strength of reinforced concrete rafts
Authors: Ranganathanm B. V. , Hendry A. W.
Published: July 2012

Summary

A description is given of an experimental and analytical investigation into the flexural strength of reinforced concrete rafts. In conformity wuh the concepts of soil mechanics, the contact pressure is generalized by paraboloids. The structural analysis is based on the yield-line theory. Some solutions based on lower bound technique are shown to give identical values for the collapse load. The magnitude of the collapse load for a rectangular raft in terms of the yield moment has been computed for a wide range of values of the three different parameters, characterizing the contact pressure distribution, the ratio of sides, and the coefficient of orthotropy. Tests carried out on reinforced plaster mortar slabs supported on springs confirm reasonably well the soundness of the structural analysis.
Some fatigue tests on reinforced concrete beams
Authors: Taylor R.
Published: July 2012

Summary

In a previous paper(1), a new method was proposed for proportioning stirrups in a reinforced concrete beam. This paper is a report of some fatigue tests on beams designed in accordance with these proposals. The results indicate that, although the shear reinforcement provided was sufficient to prevent shear failure of the beams, the inclined cracking due to shear affected the fatigue resistance of some of the beams.
Tensile membrane behaviour of uniformly loaded rectangular reinforced concrete slabs with fully restrained edges
Authors: Park R.
Published: July 2012

Summary

A theory is developed for the load carried at large deflexions by the tensile membrane action of uniformly loaded rectangular slabs with edges restrained against all translation. It is assumed that the reinforcement acts as a plastic membrane. On comparison with test results the theory is shown to be conservative. The load carried by tensile membrane action is found to be considerable and for heavily reinforced slabs it can exceed the ultimate flexural strength.
Cracking and failure in plain concrete beams
Authors: Oladapo I. O.
Published: July 2012

Summary

This paper describes experiments to determine the loads and the strains at which cracks occur in different concrete mixes; an attempt was also made to investigate whether there is any correlation between these and the measured values of load and strain at failure. Measurements of strain distribution on the tensile surfaces of beams were used to detect the presence of cracks. It was found that the formation of cracks is a gradual process. The early stages are probably due to bond cracks between the aggregates and mortar; a critical stage develops when cracks in the mortar itself link up the existing bond cracks to form a continuous pattern. In each mix, the stress at the critical load shows good agreement with that obtained from tensile splitting tests on cylinders. The strain at the critical load is not constant but varies with the strength of the mix. The load and the strain at failure are influenced by both the strain and the load at the critical stage.
Flexural rigidity, curvature and rotation and their significance in reinforced concrete design
Authors: Burnett E.
Published: July 2012

Summary

Some of the more fundamental and possibly less familiar aspects of current ultimate load theory are discussed, the behaviour of the simply supported under-reinforced concrete beam being used for illustration. The generalized relations between bending moment and curvature, and bending moment and rotation are given. The value of the mean flexural rigidity of the member is derived and compared with other possible values. The concept of the plastic hinge and the significance of elastic and inelastic contributions to the over-all deformation of the member are discussed.
Upper and lower bound solutions to the collapse of a continuous slab under uniform load
Authors: Holmes M. , Steel K. A.
Published: July 2012

Summary

Upper bound solutions to the collapse of continuous slabs may be calculated by applying the yield-line theory, but corresponding lower bound solutions are not available. R. H. Wood has discussed this lack of knowledge of lower bound or safe solutions. In the present paper, a lower bound solution to the collapse of a uniformly loaded isotropically reinforced rectangular slab, with two opposite sides continuous and the other sides simply supported, is developed. This solution is compared with the upper bound values, over a wide range of values for the ratio of the sides of the slab, and the agreement is shown to be within 8%. The solution is used to determine the distribution of moments in the slab and the loads transmitted to the perimeter beams.
The effect of grout properties on transmission length in grout-bonded post-tensioned concrete beams
Authors: Geddes J. D. , Soroka I.
Published: July 2012

Summary

The effect of the quality of grouts on transmission lengths observed after the release of one of the mechanical anchorages was investigated by tests on nineteen grout-bonded post-tensioned concrete beams. The results showed that the transmission lengths for this condition were directly related to the compressive strengths of the grouts used. Grouts containing aluminium powder possess relatively high compressive strengths when expansion is restrained during setting, as in ducts, and consequently better bonding ability, and their use is therefore worthy of consideration.
The effect of the elastic modulus of the aggregate on the elastic modulus, creep and creep recovery of concrete
Authors: Counto Upendra J.
Published: July 2012

Summary

This paper discusses some of the models currently available for the prediction of the modulus of elasticity of concrete. A new model is proposed which gives a satisfactory prediction for a wide variety of aggregates and concrete mixes. The same model explains satisfactorily the isolated effect of the elastic modulus of the aggregate on the creep and creep recovery of concrete. In order to provide a critical test of this effect, experiments were carried out on concretes made with artificial aggregates having a large range of elastic moduli. Results of these experiments are presented. It is concluded that the elastic strain, creep and creep recovery of concrete increase as the elastic modulus of the aggregate decreases.
The ultimate strength and long-term behaviour of uniformly loaded, two-way concrete slabs with partial lateral restraint at all edges
Authors: Park R.
Published: July 2012

Summary

A theory for the ultimate flexural strength of uniformly loaded, laterally restrained two-way concrete slabs (reinforced or unreinforced) is extended to include the effect on the compressive membrane action of partial restraint against lateral displacement at all the edges and axial strains in the plane of the slab. The edges of the slab are considered to be fixed against rotation and vertical translation, and a strip approximation is used with an empirical value for the deflexion at ultimate load. The theory is applicable to the interior panels of slab-and-beam floors under short-term or sustained uniform loading. It is shown that partial lateral restraint and axial strains can reduce the compressive membrane action significantly, especially in the case of thin slabs. The theory is compared with the results obtained from eight unreinforced slabs tested under sustained uniform loading and is shown to give a conservative indication of the ultimate flexural strength in most cases.
A new approach to the determination of the tensile strength of cement paste by centrifugal force
Authors: Roper H. , Bryden J. G.
Published: July 2012

Summary

A method of determining the tensile strength of a small cement paste specimen at ages varying between one and twenty-eight days has been achieved by subjecting the specimens to high centrifugal forces in an air-driven centrifuge.
The components of strain in concrete under sustained compressive stress
Authors: Illston J. M.
Published: July 2012

Summary

The strain of concrete under sustained compressive stress is examined in terms of three components, instantaneous recoverable, time-dependent recoverable and irrecoverable, defined here as elastic, delayed elastic and flow respectively. Experimental evidence is presented of the influence on each of the length of the period of loading and the age of the concrete when the load is applied. It was found that at a given age the rate of flow is virtually independent of any earlier loading and that the delayed elastic strain tends to a limiting value which varies little with the age of the concrete. The rate of occurrence of delayed elastic strain diminishes with the age of the concrete and it can be linked with the corresponding rate of flow.
Bulk storage of cement for a concrete laboratory
Authors: Lunt B. G. , van der Meulen G. J. R.
Published: July 2012

Summary

The paper describes a recently developed storage system using an air-tight welded-steel silo which discharges through a rotary-vane feeder and closed screw conveyor. The special precautions for preventing ingress of water and carbon dioxide and the facilities for fluidizing the cement are also covered in detail.
Using curvature of precast beams to measure the loss of prestress due to creep before loading
Authors: Davies R. D.
Published: July 2012

Summary

The loss of prestress due to creep before loading in small precast prestressed beams was calculated from their change of curvature. The results were checked by measuring the change in the lengths of the prestressing wires and the shrinkage of control pieces. An application of the idea to creep tests on compression specimens is mentioned.
Data on the binary system 3CaO.Al2O3-Na2O.8CaO.3 Al2O3 within the system CaO-Al2O3-Na2O
Authors: Fletcher K. E. , Midgley H. G. , Moore A. E.
Published: July 2012

Summary

Conwicke and Day showed that partial solid solution occurs in the system C3A-NC8A3 at temperatures below the liquidus. Their results indicated a marked similarity between the X-ray powder diffraction data for a preparation containing more than 3·0% Na2O and the data given by Moore for a new phase in Portland cements. The present work was almost complete when Conwicke and Day's paper was published. It generally confirms their results but gives more information on the solid solution. At the limit of solid solution at 1,350°C the sodium calcium aluminate which is formed has the composition 91·0 mol % C3A, 9·0 mol % N3A and has been indexed on an orthorhombic unit cell with a = 15·314, b = 15·394, c = 15·137 Å.
The optimum coarse aggregate content of concrete
Authors: Hughes B. P.
Published: July 2012

Summary

The best proportions in which to combine any given coarse andfine aggregates are considered with particular reference to concrete mix design. Earlier work, which was restricted to ¾ in. maximum size of aggregate and used the compacting factor test to indicate the workability of the concrete, is extended to ⅜ in maximum size of aggregate using the Vebe consistometer test. In addition to extending the range of the curves for use in mix design, the present work shows that the optimum specific volume ratio of coarse aggregate for the Vebe consistometer test is similar to that for the compacting factor test. This is a most important result since it shows that the application of the concept of particle interference is not restricted to the compacting factor test.
Tensile strains in unreinforced concrete beams
Authors: Welch G. B.
Published: July 2012

Summary

The behaviour of concretes and mortars subject to tensile strain was examined by measuring strains on the tension face of moist beam specimens during the standard flexural strength test. A wide range of concretes was examined with compressive strengths from 1,500 to more than 11,000 lb/in2 at 28 days. Initial cracking, as indicated by a significant deviation of the load-strain curve, was found to occur at tensile strains ranging from 41 to 158 × 10−6 for the range of concretes tested at 28 days. The corresponding average maximum tensile strains, measured before final crack propagation led to fracture, ranged from 75 to 240 × 10−6. These strains were affected by several factors but generally increased with increasing concrete strengths. The behaviour of mortars and concretes with high mortar content differed from that of normal concretes, and the tensile strains were much greater.
The influence of cement paste content on the creep of lightweight aggregate concrete
Authors: Rutledge S. E. , Neville A. M.
Published: July 2012

Summary

The paper is an extension to lightweight aggregate concrete of earlier work on the influence of cement paste content on the creep of concrete. It is shown that there is a simple relation between the creep after a given time under load and the content of cement paste corrected for unhydrated cement. An expression is proposed for the creep-time behaviour of concrete of any mix proportions but made with a given type of aggregate; this involves a total of four constants from two creep-time tests.
Determining the setting time of cement paste, mortar and concrete with a copper-lead electrode
Authors: Aschan Nils
Published: July 2012

Summary

The point at which the rate of hydration of the alite phase in clinker, which is very slow in the beginning, starts to accelerate and the cement paste begins to turn solid can be determined with a copper-lead electrode. This point is clearly indicated by the distinct increase of potential difference when the surface of copper oxidizes to cuprous oxide as air penetrates to the capillary space. Air dissolved in the mixing water does not cause oxidation, nor does entrained air present under practical working conditions. Because of the total absence of the disturbing influence of the aggregate, this method of determining the setting time of mortar or concrete is more accurate than the commonly used mechanical methods and it also yields results which better correspond to the actual situation. The reaction vessel need not be of any specific shape, and therefore direct placement of the electrode, for instance, in a unit mould is possible. In principle, this method is also applicable to hydraulic bonding agents other than Portland cements.
Is your research really necessary?
Authors: McIntosh J. D.
Published: July 2012

Summary

Recent events have indicated a growing concern about the effectiveness of research for the construction industry. These are reviewed, and provocative comments are offered, to stimulate a critical appraisal of the value of the subjects chosen for study. It is suggested that concrete research has tended to follow a traditional pattern, continuing to examine factors well into unrewarding regions according to the law of diminishing returns and ignoring areas which could have a major effect on the over-all cost of construction. This situation is attributed largely to the varied way in which the results of different types of investigation are received by the industry. The research worker is exhorted to spend more time in applying his critical faculties to examine how best he can serve the industry and in using his unbiased judgement to incorporate his findings into the common experience of the practitioners he serves.
The strength of concrete under combined shear and direct stress
Authors: Goode C. D. , Helmy M. A.
Published: July 2012

Summary

Thirty-nine hollow cylinders, made of five different concrete mixes, were tested under direct compression and torsion to study the failure of concrete under the ensuing biaxial state of stress. The results of these tests are compared with similar tests by other investigators and discussed in relation to various failure criteria.
Alkali reactivity of dolomitic limestone aggregate
Authors: Swenson E. G. , Gillott J. E.
Published: July 2012

Summary

Additional evidence was obtained in support of the hypothesis that excessive expansion in the alkali-carbonate rock reaction is caused by moisture uptake by the previously ‘unwetted clay’ constituent. The dedolomitization reaction is shown to be necessary only to provide access of moisture to the ‘locked-in’ clay. A microscopic method was used to determine the specific surface of the dolomitc, the quantitative nature of which made it possible to define a practical upper limit below which expansion does not occur. It was also shown that relatively small percentages of illitic clay can account for the excessive expansion shown by reactive carbonate rocks. The new techniques used included measurements of dimensional change of thin rock wafers and of compacts of clay and powdered rock.
A mathematical model for the failure of cement paste and mortars
Authors: Dougill John W.
Published: July 2012

Summary

It is suggested that structural models have only a limited use in a study of failure and an alternative mathematical model is proposed which behaves, in many ways, like hardened cement paste or mortar. The model is similar to Volkov's normal micro-inhomogeneous material, the major difference being in the failure criteria used at the microscopic level. The behaviour of the model material in simple tension is studied and it is shown that progressive fracture, or micro-cracking, occurs during all stages of loading. The mode of failure depends upon the method of test because either the material fails when the maximum stress is reached or progressive fracture continues with increased deformation and a reduction in applied stress. In addition, a ductile mode of failure is investigated and it appears that, in contrast to brittle fracture, the ultimate strength may be almost unaffected by micro-inhomogeneity.
An analysis of the creep and shrinkage effects upon prestressed concrete members under temperature gradient and its application
Authors: Arthanari S. , Yu C. W.
Published: July 2012

Summary

The influence of differential creep and shrinkage upon prestressed concrete ring structures is discussed. Expressions have been developed for finding the variation of stress and strain with time in a flexurally restrained prestressed concrete beam subjected to temperature gradient. It has been concluded that the creep phenomena can be used to the best advantage by pre-heating such structures.
Landfill capping stability: tapered solution with seepage
Authors: Zhang Bo , Fowmes Gary , D. Russell V. Jones
Published: July 2012

The capping system is one of the major structural elements in modern landfills. When using artificial sealing materials (e.g. a geomembrane) as the capping liner, the stability of the cover soils and integrity of the geosynthethics need to be assessed. Traditional design methods only consider uniform cover soil thickness with different degrees of saturation and seepage build-up (i.e. parallel submergency ratio). This paper proposes an analytical method which includes the seepage build-up in the stability analysis for the capping slope with a tapered cover soil profile, that is when cover soils become thicker from top to bottom. Both the parallel (modified) and horizontal seepage force build-up patterns have been considered and analysed. The proposed analytical methods are applied to a design case in which uniform thickness cover soils are considered. The results are comparable to those of the traditional methods and therefore they are verified. Parametric analyses have confirmed the tapered profile can effectively improve the capping slope stability and indicated that the interface shear strength (between the cover soil and the underlying geosynthetic) and cover soil shear strength have the most significant effects on the capping slope stability.
Pretreatment of oily sludge
Authors: Jing Guolin , Luan Mingming , Han Chunjie , Chen Tingting
Published: July 2012

Wet peroxide oxidation (WPO) and catalytic wet oxidation (CWO) of oily sludge were investigated. Greater than 80% chemical oxygen demand (COD) removal from oily sludge was achieved using sodium carbonate catalysed wet oxidation (WO) under the following conditions using a 0·5 l batch reactor: temperature of 330°C and concentration of sodium carbonate 200 mg/l. Greater than 90% COD removal was achieved using WPO under the following conditions: temperature of 330°C, residence time of 9 min, hydrogen peroxide excess (HE) of 0·8 and initial COD was 20 000 mg/l. Significantly more COD could be removed from oily sludge when HE was 0·8. BOD5/COD ratio was 0·52 after the oily sludge had been treated. It was concluded that WPO was a far more effective pretreatment method for removing organic compounds from oily sludge.
Novel activated carbon fibre matting from biomass fibre waste
Authors: Illingworth James M. , Rand Brian , Williams Paul T.
Published: July 2012

Waste biomass flax fibre was manufactured into a non-woven matting material. The fibrous matting was pyrolysed and chemically activated using potassium hydroxide to produce an activated carbon matting. Changes in the activation process conditions showed that increases in chemical loading, activation time and activation temperature generally resulted in greater pore volumes and higher surface areas but a reduction in carbon yield. The preparation temperature of the char precursors showed that lower temperature chars produced carbons with higher porosity but lower yield than chars produced at higher temperatures. The end product activated carbon matting had surface areas of up to 1800 m2/g with a mainly microporous size distribution (pores of <2 nm diameter), but the process conditions could be manipulated to produce a highly microporous or a mixture of microporous and mesoporous (2–50 nm pore diameters) activated carbon. The activated carbon matting characteristics can therefore be altered to produce adsorption properties tailored to a particular pollutant. The non-woven production process may be altered to produce a non-woven matting material of almost any design, width and thickness; consequently, an activated carbon fibrous matting material, also of any design, width and thickness, can be produced.
Complementary habitat use by wild bees in agro‐natural landscapes
Authors: Mandelik Yael , Winfree Rachael , Neeson Thomas , Kremen Claire
Published: July 2012

Human activity causes abrupt changes in resource availability across the landscape. In order to persist in human‐altered landscapes organisms need to shift their habitat use accordingly. Little is known about the mechanisms by which whole communities persist in human‐altered landscapes, including the role of complementary habitat use. We define complementary habitat use as the use of different habitats at different times by the same group of species during the course of their activity period. We hypothesize that complementary habitat use is a mechanism through which native bee species persist in human‐altered landscapes. To test this idea, we studied wild bee communities in agro‐natural landscapes and explored their community‐level patterns of habitat and resource use over space and time. The study was conducted in six agro‐natural landscapes in the eastern United States, each containing three main bee habitat types (natural habitat, agricultural fields, and old fields). Each of the three habitats exhibited a unique seasonal pattern in amount, diversity, and composition of floral resources, and together they created phenological complementarity in foraging resources for bees. Individual bee species as well as the bee community responded to these spatiotemporal patterns in floral availability and exhibited a parallel pattern of complementary habitat use. The majority of wild bee species, including all the main crop visitors, used fallow areas within crops early in the season, shifted to crops in mid‐season, and used old‐field habitats later in the season. The natural‐forest habitat supported very limited number of bees, mostly visitors of non‐crop plants. Old fields are thus an important feature in these arable landscapes for maintaining crop pollination services. Our study provides a detailed examination of how shifts in habitat and resource use may enable bees to persist in highly dynamic agro‐natural landscapes, and points to the need for a broad cross‐habitat perspective in managing these landscapes.
Low‐level copper exposures increase visibility and vulnerability of juvenile coho salmon to cutthroat trout predators
Authors: McIntyre Jenifer K. , Baldwin David H. , Beauchamp David A. , Scholz Nathaniel L.
Published: July 2012

Copper contamination in surface waters is common in watersheds with mining activities or agricultural, industrial, commercial, and residential human land uses. This widespread pollutant is neurotoxic to the chemosensory systems of fish and other aquatic species. Among Pacific salmonids (Oncorhynchus spp.), copper‐induced olfactory impairment has previously been shown to disrupt behaviors reliant on a functioning sense of smell. For juvenile coho salmon (O. kisutch), this includes predator avoidance behaviors triggered by a chemical alarm cue (conspecific skin extract). However, the survival consequences of this sublethal neurobehavioral toxicity have not been explored. In the present study juvenile coho were exposed to low levels of dissolved copper (5–20 μg/L for 3 h) and then presented with cues signaling the proximity of a predator. Unexposed coho showed a sharp reduction in swimming activity in response to both conspecific skin extract and the upstream presence of a cutthroat trout predator (O. clarki clarki) previously fed juvenile coho. This alarm response was absent in prey fish that were exposed to copper. Moreover, cutthroat trout were more effective predators on copper‐exposed coho during predation trials, as measured by attack latency, survival time, and capture success rate. The shift in predator–prey dynamics was similar when predators and prey were co‐exposed to copper. Overall, we show that copper‐exposed coho are unresponsive to their chemosensory environment, unprepared to evade nearby predators, and significantly less likely to survive an attack sequence. Our findings contribute to a growing understanding of how common environmental contaminants alter the chemical ecology of aquatic communities.
Effect of Hydrosoluble Chlorine–Mediated Antimicrobial Photodynamic Therapy on Clinical Parameters and Cytokine Profile in Ligature‐Induced Periodontitis in Dogs
Authors: Sorkhdini Parand , Moslemi Neda , Jamshidi Shahram , Jamali Raika , Amirzargar Ali Akbar , Fekrazad Reza
Published: July 2012

Background: Recently, a hydrosoluble chlorine composed of sodium salts chlorine e6, chlorine p6, and purpurine‐5 has been shown to be a promising photosensitizer in antimicrobial photodynamic therapy (aPDT). The aim of this study is to evaluate the effects of adjunctive application of hydrosoluble chlorine–mediated aPDT compared with scaling and root planing (SRP) alone on clinical parameters and cytokine levels in gingival crevicular fluid of dogs with experimental periodontitis.

Methods: Periodontal disease was induced by placing silk ligatures around both maxillary and mandibular teeth. After establishment of attachment loss, full‐mouth SRP was performed in all dogs. One day after SRP, each quadrant randomly received one of the following treatment modalities: hydrosoluble chlorine plus diode laser (wavelength 662 nm, power 100 mW, continuous mode, time of irradiation 20 seconds), hydrosoluble chlorine alone, laser alone, or no adjunctive treatment. The same adjunctive procedure was repeated 1 week later. Clinical parameters including periodontal probing depth, clinical attachment level, and bleeding on probing, as well as crevicular levels of interleukin‐1β and tumor necrosis factor‐α, were evaluated at baseline, at 3 weeks, and at 3 months after treatment.

Results: After both 3 weeks and 3 months, all treatment groups showed significant improvement in all clinical and immunologic parameters (P <0.001). No significant differences were found between the four groups with regard to the measured parameters (P >0.05).

Conclusion: Based on the results of this study, adjunctive use of hydrosoluble chlorine–mediated aPDT with the current setting has no additional effect on the clinical parameters or proinflammatory cytokine levels in ligature‐induced periodontitis.
Trends in Michigan Early Adolescent Immunization: 2006–2008
Authors: Rees-Clayton Erin , Montgomery JoLynn P. , Enger Kyle S. , Boulton Matthew L.
Published: July 2012

Objectives. We have described vaccine coverage of Michigan young adolescents immunized with tetanus, diphtheria, and pertussis; meningococcal conjugate; and human papillomavirus vaccines during 2006–2008.

Methods. We obtained data from the Michigan Care Improvement Registry, a state-based immunization information system that included more than 57 million vaccination records. We examined 3 overlapping cohorts of 11- and 12-year-old children (n > 350 000 in each) to assess temporal trends in vaccination coverage, characteristics of those immunized, funding sources, and vaccination sites.

Results. Vaccine uptake increased during 2006 through 2008, peaking in the summer months. More than half of children receiving more than 1 vaccine received the vaccines simultaneously. Older age, receipt of Medicaid, and prior completion of early childhood immunizations were associated with greater odds of vaccination.

Conclusions. Vaccine coverage among Michigan young adolescents is increasing but continues to be relatively low. Coverage of 11- and 12-year-old children may improve with efforts to encourage vaccination at all health care visits, an increase in public funding in support of adolescent vaccination, and continued monitoring of adolescent vaccination levels through school-based assessments.
Tobacco Crop Substitution: Pilot Effort in China
Authors: Li Virginia C. , Wang Qiongli , Xia Ning , Tang Songyuan , Wang Caroline C.
Published: July 2012

In China, approximately 20 million farmers produce the world's largest share of tobacco. Showing that income from crop substitution can exceed that from tobacco growth is essential to persuading farm families to stop planting tobacco, grown abundantly in Yunnan Province. In the Yuxi Municipality, collaborators from the Yuxi Bureau of Agriculture and the University of California at Los Angeles School of Public Health initiated a tobacco crop substitution project. At 3 sites, 458 farm families volunteered to participate in a new, for-profit cooperative model. This project successfully identified an approach engaging farmers in cooperatives to substitute food crops for tobacco, thereby increasing farmers’ annual income between 21% and 110% per acre.
Using fuzzy logic for evaluating the level of countries’ (regions’) economic development
Authors: Stojic Gordan
Published: July 2012

There are several divisions of countries and regions in the world. Besides
geo-political divisions, there also are economic divisions. The most common
economic division is the that on developed countries and the poor ones. These
divisions are a consequence of the level of: GDP, GDP per capita,
unemployment rate, industrial growth, and so on. The question is how to
define a mathematical model based on which the following will be assessed:
who is rich and who is poor, or who is economically developed and who is not?
How the boundaries of transition from one category to another can be defined?
This paper presents a model for evaluating the level of economic development
of countries and regions using "fuzzy" logic. The model was tested on a
sample of 19 EU member countries and aspirants for membership.
Changes in relative material deprivation in regions of Slovakia and the Czech Republic
Authors: Zelinsky Tomas
Published: July 2012

The aim of this article is to assess the level of relative material
deprivation in the Czech and Slovak Republics and their regions. The first
part of the article describes the level of households? equipment with
utilities and durables using the 1991 and 2001 censuses. The second part is
aimed at estimating the relative material deprivation in the Czech and Slovak
regions using EU SILC 2006-2008 microdata, i.e. approximately 15 years after
the split. The results indicate that there are significant differences in the
relative material deprivation rates between the Czech Republic and Slovakia
and among their regions. According to the results, the level of deprivation
is higher in Slovakia, and deprived households are highly concentrated in the
eastern part of Slovakia. The regions can be divided into five clusters,
while the Czech Capital Prague Region has a special position. It has the
highest level of housing deprivation and the lowest level of
durables/economic strain deprivation.