bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reinforced concrete under thermal gradients
Authors: England G. L. , Ross A. D. 
Published: July 2012

Summary The significance and current knowledge of thermal effects in concrete and reinforced concrete are reviewed briefly. It is evident that there is a need for more basic data on the shrinkage and creep of concrete subjected to high temperatures. Tests designed to obtain some of these data are described; results for the shrinkage and creep of a particular concrete at temperatures up to l40°C are presented. Some of the specimens were sealed to prevent loss of moisture, to simulate the conditions in mass concrete. It is shown that the time-dependent strains are markedly temperature-dependent. The paper then describes tests on model reinforced concrete beams subjected to a thermal gradient while flexurally restrained but without longitudinal restraint. The behaviour of the unsealed beams showed a severe departure from the predictions of conventional elastic theory, even to the extent of indicating compression in the reinforcing steel, instead of the expected tension. This was due to shrinkage and creep under the high temperatures. The behaviour of the sealed reinforced concrete specimens approximated to the predictions of elastic theory with a low value of the elastic modulus. A numerical procedure for estimating approximately the effects of time- and temperature-dependent strains in flexurally restrained beams is outlined in an Appendix.
Strain measurements on reinforced concrete columns
Authors: Ashworth R. 
Published: July 2012

Summary The change of strain in members of a reinforced concrete structure has been traced during and after construction over a period of three years using vibrating-wire strain gauges attached to the reinforcing bars and by making supplementary surface strain measurements with a Demec gauge. Total strains of the order of – 900 × 10−6 were recorded, with average steel stresses in one column of 27,400 lb/in2. The average concrete stress is estimated to have been 600 lb/in2. Short-term tests were also carried out to study the behaviour of the members under known loading conditions, and electrical resistance strain gauges attached to the reinforcing bars were used in addition to the vibrating-wire gauges. The performance of both types of embedded gauge is discussed and attention is drawn tofactors which curtailed the effective life of a number of vibrating-wire gauges.
The behaviour of prestressed concrete sections near the maximum moment
Authors: la Grange L. 
Published: July 2012

Summary Tests are described in which prestressed concrete sections were tested in pure bending in such a way that the complete moment-curvature curves could be obtained. The special requirements of the testing equipment are discussed and it is shown that there are descending branches to the moment-curvature curves of both underand over-reinforced sections. A theoretical discussion is given of the conditions of maximum moment of underand over-reinforced sections, including the cases of combinations of bending moment and axia load. The analysis is based on the stress-strain curve of concrete and it is shown that the conventional curves are not the true stress-strain curves of concrete. Attempts to obtain the actual curves are described; the parameters thus obtained are used in the analysis and give close agreement with measurements of maximum bending moments and curvatures in actual tests.
The effect on normal ⅜ in. reinforcement of adding calcium chloride to dense and porous concretes
Authors: Blenkinsop J. C. 
Published: July 2012

Summary This paper deals with a five-year investigation into the corrosion of mild steel reinforcement embedded at various depths in dense and porous concretes containing calcium chloride. Half the number of specimens were exposed to the effects of the weather on the exposure site at the Building Research Station and the remainder were half-immersed in water in the laboratory; control tests were also made with dense and porous concretes containing no calcium chloride. After five years it was found that 2% of flake calcium chloride by weight of cement added to concrete had little or no effect on the reinforcement embedded in dense concrete when the cover was at least ½ in. With porous concretes stored outside, however, there was considerably more corrosion of the bars taken from concrete containing calcium chloride than from the control concrete and some corrosion was seen even with 1½ in. cover. In no case could the corrosion be said to have reached serious proportions for reinforcement of ⅜ in. diameter or more but similar amounts of corrosion on thinner bars would probably have caused a serious reduction in the cross-section of the bar, with consequent loss of strength of any reinforced concrete unit.
Strain measurements on saturated concrete specimens
Authors: Newman K. , Lachance L. , Loveday R. W. 
Published: July 2012

Summary A programme of work on the mode of deformation and failure of plain concrete has called for the measurement of local tensile strains on the surface and the over-all deformation of saturated, as well as dry, concrete test specimens. Two different strain-measuring techniques have been developed to give this information. In the first, electrical resistance strain gauges, suitably protected, are attached to the mould and cast in situ. These local in-surface gauges are located just beneath the plane of the surface of the specimen. In the second technique, detachable gauges of any length and suitable for measuring over-all strains are manufactured by attaching electrical resistance strain gauges to Perspex strips or rings. Details are given of the methods of manufacture and use of the gauges and comparisons are made between the strains measured with the in-surface and on-surface foil gauges and roller extensometers. The different values obtained imply that the gauges and extensometers are measuring basically different properties of a deformed concrete specimen, and when absolute strain measurements are required this should be recognized.
Creep of concrete as a function of its cement paste content
Authors: Neville A. M. 
Published: July 2012

Summary It is shown that for specimens subjected to a sustained load at a constant stress/strength ratio there is a simple relation between creep and the amount of cement paste in the concrete. The cement content affects also the rate of creep, leaner mixes achieving a given proportion of their long-term creep earlier than rich mixes. This behaviour is shown to be related to the rate of increase in strength ofthe specimen while under load, and is verified for ordinary and rapid-hardening Portland cements. The prediction of creep from the relations established is discussed.
The effect of various heat treatments of the clinker on the early hydration of cement pastes
Authors: Chatterji S. , Jeffery J. W. 
Published: July 2012

Summary Three commercial Portland cement clinkers (low-heat, ordinary and sulphate-resisting) were each given three different heat treatments. The hydration reactions of cements made of these clinkers were then observed by electron-optical and X-ray diffraction techniques from 4 min to 3 months. It has been found that alumina- and iron-bearing compounds in commercial clinkers have reactivities different from those of laboratory-made C3A and C4AF. Alumina- and iron-bearing compounds in commercial clinkers can be made to approach the reactivity of pure C3A and C4AF by prolonged annealing at 1,280°C. Direct evidence of “through-solution” conversion of C4AHx to ettringite has been found.
The effective width of T beams
Authors: Severn R. T. 
Published: July 2012

Summary A method is described for the accurate determination of effective widths of isolated T beams and of T and L beams which form part of a larger structure. This method takes into account the bending stiffness of the flanges in a more satisfactory way than has been used hitherto. Some Tables of effective widths have been calculated for various loading conditions and variations in the geometry of the beams, and comparison is made, where possible, with values produced by the Comite Europeen du Bit on.
Concrete reinforced with glass fibres
Authors: Agbim C. C. 
Published: July 2012

Summary The paper is a summary of test results on the utilization of tensile strength of glass fibres for the reinforcement of concrete members. Particular reference is made to shell structures, and the paper includes the results of preliminary investigations carried out on simpler structures, aimed at obtaining exploratory information on the behaviour of composites of concrete and glass fibre.
A note on the occurrence of crystals of calcium hydroxide and ettringite in voids in hardened Portland cement paste
Authors: Gillott J. E. , Ritchie T. 
Published: July 2012

Summary The occurrence of crystals of calcium hydroxide and of ettringite (calcium sulphoaluminate) in hardened Portland cement, reported previously by others, is confirmed. Samples of hardened Portland cement paste prepared half a century ago at one of Canada's earliest cement plants were, on examination, found to contain voids in which well developed crystals had formed. The crystals occurred as thin plates and needles that were identified by optical microscopy and X-ray diffraction as calcium hydroxide and ettringite, respectively. It is of interest that the calcium hydroxide had not been altered to carbonate even though the cement samples had been stored for a long time under conditions that would be expected to promote this change.
The rheology of cement pastes and fresh mortars
Authors: Nessim A. A. , Wajda R. L. 
Published: July 2012

Summary In this paper a study of the behaviour of neat cement pastes and fresh cement mortars under shear in a rotational viscometer, especially designed for this purpose, is described. It is shown that a considerable structural breakdown occurs in the cement paste under the shearing action and a comparison between the results obtained from the viscometer and those associated with the compaction of concrete under vibration seems to suggest that a breakdown under shear does take place during the vibration of concrete. It is also shown that the rate of energy input to the paste is not constant, and the effect of this on the Vebe test is discussed. A method of measuring the workability of cement pastes and mortars is presented.
A note on a possible basis for a new method of ultimate load design of reinforced concrete slabs
Authors: Taylor R. 
Published: July 2012

Summary Because of tensile membrane action, reinforced concrete slabs can sustain loads far in excess of the ultimate load calculated by the yield-line theory. To take advantage of this, it is necessary to establish de flexion criteria for ultimate load conditions and to develop a method of calculating the corresponding load-carrying capacity. Such a method is proposed, and the possible advantages are indicated.
The volume expansion of hardened cement paste due to the presence of “dead-burnt” CaO
Authors: Chatterji S. , Jeffery J. W. 
Published: July 2012

Summary A detailed mechanism is put forward, based on new microscopic and electron-optical evidence, to explain the volume expansion of hardened cement paste due to the presence of dead-burnt CaO. It is shown that CaO first forms colloidal Ca(OH)2 and that subsequently these colloidal crystallites recrystallize to macro-crystals. During their growth from supersaturated solution, these secondary Ca(OH)2 crystals will develop a thrust against the constraining cement paste, thereby causing expansion. This process isfurther helped by the elongated habit of the secondary Ca(OH)2 crystals. The present results and those of other workers are discussed in the light of this and other hypotheses.
A radio-active method for measuring variations in density in concrete cores, cubes and beams
Authors: Harland D. G. 
Published: July 2012

Summary The paper describes an apparatus for measuring the variation of density along cores and beams of concrete. The variation of density is determined by measuring the change in the absorption of gamma radiation. The gamma rays emanate from a one millicurie source of caesium 137 and are detected by a scintillation counter. This is connected to a rate-meter and chart-recorder which continuously display the intensity of radiation transmitted as the sample traverses along its depth dimension through the gamma beam. The I'ariation in the intensity of the transmitted radiation is translated into density variations by a suitable calculation. Attention is drawn to the need to retain, for each type of specimen, the same source-sample-detector geometry, but it is shown that, with careful operation, variations in density may be measured with a standard deviation of about 1 lb/ft3. Although designedfor use with concrete specimens, the technique can be applied to any cohesive material.
The effect of mix proportions and method of testing on Poisson's ratio for mortars and concretes
Authors: Anson M. , Newman K. 
Published: July 2012

Summary Following recent studies of concrete as a composite material, this paper examines whether there is a relation between the mix proportions and properties of the constituents and the over-all Poisson's ratio for mortars and concretes. From an examination of available and new data, it is apparent that Poisson's ratio is affected by the method of testing, the mix proportions, and the moisture condition and temperature of the specimens. Approximate expressions are proposed for the static and dynamic Poisson's ratios of saturated mortars and concretes made with gravel aggregates in terms of the volume fractions and Poisson's ratios of the constituent aggregate and cement paste phases. Static and dynamic tests do not measure the same properties of concrete, and suggestions are made for the differences between them.
The flexural behaviour of slabs at ultimate load
Authors: Parkhill D. L. 
Published: July 2012

Summary The paper describes a lower-bound solution for the simply supported square slab under uniform load based on the assumption of elastic-plast ic behaviour of the slab material. It is shown that the elastic moments within the segments of a chosen yield-line pattern are everywhere statically admissible. The uniqueness of the load value is thus also established. The procedure is suitable for general application to slabs of varying geometry and loading and is capable of providing realistic ultimate-moment fields for the under-reinforced type of slab normally employed.
Some shear tests on reinforced concrete T beams with stirrups
Authors: Taylor R. 
Published: July 2012

Summary Static loading tests on eleven reinforced concrete T beams are reported. The shear reinforcement in the beams had been proportioned in accordance with proposals made in an earlier paper, the amount of this reinforcement being appreciably less than that required by the current method of design in C.P.114. The tests indicated that the amounts of shear reinforcement provided were more than adequate to ensure that the flexural capacities of the beams were attained.
Complete solutions describing the limit state of reinforced concrete slabs
Authors: Massonnet Ch. 
Published: July 2012

Summary Analytical results are established, leading to ‘complete solutions’ for the exact limit load of isotropic and orthotropic slabs. Use is made of Hopkins's and Schumann's general results on fields of moment, and rate of curvature. A criterion is developed for the kinematic admissibility of a pattern of yield lines and for the static admissibility of a field of moments. It is shown that, if two different complete solutions are known, a family of complete solutions may be derivedfrom these. Distribution of moments and support reactions is investigated, without making use of the concept of nodal force. General equations are established for the negative yield line limiting the considered plastic field of the slab, and these equations give a complete solution which agrees with the general theory of limit analysis. In working out the procedures involved in the above, the author gives examples of various loadings and shapes of slab, obtains expressions for the exact collapse loads, and states the conditions governing validity of the solutions.
Apparatus for laboratory freezing-and-thawing tests on concrete specimens
Authors: Ashworth R. 
Published: July 2012

Summary This article describes an inexpensive and easily operated refrigeration cabinet which may be used in the smaller research laboratory to carry out freezing-and-thawing tests on concrete specimens in accordance with the former ASTM test C 292-63T. The performance of the apparatus is discussed and time-temperature curves for the 48 h cycle of freezing and thawing are given, together with typical test results aiter 25 cycles.
Blastfurnace slag as aggregate for concrete
Authors: Gutt W. , Kinniburgh W. , Newman A. J. 
Published: July 2012

Summary Blastfurnace slag is an important source of dense aggregate for concrete. In an investigation lasting six years the Building Research Station has compared the properties of slag aggregates with those of crushed limestone and river gravel. Six slagsfromfive different works were tested, some being typical slags sold regularly for use as aggregate and others chosen to test the effect of specific chemical or physical characteristics. Concretes made with all these slags as coarse dense aggregate were tested for compressive and transverse strength, dimensional stability and sulphate resistance. Reinforced concretes were tested for metal corrosion. A number of tests were also made on concretes in which slag constituted both the coarse and the fine aggregate. The present paper gives the results of all these studies except the observations made concerning reinforced concrete which are the subject of a separate paper in this issue. It is shown that blastfurnace slags currently produced provide material for coarse aggregate for concrete which is satisfactory in every respect.
Steel in concrete with blastfurnace slag aggregate
Authors: Everett L. H. , Gutt W. 
Published: July 2012

Summary Tests have been carried out on the rate of weight loss of steel in aqueous extracts from four air-cooled, crystalline blastfurnace slags and on steel reinforcement in concrete prisms containing such slag as the coarse aggregate exposed for two years. The results indicate that, whereas theoretically the sulphide content of the aggregate may influence the corrosion behaviour, under practical conditions negligible corrosion occurs even at low (¾ in.) depths of cover. It is concluded that the alkalinity produced by reaction of the slag with water restricts the extent of corrosion and that blastfurnace slag may be used satisfactorily as coarse aggregate in reinforced concrete. The work described forms a part of a programme which included tests of slag concretes without metal reinforcement, for compressive and transverse strength, sulphate resistance and dimensional stability. The results of these other tests are reported in a separate paper in the same issue.
Five‐Year Changes in Periodontal Disease Measures Among Postmenopausal Females: The Buffalo OsteoPerio Study
Authors: LaMonte Michael J. , Hovey Kathleen M. , Genco Robert J. , Millen Amy E. , Trevisan Maurizio , Wactawski‐Wende Jean 
Published: July 2012

Background: Understanding of longitudinal characteristics of periodontal disease in older females is limited. This study examined 5‐year changes in periodontal disease measures among postmenopausal females.Methods: Participants were 1,025 postmenopausal, 53‐ to 83‐year‐old females who completed baseline (1997 to 2001) and 5‐year follow‐up (2002 to 2006) whole‐mouth oral examinations in a study ancillary to the Women's Health Initiative. Periodontal disease was characterized using probing depth (PD), clinical attachment level (CAL), alveolar crest height (ACH), and tooth loss. Differences in measures between examinations were used to characterize patterns of change.Results: Baseline prevalence of none/mild, moderate, and severe periodontal disease defined using criteria of the Centers for Disease Control and Prevention was 27%, 58%, and 15%, respectively. Tooth loss attributable to periodontitis occurred in 13% of females. Mean ± SD changes in whole‐mouth mean measures showed progression when based on ACH (−0.19 ± 0.49 mm) yet relatively stable disease when based on PD (0.11 ± 0.42 mm) and CAL (0.06 ± 0.58 mm). Mean change in worst‐site ACH was greater (P <0.001) in females with severe periodontitis and osteoporosis at baseline and with tooth loss during follow‐up. Periodontal changes did not differ according to baseline age, hormone therapy use, smoking status, or age at menopause.Conclusions: Five‐year changes in periodontal measures among generally healthy postmenopausal females were, on average, small and did not suggest a consistent pattern of disease progression. Females with history of severe periodontitis or osteoporosis may experience accelerated oral bone loss despite stability or small improvement in routine probing measures.
Local Public Health Systems and the Incidence of Sexually Transmitted Diseases
Authors: Rodriguez Hector P. , Chen Jie , Owusu-Edusei Kwame , Suh Allen , Bekemeier Betty 
Published: July 2012

Objectives. We examined the associations of local public health system organization and local health department resources with county-level sexually transmitted disease (STD) incidence rates in large US health jurisdictions. Methods. We linked annual county STD incidence data (2005–2008) to local health department director responses (n = 211) to the 2006 wave of the National Longitudinal Study of Local Public Health Systems, the 2005 national Local Health Department Profile Survey, and the Area Resource File. We used nested mixed effects regression models to assess the relative contribution of local public health system organization, local health department financial and resource factors, and sociodemographic factors known to be associated with STD incidence to county-level (n = 307) STD incidence. Results. Jurisdictions with local governing boards had significantly lower county-level STD incidence. Local public health systems with comprehensive services where local health departments shoulder much of the effort had higher county-level STD rates than did conventional systems. Conclusions. More integration of system partners in local public health system activities, through governance and interorganizational arrangements, may reduce the incidence and burden of STDs.
Young Adults’ Favorable Perceptions of Snus, Dissolvable Tobacco Products, and Electronic Cigarettes: Findings From a Focus Group Study
Authors: Choi Kelvin , Fabian Lindsey , Mottey Neli , Corbett Amanda , Forster Jean 
Published: July 2012

Objectives. We explored young adults’ perceptions of snus (spitless moist snuff packed in porous bags), dissolvable tobacco products, and electronic cigarettes and intention to try these products. Methods. We conducted 11 focus group discussions involving a total of 66 young adults (18–26 years old) on these new tobacco products (e.g., harmfulness, potential as quit aids, intention to try) held between July and December 2010. We analyzed discussions using a thematic approach. Results. Participants generally reported positive perceptions of the new products, particularly because they came in flavors. Few negative perceptions were reported. Although some participants believed these products were less harmful than cigarettes and helpful in quitting smoking, others thought the opposite, particularly regarding electronic cigarettes. Participants also commented that these products could be gateways to cigarette smoking. Half of the participants, including a mix of smokers and nonsmokers, admitted they would try these products if offered by a friend. Conclusions. Young adults perceive the new tobacco products positively and are willing to experiment with them. Eliminating flavors in these products may reduce young adults’ intentions to try these products.