bluuebunny/crossref_metadata_2025_split huggingface dataset:
Workability of flowing concrete
Authors: Banfill P. F. G. 
Published: October 2009

Synopsis By using the two-point test for workability, the effect of concentration of superplasticizing admixture upon workability has been found to be independent of the types of admixture and cement, Differences in the effects of proprietary admixtures are due to their different solids contents. The yield value of concrete decreases to a minimum, beyond which further additions of admixture promote segregation. Loss of workability is not necessarily more rapid in flowing concrete, and re-dosing enables workability to be maintained for more than 160 minutes without detriment the hardened strength. The melamine formaldehyde admixture caused more rapid workability loss than the naphthalene formaldehyde admixture tested, but a specific interaction between the former and a cement of low C3A/SO4 ratio was found. An acceptance criterion for flowing concrete is proposed.
Rigid–plastic theory v. truss analogy method for calculating the shear strength of reinforced concrete beams
Authors: Campbell T. I. , Chitnuyanondh L. , de V Batchelor B. 
Published: October 2009

Synopsis A comparison is made between the web crushing strengths of reinforced concrete beams predicted by a model based on the theory of plasticity and by a variable-angle truss model. The theory of plasticity model assumes rigid–plastic behaviour of the constituent materials, whereas the variable-angle truss model incorporates their actual stress–strain characteristics. It is shown that neglect of the deformations in the web steel prior to yielding and in the concrete prior to crushing leads to a high prediction for both the amount of web reinforcement required for a balanced section and the ultimate capacity of a section which is over-reinforced for shear. However, both approaches yield the same capacity for a section which is under-reinforced for shear.
The practical use of ultrasonic pulse velocity measurements in the assessment of concrete quality
Authors: Tomsett H. N. 
Published: October 2009

Synopsis The wider use of limit-state methods for the design of structures has increased the desirability of being able to assess the quality of a structure as built rather than isolated test pieces of the material supplied. Ultrasonic pulse velocity measurements are a particularly suitable way to measure the quality of a concrete structure, although the importance of competent engineering judgement in their analysis must be properly stressed. This paper indicates some ways in which the pattern of pulse velocity measurements may be used to assess the quality of concrete construction. The suggested patterns have been derived by applying the fundamental relationships, obtained by research, to site surveys and assessing the deviations permissible before the variations from the normal indicate a defect of engineering significance. The comparative evaluation of structural strength is also discussed.
The point-load strength test for concrete cores
Authors: Robins P. J. 
Published: October 2009

Synopsis The point-load test, commonly used in geotechnical practice, is evaluated for application in concrete testing. The method uses portable equipment to test concrete cores which require no further preparation after removal from the structure. This paper examines the results of a laboratory investigation in which over 450 cores were cut and tested. The influence of specimen and aggregate size, core-length/diameter ratio, and aggregate type upon point-load strengths is examined, and minimum values for the length/diameter and diameter/aggregate-size ratios are proposed. For concrete strengths greater than 20 N/mm2 a linear relationship between core point-load index and cube compressive strength was observed, and the variability of the point-load strengths compared favourably with values reported for compressive testing of cores. The advantages of both the point-load test and the uniaxial compression test for cores are discussed, and it is argued that, provided a satisfactory method can be found for estimating the effect of the coarse aggregate type upon the point-load strength index, this simple test offers a practical alternative to the compressive testing of cores.
Behaviour in shear of beams with flexural cracks
Authors: Hamadi Y. D. , Regan P. E. 
Published: October 2009

Synopsis The paper aims to clarify the way in which a reinforced concrete beam with a plain web resists shear, with particular reference to the transfer of shear forces across jkxural cracks by the action known as ‘aggregate interlock’ or ‘interface shear’. Tests were made on special specimens to study the interlock phenomonen and dowel action in isolation and on ordinary rectangular reinforced concrete beams without web reinforcement. Measurements of movements at cracks in all the tests enabled the distributions of forces at cracked sections to be estimated. From the information obtained in this way, a rational equation is developed for the prediction of diagonal tension strength. The study was made using three different aggregates – a natural gravel, and two types of lightweight aggregate.
Influence of loading history upon the compressive properties of concrete
Authors: Cook D. J. , Chindaprasirt P. 
Published: October 2009

Synopsis The influence of sustained and cyclic load histories upon the compressive properties of concrete, mortar and paste are reported. It is shown that the effects of a sustained load produce asmall increase in strength and a relatively large increase in stifiess, whereas cyclic loading results in a small decrease in strength and a relatively large decrease in stifiess. Both load histories decrease the strain at peak stress on reloading. It is proposed that sustained loads result in redistribution of stress concentrations in the cement paste and consolidation in the gel. Cyclic loads, on the other hand, produce limited microcracking. The hypothesis is supported by the substantially greater damage observed in the specimens subjected to a cyclic load and the higher specific creep, which other researchers have shown to be largely irrecoverable.
Bond stress along lapped reinforcing bars
Authors: Tepfers Ralejs 
Published: October 2009

Synopsis The state of stress along a lapped splice in reinforced concrete can be determined by using the modulus of displacement theory. The theory is based on actual displacement or local deformations in the bond zone near the surface of the reinforcement. The stresses along the anchorage length can also be estimated with moment cracks taken into account. Special attention must be paid to cracks in the cover along the reinforcement. In practice, however, the simpler equations with the concrete acting just as an adhesive between the lapped bars gives reasonable results. By using this theory, formulae can also be evaluated for other types of bond anchorage.
Assessing the strength of in situ Portland cement concrete by internal fracture tests
Authors: Chabowski A. J. , Bryden-Smith D. W. 
Published: October 2009

Synopsis The results of a programme of about 1500 internal fructure tests performed on ordinary Portland cement concrete to assess its compressive strength are reported. The influence of the type and size of uggregate upon the test results is examined as well as the effect of precompression of the concrete. The variability of the data was assessed statistically to derive relationships between the results of internal fructure tests, i.e. the indicated maximum torques and cube strength US a basis for estimating the compressive strength of in situ concrete. Considerations affecting the use of internal fracture tests as a means of assessing the strength of concrete in structures in service are briefly discussed.
The flexural strength of concrete blockwork
Authors: de Vekey R. C. , West H. W. H. 
Published: October 2009

Synopsis The results of a large number of flexural strength tests on wallettes (small masonry panels for testing) made with a range of commercially available concrete blocks are reported. The relationships between the performance of the wallettes and several properties of the block were investigated as a possible basis for a table of characteristic flexural strength values in BS 5628: Part 1: 1978, ‘the Code of Practice for Structural use of masonry’. In general, the basis chosen, compressive strength, and the levels set in the Code are satisfactory but the margins of safety may be lower for masonry made with some types of blocks and for thicker walls. Interim results for full-size walls are also given which confirm the trends indicated by the tests on wallettes.
Analysis of fresh concrete: determination of cement content by the Rapid Analysis Machine
Authors: Dhir Ravindra K. , Munday John G. L. , Ho Nyok Yong 
Published: October 2009

Synopsis The effects of several practical aspects of Rapid Analysis Machine (RAM) testing of freshly mixed concrete for its cement content are described. It is demonstrated that the RAM is capable of giving sufficiently reliable results, provided it is properly maintained throughout and used with care by a trained person. The repeatability of the RAM results was found to be better than that of results from the current BS 1881 test for analysis of fresh concrete. The RAM results are also less variable than the conventional 28 day strength results.
Bending–torsion interaction for concrete beams reinforced with steel fibres
Authors: Mansur M. A. 
Published: October 2009

Synopsis Results from an experimental investigation on steel-fibre-reinforced concrete beams under combined bending and torsion are presented, the principal variables being depth of beam and torsion to moment ratio. On the basis of the observed skew-bending mechanism of torsional failure, equations are derived for ultimate torque. The test results are then compared with the theoretical predictions. The proposed method gives good predictions of the ultimate torque and interaction behaviour of beams under combined bending and torsion.
The anchorage capacity of reinforcing bars at normal and high temperatures
Authors: Hertz Kristian 
Published: October 2009

Synopsis The anchorage failure of reinforcing bars is analysed, and it is shown that two modes of failures are possible: splitting or bond failure. It is concluded that the anchorage capacity cannot be estimated by means of a standard specimen, since splitting failure is dependent upon the geometry of the cross-section. A simple method for calculating the resistance to splitting is proposed, and a test method for determining the bond strength is presented. Test results are shown from a series of 280 specimens exposed to various maximum temperatures, and a relation between the bond strength and the ultimate limit stress of concrete under plane strain conditions is indicated. The influence of high temperatures upon the anchorage resistance is explained, and the theory is illustrated by examples.
Some properties of concrete containing sintered domestic refuse as a coarse aggregate
Authors: Wainwright P. J. , Boni S. P. K. 
Published: October 2009

Synopsis An artificia1 aggregate has been produced by pelletizing and firing the residues collected from incinerators used to burn domestic refuse. Tests on concretes made with this material as a coarse aggregate have been carried out forperiods of up to 4% years. The properties tested include compressive and tensile strength, modulus of elasticity, shrinkage and creep. The results so far obtained would appear to indicate that, under laboratory conditions, the material performs in a satisfactory manner. Although the material is not commercially available at the moment, it may be possible to produce it at a cost which would make it no more expensive than many lightweight aggregates currently on the market.
Tests on superplasticizing admixtures for concrete
Authors: Roberts M. H. , Adderson B. W. 
Published: October 2009

Synopsis The performance in concrete of nine commercial superplasticizing admixtures has been examined by using a particular test procedure to evaluate their performance and to provide comparative data on their effects. All the superplasticizers were observed to have an appreciable fluidifying action in fresh concrete so that, under appropriate conditions, they either considerably improved its workability at normal water content or permitted a water reduction of at least 10% to be made while maintaining normal workability. For very-high-workability concrete deficient in fine material, or with exceptionally high additions of superplasticizer, excessive bleeding and segregation of the fresh concrete occurred, resulting in its rejection. Some superplasticizers also tended to increase the air content of concrete and/or to have a retarding influence upon its setting and hardening characteristics; these effects produced a reduction in compressive strength in some circumstances. For water-reduced superplasticized concretes with air contents below 3%, the compressive strength values obtained at ages from 7 days to 2 years exceeded those to be expected from water reduction alone. Concretes containing super-plasticizers and with appropriate entrained air contents showed a high resistance to freezing-and-thawing actions under wet conditions.
The electrical response characteristics of setting cement paste
Authors: McCarter W. J. , Curran P. N. 
Published: October 2009

Synopsis The objective of the work presented in this paper is to investigate the changes in the electrical properties of cement paste during the first 24 hours after gauging with water. It is demonstrated that the electrical response characteristics of setting cement paste can be used as an effective means of studying the progress of cement hydration and for monitoring structuralchanges occurring within the paste
Radial temperature distributions within solid concrete cylinders under transient thermal states
Authors: Khoury Gabriel A. , Sullivan Patrick J. E. , Grainger Brian N. 
Published: October 2009

Synopsis Radial temperature gradients develop within typical concrete test cylinders during heating and can introduce structural effects which distort the material strain response of the concrete. Analytical solution of the Fourier equation, assuming infinite specimen length and invariable material properties, indicates that the maximum radial temperature difference (ΔT) obtained during heating at constant rates is directly proportional to the rate of heating and the square of the radius, and inversely related to the thermal diffusivity. A finite difference solution for a specimen heated on all sides confirms these relationships and indicates that the temperature at the centre is unaffected by end heating for a specimen length/diameter ratio greater than 1–1·5 during heating at 1°C/min. This is confirmed experimentally for gravel and lightweight concrete specimens. The effect of variations in thermal diffusively is to cause two peaks in the ΔT versus surface temperature relationship at about 160°C and 550°C corresponding to the processes of moisture loss and dissociation of Ca(OH)2 respectively. A weighted average temperature was calculated which suggests that the most suitable location to place a thermocouple to measure the average specimen temperature is at 58% of the radius. Radial temperature dlfferentials can be minimized by reducing the rate of heating and particularly the radius of the specimen. They can also be estimated by a simple relationship which, if used in conjunction with the specific test technique reported here, can provide an evaluation of the thermal diffusivity of materials.
Fracture toughness testing by means of the compact compression test specimen
Authors: Barr B. I. G. , Sabir B. B. 
Published: October 2009

Synopsis The paper describes an experimental and numerical study of the compact compression test specimen for determining the fracture toughness of concrete. A range of cubes and prisms was used in the study and the best results were achieved by means of the double-notched 100 mm and 150 mm cubes. The fracture toughness of the concrete used in the study was 0·5 MN/m3/2 and the results were shown to be independent of the test specimen geometry.
New technique for determining the electrical resistivity of concrete
Authors: Hughes B. P. , Soleit A. K. O. , Brierley R. W. 
Published: October 2009

Synopsis An improved method for measuring the electrical resistivity of concrete has been developed which eliminates difficulties due to polarization efsects and capacitive reactance. Typical results for fresh and hardened concrete obtained with the proposed technique are also presented and compared with results using more conventional techniques
Mathematical models for dowel action under monotonic and cyclic conditions
Authors: Vintzēleou E. N. , Tassios T. P. 
Published: October 2009

Synopsis On the basis of physical models describing the behaviour of dowels embedded in concrete, formulae for the prediction of dowel strength under monotonic actions are derived. In addition, formulae for calculating transverse displacements corresponding to the dowel strength are given. Theoretical values of dowel strength calculated according to equations given in this paper are compared with experimental dowel strengths reported in the literature. It is found that the proposed formulae give good predictions for both failure mechanisms (concrete crushing and yield of the bar or concrete splitting). Additionally, a formalistic model for full displacement reversals, based on the results of an experimental programme, is proposed.
Durability tests on building mortars — effect of sand grading
Authors: Harrison W. H. 
Published: October 2009

Synopsis Results are reported on a laboratory investigation into the properties and performance of mortar under simulated severe exposure, Six different sands varying from very coarse to very fine were used in OPC mortars plasticised either with lime or an air-entraining agent. Test specimens were produced by laying mortar between either wet or dry bricks and then removing the mortar bed after 24 hours. The properties of the fresh and the hardened mortar were measured. In the new durability test small pieces cut from the mortar bed were subjected to 25 wet/dry cycles. Freeze/thaw was introduced to the cycle for some of the specimens and some were subjected to wetting with sulphate solution. The results show the effect of sand grading and brick suction on the properties of the mortar and its durability. Mortars subject to little or no suction from the bricks when layed showed poorer strength and lower durability than those subject to suction. The sulphate resistance did not appear to be related to the grading of the sand used in the mortar although for many of the mixes the strength and frost resistance was reduced with the more finely graded sands.
Symmetric punching of reinforced concrete slabs
Authors: Regan P. E. 
Published: October 2009

Synopsis The paper reports punching tests on 28 reinforced concrete slabs. The tests were divided into five series primarily concerned with the effects of the arrangement of flexural reinforcement, absolute size or depth, concrete strength and ratio of reinforcement, boundary restraint and the size of the loaded area. The results are compared with the predictions of four Codes of Practice-BS 8110, CP 110, ACI 318-83 and the CEB-FIP Model Code. In regard to BS 8110 it is demonstrated that the Code generally gives a small scatter of the ratio of calculated and experimental strengths, although its method of defining the ratio of flexural reinforcement is inferior to that of CP 110. It is also shown that BS 8110 does not achieve the level of safety intended in the definition of characteristic strength. If the ddefinition of the ratio of reinforcement were improved, the intended level of safety could be attained by a 10% reduction in either the basic shear stress or the size factor ξS.
Effect of exposure time and rates of heating and cooling on residual strength of heated concrete
Authors: Mohamedbhai G. T. G. 
Published: October 2009

Synopsis The paper describes tests on 100 mm concrete cubes heated to temperatures in the range of 200–800°C to determine the effect of varying time of exposure and rates of heating and cooling on the residual compressive strength of concrete. These variables were found to have a significant effect on concrete heated to the lower range of temperatures but their effect became less pronounced at high temperatures. Almost all the loss of compressive strength occurred within two hours of exposure to the maximum temperature. Pulse velocity measurements did not predict the residual strengths accurately and appeared to be more indicative of the levels of temperature to which the concrete had been exposed.
Relationship between strength and volumetric composition of moist-cured cellular concrete
Authors: Tam C. T. , Lim T. Y. , Sri Ravindrarajah R. , Lee S. L. 
Published: October 2009

Synopsis The effect of the volumetric composition of cellular concrete, particularly water and air voids, on its compressive strength has been demonstrated to follow Feret's general formula. The increase in strength at all ages with a corresponding increase in water/cement ratio (opposite to that of mortar mixes) as obtained in the experiment has been shown to be consistent with Feret's formula. The inclusion of the degree of hydration in the modified form of Power's gel/space ratio further improves the correlation with strength when this is taken as the parameter.
An investigation of the pozzolanicity and hydraulic reactivity of a high-lime fly ash
Authors: Papayianni Joanna 
Published: October 2009

Synopsis Lignite fly ashes (LFA) often have self-cementing as well as pozzolanic properties, due to their high lime content. LFA is compatible with Portlandcement and can replace a significant percentage of cement in concrete in order to save energy and reduce costs. The properties of LFA, ground to highlight its hydraulic properties, have been investigated by means of strength and other tests on mortars and pastes, with various levels of replacement of OPC by LFA. Analysis by X-ray diffraction, differential thermal analysis-thermogravimetry and electron microscope-selected area electron diffraction methods indicated that the strength of OPC/LFA mortars is due to compounds of C-S-H gel formed by the reaction of free lime with silica, and from the hydration of dicalcium silicate which may exist in LFA. The early strength is attributed to hydrated calcium aluminate compounds and ettringite.
A simplified non-linear analysis of concrete frames
Authors: Pulmano V. A. , Bakoss S. L. , Shin Y. S. 
Published: October 2009

Synopsis This paper presents a simplified method for the analysis of reinforced concrete frames subjected to sustained service loads. The finite element model used takes into account the non-linearities due to cracking and the time-dependent effects due to creep and shrinkage. It is based on methods widely used by designers at present to analyse short-term linear behaviour. The method is suitable for implementation on microcomputers for applications in the design of medium-rise reinforced concrete frames. Predictions of the behaviour of laboratory-tested frames are shown to be in good agreement with measured values.
The relationship between permeability coefficients for concrete obtained using liquid and gas
Authors: Bamforth P. B. 
Published: October 2009

Synopsis Tests have been carried out on four concretes to measure their permeability coeficient using both water and nitrogen. In every case the gas permeability was significantly higher than the water permeability, the dlference increasing as the permeability reduced. The theory of gas slippage, first reported in 1875 and subsequently studied in relation to oil sands in 1941, has been identified as a major reason for the recorded differences betweeri the water and gas permeability coefficients for concrete. An equation relating water and gas permeability has been derived for mature, sealed-cured concrete, which takes into account the mean absolute pressure used for gas permeability measurement. This can be used to adjust gas permeability results to give a reasonable approximation of the intrinsic permeability of the concrete.