Showing papers in "Magazine of Concrete Research in 1987"
TL;DR: In this article, the effects of using crushed concrete as coarse and fine aggregates upon strength and deformation of concrete are reported, and the results show that strength and modulus of elasticity are reduced by about 10% and 35%, respectively, whereas drying shrinkage is nearly doubled when recycled aggregates are used instead of natural aggregates in comparable mixes.
Abstract: Synopsis The effects of using crushed concrete as coarse and fine aggregates upon strength and deformation of concrete are reported. The properties of recycled aggregates differ from those of natural aggregates due to the presence of a considerable proportion of mortar attached natural aggregate and loose mortar. For a medium strength concrete, the results show that strength and modulus of elasticity are reduced by about 10% and 35%, respectively, whereas drying shrinkage is nearly doubled when recycled aggregates are used instead of natural aggregates in comparable mixes. The efect of recycledfine aggregate on the deformational properties is less than that of coarse aggregate. Fresh concrete properties are only marginally affected by the use of recycled aggregates.
141 citations
TL;DR: In this article, an analytical approach for predicting the shear and moment capacity of reinforced steel-fibre-concrete (RSFC) beams is proposed, which allows for direct comparison between the efectiveness of stirrups and fibres.
Abstract: Synopsis An analytical approach for predicting the shear and moment capacity of reinforced steel-fibre-concrete (RSFC) beams is proposed. Recent plasticity analyses for shear capacity of reinforced concrete beams are extended to RSFC beams by including the contribution of the fibres. Moment capacity is derived using the usual sectional analysis and fully plasticized stress blocks and forces. By establishing relevant capacities for a given beam loaded over a range of span/depth ratios, the capacity and governing mode of failure can be predicted. The observed failure loads and modes of failure for 22 test beams agree well with the predictions. Data presented in the literature are also analysed and compared. The present approach allows for direct comparison between the efectiveness of stirrups and fibres as shear reinforcement. The results suggest that fibres can replace stirrups partially or wholly as long as parity in the shear reinforcement factor is maintained.
138 citations
TL;DR: In this paper, tests have been carried out on four concretes to measure their permeability coeficient using both water and nitrogen, and in every case the gas permeability was significantly higher than the water permeability.
Abstract: 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 w...
130 citations
TL;DR: In this paper, the authors used the British Standard initial surface absorption test (ISAT), Figg hypodermic methods (air and water), and a new test, the covercrete absorption test, to study the permeation properties of the near surface of concrete.
Abstract: Synopsis The British Standard initial surface absorption test (ISAT), Figg hypodermic methods (air and water), and a new test, the covercrete absorption test (CAT), have been used to study the permeation properties of the near-surface of concrete. The test methods are critically appraised. It is shown that the moisture condition of the concrete can greatly alter the results obtained. Data on the surface quality of concrete and its dependence on mix proportions and degree of moist curing are presented.
93 citations
TL;DR: 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.
Abstract: 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.
65 citations
TL;DR: In this article, a design method is suggested for evaluating the punching shear strength of fiber-reinforced concrete slabs, and the predictions obtained bythe suggested method are shown to be satisfactory by comparing them with the values observed in the tests carried out by the authors and previous investigators.
Abstract: Synopsis Investigations of the behaviour and strength characteristics of steel-Jihre-reinforced micro-concrete slabs subjected to punching shear are presented and discussed. A total of 12 simply-supported square slabs were tested. The parameters varied were the volume fraction of the fibres, the amount of tensile reinforcement and the concrete strength. The test results confirm that an increase infibre content improved the shear strength of the slabs; the position of the critical shear perimeter around the loaded area was also influenced by the fibre content. Based on these tests, a design method is suggested for evaluating the punching shear strength of fibre-reinforced concrete slabs. The predictions obtained bythe suggested method are shown to be satisfactory by comparing them with the values observed in the tests carried out by the authors and previous investigators.
64 citations
TL;DR: In this paper, the authors studied the mechanism of shear failure in reinforced concrete beams by using a high speed tape recorder in conjunction with electrical demountable strain transducers and related to the load history approaching failure.
Abstract: Synopsis The mechanism of shear failure in reinforced concrete beams was studied. Crackwidths at critical locations in the shear span were monitored continuously by means of a high speed tape recorder in conjunction with electrical demountable strain transducers and related to the load history approaching failure. It is shown that beam failure is preceded by splitting at the level of the steel; this is identijied to be the primary cause ofshear failure for slender beams. Further tests are described on beams where this splitting is prevented by the presence of links. In these tests, a diflerent failure mechanism isobserved with SignlJcant increase in shear capacity. The implications of theseJindings ondesign methods in codes of practice are discussed.
46 citations
TL;DR: In this article, 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.
Abstract: 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.
19 citations
TL;DR: The paper reviews the published test data and describes a series of tests on beams, both with and without shear reinforcement, concluded that the code provisions are unnecessarily conservative.
Abstract: Synopsis Provisions for the use of structural lightweight aggregate concrete are included in British codes of practice but limitations are applied to the design values that may be used This paper is concerned with the strength in shear, which is limited in the codes to 80% of that for normal-weight concrete of the same compressive strength The paper reviews the published test data and describes a series of tests on beams, both with and without shear reinforcement On the basis of the review and the tests it is concluded that the code provisions are unnecessarily conservative
18 citations
TL;DR: In this paper, the authors used the time shift principle coupled with the Arrhenius temperature dependence to obtain an overall power law relationship between creep strain and equivalent time, which enables the formulation of an extrapolation technique for basic creep strains in situations where there are time or temperature constraints on experimentation.
Abstract: Synopsis Arrhenius rate theory is used to describe the temperature dependence of basic creep of hardened cement paste, within certain temperature limits. The time shift principle is coupled with this Arrhenius temperature dependence to obtain an overall power law relationship between creep strain and equivalent time (which accounts for both temperature and time dependence). This enables the formulation of an extrapolation technique for basic creep strains in situations where there are time or temperature constraints on experimentation. Two distinct values of activation energy corresponding to two different temperature ranges, are used to arrive at possible creep mechanisms that would operate in each of these ranges.
8 citations
TL;DR: In this article, a definition for basic creep at elevated temperatures is arrived at, based on the time at which load is applied, and experimental results are presented for the basic creep of hardened cement paste and comparisons with the behaviour of various concretes.
Abstract: Synopsis A definition for basic creep at elevated temperatures is arrived at, based on the time at which load is applied. Experimental results are presented for the basic creep of hardened cement paste and comparisons are made with the behaviour of various concretes. The time function of basic creep is shown to follow a power law relationship, whereas the temperature function indicates that a rheological property, seated in the cement paste itself, would limit the structural usefulness of Portland cement-based concretes to below 600°C. Preheating to temperatures higher than the creep test temperature reduces the creep potential in general.
TL;DR: In this article, the basic bond mechanism for reinforcing bars in concrete under external pressure is considered and an existing partly cracked elastic theory for bond resistance is extended to cover both uniform and non-uniform distributions of external pressure.
Abstract: Synopsis The basic bond mechanism for reinforcing bars in concrete under external pressure is considered and an existing partly cracked elastic theory for bond resistance is extended to cover both uniform and non-uniform distributions of external pressure. Results obtained from this theory are compared with experimental results at various stages of bond failure. The prediction of pull-out force at 0·1 mm free-end slip is found to be satisfactory.
TL;DR: In this article, a three-dimensional finite element analysis is used to study the stress distribution at working stress levels in masonry constructed of hollow concrete blocks, and the stress analysis is performed by using three dimensional finite element.
Abstract: Synopsis Three-dimensional finite element analysis is used to study the stress distribution at working stress levels in masonry constructed of hollow concrete blocks. The stress analysis is perform...
TL;DR: In this paper, the tensile strain capacity of concretes with densities between 1200 and 2300 kg/m3 was determined by means of a short-term stressing technique.
Abstract: Synopsis The tensile strain capacities of concretes with densities between 1200 and 2300 kg/m3 are determined by means of a short-term stressing technique. The thermal strain capacity of lightweight aggregate concrete is up to 2½ times greater than that of flint gravel concrete of similar workability and strength. Lightweight aggregate concretes also have lower coeficients of thermal expansion and reach slightly higher maximum temperatures due to hydration. It is demonstrated that the main influencing parameter on tensile strain capacity is the strengthlelastic modulus ratio.
TL;DR: In this paper, the use of embedment strain gauges encapsulated in acrylic resin for the measurement of internal concrete strain distributions is described, and results are presented to illustrate the performance of the technique.
Abstract: Synopsis The use of embedment strain gauges—electric resistance strain gauges encapsulated in acrylic resin—for the measurement of internal concrete strain distributions infive tension specimens is described. Results are presented to illustrate the performance of the technique.
TL;DR: In this article, the fitting and use of a pressure transducer system capable of measuring, recording and analysing the oil pressure was described, and results obtained using the pressure gauge and the pressure transducers indicate that operator experience in combination with mix workability has some influence upon the accuracy of the gauge readings, and this underlines the substantial benefits of the proposed system.
Abstract: Synopsis Large fluctuations in the oil pressure within the twopoint apparatus during concrete testing make any reading of the pressure gauge open to operator bias. This paper details the fitting and use of a pressure transducer system capable of measuring, recording and analysing the oil pressure. Results obtained using the pressure gauge and the pressure transducer indicate that operator experience in Combination with mix workability has some influence upon the accuracy of the gauge readings, and this underlines the substantial benefits of the proposed system.
TL;DR: In this article, the typical geometry and mortaring practice of conventional concrete blocks with two hollow cores are described. But, the typical geometrical and mortared practice is not followed.
Abstract: Synopsis Concrete blocks with two hollow cores are commonly used in load-bearing walls. Many variations on this basic type of unit are produced. However, the typical geometry and mortaring practice...
TL;DR: In this paper, the first cracks appeared at the inverts of the voids in a concrete slabs containing longitudinal circular voids and a complex stress pattern occurs and cracks appear.
Abstract: Synopsis When concrete slabs containing longitudinal circular voids are subjected to transverse bending, a complex stress pattern occurs and the first cracks appear at the inverts of the voids. If ...
TL;DR: In this article, a simplified method for the analysis of reinforced concrete frames subjected to sustained service loads is presented, which takes into account the non-linearities due to cracking and the time-dependent effects due to creep and shrinkage.
Abstract: 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.
TL;DR: In this article, the optimum SO3, content of the plain cement mixes in the presence of the fly ash was found to be close to that of the as-received cements, it is suggested that, where large volumes of a concrete containing fly ash and admixture are to be produced, it may he worthwhile determining the optimum So3, con tent of the particular mix, to assess whether adjusting the SO3 content of mix at the batching plant may be cost and energy-efficient.
Abstract: Synopsis Earlier studies of the optimum SO3, contents of cements in the presence of chemical admixtures have been extended to mixes containing cement (both OPC and SRPC), sub-bituminous high-lime fly ash and water-reducing admixture. The hydration character istics have been studied by means of conduction calor imetry; and measurements of the compressive strength of mortars up to 56 days have been used to assess optimum SO3, contents. The optimum SO3, content of the plain cement mixes in the presence of the admixture was 1% higher than the as-received cement. The optimum SO3, content of the cement/fly ash/admixture mixes was found to be close to that of the as-received cements, It is suggested that, where large volumes of a concrete containingjy ash and admixture are to be produced, it may he worthwhile determining the optimum SO3, con tent of the particular mix, to assess whether adjusting the SO3, content of the mix at the batching plant may be cost and energy-efective.
TL;DR: In this article, the authors analyzed the deflection of reinforced concrete beams under load to verify that shear deformation of the adhesive layer between the concrete beam and its steel reinforcing plate does not cause an unacceptable loss of structural interaction.
Abstract: Synopsis The deflections of open-sandwich, reinforced concrete beams under load are analysed to verifv that shear deformation of the adhesive layer between the concrete beam and its steel reinforcing plate does not cause an unacceptable loss of structural interaction. The cumulative effect of the shear deformation, i.e. the ‘shear displacement’, is loosely analogous to the slip of steel bars in a conventionally reinforced concrete beam. The partial interaction theory introduced by Newmark et al and extended by Goodman and Popov and others is further extended to include thermal expansions, cracked concrete, and unsymmetrical loading. The accuracy of the resulting analysis is assessed by comparisons with finite element predictions and with experimental results. It is found that thin layers of adhesives with a large shear modulus are preferable from an in-service structural point of view. They lead to small shear displacements and to good control of the influence of flexural cracks.
TL;DR: A study of the concrete showed that it was made with limestone aggregate, and laboratory experiments with limestone and non-calcareous aggregates, and concretes made with them, showed that the limestone was the primary caus... as discussed by the authors.
Abstract: Synopsis Spillage of molten aluminium onto the concrete floor of the Bone Island Aluminium Smelters in Queensland, Australia has caused several serious fires which have decomposed the floor and sometimes partially melted the pot assembly, resulting in enormous repair costs and delays in production. A study of the concrete showed that it was made with limestone aggregate. The molten aluminium at about 1050°C formed ponds about 2 m in diameter and 200 mm deep. It decomposed the limestone and produced CO2 gas which was reduced by the molten aluminium to CO gas which ignited. This strongly exothermic reaction produced further heat and melted the reinforcing bars in the concrete. The moisture in the concrete formed steam and agitated the system so that the molten metal was more efectively in contact with the concrete and caused further decomposition of the limestone. Laboratory experiments with limestone and non-calcareous aggregates, and concretes made with them, showed that the limestone was the primary caus...