ICE - Institution of Civil Engineers - Virtual Library

Aircrete, also known as autoclaved aerated concrete (AAC), was first produced in the UK in the 1950s. It is one of the lightest forms of concrete, and one of the most technically advanced materials used for the manufacture of mass-produced concrete blocks. It is manufactured in a range of densities from 400 to 800 kg/m³, making it considerably lighter than conventional aggregate concrete. Approximately 3 000 000 m³ of aircrete masonry units are now produced in the UK annually, representing about a third of all concrete masonry. The main benefit is that acoustic, energy conservation, fire resistance and structural properties are provided in one product. This briefing note explains the manufacture, design and application of aircrete masonry units. Innovative methods of construction have also been made possible as a result of modern manufacturing techniques, such as thin-layer mortar jointing and blocks with handholds in the block perpends.

This paper presents an experimental investigation into the withdrawal resistance of a new connector type for use in structural timber. The structural performance of several helically shaped metal fasteners, which for some years have been used as wall ties and in masonry repairs, are investigated for use in a variety of timber connection systems. This paper describes part of a research programme investigating the withdrawal resistance and behaviour of these fasteners compared with conventional nails. It also details the effects of predrilling, density of timber, depth of penetration and timber grain orientation on the withdrawal resistance of these fasteners. The results show that helically shaped metal connectors achieve greater withdrawal resistance and exhibit a more ductile behaviour than common nails. A semi-empirical model is developed to predict the withdrawal performance of the fasteners.

The friction transfer method described in this paper can be used to estimate the in situ shear strength of bituminous pavement layers. In this method a specially devised apparatus fits on the top of the partial core and is clamped to it. A torque is applied using an ordinary torquemeter, and the maximum shear stress at failure is calculated. Comparative studies of laboratory Marshall stability and friction transfer tests produced correlation coefficients of 0·72 and 0·82 for linear and polynomial best-fit curves respectively, and the respective linear correlation coefficient for the in situ tests was found to be 0·84. The measured values for Marshall and friction transfer tests ranged from 750 to 1100 kg and from 1·2 to 1·8N/mm² respectively. The average coefficients of variation of eight series of experiments were found to be 11·07% for Marshall stability tests and 11·39% for the friction transfer method. Based on the laboratory and site experiments, and considering such factors as versatility, simplicity, speed, applicability under any site conditions by untrained operators, very low cost, easily interpreted and understood results, and good accuracy, this new method is strongly recommended for the assessment of the in situ shear strength of bituminous materials.

This paper investigates the significant curling that occurs during drying of crushed basaltic aggregate stabilised with cementitious binders. The percentage of cement (by weight) is 3%, producing stabilised materials, which are weakly cemented. These materials are commonly used in the pavement industry for constructing cement-stabilised pavements for light to medium traffic. Curling deformations, in the form of lifting off from the edges (generating a concave surface), or lifting off from the middle (creating a convex surface), are reported in drying concrete pavements. The test specimens had cross-sections measuring 75 mm × 75 mm and length of 280 mm. This paper presents experimental observations of differences in shrinkage behaviour of stabilised crushed rock drying from one or all faces (i.e. one- or three-dimensional conditions) under controlled conditions. A theoretical explanation for the perceived curling is presented on the basis of physical principles and unsaturated soil mechanics. The curling was attributed primarily to differential shrinkage strain increments that occur within the specimen and their variation with the progression of desiccation. Making use of non-linear elasticity theory, the shrinkage and curling behaviour was modelled using the finite-difference method.

Most of the reported work on creep of high-strength concrete (HSC) covers measurements of total creep on standard specimens kept in a standard environment of 50% relative humidity and 23 °C. The results of these studies are used to establish the basic creep factor of high-strength concrete, assuming that the environmental effect on creep of HSC is similar to that for normal-strength concrete (NSC). However, some recent work has shown that the effect of the environment on creep of HSC is different from that observed for NSC, which indicates that a realistic creep model for HSC needs to be developed based on more fundamental material behaviour. This paper reports a theoretical study of a composite model for predicting basic creep of concrete, considering it as a composite material of coarse aggregate, fine aggregate and cement paste. The model is based on the age-adjusted effective modulus method proposed by Bazant, and can take into account the composition of the concrete, the degree of compaction and the hydration of cement paste. The model is shown to predict basic creep measurements reported in the literature with reasonable accuracy.

Considering the increasing use of alternative fuels and raw materials in clinker manufacture for construction, the environmental behaviour of the resulting cement is a matter of particular concern. As the alternative fuels used in cement manufacture may contain elements not generally found in conventional fuels, this necessitates a study of the leaching performance of cements produced in such processes to evaluate the environmental quality of the final product and guarantee its safe use in construction. The present survey was undertaken to analyse the leaching of heavy metals and other elements from cements manufactured with both conventional and alternative fuels. The results suggest that the controlled use of alternative fuels does not affect the leaching behaviour.