Moisture damage assessment using surface energy, bitumen stripping and the SATS moisture conditioning procedure

Durability is one of the most important properties of an asphalt mixture. A key factor affecting the durability of asphalt pavements is moisture damage. Moisture damage generally results in the loss of strength of the mixture due to two main mechanisms; the loss of adhesion between bitumen and aggregate and the loss of cohesion within the mixture. Conventional test methods for evaluating moisture damage include tests conducted on loose bitumen-coated aggregates and those conducted on compacted asphalt mixtures. The former test methods are simpler and less expensive to conduct but are qualitative/subjective in nature and do not consider cohesive failure while the latter, though more quantitative, are based on bulky mechanical test set-ups and therefore require expensive equipment. Both test methods are, however, empirical in nature thus requiring extensive experience to interpret/use their results. The rolling bottle test (RBT) (EN 12697-11) for loose aggregate mixtures and the saturation ageing tensile stiffness (SATS) test (EN 12697-45) for compacted asphalt mixtures are two such methods, which experience suggests, could clearly discriminate between ‘good’ and ‘poor’ performing mixtures in the laboratory. A more fundamental approach based on surface energy (SE) measurements offers promise to better understand moisture damage. This article looks at results from the rolling bottle and the SATS tests in an attempt to better understand the underlying processes and mechanisms of moisture damage with the help of SE measurements on the constituent bitumen and aggregates. For this work, a set of bitumens and typical acidic and basic aggregate types (granite and limestone) were selected. Combinations of these materials were assessed using both the rolling bottle and SATS tests. The SE properties of the binders were measured using a dynamic contact angle Analyser and those of the aggregates using a dynamic vapour sorption device. From these SE measurements it was possible to predict the relative performance of both the simple RBT and the more complicated SATS test. Mineralogical composition of the aggregates determined using a mineral liberation analyser was used to explain the differences in performance of the mixtures considered

Basic Methods for Computing Special Functions

This paper gives an overview of methods for the numerical evaluation of special functions, that is, the functions that arise in many problems from mathematical physics, engineering, probability theory, and other applied sciences. We consider in detail a selection of basic methods which are frequently used in the numerical evaluation of special functions: converging and asymptotic series, including Chebyshev expansions, linear recurrence relations, and numerical quadrature. Several other methods are available and some of these will be discussed in less detail. We give examples of recent software for special functions where these methods are used. We mention a list of new publications on computational aspects of special functions available on our website

Clays in circular simple shear apparatus

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An experimental investigation on mechanical behaviour of CO2 saturated coal specimens

To reduce the emission of CO into the atmosphere, it is proposed to store CO into deep coalbeds which may also enhance the production of naturally-stored methane from coal formations. Many studies have been reported investigating the effect of CO injection on the flow properties to provide a means of estimating the recoverable CH and storable CO. However, assessment of the long-term integrity of stored CO and the potentially damaging effects of CO on the mechanical response of coal have been largely neglected. Understanding the geomechanical response of coalbeds to CO injection can be crucial in site selection, in designing and planning coalbed geosequestration operations. To investigate the effects of CO adsorption on the mechanical strength and stiffness of coal specimens, a series of triaxial experiments have been undertaken. Over 40 core specimens of Australian black coal from the Sydney Basin have been tested. The behaviour of water-saturated and CO saturated specimens have been investigated at confining pressures up to 5.5 MPa at room temperature. Results showed that the strength and stiffness of CO saturated specimens are significantly less than those of water saturated specimens

Some observations on the interpretation of shearbox test results

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An evaluation of direct simple shear tests on clay

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The effect of the remoulded void ratio on unit shaft friction in small-displacement piles in chalk

Small-displacement pile driving in chalk produces an annulus of crushed and remoulded putty-like material through which shaft friction is believed to be mobilised. Ultimate shaft friction is assumed to be a function of the effective angle of friction of the putty chalk interface and the radial effective stress acting on the pile shaft. The mechanisms that affect the magnitude of the latter are not well understood. It is hypothesised that the stress levels attained during shaft friction mobilisation are related to the change in void ratio that takes place as structured chalk becomes crushed during pile installation. Therefore, a general notion exists that piles installed in dense chalks will mobilise larger shaft capacities than piles driven in more porous materials, and that this is related to the void ratio of the remoulded annulus. In this context, this paper presents the results of a series of monotonic constant volume simple shear tests conducted to assess the role of the void ratio in the mobilisation of shaft friction. Results suggest that void ratio is a controlling factor and that a state-based approach for the characterisation of void ratio-shaft friction relationships may be possible