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Determination of adhesion in bitumen-mineral systems by heat-of-immersion calorimetry

I. The effect of crude oil source on adhesive performance

Journal of Thermal Analysis and Calorimetry
Authors: D. V. Nowell and M. W. Powell

Chemical factors influencing bitumen-mineral adhesion have been examined by heat-of-immersion calorimetry. Two chosen minerals (quartz and calcite) and bitumen derived from Venezuelan and Middle East crude oils were characterised and the energy released by the bitumen-mineral interaction measured. Heat-of-immersion data are correlated with the concentration of heteroatomic species present in the bitumen and the structure of the mineral surfaces. Bitumen-quartz bonding is promoted by the presence of basic species in the bitumen and bitumen-calcite adhesion is favoured by the presence of acidic groups. A mechanism is proposed to account for the observed bond energies.

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Abstract  

The stability of Supersulphated Cement (SSC) is investigated at 95°C when subjected to relative humidities of 100, 53 and 11% of water vapour. Previously [1] investigations at 25, 50, 75°C under the same conditions of humidity reported the stability of ettringite, one of the initial hydration products. At 95°C, decomposition of ettringite, is found at all humidities and is rapid at 100% relative humidity. The hydration products of cement pastes at a water cement ratio of 0.27 were determined by thermogravimetry (TG) and X-ray diffraction (XRD). The formation of the hydragarnet, plazolite is recorded during the decomposition/dehydration process enhanced by possible carbonation. Rehydration studies on the products after storage for up to 9 months were carried out using distilled water and the samples tested for ettringite content. It is concluded that ettringite in SSC is inherently unstable at 95°C.

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Abstract  

The stability of supersulphated cement (SSC) is investigated. The hydration products of cement pastes prepared at a water cement ratio of 0.27 were determined by thermogravimetry (TG) and X-ray diffraction (XRD). Ettringite, one of the initial hydration products, is shown to be stable under conditions of storage at 25, 50 and 75°C and when subject to relative humidities of 100, 53 and 11% of water vapour in each case. The effect of drying on ettringite stability at the higher temperatures is discussed in relation to the relative humidity.

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Abstract  

One of the principal uses of supersulfated cement has been for structures exposed to sea water and sulfate bearing ground waters. The resistance to such environments has been related to the absence of calcium hydroxide and the combination of much of the free alumina into ettringite during hydration. This paper reports the resistance of SSC to sulfate solutions in which ettringite has been decomposed. Prism samples were subjected to initial water storage at 25°C for both 28 days and 6 months. Samples were also cured for 6 months at 95°C and at both 11% and 100% R.H. The control samples of 28 days were compared with the 6 months samples of a more mature undecomposed SSC paste. After curing the prisms were measured and all the samples were immersed in three sulfate solutions (0.7M Na2SO4 , 0.7M MgSO4 and saturated CaSO4), and water at the same time. Measurements of linear expansion over 6 months were carried out. Core and surface material following immersion was examined by DTG and XRD. The study indicated that SSC is resistant to sodium and calcium sulfate solutions. Strong magnesium sulfate solutions decomposed the samples under all conditions. A possible mechanism for this attack is suggested.

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Journal of Thermal Analysis and Calorimetry
Authors: M. Evans, D. Nowell, and M. Powell

Abstract  

The strength of chemical bonds formed between eight rock-forming minerals and six bitumen samples were examined by heat-of-immersion calorimetry. The materials were characterised by their physical and chemical properties. The amount of energy released by the bitumen-mineral interaction was much larger than expected for an immersion reaction, exceeding usual values by a factor of up to 102. An oxidation mechanism, catalysed at the mineral surface, is proposed to account for this observation, and trends in the heat-of-immersion data are correlated with chemical properties of the bitumen and mineral samples.

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