The paper attempts a comprehensive review of in situ weathering of rock used in civil engineering construction. It also presents some new data on weathered rock from Britain which have been used to develop a proposed tentative Rock Durability Indicator scheme. This is based on simple engineering tests to help assess the potential performance of the rock in service.

It is concluded that weathering in geological time can have significant influence, under certain circumstances, on the durability of aggregate or stone in-service. Durability is defined as the rock material's ability to resist degradation during its working life and is considered to be dependent on a number of parameters; viz. the original stage of weathering of the rock mass; the degree of imposed stressing during winning, production, placing and service; the climatic; topographical and hydrological environments in-service.

The production and construction procedures can have an important influence on the mechanical strength of the material. Physical weathering processes and imposed loading generally have the most significant effect on deterioration but chemical weathering could be of significance in-service, especially in hot, wet climates.

No one engineering test can be used as an absolute predictor of performance. Combinations of common mechanical and physical tests such as water absorption, specific gravity, point load strength, modified AIV and magnesium sulphate soundness can be used in various combinations to help assess potential durability. For a more complete evaluation, environmental factors such as the climate, topography and hydrological regimes need to be taken into account.

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