【正文】 C coldworked steel losses residual strength and at 600186。C. The cement matrix is bisected by numerous fine cracks, some of which radiate from quartz grains in the fine aggregate fraction. This deep cracking and cracking associated with quartz suggest that the concrete has reached 550575186。C (_to _ quartz transition), 800186。C a red discoloration is important as it coincides approximately with the onset of significant strength loss. Any pink/red discolored concrete should be regarded as being suspect (Concrete Society, 1990). Actual concrete colours observed depend on the types of aggregate present in the concrete. Colour changes are most pronounced for siliceous aggregates and less so for limestone, granite and Lytag (shows very little colour change). The most striking colours are produced by flint (chert) and Figure 1 illustrates the colour changes of flint aggregate concrete. The red colour change is a function of (oxidizable) iron content and it should be noted that as iron content varies, not all aggregates undergo colour changes on heating. Also, due consideration must always given to the possibility that the pink/red colour may be a natural feature of the aggregate rather than heatinduced. Some widely used aggregate materials contain naturally red or pink particles. British examples include Ordovician and Permotriassic sandstones and quartzites, which are often various shades of red and any sand/gravel deposits that include materials derived from these rocks (for example, Trent river gravels). In addition, the Thames river gravels may occassionally include naturally red coloured flints. Care must also be taken when white calcined flints are present as these are monly incorporated in decorative white concrete panels and are also a mon ingredient of calcium silicate bricks. Petrographic examination is invaluable in determining the heating history of concrete as it can determine whether features observed visually are actually caused by heat rather than some other cause. In addition to colour changes of aggregate, the heating temperature can be crosschecked with changes in the cement matrix and evidence of physical distress such as cracking and microcracking. A pilation of the changes undergone by concrete as it is heated is presented in Table 2. Careful identification of microscopically observed features allows thermal contours (isograds) to be plotted through the depth of individual concrete members. In the most favourable situations contours can be plotted for 105186。C is normally taken to be the critical temperature above which, concrete is deemed to have been significantly damaged. Normally concrete exposed to temperatures above 300186。C the residual strength of structural quality concrete is not severely reduced (Malhotra, 1956). Generally, between 300186。 T246。 T246。 T246。 附件 2：外文原文 （復(fù)印件） ASSESSMENT OF FIREDAMAGED CONCRETE AND MASONRY STRUCTURES:THE APPLICATION OF PETROGRAPHY Jeremy P Ingham Halcrow Asset Engineering, Burderop Park, Swindon SN4 0QD, United Kingdom, Abstract The number of building fires has doubled over the last 50 years. There has never been a greater need for structures to be assessed for fire damage to ensure safety and enable appropriate repairs to be , even after a severe fire, concrete and masonry structures are generally capable of being repairedrather than demolished. By allowing direct examination of microcracking and mineralogical changes, petrographic examinationhas bee widely used to determine the depth of fire damage for reinforced concrete elements. Petrographicexamination can also be applied to firedamaged masonry structures built of materials such as stone, brick and mortar. Petrography can ensure accurate detection of damaged geomaterials which provides cost savings during building repair and increased safety reassurance. This paper prises a review of the role of petrography in fire damage assessments, drawing on a bination of original research and a wide range of actual fire damage investigations, undertaken by the author. Practical guidance for determining the heating history of structures is provided along with explanation of the other investigation phases required, for successful programmes of assessment and repair of firedamaged concrete and masonry structures. Keywords: Concrete, masonry, fire, petrography, optical microscopy Introduction The cost of building fires in the United Kingdom currently exceeds two million pounds per day. This cost is likely to rise as the number of building fires has increased by more than a 100% over the last 50 years (ODPM, 2021). Consequently, there has never been a greater need for structures to be assessed for fire damageto ensure safety and enable appropriate repairs to be planned. Concrete and masonry construction materials offer good resistance to fire because they are inbustible (in parison to wood) and have low thermal conductivity (in parison to steel). However, physiochemical changes and mechanical damage caused by heating will eventually promise the loadbearing capacity of concrete and masonry elements. In practice, the worst damage is usually confined to the outer surface and even severe fires seldom cause total structural collapse. Experience shows that following detailed appraisal, firedamaged structures can nearly always be reinstated using a selection of repair techniques, sometimes bined with replacement of selected structural elements. As an alternative to largescale demolition this provides very substantial savings in capital expenditure and also savings in consequential losses, by permitting much earlier reoccupation of the structure. Petrographic examination has bee widely used to determine the depth of fire damage for reinforced concrete elements. The information gained from microscopical examination of concrete samples is now ro