RAPID, CATASTROPHIC DECAY OF BUILDING LIMESTONES: IMPLICATIONS FOR MASONRY SELECTION AND LIFETIME BEHAVIOUR

石材被广泛认为是一种可持续的建筑材料，也是世界上许多有形文化遗产的宝库。有了这种认识，人们就认识到，石头的寿命是有限的，当它被放置在经常充满侵略性的城市环境中时，它的寿命会大大缩短。特别是，许多常见的建筑石灰石经历看似不可预测的，偶发的，有时是灾难性的崩溃，因为石头强度被逐渐衰减，内部应力的缓慢积累和/或遭受极端的外部应力，如严重的霜冻。在迅速衰变的过程中，可能会出现相对稳定的时期，例如，形成污染产生的硫酸钙结壳。因此，为了控制潜在的灾难性衰退，有必要了解为什么会引发快速衰退，是什么让它继续下去，如何才能停止衰退，以及如何首先避免衰退的原因。在不适当的保护可能加速腐烂的地方，以及必须在可能的替代石材和与新结构有关的石材选择之间做出选择的地方，尤其如此。为了达到这种理解，需要提出四个问题。哪些过程导致快速撤退？2.哪些物理、化学和矿物学特征决定了石头对快速后退的敏感性，这些特性在腐烂过程中如何变化？3.当石头后退时，石头表面和下面的小气候条件如何变化，这些又如何影响腐烂机制？4.是什么使得风化物质在快速流失的情况下仍能继续风化，例如，其中集中了有害的盐？这个跨学科的项目将通过对牛津和附近地区的石结构进行实地研究来研究这些问题，这些地区是由容易迅速撤退的鲕状石灰岩（例如巴斯和科茨沃尔德石灰岩）建造的。与此相关的是光纤传感器的开发，这种传感器将允许监测各个区块内与环境条件有关的水分和盐的移动，包括温度、相对湿度和表面润湿。这些数据和相同的传感器技术将与风化石的分析相结合，设计实验室实验，使用不同品种的浴石模拟故障模式和盐和水分运动的动态块撤退，并逐步庇护。将结合实地研究和受控实验室实验的结果来解释（模型）决定整体敏感性的因素，无论是快速撤退或稳定性和负责衰变的过程的操作。特别是，结果将用于确定是什么触发了分别加速和减速结石衰变系统内的变化的正反馈和负反馈。在与最终用户的讨论中，将利用这一认识来制定石灰石保护协议，并选择与特定环境条件相匹配的新石头和替代石头。

Stone is widely recognised as a sustainable construction material and as a store of much of the world's tangible cultural heritage. With this recognition has come an understanding that stone has a finite life that can be drastically curtailed when it is placed in the often-aggressive urban environments. In particular, many common building limestones experience seemingly unpredictable, episodic and sometimes catastrophic breakdown as stone strength is exceeded by gradual decay, the slow accumulation of internal stresses and/or subjection to extreme external stresses such as a severe frost. Episodes of rapid decay may be interspersed with periods of relative stability marked by, for example, the formation of pollution-derived calcium sulphate crusts. To control potential catastrophic decay it is therefore necessary to understand why rapid retreat is triggered, what allows it to continue, how it can be halted and how the causes can be avoided in the first place. This is particularly true where inappropriate conservation could accelerate decay, and where choices have to be made between possible replacement stone and stone selection in relation to new structures. To achieve this understanding four questions need to be asked.1. What processes are responsible for rapid retreat?2. What physical, chemical and mineralogical characteristics determine stone susceptibility to rapid retreat and how do these properties change during decay?3. How do microclimatic conditions at and beneath the stone surface change as stone retreats and how do these influence decay mechanisms?4. What permits continued weathering despite rapid loss, of weathered material in which, for example, damaging salts are concentrated?This interdisciplinary project will examine these questions through field studies of stone structures in Oxford and nearby areas built of oolitic limestone (e.g. Bath and Cotswold limestones) that is prone to rapid retreat. Linked to this will be the development of fibre optic sensors that will allow moisture and salt movement within individual blocks to be monitored in relation to environmental conditions, including temperature, relative humidity and surface wetting. These data, and the same sensor technology will be combined with analyses of weathered stone to design laboratory experiments using different varieties of Bath Stone to simulate breakdown patterns and the dynamics of salt and moisture movement as blocks retreat and are progressively sheltered. Results from field studies and controlled laboratory experiments will be combined to explain (model) the factors that determine overall susceptibility to either rapid retreat or stability and the operation of the processes responsible for decay. In particular, results will be used to determine what triggers positive and negative feedbacks that respectively accelerate and decelerate change within the stone decay system. This understanding will be used, in discussion with end-users, to develop protocols for limestone conservation and the selection of new and replacement stone matched to specific environmental conditions.