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This paper presents the engineering properties of ancient masonry materials and substitution materials for the preservation of Thai historical structures. The study was divided into 2 parts. For the first part, the ancient masonry materials including brick and mortar were collected from various historical sites in Bangkok and Ayutthaya provinces. The engineering properties of masonry materials were evaluated in laboratory such as compressive strength, density, chemical compositions, porosity, and water absorption. The second part was investigation to find the suitable substitution materials for historical repair mortars. Fly ash was used as a pozzolanic materials to partial replace slaked lime for making historical repair mortar. The engineering properties of historical repair mortar containing were also evaluated and compared with the ancient masonry materials obtained from the first part. The binder to sand ratio was controlled at 1:3 by weight. The slaked lime was substituted by fly ash in the ranges of 10-30% by weight. The experimental results showed that the use fly ash to a partial replace slaked lime could decrease the setting time of historical repair mortar. The compressive strength of historical repair mortars with fly ash were ranged from 1.54-2.22 MPa, depending on the level of replacement, while that of the ancient masonry materials had the compressive strength of 1.88-2.71 MPa.

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This article presents an alternative method for the long-term monitoring of heritage pagodas in Thailand. In this method, terrestrial laser scanning (TLS) is used in combination with permanent survey markers. The Wat (temple) Krachee in the Ayutthaya Province of Thailand was chosen as a case study. This temple has several fantastic elements, including an inverted bell-shaped pagoda, two intertwined trees growing within it, and a chamber inside the pagoda. The preservation team working on the pagoda encountered a challenging problem and faced a decision to trim or not to trim the tree since it has a long-term effect on the pagoda’s structural stability. A high-accuracy terrestrial laser scanner was used to collect three-dimensional point cloud data. Permanent survey markers were constructed in 2018 to be used in long-term monitoring. The 3D surveying of the temple and the monitoring of the pagoda were carried out in five sessions during a period ending in 2020. A point cloud data analysis was performed to obtain the current dimensions, a displacement analysis, and the pagoda leaning angle. The results revealed that the terrestrial laser scanner is a high-performance piece of equipment offering efficient evaluation and long-term monitoring. However, in this study, permanent survey markers were also required as a benchmark for constraining each monitoring session. The 3D point cloud models could be matched with the assumption model elements to evaluate the damaged shape and to determine the original form. The significant elements of an inverted bell-shaped pagoda were investigated. Trimming the tree was found to cause the leaning angle of the pagoda to decrease. An equation was developed for predicting the leaning angle of the Wat Krachee pagoda for preservation and restoration planning in the future. From the results of this study, it is recommended that periodic monitoring should continue in order to preserve Thai pagodas in their original forms.