J. Xu et al. / Automation in Construction 76 (2017)  85–96 95

Fig. 20. The compressive test taken over a core sample.

use of 3D scanning and 3D printing in solving a pervasive and on-going problem in architectural restoration work.

8. Limitations and future research

The research presented combined 3D scanning and 3D printing for historical building restoration, and demonstrated the potential of this approach to unlock a new restoration process. There remain some lim- itations, which need to be acknowledged to engender future work in this area:

a) Restoration of historical buildings often requires the use of the sim- ilar material. This trial uses cement mortar to substitute the stone in situ, while the technology and material science may have some room for improvement such as high-index cement mortar with steel fiber reinforcement for higher compressive strength. A mixture of sand and mountain flour with adhesive material such as epoxy resin in the future work will enhance the ability to produce a more befitting replica for a stone component;

b) Historical building components usually contain intricate carving pat- terns or designs on their surface, which require a high accuracy dur- ing reproduction. The components reproduced by this process are relatively crude and are unable to accommodate the need for repro- ducing details. Improved control of mechanical three axis motion and an intelligent nozzle for higher accuracy and flexibility of mate- rial deposition is necessary for this issue to be addressed; and

c) The reproduction process demonstrated refers to overall replication of an ornamental element or component, which entails the 6th degree of conservation intervention. Restoration as replacement or spot priming for partial damages, corrosions or losses, as the 4th degree of conser- vation intervention, requires decayed material detection techniques, smart restoration modeling algorithms for substitutable or missing parts, modified printing arts as well as compatible installation tech- niques. This is more comprehensive and of greater  significance.

The research has provided the initial building blocks for integrating 3D scanning and 3D printing technologies. The platform that has been established along with the algorithms will provide researchers with the ability to replicate and improve the system that has been proposed.

It is suggested that the real challenges ahead for construction pertain to the issues of how to reproduce the original natural materials that have been used in historical  buildings.

Acknowledgement

The presented work has been supported by the National 12th Five- Year Plan Major Scientific and Technological Issues through grant 2015BAK33B04.

摘要：三维（3D）扫描和基于水泥砂浆的3D打印技术的组合被用于开发用于再现历史建筑装饰部件的新颖过程，其传统上是劳动密集型和昂贵的构造。开发了一种用于模型切片的分层算法和喷嘴路径的修改扫描线算法。为了证明拟议的数字化生产过程的可行性，华中科技大学校园（HUST）在中国的一个受损的杯形独立底座是3D扫描，重新建模，使用特定的3D打印技术构建。对印刷底座的外观以及扫描精度进行了估计。测试和计算印刷底座的抗压强度，其垂直和横向方向分别为19.8Mpa和15.6Mpa。复制评估表明，开发过程为使用3D扫描和基于水泥砂浆的3D打印的传统建筑装饰元件的数字再现领域的未来工作提供了基础和动力。

关键词：三维扫描，3d打印，数字复制，历史建筑