6. Reproduction  evaluation

The digital reproduction process for the historical plinth presented is novel and has the potential to replace the manual procedure for a resto- ration task. However, it is necessary to evaluate this new approach pro- cess to ensure that the printed plinth provides a similar exterior as the original one and the required structural performance so as to be used in practice.

6.1. Facade  features  estimate

The scanning resolution is high for such a concrete building compo- nent, despite the encapsulation processes modeling is an approximation modeling of the physical intact plinth. The PCD file contains tens of thousands of points, which possesses an average distance of 0.10 mm between two points (Fig. 17a). The surface of the 3D solid model (STL model) is a triangular mesh incorporating a vast number of tiny triangu- lar planes determined by any of three points (Fig. 17b). The digital rep- resentation surface and geometry is akin to the original physical artefact; however, the core is slightly larger to accommodate the struc- tural adhesive filling.

In terms of visualization, there remains an obvious distinction be- tween the printed and the original plinth. This is due to the printing art and the material as: (1) the layered stack art that results in a vertical stratified surface; (2) the nozzle extrusion process that results in the cascade façade; (3) and the material proportion that affects the surface

Fig. 15. The two printed half inpidual plinths. Fig. 16. Installation of the printed plinth after post-processing.

J. Xu et al. / Automation in Construction 76 (2017)  85–96 93

reproduction quality of curved side wall of the cup-shape plinth is un- satisfactory. As the deposited strip, controlled by the nozzle diameter, was too thick to form the fine curved side wall, which is represented by a two-ladder surface. In addition the rough surface does not resemble the original due to its layered texture, and has a darker color tone com- pared to natural stone (Fig. 18a).

The distance of the central lines of adjacent strips (A) is approxi- mately 17.0– 21.5 mm. The distance between two adjacent strips (inter- val) (B) is approximately 0.5– 3.0 mm and the width of a strip (C) is approximately 15.0– 20.0 mm (Fig. 18b). The concrete texture, the mild variation of width of strips and intervals, result from the non-per- fect coordination of the pump pressure output and machine (nozzle) movement. This particularly arises for short filling paths that are thick at their endpoints and thinner at the middle sections. The 15 mm wide nozzle diameter has a direct impact on the surface uniformity, which can be improved with more strips within one unit area when the nozzle diameter is diminished. Therefore, the post-processing work is necessary for a practical reproduction of a historical building component (Fig. 16).

6.2. Compressive strength test

b

Fig. 17. (a) Detail of the PCD model of the intact plinth after manual treatment, (b) the 3D solid STL model of the intact plinth.

planeness of per strip or layer. In this instance resolution discrepancies between scanning and printing can materialize.

Factors such as size, shape, color, and uniformity, are used to   de-

Two printed half plinths are kept for a compressive strength test. The compressive strength test is taken over six core samples drilled down from the two tested half plinths. The six core samples are pided into two groups according to vertical and lateral coring directions (Fig. 19a,b). A core-drilling machine is used to drill down the core samples, which are planished at the end surfaces by a grinding machine to ensure that they are appropriate for testing (Fig. 19c). The core samples are cyl- inder-shaped of approx.70 mm both in height (H) and section diameter (d) (H/d = 1.0).