The test is intended for the 28d compressive strength and conducted at room temperature. Taking the group of vertical coring direction for example, three core samples are placed in the pressure plate and com- pressed by a press machine (Fig. 20). Three maximum force values (Fc1 , Fc2,Fc3) of the samples in the test are acquired, as well as their areas of the compression section (A1, A2, A3). The compressive strength is expressed as:

scribe the façade features of the printed plinth. A straight steel    ruler

.Fc1

 Fc2

Fc3.

and a band tape are taken to measure size parameters. The shape and color of the printed plinth can be observed by the naked eye. A steel ruler and a feeler are used to measure the strip intervals uniformity.

f cu;cor ¼

A1  þ A2

þ A3

=3 ð8Þ

The printed plinth is 0.7 m wide in diameter of the bottom surface and the height is approx. 40– 80 mm with a curved cup shape and hoar  façade,  which  is  similar  to  the  original  intact  one.  Yet     the

In Eq. (8), fcu, cor is the 28d compressive strength of the plinth in ver- tical direction, which is an average value. The 28d compressive strength in lateral direction is calculated in the same way.

a b

Fig. 18. (a) The layered texture and ladder surface, (b) the geometric features of strips.

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

c

Fig. 19. (a) Core drilling positions of vertical direction, (b) core drilling positions of lateral direction, (c) vertical core drilling and core sample after planished.

The compressive strength (fcu, cor) of the printed plinth is tested and calculated to be 19.8 Mpa and 15.6 Mpa for vertical and lateral direc- tions, respectively. The difference of fcu , cor value between vertical and lateral direction is caused by the cohesive force of layers and strips. In the vertical direction, layers of cement mortar stacked one by one by gravity and strips within a layer are orthogonal with those of the upper and lower layers according to the modified scan line algorithm. In the lateral direction, strips bond with each other due to the stickiness of the material as an external force. Thus, the weaker bonding of strips in the lateral direction leads to a lower compressive strength compared to that in the vertical.

The compressive strength of the printed cement mortar-based plinth is lower than the original stone plinth. Factors include pump pressure, nozzle diameter, layer thickness, filling path spacing, material property, maintenance measure, and environmental impact. Stable uni- form output of the pump pressure ensures the integrity of materials forming. An appropriate nozzle diameter in accord with the layer thick- ness and filling path spacing forms efficient bonding between layers and strips, while the material properties and maintenance measures as well

as favorable environment provide high forming strength for the printed components.

7. Conclusion

The process of 3D scanning is becoming an important tool for con- serving and reproducing cultural heritage artefacts. Such technology also provides an ability to acquire high spatial resolution data needed to ameliorate the effectiveness of the reproduction process. Concrete based 3D printing is now gaining interest and momentum as it begins to become mature; 3D scanning of a physical object provides a mecha- nism to derive virtual data and information and when integrated with 3D printing the reproduction of an artefact becomes a reality. The com- bined use of such technologies provides unbounded opportunities for stimulating innovation and a new digital construction process, with cor- responding algorithms for reproducing a historical building ornamental component. The approach proposed in this paper is validated through an overall digital reproduction of an inpidual plinth of a damaged curved cup shape stone, which demonstrates the future of  combined