A pilot study of laser-welding cast basalt blocks for lunar construction

Using sintered or melted regolith to produce masonry units is a promising option for constructing lunar base civil infrastructure. However, the ingredients needed to produce cementitious mortar are not easily available on the moon and using water-based mortars in the lunar vacuum could be problematic. This pilot study reports experimental trials using specimens cut from cast basalt tiles to investigate laser welding as an alternative method of bonding lunar masonry. In a bead-on-block study to identify the optimal laser parameters it was found that weld penetration was limited to 1.5 mm and that without preheating and annealing, cracking was unavoidable. Pairs of blocks were also butt-welded together autogenously and tested for flexural strength. With preheating and annealing in a furnace, it was possible to produce welds with tensile strengths of up to 16.5 N/mm (≈ 12.7 MPa). Even without preheating and annealing, a weld strength of 0.9 N/mm (≈ 0.6 MPa) was achieved. This might be sufficient to support masonry unit self-weight during construction to avoid the need for falsework. The pilot study demonstrated that although preventing cracking when welding cast regolith materials is challenging and weld penetration depth places an absolute limit on scalability, the technology shows sufficient promise to justify further trials. Improved results might be achieved in a vacuum with a controllable laser and if the porosity of the sintered or cast regolith parent material was optimised for weldability.