Final answer:
The last action to be performed when building a slab on grade from the given options is placing reinforced steel, which follows excavation, formwork, and fine grading. The reinforced steel strengthens the concrete and helps prevent cracking.
Step-by-step explanation:
When building a slab on grade, which is a concrete slab laid directly on the ground, the process involves several critical steps that must be performed in a specific order to ensure structural integrity and proper completion of the construction. Among the given options, the action that would be performed last is placing reinforced steel.
The first step in the construction of a slab on grade is excavating the site to the required depth, which involves removing soil, rocks, and other materials to create a level surface. After the site is prepared, the forming process begins, which includes installing the forms that hold the concrete in place until it sets. These forms define the edges and shape of the slab.
Next, fine grading is performed to ensure the base or subgrade is smooth and compacted to the proper density. This helps to support the weight of the slab and the structure it will bear. Fine grading is followed by the placement of reinforced steel. This reinforcement, typically made of steel mesh or rebar, is used to strengthen the concrete and minimize the possibility of cracking due to tensile forces.
The final step, not mentioned in the options but crucial to the process, is the pouring and finishing of the concrete itself. Once the concrete is poured into the forms, it will encase the reinforced steel, and finishing techniques are employed to create a smooth, level surface according to the project specifications.