According to Philippine Electrical Code 2017 Section 2.50.3.3(A)(3) lists "Concrete-Encased Electrodes" as one of the types of electrodes permitted for grounding.
(3) Concrete-Encased Electrode. A concrete-encased electrode shall consist of at least 6000 mm of either (1) or (2):
(1) One or more bare or zinc galvanized or other electrically conductive coated steel reinforcing bars or rods of not less than 13 mm in diameter, installed in one continuous 6000 mm length, or if in multiple pieces connected together by the usual steel tie wires, exothermic welding, welding, or other effective means to create a 6000 mm or greater length; or
(2) Bare copper conductor not smaller than 22 mm²
Metallic components shall be encased by at least 50 mm of concrete and shall be located horizontally within that portion☺ of a concrete foundation or footing that is in direct contact with the earth or within vertical foundations or structural components or members that are in direct contact with the earth. If multiple concrete-encased electrodes are present at a building or structure, it shall be permissible to bond only one into the grounding electrode system.
FPN: Concrete installed with insulation, vapor barriers, films or similar items separating the concrete from the earth is not considered to be in "direct contact" with the earth.
It is not necessary for the minimum length of 6000 mm in a single continuous length, multiple pieces could be used connected together by steel tie wires or exothermic welding.