Class 7 (Hardcore)
Class 7 is a hardcore material. It shall be good stone, concrete, hard tiles or other approved material not exceeding 100mm gauge with not more than 1% passing a 20mm sieve. The fill shall not be susceptible to breakdown under moist conditions and shall not contain any deleterious materials. The total sulphate content as SO3 of the material shall not exceed 1% and the total soluble salts shall not exceed 2%.