19 Construction elements, not of metal, namely, sand, artificial stone, rock being natural stone, clay ash, minerals and concrete for use as filler in net cages for erosion control for bank, river bank, canal bank, mountain and sea coast protection works, for channel linings for erosion control and for civil engineering works thereof; construction materials and elements, not of metal, namely, erosion control fabric and erosion control mats for use in natural hazard mitigation; construction materials and elements, not of metal, namely, concrete and geotextiles for use in civil engineering works