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The backfill material surrounding a tank is a critical part of a fiberglass tank installation. <br /> This brochure gives guidelines for choosing the best material to use when installing fiber- <br /> glass tanks. <br /> Xerxes specifies that gravel or crushed stone be used as a backfill material. <br /> 1. PEA GRAVEL(mix of rounded particles)must have a minimum diameter of 1/8"and <br /> a maximum diameter of 3/4'. <br /> 2. STONE CRUSHINGS should be washed and free flowing.The mix of angular <br /> particle-size should be between 1/s"and 1/2"and must meet ASTM C-33 paragraph <br /> 9.1 requirements. <br /> 3. No more than 5% of the backfill shall pass through a No.8 sieve. <br /> COARSE AGGREGATE is a more technical term for the material that meets Xerxes' <br /> backfill size requirements.The American Society for Testing and Materials(ASTM)and <br /> The American Association of State Highway Transportation Officials(AASHTO)have <br /> specifications for standard sizes of coarse aggregate.The standard sizes of coarse aggregate <br /> that meet Xerxes'pea gravel specifications are given in Table I.The standard sizes of coarse <br /> aggregate that meet Xerxes'crushed stone specifications are given in Table II. <br /> Some quarries may produce materials that meet Xerxes'requirements but are not iden- <br /> tified by a standard coarse aggregate size number.The quarry should be able to provide <br /> a specification that identifies the size or gradation of the material. If a specification for the <br /> material is not available,an independent testing laboratory can provide a sieve analysis per- <br /> formed per ASTM C-136 on a sample of the backfill material.The sieve analysis or material <br /> specification can then be compared against Xerxes'size requirements for the pea gravel or <br /> crushed stone. <br /> Another important characteristic of good backfill material is hardness or stability <br /> when exposed to water or loads. Most materials have no problem meeting the hardness <br /> requirement. Materials like soft limestone, sandstone or shale should not be used as backfill <br /> because they break down over time. <br /> I <br /> 1-4 R.1 <br />