ASTM standards are available electronically to ISU researchers via ASTM Compass.
The Digital Library does not provide text of withdrawn standards. If you need an older standard than what is available in the ASTM Compass, check the printed version. ASTM standards are published in The Annual Book of ASTM Standards (TA405 .Am35a - Parks Library, General Collection). The first volume of the set, volume 00.01, is a subject and numerical index to all of the volumes. Prior to 2013, the ISU Library purchased this set every two years.
The Annual Book of ASTM Standards includes copies of all the ASTM standards in force during a particular year - not just the ones that were updated that year. So, for example, if you need a copy of an ASTM standard published in 1963 (and that was the last time it was updated), you can use the 1963, 1964 or 1965 edition of the Annual Book of ASTM Standards - you do not need the 1963 edition specifically.
Some ASTM standards are available full-text from the Defense Standardization Program database. Occasionally, you can also find copies of older ASTM standards free on the web. Try searching Google by ASTM standard number to find them. Note that you will not find recently-published ASTM standards this way.