Standard vs. Modified Proctor for Crushed Concrete
Standard vs. Modified Proctor for Crushed Concrete
(OP)
I have two questions relating to testing crushed concrete as a backfill material. I recieved some results an environmental engineer had performed and noticed some problems.
1) The crushed concrete contains more than 30% greater than 3/4" (52%) and therefore, can I consider the standard proctor results with correction to be accurate? I suspect not as stated by the ASTM.
2) Is there any rule of thumb when performing a proctor on crushed concrete to be used as backfill (i.e. Standard vs. Modified)? For most granular soils, I usually specify modified and was wondering if there was any special reason the lab would have performed a standard proctor on the crushed concrete.
Thanks in Advance
Adam
1) The crushed concrete contains more than 30% greater than 3/4" (52%) and therefore, can I consider the standard proctor results with correction to be accurate? I suspect not as stated by the ASTM.
2) Is there any rule of thumb when performing a proctor on crushed concrete to be used as backfill (i.e. Standard vs. Modified)? For most granular soils, I usually specify modified and was wondering if there was any special reason the lab would have performed a standard proctor on the crushed concrete.
Thanks in Advance
Adam





RE: Standard vs. Modified Proctor for Crushed Concrete
2: i personally would only spec a high modified % if the material is graded and a "controlled" material...(i.e. GAB material from a quarry). another reason is that (if i remember correctly) based on the gradation, it sounds like it might be a modified D which means using the big mold with 56 blows in 5 layers with the heavy hammer...OUCH!
i would consider evaluating this like a true "rock fill" and throw out a performance spec...proofrolls, periodic tests, very thin lifts, specified gradation, big equipment, etc....but that's just me.
RE: Standard vs. Modified Proctor for Crushed Concrete
I would caution you when running a modified tests with concrete or any soft rock. You will end up crushing the rock and possibly throwing off your results. I hope this helps.
RE: Standard vs. Modified Proctor for Crushed Concrete
Secondly, Did they use a standard proctor because of the crushing factor you mentioned? If so, im assuming it was better to use a standard over a modified on this material?
RE: Standard vs. Modified Proctor for Crushed Concrete
RE: Standard vs. Modified Proctor for Crushed Concrete
RE: Standard vs. Modified Proctor for Crushed Concrete
Is the thin lifts and heavy compacting because of bridging or voids that may be created during placement with an angular gravel? Wouldnt the rock-fill be compact upon placement if its mostly gravel with no fines to fill the voids? I just cant think of what heavy compaction would achieve with this type of gravel material...although im relatively inexpierienced?
RE: Standard vs. Modified Proctor for Crushed Concrete
Thanks Again.
RE: Standard vs. Modified Proctor for Crushed Concrete