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You will want to oil the molds to help in the stripping process. Once they are cast, make sure you clean off the top of the end plates well so hardened concrete doesn't impede the turning of the end plates. At 24-hours, strip the molds and carefully twist the end plates off the gauge studs...

Was there any plastic testing performed on the concrete? What was the air content, slump, density, temperature? These are also very key in investigating low strength results. Also a good idea to weigh the cylinders when strength appears to be an issue. The more data the better. Greg

Ron is definitely in the ball park. A couple of months ago we did a mix design trial batch for a 3000/450 psi compression/flexural requirement in 30-hours. That did 8500/825 at 28-days. Greg Greg

With the brass being so soft, the pivot holes wear quite easily, and have worn to the point that they no longer hold. They will need to be replaced, or if you are set up for brazing, you can repair them. Greg

Can anyone explain why the concrete water-cementitious ratio requirements for ACI 318, Table 4.3.1, Exposure Class S3 of 0.45, is different than ACI 201.2R, Table 6.3, Class 3 exposure with a w-c ratio 0.40? I tend to take the more conservative approach of ACI 201.2R, but may need to explain to...

If you throw a bunch of air in there, you can get the strength down some more and significantly reduce subsidence and bleed. Most CLSM we do is >15% total air content for the low strength and very little bleed or subsidence. Greg

I vote for segregation over the rebar. Starting with a 4" slump and 1/2 the maximum dose of high-range water reducer, I'd suspect the slump is in the 8-10" range. At that kind of slump you really need to police the guy on the vibrator in proper use. Only vertical penetration of the vibrating...

I've used the equation to produce laboratory trial batches for time-of-set evaluations at various concrete and ambient temperatures. For that study, it got me within 2 degrees F on all the trials. From my limited experience, it seemed to hit pretty good. Greg

See ACI 211 Table 6.3.1 "Recommended Slumps for Various Types of Construction" and ACI 117 Section 2.5.1. Greg

The way things have been working in our market lately is that if the building inspector shows up on the site and has any concern whatsoever regarding the bearing soil conditions, he requires the contractor/owner enlist a geotechnical engineer to evaluate the soils. Greg

So far as I know there is no responsible reason for eliminating bearing soil inspections. I doesn't really matter how conservative you design your footings, if you have 10-feet of soft swamp muck as a bearing soil, lawyers will eventually be involved. Greg

Bridgebuster wrote: "To me, a fence is not intended to be a structural member;" If the barrier is near lanes of traffic, and wind induces a failure causing a wreck, the lawyers will certainly disagree. Greg

Wow gentlemen, I didn't think this was going to be such a can of worms when I opened it. Our involvement in projects is QA/QC where we are inspecting the welded connections. Typically if there is a discrepancy due to insufficient thickness of base metal (3/16" weld required for 1/8" thick...

Ron is right...the cylinders are to measure the quality of the concrete DELIVERED. By exposing cylinders to the same variables as the in place concrete, the conditions could influence the stengths of the cylinders such that you wouldn't know what you've got. It's also important to point out...

I think in most cases JAE is correct...the engineer of record is not familiar with SJI's typical details, and I've only ever seen the joist supplier give the standard SJI weld details. We often times see the situation where the SOR calls for a 3/16"x2" weld, and the joist seat angle material is...

The American Concrete Institute ACI 364 "Guide for Evaluation of Concrete Structures before Rehabilitation" would cover most any concrete building or issue. It will also reference other sections of the "Manual of Concrete Practice" that are too numerous to mention. Greg

Often times engineers include the weld requirements for joist bearing that are not consistent with the shop drawings submitted by the joist supplier. Should one go with the more stringent of the two, or do the structural engineer approved shop drawings supersede the plan details? Greg

hokie66, In most of our market, if you ask for an accelerator, you get a non-chloride accelerator, which is not deleterious to steel. Most of the ready mix companies don't even stock calcium chloride anymore. Greg

I guess I misspoke. What I meant is that they are not going to tell you that you must use blankets on the top and a heated enclosure on the bottom when a contractor may hang blankets from the bottom and use ground heaters and blankets above. Greg

ACI doesn't provide guidance on means and methods, such as how much insulation it will take. They do give performance requirements to meet. In your case the delivered concrete temperature from Table 3.1, line 3 would be a minimum of 65 degrees. During the protection period, the concrete...