Originally Posted by kerry

Maybe what I saw on This Old House was some kind of combo unit that looked like a tankless water heater. It definitely hung on the wall like a tankless heater and it definitely provided both domestic hot water and hot water for the heating system.

Originally Posted by MS Fowler

One of my responsibilities at my new job is getting our lab certified. One aspect of this involves curing of concrete test cylinders. The Standards requires curing in an atmosphere of greater than 98% humidity. They define this as having free moisture on all the specimens. The other requirement is that the temperature is controlled to 73 +/- 3 degrees F. As a way to simplify the climate control ( A/C usually removes moisture) we hit upon the idea of using fogger nozzles to spray water all around the curing room. There are companies that make a temperature control system that regulates the water temperature to achieve the desired temp inside the curing room. These are EXPEN$IVE-- at least in my employer's opinion.
We hit upon this solution--using the fogger nozzles and tap water to humidify and cool the room to below 65 degrees. Then use a single stage, waterproof thermostat to control the heat. Electric heaters are problematic at this high humidity level, so how about hot water baseboard heaters at opposite sides of the room, and the hot water supplied by a domestic water heater? The heat load would be very low.
My question is simply a lack of experience in hot water base board heat. It SEEMS as if the system I described would have way more capacity that required, but I would appreciate comments from people with experience in hot water heat.

Originally Posted by MS Fowler

Next question--where can I find ginned radiators?
Tom, what did your numerical references mean?

Originally Posted by Stoney

At the AASHTO/IAS certifed lab at my former employer, they just made large plywood tanks lined with fiberglass and willed with water and heated the water with immersion heaters with a thermostat suspended in roughly the center of the tank.

They still do it this way and they are still an AASHTO/IAS certifed testing lab.

I think the entire curing process is kinda odd considering it has absolutely nothing in common with the in sutu concrete that was placed in the field which is almost NEVER water cured (the only clients I know of that requires water curing is NYSDOT and DASNY). I was just at a DASNY site in Bronx NY and they have a heated water recycling system to handle the curing (they are also using blankets to prevent freezing) and it appears to be a major PITA!

On the subject of your baseboard heating system...how about an electric 40 gal HW heater as the heat source with the thermostat controller running the duty cycle?

Originally Posted by t walgamuth

Perhaps the point of it is to cure the concrete under ideal conditions so that it reaches its max strength within a much shorter time than the concrete in the building will so that if they find a weak batch it can be corrected as quickly as possible.

I believe concrete with some additives can reach about 90% of its strength in about a week. With no additives I believe it is more like a month to reach 90%. After that it tapers off but keeps getting stronger for years.

Originally Posted by kerry

Maybe what I saw on This Old House was some kind of combo unit that looked like a tankless water heater. It definitely hung on the wall like a tankless heater and it definitely provided both domestic hot water and hot water for the heating system.

Originally Posted by jaoneill

Many of the high eficiency, low mass, condensing boilers hang on the wall much as a demand heater would, and aren't much larger. In the last multi-unit building we bought I used gas fired, modulating demand heaters by Takagi as heat sources for each apartment. These are specifically designed and warrantied for either domestic hot water or hydronic heating use. They were about $700 each, have been in use for five heating seasons and trouble free. It was a great way to individualize the heating so the tenants can foot the bill for their own heat. Plan to do the same to our other buildings as cash flow allows; providing heat with todays fuel prices is a loser.

Jim

Originally Posted by MS Fowler

Tom is correct. The purpose of ideally cured and tested samples is to verify the concrete as delivered by the concrete supplier. How it is handled once on-site adds a number of variables. There is a Standard for field-cured cylinders, often used to determine when forms may be stripped, or loads applied to concrete structures. It is a different Standard than the one for LAB-cured cylinders.

One of the interesting things about concrete is that given sufficient moisture, it will continue to increase in strength, practically forever. The often quoted strength ( 300, 4000 PSI or so) is its designed strength at 28 days under ideal ( full moisture, and moderate temperature) conditions. Depending on the ingredients, concrete typically hit 60-75% of its 28 day strength in 7 days.

Originally Posted by Stoney

I can see doing lab cures for a CDM or to compare to Field cured but since in NYC the DOB requires all CDM's to be spec strength + 25% safety factor, I have rarely seen bad site placed concrete. I have seen serious issues raised over bad samples, esp Fly Ash concrete cylinders that were not cured correctly for the first 72 hours and provided erronious low break data.

But then the powers that be require testing/curing that IMHO does not reflect the real world.

I work for the firm that designed the initial high strength concrete high rises of Miami and NYC, look up 785 Eighth Avenue and check the Shear Wall PSI (12K CDM with an ultimate of 18K at 56 days).

The problem isn't the lab cure or site cure it is the adherence to prtocedures by the Site Inspector and contractor. If the ICC Code allowed the Site Inspector to control the absolute rejection of concrete that did not meet spec, life would be easire but ICC won't go there (neither will ACI) so Contractors are allowed to place material that has been "folded, spindled and mutilated to quote my ex boss" and then the EOr is asked to sign off o it.
I just spent a day writing letters of acceptance for a job where all concrete placed met or exceeded spec strength but the out of spec variables (Air, Slump, time on Site) were the problem.