Ultimate Concrete Hardness - Concrete, Stone & Masonry - DIY Chatroom Home Improvement Forum
Advertisement


Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Concrete, Stone & Masonry

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Display Modes
Old 05-04-2015, 08:49 AM   #1
Member
 
Join Date: Mar 2015
Location: Upstate NY
Posts: 478
Rewards Points: 946
Default

ultimate concrete hardness


I know that concrete cures hardest when allowed to dry or cure slowly.
I poured a small pad last Thur for a commercial dumpster. After initial set I covered it with a 60 mil roof rubber I had left from another project. I have daily been lifting the cover and wetting the surface. My question, since I don't need to put the pad into service for another week and half should I keep it covered and wet daily or uncover and let dry out.
The dumpster has steel wheels on it. Someone else mentioned removing the cover to let the heat out? Never that before.

Thanks

Advertisement

__________________



let us know how your project turns out!
Yodaman is offline   Reply With Quote
Old 05-04-2015, 09:44 AM   #2
Member
 
joed's Avatar
 
Join Date: Mar 2005
Location: Welland, Ontario
Posts: 9,317
Rewards Points: 5,430
Blog Entries: 10
Default

ultimate concrete hardness


After three days you should be able to uncover it. I would keep wetting it though if it is hot and sunny.
After two weeks the concrete is still not fully cured. The dumpster might mark it. 28 days is full cure for concrete.


Advertisement

__________________
Do not PM with questions that can be asked in a forum. I will not respond.
joed is offline   Reply With Quote
The Following User Says Thank You to joed For This Useful Post:
Yodaman (05-04-2015)
Old 05-04-2015, 09:49 AM   #3
Member
 
Join Date: Jan 2014
Location: Central Illinois
Posts: 1,574
Rewards Points: 2,008
Default

ultimate concrete hardness


Agreed.The concrete should be at 70% strength in 3 days and 28 days for full cure.
mako1 is offline   Reply With Quote
The Following User Says Thank You to mako1 For This Useful Post:
Yodaman (05-04-2015)
Old 05-04-2015, 09:49 AM   #4
Concrete & Masonry
 
Join Date: Nov 2008
Location: Wisconsin
Posts: 2,977
Rewards Points: 2,506
Default

ultimate concrete hardness


This is a simplified table, but as you see, it doesn't make much difference over the first week or two either way. You won't see a big difference until months down the road.............


Name:  curing_fig1.jpg
Views: 81
Size:  59.6 KB
jomama45 is offline   Reply With Quote
The Following 2 Users Say Thank You to jomama45 For This Useful Post:
Canarywood1 (05-04-2015), Yodaman (05-04-2015)
Old 05-04-2015, 09:50 AM   #5
Concrete & Masonry
 
Join Date: Nov 2008
Location: Wisconsin
Posts: 2,977
Rewards Points: 2,506
Default

ultimate concrete hardness


Quote:
Originally Posted by joed View Post
After three days you should be able to uncover it. I would keep wetting it though if it is hot and sunny.
After two weeks the concrete is still not fully cured. The dumpster might mark it. 28 days is full cure for concrete.

You must have edited to include that image, it wasn't there when I first started to reply.............
jomama45 is offline   Reply With Quote
Old 05-04-2015, 09:57 AM   #6
Remodel and New Build GC
 
MTN REMODEL LLC's Avatar
 
Join Date: Sep 2010
Location: Colorado @ 7651'
Posts: 3,755
Rewards Points: 3,780
Default

ultimate concrete hardness


My understanding is that concrete does not per-se dry..... it cures by requiring moisture to cure chemically....

What does confuse me is that a wet mix can be too wet and will not cure as well as a dry mjix...... guess it's a balancing act.

That is just my GC understanding..... maybe Jomama or some of our concrete specialists will clarrify/explain/detail.

Technically, I THINK concrete cures forever, with something like 95% in first 28 days or so...
__________________
Never stop learning (xcep fer speling en typeing)
MTN REMODEL LLC is online now   Reply With Quote
The Following User Says Thank You to MTN REMODEL LLC For This Useful Post:
Yodaman (05-04-2015)
Old 05-04-2015, 11:14 AM   #7
Member
 
Join Date: Mar 2015
Location: Upstate NY
Posts: 478
Rewards Points: 946
Default

ultimate concrete hardness


thanks guys, looks like everyone has the same graph except me ,

I will keep it covered and moist until we set the dumpster on it next Friday, also will put some 3/4 plywood scraps under the wheels for the following 2 weeks.

After that it will be used and abused by the truck slamming down the dumpster
__________________



let us know how your project turns out!
Yodaman is offline   Reply With Quote
Old 05-04-2015, 12:37 PM   #8
Civil Engineer
 
Join Date: Mar 2009
Location: Boston
Posts: 4,519
Rewards Points: 2,618
Default

ultimate concrete hardness


The OPS asked about "hardness", not "strength". All of the discussion was about strength, which is probably what the OPS is interested in, but not what he asked about.

Concrete cures by hydration of minerals, mostly silica, in the cement. Maximum strength in concrete is achieved by carefully measuring the ratio of sand, cement, aggregate and water, with the most critical ratio being the cement/water ratio. Optimum strength is achieved when the minimum amount of water necessary to hydrate the minerals in the cement is added, and proper curing procedures are used.

Concrete is more difficult to place when it is close to its optimum water content than when it is "wet", since the concrete is stiffer and more difficult to vibrate. So outside of a commercial or industrial project where high strength is necessary, the majority of concrete is delivered wet of optimum, and achieves less than maximum strength. This is irrelevant for essentially all residential and may commercial applications, since most people do not need anything beyond 3000 or maybe 4000 psi concrete, easily achieved with wetter than optimum concrete.

The rating on concrete (say 4000 psi) means that without use of an accelerating agent, the concrete is intended to reach 4000 psi in 28 days, which is the time when cores are taken on commercial projects to verify concrete strength. In practice, it is a very bad day if the cores come in below design strength, so in my experience concrete is usually designed to be above design strength at 28 days, since the cost is minimal (you use a little less water in the mix). If plasticity is critical, then superplasticizers are added to make the concrete flow better at low water content. This is irrelevant for residential applications.

Concrete continues to cure indefinitely. I worked on one project in Minnesota testing 80 year old concrete that was designed to be 4000 psi, and it tested out at 8000 psi.

Back to the OPS question. Concrete design strength is achieved at 28 days, the concrete continues to cure indefinitely. Concrete hardness is a totally different issue, one which might be of interest if you were running metal wheels over it. The hardness of concrete would be measured the same way any rock would be tested, which could use the Mohs scale. The Mohs scale runs from 1 - 10, where 10 is the hardest (diamond). If material A scratches material B, then A is harder than B. For a full description of the scale, see http://en.wikipedia.org/wiki/Mohs_sc...neral_hardness

In concrete, the hardness is determined by the type of rock used for the aggregate, the type of cement used, the water cement ratio, and the method of curing. The traditional method of measuring hardness in the laboratory is the Rockwell test, which measures the penetration of a standardized shape (like a ball or conical tip) into a material like steel under a standardized load. The idea is that the strength of a material is typically related to the hardness (the harder the material, the stronger it is). The relationship is not linear, and it is not perfect, but it may be useful to do nondestructive testing of in placed material.

The advantage of such a test over the traditional concrete cylinder test is that the hardness test is non-destructive, is fast, and is low cost. For this reason, engineers have tried to develop a test to measure the strength of concrete by measuring the hardness. Since concrete is not homogenous like steel, the correlation between hardness and strength is not as good as it is in steel or other metals. If you are interested in a paper on the subject of harness testing of concrete, see http://docs.lib.purdue.edu/cgi/viewc...1&context=jtrp

Conclusion: In general, strength and hardness of concrete are correlated. If the goal is hard concrete, order the strongest mix, and use careful curing procedures.
Daniel Holzman is online now   Reply With Quote
The Following 5 Users Say Thank You to Daniel Holzman For This Useful Post:
concretemasonry (05-04-2015), Fix'n it (05-04-2015), MTN REMODEL LLC (05-04-2015), SeniorSitizen (05-04-2015), Yodaman (05-04-2015)
Old 05-04-2015, 01:27 PM   #9
Member
 
Join Date: Mar 2015
Location: Upstate NY
Posts: 478
Rewards Points: 946
Default

ultimate concrete hardness


Thanks Dan, spoken like a true engineer. In my case some strength is required to hold the weight without cracking the slab, and some degree of hardness would be beneficial to minimize abrasion from the steel wheels. Since the slab is poured, the only thing I have control over now is the cure process. Currently watering it daily and covered with .06 mil rubber roofing.

It was a 3000 PSI mix with long strand fiberglass added and rebar mesh. It also has about 4" of #4 modified gravel base compacted under it.
__________________



let us know how your project turns out!
Yodaman is offline   Reply With Quote
Old 05-04-2015, 02:04 PM   #10
Member
 
Join Date: Sep 2012
Posts: 2,955
Rewards Points: 3,164
Default

ultimate concrete hardness


On DIY projects with the outdoor ambient conditions below 60F and a dew point around 45 percent I never bother covering. I'm busy just keeping the dog off that wanted to help.

When the outdoor is about 80 with a DP of kind of low I might cover and keep moist for awhile but no promises.

Above 85 forget the DIY no matter what the DP is. I looking for a indoor register close to Ole Faithful's blower wheel and a ceiling fan above with a pitcher of tea. I had my share of those upper temperatures in my younger days.
SeniorSitizen is online now   Reply With Quote
The Following User Says Thank You to SeniorSitizen For This Useful Post:
Yodaman (05-04-2015)
Old 05-04-2015, 02:37 PM   #11
Member
 
47_47's Avatar
 
Join Date: Sep 2007
Location: Springville, NY
Posts: 1,642
Rewards Points: 872
Default

ultimate concrete hardness


Shouldn't really park a car on it for 7 days. I'd be concerned about the small steel wheels and the dumpster being dropped on it until 28 days.
__________________
What we've got here is... failure to communicate. Some men you just can't reach. So you get what we had here last week, which is the way he wants it... well, he gets it.
47_47 is offline   Reply With Quote
The Following User Says Thank You to 47_47 For This Useful Post:
Yodaman (05-04-2015)
Old 05-04-2015, 03:04 PM   #12
Member
 
Join Date: May 2012
Location: Sarasota,Florida
Posts: 1,865
Rewards Points: 1,628
Default

ultimate concrete hardness


Quote:
Originally Posted by Yodaman View Post
Thanks Dan, spoken like a true engineer. In my case some strength is required to hold the weight without cracking the slab, and some degree of hardness would be beneficial to minimize abrasion from the steel wheels. Since the slab is poured, the only thing I have control over now is the cure process. Currently watering it daily and covered with .06 mil rubber roofing.

It was a 3000 PSI mix with long strand fiberglass added and rebar mesh. It also has about 4" of #4 modified gravel base compacted under it.

Don't know what that dumpster will be holding, but that 3000 psi mix sounds like it's a little on the lean side for what it's intended for, hope you poured it at a low slump.
Canarywood1 is offline   Reply With Quote
The Following User Says Thank You to Canarywood1 For This Useful Post:
Yodaman (05-04-2015)
Old 05-04-2015, 06:47 PM   #13
Member
 
Join Date: Mar 2015
Location: Upstate NY
Posts: 478
Rewards Points: 946
Default

ultimate concrete hardness


thanks all, this was a small pour so I thought I would check the boards on best curing process for hardness. In about 2 months we hope to put down a 20 x 30 mono. slab for a 2 car garage. Of all the building trades, concrete is not my strong suit so I am sure we'll have some questions. Thanks again,

Advertisement

__________________



let us know how your project turns out!
Yodaman is offline   Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Gap in concrete by corner of garage door jamb, intentional or not? daluu Concrete, Stone & Masonry 1 09-16-2012 05:23 PM
How to Calculate Store Bought Concrete Coverage by Bag Size Willie T How To Guides 9 11-29-2011 12:32 PM
Laminate Flooring on Two Different Concrete Heights mrken Flooring 4 12-14-2010 01:56 PM
New Concrete Walkway along side of house braverichard Building & Construction 0 11-03-2010 11:12 AM
How To Install Rigid Foam Insulation on Concrete earthad1 Building & Construction 9 10-26-2010 09:49 AM




Top of Page | View New Posts