First the amount of water used makes a very large difference, it afects how the sand rock and cement binds togather to make concrete. For exsample you could make a concrete ball that you could crush with your bare hand, and a simular ball that could take 2500 PSI and higher with just a difference in water as you mix it. As I and mostly my family have been in the concrete producing biz for over 80 years, I will just tell you that there is a heck of alot more in concrete than just sand rock cement and water. And I would be very surprized if you could even find concrete these days with just those in it. Btw I would not call sand and cement concrete. Here is one for you to think about. Do you think that a cannue made of concrete would float?
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- Thread starter Cliff Stamp
- Start date
HermanKnives
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cliff,
ok, now i know. just one more question: do you ever use a tool for its actual intended purpose? probly not but i had to ask.
to all
if you ever get to drive by my place, i will have the coolest carved and engraved driveway in the neighborhood
ok, now i know. just one more question: do you ever use a tool for its actual intended purpose? probly not but i had to ask.
to all
Cougar Allen
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Although concrete varies greatly in strength and toughness, that's irrelevant. The test is to attack the concrete until the edge is affected, then observe whether the damage to the edge is in the form of fracturing or of rolling and upsetting. The characteristics of the particular piece of concrete you use will determine how much the concrete is damaged -- but nobody cares (unless from idle curiosity) -- and possibly how many whacks or how hard a whack it takes before the edge is visibly damaged -- again, nobody cares. The only purpose of the test is to see what form of damage occurs to the edge, and any concrete is good enough to damage an edge.
Using concrete for the test is more convenient than wood because you don't have to spend a lot of time chopping concrete before you get the visible damage to the edge that you're looking for. You could achieve the same results on wood, "using a knife for its actual intended purpose" ... if you didn't mind taking the time, or if you had a lot of wood that needed to be chopped anyway....
By the way, this applies just as much to knives designed only for cutting as to chopping knives. Even whittling the softest wood, or cutting meat, whatever, will damage an edge eventually, and it is useful to know what form that damage will take when it eventually occurs.
-Cougar :{)
Using concrete for the test is more convenient than wood because you don't have to spend a lot of time chopping concrete before you get the visible damage to the edge that you're looking for. You could achieve the same results on wood, "using a knife for its actual intended purpose" ... if you didn't mind taking the time, or if you had a lot of wood that needed to be chopped anyway....
By the way, this applies just as much to knives designed only for cutting as to chopping knives. Even whittling the softest wood, or cutting meat, whatever, will damage an edge eventually, and it is useful to know what form that damage will take when it eventually occurs.
-Cougar :{)
Cougar I am not sure I understand you right. You are not saying that it does not matter how you get the damage are you. You can not meen that over time you will get the same damage cutting bread as you will get cutting concrete? Well, maybe you could if it was my sister inlaws bread. I think what and how a edge gets damaged is the most inprtant part of a test and what that damage is *chipping or rolling) can then be judged. Also cann't a edge just be warn away, without it being roled or chipped?
Cougar Allen
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"Just worn away" means it chipped in pieces too small to see.
With many knives in many uses the edge will be deformed without fracturing and you can steel it back to sharpness, but you can only do that a limited number of times before it starts fracturing. Bend it back and forth enough times, it breaks. Provided the user knows enough to steel the edge when it's deformed, there are two significant factors in edge-holding: how long can you use it between steelings, and how many times can you steel it before steeling is no longer enough and you have to sharpen it?
Although bashing concrete or steel pipe might seem far removed from cutting soft materials, the way it affects an edge can give you useful information. If the edge of that kitchen knife fractures at first contact with something hard, you're not going to be able to cut soft materials and restore the edge with just a few strokes on a steel the first few times it gets dull. If it deforms instead, you will. That is significant because steeling an edge back to sharpness is much faster than grinding it back to sharpness.
That isn't the whole story, of course. How easily it deforms is significant, too. Bashing concrete is not a sufficient test to prove a knife is good; it's only part of the testing process (and not even a necessary part if you don't mind doing enough cutting of softer materials to find the same information that way).
-Cougar :{)
With many knives in many uses the edge will be deformed without fracturing and you can steel it back to sharpness, but you can only do that a limited number of times before it starts fracturing. Bend it back and forth enough times, it breaks. Provided the user knows enough to steel the edge when it's deformed, there are two significant factors in edge-holding: how long can you use it between steelings, and how many times can you steel it before steeling is no longer enough and you have to sharpen it?
Although bashing concrete or steel pipe might seem far removed from cutting soft materials, the way it affects an edge can give you useful information. If the edge of that kitchen knife fractures at first contact with something hard, you're not going to be able to cut soft materials and restore the edge with just a few strokes on a steel the first few times it gets dull. If it deforms instead, you will. That is significant because steeling an edge back to sharpness is much faster than grinding it back to sharpness.
That isn't the whole story, of course. How easily it deforms is significant, too. Bashing concrete is not a sufficient test to prove a knife is good; it's only part of the testing process (and not even a necessary part if you don't mind doing enough cutting of softer materials to find the same information that way).
-Cougar :{)
Cougar Allen
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I wouldn't ask you to buy anything without trying it for yourself. Try bashing concrete and cutting soft materials for a long time with the same knives and see if you find the effects of bashing concrete have any correlation with the effects of long periods of normal use. See for yourself, don't take anything on faith....
-Cougar :{)
-Cougar :{)
Cobalt
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db, you are correct of course about concrete being very different from batch to batch as far as compressive strength is concerned(obviously measure in psi as you stated). As I'm sure you also know, tensile strength and impact resistance is very low in concrete, unless it is reinforced and even then toughness does not increase much. I think this what what Cliff was trying to point out. If you lift a piece of concrete 4 inches thick, of X length and Y width, with a compressive strength rating of say 3000 psi and one with the same measurements but 1000 psi compressive strength, both in the air and then hit each with a sledge hammer, you will not notice a difference in the two as far as toughness is concerned, because the toughness rating is so low that the difference between the two materials is irrelevant.
This is also the reason why reinforced concrete buildings in earthquake country are not used any more and were replaced with steel frame buildings. The toughness, ductility is higher in steel.
Now, having said all that, db, is right that there is a lot of difference in concrete. The concrete used in driveways and homes is much weaker than the concrete used in large high rise buildings, or in multilevel parking garages. Cliff, I think you may find that this type of concrete offers much more resistance than what you are working with and may cause considerable more damage. The reason for this is simple: the mixtures used in high strength requirement areas is much more homogenous and of higher cement density versus home/garage flooring concrete which tends have more porosity due to it's lighter strength design. You can't only look at impact toughness, hardness is also a factor and it will vary, because the stronger mixture will provide enough impact resistance to make the hardness of the cement, a factor.
db, am I going to have to nickname you: clinker. I assume that you know that term if you are in the concrete business.
This is also the reason why reinforced concrete buildings in earthquake country are not used any more and were replaced with steel frame buildings. The toughness, ductility is higher in steel.
Now, having said all that, db, is right that there is a lot of difference in concrete. The concrete used in driveways and homes is much weaker than the concrete used in large high rise buildings, or in multilevel parking garages. Cliff, I think you may find that this type of concrete offers much more resistance than what you are working with and may cause considerable more damage. The reason for this is simple: the mixtures used in high strength requirement areas is much more homogenous and of higher cement density versus home/garage flooring concrete which tends have more porosity due to it's lighter strength design. You can't only look at impact toughness, hardness is also a factor and it will vary, because the stronger mixture will provide enough impact resistance to make the hardness of the cement, a factor.
db, am I going to have to nickname you: clinker. I assume that you know that term if you are in the concrete business.
Cobalt very well said, I think you made my point much better than I did. Now here I sit with a 6 inch slump.
I'll take 2% air with my humble pie please.
Just one more thing to ad there is even a large difference in the concrete used in driveways, basements, sidewalks, foundations, home walls, and other home uses. Some of the hardest concrete you will ever find will be found on a dam not really because of the mix but because of how it hardens and staying wet.
[This message has been edited by db (edited 04-30-2000).]
I'll take 2% air with my humble pie please.
Just one more thing to ad there is even a large difference in the concrete used in driveways, basements, sidewalks, foundations, home walls, and other home uses. Some of the hardest concrete you will ever find will be found on a dam not really because of the mix but because of how it hardens and staying wet.
[This message has been edited by db (edited 04-30-2000).]
Cliff Stamp
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Herman :
As defined by the maker? I don't know, I have never asked them. Feel free if you want, the contact info for most of the makers I have worked with is in the reviews.
Db:
There are lots of people who think strength and toughness make no difference if you are not prying / hammering / chopping, makers as well as normal users (as this thread illustrates) so you are not alone. I wouldn't want a knife from anyone who thought that way though - then again it is very likely that they wouldn't want me as a customer either. No big deal as long as both sides are open, there are lots of makers and lots of buyers for everyone to get satisfied at every level of product.
Cobalt :
Excellent point I have not considered that as I have never seen concrete of that strength. Thanks for the specific examples, I'll look into it. Would you have any references for how cement and water and sand ratio determine tensile strenth, compression strength and impact toughness. As I might get curious enough to do some mixing on my own.
Cougar, excellent description, I am currently in process of writing up an explanation of how materials properties effect blade performace. Those posts are definately getting a link.
-Cliff
[This message has been edited by Cliff Stamp (edited 04-30-2000).]
As defined by the maker? I don't know, I have never asked them. Feel free if you want, the contact info for most of the makers I have worked with is in the reviews.
Db:
There are lots of people who think strength and toughness make no difference if you are not prying / hammering / chopping, makers as well as normal users (as this thread illustrates) so you are not alone. I wouldn't want a knife from anyone who thought that way though - then again it is very likely that they wouldn't want me as a customer either. No big deal as long as both sides are open, there are lots of makers and lots of buyers for everyone to get satisfied at every level of product.
Cobalt :
Excellent point I have not considered that as I have never seen concrete of that strength. Thanks for the specific examples, I'll look into it. Would you have any references for how cement and water and sand ratio determine tensile strenth, compression strength and impact toughness. As I might get curious enough to do some mixing on my own.
Cougar, excellent description, I am currently in process of writing up an explanation of how materials properties effect blade performace. Those posts are definately getting a link.
-Cliff
[This message has been edited by Cliff Stamp (edited 04-30-2000).]
Cobalt
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Cliff, unfortunatelly, I have absolutely no books, papers, blueprints or specs from which to give you the specifics on. I am living bare right now and this includes knives and all my other hobbies. Everything is 3000 miles away from me in a warehouse collecting dust and most likely rust, including all my engineering stuff. However, almost any contractor that manages high rise construction projects can give you the info.