Wow, this is a late post! I'm really sorry for such a delay; I had a terrible cold that drained so much energy out of me. Anyway, this blogpost is something I've been wanting to write for quite a while! It's a bit different from the previous ones - it's about cracked concrete in winter.
It was early December when I first noticed the cracks in the concrete around school campus. I had just finished school and was on my way to the school gate, when I saw deep cracks at the edges. I pointed them out to my friend, but she didn't think they were that different from before. But I continued to observe the concrete around the manholes, the parking spaces and the school field...the entire campus, which suddenly seemed to crumble away like a falling kingdom.
As winter progressed, it became clearer: in some areas, the concrete was sinking but in others, the concrete was rising, making huge, uneven crevices through which rainwater and snow fell. It became so bumpy that a bicycle ride through these areas was bound to get a little shakier.
So, what makes concrete crack? I've never seen any concrete road that's completely free of cracks...because all concrete has a tendency to crack. It has a low tensile strength while it has a high compressive strength (the former is only 10% ~ 20% of the latter). Another characteristic - a low thermal expansion coefficient - means that it is not flexible enough to expand or contract according to temperature. That is why the freeze-thaw cycle in the winter is a popular explanation for concrete cracking. With the changes in temperature and humidity, the concrete distends and shrinks, making irregular cracks that are difficult to maintain.
I recently saw the school maintenance staff walking around the campus, measuring the depth and length of the cracks with a paper ruler. Perhaps they are planning on getting new concrete? It won't be happening any time soon, though; snow and rainfall are still sporadic yet frequent, and a new coat of concrete in such conditions is not going to produce favorable results-!
The next two pictures don't show any cracks but contain the little beauties I saw on other parts of concrete :)
http://www.angieslist.com/articles/why-concrete-cracks-and-how-prevent-it.htm
http://civil-engg-world.blogspot.kr/2009/04/relation-between-compressive-and.html
http://en.wikipedia.org/wiki/Properties_of_concrete#Cracking
It was early December when I first noticed the cracks in the concrete around school campus. I had just finished school and was on my way to the school gate, when I saw deep cracks at the edges. I pointed them out to my friend, but she didn't think they were that different from before. But I continued to observe the concrete around the manholes, the parking spaces and the school field...the entire campus, which suddenly seemed to crumble away like a falling kingdom.
So, what makes concrete crack? I've never seen any concrete road that's completely free of cracks...because all concrete has a tendency to crack. It has a low tensile strength while it has a high compressive strength (the former is only 10% ~ 20% of the latter). Another characteristic - a low thermal expansion coefficient - means that it is not flexible enough to expand or contract according to temperature. That is why the freeze-thaw cycle in the winter is a popular explanation for concrete cracking. With the changes in temperature and humidity, the concrete distends and shrinks, making irregular cracks that are difficult to maintain.
I recently saw the school maintenance staff walking around the campus, measuring the depth and length of the cracks with a paper ruler. Perhaps they are planning on getting new concrete? It won't be happening any time soon, though; snow and rainfall are still sporadic yet frequent, and a new coat of concrete in such conditions is not going to produce favorable results-!
The next two pictures don't show any cracks but contain the little beauties I saw on other parts of concrete :)
http://civil-engg-world.blogspot.kr/2009/04/relation-between-compressive-and.html
http://en.wikipedia.org/wiki/Properties_of_concrete#Cracking
