Thursday, March 31, 2011
Cement - A swim through the Coega Harbour Wall
I took this clip some time back. I was freediving on the wall - that's my speargun you see in front of the camera. You even see a few musselcracker there in the wall.
Imagine the hydration reaction calcium aluminium silicate taking water into its structure and getting stronger - and it still continues today, even through it is very slow.
The gradual hardening of cement is a true everyday reaction.
I my next chemistry post I plan to focus on rubber and a bit of chemistry related to rubber and its use.
Monday, March 14, 2011
More about cement
Last post I showed some large scale application of cement in building a harbour wall. Cement is made from limestone and shale with other components containing aluminium and iron minerals. These are carefully mixed and heated to high temperatures with coal to form a "clinker". The clinker is then crushed and its composition is adjusted by adding gypsum to control setting times. Up to 5% of other additives may be added.
The main components of cement are 3CaO.SiO2 and 2CaO.SiO2 (tricalcium silicate and dicalcium silicate). These compounds make up the majority of the cement with the iron and aluminium clinker compounds and the gypsum making up the rest.
Cement can be made to set faster or slower by adding accelerators (e.g. calcium chloride or sodium nitrate)or retarders (e.g. citric acid, sodium gluconate).
Other additives can be added depending on the desired use. E.G. adding latex makes the cement harder and improve the workability.
When this mixture that we call cement is mixed with water it reacts with the water and sets. The reaction is called a hydration reaction, and cement can be used under water - it is hydraulic. In fact it needs the water for it to work well. Plaster is a mixture of cement and fine sand that sets hard over the brick of a wall making it smooth. If your builder is impatient and tries to speed up the drying of your cement it will be weaker, or it may crack as the water needed for hydration is lost.
When I had some building done at home my wife and the builder thought I had gone insane when they found me perched on the wall watering it with then garden hose! I wanted it hydrated.
Some times you may see concrete (cement and large pieces of stone and fine sand mixed) being covered with plastic or wet rags - these cover remain on for 48 hours - this allows the hydration to further strengthen the cement or concrete before it dries. Actually cement gradually gets stronger the longer it stays wet - the strength will double from 8 hours to three days and after another 27 days the strength will double again.
From this you can see that the impatience of builders to complete the job can lead to weakened structure.
Here is a chemistry based tip for you if you build. Keep an eye on the builder and staff - they should only mix as much cement as can be used in 1 hour (the cement bag normally reminds them anyway - printed user-directions). Do not let them mix the cement sand and water just before lunch. The cement gets started reacting and the hydration reaction is well under way while they rest in the shade for that hour or so - your structure ends up being weaker if the builder violates this procedure. Two years later your plaster is falling off the wall and the builder is long gone. The same goes for tile adhesive and grouting as these materials are also cement based.
Cement is stronly alkaline - in the manufacture the limestone breaks down to carbon dioxide gas and calcium oxide rendering it alkaline. Some alkalinity is released during hydration as well. Keep cement off your skin or it will slowly dissolve your skin.
Fact: Did you know that you can make lime Ca(OH)2 by heating sea shells or egg shells to 850 deg C?
Cement reacts with water and give off heat at the same time - in the building of large concrete structure water cooled pipes may be included to prevent cracking of the structure.
So there you have a bit of everyday chemistry - we rely on the chemical reactions of the past for our structure of the present. There is more water in your walls that you may think.
The main components of cement are 3CaO.SiO2 and 2CaO.SiO2 (tricalcium silicate and dicalcium silicate). These compounds make up the majority of the cement with the iron and aluminium clinker compounds and the gypsum making up the rest.
Cement can be made to set faster or slower by adding accelerators (e.g. calcium chloride or sodium nitrate)or retarders (e.g. citric acid, sodium gluconate).
Other additives can be added depending on the desired use. E.G. adding latex makes the cement harder and improve the workability.
When this mixture that we call cement is mixed with water it reacts with the water and sets. The reaction is called a hydration reaction, and cement can be used under water - it is hydraulic. In fact it needs the water for it to work well. Plaster is a mixture of cement and fine sand that sets hard over the brick of a wall making it smooth. If your builder is impatient and tries to speed up the drying of your cement it will be weaker, or it may crack as the water needed for hydration is lost.
When I had some building done at home my wife and the builder thought I had gone insane when they found me perched on the wall watering it with then garden hose! I wanted it hydrated.
Some times you may see concrete (cement and large pieces of stone and fine sand mixed) being covered with plastic or wet rags - these cover remain on for 48 hours - this allows the hydration to further strengthen the cement or concrete before it dries. Actually cement gradually gets stronger the longer it stays wet - the strength will double from 8 hours to three days and after another 27 days the strength will double again.
From this you can see that the impatience of builders to complete the job can lead to weakened structure.
Here is a chemistry based tip for you if you build. Keep an eye on the builder and staff - they should only mix as much cement as can be used in 1 hour (the cement bag normally reminds them anyway - printed user-directions). Do not let them mix the cement sand and water just before lunch. The cement gets started reacting and the hydration reaction is well under way while they rest in the shade for that hour or so - your structure ends up being weaker if the builder violates this procedure. Two years later your plaster is falling off the wall and the builder is long gone. The same goes for tile adhesive and grouting as these materials are also cement based.
Cement is stronly alkaline - in the manufacture the limestone breaks down to carbon dioxide gas and calcium oxide rendering it alkaline. Some alkalinity is released during hydration as well. Keep cement off your skin or it will slowly dissolve your skin.
Fact: Did you know that you can make lime Ca(OH)2 by heating sea shells or egg shells to 850 deg C?
Cement reacts with water and give off heat at the same time - in the building of large concrete structure water cooled pipes may be included to prevent cracking of the structure.
So there you have a bit of everyday chemistry - we rely on the chemical reactions of the past for our structure of the present. There is more water in your walls that you may think.
Friday, March 11, 2011
Where did you go today? Any chemistry involved?
Last week after I wrote that post I climbed into a helicopter at the PE airport and headed north east.
An internal combustion engine got me there - that combustion involved the reaction of fuel consisting mostly of carbon and hydrogen (hydrocarbon) with air which contains oxygen.
During the combustion the carbon in the fuel forms carbon dioxide. Possibly carbon monoxide will form as well, and hopefully no carbon(black smoke). The hydrogen combines with oxygen from the air to form water. Along with these gases - carbon dioxide and water vapour - comes a lot of heat. The hot gases are what drive the 4 cylinder engine in the small chopper I went up in.
Now being off the ground and a bit closer to the sun I thought of the ozone layer.
Ozone, (O3) is a form of oxygen that is unstable and readily reverts back to oxygen ( O2) as we know it, and breathe it. It has a short half life - about 30 minutes. That means the concentration drops by 50% in 30 minutes. Higher up in the atmosphere (10 -50 km up) energetic radiation from the sun can break normal oxygen apart to form two free oxygen atoms that are reactive. These can then react with another normal oxygen atom to form ozone.
O2 + light = 2 O.
O + O2 = O3
This is how ozone forms in nature. The ozone layer protects us and other life forms from UV radiation by absorbing most of that harmful light. Click here for a link to how ozone is distributed in the atmosphere.
Lightning can also split apart oxygen allowing it to form ozone.
We can make ozone using sparks in a corona discharge tube. Air (or pure oxygen) is pumped through the tube and an air ozone mixture comes out. A strong UV light will also make ozone.
Ozone is used mostly in water treatment for drinking, swimming pools, of aquaculture. It kill bugs or oxidizes unwanted pollutants.
So that is a bit of natural chemistry (photo chemistry) that happens each day, and saves our bacon in the process. Look up, and imagine the ozone formation, or next time there is a fine electric storm - imagine the lightening forming ozone.
Now back to my flip in the chopper. About 12 km northeast of the airport I looked down at the Coega harbour.
Now there's is a big project that involved plenty of chemistry.
Obviously a lot of fuel was burned to build that wall.
Each of those dolosse (wave breaking structures) lying down there on the sides of the wall weighs about 30 tonnes. That's a lot of cement used to make the concrete!
Ah! yes, I have walls around me now, and you probably do too. Mostly these walls are made of brick and cement.
What is cement?
How is it made?
How does it get hard? Does it dry? My builder says yes, in fact he wants it to dry fast so he can paint and get on with the next job.
What does the chemistry suggest? Dry it fast?
In a subsequent post I will talk about cement manufacture and setting ; and perhaps we can have a closer look at the Coega wall - I will take you into the wall, and under the water...
An internal combustion engine got me there - that combustion involved the reaction of fuel consisting mostly of carbon and hydrogen (hydrocarbon) with air which contains oxygen.
During the combustion the carbon in the fuel forms carbon dioxide. Possibly carbon monoxide will form as well, and hopefully no carbon(black smoke). The hydrogen combines with oxygen from the air to form water. Along with these gases - carbon dioxide and water vapour - comes a lot of heat. The hot gases are what drive the 4 cylinder engine in the small chopper I went up in.
Now being off the ground and a bit closer to the sun I thought of the ozone layer.
Ozone, (O3) is a form of oxygen that is unstable and readily reverts back to oxygen ( O2) as we know it, and breathe it. It has a short half life - about 30 minutes. That means the concentration drops by 50% in 30 minutes. Higher up in the atmosphere (10 -50 km up) energetic radiation from the sun can break normal oxygen apart to form two free oxygen atoms that are reactive. These can then react with another normal oxygen atom to form ozone.
O2 + light = 2 O.
O + O2 = O3
This is how ozone forms in nature. The ozone layer protects us and other life forms from UV radiation by absorbing most of that harmful light. Click here for a link to how ozone is distributed in the atmosphere.
Lightning can also split apart oxygen allowing it to form ozone.
We can make ozone using sparks in a corona discharge tube. Air (or pure oxygen) is pumped through the tube and an air ozone mixture comes out. A strong UV light will also make ozone.
Ozone is used mostly in water treatment for drinking, swimming pools, of aquaculture. It kill bugs or oxidizes unwanted pollutants.
So that is a bit of natural chemistry (photo chemistry) that happens each day, and saves our bacon in the process. Look up, and imagine the ozone formation, or next time there is a fine electric storm - imagine the lightening forming ozone.
Now back to my flip in the chopper. About 12 km northeast of the airport I looked down at the Coega harbour.
Now there's is a big project that involved plenty of chemistry.
Obviously a lot of fuel was burned to build that wall.
Each of those dolosse (wave breaking structures) lying down there on the sides of the wall weighs about 30 tonnes. That's a lot of cement used to make the concrete!
Ah! yes, I have walls around me now, and you probably do too. Mostly these walls are made of brick and cement.
What is cement?
How is it made?
How does it get hard? Does it dry? My builder says yes, in fact he wants it to dry fast so he can paint and get on with the next job.
What does the chemistry suggest? Dry it fast?
In a subsequent post I will talk about cement manufacture and setting ; and perhaps we can have a closer look at the Coega wall - I will take you into the wall, and under the water...
Friday, March 4, 2011
Every Day Chemistry
There are some aspect of chemistry we experience every day.
Can you think of some everyday chemistry - outside of your body, that is?
Let me ask a you few questions:
1. Where did you go today?
2. What chemical reactions took place to get you there while you travelled?
3. What place/s did you visit?
4. What chemistry took place to build that place, or to decorate it?
Take some time to think about it and I will cover a reaction or two in my next post.
I will leave you with though video clip. It is a though provoking talk by Thomas Thwaites entitled: "How I built a toaster -- from scratch"
Enjoy.....
Can you think of some everyday chemistry - outside of your body, that is?
Let me ask a you few questions:
1. Where did you go today?
2. What chemical reactions took place to get you there while you travelled?
3. What place/s did you visit?
4. What chemistry took place to build that place, or to decorate it?
Take some time to think about it and I will cover a reaction or two in my next post.
I will leave you with though video clip. It is a though provoking talk by Thomas Thwaites entitled: "How I built a toaster -- from scratch"
Enjoy.....
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