March 31, 2009, 9:48 pm
Remixing concrete to be environmentally friendly
Concrete is the builder's dream material of the modern age - when reinforced with steel it can support enormous structures, but technology has now added a whole range of additional properties to increase its strength and durability, and even its ability to stay clean!
[New York Times]
The Romans were the first to use concrete on a large scale - do you know what molecules are used in making modern concrete ?
First you need cement , which is calcium hydroxide, Ca(OH)2
For extra early strength in the concrete, pozollans can be added which contain silica and react chemically with the calcium hydroxide to make calcium silicates.
Crushed rocks are added, with some sand and water, and the mixture is mixed well. The cement binds the other components... and in a short time the concrete sets hard.
So where is the environmental issue?
The manufacture of Portland cement produces 5% of the world's carbon dioxide , which is a major greenhouse gas.
Replacing some of the cement in concrete mixes with pollozans that are industrial waste products reduces the carbon footprint of the concrete as well as giving it slightly different properties.
But some scientists are going a step further by making concrete that can actually capture carbon dioxide from the atmosphere - this is called sequestering.