A Concrete Fix to Global Warming

Comments

• Carbonation of Concrete jaywetmore on 07/23/2008 at 12:32 PM

  Posts: 1 Avg Rating:

  For engineers evaluating the condition of concrete to determine remaining life, the extent of carbonation is an important indicator. The closer the carbonation is to the reinforcing steel the shorter the remaining life. Concrete's high alkalinity inhibits the oxidation of the reinforcing steel. Carbonation neutralizes the concrete, resulting in less protection for the metal reinforcement. Carbonation is contra-indicated for reinforced and prestressed concrete. It is ok in unreinforced concrete like you might find in a sidewalk. Rate this comment: (Reply)

  • 	Re: Carbonation of Concrete Siphon on 07/26/2008 at 6:18 AM
    Posts: 112 Avg Rating:	Reinforced concrete can be done with other materials, such as composites. They don't oxidize much at all. This is an emerging industry because it's possible to make higher quality reinforced concrete. Rate this comment: (Reply)

  • 	Re: Carbonation of Concrete ralph@bfmarch.com on 08/01/2008 at 10:15 AM
    Posts: 1	"Concrete's high alkalinity inhibits the oxidation of the reinforcing steel." Sounds like more, not less protection for the steel against rusting. What am I missing? Rate this comment: (Reply)

• Does this apply to AAC blocks? mulp on 07/23/2008 at 4:17 PM

  Posts: 5 Avg Rating:

  Aerated autoclaved concrete is attractive as an inert insulating block, but it obviously requires autoclaving to cure the foamed concrete.  The autoclaving not only adds to the cost, but also to the carbon gas emissions from the burning of coal to produce the steam. AAC blocks and panels can replace standard concrete blocks for many application, and for green construction are getting a lot of attention. But their cost in dollars and CO2 emissions are short term obstacles. Rate this comment: (Reply)

• 	CO2 reduction Siphon on 07/26/2008 at 6:20 AM
  Posts: 112 Avg Rating:	If concrete is 5% of human CO2 emissions, and this new concrete reduces emissions by 20%, then that's a 1% reduction of total emissions. Nice - every little bit helps - but not spectacular. By the time this tech is widely implemented, concrete use will highly likely be much larger than 120% of today's levels, making total CO2 emissions from concrete bigger than today. Rate this comment: (Reply)

• 	concrete vs cement kearley on 07/30/2008 at 6:35 PM
  Posts: 1 Avg Rating:	I believe it is the manufacturing of cement NOT concrete that is 5% of man-made C02 - can someone confirm? Rate this comment: (Reply)

• The Carbonation of Dense Concretes John Harrison on 09/03/2008 at 12:42 AM

  Posts: 1

  1. There are no technical or sequestration advantages in using considerable energy to make Portland cement in which silicates and to a lesser extent aluminates predominate only to carbonate them as many researchers are attempting to do. 2. The carbonation of Portlandite which is a minor but significant component formed on the hydration of Portland cement increases strength but lowers the pH resulting in the break down of the passive oxide layer on steel and thus corrosion. 3. How carbonation occurs depends mainly on the maturity of the concrete, the partial pressure of CO2, humidity and permeability. 4. The construction of special carbonation rooms near point sources of CO2 and the logistics involved in moving either fresh concrete or finished product to such rooms or other facilities is and will become increasingly more prohibitive. 5. Because the carbonation of silicate and aluminate phases occurs much more readily in uncured concretes it is not only cheaper but technically much better to optimise natural carbonation. Better microstructure as well as chemical stability is the main outcome. 6. It is also more economical to naturally carbonate concretes provided rate issues and in the case of pre-mix concrete, pH issues if steel reinforcing is to be used, can be overcome. Rate this comment: (Reply)