>>Portland cement, which is the most common type, is made by grinding up limestone, mixing it with sand and clay then cooking it at extremely high heat – up to 1,450° C (2,642° F). Not only does the energy used to heat the mixture produce huge amounts of carbon dioxide, but the greenhouse gas is also released by the limestone itself during this process. In all, that means about 1 kg of CO2 is released for every kilogram of cement produced, which adds up to a staggering 8 percent of global CO2 emissions.

Rather than heating the ground-up limestone, the new process uses an electrolyzer, where electrodes split water molecules into oxygen and hydrogen. Doing so creates an acid at one electrode and a base at the other. The limestone is dissolved in the acid, and calcium hydroxide is created at the other end, in solid flakes. These flakes of lime can then be harvested to produce cement.<<

https://newatlas.com/materials/cement-electrolysis-technique-no-carbon-emissions/

PermeateFree said:

>>Portland cement, which is the most common type, is made by grinding up limestone, mixing it with sand and clay then cooking it at extremely high heat – up to 1,450° C (2,642° F). Not only does the energy used to heat the mixture produce huge amounts of carbon dioxide, but the greenhouse gas is also released by the limestone itself during this process. In all, that means about 1 kg of CO2 is released for every kilogram of cement produced, which adds up to a staggering 8 percent of global CO2 emissions.

Rather than heating the ground-up limestone, the new process uses an electrolyzer, where electrodes split water molecules into oxygen and hydrogen. Doing so creates an acid at one electrode and a base at the other. The limestone is dissolved in the acid, and calcium hydroxide is created at the other end, in solid flakes. These flakes of lime can then be harvested to produce cement.<<

https://newatlas.com/materials/cement-electrolysis-technique-no-carbon-emissions/

I’ve been worried about the carbon emissions from cement manufacture. There are two sources of CO2 from cement manufacture, in the conversion of calcium carbonate to calcium oxide and in the heating.

The magnitude gets a mention in http://www.globalcarbonatlas.org/en/CO2-emissions

Of the 36,153 megatonnes of CO2 produced by non-agricultural anthropogenic sources in 2017.
Cement manufacture accounts for 1,477 megatonnes.
Which is 4.1%, high enough to be significant.

Some of this CO2 later gets absorbed back by the concrete and mortar over long periods of time, turning calcium hydroxide back into calcium carbonate. The rate of CO2 absorption varies considerably.

mollwollfumble said:

PermeateFree said:

>>Portland cement, which is the most common type, is made by grinding up limestone, mixing it with sand and clay then cooking it at extremely high heat – up to 1,450° C (2,642° F). Not only does the energy used to heat the mixture produce huge amounts of carbon dioxide, but the greenhouse gas is also released by the limestone itself during this process. In all, that means about 1 kg of CO2 is released for every kilogram of cement produced, which adds up to a staggering 8 percent of global CO2 emissions.

Rather than heating the ground-up limestone, the new process uses an electrolyzer, where electrodes split water molecules into oxygen and hydrogen. Doing so creates an acid at one electrode and a base at the other. The limestone is dissolved in the acid, and calcium hydroxide is created at the other end, in solid flakes. These flakes of lime can then be harvested to produce cement.<<

https://newatlas.com/materials/cement-electrolysis-technique-no-carbon-emissions/

I’ve been worried about the carbon emissions from cement manufacture. There are two sources of CO2 from cement manufacture, in the conversion of calcium carbonate to calcium oxide and in the heating.

The magnitude gets a mention in http://www.globalcarbonatlas.org/en/CO2-emissions

Of the 36,153 megatonnes of CO2 produced by non-agricultural anthropogenic sources in 2017.
Cement manufacture accounts for 1,477 megatonnes.
Which is 4.1%, high enough to be significant.

Some of this CO2 later gets absorbed back by the concrete and mortar over long periods of time, turning calcium hydroxide back into calcium carbonate. The rate of CO2 absorption varies considerably.

> The limestone is dissolved in the acid, and calcium hydroxide is created at the other end, in solid flakes. These flakes of lime can then be harvested to produce cement. Of course, carbon dioxide is still produced during the process, as the limestone dissolves. But it isn’t released into the air – instead, it can be captured.

I’m pleasantly surprised at how good this process is. Normally, CaCO3 is reduced to CaO which is reacted with water to produce Ca(OH)2. The first process requires energy and tge second releases it. By going straight from CaCO3 to Ca(OH)2 in the electrolytic process energy is saved. But don’t let the slaked lime set in place, it has to be transported fast to where it is used, unlike CaO which can be stored indefinitely in a dry environment.

mollwollfumble said:

mollwollfumble said:

PermeateFree said:

>>Portland cement, which is the most common type, is made by grinding up limestone, mixing it with sand and clay then cooking it at extremely high heat – up to 1,450° C (2,642° F). Not only does the energy used to heat the mixture produce huge amounts of carbon dioxide, but the greenhouse gas is also released by the limestone itself during this process. In all, that means about 1 kg of CO2 is released for every kilogram of cement produced, which adds up to a staggering 8 percent of global CO2 emissions.

Rather than heating the ground-up limestone, the new process uses an electrolyzer, where electrodes split water molecules into oxygen and hydrogen. Doing so creates an acid at one electrode and a base at the other. The limestone is dissolved in the acid, and calcium hydroxide is created at the other end, in solid flakes. These flakes of lime can then be harvested to produce cement.<<

https://newatlas.com/materials/cement-electrolysis-technique-no-carbon-emissions/

I’ve been worried about the carbon emissions from cement manufacture. There are two sources of CO2 from cement manufacture, in the conversion of calcium carbonate to calcium oxide and in the heating.

The magnitude gets a mention in http://www.globalcarbonatlas.org/en/CO2-emissions

Of the 36,153 megatonnes of CO2 produced by non-agricultural anthropogenic sources in 2017.
Cement manufacture accounts for 1,477 megatonnes.
Which is 4.1%, high enough to be significant.

Some of this CO2 later gets absorbed back by the concrete and mortar over long periods of time, turning calcium hydroxide back into calcium carbonate. The rate of CO2 absorption varies considerably.

> The limestone is dissolved in the acid, and calcium hydroxide is created at the other end, in solid flakes. These flakes of lime can then be harvested to produce cement. Of course, carbon dioxide is still produced during the process, as the limestone dissolves. But it isn’t released into the air – instead, it can be captured.

I’m pleasantly surprised at how good this process is. Normally, CaCO3 is reduced to CaO which is reacted with water to produce Ca(OH)2. The first process requires energy and tge second releases it. By going straight from CaCO3 to Ca(OH)2 in the electrolytic process energy is saved. But don’t let the slaked lime set in place, it has to be transported fast to where it is used, unlike CaO which can be stored indefinitely in a dry environment.

Reducing GHG emissions is a big thing in the concrete world.

Amongst the techniques currently used are:

Replace cement with other cementitious materials, mainly fly ash or slag.
Replace cement with limestone.
Optimise the mix design to get the required strength with less cement.
Optimise the design to reduce the concrete strength required.
Optimise the design to reduce the volume of concrete required.
Use alternative cements, such as “geopolymers”.

The technique described sounds interesting though, if it can be implemented on a commercial scale.