Dear Saeed,

This is an interesting and topical subject.

In the 1990s, an experimental site named Biosphere 2 was installed in the Arizona desert to replicate a viable ecosystem. In this closed environment, scientists surprisingly discovered that oxygen levels were decreasing unexpectedly. They then found that the walls of the cabin, made of cement, had absorbed some, without knowing exactly how much. If the amount of CO2 that can be absorbed by the cement is high, a world of possibilities could open. The idea would be to capture the CO2 produced during the manufacture of cement. CO2 would be used to produce fuel that would go, for example, in an airplane, and the aircraft would produce CO2 that would subsequently be absorbed by the cement. This gives a closed cycle. We do not add CO2 to the atmosphere because we recover it after generating it. Cement production is a polluting activity that should remain, even after the abandonment of oil and coal. Plants that produce cement, now considered as major polluters, could therefore be part of the solution of tomorrow.

On the other hand, for the first time, the degradation of cements over time has been translated by researchers in terms of CO2 absorption. It is a new, important and rapidly growing carbon sink that must now be taken into account. Between 1930 and 2013, about 4.5 billion tons of carbon were sequestered in cements, according to an international study conducted by the Chinese Academy of Sciences. This storage occurs over time and the degradation of cements through a carbonation process that reacts the calcium hydroxide contained in the cements with atmospheric carbon dioxide. This is the first time this amount has been evaluated and it has never been taken into account in carbon balances. But, as the researchers pointed out in an article published in the journal Nature Geoscience, if the degradation of the cement makes it possible to capture atmospheric carbon, the manufacture of cement and in particular of "clinker" (its main constituent forming a solid paste of limestone and clay) is a generator of greenhouse gases. The manufacture of cements is responsible for about 5% of anthropogenic carbon emissions and the degradation of these same cements, for the period 1930-2013, offs about 43% of these emissions. In the end, the balance of the cement remains negative but the delta could decline further in the next few years. Indeed, according to this study, this phenomenon is growing rapidly: from 0.10 Gt C / year (billion tonnes of carbon per year) in 1998 to 0.25 Gt C / year in 2013. The cements thus constitute a new carbon sink, which must now be integrated into climate modeling, that what the scientists point out.

Traditional concrete or Portland concrete is manufactured by heating limestone and clay at 1500 ° C in giant kilns. The considerable amount of energy required to heat the raw material, as well as the chemical reactions that take place during the decomposition of the limestone, produce, according to the International Energy Agency, some 0.83 tons of CO2 per ton of cement. When cement is mixed with water in the construction, each tonne absorbs 0.4 tonnes of CO2. There remains a net production of 0.4 tonnes of CO2 for every tonne of cement used. Novacem (a company from the Imperial College of London) is developing a cement based on magnesium oxide, a derivative of mineral silicates. Heated at a much lower temperature of 650 ° C, it emits less than 0.5 tonnes of CO2 per tonne of cement produced. But the crucial point is its ability to absorb large amounts of CO2 when it hardens.

Regards

Bachir ACHOUR

Dear Professor Bachir

very useful and complete answer, I had some studies on biological concrete, also some biological studies, there are a kind of bacteria which produces oxygen in aquatic environment I hope to work on this topic but I was wondering is there any study on this issue already, I got my answer perfectly, the so called bacteria is cyanobacteria.

many thanks for your response.

Best wishes

May any Green Blue algae or such type will be in the small vicinity of or micropores will also act as phenpmenon oxygen release

Dear Saeed,

In fact, I do not know of any particular study on this subject. This is very interesting because the cyanobacteria, despite a possible superficial and ecological resemblance, are not algae but colonial bacteria. They are most often filamentous forms of possibly sticky consistency, the largest number of which is microscopic. Despite their vernacular name they can take various colors and are rarely blue. These colors come from blue (phycocyanin) and red (phycoerythrin) pigments that mask chlorophyll a.

The oxyphotobacteria carry out oxygenic photosynthesis and can therefore transform solar energy into chemical energy usable by the cell by fixing carbon dioxide (CO2) and releasing oxygen (O2). Some of them can in certain conditions fix the dinitrogen. They are able to consume the organic carbon present in their environment.

CO2 fixation has been attested for at least 3.7 billion years, but nothing is known about the organisms that cause it. Cyanobacteria and their ancestors produced a major ecological upheaval by their release of oxygen into the atmosphere (they are responsible for the Great Oxidation by 2.45 billion years ago) and by their contribution to the first biological carbon sink and a deacidification of the oceans, when organized in fixed colonies (stromatolites), capable of producing limestone.

Regards

Bachir ACHOUR