The question of the ecology of concrete, raised more and more often within the construction industry, is much more complex than it would appear at first glance.
First, we should remember that cement production causes CO2 emissions. Saying nothing of the disputes between the supporters and opponents of the thesis that climate warming is attributable first and foremost to humanity’s actions, it is, regardless, a fact that the emission of CO2 to the atmosphere is not a very ecological activity. Due to this, the cement burning technology is undergoing constant modifications with regard to decreased emissions of noxious gasses. Some manufacturers take pride in having implemented more ecological methods that actually decrease the emissions of carbon dioxide during cement production. This way, CO2 emissions can be decreased by over 30 percent. Neither should we forget that hardening concrete absorbs carbon dioxide, thus the ecological costs of its production should be reduced by the amount of absorbed gas.
Furthermore, there is more advanced research underway, intended to find an ecological material that could partially replace cement in concrete mixtures and thus decrease its production. Ashes created by burning the by-products obtained when burning biofuels are currently undergoing testing. Time will tell if they are a suitable replacement, but the prospects look quite good.
The use of admixtures and additives remains a controversial issue. It is presently difficult to imagine a situation where the construction industry stops enriching concrete mixtures with plasticizers, air entraining admixtures or distributed reinforcement completely. Even ordinary composite, used e.g. for constructing foundations, should simply be properly enriched. Special concretes, used in the industry or for the construction of dams, bridges, etc., downright have to contain proper additives. The life of concrete and its resistance to destructive factors hinges on them.
If it ever turns out that there exist natural and ecological substances that harden concrete perfectly against, e.g., the effects of acids or damage caused by vibrations or the cavitation effect, then they will surely be taken into account when planning the composition of concrete. Until that happens, we are forced to stay with the technology currently in use. Of course, it is important to remember that additives and admixtures that end up in concrete are thoroughly examined with regard to possible harmful effects on health. You have no reason to be concerned in that respect.