The Best Paths to Green Concrete. Discussion on alternative binders to Portland cement for sustainable cementitious materials

The main challenge for concrete industry - and in general for construction materials - is to serve the two major needs of human society, the protection of the environment, on one hand, and the requirements of buildings and infrastructures by the world’s growing population, on the other. In the past concrete industry has satisfied these needs well. However, for a variety of reasons, the situation has changed dramatically in the last years. First of all, the concrete industry is the largest consumer of natural resources. Secondly, Portland cement, the binder of modern concrete mixtures, is not as environmentally friendly. The world's cement production, in fact, contributes to the earth's atmosphere about 7% of the total CO2 emissions, CO2 being one of the primary greenhouse gas (GHG) responsible for global warming and climate change. As a consequence, concrete industry in the future has to face two antithetically needs. In other words, how the concrete industry can feed the growing population needs being - at the same time - sustainable? The answer to this question is represented by the “3R-Green Strategy” widely discussed in the first chapter of this PhD thesis: Reduction in consumption of gross energy for construction materials production, Reduction in polluting emissions and Reduction in consuming not renewable natural resources. In particular, this thesis is focused on the alternative binders to Portland cement such as alkali-activated slag cements and calcium sulphoaluminate cement-based binders in order to manufacture sustainable mixtures for special applications such as repair mortars, lightweight reinforced plasters and concretes for slabs on ground. The experimental results show the feasibility of manufacturing both EN 1504-3 R3 class mortars and Portland-free concretes for jointless slabs on ground with calcium sulphoaluminate cement, supplementary cementitious materials (fly ash, ground granulated blast furnace slag) and hydrated lime instead of Portland cement. Moreover, alkali-activated mortars and concretes seem to be a reasonable alternative to natural hydraulic lime-based and/or traditional Portland cement-based mixtures for rehabilitation or restoration of ancient masonry buildings and existing concretes structures. Finally, a new sustainability index was developed taking into account the environmental impact, the performances and the durability of mixtures. In particular, in the environmental impact section, the natural raw materials consumption, the greenhouse gas emissions and the energy consumption have been considered. Furthermore, depending on the applications and the environments, design parameters and properties related to durability have been assigned to each mixture. less