ALCALINE CONCRETES FREE OF FORTLAND CEMENT

Abstract

Nowadays Portland cement concrete is the most widely used building material. Its mechanical properties, the quality price ratio, performance in general, have contributed to the success of this material along 20th century. However the process of fabrication of Portland cement involves some problems (energetically and environmentally speaking) affecting the general opinion of modern societies on the potential risks of such a process of fabrication: Very high temperatures need to be reached (1400°C - 1500°C), natural quarries are destroyed during the extraction of raw materials; CO, and NO, are emitted to the atmosphere. Finally, traditional concrete also presents some durability problems, which are currently difficult to overcome. This paper offers some results obtained in an ongoing investigation. The investigation is related with the elaboration of alkaline concrete: concrete in which the Portland cement is completely replaced (100%) by fly ash and the mixing water by an alkaline dissolution. This new alkaline concrete may reach a compressive strength of 50-60 MPa at 20 hours after the mixing. Additionally, alkaline concrete has a very good dimensional stability (it hardly undergoes shrinkage). Also, the adherence between the matrix and the steel reinforcement is very good; and because of the very similar chemical and mineral composition of alkaline cements with natural zeolites, it is expected that the new concrete will have very good durability properties. Finally the price of the new concrete is competitive with Portland cement concrete prices and the application of the new material in the precast industry could be done with almost no problems.