Determination of the extreme reduction of concrete strength due to acid mine drainage by laboratory tests on specimens located in a real environment

Abstract

The reduction in durability due to the drainage of acidic mine water is a serious problem that causes the deterioration of the structural materials located in this type of environment, spreading throughout all the sulphide mining operations of the world, and in particular, in the Iberian Pyritic Belt where there are a large number of abandoned mines.In this research the evolution over time of the mechanical characteristics of concrete affected by acid mine drainage has been studied, as well as some properties of concrete that are closely related to durability. Several samples of concrete (40 MPa of compressive strength, w/c ratio of 0.45, 435 kg/m3 of sulphate resistant cement), were subjected to a real acidic environment, allowing the harmful effects of erosion and the action of bacteria to be taken into account. The samples were subjected to this acidic environment for six months, five of them being extracted every two months.From the two types of tests carried out, one destructive and the other non-destructive, the concrete strength was determined, as well as an estimate of its quality, porosity and air permeability. Through this process, it has been possible to obtain an approximate evolution of the deterioration of the concrete mechanical properties.A significant deterioration of concrete has been confirmed, with a considerable loss of the surface cement paste and fine aggregate, together with a substantial reduction in the concrete strength (over 40% in just six months, this value being much higher than obtained in previous investigations carried out by other researchers in the synthetic environment) and an increase in porosity, all with a very rapid evolution over time.