Case study of permeability-reducing admixture use in anti-flotation slabs: building in Brasilia, Brazil

Abstract

The time that the concrete must keep its properties, known as service life, it is an important design parameter for the performance of concrete structures. A porous concrete has a higher degree of water and aggressive permeability agents, which can cause deterioration of the reinforcement for mechanisms such as corrosion, besides not ensuring the watertightness, for example, on slabs under negative hydrostatic pressure (anti-flotation slabs). This type of slab has been used for the purpose of enabling or facilitating constructive actions associated with structures located beneath the groundwater table. There are several advantages of this type of construction: reduction of environmental impacts as it prevents the installation of permanent submersible pump systems, which reduces the use of electricity; nonoccurrence of settlement caused by the lowering of the groundwater table, which extends to the nearby areas of the construction site; and less impact to the groundwater table, which has serious consequences on the availability of this resource in urban areas. This paper presents a case study on the concreting of an anti-flotation slab, 30 cm thick and volume of 750 m3, of reinforced concrete, in a mixed use residential/commercial building, located in Northwest Sector, Brasilia, Brazil. To ensure the watertightness of this anti-flotation slab, a permeability-reducing admixture was used to prevent hydrostatic condition, known for its ability to promote the sealing of cracks up to 0.4 mm by self-healing phenomenon. The results showed that both the composition of the concrete (containing permeability-reducing admixture) and setting the appropriate constructive strategies were essential to ensure an intact and tight structure.