Fast material disintegration of cement concrete in the exterior

Abstract

Over the recent years the amount of fast destruction defects of cement paste matrix has increased markedly for exposed concrete structures of highway and airport pavements. The accelerated destruction of silicate structure is unusual due to its irregular occurrence. It only occurs at 30 to 50% of newly built pavements (in continuous segments). The issue is applicable to loaded as well as unloaded pavements. Detailed diagnostics found that the probable cause is based on concurrently occurring expansive reactions in capillaries, cracks and pores in the cement paste matrix. In defect spots the presence of several expansive substances was proven, wherein the biggest question poses the unexpectedly high potassium concentration. Potassium is only contained at best in trace amounts in road concrete input components in the Czech Republic. Neither existing regulations nor standards sufficiently deal with this type of defects of cement concretes. If they mention the existence of this issue at all, they are just limited to recommendations. Since the modification of the existing commercially produced cements to pavements is still improbable, the solutions to this issue seem problematic.

The verification of the possibility of alkalis penetration from the surrounding environment into the concrete pavement slabs

“…This topic is currently being addressed here through a research project that focuses specifically on the issue of the possibility of degradation of concrete pavements due to alkalis from the external environment. Partial results confirming this possibility have already been published [14,15] and this paper builds on these our already published results.…”

“…In one of the research stages of the project, laboratory tests simulating the infiltration and chemical action on the PCCP slabs through various media through commonly used structural pavement layers were carried out. Previously, the possibility of aggressive elements penetrating the PCCP in the form of direct contact of the concrete by its partial immersion in the aggressive solution and through indirect contact via partial immersion of various base layers has already been tested in the laboratory [14,15]. In this case, potassium in the form of ions was entrained by water through the PCCP pore capillary system.…”

“…Potassium was identified as the aggressive element that has been shown to be essential and most indicative of ASR in PCCP based on previous testing and observations [14,15]. Its migration in the concrete structure is linked to the moisture regime in the structure.…”