A study on the mechanical properties of self-compacting concrete at high temperature and after cooling

摘要

Self-compacting/consolidating concrete (SCC) is certainly one the most innovative material used today by the construction industry, because of its astonishing workability and low permeability, both properties being ensured by the large amounts of fine aggregates, the special additives and the fillers, that characterize SCC's mix compared to traditionally-vibrated concrete (VC). Since many of the structures where SCC is used (like tunnel linings, off-shore structures, containment shells, bridge decks, slabs on grade) are often required to face severe environmental conditions, such as fire, information on SCC's behavior at high temperature is badly required, because SCC's more dense or compact microstructure, with smaller and less connected pores, may in principle make this material more heat-sensitive than VC, as occurs in high-performance/high-strength concrete. While the thermal effects on VC have been extensively investigated in the last 20 years and several studies have been devoted to SCCs spalling in fire, only in the last few years due attention has been paid to the mechanical properties of SCCs at high temperature ("hot" properties) and/or after cooling ("residual" properties). The few of papers on this subject, however, give limited information on the stress-strain curves in compression and on the tensile behavior, that are the first objective of this project, with reference to three self-compacting "limestone" concretes (target strength fc = 50, 80 and 95 MPa). The second objective is to synthesize the test results available in the literature and to make systematic comparisons, something that is not as simple as one may expect, because of the different heating rates, specimen types, and procedures in data treatment and presentation. The agreement, however, is more than satisfactory and confirms what has been more or less overtly indicated in previous studies, that the thermal and mechanical behavior of SCC at high temperature is hardly different from that of VC, at least in quasi-static thermal conditions and uniaxial loading.