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

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 f c = 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

High-temperature behavior of SCC in compression: Comparative study on recent experimental campaigns

The 20 years since the introduction of self-compacting/self-consolidating concrete (SCC) have given plenty of opportunities for researchers, designers, and contractors to become familiar with SCC innovative properties and structural effects. The workability and durability of SCC have been investigated extensively, together with the tendency of SCC members to spall in fire, because of pore pressure, thermal self-stresses, and applied stresses. The interest for the constitutive behavior of SCC at high temperatures, however, is relatively recent, as most of the studies (not more than a dozen in total) have been published in the last 10 years. Though limited in number, these studies shed sufficient light on the behavior of SCC at high temperatures, in quasi-steady conditions, as demonstrated in this paper. This paper describes 11 experimental campaigns carried out in Belgium, China, Croatia, France, Germany, Greece, Italy, Sweden, and the United States, each with its own specimens, mix designs, test procedures, and methods for the treatment of test results. The experimental results considered in this paper concern both normal-strength and high-performance/high-strength concretes, generally devoid of fibers, unstressed during the heating process, and tested in uniaxial compression. The conclusion of this comparative study is that at high temperatures, SCC tends to behave similarly to ordinary vibrated concrete (VC), and that American Concrete Institute (ACI)-ASCE provisions for ordinary calcareous or siliceous concrete at high temperatures or past cooling are also applicable to SCC

Thermal and Mechanical Properties at High Temperature of a Very High-Strength Durable Concrete

A very high-strength microconcrete containing polymeric fibers and quartzitic aggregates, but no silica fume, has been investigated both at high temperature and after cooling, in order to evaluate the thermal diffusivity and the mechanical decay as a function of the temperature, since there is still scanty information in the literature on the high-temperature behavior of this family of materials. The very high-strength concrete investigated turned out to be very efficient, since a) its compressive strength exhibits a decay very close to that of normal-strength concrete, with no sizable differences between the “hot” and “residual” properties; b) its specific fracture energy increases very much indeed with the temperature; and c) its rather low thermal diffusivity guarantees good insulation properties. As an application of this material, the parking apron of an airport and its two-layered pavement subjected to a hot spot have been considered, in order to investigate whether delamination at the interface between the top VHSC layer and the bottom normal strength concrete layer and/or cracking in the bottom layer may occur. The performance of the pavement was analyzed for different values of the thickness of the top VHSC layer and also for different values of its thermal properties, and proved to be very satisfactory in terms of tensile behavior. However, the critical factor remains the initial heating rate