IN-SITU AND LABORATORY EVALUATION OF CHLORIDE PENETRATION AND FREEZE-THAW DURABILITY OF HIGH-PERFORMANCE CONCRETE SLABS

摘要

Nine high-performance concrete (HPC) slabs were exposed to an outdoor environment for four years at the University of Sherbrooke in Quebec, Canada. The slabs, made of ASTM TypeⅠand Ⅲ cements, were produced with/without entrained air at different W/B (0.25-0.30) and with/without silica fume. All the slabs were uniformly and regularly exposed to freeze-thaw cycles and to deicing salts. The compressive strength and the accelerated chloride penetration (ASTM C1202) were measured on molded samples and cores from the outdoor slabs. Accelerated laboratory freeze-thaw tests (ASTM C666) and deicing-salt scaling tests (ASTM C 672) were also performed to compare the laboratory and in situ behavior of HPC. No sign of freeze-thaw degradation was observed after four years of outdoor exposure, even if most of the non-air-entrained HPC were not durable under accelerated freeze-thaw testing. The low relative humidity measured at 75 mm under the slab surface (85-92% after 4 years) suggests that all these concretes should have satisfactory long-term freeze-thaw resistance under natural exposure conditions. The results show that chloride-ion penetration is relatively fast during the first two years and greatly depends on the mix design of the HPC. The W/B, silica fume, finer cement (Type IE) and air entrainment can very effectively reduce the chloride-ion penetration in HPC. The in-situ total chloride content measurements tend to indicate that HPC with compressive strength over 70 MPa, or a total charge under 1000 coulombs, offer approximately the same resistance to chloride penetration.