Chloride intrusion into thermally damaged self-compacting concrete

Abstract

The post-heating resistance of limestone SCC against chloride intrusion is investigated considering key parameters such as water-to-cement ratio (0.4, 0.45, and 0. 5), relative humidity and elevated temperature (300 and 400°). SCC mixtures were proportions to confirm to universal specification with regard to different workability requirements.Chloride profiles were determined for post-heated and companion prismatic (100x100x250mm) specimens, kept at room temperature. Consequently, diffusion coefficients were determined upon Fick's steady state formula. Post-heating damage was quantified, as well, using various techniques such as ultrasonic pulse velocity waves, resonant frequency, compression test measurements. The results indicated significant reductions in compressive strength and estimated dynamic modulus ranging from (20 to 60%) and (10 to 40%), respectively, with a corresponding increase in chloride diffusion coefficient reaching 80%. Both temperature and relative humidity levels had tangible impact on post-heating damage of SCC, hence percentage increase in chloride diffusion coefficient. The empirical models developed in this work showed excellent correlation between various damage indices and the percentage increase in diffusion coefficient.Furthermore, the electrical charge passing through SCC compared very well with the percentage increase in diffusion coefficient.Keywords: Corrosion, Chloride, Self-compacting concrete, Diffusion, Thermal-damage. IntroductionCorrosion of reinforcing steel in concrete is the most significant deterioration process affecting reinforced concrete structures. The two most important causes of corrosion of the reinforcing steel are carbonation and chloride contamination of the concrete. The ingress of chloride into concretes depends upon many factors; the most important of which is the cracking status of the concrete structures. Cracking in concrete structures may be inherent or as result of structural design faults, construction deficiencies, fire attack and/or lack of long term durability (Saetta 2005). Corrosion is accompanied by a loss of rebar cross-section and a build-up of corrosion products, which occupy a larger volume than the original metal from which they were derived. This generates tensile stresses causing cracking and spalling of the cover, which may results in significant deterioration in structural elements in a short of period of time.Research works, concerned with the effect of load induced cracks on the chloride profile in concrete, showed that chloride ingress in concrete is dependent upon the size and depth of generated cracks (Rodriguez 2001;Gowripalan et al. 2005). The research findings indicated that relatively high pre-loading stresses are needed to affect significantly the ingress of chloride into concrete. Those investigated the effect of moisture content and freezing and thawing on the chloride profile revealed that relatively high number of freezing and thawing cycles would be needed to create internal damaged; that is high Research Significance...