The influence of Arabian Gulf environment on mechanisms of reinforcement corrosion

The reduction in the useful-service life of reinforced concrete construction in the Arabian Gulf is attributed to reinforcement corrosion. While this phenomenon is primarily related to chloride ions, the concomitant pressure of sulfate salts may accelerate the deterioration process. Another factor which might influence reinforcement corrosion is the elevated ambient temperature. While few studies have been conducted to evaluate the individual effect of sulfate contamination and temperature on chloride binding and reinforcement corrosion, the synergistic effect of these factors on concrete durability, viz.-a-viz., reinforcement corrosion, needs to be evaluated. Further, the environmental conditions of the Arabian Gulf are also conducive for accelerated carbonation. However, no data are available on the concomitant effect of chloride-sulfate contamination and elevated temperature on the carbonation behaviour of plain and blended cements.This study was conducted to evaluate the conjoint effect of chloride-sulfate contamination and temperature on the pore solution chemistry and reinforcement corrosion. The effect of chloride-sulfate contamination and elevated temperature on carbonation in plain and blended cements was also investigated. Pore solution extraction and analysis, X-ray diffraction, differential thermal analysis, scanning electron microscopy, DC linear polarization resistance and AC impedance spectroscopy techniques were utilized to study the effect of experimental parameters on chloride binding, reinforcement corrosion and carbonation.The results indicated that the concomitant presence of chloride and sulfate salts and temperature significantly influences the durability performance of concrete by: (i) decreasing the chloride binding, (ii) increasing reinforcement corrosion, and (iii) accelerating the carbonation process. To avoid such deterioration, it is advisable to minimize both chloride and sulfate contamination contributed by the mixture ingredients. Due to the known harmful role of sulfate ions in decreasing the chloride binding and increasing reinforcement corrosion, limits on allowable sulfate contamination in concrete should also be established

Usage of cement kiln dust in cement products - Research review and preliminary investigations

Large quantity of dust, commonly known as cement kiln dust (CKD), is produced during the production of Portland cement. In order to meet environmental requirements, CKD is disposed off in land fills. Recently, there has been a trend of utilizing it for soil stabilization, treatment of sewage, etc. Also, attempts were made at using it in cement products. This paper reviews the work conducted on the latter aspect and reports results of tests conducted by the authors to investigate the properties of cement-CKD combination. Results indicate that CKD does not adversely affect the properties of cement mortar. However, the implication of high chloride concentration and alkalinity of CKD on concrete durability needs to be studied

Performance of plain and blended cements exposed to high sulphate concentrations

The sulphate resistance of plain (ASTM C150 Type I and Type V) cements and cements blended with silica fume. fly ash. blast furnace slag or Superpozz, a new generation of supplementary cementing materials, exposed to sodium sulphate solutions was evaluated in this study. Cement mortar specimens were exposed to sulphate concentrations of up to 25000 ppm. The sulphate resistance of the selected cements was evaluated by visual examination and measuring expansion and reduction in the compressive strength. Morphological changes in cements, due to sulphate exposure, were evaluated by scanning electron microscopy. The mineralogical changes in cements exposed to a solution with 15 000 ppm sulphate were evaluated. Cracks were noted in Type I and silica fume cement mortar specimens exposed to a sulphate concentration of 15 000 ppm or more. In type V cement. the sulphate tolerance was 25000 ppm. Cracks were not noted in the blast furnace slag. fly ash. and Superpozz cement mortar specimens exposed to 25000 ppm sulphate solution. It is suggested to use Type V cement or Type I cement blended with fly ash, blast furnace slag or Superpozz in sulphate-bearing environments

Usage of cement kiln dust in cement products - Research review and preliminary investigations

Large quantity of dust, commonly known as cement kiln dust (CKD), is produced during the production of Portland cement. In order to meet environmental requirements, CKD is disposed off in land fills. Recently, there has been a trend of utilizing it for soil stabilization, treatment of sewage, etc. Also, attempts were made at using it in cement products. This paper reviews the work conducted on the latter aspect and reports results of tests conducted by the authors to investigate the properties of cement-CKD combination. Results indicate that CKD does not adversely affect the properties of cement mortar. However, the implication of high chloride concentration and alkalinity of CKD on concrete durability needs to be studied

Correlations between Depth of Water Penetration, Chloride Permeability, and Coefficient of Chloride Diffusion in Plain, Silica Fume, and Fly Ash Cement Concretes

An experimental study was conducted to evaluate correlations between the depth of water penetration, chloride permeability, and coefficient of chloride diffusion in plain, silica fume, and fly ash cement concretes. A total of 27 concrete mixtures were prepared by varying the water to cementitious materials ratio and cementitious materials content and using Type I, fly ash (20 %), and silica fume (7.5 %) cements. The test results were statistically analyzed to develop correlations between the depth of water penetration, chloride permeability, and coefficient of chloride diffusion. A good correlation was noted between the depth of water penetration and chloride diffusion, and Chloride permeability and coefficient of chloride diffusion (R2>0.80)

CORROSION OF FUSION-BONDED EPOXY COATED BARS IN CHLORIDE-CONTAMINATED PLAIN AND SiLICA FUME CEMENT CONCRETES EXPOSED TO VARYING TEMPERATURE

Fusion bonded epoxy coated (FBEC) bars are being utilized by the construction industry in several regions of the world to minimize corrosion damage to the reinforced concrete structures. While the use of FBEC bars in concrete is debated among the concrete technologists, contractors and owners are using them as one of the methods to enhance the useful service-life of reinforced concrete construction. Several studies have been conducted at King Fahd University of Petroleum and Minerals to develop methodologies for enhancing concrete durability under severe environmental conditions of the region. One of the studies has been to evaluate the usefulness of FBEC bars under local conditions, which are characterized by high chloride contamination in concrete and elevated environmental temperature. The effect of high chloride concentration and elevated temperature in conjunction with damage to the FBEC on the corrosion of the substrate metal was studied in plain and silica fume cement concretes. The corrosion current density on mild steel and damaged FBEC bars was noted to increase with an increase in temperature. The performance of FBEC bars in the silica fume cement concrete was better than that in the plain cement concrete at both normal and elevated temperatures. The long-term performance of FBEC bars was satisfactory at elevated temperatures in the silica fume cement concrete specimens even with up to 2% chloride, by weight of cement

CORROSION OF FUSION-BONDED EPOXY COATED BARS IN CHLORIDE-CONTAMINATED PLAIN AND SiLICA FUME CEMENT CONCRETES EXPOSED TO VARYING TEMPERATURE

Fusion bonded epoxy coated (FBEC) bars are being utilized by the construction industry in several regions of the world to minimize corrosion damage to the reinforced concrete structures. While the use of FBEC bars in concrete is debated among the concrete technologists, contractors and owners are using them as one of the methods to enhance the useful service-life of reinforced concrete construction. Several studies have been conducted at King Fahd University of Petroleum and Minerals to develop methodologies for enhancing concrete durability under severe environmental conditions of the region. One of the studies has been to evaluate the usefulness of FBEC bars under local conditions, which are characterized by high chloride contamination in concrete and elevated environmental temperature. The effect of high chloride concentration and elevated temperature in conjunction with damage to the FBEC on the corrosion of the substrate metal was studied in plain and silica fume cement concretes. The corrosion current density on mild steel and damaged FBEC bars was noted to increase with an increase in temperature. The performance of FBEC bars in the silica fume cement concrete was better than that in the plain cement concrete at both normal and elevated temperatures. The long-term performance of FBEC bars was satisfactory at elevated temperatures in the silica fume cement concrete specimens even with up to 2% chloride, by weight of cement