Salah U. Al-Dulaijan

Sulfate resistance of plain and blended cements exposed to varying concentrations of sodium sulfate

Concrete deterioration due to sulfate attack is the second major durability problem, after reinforcement corrosion. This type of deterioration is noted in the structures exposed to sulfate-bearing soils and groundwater. Though concrete deterioration due to sulfate attack is reported from many countries, the mechanisms of sulfate attack have not been thoroughly investigated, particularly the effect of sulfate concentration and the cation type associated with the sulfate ions on concrete deterioration. This study was conducted to evaluate the performance of plain and blended cements exposed to varying concentrations of sodium sulfate for up to 24 months. Four types of cements, namely Type I, Type V, Type I plus silica fume and Type I plus fly ash, were exposed to five sodium sulfate solutions with sulfate concentrations of 1%, 1.5%, 2%, 2.5% and 4%. These concentrations are representative of the sulfate concentration in highly saline soils. The sulfate resistance was evaluated by visual examination and measuring the and reduction in compressive strength. The maximum deterioration, due to sulfate attack, was noted in Type I cement followed by silica fume and Type V cements. The performance of Type V, Type I plus silica fume and Type I plus fly ash was not significantly different from each other. The enhanced sulfate resistance noted in the Type I cement blended with either silica fume or fly ash indicates the usefulness of these cements in both sulfate and sulfate plus chloride environments.

Effect of waterproofing coatings on steel reinforcement corrosion and physical properties of concrete

Abstract This paper reports the results of a study conducted to evaluate steel reinforcement corrosion and some physical properties of concrete specimens coated with two polymer-based, a cement-based polymer-modified, and a cement-based waterproofing coatings. The coated and uncoated concrete specimens were subjected to accelerated corrosion to determine the time-to- corrosion initiation. The physical properties were also evaluated by subjecting the concrete specimens to wetting/drying cycles and heating/cooling cycles for five months. The physical properties evaluated were water absorption, water permeability, chloride permeability, and adhesion. The accelerated corrosion test results clearly showed that the specimens coated with the polyurethane elastomer-based waterproofing material performed better than concrete specimens coated with other waterproofing materials. This was followed by the specimens coated with cement-based polymer modified, epoxy-based, and cement-based coatings in descending order. The two polymer-based coatings showed better performance than the cement-based polymer-modified and cement-based coatings in terms of the evaluated physical properties.

Mechanical properties and durability characteristics of polymer- and cement-based repair materials

This study was conducted to evaluate the mechanical properties and durability characteristics of nine polymer- and cement-based repair mortars. Mechanical properties, such as compressive, tensile and flexural strength, elastic modulus, shrinkage and thermal expansion were studied. The durability characteristics of the repair materials were evaluated by measuring: (i) chloride permeability, (ii) electrical resistivity and (iii) carbonation depth. The mechanical properties of the selected repair mortars did not vary very significantly from each other. The elastic modulus of the polymer-based repair mortars was less than that of the cement-based repair mortars. This will lead to a reduced drying shrinkage cracking in the former repair mortars compared to the latter. The electrical resistivity of polymer-based repair mortars was more than that of cement-based repair mortars. Such a trend was not noted in the chloride permeability data. The chloride permeability in all the repair materials was very low according to ASTM C 1202 criteria. Enhanced carbonation was noted in some of the polymer-based repair mortars.

29SI MAS-NMR HYDRATION AND COMPRESSIVE STRENGTH STUDY IN CEMENT PASTE

Abstract 29 Si MAS-NMR measurements of cement have been used to follow the hydration process in cement pastes. Samples prepared using a w/c ratio of 0.45 and type I cement have been cured at temperatures over the range 20 to 55°C with curing times of 3 to 28 days. Compressive strength values for samples subjected to the same time/temperature curing regime were also obtained. The compressive strength is found to show a linear dependence on hydration as characterized in terms of the NMR Q 0 , Q 1 and Q 2 silicate polymerization states. Solid state 29 Si NMR measurements appear promising as a means of monitoring cement/concrete strength.

Evaluation of bond using FRP rods with axisymmetric deformations

Abstract This paper presents experimental results obtained with the direct pull-out test using machined and wrapped glass/vinylester, carbon/vinylester, and carbon/epoxy FRP rods with axisymmetric lugs. The typical results are given as nominal shear stress vs. free- and loaded-end slip. Experimental results obtained from strain probes used during the pull-out test are presented as shear stress vs. strain. Machined glass/vinylester FRP rods with embedded lengths including five and 10 lugs, and different lug widths and heights were studied. The failure mode consisted of the shearing off of the lugs without concrete damage. Four concrete mixtures with strengths ranging from 32 to 66.1 MPa were examined. Provided that enough confinement is used, it was found that the concrete strength has no noticeable effect on the shear strength and failure mode of FRP rods. Results showed that the FRP–concrete bond is controlled by the lug dimension and shear strength of the resin. The shear strength of the wrapped lugs is less than that of machined ones due to fiber orientation and weaker interfacial bond between the wrapped strands and rod surface.

Effect of steel manufacturing process and atmospheric corrosion on the corrosion-resistance of steel bars in concrete

This paper presents results of a study conducted to evaluate the effect of steel manufacturing process and the surface condition of reinforcing steel on their corrosion-resistance when embedded in concrete. Steel bars produced by water quenching and air-cooling were utilized. The corrosion-resistance of fresh bars, i.e., those that were clean and shiny, and those exposed to atmosphere and accelerated salt spray, when embedded in concrete, was evaluated. The corrosion-resistance of the clean and corroded reinforcing steel bars was assessed by measuring corrosion potentials and corrosion current density. Accelerated impressed current technique was also utilized to evaluate the corrosion-resistance of clean and corroded reinforcing steel bars in concrete. A longer time-to-initiation and lower rate of reinforcement corrosion was noted in the concrete specimens prepared with water-quenched steel bars compared to similar bars manufactured by the hot-rolling process. Similarly, the rate of reinforcement corrosion in the concrete specimens prepared with corroded steel bars, exposed to atmosphere for 12 months and salt spray, was less than that on the unexposed bars. The data developed in this study also indicate that the surface layer formed on the water-quenched steel bars, due to the cooling process, provides protection to the metal substrate as against the loose mill scale formed on the steel bars produced by the air-cooling process.

Effect of cyclic loading on bond behavior of GFRP rods embedded in concrete beams

Three types of glass fiber-reinforced plastic (GFRP) rods with different surface configurations were embedded in concrete beams to determine their bond behavior under cyclic loading. Load amplitudes and numbers of cycles were chosen based on the GFRP rod type and its bond behavior in virgin beams loaded monotonically to failure. After completion of cyclic loading, all beams were tested quasi-statically to failure to determine the residual bond strength. Results were presented as load-slip curves, load-midspan displacement curves, and slip versus number of cycles curves. In all types of GFRP rod evaluated, cumulative slip increased as the number of cycles and/ or loading amplitude increased. The bond strength in cyclically loaded beams increased relative to the bond strength in virgin beams.

Effect of inhibitor treatment on corrosion of steel in a salt solution

This study examined experimentally different chemicals for inhibition of steel corrosion in a simulated aqueous solution for the industrial marine atmosphere of the Arabian Gulf region. The literature reported various inhibitors that can help in protection against metal corrosion in aqueous environments. Among them, 10 inhibitors (calcium silicate, cyclohexylamine, n-methylcyclohexylamine, dicyclohexylamine nitrite, sodium benzoate, sodium nitrate, sodium nitrite, sodium phosphate, sodium dihydrogen orthophosphate, and magnesium nitrate hexahydrate) were obtained and corrosion resistance of inhibitor applied steel specimens were examined in the simulated solution (2 wt.% NaCl and 1 wt.% Na2SO4). Test specimens were prepared from locally produced reinforcing steel products. Treatment of steel with either dicyclohexylamine nitrite or sodium dihydrogen orthophosphate both at 10 mM concentration for 1 day at room temperature resulted in significant inhibition of corrosion. No significant improvement in corrosion inhibition was observed either with an increase in inhibitor concentration at room temperature or with an increase in inhibitor application temperature at 10 mM concentration. A further study is planned to examine the inhibition performances of the two inhibitors under actual atmospheric conditions in the Arabian Gulf region (industrial marine environment).

Effect of rebar cleanliness and repair materials on reinforcement corrosion and flexural strength of repaired concrete beams

Abstract This paper presents result of a study conducted to evaluate the effect of two rebar cleaning procedures and repair materials on reinforcement corrosion and flexural strength of repaired concrete beams. The steel bars in the reinforced concrete beams were corroded to varying degrees to simulate field situations and then repaired utilizing two different cleaning techniques and two repair materials. The repaired beams were then tested in flexure to evaluate the effect of cleaning method and repair materials on the corrosion-resistance and flexural capacity of repaired beams. The electrochemical behavior of cleaned and corroded steel bars was evaluated by conducting a DC potentiodynamic scan. The data indicated an insignificant change in the flexural strength of repaired beams regardless of the cleaning techniques or the repair materials. The accelerated corrosion data indicated lowest corrosion rate in the concrete specimens repaired with polymer-modified cement mortar after cleaning the bars by sand blasting (SB). The DC polarization data indicated the formation of a stable passive film on the steel bars cleaned by SB compared to uncleaned bars and those cleaned by wire brush.

Inhibition of atmospheric corrosion of mild steel by sodium dihydrogen orthophosphate treatment

The purpose of this study was to evaluate the effectiveness of sodium dihydrogen orthophosphate as an inhibitor to slow down or prevent atmospheric corrosion of the local mild steel during storage in the Arabian Gulf region. In light of the results of some preliminary studies, sodium dihydrogen orthophosphate was selected for further evaluation against atmospheric corrosion of steel after it was applied at 10 mM concentration for 1 day at room temperature.