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Abstract
This investigation aims to study the effect of using mineral admixtures on the durability of concrete. Sulfate attack and corrosion are the most famous durability problem of concrete structures in our country. Many concrete structures were deteriorated as a result of the lack of information about the mechanism of the aggressive environmental conditions. This study included two sections. These sections were sulfate attack and corrosion. The used mineral admixtures in the two sections were silica fume and metakaolin additives.
For sulfate attack section, magnesium sulfate was chosen because there were contradictions in the experimental test results of magnesium sulfate resistance of concrete containing mineral admixtures. In this section, mortar specimens, concrete specimens and reinforced concrete columns were considered. These specimens were subjected to cycles of wetting and drying of 5.0 % magnesium sulfate by weight for 700 days.
The effect of percentage of mineral admixtures cement replacement, w/cm ratio, cement content and cement type are studied. The used percentages of mineral admixtures were 0.0, 10.0, 15.0 and 25.0 % by weight. 0.50 and 0.40 w/cm ratio were considered. The used cements were Type I and Type V Portland cement with contents of 300, 350 and 450 kg/m3.
Also, the effect of using 0.1 % polypropylene fibers on magnesium sulfate resistance of concrete containing silica fume was studied.
Weight, compressive strength, ultrasonic pulse velocity and dynamic modulus of elasticity loss in addition to expansion strain were used to evaluate the effect of the studied parameters.
A simplified method was suggested to correlate the experimental test results with the field applications. This method can be used to estimate the compressive strength reduction for concrete subjected to any concentration of magnesium sulfate attack after a certain age.
This method will be taken in design considerations of any new concrete structure element that will subjected to magnesium sulfate attack.
An accelerating corrosion test was used to study the corrosion resistance of concrete containing mineral admixtures,. The used voltage in this test was 55 DC volts. The current intensity was measured along time.
In this section, the effect of percentage of mineral admixtures, w/cm ratio, cement content and cement types were studied. The used percentages of mineral admixtures were 0.0, 10.0, 15.0 and 25.0 % by weight. 0.50 and 0.40 w/cm ratio were considered. The used cements were Type I, Type II and Type V Portland cement with 350 and 450 kg/m3.
The effect of seawater medium and value of applied voltage in the accelerating test were studied.
Time of first crack, critical time, propagation time, concrete resistivity, corrosion tendency factor and weight loss on steel reinforcement were used to evaluate the effect of the studied parameters.
From the test results of section I, based on the same compressive strength, silica fume and metakaolin, did not enhance the magnesium sulfate resistance. Also, the use of high cement content of Type V Portland cement with lower w/cm ratio achieved good resistance to 5.0 % magnesium sulfate attack. The experimental test results of concrete specimens and reinforced concrete columns confirmed the test results of mortars specimens.
Also, the use of 0.1 % polypropylene fibers enhances the magnesium sulfate resistance of concrete where the use of polypropylene fibers reduced weight, compressive strength, ultrasonic pulse velocity and dynamic modulus of elasticity loss and achieved lower expansion strain compared with concrete without polypropylene fibers.
The test results of section II showed that the use of mineral admixtures up to 15.0 % enhanced the corrosion resistance of concrete.
A good performance of concrete made with Type I Portland cement compared with Type II and Type V Portland cement was achieved both for concrete specimens cured in potable water and seawater mediums.