Study On Sulfate Attack Mechanism And Modifications Of Concrete In West Of China

Concrete sulfate attack is one of the most important factors that affect concrete durability. In China western region, there is a large number of sailine soils and lakes containing sulfate ions, that seriously affect the building working life. So, It is of great significance that researching sulfate resistant of concrete and exploring corrosion machanism and improvement approaches to ensure project quality and improve buiding working life. The paper, which simulated sulfate condition, firstly, researched on the influence and sensitivity of different factors, analyzed the sulfate attack characters that cement mortar specimens of different water-binder ratios and different fly ash dosage soaked in different concentration sulfate solutions, by using orthogonal test method, and obtained sulfate ions distriubution in different cement motar specimens, through using bariun sulfate gravimetry. Secondly, based on the above experiments, the paper analyed concrete erosion characteristics in sulfate dry-wet circulation. Lastly, concrete micro-damage mechanism was analyzed, through the SEM scanning eletron microscopy technique. The conclusions as follows:(1) Using apparent observation, mass loss rate and strength loss rate as evaluation indicators of concrete sulfate-resistance property. The Strength loss rate was better than the apparent observation and mass loss rate. The apparent observation and mass loss rate can only be used as assistant evaluation indicators, strength loss rate can be used as the main indicator.(2) In the test of cement sulfate immering for a long term, when the water-binder ratio was 0.5, fly ash content was 20%, and the sulfate solution concentration was 5%, the cement specimens’ strength loss was minimal, and cement sulfate-resistance was best. And also, when the cement was mixed fly ash excessively, the specimens’ strength was significantly decreased. In the concrete sulfate dry-wet cycling test, when the fly ash content was 20%, the concrete strength was C45(the water-binder ratio was 0.45), the concrete sulfate-resistance was best.(3) The concrete sulfate erosion process can be divided into two stages. At the beginning of the erosion, concrete became more denser due to the pore was filled with erosion product, such as etrringite and plaster. The specimens’ quality and strength had increased. At the later period of erosion, specimens cracked, and corners spalled, the specimens’ quality and strength decreased rapidly, because of erosion products overproducted. Microscopic and macroscopic varying patterns were on the same.(4) Concrete sulfate attack is a process that sulfate ions gradually delivered into the interior of specimens. The higher the concentration of sulfate ions, the more serious erosion. When the water-binder ratio of 0.5, the sulfate ions concentration of specimens was low, and the speed of sulfate ions transmission was minor. When the water-binder ratio was less than 0.5, the more fly ash content, the lower the internal specimens’ sulfate ions concentration. When the water-cement ratio was greater than 0.5, with the increase of fly ash content, the sulfate ions transmission rate was increased.(5) In general, when fly ash is 20%, water-binder ratio is about 0.45, the concrete can maintain its performance, but also has good resistance to sulfate attack.