Effects of Cement and Fly Ash Contents in Concreteagainst Sulfuric Acid Attack

Abstract

In this investigation, the effects of cement and fly ash contents in concrete against sulfuric acid attack were studied. Fly ash from Mae Moh thermal power plant was used as cement replacements of 0, 20, 30, 40 and 50% by weight. The cementitious material contents (cement plus fly ash) in concrete were varied as 300, 400, 500 and 600 kg/m3. Twenty mix proportions were prepared to cast 160 specimens of 10x20 concrete cylinder. The concrete specimens were removed from the mold after 24 hours and then cured in water for 28 days, after that they were divided into 2 groups.The first group was tested for 28 days compressive strength and the second group was immersed in 3% by weight of sulfuric acid solution. Weight losses of concrete specimens were measured after immersing in the acid solution at the age of 3, 7, 14, 2 1 and 2 8 days.

The results showed that concrete having the same cementitious material contents and without fly ash gave the highest compressive strength at 28 days for every mix proportion, and the compressive strength was higher as increasing the cement content. The increase of cement content in concrete resulted in the less required of water-cement ratio for concrete with the same slump,however it did not reduce the weight loss due to the sulfuric acid attack. In contrast, it even increased the attack by the sulfuric acid. The concrete with cement replaced by fly ash reduced the degree of sulfuric acid attack as compared to the one without fly ash which having the same cementitious material content. Concrete with cementitious material content of 300 kg/m3 and with 50% of fly ash replacing cement was the best to stand against the sulfuric acid attack, however its compressive strength was also low. In summary, the selection of concrete mix proportion against the sulfuric acid attack must be considered on cement content, cementitious material content, and the percentage of cement replacement by fly ash in order to achieve a good resistance to sulfuric acid attack as well as a reasonable compressive strength.