혼화제(混和劑)가 콘크리트의 내산성(耐酸性)과 물리적성질(物理的性質)에 미치는 영향(影響)에 관(關)한 실험적(實驗的) 연구(硏究) = Experimental Studies on Influence of Admixtures on Acid Resistance and Physical Properties of Concrete

다국어 초록 (Multilingual Abstract)

This resarch was attempted as one of studies for improving the quality of concrete, especially for better chemical resistance of concrete to corrosive action of acid. In this study, concrete specimens were made in accordance with the Korean Standards Specifications for concrete, using various admixtures, additives for normal cement, and pozzolan cement. They were tested for strength, absorption and acid-resistance. In mix designs of concrete, different levels of fly ash substituted for cement were varied from 10 to 30 per cent by weight of the normal cement content of the mix. Pozzolith, vinsol resin and fly ash were used as admixtures, of which fly ash was added to the mix in an amount equal to 10 per cent by weight of the cement of the mix, and pozzolan cement whose pozzolan content was amounted to 20 per cent by weight of the mill cement, was used as a different brand of cement.
In the tests, compressive strengths of specimens were measured at the following ages; 7-days, 28-days, 3-months and 6-months. Absorption test was made by immersing specimens in the water kept at boiling temperature for 5 hours. In addition, aeid corrosion test was made by exposing 3-months old specimens to the same concentration of 0.1N solutions of hydrochloric acid (HCl), nitric acid (HNO₃), sulfuric acid (H₂SO₄) and phosphoric acid (H₃PO₄) for 8 weeks. Each old acid solution was changed to fresh one at interval of 2 weeks, and their pH values of both old and fresh solutions were measured by using glass electrode pH meter. The results obtained from the data secured in this test are summarized as follows:
1. Fly ash, when substitutes cement in amounts of 10 to 30 per cent by weight of cement, reduces absorption by concrete, and also remarkably reduces the acid-resistance of concrete to acid solutions as fly ash contents are increased. The compressive strength of concrete containing fly ash of 10 per cent by weight of cement decreases a little. However,, by the use of fly ash of 20 per cent by weight of cement as an optimum content of fly ash, compressive strength is distinctively increased at all ages and the early-strength. of concrete is retarded by the use of fly ash by 30 per cent and some 3 months of curing time is required for fly ash concrete to equal or exceed the strength of plain concrete. Accordingly, fly ash could be used for making concrete in an amount equal to 30 per cent by weight of cement, providing that the low-early strength of fly ash concrete is not a handicap. It may be suggested that the early-strength of fly ash concrete would be attained by high temperature curing, the use of high early-strength cement or the use of admixtures that encourage early-strength of the concrete.
2. Strengths of concrete made by adding pozzolith, vinsol resin and fly ash are higher, at all ages, and the difference among their strengths is not significant. Pozzolith, vinsol resin and fly ash as admixtures exhibited promising results in lowering the absorption of concrete and especially vinsol resin and fly ash increase the resistance of concrete to acid solutions. They are the most acid-resistant among all treatments in this experiment.
3. Pozzolan concrete, whose pozzolan content amounted to 20 per cent by weight of mill cement, has the highest strengths at all ages and among all treatments in this experiment. Absorption of pozzolan concrete is lower than plain concrete and fly ash concrete substituted for cement up to 20 per cent by fly ash. However, it is somewhat higher than concrete containing admixtures such as fly ash, vinsol resin,pozzolith or fly ash concrete of 30 per cent replacement by fly ash by weight of the cement. Pozzolan cement decreases remarkably the resistance of concrete to acid solution, contrary to its high strength, so that it may not be feasible when exposed to acid waters or acid soils.
4. As far as improvement of physical property is concerned, it is evident that the use of admixtures, additives and pozzolan
cement in experimental mix designs of concrete is definitely effective than the use of normal cement only. In order to make better acid-resistant concrete as well as improvement of physical properties of concrete, it may be recommendable to use pozzolith and fly ash as adimixtures in mix design of concrete.
5. Through physical and acid resistance tests, plain concrete for which no admixtures or additives are used has higher strength, lower absorption and better acid-resistance as the mix is richer. Consequently, it may be said that a rich mix is one of the important factors to make better quality of plain concrete.
6. It is found that corrosive action of acid to concrete is attributed to the concentration of acid solution, pH value and type of acid, and that, in process of acid corrosion, the lower acidity of solution, the wider range of variation of pH value results, and the more acid corrosion of concrete occures due to an intensive chemical reaction.
7. It is known that the action of acid on concrete not only may increase corrosion of concrete but may reduce compressive strength of concrete, may result in increasing absorption by concrete, when concrete is exposed to acid waters.