카제인으로 고결된 모래의 강도 및 내구성 평가

Evaluation of Strength and Durability of Casein-cemented Sand

Abstract

카제인은 우유 속에 약 3% 함유되어 있으면서, 우유에 함유된 전체 단백질의 약 80%를 차지한다. 카제인에 수산화칼슘 및 수산화나트륨 수용액을 섞으면 고결력이 발생하며, 이러한 고결방식은 목재나 건조한 환경에 적용하는 것이 일반적이다. 본 연구에서는 지하수위가 존재하는 토사의 고결을 위해 물에 약한 카제인 고결제의 구성성분을 조절하거나 새로운 성분을 추가하여 내수성을 향상시키고자 하였다. 이를 위해 낙동강모래에 고결제로 가장 많이 사용되는 시멘트뿐 아니라 위스콘신대학에서 제시한 표준 카제인 고결제를 비롯한 다양한 카제인 고결모래 공시체를 제작하였다. 6 종류의 카제인 고결모래 중에서 표준 카제인 고결제에 수산화칼슘을 30% 증가시키고 수산화나트륨을 50% 감소시킨 것이 가장 우수한 강도와 내구성을 나타내었다. 이렇게 개선된 카제인 고결제를 1-4% 혼합하여 만든 공시체의 일축압축강도와 반복건습으로 인한 내구성지수를 시멘트 고결모래 공시체와 비교하였다. 그 결과, 카제인비 4%인 고결모래 공시체의 입축압축강도와 내구성지수는 6,253kPa 및 92%로 일축압축강도 1,500kPa 및 내구성지수 62%인 시멘트비 8%인 고결모래 공시체보다 우수한 것으로 나타났다. 또한, 카제인이 3% 이상 함유된 고결모래 공시체는 반복적인 건습 작용에도 80% 이상의 양호한 내구성을 유지하였다.

About 3% of Casein is included in milk and it accounts for 80% of milk's protein. It has an adhesive property when mixed with calcium hydroxide and sodium hydroxide solutions. It has been usually used to bond woods under dry condition but becomes weak when exposed to moisture. Such weakness is very critical when casein is applied for soil cementation under groundwater condition. Therefore, this study was aimed to protect such weakness by changing or adding certain ingredients of casein adhesive. Two types of cemented specimens were prepared with Nakdong river sand and tested for unconfined compressive strength and durability. Each specimen was mixed with casein or cement. Ingredients of casein binder suggested by the University of Wisconsin, which is called a standard casein recipe, was also prepared. This study tried 6 different types of casein binder recipe. Among them, one with 30% hydroxide calcium increase and 50% hydroxide sodium decrease compared with the standard casein was most effective. Based on the most effective casein recipe, cemented sand with 1-4% of casein ratio was prepared and tested. The unconfined compressive strength and durability index were 6,253kPa and 92% for the specimen with 4% of casein ratio and 1,500kPa and 62% for the one with 8% of cement ratio. Therefore, casein cemented sand showed better performance. In addition, over 3% of casein cemented sand had over 80% durability index.

Fig. 1. Nakdong river sand

Fig. 2. Structure of casein molecule (Min, 2016)

Fig. 3. Progress of making casein adhesive

Fig. 4. Results of unconfined compression test using cement

Fig. 5. Results of unconfined compression test using standardcasein

Fig. 6. Elasticity and toughness of standard casein

Fig. 7. SEM images of cemented sands

Fig. 8. Cemented specimen with standard casein under water

Fig. 9. Comparison of (a) unconfined compressive strength and (b) durability index for cemented sand with cement and standard casein

Fig. 10. Results of unconfined compression and durability tests using adjusted casein

Fig. 12. Results of unconfined compression and durability tests using recommended casein

Fig. 13. Comparison of unconfined compressive strength and durability for cemented sand with different binders

Fig. 14. Results of slaking test

Fig. 11. C-3 specimen under water

Table 1. Material properties of Nakdong river sand

Table 2. Binder components of standard casein (Forest products laboratory, 1967)

Table 3. Testing results of cemented sands with cement

Table 4. Testing results of cemented sands with standard casein

Table 5. Elastic modulus and toughness of standard casein

Table 6. Testing results of cemented sand with adjusted casein

Table 7. Testing results of cemented sands with recommended casein

Table 8. Results of slaking test