PURPOSES : In this study, experimental findings regarding the frost resistance of concrete incorporated with mineral admixtures such as fly ash (FA) and ground granulated blast-furnace slag (SG) are presented. METHODS : To evaluate the performance of the abovementioned concretes under repeated freezing and thawing environments, based on the ASTM C 666 standard, the relative dynamic modulus of elasticity and mass ratio measurements are performed regularly. Furthermore, based on the ASTM C 672 standard, the concretes are exposed to 4% CaCl2 and NaCl salt solutions along with repeated 50 cycles of freezing and thawing. Subsequently, the scaling resistance is evaluated based on the scaled-off mass content and visual examination. RESULTS : SG is less effective in enhancing the scaling resistance of concrete compared with FA. However, the concrete incorporated with SG is more resistant to repeated freeze-thaw actions compared with OPC concrete. Meanwhile, compared with OPC concrete, the concrete incorporated with FA indicates a similar performance in terms of scaling resistance and better resistance against repeated freeze-thaw actions. CONCLUSIONS : The frost resistance of concrete depends significantly on the types of mineral admixtures used in concrete. This emphasizes the importance of selecting the appropriate binder to achieve durable concrete pavements in cold climate regions.

PURPOSES : In this study, an ASR-reducing (alkali-silica reaction) cement was developed to prevent the blow-up of concrete pavements. To develop ASR-reducing cement, various amounts of ground granulated blast furnace slag (GGBFS), and fly ash (FA) were substituted with Portland cement, and the ASR reduction effect was verified through various experiments. METHODS : The physical properties of ASR-reducing cement, varying with the substitution amounts of GGBFS and FA, were verified through compressive strength tests. In addition, the ASR reduction effect was examined using accelerated mortar bar tests. Furthermore, the reasons for the ASR reduction were investigated using microstructural analysis techniques, such as XRD and TG/DTG. RESULTS : There was a difference in the compressive strength results according to the amount of GGBFS and FA substitution. In addition, the samples with GGBFS and FA exhibited relatively lower compressive strengths at 3 days, than OPC samples, but the compressive strength at 28 days was higher than that of the OPC samples. The samples with GGBFS and FA had higher compressive strength at 28 days than OPC samples, because the substituted GGBFS and FA induced pozzolanic reaction. Through XRD and TG/DTG analyses, various degrees of pozzolanic reaction occurring in the samples were examined, and a more active pozzolanic reaction occurred in the samples with FA than in the samples with GGBFS. Therefore, it appeared that the ASR reduction effect occurred because of the induced pozzolanic reaction. CONCLUSIONS : GGBFS and FA substituting Portland cement indicated an ASR reduction effect, which was owing to the pozzolanic reaction. In addition, FA indicated a greater ASR reduction effect than GGBFS, which suggested that FA induced a more active pozzolanic reaction than GGBFS.

PURPOSES: The scaling of a concrete surface caused by the combined effects of frost and de-icing salts is one of the main reasons for the need to repair transportation infrastructures in cold-climate regions. This study describes the results of attempts to determine the scaling resistance of concrete incorporating mineral admixtures such as fly ash, GGBFS, and silica fume, and subjected to the actions of frost and salt. METHODS : Conventionally, to evaluate the fundamental properties of concrete, flexural and compressive strength measurements are regularly performed. Based on the ASTM C 672 standard, concrete is subjected to 2%, 4%, and 8% CaCl2 salt solutions along with repeated sets of 50 freeze/thaw cycles,and the scaling resistance was evaluated based on the mass of the scale and a visual examination. RESULTS : It was observed that silica fume is very effective in enhancing the scaling resistance of concrete. Meanwhile, concrete incorporating GGBFS exhibited poor resistance to scaling, especially in the first ten freeze/thaw cycles. However, fly ash concrete generally exhibited the maximum amount of damage as a result of the frost-salt attack, regardless of the concentrations of the solutions. CONCLUSIONS: It can be concluded that the scaling resistance of concrete is highly dependent on the type of the mineral admixture used in the concrete. Therefore, to provide a durable concrete pavement for use in cold-climate regions, the selection of a suitable binder is essential.

본 연구는 고로슬래그미분말 및 실리카흄과 같은 광물질혼화재를 사용한 시멘트콘크리트 포장의 성능에 대한 역학적, 물리적 평가를 수행하였다. 광물질혼화재 사용 시멘트콘크리트 포장의 휨강도, 압축강도, 통과전하량, 염소이온 확산계수 및 초기표면흡수율을 소정의 재령에서 측정하였으며, 그 결과를 기준 콘크리트 포장의 성능과 비교하였다. 실험결과, 광물질혼화재의 종류에 따라 시멘트 콘크리트 포장의 강도거동은 다르게 나타났으며, 대체적으로 실리카흄을 사용한 콘크리트의 압축강도 발현이 다소 우수하게 나타났다. 뿐만 아니라, 콘크리트의 염소이온 확산계수는 기준 콘크리트에 비하여 매우 작은 경향을 나타냄으로써, 이는 광물질혼화재를 사용한 시멘트콘크리트 포장의 우수한 내염성을 다시 한번 확인 할 수 있었다. 도출된 실험결과를 바탕으로 하여, 향후 고성능 시멘트콘크리트 포장 설계를 위한 재료적 기초 데이터를 제시하고자 한다.

Smart construction materials have recently been interesting to improve the performance of cement composites and concretes. Especially, no repairing system is required for concrete structures by using self healing concrete, which can close cracks on concrete by itself. Mineral admixtures, capsules and bacteria are the most used for self healing concrete technology. In this study, high strength concrete with mineral admixtures were utilized to develop self healing capacity. Comparison with water flow test and image captures were conducted.

본 연구에서는 지오폴리머 결합재인 고로슬래그를 분쇄할 때 석고의 혼입 여부, 고로슬래그와 플라이애시의 혼합비율과 수축저감제 첨가 여부를 변수로 하여 실험하였다. 실험에서는 슬럼프플로우를 측정하여 작업성을 파악하였으며, 압축강도와 휨강도 및 건조수축을 측정하여 역학적 성능을 파악하였다. 석고를 혼입한 고로슬래그는 혼입하지 않은 고로슬래그에 비해 슬럼프플로우가 커지는 경향을 보였으며, 고로슬래그와 플라이애시의 혼합비율이 5:5인 경우가 혼합비율이 8:2인 경우보다 슬럼프플로우가 커지는 경향을 보여 석고와 플라이애시가지오폴리머의 작업성을 높여주는 것으로 나타났다. 석고를 혼입하지 않은 고로슬래그를 사용한 지오폴리머는 석고를 혼입한 고로슬래그를 사용한 경우보다 압축강도와 휨강도가 모두 크게 나타났으며, 고로슬래그와 플라이애시의 혼합비율이 8:2인 경우가 혼합비율이 5:5인 경우보다 압축강도와 휨강도가 커지는 경향을 보였다. 석고를 혼입하지 않은 고로슬래그를 사용하고 플라이애시의 혼합비율을 높일수록 건조수축은 감소되었으며 수축저감제도 지오폴리머의 건조수축 저감에 효과적임을 알 수 있었다.

In this study, deterioration degrees of concrete was investigated at a lab under cycling freeze-thaw, which is major durability performance deterioration factors of concrete. After 300 cycles of freeze-thaw, relative dynamic modulus of elasticity and compressive strength of concrete mixed with normal Portland, SF, and Ny over 90 to 93% showed relatively low resistance of approximately 78 to 87% of those values of FA-PP-02. The SF-01 specimen showed the most excellent freeze-thaw resistance among the tested high performance concrete.

The influence of mineral admixture content on the bleeding of cement-based grouts. Replacement of fly ash increased the bleeding, but the increase of the content of blast furnace slag as well as silica fume led to the reduction in the bleeding. Especially 15% replacement of silica fume showed the best performance against normal bleeding as well as channel bleeding.

연약지반의 점토퇴적물을 시멘트와 함께 생석회, 소석회, 석고, 고령토, 제올라이트, 규조토 등의 광물재료를 혼합하여 고화 반응시킨 후 양생시간에 따른 물성변화와 반응생성물을 조사하였다. 그 결과, 시멘트로는 포틀랜드 시멘트보다는 슬래그시멘트가 점토의 고화반응에 따른 강도발현이 큰 것으로 나타났다. 그리고 슬래그시멘트와 함께 각종 광물재료와 고화 반응시킨 실험결과에서는, 석고가 가장 높은 강도발현을 나타냈다 따라서 슬래그시멘트와 석고에 대해 이들의 혼합비를 달리하여 고화 실험을 수행하였다. 그 결과, 슬래그시멘트 70%, 석고 30%의 비율에서 가장 좋은 강도발현을 보이는 것으로 나타났다. 이 실험의 고화반응물에서는 에트린자이트 등의 반응생성물이 포함되었다. 이것은 석고가 슬래그시멘트의 효율적인 수화반응을 촉진시켜서 높은 강도 발현에 기여 한 것으로 생각된다. 이러한 실험 결과는 연약지반의 안정화 처리에 유용한 자료로 이용될 것으로 보인다.