PURPOSES : The purpose of this study is to experimentally analyze the flexural strength characteristics of cement mortar mixtures simultaneously incorporated with graphene oxide (GO) and polyvinyl alcohol (PVA) fibers, and to understand the composite effect of those on enhancing resistance against the initiation and progression of micro-cracks, as well as the control of macro-cracks in flexural behavior.
METHODS : Cement mortar(w/c=0.5) specimens for flexural strength test, mixing 6 mm and 12 mm PVA fibers at 1% and 2% volume ratios, were fabricated. Additionally, specimens incorporating GO at a cement weight ratio of 0.05% were prepared for each mixture to analyze the effect of GO. Therefore total eight types of mixture were prepared. The fabricated specimens were subjected to flexural strength tests after curing in waterbath for 7 and 28 days. Concurrently, digital images for analyzing deformation in accordance with loading history were obtained at a rate of 20 Hz using the DIC technique. Through displacement and strain calculation via DIC, the flexural behavior characteristics of the mixtures combined with GO and PVA fibers were precisely analyzed. Furthermore, the composite effect on flexural behavior characteristics when GO and PVA fibers are incorporated was discussed.
RESULTS : For the PVA fiber-reinforced cement mortar mixture, the incorporation of 0.05% GO increased the crack initiation load by up to 23%, and the maximum resistive load after cracking by up to 24%. Moreover, introducing GO into the PVA fiber-reinforced mixture increased the flexural strain just before cracking by approximately 30 to 50%, while the maximum resistive load after cracking exhibited similar strain levels with or without GO incorporation. Therefore, under flexural behavior, the integration of GO might delay crack initiation by increasing the strain concurrent with the rise in flexural stress before crack occurrence. It also seems to contribute to reducing crack expansion by synergistically interacting with PVA fibers after crack occurrence.
CONCLUSIONS : It was experimentally examined that the flexural strength of PVA fiber reinforced cement mortar is improved by incorporating GO. Moreover, GO enhances resistance of crack occurrance and reduces crack propagation in combination with PVA fibers. This study suggests that simultaneous incorporation of GO and PVA fibers can synergistically improve the performance of cement composites.

ABSTRACT
1. 서론
2. 실험방법
    2.1. 재료
    2.2. 시편 제작
    2.3. 휨강도 실험
    2.4. DIC (Digital Image Correlation)
3. 실험결과 및 토의
    3.1. 하중-변위 거동
    3.2. 휨강도
    3.3. DIC 분석
4. 결론
REFERENCES

• 조병휘(상명대학교 건설시스템공학과 교수) | Cho Byoung Hooi Corresponding author
• 정성균(상명대학교 휴먼지능로봇공학과 교수) | Jeong Seong-Kyun