Research On Short-and Long-term Mechanical Properties Of Bfrp Bar Reinforced Marine Sand Concrete Beams

Reefs are among the most hostile environments in the nature due to the coupling effect of high temperature, high humidity and salt mist. As the development of the reefs in the South China Sea, the durability problems of infrastructure on the reefs become more and more serious, including corrosion of steel and corrosion expansion crack of concrete, leading to a short life time of infrastructures ranging from five to ten years. Thus, the large-scale development and construction on the reefs are restricted. To overcome those problems, the traditional measures include the adoption of high densified concrete, corrosion inhibitor, coating on the steel and stainless steel. However, these measures are difficult to be implemented due to the high transportation expenses and long construction period on the reefs. Basalt fiber reinforced polymer (BFRP) bar possesses the advantages of light weight, high strength and corrosion resistance, providing a new method to solve the durability problem of infrastructures on the reefs. Meanwhile, the adoption of a novel type of concrete using coral reef as aggregate can save the high transportation expenses of construction materials. Based on the above background, coral reef concrete and BFRP bar were proposed to replace traditional concrete and steel bar in this paper, to realize the economy and durability of infrastructures on the reefs. The researches were carried out from the aspects of the basic mechanical properties of coral reef concrete, the bond behavior of the interface between BFRP bars and coral reef concrete, and the flexural behavior of coral reef concrete beams reinforced by BFRP bars. The main research contents are shown as follows.1. The effects of aggregate grading, water-cement ratio and curing age on the axial compressive strength were researched through axial compression tests on the test cubes of coral reef concrete. The failure modes under different curing ages were compared. The optimized water-cement ratio was determined to be 0.54. The coral reef concrete cubes with silver sand demonstrated higher strength than those without silver sand.2. Bond behavior tests were conducted on 84 BFRP bar-coral reef concrete pull-out specimens after corrosion. The effects of diameter of BFRP bar, temperature, corrosion form (dry-wet cycle and immersion) on bond behavior were researched. The characteristics of different bond-slip stages, bond failure mechanisms and degradation of bond strength were analyzed and compared with those of steel bar-coral reef concrete. The results showed a favorable bond behavior between steel bars and coral reef concrete.12 mm BFRP bars performed a stable bond strength, without obvious impact by corrosion. Most of the specimens showed a slight increase of bond strength. In contrast, the bond strength of 8 mm and 16 mm BFRP bars demonstrated a significant decrease after corrosion due to the change of bond failure mechanism.3. Flexural tests were conducted on ten coral reef concrete beams reinforced by BFRP barsafter dry-wet cycle at different temperatures. The results were compared with four coral reef concrete beams reinforced by steel bars. Degradation law was analyzed from loading capacity, failure mode, distribution of deflection and crack propagation. The failure mode of coral reef concrete beams reinforced by steel bars was flexural failure, regardless of corrosion, and the ultimate failure was dominated by concrete crush. The failure mode of coral reef concrete beams reinforced by BFRP bars transformed from flexural failure to bending-shear failure and shear compression failure as the increase of temperature and aging time.4. The formula of basic anchorage length between BFRP bar and coral reef concrete, and its correction factors in different environments were proposed on the basis of pull-out tests. Based on the flexural test of concrete beams, it was pointed out that the formula of flexural capacity in the design specification was conservative and the formula of crack width of coral reef concrete beam reinforced by BFRP bars and its correction factors were proposed.