Experimental Research On Frost Resistance Behavior Of Basalt Fiber Reinforced Marine Concrete

The sustainable growth of concrete demand makes the seemingly rich river sand resources continue facing shortages.In some areas,the predatory exploitation of river sand causes serious consequences such as soil erosion and farmland destruction.Considering the current situation of China's lack of river sand resources in some areas,in the premise of ecological protection and rational exploitation of natural resources,the use of sea sand to replace river sand has become an inevitable choice.Freeze-thaw failure is one of the main factors to cause the damage of concrete constructions.Current researches on the durability of sea-sand concrete mainly focus on impermeability and corrosion resistance and take less attention to freeze-thaw failure.This thesis aims to study the frost resistance of sea-sand concrete and desalted sea-sand concrete under the action of freeze-thaw cycles and analyze mechanism of freeze-thaw cycles.Meanwhile,this study uses basalt fiber as an internal material to study its improvement of mechanical properties and provide reference for large-scale engineering applications on sea-sand concrete.The research contents are as follows:In this study,original sea sand and desalinated sea sand were used as fine aggregate,respectively.12 groups of concrete specimens with strength of C60 were made with the volume of basalt fiber volume and the variety of mineral admixture as variables.The compressive and flexural tests were carried out and the influence of different dosage of sand,different volume content of basalt fiber and different mineral admixtures on compressive strength and flexural strength were given.The test results show that the desalinated sea sand concrete compressive strength and flexural strength were better than that of sea sand concrete specimens,compressive strength and flexural strength showed first increased and then decreased trend: the compressive strength is the best when the basalt fiber volume is 0.1%;the flexural strength is the best when the basalt fiber volume is 0.2%.Adding silica fume can improve the compressive strength and flexural strength of sea sand concrete.Fly ash has the effect of reducing the compressive strength and has less effect to improve the flexural strength.Freeze-thaw cycle tests of two kinds of concrete were carried out by fast freezing method.By measuring the mass loss rate and relative dynamic elastic modulus under different times of freezing and thawing cycles,study on the effect of different sand,different basalt fiber content and different mineral admixtures on the frost resistance of concrete was performed.Results show that the frost resistance of sea-sand concrete is much behind the desalted sea-sand concrete.Basalt fiber reduces the mass loss rate and the relative dynamic elastic modulus loss rate.The basalt fiber content has different effects for sea-sand concrete and desalted sea-sand concrete.The frost resistance improves with basalt fiber content increased for sea-sand concrete.Desalted sea-sand concrete shows optimal frost resistance with 0.2% volume ratio of basalt fiber.Fly ash is not conducive to frost resistance and silica fume improves frost resistance less obviously than basalt fiber.The study of pore structure by mercury intrusion porosimetry shows that the pore size distribution of desalted sea-sand concrete is better than that of sea-sand concrete.The volume of harmless pores decrease and harmful pores increase after freezing-thawing which makes the pore structure deteriorated.Basalt fiber improves the porosity for both series of the concrete and it works like air-entraining agent to a certain extent.Basalt fiber increases the porosity of harmless and less harmful pores.