| In the soft water environment,sand-free macroporous concrete is susceptible to corrosion,resulting in durability degradation of engineering structures and shortened service life.In order to study the corrosion characteristics of sand-free macroporous concrete,this paper uses ammonium chloride solution to carry out accelerated corrosion tests of sand-free macroporous concrete specimens and their paste specimens with different mineral admixtures(fly ash,silica fume,slag powder)types and dosages.Through the indexes of calcium ion dissolution,porosity,permeability coefficient and corrosion depth of sand-free macroporous concrete paste specimens,the effects of mineral admixtures types and dosages on the corrosion resistance of sand-free macroporous concrete were studied.By analyzing the appearance,compressive strength,microstructure and calcium-silicon ratio,the corrosion damage degradation mechanism of sand-free macroporous concrete was studied.The numerical model of sand-free macroporous concrete was constructed by PFC discrete element particle flow software.The meso-scale failure of sand-free macroporous concrete during compressive strength test was studied from the contact force between particles,crack development and model cracking.The main research results are as follows :(1)Under the action of corrosion,the calcium ion dissolution,porosity,permeability coefficient and the corrosion depth of the paste specimens of the sand-free macroporous concrete increase with the increase of the corrosion time,and the reasonable single-doped fly ash,silica fume or slag powder can effectively reduce the effect of corrosion on the sand-free macroporous concrete,reduce the growth rate of calcium ion dissolution,porosity,permeability coefficient and corrosion depth,and effectively improve the corrosion resistance.(2)Under the action of corrosion,the hardened cement coating layer on the aggregate surface of sand-free macroporous concrete appears to be thinner,loose,shedding,increase of micro-structure pores and decrease of calcium-silicon ratio,resulting in a decrease in compressive strength.Reasonable single-doped fly ash,silica fume or slag powder can effectively reduce the degree of corrosion damage and deterioration of the hardened cement coating layer of sand-free macroporous concrete,improve the compressive strength of the specimen before and after corrosion,and reduce the loss rate of compressive strength.(3)Numerical model of sand-free macroporous concrete in the compressive strength test simulation process,the maximum value of inter-particle contact force reaches its maximum at the point corresponding to the peak stress;the contact bond strength between particles decreases under the effect of dissolution,resulting in a decrease in the maximum value of contact force,while reasonable single admixture of fly ash,silica fume or slag powder can improve the contact state between particles and increase the contact bond strength. |
