Performance of shaft lining concrete under the coupling effect of early-age frozen soil pressure and negative temperature

The effects of early-age frozen pressure,negative temperature,and early-age load and negative temperature coupling on the strength,chloride diffusion and acoustic emission characteristic of freezing shaft wall C60 concrete were studied,and the internal microcracks were analyzed by scanning electron microscopy(SEM). It is found that the earlier the early-age load applies,the greater effect it has on the 28 d compressive strength of the concrete. But when the external load is applied 3 d later and the load level is less than 40% of the day's strength,the 28 d compressive strength of the concrete is almost not affected. A negative temperature environment of the freezing shaft wall can delay early concrete hydration,and antifreeze speeds up the development of concrete hydration and strength. Under the early-age load and negative temperature coupling effect,the 28 d compressive strength and durability of the concrete decrease,the chloride diffusion coefficient increases apparently,the concrete permeability changes from middle to high,the internal microcracks and deficiencies lead to advancing the active phase of acoustic emission,and the concrete presents apparent plastic deformation.