Effect of Fly Ash and Early Strength Agent on Durability of Concrete Exposed to the Cyclic Sulfate Environment

The effect of fly ash and early strength agent on resistance of concrete to the cyclic sulfate environment was studied.Concrete specimens made with ordinary portland cement or ordinary portland cement incorporating fly ash with the replacement of 10% or 20%,or 1% early strength agent and fly ash with the replacement of 20%,were made and subjected to 250 cycles of exposure to the cyclic sulfate environment.Concrete properties including loss of mass,chloride ion diffusion coefficient,compressive strength and flexural strength were measured.Microstructure and chemical component of samples were determined by means of X-ray diffraction,scanning electron microscopy and energy dispersive spectroscopy.The experimental results indicated that effect of fly ash on the cyclic sulfate resistance of concretes was mostly dependent on the amount of fly ash.Early strength agent improved performances of concrete with 20% fly ash exposed to cyclic sulfate environment.

Experimental on C50 Ultra-high-early Strength Concrete

In this paper,C50 ultra-high-early-strength concrete was prepared with rapid-harden sulphoaluminate cement,alkali carbonate early strength agent,inorganic tribasic acid retarder and polycarboxylate water reducing agent. The properties testing results of C50 ultra-high-early-strength concrete indicated that the compressive strength at 12 h exceeded 37 MPa and at 3 d exceeded 59 MPa. Compared to the C50 ordinary reference concrete,the durability of C50 ultra-high-early strength concrete was investigated. The results indicated that C50 ultra-high-early-strength concrete had the same chloride ion permeability resistance,carbonization resistance and abrasion resistance to the C50 ordinary concrete. As to the sulfate resistance,the ultra-high-early-strength concrete was much better than the ordinary concrete.