Impact of Sulfate Ion on Dolomite Concrete Performance

Document Type : Original Article

Authors

1 Ph.D. Civil Engineering Branch.

2 Lecturer, Ph.D., Civil Engineering Department, Military Technical College. Cairo. Egypt.

Abstract

Concrete deterioration is an important cause of sudden collapse of buildings. Sulfate ion
attack is a prominent cause of concrete deterioration. The main cause of sulfate attackinduced
damage is ettringite formation in voids, cracks, and contact zones between aggregates
and hardened cement paste. Scanning electron microscopy (SEM) images are taken to detect
delayed ettringite crystal development in voids. General diffusion equations are utilized to
investigate the sulfate ion ingress and the distribution of sulfate ion concentration in concrete
related to time. A numerical model demonstrates the relation between the diffusion coefficient
and concentration. A computer program is developed to model the problem of ion diffusion in
concrete. The sulfate attack on concrete by one-dimensional diffusion process is simulated.
The numerical model demonstrates the relation between the diffusion coefficient and
concentration.
The computer program is developed to calculate the SO4 ion diffusion. Compared with the
SO4 ion diffusion coefficient in free water, the high diffusion value and the low compressive
strength of concrete specimen are the values of concrete deterioration. The experimental
program included mix design of 6 concrete mixes. The parameters of the experimental
program were: cement type and content, presence of silica fume, sulfates concentration, and
exposure period.
The results show that, the concrete deterioration by sulfate attack is strongly influenced by the
sulfates concentration in the aggressive medium and the exposure time. There is a linear
relation between strength loss and concentration for mixes containing silica fume. Ordinary
Portland cement (OPC) concrete limits the strength reduction about 10% after one year
exposure to 5,000 ppm sulfate solution. In case of 100,000 ppm sulfate solution, the reduction
is (13.1%). Increasing the cement content increases the strength loss by sulfates attack even in
the presence of silica fume.

Keywords