Effect of fly ash and early strength agent on durability of concrete exposed to the cyclic sulfate environment

Abstract

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.

Microstructural and Microanalytical Study on Concrete Exposed to the Sulfate Environment

“…Therefore, the presence of mineral admixtures is known to affect the sulfate resistance of concrete. The physical and mechanical properties of concrete incorporating mineral admixtures under the sulfate exposure have been studied in prior work [13,14]. In this study, microstructure analyses are performed to investigate the effect of mineral admixtures on the deterioration mechanism of concrete subjected to sulfate attack.…”

Nano-SiO2 Recycled Concrete Anti-Sulfate Performance and Damage Mechanism Research

“…As the size of SiO 2 in the nanostructure decreases, many atoms are generated uniformly, thus increasing the chemical processes. NS has a huge surface energy, the particles are in a highly reactive state, and the reaction of atoms with other foreign atoms increases the volcanic ash reaction of NS [33]. (Equations ( 4)-( 6)).…”

Numerical Simulation of Concrete Attacked by Sulfate under Drying–Wetting Cycles Coupled with Alternating Loads

“…By substituting Equations ( 12)-( 14) into (11), the change in concrete porosity due to cement hydration and damage can be calculated: Because concrete is a porous medium structure, the diffusion of SO 4 2− in concrete is different from that in pure liquid, and the diffusion coefficient is influenced by the internal porosity and the tortuosity degree of the concrete. Fick's law assumes a constant diffusion coefficient, so the diffusion coefficient of SO 4 2− must be corrected to establish the transport model of SO 4 2− transport in the concrete with accuracy.…”

“…Expansion products fill pores and initially increase the strength of the concrete structures [9]. However, later in time, the excessive gypsum and ettringite in the concrete eventually lead to cracking and expansion, and the service life is greatly reduced [10,11]. Concrete that is exposed to drying-wetting cycling conditions is more seriously damaged by sulfate than concrete in a persistently moist environment [12][13][14].…”