Jianming Gao

Time dependent chloride diffusion coefficient in concrete

In order to study how to correctly apply the two different time dependencies to service life prediction models, the definition of parameters in the time dependent equation using the long-term test method and the short-term test method, and its relationship were discussed. The experimental results show that, as the two time dependencies have different meanings, they have different manners when handled in service life prediction models. Time dependency of chloride diffusion coefficients in concrete was obtained by fitting experimental data. A large number of accurate experimental data were required to fit the formula of time dependency to ensure the accuracy of service life prediction model.

Performance of Concrete Subjected to Severe Multiple Actions of Composite Salts Solution under Wet-Dry Cycles and Flexural Loading in Lab

Several action regimes were employed, namely, those exposed to solutions containing single and/or composite chloride and sulfate salts, and under wet-dry cycles and/or flexural loading. The variations in dynamic modulus of elasticity (Erd values) were monitored, as well as the key factor impacting on the chloride ingress when concrete subjected to multiple action regimes was identified by the method of Grey Relation Analysis (GRA). The changes in micro-structures and mineral products of interior concrete after different action regimes were investigated by means of X-ray diffraction (XRD), mercury intrusion technique (MIP), and scanning electron microscopy (SEM). The test results showed that the cyclic wet-dry accelerated the deterioration of OPC concrete more than the action of 35% flexural loading based on the results of Erd values and the GEA. The analyses from micro-structures could give certain explanations to the change in Erd values under different action regimes.

Effect of polymer-based grinding aid on sulfate attacking resistance of concrete

Influences of polymer-based grinding aid (PGA) on the damage process of concrete exposed to sulfate attack under dry-wet cycles were investigated. The mass loss, dynamic modulus of elasticity (Erd), and S and Ca element contents of concrete specimens were measured. Scanning electron microscopy (SEM), mercury intrusion porosimetry(MIP), and X-ray diffractometry(XRD) were used to investigate the changing of microstructure of interior concrete. The results indicated that PGA was capable of reducing the mass loss and improving the sulfate attack resistance of concrete. X-ray fluorescence (XRF) analysis revealed that PGA delayed the transport process of sulfate ions and Ca ions. In addition, MIP analysis disclosed that the micropores of concrete with PGA increased in the fraction of 20–100 nm and decreased in the residues of 200 nm. Compared with the blank sample, concrete with PGA had more slender and well-organized hydration products, and no changes in hydration products ratio or type were observed.

Microstructure Evolution from X-CT Measurements for Concrete/mortar under Multi-actions of Composite Salts Dry-wet Cycles and Loading

Inthis research, microstructure evolution forconcrete/mortar under multi-actions of composite salts dry-wet cycles and loading was investigated through X-CT measurements. The evolution process of pores and micro-cracking with the erosion time were tracked. Compared the different erosion actions, it was found that dry-wet cycles promoted the pores become connected gradually. Besides, the dry-wet cycles accelerated the damage seriously on interface area between concrete and aggregate, whistle, loading contributes to the cracking propagation toward the internal. Moreover, fly ash played a positive role in the increasing of the number of harmless holes again and contributed to the durability of concrete.