Influence Of Mineral Admixtures And Shrinkage Reducing Admixtures On Transport Properties Of Concrete

To improve the durability performance and service life of concrete exposed to severe environments, such as saline soil and salt lake areas, this dissertation studies the influence of mineral admixtures (high-Ca fly ash and ground blast furnace slag, high-Ca FA and GBFS) and shrinkage reducing admixtures (SRAs) on water and chloride ions transport in concrete via drying, chloride binding capacity, ponding, chloride migration, wick action and electrical resistivity tests. The relationships between the formation factors and transport properties/service life are discussed as well And this study is aimed to provide the scientific support for the utilization of concrete containing mineral admixtures/SRAs in severe environments and establish the foundations for the rapid estimation of durability performance and service life of concrete using its formation factor.Within the dosage level of 50% w.t, the intrinsic permeability of concrete, which is smaller than that in OPC40 by 7%-61%, firstly decreases and then increases as the high-Ca FA/GBFS dosage level increases. The concrete containing high-Ca FA/GBFS has dramatically higher chloride binding capacity and tortuosity while its apparent chloride diffusion coefficient greatly decreases by 83%-86% and 49%-69%, respectively. After subjecting to wick action for 4 months, the concrete containing high-Ca FA/GBFS contact with NaCl and MgCl2 solutions has a smaller chloride penetration depth by 43%-62% and 18%-54% compared to OPC40, respectively. As indicated above, the addition of high-Ca FA and GBFS greatly mitigates water and chloride ions transport in concrete.SRA has little influence on the microstructure and chloride binding capacity of concrete. It helps decrease the apparent chloride diffusion coefficient of concrete by 13%-52%, which is inversely proportional to the increased viscosity of the concrete pore solution. At the same degree of saturation, the concrete with a higher SRA content has a smaller moisture diffusivity and its drying rates at late periods are higher than those in plain concrete. SRA helps slow down the transport process of water and chloride ions in concrete; And with the transport properties of plain concrete and the quantitative relations between SRA content and the properties of the pore solutions, it turns to be possible to mathematically predict water and chloride ions transport in concrete with SRA.The resistivity of the pore solution of concrete has no influence on the formation factor of a saturated concrete, which is only related to the concrete microstructure. Among concretes with varying water to binder ratios and SRA contents, the product of the formation factors and the viscosity ratios, F*ηSRA/η%OSRA, is linearly related to 1/x2 (the reciprocal of the chloride diffusion depth square). However, the relation in concrete with high-Ca FA/GBFS deviates the above linear relation due to their greatly improved chloride binding capacities. The effective chloride diffusion coefficient can be reliably obtained using the formation factor of concrete, and the formation factor in concrete with varying water to binder ratio is linearly related to its service life, which indicates the feasibility of service life prediction with the formation factor.