Reliable characterization of the pore structure is essentially important for transport-related durability studies of cementitious materials. Mercury intrusion porosimetry has been commonly used for pore structure measurement while the ink-bottle effect significantly affects the trustworthiness of pore size features of cementitious materials. Pressurization-depressurization cycling mercury intrusion porosimetry (PDC-MIP) is an alternative approach previously reported with the purpose to provide better estimates of pore size results. It is found however that the PDC-MIP greatly overestimates the ink-bottle pore volume owing to the incomplete extrusion of mercury in throat pores after the pressurization-depressurization cycle. Intrusion-extrusion cyclic mercury porosimetry (IEC-MIP), as a further improvement, is then described, which can reliably capture the ink-bottle effect and obtain a clear picture of the distribution of the ink-bottle pores in cementitious materials. The ink-bottle effect of cement pastes is observed being pore size-dependent and the role of critical pores is emphasized. Water-cement ratio primarily changes the effective porosity while plays a minor role in the ink-bottle porosity. The addition of reactive blends substantially enhances the ink-bottle effect during mercury penetration into small pores. IEC-MIP tests, together with a unique data analysis, enable to obtain a more truthful pore size distribution.

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The proper disposal of steel slag has always been a great challenge for the metallurgical industry in China and around the world. In this work, the steel slag aggregate (SSA) was surface pretreated (PSSA) and applied into asphalt mixture. The adhesive behavior between the bitumen and five different types of aggregates (i.e., limestone, diorite, diabase, SSA, PSSA) were evaluated based on the contact angle and binder bond strength tests. The pavement performance of three asphalt mixtures which contain normal aggregate, SSA and PSSA respectively, was analyzed by Marshall stability test, wheel-tracking rutting test, low-temperature bending creep test and water sensitivity test. The results showed that surface modification can improve the surface properties of SSA, reduce its contact angle with bitumen, and eventually lead to the improvement of adhesion between them. In addition to the satisfied low-temperature properties, PSSA was found to significantly improve the anti-rutting property and reduce the water sensitivity of asphalt mixture. This work is expected to promote an alternative application for recycling of SSA in pavement engineering.@en

The influences of liquid-binder ratio and mixing sequence on the performance of superabsorbent polymer (SAP)-containing alkali-activated slag (AAS) mortar are investigated in this study. It is found that the SAP absorbs much less liquid in upper supernatant of AAS than in water. Mixing SAP with liquid first induces a larger absorption capacity of the SAP than mixing it with solid first. Increasing the liquid-binder ratio improves the flowability but reduces the strength of AAS mortar with SAP. Nonetheless, the strength of internally cured mixtures is higher than that of the reference even with an extra liquid-binder ratio of 0.09. The reason behind lies in the refinement of capillary and gel porosity by internal curing, despite the presence of large voids originated from SAP. The autogenous shrinkage of AAS paste is reduced significantly by the incorporation of SAP but the further mitigating effect of increased liquid-binder ratio is limited.

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Internal curing by superabsorbent polymer (SAP) has been applied in alkali-activated slag (AAS) systems by a few previous studies with the purpose to mitigate the autogenous shrinkage. However, the effects of SAP on other properties of AAS have been rarely studied. In this paper, the workability, strength, permeability, and frost resistance of AAS mortar with synthesized SAP are investigated besides the autogenous shrinkage. Two SAP introducing ways (dry mixing and wet mixing) are considered. It is found that the flowability of AAS mortar decreases with the increase of SAP dosage regardless of the introducing way. The strength and permeability increase with the SAP dosage when it is below a certain amount depending on the mixing way. The autogenous shrinkage can be mitigated significantly by the incorporation of SAP and the mitigating effect is more pronounced by wet mixing. The frost resistance becomes better when more SAP is introduced in either way. The mechanisms behind these phenomena are explained based on the characterization results on the reaction kinetics, reaction products and pore structure of the mixtures with SAP.

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Concrete is rarely saturated. Reliable durability design of marine concrete structures requires a solid understanding of the long-term chloride transport in unsaturated concretes. This paper presents a critical analysis of the time-dependent chloride diffusion coefficient in unsaturated cementitious materials exposed to marine environment. Evolutions of pore structure and chloride diffusion coefficient in saturated cementitious materials, along with the role of the degree of water saturation in long-term chloride diffusion, are analyzed. It is emphasized that the long-term sharp decrease of the chloride diffusion coefficient in marine cementitious materials is not primarily caused by densification of the microstructure due to hydration, but by the decreasing degree of water saturation with depth in the surface part of the materials. The effects of water/binder ratio and supplementary cementitious materials on chloride diffusion coefficient are different between saturated and unsaturated cementitious materials.

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Conceptual analysis is performed to examine the effects of pore features on the water continuity in unsaturated porous systems. The roles of pore features in relative chloride diffusion coefficient (Drc) of mortar specimens at various degrees of water saturation (Sw) were studied based on mercury intrusion porosimetry and resistivity tests. It is found that the role of pore structure in the Drc-Sw relationship is a result of its effect on the water continuity. Porosity and tortuosity are not relevant to the Drc-Sw relationship. A finer pore size distribution or lower pore connectivity tends to result in a lower Drc. The pore size effect on the Drc is pronounced primarily at high Sw, while the Drc is dominated by the pore connectivity at low Sw. Cement mortar with a higher water-to-binder ratio shows larger chloride diffusion at high relative humidity levels but smaller chloride diffusion at low relative humidity levels.@en

Microstructure-property relationship has drawn strong attention in modern material science. The progress achieved in this field relies on a common basis that the material performance originates from the microstructure. This paper brings together new insights and facts from experiments regarding the pore size dependent connectivity and its relation to ionic transport property in saturated cementitious materials. An innovative measurement, i.e. intrusion-extrusion cyclic mercury porosimetry (IEC-MIP), is proposed to distinguish between the small capillary pores that are present within clusters of hydration products and the large capillary pores that are left out of hydration products. The distribution of connectivity as a function of pore size in cementitious materials is analyzed. A novel transport parameter, i.e. connectivity of small capillary pores, is introduced and quantified by IEC-MIP measurements. The ionic transport was measured by means of rapid chloride migration tests. A power relationship is established between connectivity of small capillary pores and chloride migration coefficient for cementitious materials irrespective of the binder type.

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