Surface Sorptivity Research Articles

Durability properties of structural concretes containing secondary cementitious materials

This study investigated the durability properties of structural concretes incorporating secondary cementitious materials of fly ash and ground granulated blast-furnace slag (GGBS). The compressive strength and porosity were taken as basic properties, and the transport properties measured included electrical conductivity, chloride diffusivity, capillary absorption and gas permeability. Correlation analysis was performed on the basic and transport properties, and the pore structure of structural concretes was characterized into different patterns in terms of the connectivity and the tortuosity. The results show that (a) the concrete pores are refined by mineral admixtures and Archie’s law can describe the pore connectivity and tortuosity for saturated specimens; (b) all the transport properties correlate well with water-to-binder (w/b) ratios and the concretes with GGBS show a pronounced effect of oven-drying and self-desiccation on pore structure; and (c) chloride diffusivity and surface sorptivity correlate better with compressive strength, while chloride diffusivity, sorptivity and gas permeability should be treated as independent properties.

Evaluation of Relationship between Water Absorption and Durability of Concrete Materials

Environment has significant effects on the water absorption of concrete materials. This paper presents an experimental study of the influence of water absorption on the durability of concrete materials. A detailed analysis is also presented in order to establish useful relationship between them. Concrete specimens of different water absorption were prepared through different curing conditions, and results indicated that curing condition can significantly affect the surface water absorption. SEM photos also showed that different curing conditions caused different microstructure. After 28-days curing, compressive strength, permeability, sulfate attack, and chloride ion diffusion of concrete samples were investigated. As a result, both of surface sorptivity and internal sorptivity have no clear relationship with compressive strength. Results obtained also showed that only surface water absorption related to the performance of concrete including permeability, sulfate attack, and chloride ion diffusion. In addition, both impermeability and resistance to sulfate attack were linearly associated with surface sorptivity, and both correlation coefficients were not less than 0.9. Furthermore, chloride ion diffusion coefficient has exponent relation to surface water absorption with higher correlation coefficient. However, no apparent relationship was found between internal water absorption and durability like impermeability, resistance to sulfate attack, and chloride ion diffusion.

Study on water sorptivity of the surface layer of concrete

This paper presents the results from a study of water sorptivity of concrete surface layer. The sorptivity is characterized by a surface sorptivity index as measured by Autoclam. In this study, different types of concrete were immersed in ultrapure water and NaCl solution prior to the sorptivity test. The influences of several factors on the value and evolution of concrete surface sorptivity index are discussed. It is found that: concrete surface sorptivity is a function of the pore structure, higher porosity and lower tortuosity lead to higher surface sorptivity; as cured in moist condition for 1 month, the surface sorptivity is an increasing function of w/c in plain cement concretes, and an increasing function of fly ash replacement if w/b is kept constant; surface sorptivity increases as immersed in ultrapure water in the first month of immersion due to leaching, and decreases thereafter as the continuous hydration of cementitious materials makes the pore structure finer and finer; the immersion in NaCl solution limits the effect of leaching because of the formation of calcium oxychloride compounds, and results in lower long-term surface sorptivity index as compared with the ultrapure water immersion, due to the formation of Friedel’s salt which reduces the pore volume and blocks the pore network.

Study of the relationship between scaling resistance and sorptivity of concrete

The aim of this study is to analyze the relationship between scaling resistance and sorptivity of concrete surfaces. Five types of air-entrained concretes containing cementitious materials (25%–35% fly ash, 25–35 slag, 1%–2% silica fume) were submitted to scaling tests according to ASTM C672 procedure, after 14 and 28 days of moist curing. These concretes were also submitted to sorptivity testing. Results show a clear correlation between scaling test results and sorptivity measurements. Low surface sorptivity (<0.1 mm/min1/2) always indicates satisfactory scaling resistance. These results show that to obtain adequate scaling resistance, curing conditions and mix design must be optimized to promote the development of a dense and impervious concrete skin that resists external water penetration. Lengthening of the moist-curing period of concrete incorporating cementitious materials systematically decreases sorptivity and improves its scaling resistance, especially for concrete containing fly ash.

Characterizing the effect of compressive damage on transport properties of cracked concretes

This paper reports a comprehensive experimental investigation on the impact of mechanical cracking on transport-related properties of concrete, including air permeability, surface sorptivity and electrical resistance. Cylinder specimens of \(\phi150\,\hbox {mm}\times400\,\hbox{mm}\) are subject to cyclic axial compressive loading and different damage levels are generated by changing cyclic loading numbers under displacement control. The characterization parameters of cracking include scalar damage factor, residual strains and open porosity. Prior to and after loading, for each specimen, the ultrasonic pulse velocity is measured perpendicular to the loading direction and both residual axial and lateral strains are recorded by strain gauges. Two discs of 50 mm thick are cut out from the middle height of each unloaded concrete cylinder and dried to constant weight at 60°C. Thereafter, the discs are subject to gas permeability, water sorptivity, open porosity and electrical resistance tests. The correlations are discussed in depth for damage characterization indicators and damage-altered transport properties, in particular, the relation between altered gas permeability and ultrasonic damage is quantified. From the obtained data, it is found that ultrasonic damage factor is correlated strongly with altered gas permeability while open porosity is well correlated to altered sorptivity and electrical resistance.

The effects of air content on permeability of lightweight concrete

Air entraining agent is used to control the floatation of lightweight aggregate (LWA) in lightweight aggregate concrete (LWAC), therefore reducing the segregation of LWAC. At the same time, using an air entraining agent will affect the water sorption of the concrete. In this paper, two lightweight concrete mixes of density 1000 kg/m 3 and air content of 13.5% and 31.9% were compared and the effects of entrained air on the strength, surface sorptivity, and chloride permeability of LWAC are presented. Results show that the use of porous LWA would not lower the permeability resistance of concrete. Entrained air had little effect on sorptivity but a major effect on chloride permeability. The weaker pores' network in the cement paste is the basic cause for the high chloride permeability of concrete than the use of porous LWA. Although chloride permeability of low density LWAC concrete decreased with age of concrete, it was found that the concrete was not dense enough to stop the chloride ion to penetrate through the concrete before the concrete mature at 90 days.