Zhengxian Yang

Corrosion of Deicers to Metals in Transportation Infrastructure: Introduction and Recent Developments

Chemicals used in the snow and ice control operations (also known as deicers) may cause corrosion damage to the transportation infrastructure such as reinforced or pre-stressed concrete structures and steel bridges. This review presents a synthesis of information regarding the impacts of both chloride-based and acetate/formate-based deicers on metals especially steel rebar in concrete, common test methods to quantify such impacts, and countermeasures to manage such impacts. There are many ways to manage the corrosive effects of deicers, such as: selection of high-quality concrete, adequate concrete cover and alternative reinforcement, control of the ingress and accumulation of deleterious species, injection of beneficial species into concrete, and use of non-corrosive deicer alternatives and optimal application rates.

Transport Properties of Carbon-Nanotube/Cement Composites

This paper preliminarily investigates the general transport properties (i.e., water sorptivity, water permeability, and gas permeability) of carbon-nanotube/cement composites. Carboxyl multi-walled carbon nanotubes (MWNTs) are dispersed into cement mortar to fabricate the carbon nanotubes (CNTs) reinforced cement-based composites by applying ultrasonic energy in combination with the use of surfactants (sodium dodecylbenzene sulfonate and sodium dodecyl sulfate). Experimental results indicate that even at a very small dosage the addition of MWNTs can help decrease water sorptivity coefficient, water permeability coefficient, and gas permeability coefficient of cement mortar, which suggests that CNTs can effectively improve the durability properties of cement-based composites.

Laboratory Assessment of a Self-Healing Cementitious Composite

This paper presents work in the laboratory assessment of a new family of self-healing materials that hold promise for “crack-free” concrete or other cementitious composites. This innovative system features the design of passive smart microcapsules (PSMs) with oil core and silica gel shell, prepared through an interfacial self-assembly process and sol–gel reaction. Methylmethacrylate monomer and triethylborane were chosen as the healing agent and the catalyst for use in the system and were microencapsulated. The microcapsules were subsequently dispersed in fresh cement mortar along with carbon microfibers. The morphology of the microcapsules was examined by using a field emission scanning electron microscope. Mechanical tests and electrochemical impedance spectroscopy measurements were carried out to evaluate the self-healing effect of PSMs and the possible physicochemical changes or interactions in the carbon microfiber–reinforced mortar matrix.

Micromechanical properties of a new polymeric microcapsule for self-healing cementitious materials

Self-healing cementitious materials containing a microencapsulated healing agent are appealing due to their great application potential in improving the serviceability and durability of concrete structures. In this study, poly(phenol–formaldehyde) (PF) microcapsules that aim to provide a self-healing function for cementitious materials were prepared by an in situ polymerization reaction. Size gradation of the synthesized microcapsules was achieved through a series of sieving processes. The shell thickness and the diameter of single microcapsules was accurately measured under environmental scanning electron microscopy (ESEM). The relationship between the physical properties of the synthesized microcapsules and their micromechanical properties were investigated using nanoindentation. The results of the mechanical tests show that, with the increase of the mean size of microcapsules and the decrease of shell thickness, the mechanical force required to trigger the self-healing function of microcapsules increased correspondingly from 68.5 ± 41.6 mN to 198.5 ± 31.6 mN, featuring a multi-sensitive trigger function. Finally, the rupture behavior and crack surface of cement paste with embedded microcapsules were observed and analyzed using X-ray computed tomography (XCT). The synthesized PF microcapsules may find potential application in self-healing cementitious materials.

Possibilities for improving corrosion protection of reinforced concrete by modified hydrotalcites – a literature review

Modified Hydrotalcites (MHTs) represent a group of technologically promising materials for improving corrosion protection in concrete owing to their low cost, relative simplicity of preparation, and plenty of composition variables. Numerous academic and commercial studies on MHTs have been carried out, but few of them on cementious materials particularly in exploiting their potential application in corrosion protection of reinforced concrete. In this paper, the corrosion mechanism in reinforced concrete and concrete properties that affect it are briefly inroduced. In addition, the existing knowledge with regard to synthesis and characterization methods of MHTs, ion exchange within the MHT structure as well as the application of MHTs in cementitious materials were reviewed.

Recent Advances in Intrinsic Self-Healing Cementitious Materials

Self-healing is a natural phenomenon whereby living organisms respond to damage. Recently, considerable research efforts have been invested in self-healing cementitious materials that are capable of restoring structural integrity and mechanical properties after being damaged. Inspired by nature, a variety of creative approaches are explored here based on the intrinsic or extrinsic healing mechanism. Research on new intrinsic self-healing cementitious materials with biomimetic features is on the forefront of material science, which provides a promising way to construct resilient and sustainable concrete infrastructures. Here, the current advances in the development of the intrinsic healing cementitious materials are described, and a new definition of intrinsic self-healing discussed. The methods to assess the efficiency of different healing mechanisms are briefly summarized. The critical insights are emphasized to guide the future research on the development of new self-healing cementitious materials.

Laboratory Investigation into the Modification of Transport Properties of High-Volume Fly Ash Mortar by Chemical Admixtures

AbstractThis work aims to optimize the transport properties of high-volume fly ash (HVFA) mortars that replace Portland cement with a Class C fly ash at 60% by weight. Ten chemical admixtures (five...

Effect on Mechanical Properties and Chloride Penetration Resistance of Modified Hydrotalcite in Cement Mortar

In this paper, two types of modified hydrotalcites (MHT-pAB and MHT-NO2) were incorporated into cement mortars with two dosage levels (replacing 5 and 10 % cement) and a constant water-to-(cement + MHT) ratio of 0.50. Designated testing programme including strength test, porosity test, and rapid chloride migration were employed to investigate the effect of modified hydrotalcites on chloride penetration in cement mortar. The results based on these tests revealed that the incorporation of MHT-pAB at 5 % dosage in mortar specimens produced a notably improved resistance to chloride ingress with no or minor influence on the development of mechanical strength, which further confirmed the possibilities for using modified hydrotalcite as a chloride scavenger in cement mortars.

The Effect of Modified Hydrotalcites on Mechanical Properties and Chloride Penetration Resistance in Cement Mortar

In this paper, two types of modified hydrotalcites (MHT) were incorporated into cement mortars with two dosage levels (replacing 5% and 10% cement by mass). Designated testing programme including strength test, porosity test, and rapid chloride migration and diffusion test were employed to investigate the effect of modified hydrotalcites on chloride penetration in cement mortar. The results based on these tests showed the incorporation of MHT-pAB at 5% dosage in mortar specimens produced a notably improved chloride diffusion resistance with no or minor influence on the development of mechanical strength.