Pore Filling Effect of Forced Carbonation Reactions Using Carbon Dioxide Nanobubbles

Various methods for repairing and modifying concrete surfaces have been proposed and applied to improve the durability of existing concrete structures. Surface modification through forced carbonation is a method of densification that forms calcium carbonate in the pores on the surface of concrete to improve its durability. In this study, to evaluate the applicability of this surface modification method to existing buildings, a series of experiments was conducted in which mortar specimens were repeatedly immersed in a carbon dioxide nanobubble aqueous solution. By evaluating the weight change and absorption rate, it was determined that the higher the water/cement ratio of the mortar specimen, the higher the pore filling effect owing to immersion in the carbon dioxide nanobubble aqueous solution. In addition, the effect of clogged pores generated by the precipitation of calcium carbonate was confirmed, and it was found that the higher the water/cement ratio of the mortar specimen, the higher the pore filling effect due to clogging. We believe that our findings contribute to the development of research and construction practices associated with concrete repair and restoration.

Influence of Plantain Pseudostem Fibres and Lime on the Properties of Cement Mortar

This study investigated the properties of cement mortar with lime reinforced with plantain pseudostem fibres. Experimental specimens with 0, 0.25, 0.5, 0.75, and 1% fibre contents by weight of sand and 10% lime content by weight of cement were prepared and tested on 7, 14, 21, and 28 days of curing for density, tensile strength, compressive strength, SEM, and EDS. The 0.25% plantain pseudostem fibre reinforced mortar achieved 23.4% compressive strength improvement over unreinforced mortar specimens. There was between 6.89 and 13.80% increase in tensile strength of the plantain pseudostem fibre reinforced mortar over the unreinforced mortar specimens. A positive linear correlation was found between the compressive strength and tensile strength of cement mortar reinforced with plantain pseudostem fibres and lime with coefficient of determinant (R2) values between 0.909 and 0.869. It was also observed that the plantain pseudostem fibre reinforced mortar specimen had some microcracks and voids from the SEM analysis. Furthermore, EDS analysis showed the presence of calcium silicate hydrate with a Ca/Si ratio of between 1.02 and 2.49, and Al/Si ratio of between 0.76 and 0.81 as the main oxide. It therefore concluded that the incorporation of plantain pseudostem fibre and lime positively influenced the properties of the cement mortar with the 0.25% fibre content being recommended for construction application.

Application of Ag/AgCl Sensor for Chloride Monitoring of Mortar under Dry-Wet Cycles

An Ag/AgCl electrode used as a corrosion sensor in a reinforced concrete structure is considered as having good application prospect. However, its performance under complex conditions, such as dry-wet cycle condition, is not affirmed. In the current study, the performance of Ag/AgCl as chloride selective electrode in mortar exposed to dry-wet cycle condition was investigated. A simple Ag/AgCl electrode was prepared and fabricated by electrochemical anodization. These Ag/AgCl electrodes were embedded into a mortar specimen with temperature sensors, humidity sensors and anode ladder monitoring system (ALS). After 28 d curing time, the upper surface of mortar specimen was wetted (with 5% NaCl solution) and dried regularly. The obtained results indicate that Ag/AgCl electrode responds to the ingress of chloride ion, sensitively. The chloride ion concentration variation can be reflected by the potential trend. Furthermore, the balance potential of Ag/AgCl electrodes is influenced by dry-wet cycles. Compared with ALS, it demonstrates that Ag/AgCl electrodes are more sensitive to chloride. The research provides the key element for the specific application of Ag/AgCl electrode for corrosion monitoring in the future.

Effect of Graphene Oxide/Graphene Hybrid on Mechanical Properties of Cement Mortar and Mechanism Investigation

This paper evaluated the effect of graphene oxide/graphene (GO/GR) hybrid on mechanical properties of cement mortar. The underlying mechanism was also investigated. In the GO/GR hybrid, GO was expected to act as a dispersant for GR while GR was used as reinforcement in mortar due to its excellent mechanical properties. For the mortar specimen, flexural and compressive strength were measured at varied GO to GR ratios of 1:0, 3:1, 1:1, 1:3, and 0:1 by keeping the total amount of GO and GR constant. The underlying mechanism was investigated through the dispersibility of GR, heat releasing characteristics during hydration, and porosity of mortar. The results showed that GO/GR hybrid significantly enhanced the flexural and compressive strength of cement mortars. The flexural strength reached maximum at GO:GR = 1:1, where the enhancement level was up to 23.04% (28 days) when compared to mortar prepared with only GO, and up to 15.63% (7 days) when compared to mortar prepared with only GR. In terms of compressive strength, the enhancement level for GO:GR = 3:1 was up to 21.10% (3 days) when compared with that of mortar incorporating GO only. The enhancement in compressive strength with mortar at GO:GR = 1:1 was up to 14.69% (7-day) when compared with mortar incorporating GR only. In addition to dispersibility, the compressive strength was also influenced by other factors, such as the degree of hydration, porosity, and pore size distribution of mortar, which made the mortars perform best at different ages.

Crack Width Estimation of Mortar Specimen Using Gas Diffusion Experiment

Maintenance of structures using self-healing concrete technologies has recently been actively studied. However, unlike the technological development of self-healing concrete, research focused on evaluating the self-healing performance is insufficient. Although water permeability experiments are widely used, the reliability of the test results may be reduced due to the viscosity of water and the possibility of elution of material inside the specimen. In this study, we propose a gas diffusion test for estimating the crack width and eventually for application to evaluation of the self-healing performance. The results verified that the proposed method can be effectively applied to the estimation of crack width.