Morphology Changes and Fillers migration in Urethane Composites during Thermal Degradation.

Polyurethane composite coatings are frequently applied to strengthen the barrier properties of various construction materials such as wood, metal and concrete. The changes of color and glossiness of the composite coatings for building materials proceeds more slowly than that of polyurethane because of containing fillers and several types of additives. However, the most critical barrier properties have not been studied directly based on the difference from the degradation mechanism of polyurethane coatings. Additionally, the difference in thermal and UV degradation mechanisms of coatings is not clear in the existing studies dealing with conventional accelerated weathering tests and outdoor exposure tests. Therefore, the behavior of the filler contained in the coatings was observed using an oven to accelerate thermal degradation. The chemical analysis of the coating surface by XPS and the analysis of the images and elemental mappings by SEM-EDS were carried out, and the mechanism of degradation progress was investigated. In addition, the temperature dependency of the degradation was studied in changing the heating temperature. It was suggested that polymer and fillers interact in promoting mass transfer at the same time as the thermal degradation reaction consequently

Intrinsic Differences on the Photodegradation Mechanisms between Pigmented and Non-Pigmented Coatings Determined by Multi-Scale Analysis

Multi-scale analysis of photodegradation are conducted for pigmented coating containing acrylic urethane + TiO2 pigment and for non-pigmented coating containing only acrylic urethane. We discuss the intrinsic differences in the photodegradation mechanism between the pigmented and nonpigmented coatings and the effect of the interface between the pigment and the binder. Photo-aging tests are conducted using artificial ultraviolet (UV) irradiation under conditions of 60 °C and dry atmosphere. The results of Fourier transform infrared spectroscopy (FTIR), solvent swelling experiments, ultrasonic measurements of elastic moduli, and colourimetry used for material characterisation before and after photo-aging. Although the behaviour of E and the carbonyl index (CI) show common trends for both samples, the overall trends of yellowness index (YI) and swelling degree (Q) differ significantly between the pigmented and non-pigmented samples. The results reveal that changes in macroscopic properties may not necessarily correspond with the CI behaviour and that characteristic interfacial effects exist between the pigment and the binder. The onsets of coating erosion and chalking are observed in the pigmented coating as surface topological changes. The different behaviour of YI and Q between the sample types can be attributed to the interfacial effect at pigment/binder interface based on the photocatalytic effect from TiO2 pigmen

Evaluation on the Mechanical Performance of Low-Quality Recycled Aggregate Through Interface Enhancement Between Cement Matrix and Coarse Aggregate by Surface Modification Technology

In this study, a quantitative review was performed on the mechanical performance, permeation resistance of concrete, and durability of surface-modified coarse aggregates (SMCA) produced using low-quality recycled coarse aggregates, the surface of which was modified using a fine inorganic powder. The shear bond strength was first measured experimentally and the interface between the SMCA and the cement matrix was observed with field-emission scanning electron microscopy. The results showed that a reinforcement of the interfacial transition zone (ITZ), a weak part of the concrete, by coating the surface of the original coarse aggregate with surface-modification material, can help suppress the occurrence of microcracks and improve the mechanical performance of the aggregate. Also, the use of low-quality recycled coarse aggregates, the surfaces of which were modified using inorganic materials, resulted in improved strength, permeability, and durability of concrete. These results are thought to be due to the enhanced adhesion between the recycled coarse aggregates and the cement matrix, which resulted from the improved ITZ in the interface between a coarse aggregate and the cement matrix

Mathematical Modeling of Outdoor Natural Weathering of Polycarbonate: Regional Characteristics of Degradation Behaviors

Many natural exposure sites have been developed to ensure the reliability of materials intended for outdoor use. However, the effects of local climate on aging have not been completely understood. This study aimed to elucidate the regional characteristics of natural aging. Non-stabilized and stabilized polycarbonates were monitored in terms of their appearance (yellowing and loss of gloss) during natural weathering at five exposure sites (Tokyo, Kagoshima, Okinawa, Florida, and Arizona) in conjunction with climate fluctuation for up to 24 months. Three approaches were employed to characterize the natural aging behaviors: (i) modeling the rate function of degradation, (ii) evaluating the contribution ratio of individual degradational factors, and (iii) estimating the "synchronicity" by cross-correlation analysis with the climate dataset. The aging rates were the highest in Arizona and lowest in Kagoshima among the five exposure sites. First, prediction curves were constructed from the degradation rate function (variables: UV irradiation, temperature, and humidity), and these curves were found to agree well with the measured aging behaviors. Second, the exposure data in Arizona demonstrated strong temperature dependence, while those in Okinawa and Florida had stronger dependence on UV irradiation compared to other sites. Lastly, the synchronicity between UV irradiation and temperature was the highest in Arizona and lowest in Kagoshima, which can explain the significantly faster deterioration in Arizona and the slow deterioration in Kagoshima

Disassembly Properties of Cementitious Finish Joints Using an Induction Heating Method

Efficient maintenance and upgrading of a building during its lifecycle are difficult because a cementitious finish uses materials and parts with low disassembly properties. Additionally, the reuse and recycling processes during building demolition also present numerous problems from the perspective of environmental technology. In this study, an induction heating (IH) method was used to disassemble cementitious finish joints, which are widely used to join building members and materials. The IH rapidly and selectively heated and weakened these joints. The temperature elevation characteristics of the cementitious joint materials were measured as a function of several resistor types, including wire meshes and punching metals, which are usually used for cementitious finishing. The disassembly properties were evaluated through various tests using conductive resistors in cementitious joints such as mortar. When steel fiber, punching metal, and wire mesh were used as conductive resistors, the cementitious modifiers could be weakened within 30 s. Cementitious joints with conductive resistors also showed complete disassembly with little residual bond strength

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