Durability and Aesthetics of Architectural Concrete under Chloride Attack or Carbonation

Analysis on determinants of carbon emissions from plaza ground paving during the construction stage based on life cycle assessment

The carbon emissions of paving projects are the focus of urban managers and researchers. By introducing the life cycle assessment (LCA) method and drawing up the study time and boundary, this study analyzed the carbon emissions activities of the plaza ground paving project and established a computational model of the cast-in-place architectural concrete (CAC) and natural stone pavement's life cycle during the construction stage by comprehensively utilizing the carbon emission coefficient method and the direct source consumption statistics method of the production line. Based on the model, this study employed the ground paving of a top-notch Theme Park Plaza in Beijing as a sample to calculate the carbon emissions of two different types of building materials at various phases of their life cycle and made a comparative evaluation. It is concluded that the carbon emissions (expressed in CO2) produced by the CAC ground in the sample area is 75.46 kg CO2/m2, while that of the natural stone pavement is 110.81 kg CO2/m2. Our results demonstrate significantly linear relationship between the overall emissions of carbon and the material carbon factor. This study adds to the body of knowledge by calculating the carbon emissions and determining the trend of carbon footprint for ground paving. Furthermore, the study's findings can be used to enhance construction management options and choose green materials. The findings can also be used to provide supporting theories for the development of regulations and carbon reduction policies based on constructing energy conservation and greenhouse gas reduction.

Preparation and Color Performance of White Ultra-High-Performance Concrete with Large Fraction of Quaternary Binders

White ultra-high-performance concrete (WUHPC) performed outstanding mechanical, durability, and aesthetical properties, which was preferred in infrastructure to avoid the secondary painting, decrease the maintenance, and prolong the service life. Supplementary cementitious materials (SCMs) were often used in WUHPC to reduce the environment impacts and material costs. In this study, limestone powder (LP), metakaolin (MK), and silica fume (SF) were used as SCMs to largely substitute white Portland cement (WPC) to prepare WUHPC, the effects of substituted ratio on flowability, strength, and whiteness were studied, and the hydration products were also analyzed by quantitative-XRD method and SEM. The whiteness was calculated in chromatic space CIELAB by measuring tristimulus values of L, a*, and b*, and the controlled factor on whiteness was also investigated. As the results, the WUHPC with compressive strength exceeded 150 MPa and whiteness over 90 was prepared with WPC substitution of 35~65%. The SF improved the flowability and strength about 10% due to its filling and ball effect, while the irregular particle sharp and non-uniform size distribution of MK caused the reversed development. The increased dosage of raw materials with higher L value, such as LP and MK, made the WUHPC whiter. The hydration products with varied SCMs ratio were in the same category by different content. It was supposed that CaCO₃ and C-S-H gel in hydration products caused higher whiteness, while C₃S, CaMg(CO₃)₂, and SiO₂ were against the whiteness. The results proved that with a large fraction of SCMs, the WUHPC with high strength and good appearance were prepared, and the whiteness of WUHPC were both controlled by the raw materials and the content of hydration products.

Investigation on Aesthetic and Water Permeability of Surface Protective Material under Accelerated Weathering

In this paper, experiments were conducted on the effects of aesthetic and durability of three representative surface protective material under accelerated weathering test for 5000 h. First, the adaptability of the surface protective material coating to the substrate was proven by examining the aesthetic properties and the water permeability of the building materials. Second, the pollutant resistance of the surface protective material coating to artificial stain was assessed using xenon-arc light. The result shows that the appearance of the silane types did not change significantly, and the water permeability was improved. In addition, the silicate types did not improve water permeability and the surface color was changed. Fluor- resin types effectively improved the water permeability, but the surface color became dark. Sample measurements showed changes in the average width of the contamination after weathering, with an increase after spray cleaning and ultrasonic cleaning. However, it was observed that after washing the pollution average width of all specimens due to weathering at 5000 h was almost as much or smaller than the initial value.