Lime and Cement Plasters from 20th Century Buildings: Raw Materials and Relations between Mineralogical–Petrographic Characteristics and Chemical–Physical Compatibility with the Limestone Substrate

Characterization of Pore Size Distribution and Water Transport of UHPC Using Low-Field NMR and MIP

Water transport is vital for the durability of ultra-high performance concrete (UHPC) in engineering, but its absorption behavior requires further comprehension. This study investigates the impact of silica fume (SF) and metakaolin (MK) on water absorption in UHPC matrix with a high volume of limestone powder (LS) under two curing temperatures, and the variation in water transport with pore size obtained by low field nuclear magnetic resonance (LF-NMR). Relations between cumulative water absorption with other properties were discussed, and the pore size distribution (PSD) measured by Mercury intrusion porosimetry (MIP) was compared with that determined by LF-NMR. Results showed that MK outperformed SF in reducing water absorption in UHPC matrix, containing 30% LS under steam curing due to the synergistic effect between MK and LS. The incorporation of LS greatly affected the water absorption process of UHPC matrix. In samples without LS, capillary and gel pores absorbed water rapidly within the first 6 h and slowly from 6 h to 48 h simultaneously. However, in samples with 30% LS, gel pore water decreased during water absorption process due to the coarsening of gel pores. MK was able to suppress gel pore deterioration caused by the addition of a large amount of LS. Compared with PSD measured by MIP, NMR performed better in detecting micropores (<10 nm).

Study on the Application of Sediment-Based Embankment Building and Ultra-High-Performance Concrete (UHPC) Preparation in the Resource Utilization of Yellow River Sediment

The Yellow River is difficult to control. Little water and a large amount of sediment results in sediment accumulation in its lower reaches as sediment inflow exceeds transport capacity. Reducing this sediment deposition is essential for harnessing the Yellow River. Included in this process is the rational use of the sediment. Many researchers have investigated usage of Yellow River sediment as an aggregate material for concrete production, but there are still some problems (e.g., low resource utilization and low strength of the concrete made from Yellow River sediment). To make up the deficiency in the existing research, this study proposes two methods of sediment utilization. One is to use Yellow River sediment to build embankments, and the other is to use ultra-fine Yellow River sand to prepare ultra-high-performance concrete (UHPC). Test results reveal that the prepared high-strength concrete performs well in each test, including: fluidity, mechanical properties, pore structure, ecological evaluation, microscopic measurement of the interface transition zone, and economic analysis.

Heritage Building Preservation in the Process of Sustainable Urban Development: The Case of Brasov Medieval City, Romania

This paper aims to present a comprehensive review of the literature on the definition and development of the concepts of heritage and sustainability. The harmful effects of various pollutants on the materials widely used in the construction of monuments/buildings, which are part of the national and international cultural heritage, are also highlighted. In addition, the paper draws attention to modern techniques for investigating the composition and diagnosis of the alteration of buildings materials with the focus on stone, limestone, and mortars/concrete. The present research also emphasizes that in the case of heritage buildings, different skills are needed not only related to heritage conservation and rehabilitation, but also skills related to heritage planning processes, and to sustainable constructions. For exemplification, the manuscript proposes specific conservation principles based on the case of Brasov city, located in the heart of Romania and being par excellence a medieval town with representative buildings for that period.

Life Cycle Assessment of Off-Site Construction Using Ultra-High-Performance Concrete

This study aims to evaluate the environmental impacts of off-site construction using ultra-high-performance concrete (UHPC) and different curing methods. Life cycle assessment (LCA) is implemented to evaluate the environmental impacts of the proposed UHPC and the traditional concrete (TC) under different curing conditions from cradle to gate. Unlike the previous studies that considered the function unit of concrete as 1 m3, this study investigates the concrete elements with the same load capacity. Comparison is made between off-site water bath heating curing (HC) ultra-high-performance concrete (UHPC), on-site UHPC, off-site HC traditional concrete (TC), on-site TC, and off-site CO2 curing TC. The LCA results show that UHPC is generally better than TC in terms of environmental impacts. Using off-site CO2 curing further improves its environmental benefits. The off-site HC UHPC shows higher productivity and higher environmental impacts compared to the on-site construction method. However, when the design load capacity of the concrete increases, the difference between off-site construction using 50 °C HC UHPC and on-site curing (20 °C HC UHPC) decreases.