Search Results (5)

This study investigates the impact of widely used mineral fillers in self-compacting concrete compositions applied in vibration-free reinforced concrete production technology, as a means of enhancing rheological characteristics and cost-effectiveness. Three distinct types of mineral fillers, including the well-studied fillers microsilica and metakaolin, as well as the lesser-explored filler Kazakhstani natural opal-chalcedony opoka, are examined in this research. In addition to the evaluation of conventional rheological and performance properties of concretes containing these fillers, the internal processes within the cement–filler matrix are analyzed. This includes X-ray phase analysis and microstructural examination of cement hydration products in combination with a superplasticizer and each of the three minerals. The findings confirm the potential for optimizing the rheological parameters of the concrete mixture by substituting up to 15% of the cement with mineral fillers, achieving optimal viscosity and workability. It is established that compositions with the addition of microsilica and metakaolin have a more homogeneous structure, mainly represented by low-basicity calcium hydrosilicates of the CSH(B) type, along with an increase in compressive strength of up to 10%. The addition of these mineral fillers to C30/35 strength class self-compacting concrete resulted in improved frost resistance up to F300, a reduction in volumetric water absorption by up to 30%, and a decrease in shrinkage deformations by 32%. The developed SCC compositions have successfully passed production testing and are recommended for implementation in the operational processes of reinforced concrete product manufacturing plants. Full article

In high-altitude and cold regions, external dynamic geological processes, such as glacial melting and other processes are intense, which frequently results in surface dynamic geological processes, such as slope collapse, landslides, debris flows, and ice avalanches along the route. For high and steep slopes in high-altitude regions containing controlled fractures, the key is to grasp the water-heat process and the evolution of the frost heaving force induced by it within the fractures. This can then lead to the exploration of the multi-phase and multi-field damage propagation, and a disaster mechanism within the fractures under repeated freezing and thawing. The visual tracking of the water-heat migration process within the fractured rock mass is helpful in observing the evolution process of frost-heaving force and providing a theoretical basis for the frost-heaving mechanism. First, research on particle tracking, thermal imaging tests, and image processing technology was conducted to demonstrate that particle tracking and thermal imaging techniques can track the freezing front within the rock fractures and the migration of liquid water inside the rock. Then, by selecting fluorescent particles and improving the observation window and using a waterproof insulation cardboard, the development of a visualization device system for the water-heat migration process was achieved, allowing the tracking of the water-heat migration process. The results of the verification test showed that under freezing and thawing conditions, the experimental device could effectively track the temporal and spatial changes of water-heat migration inside and outside the rock fractures and monitor the real-time changes of the freezing front. Reliable experimental results were obtained, which provided a visual record of the water-heat migration and water-ice phase transition within the fractured rock mass during the freezing and thawing process. Combining thermal imaging technology with the real-time recording of the motion rate of fluorescent particles, this experiment described the movement speed of the freezing front and the convection of free water within the fractures in rock water-heat migration, which is of significant importance for the study of the frost-heaving force under the influence of water-heat migration. Full article

Accurately assessing the variation in the frost-free season (FFS) can provide decision support for improving agricultural adaptability and reducing frost harm; however, related studies were inadequate in terms of the Qinghai–Tibet Plateau (QTP). This study analyzed the spatiotemporal changes in the first frost day in autumn (FFA), last frost day in spring (LFS), FFS length and effective accumulated temperature (EAT) during the 1978–2017 period, and their influences on spring wheat potential yield on the QTP, based on daily climatic data and the methodology of Sen’s slope and correlation analysis. The results showed that the annual average FFA and LFS occurred later and earlier from northwest to southeast, respectively, and both the FFS length and EAT increased. From 1978 to 2017, the average regional FFA and LFS were delayed and advanced at rates of 2.2 and 3.4 days per decade, and the FFS and EAT increased by 5.6 days and 102.7 °C·d per decade, respectively. Spatially, the increase rate of FFS length ranged from 2.8 to 11.2 days per decade throughout the QTP, and it was observed to be larger in northern Qinghai, central Tibet and Yunnan, and smaller mainly in eastern Sichuan and southern Tibet. Correspondingly, the increase rate for EAT ranged from 16.2 to 173.3 °C·d per decade and generally showed a downward trend from north to south. For a one-day increase in the FFS period, the spring wheat potential yield would decrease by 17.4 and 9.0 kg/ha in altitude ranges of <2000 m and 2000–3000 m, but decrease by 24.9 and 66.5 kg/ha in the ranges of 3000–4000 m and >4000 m, respectively. Future studies should be focused on exploring the influence of multiple climatic factors on crop production using experimental field data and model technologies to provide policy suggestions. Full article

A person spends most of his life in rooms built from various building materials; therefore, the optimization of the human environment is an important and complex task that requires interdisciplinary approaches. Within the framework of the new theory of geomimetics in the building science of materials, the concepts of technogenic metasomatism, the affinity of microstructures, and the possibilities of creating composites that respond to operational loads and can self-heal defects have been created. The article aims to introduce the basic principles of the science of geomimetics in terms of the design and synthesis of building materials. The study’s novelty lies in the concept of technogenic metasomatism and the affinity of microstructures developed by the authors. Novel technologies have been proposed to produce a wide range of composite binders (including waterproof and frost-resistant gypsum binders) using novel forms of source materials with high free internal energy. The affinity microstructures for anisotropic materials have been formulated, which involves the design of multilayered composites and the repair of compounds at three levels (nano-, micro-, macro-). The proposed theory of technogenic metasomatism in the building science of materials represents an evolutionary stage for composites that are categorized by their adaptation to evolving circumstances in the operation of buildings and structures. Materials for three-dimensional additive technologies in construction are proposed, and examples of these can be found in nature. Different ways of applying our concept for the design of building materials in future works are proposed. Full article

Frost layer on the outdoor air heat exchanger surface in an air-source heat pump (ASHP) can decrease the system coefficient of performance (COP). Although the common defrosting and anti-frosting methods can improve the COP, the periodic defrosting not only reduces the system energy efficiency but also deteriorates the indoor environment. To solve these problems, it is necessary to clearly understand the frosting phenomenon and to achieve the system frost-free operation. This paper focused firstly on the analyses of frosting pathways and frosting maps. Followed by summarizing the characteristics of frost-free technologies. And then the performances of two types of frost-free ASHP (FFASHP) systems were reviewed, and the exergy and economic analysis of a FFASHP heating system were carried out. Finally, the existing problems related to the FFASHP technologies were proposed. Results show that the existing frosting maps need to be further improved. The FFASHP systems can not only achieve continuous frost-free operation but reduce operating cost. And the total COP of the FFASHP heating system is approximately 30–64% higher than that of the conventional ASHP system under the same frosting conditions. However, the investment cost of the FFASHP system increases, and its reliability also needs further field test in a wider frosting environment. In the future, combined with a new frosting map, the control strategy for the FFASHP system should be optimized. Full article