Tropical cyclones (also known as hurricanes or typhoons) are among the most destructive natural disasters globally, causing huge fatalities and economic losses annually. Existing data indicate that global climate change has slowed the translation speed of tropical cyclones, and an inverse relationship exists between translation speed and cyclone-induced rainfall. Furthermore, while the total number of tropical cyclones worldwide shows a declining trend, the frequency of Category 4~5 hurricanes (i.e., super typhoons) has increased overall. The 2017 Atlantic hurricane season caused economic losses of US$125 billion in the United States. In 2025, a hurricane in Texas triggered heavy rainfall, resulting in over 130 fatalities. Hainan Island is located along the core generation and movement path of typhoons, making it one of the regions in China most frequently affected by these storms. In 2014, Super Typhoon Rammasun made landfall in Wenchang, Hainan Province, becoming the strongest typhoon on record to strike China (landfall intensity 70  m·s⁻¹). It caused 24 deaths or missing persons on Hainan Island and direct economic losses of RMB¥11 billion. In 2024, Super Typhoon Yagi, with a landfall intensity second only to that of Super Typhoon Rammasun (62  m·s⁻¹), similarly made landfall in Wenchang, Hainan Province. However, its destructive impact far exceeded that of the Super Typhoon Rammasun, causing 4 deaths and direct economic losses exceeding RMB¥60 billion in Hainan Island.　　Super Typhoon Yagi (international designation: 2411) formed over the ocean east of the Philippines on September 1, 2024, and made landfall along the coast of Wengtian, Wenchang on September 6 (minimum central pressure 915 hPa). It then crossed Haikou and Chengmai before moving into the Qiongzhou Strait and subsequently entering the Beibu Gulf. The area on Hainan Island covered by Force-12-and-above winds was affected for over 9 hours, far exceeding the 3 hours during Super Typhoon Rammasun in 2014. The minimum pressure and maximum wind speed recorded in Wenchang both broke all previous land-based observational records for typhoons in China. From September 4 to 8, Hainan Island experienced widespread heavy to torrential rain, with a maximum accumulated rainfall of 691.2 mm at Jianfeng town, Ledong. Wenchang's precipitation broke its historical daily maximum rainfall record for September. In Haikou, more than 100,000 people were evacuated, about 400 houses collapsed, over 30,000 houses were damaged, the crop-affected area reached 570 km², and direct economic losses exceeded RMB¥26.3 billion. In Wenchang, more than 25,000 houses were damaged, the crop-affected area was about 180 km² (with 110 km² of total crop failure), and economic losses amounted to approximately RMB¥32.7 billion. In recent years, Hainan Province has significantly improved its typhoon defense capabilities by revising engineering construction and equipment-use standards and refining pre-disaster emergency plans, leading to a notable reduction in casualties. However, with continued population and economic growth in coastal areas, the risks posed by super typhoons continue to rise, and the resulting economic losses are becoming increasingly difficult to bear.　　Worldwide, foundational theories and forecasting research on the generation and development of tropical cyclones from a meteorological perspective have been well established, and related findings have played a significant role in reducing tropical cyclone disasters. However, the sporadic occurrence of landfalling super typhoons and their marked regional variability have resulted in relatively limited research on their powerful dynamic impacts on the ground. There is still a lack of sufficient data and experience to systematically reveal their disaster-causing mechanisms, and mature solutions for adaptation and disaster prevention and mitigation strategies have yet to be developed. As a fundamental means for major disaster assessment and scientific research, systematic field investigations are crucial. Following the passage of Super Typhoon Yagi across Hainan Island in 2024, the School of Civil Engineering and Architecture of Hainan University organized an interdisciplinary typhoon disaster investigation team composed of nearly one hundred faculty and students. The team conducted field surveys in the affected areas for over ten days. The survey covered regions within the Force-10-to-17 wind circles of Super Typhoon Yagi and focused on nine categories of buildings and structures that showed obvious damage (building envelopes, high-rise buildings, tall/steel structures, temporary buildings, agricultural greenhouse buildings, road infrastructure, photovoltaic structures, power and communication facilities, wind power generation systems), as well as coastal erosion and treefall conditions. More than 1,000 individual structures/sites were surveyed. A multi-source “space-air-ground” data acquisition approach was adopted: field studies were carried out to collect background information and record structural damage patterns and severity; handheld laser rangefinders and accelerometers were used to quantify damage parameters; satellite remote sensing and UAV(Unmanned Aerial Vehicle) aerial imagery were employed to analyze coastal erosion and treefall; questionnaire surveys and subjective perception assessments were applied to quantify wind-induced vibration comfort in high-rise buildings. For data processing, most surveyed objects were classified according to function, location distribution, and other characteristics, and disaster losses were graded to summarize damage patterns. Representative cases were selected for in-depth analysis of disaster causes. The investigation received support and guidance from the Hainan Meteorological Service, Hainan Provincial Department of Housing and Urban-Rural Development, Hainan Provincial Department of Transportation, Hainan Provincial Department of Emergency Management, and Hainan Provincial Department of Natural Resources and Planning. Substantial assistance during field visits and data collection was provided by the People’s Government of Dongying Town in Lingao County, Gengdushanfang, the Mei’ao Village Committee, and Shuichongpo Village in Ding’an County. Enterprises including Hainan Xinyi Mining Co., Ltd., Hainan Zhelian Steel Structure Group Co., Ltd., Hainan Holdings & Energy China Co., Ltd., Wenchang Luneng Hilton Hotel, Hainan Zhipu Agricultural Technology Development Co., Ltd., and Hainan Yabang Integrated Housing Co., Ltd. also offered active cooperation and support.　　The investigation results show that many meteorological stations recorded wind pressures exceeding the design load standards for buildings, and wind-speed amplification due to topographic effects was observed in some areas. For instance, the high-rise building cluster near Haikou Bay experienced a local wind-speed increase of 20%~30% due to the Venturi effect; the peak dynamic wind pressure on windward building envelopes exceeded 5 kPa (nearly 50% above the design load for conventional buildings). Existing building envelopes, temporary structures, power facilities, and agricultural greenhouse buildings exhibited insufficient resistance to super typhoons, indicating an urgent need to revise relevant construction codes in typhoon-prone regions. The sandy coastline in Wenchang showed shoreline retreat on the order of meters, necessitating heightened attention and the formulation of long-term protection strategies. Secondary hazards such as heavy rainfall and treefall severely impacted the service life of highways and urban roads; resilience should be enhanced through improved drainage systems and roadside tree planning. Treefall patterns were directly related to geographic location, surrounding built environment, and tree species; rational spatial planning can help reduce disaster losses. The disaster prevention and emergency response to Super Typhoon Yagi once again demonstrated that securing communications, transportation, and water and power supply is central to emergency management and plays a key role in reducing losses and casualties. It is essential to strengthen relevant standards and promote the application of new disaster prevention and mitigation technologies in these sectors. The impact area and damage severity of super typhoons are directly linked to geographical location, terrain, land use and other factors, exhibiting marked regional characteristics. Given that the two strongest typhoons on record to strike China both landfall in Wenchang, Hainan Province, causing enormous economic losses to Hainan Island, it is recommended to establish a Typhoon Disaster Prevention and Mitigation Research Center in Hainan Island. The center would systematically investigate the occurrence patterns of typhoon disasters, innovative technologies for disaster prevention, avoidance, mitigation and post-disaster recovery, as well as related laws, regulations and policy measures, while fostering international exchange and cooperation to support scientific decision-making by the government.

Moisture penetration and aggressive ion intrusion are primary factors reducing concrete durability. To address this problem, this study utilizes polydimethylsiloxane (PDMS) to modify fly ash and recycled concrete micropowder to be prepared into the corresponding hydrophobic particles, and explores the effects of separately admixed PDMS and its composite admixed with two types of hydrophobic particles on the compressive strength, hydrophobicity, and microstructure of geopolymer concrete experiments. The results showed that adding PDMS decreased the 28 day compressive strength of concrete by 24.06%. when mixed with hydrophobic fly ash particles, the strength loss increased to 29.46%, whereas blending PDMS with hydrophobic recycled concrete micropowder reduced the loss to 20.14%. In terms of hydrophobity, PDMS significantly decreased concrete wettability. The 12-hour water absorption of the specimen mixed with hydrophobic recycled concrete micropowder was only 1.5%, representing a 78% reduction compared to control group. Droplet contact angle measurements revealed that PDMS changed the concrete surface from hydrophilic (contact angle <90°) to hydrophobic, with the angle further increasing to 136° when combined with hydrophobic fly ash particles. Microstructural analysis showed an increasing in average pore size for all PDMS modified samples. The smallest increase (1.015 nm) occurred with PDMS alone, while the largest increase (3.602 nm) was observed in the system combining PDMS and hydrophobic fly ash particles. Overall, the composite of PDMS and hydrophobic recycled concrete micropowder demonstrated the best performance, achieving strong hydrophobicity while maintaining superior mechanical properties.