2021, a 12-storey apartment building built in 1981 on the seashore of Miami, Florida, USA, partially collapsed, as shown in Figure 1 and Figure 2, causing heavy casualties. The incident attracted worldwide attention.
Figure 1 The seaside location
of the collapsed apartment Figure 2 The site
of the partial collapse of the apartment building The New York Times and The Economist, well-known international media, cited the preliminary investigation of authoritative scientific institutions, which showed that the sea level rise brought about by climate change caused the backflow of seawater. As a result, a large amount of seawater was detained in the foundation and surrounding areas of the apartment building for a long time, which caused corrosion damage to the cement concrete and internal reinforcement of the building structure, which was the possible cause of the collapse of the apartment. The day after the
collapse, on June 25, 2021, the National Institute of Standards and Technology of the Ministry of Commerce began deploying a team of six scientists and engineers to work with federal and local authorities to collect and preserve relevant materials and information that may help understand the cause of the collapse. The team's work is divided into five areas: evidence preservation, material science, geotechnical engineering, structural engineering, remote sensing and data visualization. The team's ultimate goal is to determine the technical cause of the collapse, recommend changes to building codes, standards, and practices, or other appropriate actions to improve the structural safety of the building.
NIST States that the investigation of structural disasters will take several years to complete; the progress of the investigation will be continuously updated on the website. Recent developments are:
on June 15, 2022, preparations are underway to commence invasive testing and further collection of physical evidence;
on September 29, 2022, field testing has been completed and the next consultation meeting has been announced.
It can be seen that in the United States, the Miami building collapse incident is being systematically investigated and studied, and it is estimated that the results will not be available until several years later. The incident of building collapse in
the United States is not flat, but another wave is rising again. On October 27, 2022, city officials in Miami, Florida, ordered an emergency evacuation of a seaside apartment building in Port Royal. The building was built in 1971, and during the safety certification of the 50-year-old building, it was found that the reinforced concrete beams of the apartment had moved excessively from the starting position of the garage floor, resulting in a dangerous situation, so an unsafe notice was issued. The official order has once again stirred up the aftermath of the collapse of the building in 2021 and caused panic among nearby residents.
In China, after receiving information about the Miami building collapse incident, the relevant units consulted and studied the on-site investigation data and the international authoritative media's account of the cause of the collapse. On this basis, it is proposed to set up a pilot project to replace Portland cement with ferroaluminate cement in coastal engineering construction. In addition to the characteristics of rapid hardening and high strength
, ferroaluminate cement also has the advantage of seawater corrosion resistance. After immersion in Sanya seawater, the flexural strength does not decrease, but increases. After 24 months of immersion, the flexural strength increases by 36%, that is, the corrosion resistance coefficient K24 is 1.36; The flexural strength of the corresponding Portland cement decreases by 52% after immersion in Sanya seawater for 24 months, that is, its corrosion resistance coefficient K24 is only 0.48.
Chloride permeability coefficient is an important parameter for durability design and service life assessment of concrete structures. The comparison of chloride ion permeability coefficients of ferroaluminate cement and ordinary Portland cement concrete with different water-cement ratios is shown in Fig. 3. It can be seen that under the same conditions, the chloride ion permeability coefficient of aluminoferrite cement is much lower than that of ordinary Portland cement concrete.
Fig. 3 The anti-chloride ion permeability coefficient
of different concrete was approved by the National Development and Reform Commission, and the pilot project was carried out in the coastal Zhangzhou Hualong 1 nuclear power project. The concrete will be poured formally for the first time on December 31,
2021, with the single piece volume of 574.52m3, as shown in Figure 4. The pouring was successful at one time.
Fig. 4 First formal pouring
of aluminoferrite cement concrete in Hualong One Project On September 10, 2022, the first mass concrete was poured, with a one-time concrete pouring of 1100 m3, as shown in Fig. 5. The first mass concrete pouring was successful.
Fig. 5 The pilot project of replacing Portland cement with aluminoferrite cement for the first mass pouring
of aluminoferrite cement concrete has achieved complete success. In order to solve the world's difficult problem of durability of seaside buildings, it provides a powerful Chinese solution.
Author:
1. Wang Yanmou & nbsp; Former Party Secretary and Director of
the State Bureau of Building Materials 2. Qi Dongyou & nbsp; Director
of Key Laboratory of Sulphur (Iron) Aluminate Cement, Technical Supervision and Research Center
of Building Materials Industry 3. Wang Zhiyong, Deputy Director
of Key Laboratory of Sulphur (Iron) Aluminate Cement
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