Over the span of civilization, numerous materials have been utilized to construct ever-more-complex buildings. A material with a long history of use is brick. A research paper published online in October 2021 in Scientific Reports has considered current research into ancient masonry and studied blue brick in a modern building in Kaifeng, China. The results and conclusions of the study will help to develop a better scientific understanding of its properties that will help the modern construction industry.
A 600-year-old Ming Dynasty City Wall in Xi'an, Shaanxi, China. Image Credit: JUN YANG/Shutterstock.com
The History of Blue Bricks and Construction in China: An Overview
In ancient times, Chinese buildings were primarily masonry and wooden structures. This caused problems with fire resistance and durability. However, masonry elements showed better degrees of fire resistance, engineering adaptability, and durability. The primary load-bearing architectural elements in China since the Warring States Period (475-221 BC) have been blue bricks. The technology was unsophisticated during this period.
During the Qin-Han period (221 BC – 220 AD) blue brick technologies and firing processes matured but use (alongside grey tiles) was mainly constricted to Imperial buildings and the royal palace. However, during the latter years of the Han dynasty use of blue brick became more widespread.
The Three Kingdoms (220-280 AD) Wei, and Jin dynasties periods saw the spread of blue bricks into more city buildings. A millennia later, the Ming (1368 – 1644 AD) and Qing dynasties (1644-1912) popularized their use.
The period between 1840 and the formation of the People’s Republic of China in 1949 brought about a transition in architecture to modern styles. Old became new, East and West became intersected, and new materials and processes were explored in construction.
Historic masonry structures were held in high regard, being vital for cultural inheritance and having high artistic and scientific merit. A raft of policies was enacted to preserve important ancient structures.
Today, China is a microcosm of architectural history, with the ancient rubbing shoulders with the ultra-modern. Studying brick masonry, which has such a long history of use in the country, is vital for the restoration of historic buildings and can inform modern construction using the material.
Protecting Ancient Masonry Structures from Environmental Stresses and Human Activity
Time, the environment, and human activity affect all structures. Improper restoration causes damage to masonry structures. Wall cracking, pulverization and peeling, frost damage, and decreased brick strength can all damage the structure, leading to critical issues that can cause irreparable damage and safety issues in modern masonry buildings.
Policies that concentrate on historical building preservation and cultural heritage protection with protection, reuse, rational use, and proper management have led to increased interest in the protection of ancient masonry structures. The fundamental properties of ancient brick and damage protection have been studied by many domestic and foreign researchers.
Recent Research into Blue Brick Properties
Many recent studies into ancient masonry structures have concentrated on water absorption, compressive properties, and salt resistance of brick materials. The research was also predicated on the differences between brick production and materials in different ancient Chinese regions and dynasties. Achieving compatible renovation techniques in ancient masonry structures has proved challenging.
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One study was carried out by Gao et al. The research used a variety of analytical techniques such as X-ray fluorescence, XRD, as well as physical tests to study bricks on the Xi’an city walls tiles.
It was discovered that the mechanical properties of the bricks decreased slightly due to environmental erosion, whilst having superior chemical and physical properties, attesting to Ming dynasty brick-making techniques. A team led by Liu studied weathering on blue bricks in the old town of Pingyao.
Veronica et al. determined that the load-bearing capacity of masonry buildings is directly affected by the impact of moisture on blue brick’s thermal and mechanical properties. Ding et al. carried out compression tests on blue brick masonry in modern cultural buildings, determining the material’s design value of compressive strength.
Most notably, Cheraghcheshm et al. improved the application performance of blue brick by modifying its surface with silver nanoparticles.
Studying Blue Bricks at the Kaifeng People’s Conference Hall
Limitations exist in current research, such as methods, means, depth, as well as limitations on test instruments. Methods and materials for protection must be selected which consider the preservation state of cultural structures as well as material properties.
To better inform renovation techniques, a study was carried out on blue bricks at the People’s Conference Hall in Kaifeng in east-central Henan province. This masonry structure was built in 1928. Exposure to environmental stress has caused cracking, powdering, and flaking on the blue bricks on the external walls. Years of changing use and erosion have left the bricks damaged and compromised the building’s structure.
Basic material tests were carried out to elucidate the material’s properties. Phase analysis of samples was carried out with XRD. Mechanical performance tests were carried out with the WDW-600 E universal testing machine. The maximum load was 60t.
Pore characteristics and phase analysis provided information on mineral composition and pore characteristics. Based on an analysis of pore characteristics, the bricks were found to be of high quality. Frost tests produced information on the environmental weathering impact on the samples. The strength of the bricks was assessed using compressive testing. Softening coefficient tests helped to determine the brick’s water resistance.
Results of the study have been used to direct repair and renovation of the People’s Conference Hall and provide a reference for the properties of blue bricks in other buildings of the same period.
How This Study Affects the Future of Blue Brick Renovation
Building on contemporary research into the properties of ancient blue brick used across China, this study will help to preserve culturally important building in the nation. The study has implications for both ancient and more modern masonry buildings and helps achieve “compatible renovation” due to information on the material’s properties and helps inform the selection of appropriate materials.
Further Reading
Ma, S et al. (2021) Experimental Study on the properties of modern blue clay brick for Kaifeng People’s Conference Hall [online] Nature Scientific Reports 11: 20631 | nature.com. Available at:
https://www.nature.com/articles/s41598-021-00191-z
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