Red bricks are traditional building materials made from clay, shale, or coal gangue. These raw materials are crushed, mixed, and kneaded before being shaped by hand or machine. After drying, they are fired at around 900°C in an oxidizing environment, resulting in the characteristic red color. Known as sintered clay bricks, their technical grade typically ranges from 75 to 100. The standard size of a red brick is 240 x 115 x 53 mm. They can appear in shades of red or dark black depending on the composition and firing process.
Red bricks have good strength and durability, and their porous structure gives them natural insulation properties for both heat and sound. This makes them ideal for walls, columns, arches, chimneys, floors, and foundations. Historically, they were widely used in old buildings and have been part of construction since ancient times. The Romans are credited with developing red bricks, and many classical European structures still show traces of this material in their walls and roofs.
In ancient China, brick-making techniques were already well developed during the Warring States period. However, due to social hierarchies, only certain classes were allowed to use red bricks. As a result, additional steps were taken to modify the final product after firing. During the late Qing Dynasty and the Republic of China era, the knowledge of red brick production became more accessible to the general public.
The traditional Chinese method of making bricks involved sealing the kiln during the high-temperature stage, limiting oxygen supply. This caused the iron in the bricks to reduce from ferric oxide (red) to ferrous oxide (green), resulting in blue bricks. Research has shown that blue bricks perform better in oxidation, hydration, and atmospheric erosion compared to red bricks. Ancient Chinese "Qin bricks and Han tiles" have survived for thousands of years. However, the complex firing process, high energy consumption, and limited output made it difficult to scale up production. With the development of industrial brick-making equipment like wheel kilns and extruders, red bricks saw significant advancements, while blue bricks gradually faded out of mainstream use except in historical preservation projects.
As technology progresses and environmental awareness grows, new types of unfired bricks are emerging. Despite this, experts still consider red bricks to be among the best options for wall construction in terms of performance and comfort. It's likely that red bricks will continue to hold a strong position in the construction industry for years to come.
Since the reform and opening-up policy, China's red brick industry experienced rapid growth. However, many small-scale brick factories engaged in unregulated burning, leading to severe farmland destruction. In response, the government introduced policies starting in 1993 to restrict and ban the production of clay solid bricks. These measures, known as the "clay brick restriction policy," aimed to protect arable land while promoting the use of alternative materials such as shale and coal gangue-based bricks.
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