China is a developing country with coal as its main energy source. In primary energy consumption, coal accounts for more than 70%, more than double the world average. In the future, China's energy structure will still be dominated by coal. Coal gangue is a solid waste produced in the process of coal production and processing, and its annual emission is equivalent to about 10% of the coal output in that year. At present, it has accumulated 4.5 billion tons, with an area of about 1? 20,000 hectares, which is one of the largest industrial and mining solid wastes in China. While enjoying the industrial innovation brought by coal as energy, human beings also suffer from air pollution, water pollution and soil pollution caused by spontaneous combustion and stacking of coal gangue.

The frequent occurrence of spontaneous combustion, landslide and debris flow accidents in coal gangue hill made me decide to engage in the research of comprehensive utilization of coal gangue. During my work in china academy of railway sciences, I found that with the large-scale construction of high-speed railway, mineral admixtures (represented by fly ash and slag) that give high workability and durability to concrete are increasingly in short supply, which seriously affects the project construction and project budget. It is also found that if coal gangue lightweight aggregate concrete is applied to the deck concrete and collision wall of railway bridges, not only the dead load of bridges can be reduced, but also the cost of lightweight aggregate concrete can be reduced. Encouraged by Mr. Zhao Guotang, the chief engineer of Beijing-Shanghai high-speed railway, he came up with the idea of writing this book, with the purpose of reminding people of the effect of "throwing bricks to attract jade" and promoting more people to pay attention to and study the comprehensive utilization of coal gangue.

In view of the mineral composition and physical and chemical characteristics of coal gangue, this book focuses on the comprehensive utilization of coal gangue building materials in line with the principle of "making the best use of everything and using local materials", and tries its best from the comprehensive utilization principle based on the physical and chemical properties of coal gangue, the activation mechanism of coal gangue, the active admixture of coal gangue cement, the aggregate material of coal gangue minerals, the mineral admixture of coal gangue concrete, the solid soil material of coal gangue and the building materials products of coal gangue (coal gangue bricks and light aggregate). In the aspect of basic research, based on the coordination of silicon-aluminum structure, advanced micro-testing methods are selected to try to establish the relationship between the micro-properties of coal gangue and its macro-structural properties, and to reveal the source of its gelling activity. In the research of application technology, we pay attention to the durability and long-term performance of coal gangue building materials system, including the corrosion resistance of coal gangue cementitious materials, carbonation resistance, frost resistance, chloride ion penetration resistance, corrosion resistance and shrinkage resistance of steel bars, and wet cycle resistance, corrosion resistance and frost resistance of coal gangue soil consolidation materials, in order to eliminate the doubts of engineering circles about the durability of coal gangue building materials and promote the large-scale utilization of coal gangue. This book starts with the basic theory, highlights the application technology of coal gangue, and strives to combine theoretical research with applied research, experimental research with engineering application, and applied problems with solutions. It can be used as a reference for scientific and technical personnel engaged in building materials, coal, chemical industry, electric power and other industries as well as teachers and students of related majors in colleges and universities.

This book consists of seven chapters, and I am responsible for the compilation and revision of the outline and content organization. Xiao, a lecturer of Changzhou Institute of Engineering and Technology, participated in the compilation of the sixth chapter, and Dr. Tsinghua University participated in the compilation of the seventh chapter.

Most of the research work of this book was done in Tsinghua University. Thanks to Academician Ye Danian and Professor Sun Henghu for their long-term encouragement, love and support. Special thanks to Academician Ye for reviewing and prefacing this book. Xie Yongjiang, a researcher from china academy of railway sciences, and Zhao Guotang, a researcher from Beijing-Shanghai high-speed railway, put forward constructive opinions on the writing style and outline of this book, and reviewed the manuscript. Their encouragement gave me confidence to write this book. Academician Sun Wei of Southeast University gave me care and guidance, which enabled this book to be successfully completed. Thanks to Academician Sun for preface to this book. Dr. Chen Hongxia, Dr. Li Yu, Dr. Yi Zhonglai, Tie Xuchu, Tan, Zhu Changhua and Rao Zeqing provided a lot of information and help in my writing process, and I would like to thank them. Finally, I want to thank my beloved wife, Wang Conghui, for her understanding and support, so that I can devote myself to my work.

The publication of this book has been strongly supported and helped by the leaders of china academy of railway sciences Railway Architecture Research Institute, and I would like to express my heartfelt thanks!

This book refers to some literatures, and I would like to express my heartfelt thanks to the authors of these literatures and the researchers who are committed to the comprehensive utilization of coal gangue! Due to the less application of coal gangue engineering, involving many specialties and wide knowledge, and the author's limited knowledge level, omissions in the book are inevitable, please correct me!

Li Huajian

Beijing, May 2009