Principle and Application of Concrete Admixtures

Author: Chen Jiankui
Publisher:
Publish Date: 2004-04-01
Features: Cement concrete is a major artificial building material in contemporary times. China's annual cement production has exceeded 400 million tons, accounting for about one-third of the world's annual cement output. The consumption of concrete is also the highest among all countries, with widespread use in both national key construction projects and rural buildings. Since the invention of Portland cement in 1824, the application of concrete and reinforced concrete has become increasingly extensive, and concrete science and technology have continuously advanced. Starting in the 1930s, the use of concrete admixtures, primarily air-entraining and plasticizing agents, has had a significant, even decisive, impact on the four key factors of high-quality concrete: durability, strength, workability, and economy. Today, admixtures have become an indispensable component of modern concrete, and the addition of high-quality admixtures has become a necessary technical approach for concrete modification. Over the more than 60 years of development of concrete admixtures, the use of air-entraining agents has played a prominent role in improving the durability of concrete. By adding a very small dose (0.002~0.01) of air-entraining agent, a large number of microbubbles can be introduced into the concrete. Under the optimal air content (about 4~6), the concrete's resistance to freeze-thaw cycles can be improved more than tenfold, significantly enhancing its durability. At the same time, workability and uniformity are also noticeably improved, benefiting the overall quality of the project. High-efficiency water-reducing agents (also known as superplasticizers), which emerged in the early 1960s, brought a major breakthrough in concrete modification. By adding a small amount (around 1) of high-efficiency water-reducing agent and using conventional concrete processes, high-strength concrete with a 28-day compressive strength of 60~120 MPa can be prepared. In the early 1970s, flowable concrete formulated with superplasticizers was developed and has since been widely used. Entering the 1990s, the new concept of high-performance concrete (High-Performance Concrete, abbreviated as HPC), first proposed by the United States, was introduced. Its basic requirements are that the concrete should exhibit excellent durability, workability, and strength. The driving force behind the development of high-strength concrete into high-performance concrete is the need for architectural engineering development, such as high-rise construction, heavy loads, large spans, large volumes, rapid construction, cost-effectiveness, energy savings, and the specific requirements of special projects. As a result, high-performance concrete has been widely adopted as a new, highly efficient building material for the new century. Alongside the development of concrete materials, concrete admixtures have also moved toward high efficiency, multifunctionality, and compounding. The use of composite admixtures can improve the workability (e.g., increasing fluidity, reducing time-dependent flow loss) and stability (e.g., homogeneity, non-separation, non-leakage) of fresh concrete, regulate the hydration and hardening process of cement (e.g., delaying heat release during hydration, early strength, high strength), improve the pore structure of concrete (e.g., achieving lightweight, high strength, durability), enhance volume stability (e.g., shrinkage compensation, impermeability, crack resistance), and impart certain special properties to the concrete. Therefore, the development and application of high-efficiency, multifunctional, and composite admixtures will undoubtedly drive the advancement of concrete preparation processes and new concrete materials, such as flowable concrete, self-leveling self-compacting concrete, underwater pouring concrete, macrodefect-free cementitious materials, and high-performance concrete. This book is a compilation of the author's research and practical experiences, integrating domestic and international literature. It provides detailed discussions on the action mechanisms, characteristic sources, production methods, and application technologies of admixtures. Additionally, it covers the performance and applications of high-strength, flowable, and high-performance concrete, as well as topics like winter construction, steam curing, and shrinkage compensation. Such comprehensive coverage is uncommon in similar specialized books and can serve as a valuable guide for the rational use of concrete admixtures.