Concrete binders, mineral additions and chemical admixtures: state of the art and challenges for the 21st century

摘要

Although a wide range of concrete binders is available for specialist applications, by far the greatest volume is based on Portland cement. Mineral additions to Portland cement, particularly of artificial pozzolans such as fly ash, silica fume and blast furnace slag, and the use of more chemically specific admixtures continue to gain acceptance in many parts of the world. Although the hydrate mineralogy of the Portland cement systems is not radically altered by the presence of pozzolans, the content of C-S-H gel is generally increased at the expense of Ca(OH)_2 due to the reactive SiO_2 contents of the pozzolans, giving lower capillary porosities and therefore higher strengths and durability. Limestone fillers are also gaining acceptance and in some cases improve strengths and durability even at levels of replacement of up to 20percent. For concretes where early strengths are less important than long term strengths and durability, mineral additions can be used to reduce CO_2 emissions and lower production costs. Systems containing two or more mineral additions combined with the optimum use of admixtures are creating opportunities for the development of high strength, highly durable concretes without compromising workability.