第9章 水泥基材料研究进展.ppt

第9讲 混凝土研究进展 高强混凝土与高性能混凝土 纤维增强混凝土 活性粉末混凝土 9.1 高强混凝土 为什么混凝土要高强？ Thirty years ago, tall buildings in Manhattan (New York City) were almost all steel-frame. Today, perhaps one-third of tall commercial buildings are concrete frame. It is believed that the choice of steel frame vs. reinforced concrete frame was decided in favor of the latter primarily on account of the high construction speed. the load-carrying capacity of columns in multistory buildings increased 4.7 times for a threefold increase in price. For the construction of reinforced-concrete-frame buildings, 30 stories and higher, normal-size columns can be made in the upper third of the building with conventional 30 to 35 MPa concrete; however, the use of high-strength concrete is justified for slender columns in the lower two-thirds of the building. 高效减水剂与高强混凝土 In the late 1960s, high-range water reducing admixtures (superplasticizers) composed of salts of naphthalene sulfonate and melanine sulfonate were developed in Japan and Germany, respectively. The first applications in Japan were confined to high-strength precast products and cast-in-place girders and beams for bridges. In Germany, initially the objective was to develop underwater concrete mixtures possessing high fluidity without segregation. As it is possible to achieve both high strength and high workability simultaneously with the superplasticized concrete mixtures, they were found to be very suitable for use in the production of cast-in-place structural components for tall buildings。 高强混凝土定义 Concrete is defined as “high-strength” solely on the basis of compressive strength at a given age. In the 1970s, before the advent of superplasticizers, concrete mixtures that showed 40 MPa or more compressive strength at 28 days were called high-strength concrete. Later, when 60 to120 MPa concrete mixtures became commercially available, in 2002 the ACI Committee on High Strength Concrete revised the definition to cover mixtures with a specified design str