土木工程专业英语 陈瑛 2.2 Properties of Concrete 新.pptVIP

2.2 Properties of Concrete 4.1 Compressive Strength Cube Compressive Strength 立方体抗压强度 The cube compressive strength of concrete is given in terms of the characteristic compressive strength of 150mm size cubes tested at 28 days The characteristic strength (fcu) is the value on the x-axis below which 5% of the total area under the curve falls. The value of fcu is lower fcu,m than by 1.65σ, where σ is the standard deviation of the normal distribution. Strength Grade of Concrete Concrete is graded on the basis of its characteristic compressive strength of 150mm size cube at 28 days and expressed in Uni-axial Stress versus Strain Behavior in Compression 4.2 Tensile Strength轴心抗拉强度 Axial tensile strength ft Splitting tensile strength Specimen: prism[5 prizEm], cylinder [5silindE] 4.2. Tensile Strength 4.3 The modulus of elasticity Ec混凝土的弹性模量 弹性模量的测定方法Estimation of Elastic modulus 4.4 Shrinkage of Concrete Concrete, like all other materials, will slightly change in volume when it dries out. Shrinkage: Due to water loss to atmosphere (volume loss). Plastic shrinkage occurs while concrete is still “wet” Drying shrinkage occurs after concrete has set Most shrinkage occurs in first few months (~80% within one year). Cycles of shrinking and swelling may occur as environment changes. Temperature 4.4 Shrinkage of Concrete As the concrete dries, it shrinks in volume, probably due to the capillary tension that develops in the water remaining in the concrete. Conversely, if dry concrete is immersed in water, it expands, regaining much of the volume loss from prior shrinkage. Drying Shrinkage Cracking Shrinkage, which continues at a decreasing rate for several months, depending on the configuration of the member, is a detrimental property of concrete in several respects The magnitude of the ultimate shrinkage strain depends on Cement and water content Shrinkage is a function of W/C ratio Less water in the mixture, less water to escape, less shrinkage higher c