第五章-变形耐久性.pptx

低、负温强度发展低、负温强度发展 冻融循环冻融循环 盐的腐蚀盐的腐蚀 氯离子侵蚀氯离子侵蚀 钢筋锈蚀钢筋锈蚀 干燥、温差、热应力引起的裂缝干燥、温差、热应力引起的裂缝 碱骨料反应碱骨料反应 对多年冻土的热挠动对多年冻土的热挠动 冻土融沉及隆起的影响冻土融沉及隆起的影响 风蚀风蚀1 1抗渗性抗渗性(Permeability渗透性渗透性)l Permeability refers to the ease with which water can pass through the concrete.l Low permeability is an important requirement for hydraulic structures and in some cases watertightness of concrete may be considered to be more significant than strength although,other conditions being equal,concrete of low permeability will also be strong and durable.l2 2抗冻性抗冻性(Freeze Resistance/Weathering)l Damage to concrete from freezing and thawing arises from the expansion of porewater during freezing;The resistance of concrete to freezing and thawing can be improved by increasing its impermeability.This can be achieved by using a mix with the lowest possible water-cement ratio compatible with sufficient workability for placing and compacting into a homogeneous（均匀均匀的）的）mass.Durability can be further improved by using air-entrainment.l3 3抗侵蚀性抗侵蚀性(Chemical Attack)l In general,concrete has a low resistance to chemical attack.There are several chemical agents which react with concrete but two forms of attack are most common,namely leaching and sulphate attack.lChemical agents essentially react with certain compounds of the hardened cement paste and the resistance of concrete to chemical attack therefore depend largely on the type of cement used.l4 4碱骨料反应碱骨料反应(Alkali-Aggregate Reaction)l Certain aggregates can react chemically with the alkaline content of cement to form alkaline silica gel.When this happens these aggregates expand or swell（肿肿胀）胀）resulting in cracking and disintegration of concrete.l5 5混凝土的碳化混凝土的碳化(Carbonizition)l总之，混凝土的耐久性决定于材料的品质、内部密总之，混凝土的耐久性决定于材料的品质、内部密实度、施工质量三个方面。实度、施工质量三个方面。l In order to produce a durable concrete care should be taken to select suitable constituent materials.It is also important that the mix contains adequate quantities of materials in proportions suitable for producing a homogeneous and fully compacted concrete mass.6 6、提高耐久性的措施：、提高耐久性的措施：（1 1）合理选择水泥品种，优质骨料。）合理选择水泥品种，优质骨料。（2 2控制）控制W/CW/C和水泥用量，提高密实度。和水泥用量，提高密实度。（3 3）掺外加剂。）掺外加剂。（4 4）加保护层。）加保护层。（5 5）提高施工质量）提高施工质量第五节混凝土的变形性能第五节混凝土的变形性能(Deformation)l1 1、化学收缩、化学收缩（chemical shrinkage）l2 2、干缩变形（、干缩变形（drying shrinkage）l3 3、温度变形、温度变形temperature l4 4、荷载作用下的变形、荷载作用下的变形1 1、化学收缩、化学收缩 化学收缩是指混凝土拌合物在水化过程化学收缩是指混凝土拌合物在水化过程中，由于水泥水化生成物体积比体积小，而中，由于水泥水化生成物体积比体积小，而产生的收缩产生的收缩。chemical shrinkage In a set concrete,as hydration proceeds,a net decrease in volume occurs since the hydrated cement gel has a smaller volume than the sum of the cement and the water constituents.As hydration continues in an environment where the water content is constant,such as inside a large mass of concrete this decrease in volume of the cement paste results in shrinkage of the concrete.This is known as autogenous shrinkage(chemical shrinkage)because as the name implies,it is self-produced by the hydration of cement.2 2、干缩变形、干缩变形 由于混凝土内部吸附水分蒸发，由于混凝土内部吸附水分蒸发而引起凝胶体失水收缩，毛细管水分而引起凝胶体失水收缩，毛细管水分蒸发，混凝土系统内的颗粒受毛细管蒸发，混凝土系统内的颗粒受毛细管压力作用而产生体积收缩压力作用而产生体积收缩。drying shrinkagelWhen a hardened concrete cured in water,is allowed to dry it first loses water from its voids and capillary pores and only starts to shrink during further drying when water is drawn out of its cement gel.This is known as drying shrinkage 3 3、温度变形、温度变形 和其他材料一样，也具有热胀和其他材料一样，也具有热胀冷缩的性质。混凝土的温度膨胀系冷缩的性质。混凝土的温度膨胀系数约为数约为1010 1010-5-5。对大体积混凝土不。对大体积混凝土不利。利。The temperature of the environment have a significant effect on both the rate and magnitude（数量）of shrinkage in as much as they affect the movement of water in concrete.4 4、荷载作用下的变形（、荷载作用下的变形（deformation）l短期荷载作用下的变形短期荷载作用下的变形l Concrete deforms under load,the deformation increasing with the applied load and being commonly known as elastic deformation.Concrete continues to deform with time,under constant load,this is known as time-dependent deformation or creep.4 4、荷载作用下的变形、荷载作用下的变形l徐变徐变(creep)：混凝土在长期荷混凝土在长期荷载作用下，沿作载作用下，沿作用力方向的变形，用力方向的变形，且随时间的延长且随时间的延长而增长，即荷载而增长，即荷载不变但变形仍随不变但变形仍随时间增长。时间增长。