问题 问答题 简答题

常用矿物外加剂有哪些?掺入到混凝土中的优点和缺点有哪些?其物理化学作用原理是什么?

答案

参考答案:

①有胶凝性(或称潜在活性)的。如粒化高炉矿渣、水硬性石灰。②有火山灰性的。火山灰性系指本身没有或极少有胶凝性,但其粉末状态在有水存在时,能与Ca(OH)2在常温下发生化学反应,生成具有胶凝性的组分。例如硅灰、粉煤灰、原状的或煅烧的酸性火山玻璃和硅藻土、某些烧页岩和黏土等。③同时具有胶凝性和火山灰性的。如高钙粉煤灰或增钙液态渣、沸腾炉(流化床)燃煤脱硫排放的废渣(固硫渣)等。粒化高炉矿渣实际上也同时具有火山灰性。④其他。本身具有一定化学反应性的材料,如磨细的石灰岩、石英砂、白云岩以及各种硅质岩石的产物。这类材料过去一直被看做是惰性的物质。优点:在配制混凝土时加入较大量矿物细掺料,可降低温升,改善工作性,增进后期强度,并可改善混凝土的内部结构,提高抗腐蚀能力。矿物细掺料对碱集料反应有抑制作用,国外将这种混合材料称为辅助胶凝材料,是高性能混凝土不可缺少的组分。缺点:含碳量高的粉煤灰需水量大,对混凝土的流变性、强度和变形都有不利影响。

阅读理解

Hunting with birds is a very old sport. In some countries the golden eagle is used for hunting wild animals. They are used for hunting foxes and wolves.

Training an eagle to hunt takes a long time. Hunters catch young eagles in nets made of hair. After being trained the eagle is taken to a field. A blindfold over the bird’s eyes keeps it quiet until the hunter is ready.

The eagle sits in the arm of the hunter. The hunter’s arm is covered with a long, special glove to protect it from the sharp claws of the bird. In the field, as soon as the hunter sees a fox or a wolf, he removes the blindfold. The eagle quickly flies into the air and began to look for the wild animal.

The eagle sees the animal and catches it with claws like steel. Its beak and claws are strong enough to hold the animal. Usually, the bird carries the animal back to the hunter. Sometimes fast animals with good eyes can get away.

61.A hunting eagle is trained when_________.

A.it is still young          B.it is taken to a field

C.its eyes are covered with a blindfold

D.the hunter is ready

62.Hunters use nets made of hair to ________.

A.train young foxes     B.catch young wolves

C.train young eagles    D.catch young eagles

63.The trained eagle_______.

A.carries the hunter home

B.wears a blindfold when hunting an animal

C.is covered with a long, special glove

D.has strong claws like steel

64.A hunter wears a special glove to _______.

A.protect his arm from the sharp claws of a trained eagle

B.protect his arm from the sharp claws of a young fox

C.protect his arm from the sharp claws of a young wolf

D.protect his arm from the sharp claws of wild animals

65.According to the text, which of the following is true?

A.Fast animals with sharp eyes are sometimes difficult to catch

B.As soon as the blindfold is removed, the eagle flies into a tree

C.Hunters always blindfold young eagles before training them.

D.Sometimes hunters train young foxes they have caught.

单项选择题