特种混凝土与普通混凝土的区别？

普通混凝土是由水泥、粗骨料、细骨料和水拌合，经硬化而成的一种人造石材。
特种混凝土
是根据工程环境的要求对混凝土的性质提出特殊的要求，如轻质混凝土、道路混凝土、水工混凝土、耐热混凝土、耐酸混凝土及防辐射混凝土等，这些特种混凝土根据自身所处环境和使用要求对配合比及添加剂有不同的要求

PRESTRESSED CONCRETE

A prestressed concrete unit is one in which engineered stresses have been placed before it has been subjected to a load. When PRETENSION- ING is used, the reinforcement (high-tensile- strength steel strands) is stretched through the form between the two end abutments or anchors. A predetermined amount of stress is applied to the steel strands. The concrete is then poured, encasing the reinforcement. As the concrete sets, it bonds to the pretensioned steel. When it has reached a specified strength, the tension on the reinforcement is released. This prestresses the concrete, putting it under compression, thus creating a built-in tensile strength.

POST-TENSIONING involves a precast member that contains normal reinforcing in addition to a number of channels through which the prestressing cables or rods maybe passed. The channels are usually formed by suspending inflated tubes through the form and casting the concrete around them. When the concrete has set, the tubes are deflated and removed. Once the concrete has reached a specified strength, prestressing steel strands or TENDONS are pulled into the channels and secured at one end. They are then stressed from the opposite end with a portable hydraulic jack and anchored by one of several automatic gripping devices.

Post-tensioning may be done where the member is poured or at the jobsite. Each member may be tensioned, or two or more members may be tensioned together after erection. In general,post-tensioning is used if the unit is over 45 ft long or over 7 tons in weight. However, some types of pretensioned roof slabs will be considerably longer and heavier than this. When a beam is prestressed, either by pre- tensioning or post-tensioning, the tensioned steel produces a high compression in the lower part of the beam. This compression creates an upward bow or camber in the beam (fig. 7-19). When a load is placed on the beam, the camber is forced out, creating a level beam with no deflection. Those members that are relatively small or that can be readily precast are normally pretensioned. These include precast roof slabs, T-slabs, floor slabs, and roof joists.

SPECIAL TYPES OF CONCRETE

Special types of concrete are essentially those with unique physical properties or those produced with unusual techniques and/or reproduction processes. Many special types of concrete are made with portland cement as a binding medium; some use binders other than portland cement.

Here is a course on concrete and masonary:

Click 'next' to go to the next page, it has a lot of information about types of concrete.

http://www.tpub.com/content/engineering/14069/css/14069_243.htm

一个是特种，一个是普通呀！
这题好像不是外语类的？！