2.1 Reinforced Concrete
Plain concrete is formed from a hardened mixture of cement ,water ,fine aggregate, coarse aggregate (crushed stone or gravel),air, and often other admixtures. The plastic mix is placed and consolidated in the formwork, then cured to facilitate the acceleration of the chemical hydration reaction lf the cement/water mix, resulting in hardened concrete. The finished product has high compressive strength, and low resistance to tension, such that its tensile strength is approximately one tenth lf its compressive strength. Consequently, tensile and shear reinforcement in the tensile regions of sections has to be provided to compensate for the weak tension regions in the reinforced concrete element.
It is this deviation in the composition of a reinforces concrete section from the homogeneity of standard wood or steel sections that requires a modified approach to the basic principles of structural design. The two components of the heterogeneous reinforced concrete section are to be so arranged and proportioned that optimal use is made of the materials involved. This is possible because concrete can easily be given any desired shape by placing and compacting the wet mixture of the constituent ingredients are properly proportioned, the finished product becomes strong, durable, and, in combination with the reinforcing bars, adaptable for use as main members of any structural system.




1.1鋼筋混凝土
素混凝土是由水泥、水、細骨料、粗骨料（碎石或；卵石）、空氣，通常還有其他外加劑等經過凝固硬化而成。將可塑的混凝土拌合物注入到模板內，并將其搗實，然后進行養(yǎng)護，以加速水泥與水的水化反應，最后獲得硬化的混凝土。其最終制成品具有較高的抗壓強度和較低的抗拉強度。其抗拉強度約為抗壓強度的十分之一。因此，截面的受拉區(qū)必須配置抗拉鋼筋和抗剪鋼筋以增加鋼筋混凝土構件中較弱的受拉區(qū)的強度。
由于鋼筋混凝土截面在均質性上與標準的木材或鋼的截面存在著差異，因此，需要對結構設計的基本原理進行修改。將鋼筋混凝土這種非均質截面的兩種組成部分按一定比例適當布置，可以最好的利用這兩種材料。這一要求是可以達到的。因混凝土由配料攪拌成濕拌合物，經過振搗并凝固硬化，可以做成任何一種需要的形狀。如果拌制混凝土的各種材料配合比恰當，則混凝土制成品的強度較高，經久耐用，配置鋼筋后，可以作為任何結構體系的主要構件。
澆筑混凝土所需要的技術取決于即將澆筑的構件類型，諸如：柱、梁、墻、板、基礎，大體積混凝土水壩或者繼續(xù)延長已澆筑完畢并且已經凝固的混凝土等。對于梁、柱、墻等構件，當模板清理干凈后應該在其上涂油，鋼筋表面的銹及其他有害物質也應該被清除干凈。澆筑基礎前，應將坑底土夯實并用水浸濕6英寸，以免土壤從新澆的混凝土中吸收水分。一般情況下，除使用混凝土泵澆筑外，混凝土都應在水平方向分層澆筑，并使用插入式或表面式高頻電動振搗器搗實。必須記住，過分的振搗將導致骨料離析和混凝土泌漿等現(xiàn)象，因而是有害的。