Prestressed concrete girders

Prestressed concrete girders are the leading choice for bridge construction across the country, and it's easy to understand why. Compared to other materials and bridge superstructures, studies show prestressed I-beam girders have the longest service life and require less maintenance.

 

The Earth's Structure

​​The earth is made up of three different layers: the crust, the mantle and the core. 

The crust

This is the outside layer of the earth and is made of solid rock, mostly basalt and granite. There are two types of crust; oceanic and continental. Oceanic crust is denser and thinner and mainly com​posed of basalt.  Continental crust is less dense, thicker, and mainly composed of granite.

The mantle

The mantle lies below the crust and is up to 2900 km thick.  It consists of hot, dense, iron and magnesium-rich solid rock. The crust and the upper part of the mantle make up the lithosphere, which is broken into plates, both large and small. To learn more about these plates see the Plate Tectonics page​. 

The core

The core is the centre of the earth and is made up of two parts: the liquid outer core and solid inner core. The outer core is made of nickel, iron and molten rock. Temperatures here can reach up to 50,000 C.

SOME FORMS OF CRUST

FOLD: 

Permanent wavelike deformation in layered rock or sediment. 

FAULT: 

A fracture in bedrock along which rocks on one side have moved relative to the other side. 

JOINT: 

A fracture on a rock without noticeable movement.