Concrete is a mixture of cement, water, sand, gravel, crushed rock, or other aggregates. Sometimes, one or more admixtures are added to change certain characteristics of the concrete, such as workability, durability, and time of hardening.
Top 100 Colleges by Highest Tuition. Here are the top 100 most expensive colleges by tuition for the 2008-2009 school year. The latest numbers can be found in our most expensive colleges ranking. Notes: Some colleges like Bates College, Colby College, Middlebury College, and Union College have a comprehensive fee (tuition + room/board).
The view of the spectacular Mount Elbert, the highest peak in Colorado. Colorado is the highest state in the US in terms of mean elevation, which is 6,800 feet above sea level. The state also has a diverse topography. It has tall, jagged mountain peaks, vast stretches of plains, deserts, mesas, and canyons.