Concrete Materials & Methods ARCH 330 Fall 2008

Concrete and Cement Concrete is a rocklike material produced by mixing coarse and fine aggregates, Portland cement, and water; then allowing the mixture to harden. There are eight type of Portland cement; Type I is used for most purposes in construction. Type II and V is used when concrete is in contact with water and has a high concentration of sulfates. Type II hardens more quickly than the other types. Type IV is used in massive structure such as dams where excessive heat is a concern.

Aggregates and Water Aggregates make up roughly ¾ of the volume of concrete. Water is required as a reactant in the curing of the concrete. More the water the more fluid it becomes and it is easier to work. Air-entrainment- adding air bubbles in the concrete makes it easier to work but most importantly increases resistance to freeze thaw cycles.

Curing Concrete Because concrete cures by hydration and not by drying, it is essential that concrete be kept moist until its required strength is achieved. Concrete can segregate (segregation) easily, which means that the coarse aggregate works its way to the bottom of the form and the water and cement paste rise to the top. It should not be dropped a distance of no more than 3-4 feet. Vibration reduces segregation. Concrete is designed on the basis of the strength that it reaches after 28 days. Low and high temperatures make concrete curing more difficult. Low temperature the curing proceeds at a much reduced rate. In hot temperatures, the hydration reaction is greatly accelerated.

Concrete Measured and sold by the cubic yard. Proper mix design Responsibility of the concrete plant Tests on concrete Slump test- proper flow ability Compression tests- at 1,3,7 and 28 days

Slump Test

Test Cylinder - Compressive strength

Concrete as a building material Concrete-Cement/Water/Aggregate Formwork Reinforcing Place/Pour Concrete

Concrete Construction Slab on Grade/Elevated Slabs Footings/Walls/Columns Below grade and above Tilt-Up Construction Pre-cast Concrete Post-Tension Architectural Concrete

Building Materials Soils/Earthwork Concrete Structural Steel Wood

Handling Concrete Don’t add water Check form work Concrete to be placed not poured Don’t overwork concrete Curing improves concrete Correct cylinder making Hot and cold weather concerns