Concrete Compression Analysis By Anthony Avilla, Michael Sullivan, and Jeremy Brickman ENGR 45, SRJC 12/5/05
What is Concrete Exactly? Concrete is a composite building material made from the combination of aggregate and cement binder. The most common form of concrete is Portland cement concrete, which consists of mineral aggregate (generally gravel and sand), Portland cement and water. The two major components of concrete are a cement paste and inert materials. The cement paste consists of portland cement, water, and some air either in the form of naturally entrapped air voids or minute, intentionally entrained air bubbles. The inert materials are usually composed of fine aggregate, which is a material such as sand, and coarse aggregate, which is a material such as gravel, crushed stone, or slag. In general, fine aggregate particles are smaller than 6.4 mm (.25 in) in size, and coarse aggregate particles are larger than 6.4 mm (.25 in). Depending on the thickness of the structure to be built, the size of coarse aggregate particles used can vary widely. In building relatively thin sections, a small size of coarse aggregate, with particles about 6.4 mm (.25 in) in size, is used. At the other extreme, aggregates up to 15 cm (6 in) or more in diameter are used in large dams. In general, the maximum size of coarse aggregates should not be larger than one-fifth of the narrowest dimensions of the concrete member in which it is used.
History The Assyrians and Babylonians used clay as cement. The Egyptians used lime and gypsum cement. The Roman Empire, cements made from pozzolanic ash/pozzolana and an aggregate made from pumice were used to make a concrete very similar to modern portland cement concrete. In 1756, British engineer John Smeaton pioneered the use of portland cement in concrete, using pebbles and powdered brick as aggregate. In modern day mixtures use of recycled/reused materials for concrete ingredients.
Mechanics Concrete does not solidify because water evaporates, but rather cement hydrates, gluing the other components together and eventually creating a stone-like material. During hydration and hardening, concrete needs to develop certain physical and chemical properties, among others, mechanical strength, low permeability to ingress of moisture, and chemical and volume stability. The ultimate strength of concrete is related to water/cement ratio and the size, shape, and strength of the aggregate used. Concrete with lower water/cement ratio (down to 0.35) makes a stronger concrete than a higher ratio. Concrete made with smooth pebbles is weaker than that made with rough-surfaced broken rock pieces for example.
Properties Composite When set, has high compressive strength, low tensile strength Brittle Withstands high temperatures Behaves as a ceramic
Properties QUIKRETE ® Fast-Setting Concrete #1004-50 QUIKRETE ® 5000 High Early Strength Concrete Mix #1007 Mix meets or exceeds the strength requirements of ASTM C387. It will achieve a compressive strength of 2500 psi (17.3 MPa) at 7 days and 4000 psi (27.6 MPa) at 28 days when tested in accordance with applicable standards. QUIKRETE ® Concrete Mix #1101 (Ready-To- Use) QUIKRETE ® Fiber-Reinforced Concrete Mix #l006-60
Chemistry of Cement H = H 2 O C 3 S = 3CaO. SiO 2 C 2 S = 2CaO. SiO 2 C 3 A = 3CaO. Al 2 O 3 Cs = CaSO 4 Ch = Ca(OH) 2 C 4 AF = 4CaO. Al 2 O 3. Fe 2 O 3 2C 3 S + 6H 3Ch + C 3 S2H 3 2C 2 S + 4H Ch + C 3 S2H 3 C 3 A + 10H + CsH 2 C 3 ACSH 12 C 3 A + 12H + Ch C 3 AChH 12 C 4 AF + 10H + 2Ch C 6 AFH 12 Chemical Reactions Chemical Composition Constituents and Nomenclature
Application of Concrete Pavements Building structures Foundations Motorways/roads Overpasses Dams Parking structures Bases for gates/fences/poles Cementing bricks or blocks in walls Any structure requiring high compressive strength and durability Can be used for structures demanding high temperature performance Although brittle, when cast around rebar, can be used in structures requiring ductility or moderate tensile demands
What We Did! Cut PVC pipe into 9 in. segments Squared off bottom end of each segment Determined directed ratio of water to concrete (by volume) For each product of concrete, we mixed samples containing varying quantities of water (at directed ratio, 15% higher, and 15% lower) Poured samples into PVC casts Allowed samples to set for five days Removed PVC casts Applied compression tests Obtained and analyzed data
Compression Test This is the apparatus that we used to test our concrete samples for our compression analysis
Our “ideal” water concentration samples should have theoretically had the greatest compression, but since they did not, we should have added more water (such as 15% more) or until visually satisfying. Therefore giving the “ideal” concentration the highest compression and the 15% more and 15% less, a lower compression result. Some of our samples had so little water that they just crumbled under compression and gave no data reading.