Stamped Concrete do-it-yourself
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We are decorative Concrete Contractors serving the south east USA and we get alot of emails on do-it-yourself tips and cries for advice....
Well..Concrete is a tricky business....done by many..but perfected by only a fraction of a handful. Molding, engraving, coloring and carving concrete is an ancient art that goes back literally millions of years (see my timeline of concrete link on my home page)
Well...your at this website 'cause the wife is tired of lookin' at the miserable slab of concrete in the back yard that you call a "patio" or you have a little more grass to mow then you would prefer...nonetheless..Do it yourself stamped concrete sounds just like what the doctor ordered...sweet patio...nice and CHEAP..
Well my cyber-friend...here you go:
The technicians at concreteforever.com Highly recommend only trained ACI Stamping technicians perform all work. All work shall meet ASTM C 94 and ACI 332 requirements for placement of concrete surfaces. This includes sub-grade preparation and forming concrete. Concrete arrives on site with the lithochrome, color hardener or integral color added (.024 % tricalcium per yard) together with the ASTM reinforcing fibers (thoroughly mixed). The concrete is then poured into forms at a thickness of 4-6 inches, screeded, bull floated, and edged before applying clear or colored release agent to the surface. Release agent is applied evenly over the entire surface before stamping. While in the plastic state, stamping commences using stamp molds and tampers to achieve the desired texture. When the concrete is set, excess release agent is washed off and control cuts (.34% of the thickness of the slab) are made in the surface. When the surface is dry, Pressure washing begins and engraving . Then dual coats of Concreteforever resin-coat clear (gloss or matte) acrylic sealer is applied to protect the surface from fading, staining and the elements.
In freeze-thaw areas, the concrete mix design shall be a minimum 4,500 psi (29mpa). With an average compressive strength which achieves 4,500 psi at 28 days +. Portland Cement shall meet the requirements of ASTM-C 150. Cement content shall be 611 lbs./yd., 1 yard fiber/yd, one 12 lb. pail integral color/yd. Slump is equal to 4" + 1", maximum water-cement ratio shall be .44 by weight. Coarse aggregate shall be accordance with ASTM-C 33 size 3/4" minus aggregate, air-entrainment 7%.
In non-freeze areas, the concrete mix design shall be a minimum 4,000 psi, compressive strength shall be 4,000 psi at 28 days +. Portland Cement shall meet the requirements of ASTM-C 150. Cement content shall be 564 lbs./yd., 1 yard fiber/yd, one 12 lb. pail integral color/yd. Slump is equal to 4" + 1", maximum water-cement ratio shall be .44 by weight. Coarse aggregate shall be accordance with ASTM-C 33 size 3/4" minus aggregate, air-entrainment 7%. Water is the key ingredient, which when mixed with cement, forms a paste that binds the aggregate together. The water causes the hardening of concrete through a process called hydration. Hydration is a chemical reaction in which the major compounds in cement form chemical bonds with water molecules and become hydrates or hydration products. Details of the hydration process are explored in the next section. The water needs to be pure in order to prevent side reactions from occurring which may weaken the concrete or otherwise interfere with the hydration process. The role of water is important because the water to cement ratio is the most critical factor in the production of "perfect" concrete. Too much water reduces concrete strength, while too little will make the concrete unworkable. Concrete needs to be workable so that it may be consolidated and shaped into different forms (i.e.. walls, domes, etc.). Because concrete must be both strong and workable, a careful balance of the cement to water ratio is required when making concrete.
Aggregates are chemically inert, solid bodies held together by the cement. Aggregates come in various shapes, sizes, and materials ranging from fine particles of sand to large, coarse rocks. Because cement is the most expensive ingredient in making concrete, it is desirable to minimize the amount of cement used. 70 to 80% of the volume of concrete is aggregate keeping the cost of the concrete low. The selection of an aggregate is determined, in part, by the desired characteristics of the concrete. For example, the density of concrete is determined by the density of the aggregate. Soft, porous aggregates can result in weak concrete with low wear resistance, while using hard aggregates can make strong concrete with a high resistance to abrasion.
Aggregates should be clean, hard, and strong. The aggregate is usually washed to remove any dust, silt, clay, organic matter, or other impurities that would interfere with the bonding reaction with the cement paste.
The concrete (or specifically, the cement in it) needs moisture to hydrate and cure (harden). When concrete dries, it actually stops getting stronger. Concrete with too little water may be dry but is not fully reacted. The properties of such a concrete would be less than that of a wet concrete. The reaction of water with the cement in concrete is extremely important to its properties and reactions may continue for many years. This very important reaction will be discussed in detail in this section.
Portland cement consists of five major compounds and a few minor compounds. The composition of a typical portland cement is listed by weight percentage in Table 2.
Cement Compound Weight Percentage Chemical Formula
Tricalcium silicate 50 % Ca3SiO5 or 3CaO.SiO2
Dicalcium silicate 25 % Ca2SiO4 or 2CaO.SiO2
Tricalcium aluminate 10 % Ca3Al2O6 or 3CaO .Al2O3
Tetracalcium aluminoferrite 10 % Ca4Al2Fe10 or 4CaO.Al2O3.Fe2O3
Gypsum 5 % CaSO4.2H2O
Composition of portland cement with chemical composition and weight percent.
When water is added to cement, each of the compounds undergoes hydration and contributes to the final concrete product. Only the calcium silicates contribute to strength. Tricalcium silicate is responsible for most of the early strength (first 7 days). Dicalcium silicate, which reacts more slowly, contributes only to the strength at later times. Tricalcium silicate will be discussed in the greatest detail.
The equation for the hydration of tricalcium silicate is given by:
Tricalcium silicate + Water--->Calcium silicate hydrate+Calcium hydroxide + heat
2 Ca3SiO5 + 7 H2O ---> 3 CaO.2SiO2.4H2O + 3 Ca(OH)2 + 173.6kJ
Upon the addition of water, tricalcium silicate rapidly reacts to release calcium ions, hydroxide ions, and a large amount of heat. The pH quickly rises to over 12 because of the release of alkaline hydroxide (OH-) ions. This initial hydrolysis slows down quickly after it starts resulting in a decrease in heat evolved.
The reaction slowly continues producing calcium and hydroxide ions until the system becomes saturated. Once this occurs, the calcium hydroxide starts to crystallize. Simultaneously, calcium silicate hydrate begins to form. Ions precipitate out of solution accelerating the reaction of tricalcium silicate to calcium and hydroxide ions. (Le Chatlier's principle). The evolution of heat is then dramatically increased.
The formation of the calcium hydroxide and calcium silicate hydrate crystals provide "seeds" upon which more calcium silicate hydrate can form. The calcium silicate hydrate crystals grow thicker making it more difficult for water molecules to reach the unhydrated tricalcium silicate. The speed of the reaction is now controlled by the rate at which water molecules diffuse through the calcium silicate hydrate coating. This coating thickens over time causing the production of calcium silicate hydrate to become slower and slower.
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Copyright © 2005 Concreteforever.com. All Rights Reserved