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* CLICK LINKS AT BOTTOM OF PAGE FOR AN INSTANT VIRTUAL ESTIMATE FOR YOUR NEW DRIVEWAY, PATIO OR WALKWAYS!*** - What is stamped concrete? Stamped concrete begins with regular concrete. A powdered dye (color) is spread onto the surface and /or an ahmixture mixed all the way through the wet concrete and trowelled in. Then a second color (also known as releasing agent) is cast on the surface. Before the concrete hardens a set of rubber molds (stamps) are used to imprint textures into its hydrating surface. The result will look like slate, cobblestone, brick, marble, or many other materials. Why is the base so important? Concrete is a mirror image of what it is poured over. Without an adequate base (usually 2-4 inches of compacted rock, sand, gravel or road base) flatwork can settle, separate and develop uneven surfaces. Will decorative concrete last as long and as well as regular concrete? Our product is 4-6" thick, (driveways are 6"-7" thick and patios are 4" or more) 4,000-4,500 psi concrete. We match or exceed the normal requirements for a strong finish that withstands years of normal use. Over the years we have experimented with different proportions of tri-calcium silicate and bi-calcium silicate in terms of performance variables, one important property is the compressive strength. Previously, our technicians at concreteforever.com developed a mathematical model relating cement particle-size distribution to strength development. Assuming that the depth of the hydrated layer is independent of particle diameter (which also is assumed tacitly in the NIST cement hydration model) and proportional to the square root of time, he was able to quantitatively predict the effects of particle-size distribution on strength evolution. More recently, David Hunt, Founder of concreteforever.com also showed that cement fineness is an important factor influencing compressive strength, with phase compositions becoming significant at later ages. In this study, we also have attempted to predict the compressive strength development of standard ASTM C 10914 mortar in relation the compressive strength required for residential use in Houston, Texas. Simply put, When our concrete arrives on site we modify the mixture depending on the humidity, tempture and soil conditions to minimize concrete cracking and potential displacement that may occur with an improperly mixed batch of concrete. (these factors are never taken into consideration at the concrete plant) Can stamped concrete (decorative concrete) be found in commercial settings? Absolutely, stamped concrete can be found throughout the world and at many distinguished hotels, casinos, resorts, etc. A famous example would be Disneyland and Disney World. Why is decorative concrete (stamped concrete) more expensive than traditional concrete? Recently, I have received inquiries into the cost of decorative cement work in comparison to traditional cement work. Let me describe the two concepts... Traditional cement (also called concrete) work is what you would find around older homes. Examples would be a plain smooth or brushed finish driveway, curb or sidewalk. Rarely were there any designs unless a creative contractor carved shapes into the concrete while it was still wet. The process for installing this type of concrete is a fairly simple one, perfected by many... Not so perfected by many as well... Under the best circumstances it involves little ground preparation, setting forms and the pour. Finishing would require some tamping, floating, troweling and usually brooming the surface. Although this can be tedious work it is normally a simple process when completed by an experienced concrete driveway contractor or concrete patio contractor. Decorative concrete (Concrete Stamping) work is a relatively new concept but really goes back many years. You may have seen a concrete sidewalk leading into a business or mall that looked like a rustic stone path with one or more colors. This design is becoming very popular because it is so complimentary of landscapes and homes. Many people are even having decorative concrete finishes installed in rooms of their homes. Kitchens are among the most common requests. Properly finished decorative concrete can look very elegant or rustic depending on what look is desired. While decorative concrete is the most desired these days it is also the most difficult finish to perfect and requires much more preparation, finishing, and skill. When the contractor actually gets to the point where the concrete driveway, patio or walkway can be stamped (process to apply the decorative appearance) time is crucial. There are very limited amounts of time for the various applications and any mistakes can leave a finish that the homeowner is not satisfied with. Stamping Concrete is an art and I only know one other stamped concrete artisan (besides my crew and myself) in a 200 mile radious from Houston that have perfected this ancient art. This person I refer to is my mentor..... After the concrete is poured and finished the job is not complete. Clean up for this type of finish is more difficult because of the various colors that are involved. After a day or so the contractor will have to return to the job site to pressure wash the excess color/release for the perfect finish and look, then resin-coat the concrete. Simply put decorative concrete is a much more labor-intensive process but most feel it is worth the cost because of the unique, prestigious and elegant look. How is decorative concrete colored? AAA Affordable Concrete Contractors of Houston uses two methods to color decorative concrete. Using the first method, color is spread onto the surface by hand using the “dry shake method,” then worked into the surface using hand tools. After the color is applied and worked into the fresh cement, a release/hardener is applied. The release/hardener serves a duel purpose. It adds a tremendous amount of strength and it highlights and acts as a second color, which gives the stamped pattern and overall color a defining and distinguished look. The second method used is when the color is mixed directly inside the concrete at the concrete plant and mixed inside the truck. The concrete is the colored throughout from the top to the bottom instead of just ¼” into the surface. The release/hardener is applied using this method as well. The second method tends to be slightly more expensive since the cost of the material will increase. Both are good methods and not one is better than the other. Which method is used depends on the conditions and what look the customer is trying to accomplish. "I can't afford to do my entire project all at once. Can I do half now and half later?" Decorative concrete is surprisingly affordable. Best of all, every project can be done in stages. It is not a problem to pick up a pattern from one area and connect up to another area of your project at a later time. When is it necessary to reinforce concrete? It is always an advantage in the long term to add re-bar (reinforcement bar). This guarantees that concrete will settle evenly and avoids uneven surfaces, and cracks that widen over time. The soil here in Houston is comprised of mostly clay...unstable to say the least
posted by concreteforever at 6:00 AM 0 comments
Monday, August 30, 2004
Houston Concrete Contractors
Houston Concrete Contractors
posted by concreteforever at 6:22 PM 0 comments
Houston Concrete - Driveways - Concrete Patios
Houston Concrete - Driveways - Concrete Patios
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Let us design your next masonry project for your dream driveway, patio, pool or watergarden!DECORATIVE CONCRETE STUNNING PATIOS, QUARRY TILE, STONES, SLATE ALL TYPES MASONRY, POOLS AND DRIVEWAY SPECIALISTSCLICK LINKS AT BOTTOM OF PAGE FOR AN INSTANT VIRTUAL ESTIMATE FOR YOUR NEW DRIVEWAY, PATIO OR WALKWAYS!- Serving ALL of Houston and surrounding areas:Click the CONTACT button for a fast and FREE in home estimateWe Meet or EXCEED all City of Houston Concrete specifications!We Are THE #1 Custom pool and jacuzzi builder in Houston. Turn-key installations - 20k gallon Custom Exotic Swimming pools w/ waterfalls, jacuzzi and auto cleaners from $19,900.00!Want a custom pool "half in" your home "half out"?-DONE!Want a custom fountain to compliment your water garden?-DONE! Do you want to transform your backyard into paradise?-DONE!Just call OR Email the folks at ConcreteForever.com for a Fast, courteous and FREE IN HOME CONSULTATION AND DESIGNHouston and surrounding areas specialists in decorative concrete foundations, Slate and stone installations, ashlar cut slate, Roman slate fan designs for your portico, cobblestones, granite driveways, retainer walls, soil erosion prevention and drain remediation, Custom driveway and patio specialists, Sunroom and remodeling builders serving all of southeast Texas Fast driveway concrete saw cut, break out and haul removal & replacement in Houston and surrounding areas. Brilliant decorative flagstone borders & flagstone trim, Custom decorative concrete counter tops, outside grills, fire pits, flagstone walls, flagstone counter tops. Acrylic flagstone and ledge stone waterfalls and fountains, flagstone, ledgestone fireplaces and morePermit, engineering & design servicesPool Patios, Custom Pools, jacuzzi's, decorative patios & decksStamped & colored concrete patios and drivewaysFree estimates and NO DEPOSIT REQUIREDBobcat & dumptruck serviceBest decorative concrete driveway in Houston!Intricate Interlocking paver designs for the upscale homeExceeds all Houston concrete driveway specificationsPrompt concrete deliveryConcrete pumping for the hard to reach patioConcrete Driveways in houston must have 2-3"sand base!Concrete driveways in Houston must have #3 steel rebar! reinforcement @ 12-15"o.c. each way encased in 6" concrete!All decorative concrete driveways poured with an average compressive strength of 4,000 p.s.i. concrete! Patio concrete = 3,500 psiPavers, pavestones, interlocking, limestone, granite, cobblestones & more! Custom concrete services since 1986, serving all of Harris county and metro Houston areapost-tension foundations, Masonry, brick, block,stone, etcFree estimates, all types masonry; Largest Houston stamped concrete company in town! artisans in brick, block, stone, stucco, stunning water gardens, dream patio designs,Exotic stonework, all types masonry projects from fire-pits, retainer walls, fireplace systems, stucco, stone, marble and more!Exotic faux concrete countertops to match your home decor * Innovative designs, online virtual FREE estimates just click on the links below to estimate in seconds your dream patio, driveway or custom masonry! Concreteforever.com!
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Permit, engineering & design servicesPool Patios, Custom Pools, jacuzzi's, patios & decksStamped & colored concrete patios and drivewaysFree estimates and NO DEPOSIT REQUIREDBobcat & dumptruck serviceBest stamped concrete driveway in Houston!Exceeds all Houston concrete driveway specificationsPrompt concrete deliveryPavers, pavestones, interlocking, limestone, granite, cobblestones & more! Custom concrete services since 1986, serving all of Harris county and metro Houston areapost-tension foundations, Masonry, brick, block,stone, etcFree estimates, all types masonry; brick, block, stone, stucco, stunning water gardens, dream patio designs.Exotic stonework, all types masonry projects from fire-pits, retainer walls, fireplace systems, stucco, stone, marble and more!Exotic concrete countertops to match your home decor
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posted by concreteforever at 6:19 PM 0 comments
Sunday, August 29, 2004
Americas source for info on decorative concrete
Americas source for info on decorative concreteWhat is stamped concrete? Stamped concrete begins with regular concrete. A powdered dye (color) is spread onto the surface and /or an ahmixture mixed all the way through the wet concrete and trowelled in. Then a second color (also known as releasing agent) is cast on the surface. Before the concrete hardens a set of rubber molds (stamps) are used to imprint textures into its hydrating surface. The result will look like slate, cobblestone, brick, marble, or many other materials. Why is the base so important? Concrete is a mirror image of what it is poured over. Without an adequate base (usually 2-4 inches of compacted rock, sand, gravel or road base) flatwork can settle, separate and develop uneven surfaces. Will decorative concrete last as long and as well as regular concrete? Our product is 4-6" thick, (driveways are 6"-7" thick and patios are 4" or more) 4,000-4,500 psi concrete. We match or exceed the normal requirements for a strong finish that withstands years of normal use. Over the years we have experimented with different proportions of tri-calcium silicate and bi-calcium silicate in terms of performance variables, one important property is the compressive strength. Previously, our technicians at concreteforever.com developed a mathematical model relating cement particle-size distribution to strength development. Assuming that the depth of the hydrated layer is independent of particle diameter (which also is assumed tacitly in the NIST cement hydration model) and proportional to the square root of time, he was able to quantitatively predict the effects of particle-size distribution on strength evolution. More recently, David Hunt, Founder of concreteforever.com also showed that cement fineness is an important factor influencing compressive strength, with phase compositions becoming significant at later ages. In this study, we also have attempted to predict the compressive strength development of standard ASTM C 10914 mortar in relation the compressive strength required for residential use in Houston, Texas. Simply put, When our concrete arrives on site we modify the mixture depending on the humidity, tempture and soil conditions to minimize concrete cracking and potential displacement that may occur with an improperly mixed batch of concrete. (these factors are never taken into consideration at the concrete plant) Can stamped concrete (decorative concrete) be found in commercial settings? Absolutely, stamped concrete can be found throughout the world and at many distinguished hotels, casinos, resorts, etc. A famous example would be Disneyland and Disney World. Why is decorative concrete (stamped concrete) more expensive than traditional concrete? Recently, I have received inquiries into the cost of decorative cement work in comparison to traditional cement work. Let me describe the two concepts... Traditional cement (also called concrete) work is what you would find around older homes. Examples would be a plain smooth or brushed finish driveway, curb or sidewalk. Rarely were there any designs unless a creative contractor carved shapes into the concrete while it was still wet. The process for installing this type of concrete is a fairly simple one, perfected by many... Not so perfected by many as well... Under the best circumstances it involves little ground preparation, setting forms and the pour. Finishing would require some tamping, floating, troweling and usually brooming the surface. Although this can be tedious work it is normally a simple process when completed by an experienced concrete driveway contractor or concrete patio contractor. Decorative concrete (Concrete Stamping) work is a relatively new concept but really goes back many years. You may have seen a concrete sidewalk leading into a business or mall that looked like a rustic stone path with one or more colors. This design is becoming very popular because it is so complimentary of landscapes and homes. Many people are even having decorative concrete finishes installed in rooms of their homes. Kitchens are among the most common requests. Properly finished decorative concrete can look very elegant or rustic depending on what look is desired. While decorative concrete is the most desired these days it is also the most difficult finish to perfect and requires much more preparation, finishing, and skill. When the contractor actually gets to the point where the concrete driveway, patio or walkway can be stamped (process to apply the decorative appearance) time is crucial. There are very limited amounts of time for the various applications and any mistakes can leave a finish that the homeowner is not satisfied with. Stamping Concrete is an art and I only know one other stamped concrete artisan (besides my crew and myself) in a 200 mile radious from Houston that have perfected this ancient art. This person I refer to is my mentor..... After the concrete is poured and finished the job is not complete. Clean up for this type of finish is more difficult because of the various colors that are involved. After a day or so the contractor will have to return to the job site to pressure wash the excess color/release for the perfect finish and look, then resin-coat the concrete. Simply put decorative concrete is a much more labor-intensive process but most feel it is worth the cost because of the unique, prestigious and elegant look. How is decorative concrete colored? AAA Affordable Concrete Contractors of Houston uses two methods to color decorative concrete. Using the first method, color is spread onto the surface by hand using the “dry shake method,” then worked into the surface using hand tools. After the color is applied and worked into the fresh cement, a release/hardener is applied. The release/hardener serves a duel purpose. It adds a tremendous amount of strength and it highlights and acts as a second color, which gives the stamped pattern and overall color a defining and distinguished look. The second method used is when the color is mixed directly inside the concrete at the concrete plant and mixed inside the truck. The concrete is the colored throughout from the top to the bottom instead of just ¼” into the surface. The release/hardener is applied using this method as well. The second method tends to be slightly more expensive since the cost of the material will increase. Both are good methods and not one is better than the other. Which method is used depends on the conditions and what look the customer is trying to accomplish. "I can't afford to do my entire project all at once. Can I do half now and half later?" Decorative concrete is surprisingly affordable. Best of all, every project can be done in stages. It is not a problem to pick up a pattern from one area and connect up to another area of your project at a later time. When is it necessary to reinforce concrete? It is always an advantage in the long term to add re-bar (reinforcement bar). This guarantees that concrete will settle evenly and avoids uneven surfaces, and cracks that widen over time. The soil here in Houston is comprised of mostly clay...unstable to say the least
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Let Concreteforever.com design/Build your next Exotic patio, driveway, fire pit, stamped patio, stamped concrete patio, stamped driveway, Certified Concrete Contractors, stamped concrete samples, stamped concrete contractors, Patterned concrete, stamped concrete, patterned cement, stamped cement, Residential and Commercial concrete contractors, concrete foundation contractors, stamped concrete contractors, stamped concrete driveways, Give your patio a new image with authentic stamped articulate decorative concrete from affordable concrete contractors, fire-pit, patio extension, driveways extension or masonry project for your dream driveway, exotic hardscapes, Let the our ASI Certified Stamped concrete contractors and technicians perform your next exotic concrete hardsape, patio, pool or watergarden! Stamped concrete contractor in houston texas, stamped cement, stamped concrete contractors, stamped concrete driveway, concrete contractors for your foundation, stamped concrete, decorative stamped concrete, Custom Hardscape concrete work in Houston area- We are a full service design and build general contractor designing and constructing innovative residential and commercial structures from the footer to the roof we provide competitive, artistic and elaborate articulate construction from framing to molding, tray ceilings, new home construction and full phase remodeling..let AAA Affordable Concrete Contractors work for you! FREE ONLINE CONCRETE CALCULATOR BELOW! - Certified flatwork technicians-DECORATIVE CONCRETE-STUNNING PATIOS, QUARRY TILE, STONES, SLATE ALL TYPES MASONRY, POOLS Patio AND DRIVEWAY SPECIALISTShttp://www.concreteforever.com/
This site is updated daily at 7:00 a.m. Central Time.Keyword Index; Houston concrete,concrete houston texas, concrete patio stamp, driveway stamp, stamp cement, stamp concrete, flagstone houston, concrete contractors, contractors, concrete contractors, cement contractors, concrete contractor, contractor, houston flagstone, houston flagstone patios, patios of houston, flagstone trim, houston flagstone contractors, The price of concrete or the price of stamped concrete is much less than you may think when compared to laying a brick by brick or stone by stone patio or driveway, stamped concrete, patterned concrete, decorative concrete, residential contractors, building contractors, remodeling contractors, houston stamped concrete, stamped concrete contractors, patterned and colored concrete, are just some of the specialty construction performed by the finishers at concreteForever, decorative concrete houston, houston custom concrete, flagstone and stone masons, concrete houston, houston concrete, concrete houston texas, houston cement, slab, slabs, concrete slab, concrete slabs, cement houston, houston patio, resurface your concrete, resurfacing techniques, patio houston texas Fast driveway or patio concrete saw cut, break out and haul removal, repair & replacement in Houston and surrounding areas. Driveway replacement, concrete driveway replacement, concrete patio replacement, cement replacement, Brilliant decorative flagstone borders & stunning stamped and patterned concrete, flagstone trim, Custom decorative concrete counter tops, outside grills, fire pits, flagstone walls, flagstone counter tops, Decorative concrete, stucco contractors, decorative stucco and dryvit, decorative cement, pATIO, pATIOS, DECORATIVE PATIOS AND DRIVEWAYS,Stamped concrete, patterned concrete, stamped patio, stamped patios, stamped driveways, decorative driveways, Acrylic flagstone and ledge stone waterfalls and fountains, flagstone, ledgestone fireplaces and more FREE DO-IT-YOURSELF ESTIMATE CALCULATOR BELOW! Fastest Search on Earth! Google.com
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AAA Affordable Concrete Contractors of Houston
AAA Affordable Concrete Contractors of Houston
Let Concreteforever.com design/Build your next Exotic patio, driveway, fire pit, stamped patio, stamped concrete patio, stamped driveway, Certified Concrete Contractors, stamped concrete contractors, Patterned concrete, stamped concrete, patterned cement, stamped cement, Residential and Commercial concrete contractors, concrete foundation contractors, stamped concrete contractors, stamped concrete driveways, Give your patio a new image with authentic stamped articulate decorative concrete from affordable concrete contractors, fire-pit, patio extension, driveways extension or masonry project for your dream driveway, exotic hardscapes, Let the our ASI Certified Stamped concrete contractors and technicians perform your next exotic concrete hardsape, patio, pool or watergarden! Stamped concrete contractor in houston texas, stamped cement, stamped concrete contractors, stamped concrete driveway, concrete contractors for your foundation, stamped concrete, decorative stamped concrete, Custom Hardscape in Houston area- We are a full service design and build general contractor designing and constructing innovative residential and commercial structures from the footer to the roof we provide competitive, artistic and elaborate articulate construction from framing to molding, tray ceilings, new home construction and full phase remodeling..let AAA Affordable Contractors work for you! FREE ONLINE CONCRETE CALCULATOR BELOW! - Certified flatwork technicians-DECORATIVE CONCRETE-STUNNING PATIOS, QUARRY TILE, STONES, SLATE ALL TYPES MASONRY, POOLS Patio AND DRIVEWAY SPECIALISTS
Let Concreteforever.com design/Build your next Exotic patio, driveway, fire pit, stamped patio, stamped concrete patio, stamped driveway, Certified Concrete Contractors, stamped concrete contractors, Patterned concrete, stamped concrete, patterned cement, stamped cement, Residential and Commercial concrete contractors, concrete foundation contractors, stamped concrete contractors, stamped concrete driveways, Give your patio a new image with authentic stamped articulate decorative concrete from affordable concrete contractors, fire-pit, patio extension, driveways extension or masonry project for your dream driveway, exotic hardscapes, Let the our ASI Certified Stamped concrete contractors and technicians perform your next exotic concrete hardsape, patio, pool or watergarden! Stamped concrete contractor in houston texas, stamped cement, stamped concrete contractors, stamped concrete driveway, concrete contractors for your foundation, stamped concrete, decorative stamped concrete, Custom Hardscape in Houston area- We are a full service design and build general contractor designing and constructing innovative residential and commercial structures from the footer to the roof we provide competitive, artistic and elaborate articulate construction from framing to molding, tray ceilings, new home construction and full phase remodeling..let AAA Affordable Contractors work for you! FREE ONLINE CONCRETE CALCULATOR BELOW! - Certified flatwork technicians-DECORATIVE CONCRETE-STUNNING PATIOS, QUARRY TILE, STONES, SLATE ALL TYPES MASONRY, POOLS Patio AND DRIVEWAY SPECIALISTS
Wednesday, January 19, 2000
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Scientific Principles of Concrete Cement Houston
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CONCRETE........What is in This Stuff?
The importance of concrete in modern society cannot be under-estimated. Look around you and you will find concrete structures everywhere such as buildings, roads, bridges, and dams. There is no escaping the impact concrete makes on your everyday life. So what is it?
Concrete is a composite material which is made up of a filler and a binder. The binder (cement paste) "glues" the filler together to form a synthetic conglomerate. The constituents used for the binder are cement and water, while the filler can be fine or coarse aggregate. The role of these constituents will be discussed in this section.
Cement, as it is commonly known, is a mixture of compounds made by burning limestone and clay together at very high temperatures ranging from 1400 to 1600 [[ring]]C.
Although there are other cements for special purposes, this module will focus solely on portland cement and its properties. The production of portland cement begins with the quarrying of limestone, CaCO3. Huge crushers break the blasted limestone into small pieces. The crushed limestone is then mixed with clay (or shale), sand, and iron ore and ground together to form a homogeneous powder. However, this powder is microscopically heterogeneous. (See flowchart.)
Figure 1: A flow diagram of Portland Cement production.
The mixture is heated in kilns that are long rotating steel cylinders on an incline. The kilns may be up to 6 meters in diameter and 180 meters in length. The mixture of raw materials enters at the high end of the cylinder and slowly moves along the length of the kiln due to the constant rotation and inclination. At the low end of the kiln, a fuel is injected and burned, thus providing the heat necessary to make the materials react. It can take up to 2 hours for the mixture to pass through the kiln, depending upon the length of the cylinder.
Rotary kiln;
As the mixture moves down the cylinder, it progresses through four stages of transformation. Initially, any free water in the powder is lost by evaporation. Next, decomposition occurs from the loss of bound water and carbon dioxide. This is called calcination. The third stage is called clinkering. During this stage, the calcium silicates are formed. The final stage is the cooling stage.
The marble-sized pieces produced by the kiln are referred to as clinker. Clinker is actually a mixture of four compounds which will be discussed later. The clinker is cooled, ground, and mixed with a small amount of gypsum (which regulates setting) to produce the general-purpose portland cement.
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. It is then separated into various sizes by passing the material through a series of screens with different size openings.
Table 1: Classes of Aggregates class examples of aggregates used uses
ultra-lightweight vermiculite
ceramic spheres
perlite lightweight concrete which can be sawed or nailed, also for its insulating properties
lightweight expanded clay
shale or slate
crushed brick used primarily for making lightweight concrete for structures, also used for its insulating properties.
normal weight crushed limestone
sand
river gravel
crushed recycled concrete used for normal concrete projects
heavyweight steel or iron shot
steel or iron pellets used for making high density concrete for shielding against nuclear radiation
The choice of aggregate is determined by the proposed use of the concrete. Normally sand, gravel, and crushed stone are used as aggregates to make concrete. The aggregate should be well-graded to improve packing efficiency and minimize the amount of cement paste needed. Also, this makes the concrete more workable.
Properties of Concrete
Concrete has many properties that make it a popular construction material. The correct proportion of ingredients, placement, and curing are needed in order for these properties to be optimal.
Good-quality concrete has many advantages that add to its popularity. First, it is economical when ingredients are readily available. Concrete's long life and relatively low maintenance requirements increase its economic benefits. Concrete is not as likely to rot, corrode, or decay as other building materials. Concrete has the ability to be molded or cast into almost any desired shape. Building of the molds and casting can occur on the work-site which reduces costs.
Concrete is a non-combustible material which makes it fire-safe and able withstand high temperatures. It is resistant to wind, water, rodents, and insects. Hence, concrete is often used for storm shelters.
Concrete does have some limitations despite its numerous advantages. Concrete has a relatively low tensile strength (compared to other building materials), low ductility, low strength-to-weight ratio, and is susceptible to cracking. Concrete remains the material of choice for many applications regardless of these limitations.
Hydration of Portland Cement
Concrete is prepared by mixing cement, water, and aggregate together to make a workable paste. It is molded or placed as desired, consolidated, and then left to harden. Concrete does not need to dry out in order to harden as commonly thought.
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.
Schematic illustration of the pores in calcium silicate through different stages of hydration.
The above diagrams represent the formation of pores as calcium silicate hydrate is formed. Note in diagram (a) that hydration has not yet occurred and the pores (empty spaces between grains) are filled with water. Diagram (b) represents the beginning of hydration. In diagram (c), the hydration continues. Although empty spaces still exist, they are filled with water and calcium hydroxide. Diagram (d) shows nearly hardened cement paste. Note that the majority of space is filled with calcium silicate hydrate. That which is not filled with the hardened hydrate is primarily calcium hydroxide solution. The hydration will continue as long as water is present and there are still unhydrated compounds in the cement paste.
Dicalcium silicate also affects the strength of concrete through its hydration. Dicalcium silicate reacts with water in a similar manner compared to tricalcium silicate, but much more slowly. The heat released is less than that by the hydration of tricalcium silicate because the dicalcium silicate is much less reactive. The products from the hydration of dicalcium silicate are the same as those for tricalcium silicate:
Dicalcium silicate + Water--->Calcium silicate hydrate + Calcium hydroxide +heat
2 Ca2SiO4 + 5 H2O---> 3 CaO.2SiO2.4H2O + Ca(OH)2 + 58.6 kJ
The other major components of portland cement, tricalcium aluminate and tetracalcium aluminoferrite also react with water. Their hydration chemistry is more complicated as they involve reactions with the gypsum as well. Because these reactions do not contribute significantly to strength, they will be neglected in this discussion. Although we have treated the hydration of each cement compound independently, this is not completely accurate. The rate of hydration of a compound may be affected by varying the concentration of another. In general, the rates of hydration during the first few days ranked from fastest to slowest are:
tricalcium aluminate > tricalcium silicate > tetracalcium aluminoferrite > dicalcium silicate.
Heat is evolved with cement hydration. This is due to the breaking and making of chemical bonds during hydration. The heat generated is shown below as a function of time.
Rate of heat evolution during the hydration of portland cement
The stage I hydrolysis of the cement compounds occurs rapidly with a temperature increase of several degrees. Stage II is known as the dormancy period. The evolution of heat slows dramatically in this stage. The dormancy period can last from one to three hours. During this period, the concrete is in a plastic state which allows the concrete to be transported and placed without any major difficulty. This is particularly important for the construction trade who must transport concrete to the job site. It is at the end of this stage that initial setting begins. In stages III and IV, the concrete starts to harden and the heat evolution increases due primarily to the hydration of tricalcium silicate. Stage V is reached after 36 hours. The slow formation of hydrate products occurs and continues as long as water and unhydrated silicates are present.
STRENGTH of Concrete
The strength of concrete is very much dependent upon the hydration reaction just discussed. Water plays a critical role, particularly the amount used. The strength of concrete increases when less water is used to make concrete. The hydration reaction itself consumes a specific amount of water. Concrete is actually mixed with more water than is needed for the hydration reactions. This extra water is added to give concrete sufficient workability. Flowing concrete is desired to achieve proper filling and composition of the forms. The water not consumed in the hydration reaction will remain in the microstructure pore space. These pores make the concrete weaker due to the lack of strength-forming calcium silicate hydrate bonds. Some pores will remain no matter how well the concrete has been compacted.
Figure 5: Demonstrating the relationship between the water/cement ratio and porosity. (the empty space)is determined by the water to cement ratio. The relationship between the water to cement ratio and strength is a very important issue when determining the compressive strength necessity for your particular project
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Scientific Principles of Concrete Cement Houston
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CONCRETE........What is in This Stuff?
The importance of concrete in modern society cannot be under-estimated. Look around you and you will find concrete structures everywhere such as buildings, roads, bridges, and dams. There is no escaping the impact concrete makes on your everyday life. So what is it?
Concrete is a composite material which is made up of a filler and a binder. The binder (cement paste) "glues" the filler together to form a synthetic conglomerate. The constituents used for the binder are cement and water, while the filler can be fine or coarse aggregate. The role of these constituents will be discussed in this section.
Cement, as it is commonly known, is a mixture of compounds made by burning limestone and clay together at very high temperatures ranging from 1400 to 1600 [[ring]]C.
Although there are other cements for special purposes, this module will focus solely on portland cement and its properties. The production of portland cement begins with the quarrying of limestone, CaCO3. Huge crushers break the blasted limestone into small pieces. The crushed limestone is then mixed with clay (or shale), sand, and iron ore and ground together to form a homogeneous powder. However, this powder is microscopically heterogeneous. (See flowchart.)
Figure 1: A flow diagram of Portland Cement production.
The mixture is heated in kilns that are long rotating steel cylinders on an incline. The kilns may be up to 6 meters in diameter and 180 meters in length. The mixture of raw materials enters at the high end of the cylinder and slowly moves along the length of the kiln due to the constant rotation and inclination. At the low end of the kiln, a fuel is injected and burned, thus providing the heat necessary to make the materials react. It can take up to 2 hours for the mixture to pass through the kiln, depending upon the length of the cylinder.
Rotary kiln;
As the mixture moves down the cylinder, it progresses through four stages of transformation. Initially, any free water in the powder is lost by evaporation. Next, decomposition occurs from the loss of bound water and carbon dioxide. This is called calcination. The third stage is called clinkering. During this stage, the calcium silicates are formed. The final stage is the cooling stage.
The marble-sized pieces produced by the kiln are referred to as clinker. Clinker is actually a mixture of four compounds which will be discussed later. The clinker is cooled, ground, and mixed with a small amount of gypsum (which regulates setting) to produce the general-purpose portland cement.
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. It is then separated into various sizes by passing the material through a series of screens with different size openings.
Table 1: Classes of Aggregates class examples of aggregates used uses
ultra-lightweight vermiculite
ceramic spheres
perlite lightweight concrete which can be sawed or nailed, also for its insulating properties
lightweight expanded clay
shale or slate
crushed brick used primarily for making lightweight concrete for structures, also used for its insulating properties.
normal weight crushed limestone
sand
river gravel
crushed recycled concrete used for normal concrete projects
heavyweight steel or iron shot
steel or iron pellets used for making high density concrete for shielding against nuclear radiation
The choice of aggregate is determined by the proposed use of the concrete. Normally sand, gravel, and crushed stone are used as aggregates to make concrete. The aggregate should be well-graded to improve packing efficiency and minimize the amount of cement paste needed. Also, this makes the concrete more workable.
Properties of Concrete
Concrete has many properties that make it a popular construction material. The correct proportion of ingredients, placement, and curing are needed in order for these properties to be optimal.
Good-quality concrete has many advantages that add to its popularity. First, it is economical when ingredients are readily available. Concrete's long life and relatively low maintenance requirements increase its economic benefits. Concrete is not as likely to rot, corrode, or decay as other building materials. Concrete has the ability to be molded or cast into almost any desired shape. Building of the molds and casting can occur on the work-site which reduces costs.
Concrete is a non-combustible material which makes it fire-safe and able withstand high temperatures. It is resistant to wind, water, rodents, and insects. Hence, concrete is often used for storm shelters.
Concrete does have some limitations despite its numerous advantages. Concrete has a relatively low tensile strength (compared to other building materials), low ductility, low strength-to-weight ratio, and is susceptible to cracking. Concrete remains the material of choice for many applications regardless of these limitations.
Hydration of Portland Cement
Concrete is prepared by mixing cement, water, and aggregate together to make a workable paste. It is molded or placed as desired, consolidated, and then left to harden. Concrete does not need to dry out in order to harden as commonly thought.
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.
Schematic illustration of the pores in calcium silicate through different stages of hydration.
The above diagrams represent the formation of pores as calcium silicate hydrate is formed. Note in diagram (a) that hydration has not yet occurred and the pores (empty spaces between grains) are filled with water. Diagram (b) represents the beginning of hydration. In diagram (c), the hydration continues. Although empty spaces still exist, they are filled with water and calcium hydroxide. Diagram (d) shows nearly hardened cement paste. Note that the majority of space is filled with calcium silicate hydrate. That which is not filled with the hardened hydrate is primarily calcium hydroxide solution. The hydration will continue as long as water is present and there are still unhydrated compounds in the cement paste.
Dicalcium silicate also affects the strength of concrete through its hydration. Dicalcium silicate reacts with water in a similar manner compared to tricalcium silicate, but much more slowly. The heat released is less than that by the hydration of tricalcium silicate because the dicalcium silicate is much less reactive. The products from the hydration of dicalcium silicate are the same as those for tricalcium silicate:
Dicalcium silicate + Water--->Calcium silicate hydrate + Calcium hydroxide +heat
2 Ca2SiO4 + 5 H2O---> 3 CaO.2SiO2.4H2O + Ca(OH)2 + 58.6 kJ
The other major components of portland cement, tricalcium aluminate and tetracalcium aluminoferrite also react with water. Their hydration chemistry is more complicated as they involve reactions with the gypsum as well. Because these reactions do not contribute significantly to strength, they will be neglected in this discussion. Although we have treated the hydration of each cement compound independently, this is not completely accurate. The rate of hydration of a compound may be affected by varying the concentration of another. In general, the rates of hydration during the first few days ranked from fastest to slowest are:
tricalcium aluminate > tricalcium silicate > tetracalcium aluminoferrite > dicalcium silicate.
Heat is evolved with cement hydration. This is due to the breaking and making of chemical bonds during hydration. The heat generated is shown below as a function of time.
Rate of heat evolution during the hydration of portland cement
The stage I hydrolysis of the cement compounds occurs rapidly with a temperature increase of several degrees. Stage II is known as the dormancy period. The evolution of heat slows dramatically in this stage. The dormancy period can last from one to three hours. During this period, the concrete is in a plastic state which allows the concrete to be transported and placed without any major difficulty. This is particularly important for the construction trade who must transport concrete to the job site. It is at the end of this stage that initial setting begins. In stages III and IV, the concrete starts to harden and the heat evolution increases due primarily to the hydration of tricalcium silicate. Stage V is reached after 36 hours. The slow formation of hydrate products occurs and continues as long as water and unhydrated silicates are present.
STRENGTH of Concrete
The strength of concrete is very much dependent upon the hydration reaction just discussed. Water plays a critical role, particularly the amount used. The strength of concrete increases when less water is used to make concrete. The hydration reaction itself consumes a specific amount of water. Concrete is actually mixed with more water than is needed for the hydration reactions. This extra water is added to give concrete sufficient workability. Flowing concrete is desired to achieve proper filling and composition of the forms. The water not consumed in the hydration reaction will remain in the microstructure pore space. These pores make the concrete weaker due to the lack of strength-forming calcium silicate hydrate bonds. Some pores will remain no matter how well the concrete has been compacted.
Figure 5: Demonstrating the relationship between the water/cement ratio and porosity. (the empty space)is determined by the water to cement ratio. The relationship between the water to cement ratio and strength is a very important issue when determining the compressive strength necessity for your particular project
houston hardscapes
hardscape
concrete slab
concrete houston
american concrete
concrete hardscape
concrete patio
hardscape designs
concrete counter
cemen
--------------------------------------------------------------------------------
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Concrete Houston, Stamped C...
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Historical Timeline of Conc...
Home
Houston Pier and Beam Concr...
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Stamped Concrete Patios, Dr...
Houstons #1 Home Builders
Instantly estimate your dream Patio!
Houston Concrete Contractors
stamped concrete Lithochrome color chart
Are you Ready?
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