To ensure a level of consistency between cement-producing plants, certain chemical and physical limits are placed on cements. These chemical limits are defined by a variety of standards and specifications. For instance, Portland cements and blended hydraulic cements for concrete in the U.S. conform to the American Society for Testing and Materials (ASTM) C150 (Standard Specification for Portland Cement), C595 (Standard Specification for Blended Hydraulic Cement) or C1157 (Performance Specification for Hydraulic Cements). Some state agencies refer to very similar specifications: AASHTO M 85 for Portland cement and M 240 for blended cements. These specifications refer to standard test methods to assure that the testing is performed in the same manner. For example, ASTM C109 (Standard Test Method for Compressive Strength for Hydraulic Cement Mortars using 2-inch Cube Specimens), describes in detail how to fabricate and test mortar cubes for compressive strength testing in a standardized fashion. Type II cements are limited in C150/M 85 to a maximum of 8 percent by mass of tricalcium aluminate (a cement phase, often abbreviated C3A), which impacts a cement’s sulfate resistance. Certain oxides are also themselves limited by specifications: For example, the magnesia (MgO) content which is limited to 6 percent maximum by weight for portland cements, because it can impact soundness at higher levels.
For a good concrete mix, aggregates need to be clean, hard, strong particles free of absorbed chemicals or coatings of clay and other fine materials that could cause the deterioration of concrete. Aggregates, which account for 60 to 75 percent of the total volume of concrete, are divided into two distinct categories--fine and coarse. Fine aggregates generally consist of natural sand or crushed stone with most particles passing through a 3/8-inch sieve. Coarse aggregates are any particles greater than 0.19 inch, but generally range between 3/8 and 1.5 inches in diameter. Gravels constitute the majority of coarse aggregate used in concrete with crushed stone making up most of the remainder.
In its simplest form, concrete is a mixture of paste and aggregates, or rocks. The paste, composed of portland cement and water, coats the surface of the fine (small) and coarse (larger) aggregates. Through a chemical reaction called hydration, the paste hardens and gains strength to form the rock-like mass known as concrete. Within this process lies the key to a remarkable trait of concrete: it's plastic and malleable when newly mixed, strong and durable when hardened. These qualities explain why one material, concrete, can build skyscrapers, bridges, sidewalks and superhighways, houses and dams. Cement is one of the four components that makes ready mix concrete. The cement is a bonding agent. Just like a glue that bounds the stone and the sand together to create the concrete once it hardens and bonds. The water is the catalyst which the cement consumes during the bonding chemical process. The cement we use is a type-2 portlan cement designed to cure for 28 days. It’s important that your concrete remains moist during that time to ensure it comes to maximum strength.
The key to achieving a strong, durable concrete rests in the careful proportioning and mixing of the ingredients. A mixture that does not have enough paste to fill all the voids between the aggregates will be difficult to place and will produce rough surfaces and porous concrete. A mixture with an excess of cement paste will be easy to place and will produce a smooth surface; however, the resulting concrete is not cost-effective and can more easily crack. Portland cement's chemistry comes to life in the presence of water. Cement and water form a paste that coats each particle of stone and sand—the aggregates. Through a chemical reaction called hydration, the cement paste hardens and gains strength. The quality of the paste determines the character of the concrete. The strength of the paste, in turn, depends on the ratio of water to cement. The water-cement ratio is the weight of the mixing water divided by the weight of the cement. High-quality concrete is produced by lowering the water-cement ratio as much as possible without sacrificing the workability of fresh concrete, allowing it to be properly placed, consolidated, and cured. A properly designed mixture possesses the desired workability for the fresh concrete and the required durability and strength for the hardened concrete. Typically, a mix is about 10 to 15 percent cement, 60 to 75 percent aggregate and 15 to 20 percent water. Entrained air in many concrete mixes may also take up another 5 to 8 percent.
Almost any natural water that is drinkable and has no pronounced taste or odor may be used as mixing water for concrete. Excessive impurities in mixing water not only may affect setting time and concrete strength, but can also cause efflorescence, staining, corrosion of reinforcement, volume instability, and reduced durability. Concrete mixture specifications usually set limits on chlorides, sulfates, alkalis, and solids in mixing water unless tests can be performed to determine the effect the impurity has on the final concrete. Although most drinking water is suitable for mixing concrete, aggregates are chosen carefully. Aggregates comprise 60 to 75 percent of the total volume of concrete. The type and size of aggregate used depends on the thickness and purpose of the final concrete product. Relatively thin building sections call for small coarse aggregate, though aggregates up to six inches in diameter have been used in large dams. A continuous gradation of particle sizes is desirable for efficient use of the paste. In addition, aggregates should be clean and free from any matter that might affect the quality of the concrete.
Soon after the aggregates, water, and the cement are combined, the mixture starts to harden. All portland cements are hydraulic cements that set and harden through a chemical reaction with water call hydration. During this reaction, a node forms on the surface of each cement particle. The node grows and expands until it links up with nodes from other cement particles or adheres to adjacent aggregates. Once the concrete is thoroughly mixed and workable it should be placed in forms before the mixture becomes too stiff. During placement, the concrete is consolidated to compact it within the forms and to eliminate potential flaws, such as honeycombs and air pockets. For slabs, concrete is left to stand until the surface moisture film disappears, then a wood or metal handfloat is used to smooth off the concrete. Floating produces a relatively even, but slightly rough, texture that has good slip resistance and is frequently used as a final finish for exterior slabs. If a smooth, hard, dense surface is required, floating is followed by steel troweling. Curing begins after the exposed surfaces of the concrete have hardened sufficiently to resist marring. Curing ensures the continued hydration of the cement so that the concrete continues to gain strength. Concrete surfaces are cured by sprinkling with water fog, or by using moisture-retaining fabrics such as burlap or cotton mats. Other curing methods prevent evaporation of the water by sealing the surface with plastic or special sprays called curing compounds. Special techniques are used for curing concrete during extremely cold or hot weather to protect the concrete. The longer the concrete is kept moist, the stronger and more durable it will become. The rate of hardening depends upon the composition and fineness of the cement, the mix proportions, and the moisture and temperature conditions. Concrete continues to get stronger as it gets older. Most of the hydration and strength gain take place within the first month of concrete's life cycle, but hydration continues at a slower rate for many years.
Oh we don't like delays, so we will do everything we can to keep this from happening. But we live and work in the real world so delays can happen. But here at On Site Concrete Inc. will work as hard as we can to avoid any delays in production and the expected delivery date.
Just some random pictures of things we have done and dogs we have rescued.
This is a manhole base being set with the City Of Sacramento water department.
Getting ready for a CalTrans night job in the rain in the town of Folsom.
Here you can see how a basement is added to a home in Sacramento that was originally built on a stone foundation.
This is just a picture we took one day when we had some extra time and the UAV at the yard.
This is Jake and Marty back when it all started in 2002. This was at our first location in the City of Sacramento.
Working at the end of the active runway at Sacramento International Airport.
We have been on many episodes of Yard Crashers. See our YouTube channel for some of them.
Setting fence posts outside of Davis California for a soccer complex.
Pouring the retaining wall for an above ground pool overlooking Folsom Lake.
If our concrete can hold up there 500 foot tower, then it can hold up your project.
This is the last tie in for the Elkhorn Bvd drainage tunnel. The tunnel is 15 foot tall.
Pouring the wall along Folsom BVD near Power Inn Rd. This is a sound wall and car barrier.
Someone dumped this puppy off on Jackson Highway. If it wasn't for Indy he would have been hit for sure.
Just like the others he was dumped off. People can be so cruel. He only took a cookie to trust us..
This girl took 4 years to trust us. One day she just showed up. But would not trust anybody.
This is 1 of 5 dogs we rescued. People have abandon dogs at our yard. It took 2 years for him to trust us.
This was about 1 month after Charlie began to trust us and play with us. It was a 4 year process..
This was the moment we were able to touch her. Over 4 long years in the making to get her to do this.. YES!!
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