Concrete Knowledge Center

Kearney Concrete Co. offers this section to inform contractors, homeowners and purchasers on the basic vocabulary of our industry. The following terms and definitions are widely used in our industry and are provided to assist you when you call to order concrete, acquire information on your next project, or have questions about optimizing your concrete mix.

Concrete

We specialize in producing high quality concrete.  We will work to ensure the concrete mix design meets the strength, performance, and durability you desire for your project.  We strictly adhere to all ACI guidelines and with our chemical admixtures, have the ability to produce high-quality concrete that will meet and exceed your expectations.  In general, the basic materials required to produce concrete are cement, aggregate, water, and chemical admixtures.

Cement

Holcim Cement is our cement provider and we use the terminal located in Superior, Nebraska. Currently, we have the ability to keep nearly 750,000 pounds of cement on hand to complete your projects and are seeking future expansion opportunities.  Commonly used types of cement as defined by ACI: ASTM C 150 defines five types of Portland cement, but only four are typically used in residential construction. Type I is a general purpose cement; Type II is a cement that provides moderate protection against sulfate attack; Type III is high-early-strength cement that is sometimes used to achieve faster setting and increased early strengths; and Type V is a cement that is used where severe

exposure to sulfates is anticipated. Blended cement, defined by ASTM C 595, and hydraulic cement, defined by ASTM C 1157, are occasionally used in residential construction. Blended cements consist of preblended combinations of portland cement and supplementary cementitious materials.”

Aggregate

Broadfoot Sand and Gravel Company supplies us with our 3/8 nominal fine aggregate (Commonly recognized as 47B Fine Aggregate).  Depending on your job, different types of fine aggregates are available.  In central Nebraska, our concrete gravel is unique because of our specific location along the North Platte River.

Limestone in the form of ¾ nominal White Rock (Commonly recognized as 47B Course Aggregate)is our most popular course aggregate.  We do have the ability to attain any type of course aggregate to any project’s unique specifications.  Adding ¾ nominal White Rock to your concrete mix design increases the overall durability and performance of your concrete.  The use of 47B course aggregate in exterior concrete is recommended for our location.

Water

Water affects the concrete’s consistency and workability.  In general, the more water added to your concrete mix design, the concrete’s viscosity increases.  However, the downside of adding a lot of water to your concrete mix design increases the water/cement ratio, which affects the concrete’s overall performance.  If your project requires the use of high slump concrete (6-8 inch slump), this can be achieved while maintaining specified water/cement ratios.

Chemical Admixtures

ACI 116R-00 defines the term admixture as “a material other than water, aggregates, hydraulic cement, and fiber reinforcement, used as an ingredient of a cementitious mixture to modify its freshly mixed, setting, or hardened properties and that is added to the batch before or during its mixing.” In ACI 212.3R it is stated that “chemical admixtures are used to enhance the properties of concrete and mortar in the plastic and hardened state. These properties may be modified to increase compressive and flexural strength at all ages, decrease permeability and improve durability, inhibit corrosion, reduce shrinkage, accelerate or retard initial set, increase slump and workability, improve pumpability and finishability, increase cement efficiency, and improve the economy of the mixture. An admixture or combination of admixtures may be the only feasible means of achieving the desired results. In certain instances, the desired objectives may be best achieved by mixture changes in addition to proper admixture usage.” Chemical admixtures are materials that are added to the constituents of a concrete mixture, in most cases, specified as a volume in relation to the mass of the cement or total cementitious materials. The admixtures interact with the hydrating cementitious system by physical and chemical actions, modifying one or more of the properties of concrete in the fresh and/or hardened states. Concrete is composed principally of aggregates, hydraulic cement, and water, and may contain other cementitious materials and chemical admixtures. It will contain some amount of entrapped air and may also contain purposely entrained air obtained by use of a chemical admixture or airentraining cement. Chemical admixtures are also frequently used to accelerate, retard, improve workability, reduce mixing water requirements, increase strength, improve durability, or alter other properties of the concrete. There are many kinds of chemical admixtures that can function in a variety of ways to modify the chemical and physical properties of concrete. This bulletin provides information on the types of chemical admixtures and how they affect the properties of concrete, mortar, and grout. (http://www.concrete.org/general/fE4-03.pdf)

Chemical Admixtures that we currently stock are:

  • RECOVER – Hydration stabilizer used especially in hot weather that increases the concrete’s workability over a longer time period
  • GLENIUM 7700 – High range water reducing admixture
  • MB-AE 90 – Air entraining admixture designed to give exterior concrete (non-power troweled concrete slabs) freeze/thaw capability. (Crucial in Nebraska–a must have!)
  • POLYHEED 900 – Mid range water reducing admixture
  • POZZOLITH 122 HE – Calcium Chloride accelerating admixture designed to speed the set and cure of the concrete **This chemical is corrosive to steel**
  • POZZUTEC 20+ – Non-chloride accelerating admixture designed to speed the set and cure of the concrete  **This chemical is not corrosive to steel**

Finally, we have the ability to attain any chemical admixture required to complete your project.  Please contact us for more information!

Water/Cement Ratio

  • Definition
    • It is the ratio of the weight of water to the weight of cement used in a concrete mix and has an important influence on the quality of concrete produced. A lower water-cement ratio leads to higher strength and durability, but may make the mix more difficult to place. Placement difficulties can be resolved by using plasticizers or super-plasticizers.

Slump

  • Definition
    • Slump is a measure of concrete consistency or fluidity. For given proportions of cement and aggregates (without admixtures), the higher the slump, the wetter the mix.  Four-inch (4”) slump is very common with normal weight concrete and is a good average slump.  Above-average slump—due to the addition of water—considerably reduces the strength, durability and permeability of concrete and can cause segregation. When possible, admixtures should be used instead of water to achieve higher slump.

Compressive Strength

  • Definition
    • Is the capacity of a material or structure to withstand axially directed pushing forces. When the limit of compressive strength is reached, materials are crushed. Concrete can be made to have high compressive strength, e.g. many concrete structures have compressive strengths in excess of 7200 PSI, whereas a material such as soft sandstone may have a compressive strength as low as 725 to 1450 PSI. Compressive strength is often measured on a universal testing machine. Measurements of compressive strength are affected by the specific test method and conditions of measurement. Compressive strengths are usually reported in relationship to a specific technical standard. The standard compressive strength test for concrete is: ASTM C39 / C39M – 11a Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens. More information can be found at http://www.astm.org/Standards/C39.htm.

 

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