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Capturing the South Texas Market: Southwest Concrete Products, L.P. Opportunities for Concrete Education Expand The Importance of Testing Concrete Masonry Units Learning the Benefits of Concrete Masonry All About OSHA - Post Inspection (Part 3 of 3) Company Exceeds Industry Prediction: Bark River Concrete Products Expand Your Product Line: Antiquing Machine and Founders Spray Machine Besser Block Talk: Bullnose Concrete Masonry Units
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Production
Tip Lightweight Block Production Throughout the concrete masonry industry there are many producers using large quantities of lightweight material. The production of lightweight units requires extra attention to the mixing procedures because of the unique properties of lightweight aggregates. In order to be considered lightweight, the aggregate must be composed predominately of lightweight cellular and granular inorganic material. In general terms, any air-dried concrete with a density of 105 pounds or less per cubic foot (1680 kg/cu m) is considered lightweight. The various types of structural lightweight materials are described in ASTM C331. The classifications follow: Manufactured lightweights: These are aggregates prepared by expanding, pelletizing or sintering products such as blast furnace slag, clay, fly ash, shales and slates. Natural lightweights: These are aggregates prepared by processing natural materials such as pumice, scoria, tuff and diatomite. By-product lightweights: These are aggregates consisting of end products from coal or coke combustion. Care should be taken in transporting, storing and retrieving lightweight aggregates because of their segregation characteristics. Segregation can occur in bins, during transportation to the yard, or while conveying the material from one point to another in your facility. Many companies wet the lightweight material to minimize segregation. Lightweight particles have a thirst that must be satisfied to get the best use of the cement, which acts as the binder in the mix. Proper hydration of the lightweight aggregate will produce concrete that is strong and less likely to chip or spall. The unique qualities of lightweight aggregates require a different mixing procedure than is used for regular sand and gravel mixes. It is important to know the percent of moisture content in the lightweight aggregates being utilized in production of the concrete masonry units. This can be done using a simple calculation. Grab a handful of the aggregate and weigh it. Oven dry the aggregate and weigh it again. Subtract the dry weight from the wet weight and divide by the dry weight, multiply by 100 to discover the percent of moisture contained in the sample.
Lightweight particle
The scales can now be adjusted to compensate for the moisture that is already contained in the lightweight aggregate. This helps to keep the cement to aggregate ratio consistent and the yield of concrete products per mix more accurate. After considerable research, it is now accepted that the following mixing sequence for production of lightweight concrete masonry units gives optimum results. Safety First: Always follow lockout/tagout and, if applicable, confined spaces procedures before starting the mixer. Contact federal or state OSHA to determine if your mixer is classified as a confined space. Lightweight Mixing Instructions 1. Charge (load) mixer with all aggregates 2. Add ½ to ¾ of the total mixing water based on the absorption characteristics of the aggregate used. Use of a gauge or metering device is recommended for accurate measurement. The water should be pure enough to drink. Water should be added from more than one distribution point such as a spray bar to produce a uniform mix. 3. Mix for a minimum of 30 seconds. 4. Add all cementitious materials. 5. Add the balance of the mixing water. 6. Continue mixing for a minimum of 2 to 4 minutes in a ribbon mixer. 7. When tempering water is required to return the mix to proper consistency, mix for an additional minute. 8. Test the first batch for the moisture requirements and consistency. Follow this mixing procedure for lightweight production to produce strong, aesthetically pleasing concrete masonry units and the potential for increased yields.
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