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Quality Control for Interlocking Concrete Pavement Production06-01-00 | 16
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 Pavestone personnel are specially trained to make fine-tuned adjustments during batching and mixing to ensure consistent quality.

Landscape Architects and specifiers can benefit from a basic understanding of the manufacturing process and quality control procedures used in the production of interlocking concrete paving stones. This knowledge gives the designer the ability to understand the technical aspects of installation and performance and some of the variables that can come into play. This is important because the quality and consistency of "dry cast" products can be extremely sensitive to variations in the raw materials, (such as cement, aggregates, water, and pigments), that are used in mechanized production.

According to George Gilbert, Vice President of Operations for Pavestone Co. of Dallas, Texas, Landscape Architects and engineers frequently take the time to visit its production facilities and observe the actual fabrication process in person.

"When you're applying a systematic approach to quality control there are three important control points for ensuring consistent production of interlocking concrete paving stones," explained Gilbert. "The control and inspection of incoming raw materials, close monitoring of the batching and mixing process, and testing for conformation are key elements for success and are extremely important for production of a consistent finished product."

In-house quality control personnel, in addition to monitoring incoming raw materials, also ensure that the mixture of pigments, chemicals, cement, aggregates and other additives are consistent for each product. In many cases suppliers of these raw materials assist in the process by supplying up-to-date test reports. Quality tests are conducted on a routine basis to assist in controlling the batch proportioning, aggregate gradation, and aggregate moisture content. The quality control program also involves frequent inspection of the equipment, including the mixers, scales and molds.

 Concrete paving stones are frequently measured for conformance to ASTM standards. Visual inspections are also completed on a routine basis

According to Gilbert, who has been involved in paver production for almost 20 years, there is much more to the process of quality control than simple routine testing and inspection. "The number of variables involved is such that it often becomes more of an art than a science. The fact is, the texture and composition of raw materials can quite easily change several times within an eight-hour shift. Moisture content is particularly important in this regard. Our production personnel are specially trained to make fine tuning adjustments on an ongoing basis. They are also encouraged to take corrective action when they see something that's not in accordance with our quality standards."

"On a number of occasions we've taken production personnel right to point-of-sale locations to examine the finished product. This gives our staff a chance to see the product from the point of view of the end-user. This approach has been very effective in developing a team approach to quality control."

"In effect, each shift is responsible for confirming that the raw materials are acceptable and for inspecting the molds and equipment to ensure they are in top-notch condition. They are also responsible for ensuring that the finished product meets our own in-house quality control standards and the ASTM standard. We also schedule periodic meetings to review laboratory tests, and analyze production records." In Gilbert's view, it's a process that involves continuous improvement. "Every bundle of interlocking concrete paving stones we produce is labeled and bar-coded. When required we can track our records back to the date it was produced."

 Pavestone frequently organizes tours for landscape architects, specifiers and engineers.

In addition to this intensive scrutiny of the production process itself, considerable attention is paid to the quality control of the finished product. This includes sampling the product for quality control standards and independent third party testing in accordance with established ASTM standards. Paving stones are typically tested for compressive strength, absorption, resistance to freezing and thawing, and abrasion resistance. Paving units are also visually inspected to ensure they are free of defects. Typically, interlocking concrete paving stones are expected to meet or exceed the requirements listed in ASTM C 936-96, Standard Specification For Solid Concrete Interlocking Paving Units. There are also several ASTM standards, which are applicable to the various components of interlocking concrete paving stone manufacture and installation.

Gilbert also pointed out that the quality control process for colors and textures often extends into the field. "On many occasions we are involved with color matching and supplying paving stones for installation of site mock-ups. In the case of tumbled pavers, which are becoming increasingly popular, it is common for the Landscape Architect to be directly involved in achieving the right effect and texture. In fact, some of the new equipment we have allows us to modify the tumbled effect to meet specific design criteria for the Landscape Architect." LASN

 Monitoring and inspections of incoming raw materials is extremely important to ensure consistent paver quality.
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