Strengthening the concrete supply chain

| Published on May 8, 2014

By understanding customer concerns, aggregate producers can differentiate product offerings and provide better customer service.

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Providing high-quality customer service often boils down to understanding your customer’s needs and helping to solve their problems.

Tim Cost, senior technical service engineer for Holcim (US) Inc, says that a number of emerging trends can improve product performance throughout the construction materials supply chain. Aggregates producers can differentiate themselves from the competition by understanding these trends and meeting customer needs.

Aggregate grading

Research into concrete cracking suggests that using a wider range of product sizes may help prevent cracking.

Tim Cost

Tim Cost

“One of the things that state DOTs (Departments of Transportation) are studying more and more closely these days is how enhanced aggregate gradings can improve the quality of concrete and can, perhaps, reduce the incidence of cracking, especially on bridge decks,” Cost says.

“Some of the new specifications that are evolving call for improved gradings for concrete aggregates,” he adds. “This often necessitates the concrete producer to use a third and even a fourth aggregate in their concrete, rather than just a fine or coarse aggregate, which has traditionally been the default.”

These additional sizes are often intermediate sized materials, which can pose a production challenge for some aggregate producers. The same size range of material is frequently used in asphalt specs, leaving available sources somewhat depleted.

“Even places where the predominant coarse aggregate for concrete might be a crushed limestone or granite, an available intermediate aggregate might be a pea gravel, perhaps at some cost premium,” Cost notes.

While results can differ from one region — and geology — to another, Cost says that many concrete producers are seeing a variety of benefits to enhanced aggregate grading. Besides reducing cracking, it can also improve concrete pumpability and finishing.

“Every day, we’re finding more and more justification for it,” he says.

Concrete curing

Another area of research shows that replacing a small percentage of the natural sand in concrete mixes with lightweight aggregate fines can positively impact curing. In fact, some state Departments of Transportation, including Louisiana DOT, are beginning to consider lightweight aggregates in the mix design for bridge decks.

Lightweight aggregates are generally expanded shale, clay or slate that has been processed through a kiln and crushed into fine particles in the general size ranges of natural sands.

Because the fine particles are porous, they absorb and retain some mix water in the concrete. As the free mix water in the paste is consumed by hydration or lost to evaporate over time, Cost says, these particles can release water back into the paste.

“Internal curing is a way of keeping the concrete saturated in a more perfect way than through external curing,” he explains. “To replace the moisture loss using the internal porous particles, you slow the shrinkage rate of concrete way down over time, and it’s really useful in mitigating cracking.”

Numerous studies on the use of lightweight fine aggregates in concrete are under way, including one by Purdue University’s Michael Golias, Javier Castro and Jason Weiss. The percentage of lightweight aggregates to be used depends on a number of factors including the top sizes and type of material.

“It’s not a great deal; it may be around 15 percent of your sand,” Cost says. “Implementation of this is just beginning in many areas, but I think you’re going to be hearing more and more about it.”

Material handling and specs

In addition to tracking materials trends, operators should also consider how specification changes may impact their customers. For example, as natural aggregates become depleted in certain areas, local supplies are supplemented with material imported into the market.

“When crushed stone is mined and brought in by a barge or ship, the amount of handling that is involved sometimes generates additional fracture fines in the supply that may increase the amount of material passing the #200 sieve, often in excess of what’s allowed,” Cost says.

While DOT specifications were designed to prevent organic-type fines such as clay particles in natural aggregates, what some are finding is that the dust fracture fines from crushed stone may not be deleterious at all, and may, in some cases, be beneficial.

“The state DOTs are having to take a second look at their specifications and evaluate whether that’s a justified requirement any more,” he explains. “Specifications require continual review in the interest of quality.”

By paying attention to developing research and specifications, aggregate producers can help customers solve operational challenges and move from a commodity mentality to a service-oriented partnership with their customers.

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