Greener Cement Achieves Capital Improvement Project

 

Protecting the Environment, Enriching the Community

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At cement plants, proper moisture content is one of the biggest considerations for raw material handling and preparation. It’s a situation familiar to Goldilocks: Materials shouldn’t be too wet nor too dry, but “just right.” By reducing the moisture content of the raw materials, significant energy savings can be achieved for the raw feed that enters the preheater/precalciner system.
 

A lower moisture content in raw materials not only saves energy, but also helps eliminate blockages in the material transport systems. These systems include belts and chutes that would otherwise make the feed material sticky during periods of high precipitation. By contrast, having enough moisture in the raw feed helps reduce or eliminate dusting when handling materials during dry weather periods. The appropriate moisture content is therefore critical to three criteria: minimizing energy use, promoting efficient material handling, and protecting air quality.

 

Investing in their Own Future – Through Testing 

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When Monarch initiated a capital improvement project at the Humboldt plant – a raw materials storage facility designed to keep the materials “just right,” the company made a strategic decision to test its own newly developed Type IL portland-limestone cement (PLC) before bringing that cement to market.  With its increased limestone content, PLC offers up to 10% savings in CO2 compared to the more traditional portland cement formulations. Until this project, Monarch’s predominant product was Type I/II portland cement. 
 

The 97,500-square-foot industrial building requiring 6,000 cubic yards of cast-in-place concrete offered an opportunity for Monarch to test the new cement’s performance versus its traditional Type I/II product in a demanding application. The construction comprised above- and below-grade members, as well as vertical and horizontal members, including the foundation, piers and piles, walls, interior floor slab, , and surrounding pavement. These members would be put to the test, as operations at the storage facility involve fully loaded tractor trailers delivering materials inside the building and other heavy equipment such as front-end loaders and 75-ton dump trucks handling materials within the 300- by 325-foot building. With a Midwest location, concrete at the Humboldt facility needed to be highly durable in order to withstand the numerous freeze-thaw cycles that occur annually to provide a long lifespan.  
 

With these goals in mind, the materials storage building was both a construction project and a research project. A single mix design was identified to meet all the design criteria for the various classes of concrete required for the project and to maximize the amount of data that could be generated. The initial footings and wall placements were made with Type I/II cement before switching to the PLC mix for most of the project. Properties measured to compare the mixes were compressive strength, surface resistivity, water demand, air-entraining admixture dosage, and consistency (slump), while color was also evaluated. More than 250 concrete samples were tested throughout the project, with the PLC concrete showing virtually identical performance to the portland cement concrete. Compressive strengths at seven days were 4,400 psi, increasing to 5,500 psi by 28 days and 5,800 psi by 56 days.
 

Admixture Technology as a Solution to Variable Placing Conditions

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Construction work occurred from April through early December 2021. The eight-month schedule encompassed spring to late fall weather, with temperatures ranging from 48 to 94 degrees Fahrenheit. That included winds up to 25 miles per hour at times and relative humidities from quite low (23%) to very high (97%). Concrete was placed primarily by pump as well as truck chutes, with finishes including hand-finished, floated, troweled, broomed, and formed surfaces. 
 

Concrete properties were adjusted for weather and other placing conditions by varying the type and dosage of admixtures. Of note, two types of fiber mesh were included in the concrete mix to enhance the concrete properties and improve performance. As part of its work, the experienced crew was asked to evaluate finishability and set times compared to portland cement mixes. They reported no significant difference in either characteristic.
 

“We didn’t notice any major differences when working with the PLC mix,” said Chris Roberts, President of Roberts Concrete, Wichita, Kansas.

“It seemed similar to an ash mix, a standard mix.”  
 

According to Roberts, it was the first time their crews had worked with PLC. Roberts’ crews poured 600 to 700 yards at a time, testing after each one since they were working with a new type of mix for them. 
 

“We were diligent about taking tests on every pour, monitoring breaks and getting the ratios right,” said Roberts. 
 

The end result was a successful concrete placement with a more sustainable mix design. Proving performance of a greener cement formulation for its own property development before introducing a tested product to their customers, Monarch has advanced its product line while continuing to help customers drive down concrete’s carbon footprint in the Midwest region they serve.