When I was an area manager, I had to make rare jobsite visits to discuss a concrete problem. Usually, I’d try to avoid assessing blame for the problem by reminding the client that, “Concrete gets hard and then it cracks.” While the saying might be true, it rarely solved the issue.
That’s why I’m excited about the new crack-reducing admixture the scientists at BASF’s Construction Chemicals division announced at World of Concrete in January. They predict that when producers include this product in their mix, project owners, contractors, and inspectors may never see an unwanted crack again.
MasterLife CRA 007 was developed as part of a company-wide initiative to promote collaboration among BASF researchers worldwide. The admixture is the first of what company officials hope to be a continuous line of new innovations.
On its own, the MasterLife CRA 007 admixture will typically not eliminate concrete cracks. Producers must provide a concrete mixture that is well-proportioned for low shrinkage and contractors must follow industry-accepted good concreting practices. But the admixture will significantly minimize the potential for drying shrinkage cracking to such an extent that cracks may not form.
This class of shrinkage-reducing admixture uses a patent-pending technology that limits initial crack width in high-performance, crack-prone (HPCP) concrete mixtures. Concrete mixess that were tested in accordance with the ASTM C1581 ring test method showed crack widths of about 0.007 inches. At this width, the crack is nearly invisible to the naked eye.
How it works
MasterLife CRA 007 admixture reduces the surface tension of water in the capillary pores of concrete. This gradual relief of stress within the concrete matrix during drying minimizes the potential for cracking and delays the time to crack. When comparing MasterLife CRA 007 to untreated concrete specimens using the ASTM C 1581/C 1581M ring test, researchers found that, should cracking occur, initial crack widths are much narrower, averaging about 1/10 the typical crack width.
The admixture is designed for HPCP mixtures, commonly used on liquid-retaining structures such as water and wastewater treatment facilities, bridge decks, and jointless slabs. Crack widths in concrete batched with the product do not transport water and have the potential to self-heal over time. By minimizing the ingress of chlorides, sulfates, and other potentially harmful materials into the concrete, the admixture increases concrete durability and service life.
MasterLife CRA 007 admixture meets the requirements of ASTM C494, Standard Specification for Chemical Admixtures for Concrete, Type S, Specific Performance Admixtures. And for most applications, MasterLife CRA 007 admixture and fibers complement each other and will work synergistically to significantly minimize the potential for cracking and, in the event of cracking, to efficiently control crack widths.
“Many of today’s concrete specifications are embracing performance-based solutions,” says Charles Nmai, Manager, Engineering Services, BASF–Admixture Systems. “BASF is committed to developing products like MasterLife CRA 007 admixture that improve concrete performance through enhanced durability, extending the service life of structures and minimizing cost and environmental impact.”
For more information about MasterLife CRA 007, visit www.basf-admixtures.com/masterlife-CRA-007.