News Detail

In My Corner: Chemical Admixtures!

1/2/2023

Happy New Year! I sincerely hope that you had a restful and memorable holiday season and are recharged for a productive 2023 as ACI continues its leadership position in addressing issues in the concrete construction industry.

The January issue of Concrete International is always themed “Admixtures,” and having spent my career working for a specialty construction chemicals company, I couldn’t pass up the opportunity to write about admixtures, with a particular focus on their use in enabling sustainable concrete construction.

When I sat down to write this memo, a news headline regarding the decades-old drought in the western United States caught my attention—concern over a potential scenario where Lake Mead and Lake Powell on the Colorado River drop to levels that will be too low to provide water and hydropower! In June 2022, federal officials instructed seven states that rely on that river’s water to devise plans to drastically reduce annual water diversions by about 15 to 25%. Unfortunately, negotiations didn’t produce an agreement. In a recent news release, Interior Secretary Deb Haaland reiterated the U.S. Department of the Interior’s desire “to pursue a collaborative and consensus-based approach to addressing the drought crisis afflicting the West” but, if necessary, the Department will take decisive action to protect the Colorado River System. Several states have implemented water management systems and are promoting efficient use of water and water conservation. So, how can the concrete industry help?

Infrastructure development requires concrete; globally, about 4.4 billion tons of concrete are produced annually. And that quantity is projected to increase to over 5.5 billion tons by 2050 as developing countries rapidly urbanize. For decades, water-reducing admixtures have been used to reduce mixture water content and thus preserve one of the world’s most precious natural resources. I estimate that in 2021 alone, ready mixed concrete producers in the United States used these admixtures to save more than 1 billion gal. (4 billion L) of water! Due to recent advancements in engineered dispersant chemistries, we now have high-range water-reducing admixtures that can also allow reduced mixing times while providing rheological properties that enhance concrete placement, consolidation, and finishing. Thus, these admixtures are providing sustainability benefits well beyond reducing the consumption of water.

Other admixtures are also contributing to those efforts. First introduced in the late 1980s, hydration-controlling admixtures (HCAs) extend the life of freshly batched concrete and facilitate long time-to-discharge applications, including projects requiring long hauls to the jobsite. The ability of HCAs to control cement hydration in fresh concrete is a primary reason why the 90-minute rule for concrete discharge, which dates back to 1935, is no longer a requirement in ASTM C94/C94M, “Standard Specification for Ready-Mixed Concrete.” The first HCA was introduced primarily to help concrete producers reduce concrete waste to address Environmental Protection Agency pollution concerns. This practice of treating returned fresh concrete with an HCA prior to reusing it in a new load of concrete led to the development of ASTM C1798/C1798M, “Standard Specification for Returned Fresh Concrete for Use in a New Batch of Ready-Mixed Concrete” in 2016. As noted by Richard Szecsy, FACI, in a 2017 Construction & Demolition Recycling article, “because of this new standard, the industry can participate in a more sustainable construction practice in which millions of cubic yards of concrete can now be recycled in a way that is safe for end users and provides a more conscious approach to environmental stewardship.”

In recent years, other admixtures have been introduced to treat returned concrete for subsequent beneficial use, such as road base or backfill material. These admixtures work by different mechanisms, including gelling and stiffening fresh concrete very rapidly to granulize the concrete. In addition to eliminating the need for on-site concrete crushing, these admixtures provide concrete producers an environmentally sustainable solution to address returned concrete by diverting waste material into beneficial applications.

Lastly, durability-enhancing admixtures—such as corrosion inhibitors, shrinkage/crack reducers, and lithium-based admixtures for mitigation of alkali-silica reaction—play a significant role in boosting another key aspect of sustainable construction: achieving very long service lives with minimal, if any, repairs. Detailed information on the sustainability benefits of chemical admixtures is available in ACI-PRC-130-19, Report on the Role of Materials in Sustainable Concrete Construction.

Once again, a Happy New Year to all!

Charles K. Nmai