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History of Concrete Admixtures

Source: | Updated: Mar 22, 2016

There can be little doubt that some of the most significant changes in concrete material technology are attributed to advancements in chemical admixtures for concrete in the past 20 years. The precast concrete industry has been at the heart of the new engineering properties enabled by chemical admixtures such as moving from 4-in. slump concrete to self-consolidating concrete (SCC). Before we look at what may be ahead in chemical admixtures, let’s take a look at where we’ve been and where we are now.

 

Concrete Admixture

Admixtures have been used in concrete and mortar since at least the Roman Empire. The Romans found that certain materials such as milk, blood and lard, as well as organic materials such as molasses, eggs and rice paste allow greater workability in cementitious mixtures.

 

While the first patent for calcium chloride in concrete goes all the way back to 1873 in Germany, modern admixture technology started with basic air-entraining agents, retarders, accelerators and water reducers in the 1930s in North America.

However, it was not until the 1950s that these types of products began to see widespread use in concrete. ASTM first published its C494 standard in 1962, now titled “Historical Standard: Standard Specification for Chemical Admixtures for Concrete,” which set performance criteria for five types of admixtures: A, B, C, D and E. Types F and G, high-range water-reducing admixtures, were not added to the C494 standard until 1980. In 1962, only 36 states required or allowed the use of admixtures in concrete.

ACI Committee 212 publishes the “Report on Chemical Admixtures for Concrete,” which did not include high-range water reducers (HRWRs) in their document until 1981. While the 1970s saw a sharp increase in the use of admixtures in concrete, a 1982 survey found that only 71% of the concrete produced in the United States contained water-reducing admixtures, and that less than 2% contained HRWRs.

In 1979, the first corrosion-inhibiting admixture was introduced to help mitigate the impact of chloride salt (NaCl) attack on steel reinforcement. Almost 20 years later (1996), shrinkage-reducing admixtures followed and helped to address cracking issues associated with autogenous drying in high-performance concrete.

The 1980s and ’90s continued to see increased use of admixtures in concrete, which included significantly more frequent projects specifying the use of HRWRs as the placement benefits of higher slumps and improved durability of lower water-cementitious material (w/c) ratio concretes were realized.

Still, the biggest change in concrete in North America occurred with the introduction of a new HRWR technology that greatly expanded the plastic and hardened properties of concrete and, in the case of SCC, created a new concrete terminology.

 

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