For years, ready-mixed concrete producers have met the challenge of producing concrete that flows easily and hardens quickly. The result has been an industry frozen in a time warp in which all slumps are created equal and set time is king.

Precasters face a similar problem. The need for high-cement-content mixes that attain fast sets for quick form stripping often results in concrete that attains two or three times the ultimate strength but that also is extremely harsh and requires excessive vibration. The ability to cast several elements and use the same forms in the same shift would increase labor efficiency and equipment utilization.

The latest generation of plasticizing admixtures has failed to solve these problems. It is difficult to understand that less water still can provide not only increased viscosity and greater workability but also the same chemical reaction that occurs with the amount of water typically used in a mix design.

The article describes how earlier versions of high-range water-reducing admixtures (HRWRAs) left little cement particle surface area open and how new-generation HRWRAs leave more surface area open and also attract more water molecules for more hydration.

The article includes a box listing the different types of admixtures.