Concrete mixture proportioning has evolved into an intricate undertaking. The introduction of super-plasticizers and shrinkage-reducing admixtures along with the increased use of supplementary materials such as fly ashes and calcined clays as well as the fine tuning of concrete composition and fineness to boost early-age strengths, have turned cement mixing into a task of mind-numbing complexity. It's now up to the construction industry to assure the quality of these increasingly complex concretes and optimize both their short term and long term performance. Luckily, researchers in the Building and Fire Research Laboratory (BFRL) at the National Institute of Standards and Technology (NIST), along with some industrial partners, have put together a set of comprehensive web tools designed to help them do just that. The Virtual Cement and Concrete Testing Laboratory (VCCTL) consortium, the Building Materials Division's electronic monograph, a computer-integrated knowledge system (CIKS), a concrete optimization software tool (COST) and an online collection of 3-D microstructures should come as a blessing to the overwhelmed engineer.

The objective of the first of these tools, The Virtual Cement and Concrete Testing Laboratory (VCCTL) consortium, is to provide a means to virtually test new cement and concrete mixtures and by doing so reduce the actual physical testing that this development typically requires. The models that the virtual testing system provides predict the chemical, physical and microstructural changes that occur as cement hardens. Thus, they can be used to examine the influence of water/cement ratios, cement particle size distribution, mineral admixtures and gypsum form and content on the developing properties of concrete. Other properties the system can predict at present include: chemical shrinkage, heat release and temperature rise, setting, diffusivity and strength developing. In addition, the consortium hopes to enhance the models to take the effects of supplementary materials into account and to be able to predict the composition of the fluid in the pores. They are also trying to compute the mechanical properties of 3-D cement-based microstructures as well as measure and model concrete's flow properties. If successful, the consortium will save the concrete construction industry a great deal of time and money and speed up the pace of the R&D process.

Another web tool is a virtual library of cement-based research papers published by the Building Materials Division of BFRL. This "electronic monograph," as it has been named, is archived online and amounts to 2,300 pages of material on cement science. Microstructure characterization and development, mechanical properties and degradation mechanisms are among the wealth of topics that it covers. Many of the models that this database contains can be downloaded from the site, providing those in the cement construction industry with an immeasurable resource.

The NIST also offers a computer-integrated knowledge system (CIKS) that predicts the service life of reinforced concrete exposed to chlorides. The CIKS features mixture proportioning according to accepted specifications for normal and high performance concrete accompanied by predictions of concrete diffusivity, service life and rate of chloride ingress.

Yet another web resource for the industry is a concrete optimization software tool (COST.) Developed by the BFRL in collaboration with the Federal Highway Administration and the Statistical Engineering Division of the Information Technology Laboratory (ITL), the objective of COST is to optimize concrete performance by computing available raw materials and user-defined performance attributes. The user selects the factors to be optimized and the COST system recommends a set of mixture proportions to be prepared and tested to achieve the most efficient identification of the optimum. The user then inputs the test results and the system performs graphical and statistical analyses to determine the mixture proportions that provide optimum performance.

Finally, there is a web site created by NIST that contains 3-D microstructural images of the hardening processes of cement, plaster of Paris and building bricks. It also includes 3-D data files, a description of the material imaged for each data set, and a collection of computer programs that can be used to process and analyze the images.

These tools mark an auspicious beginning to a new chapter in concrete technology. In our current electronic age, these computer-based tools will provide a means to optimize the performance of concrete in all of its many applications.

To visit the web sites described above, please go to: http://www.bfrl.nist.gov

Source: E-Concrete? Believe It!
Dale P. Bentz
Constructor, Feb. 2002
http://www.agc.org/NewsBulletins/constructor_default.asp