Each year more than 5 billion cubic yards of concrete is used in buildings, bridges, roads and countless other structures. That's enough to fill 166,000 Olympic-sized swimming pools.

With concrete in such high demand, researchers are constantly working to improve its main ingredient, cement paste. Cement paste forms when cement reacts with water, along with other ingredients such as gravel, sand or crushed stone.

Zachary Grasley, assistant professor in the Zachry Department of Civil Engineering at Texas A&M, is one of those researchers.

Grasley's research focuses on cement-based materials, and one current project earned Grasley the prestigious National Science Foundation Faculty Early Career Development (CAREER) Award in 2009.

Grasley is measuring the mechanical properties - such as stiffness, or viscoelasticity, which incorporates aspects of both fluid behavior (viscosity) and solid behavior (elasticity) - of the nanometer-scale phases inside cement-based materials. He will use the measurements to develop a computational model to predict the properties of the bulk material used in construction.

Materials with viscoelastic properties can relax away a force that is exerted upon them. This is one reason that viscoelastic properties in concrete are important. If concrete is designed with significant viscoelastic properties, then it will be able to relieve stresses and in the end reduce the risk of cracking and damage.

"The idea here is primarily to develop a predictive model," Grasley explains. "The tests to characterize viscoelastic properties of cement-based materials are difficult, so it would be very nice to be able to predict those properties simply by considering the chemistry and other properties of the cement that is used in concrete."

However, Grasley points out that sometimes having high viscoelasticity can be too much of a good thing.

"If you have a column on a bridge and you've got a viscoelastic material - concrete - that column will get shorter with time because of the mass that is sitting on it," Grasley explains.

The project is nearing the end of the first of three stages. During this part of the project, tests measure the viscoelastic properties of the primary reaction phase of cement-based materials, the calcium-silicate-hydrate phase.

To do this, Grasley uses an atomic-force microscope. The microscope has a probe with a tiny tip that is inserted into a puck of hardened cement paste fixed in epoxy and polished to a shiny, smooth finish. He can estimate the viscoelastic properties of the cement paste from the applied force and the resulting gradual displacement of the probe tip into the sample.

Grasley says this is one of the first attempts to measure the viscoelastic properties of cement paste at this length scale.
Once the properties of the materials are known, stage two can begin. In this phase, the properties are entered into Grasley's computational model. The model includes individual reaction products, but Grasley is trying to find out the property of the entire model, not just the products or smaller phases.

"We expect concrete to be in service for years, decades even," Grasley says. "But concrete is constantly changing and chemically reacting, which changes its properties. We'd like to be able to predict viscoelasticity on the macroscale over a long time scale."

After the computational model is complete, stage three, testing, begins. The goal of stage three is to test the computational model for accuracy.

"Since much of the concrete construction in the world is publicly funded by taxpayers, everyone has the potential to benefit from concrete with improved design," Grasley says. "Concrete is the most widely used material in the world after water. So it is pretty important. It has a huge impact on societies."