Unit 10

1. Read and translate the text durability of building materials

Problem

Deterioration of the infrastructure imposes huge costs on society, directly for repair and replacement, and indirectly by hampering economic activity and  reducing quality of life. Moreover, manufacture of building materials contributes significantly to global warming. Our goal is to understand the fundamental mechanisms by which salt, ice, and other environmental agents cause damage to concrete and stone, so that the processes can be delayed or prevented. The same physical mechanisms imperil monuments and works of art. So much of our effort is focused on conservation of cultural heritage. Geo-sequestration of CO2 is an essential component of plans to reduce greenhouse gases. The first sites that are likely to be used for CO2 injection are depleted petroleum reservoirs where impermeable rock layers trapped oil and gas for millions of years.

Those sites could be vulnerable to leakage if there are flaws in the cement used to fill the wells formerly used for extraction. Therefore, we are studying the rate of corrosion of cement in carbonic acid, and the change in transport and mechanical properties of the corroded cement.

The goal is to predict the rate of leakage through pre-existing cracks or gaps in cement-sealed wells

Approach

We investigate the fundamental mechanisms responsible for damage to stone and concrete, so that we can attack the cause, rather than treating the symptoms.

Modeling is used to predict the effects of suspected mechanisms, and experiments, often using novel methods, provide quantitative tests of the models.

Once the mechanisms are identified, protective measures can be developed to thwart them.

Recent Findings

The cause of “salt scaling” damage to concrete was  explained in the thesis research of John Valenza, and the mechanism of action of air voids during freezing  of concrete has been explained by the work of  Zhenhua Sun. The strain caused by freezing of mortar can be quantitatively predicted by poromechanical calculations. Tim Wangler’s research explained the buckling mechanism leading to damage of clay-bearing stone, and showed that certain surfactants can suppress the swelling

Polymer treatments being developed by Meg McNall protect limestone from damage by sulfate salts

Impact

Our research demonstrates that fundamental understanding of damage mechanisms can lead to effective preventive measures. Treatments to reduce damage to stone containing swelling clays, and limestones containing salts, are ready for field testing. 

Methods for enhancing frost resistance of concrete (by introduction of nucleating agents) and corrosion resistance of marble (by epitaxial deposition of  durable mineral films) are being developed. A reactive transport model to describe corrosion of cement paste by carbonic acid has been developed, and is validated by experiment. This will be applied to predict the risk of leakage of geo-sequestered CO2.