Surface magnetic relaxation in cement pastes

Area of Science:

• Materials Science
• Physical Chemistry
• Geophysics

Background:

• Surface magnetic relaxation in porous media is typically explained by hindered rotation or surface paramagnetic impurities.
• In cement pastes, an alternative explanation involving dipole interactions of adsorbed water of hydration on grain surfaces is proposed.

Purpose of the Study:

• To investigate the mechanism of surface magnetic relaxation in cement pastes.
• To explore the role of adsorbed water of hydration and water exchange in surface relaxation.
• To determine the rate-limiting factors governing surface magnetic relaxation in this material.

Main Methods:

• Analysis of magnetic relaxation times in cement pastes.
• Modeling of water exchange dynamics between mobile and adsorbed phases.
• Comparison of hydrate relaxation times with measured surface relaxation times.

Main Results:

• The hydrate relaxation time was measured at 17 microseconds, while the surface relaxation time was observed to be 30-40 microseconds.
• The observed difference is consistent with an exchange model where the exchange time between mobile and adsorbed water is comparable to the hydrate relaxation time.
• The proposed exchange model predicts a decrease in surface relaxation time with increasing temperature.

Conclusions:

• Surface magnetic relaxation in cement pastes is primarily governed by dipole interactions of adsorbed water of hydration.
• The exchange rate between mobile pore water and adsorbed water is the rate-limiting step for surface relaxation.
• Further experimental validation is underway to confirm the temperature dependence of surface relaxation time.