NANOSCALE MEASUREMENTS OF CEMENT HYDRATION DURING THE INDUCTION PERIOD Jeffrey S. Schweitzer Department of Physics University of Connecticut Storrs, Ct, USA 2nd International Symposium on Nanotechnology in Construction Bilbao, Spain November 2005

Collaborators Richard A. Livingston, FHWA Claus Rolfs, Hans-Werner Becker, Ruhr Universität Bochum, Germany Stefan Kubsky, Synchrotron SOLEIL, Saint-Aubin, Gif- sur-Yvette CEDEX, France Timothy Spillane, University of Connecticut Marta Castellote Armero, Paloma G. de Viedma, IETcc (CSIC), Madrid, Spain Walairat Bumrongjaroen (University of Hawaii) Supaluck Swatekititham (Chulalongkorn University)

Study of the Induction Period The details of the kinetics of the cement curing reactions are not known The reactions appear to be initiated at the grain surfaces Hydrogen plays a key role in the reaction process Studying the change in hydrogen concentration as a function of depth and time will provide insight into the reactions

Nuclear Resonant Reaction Analysis (NRRA) Use of a narrow resonance (~ 1 keV) permits good spatial resolution Use of inverse kinematics (a 15 N beam) provide large dE/dx, which improves spatial resolution A well isolated resonance provides the ability to have deep probing of the sample (~ 2-3 microns) All of these are provided by the 6.4 MeV 15 N(p,  ) 12 C reaction

Resonance cross section Energy (MeV) 1 H( 15 N,  ) 12 C

Resonant Reaction Depth Profiling

Pellet Preparation Pure triclinic C 3 S powder Pressed into 13 mm dia. ring molds Fired at 1600 ºC to fuse upper surface Epoxied to stainless steel backing or with no backing Stored under nitrogen until used

Sample Preparation Saturated Ca(OH) 2 Solution ( pH=12.5) Isothermal (10, 20 or 30 °C ) N 2 Purge of solution Specimens removed sequentially at specified times Hydration stopped using methanol rinse Specimens dried to Torr vacuum

Typical Experimental Plan Temperature Number of Pellets Time Span o CHrs

Measurements Typical scan takes about one hour Chamber vacuum < Use of two beam charge states to cover complete energy range to 11 MeV Only background in gamma-ray spectrum is from cosmic rays Beam-line cold trap minimizes carbon buildup

Beam Energy Resolution

Time Progression

Typical Scan at Early Times

C 3 S at 30 o C

Temperature Dependence of Induction Time

Hydrogen Profile Pre-breakdown

Hydrogen Profile Post-breakdown

Reaction zones in hydrating C 3 S during the induction period.

H Concentration with Retarder and Accelerator

Comparison of Profiles

Comparison with Belite

Time Dependence of Belite Hydration Profiles

Highly Accelerated

Lightly Accelerated

Figure 5: Hydration profiles for C 3 A at various times. The 0 minute sample was not hydrated, but was treated with methanol and then stored in the vacuum with the others.

Ternary Diagram of Glass Composition

Glass Hydration Procedure Saturated Li(OH) 2 Solution ( pH=12) N 2 purge to prevent carbonation Specimens removed at 72 hours Hydration stopped using methanol rinse Specimens dried in Torr vacuum

NRRA Results of FF Series

NRRA Results of Low-Ca CF

NRRA Results of High-Ca CF

Future Research Effects of Al 2 O 3, Fe 2 O 3 in alite Effect of time-varying solution chemistry Effects of accelerators & retarders Relationship between surface layers and time of initial set Effects of cement storage conditions, i.e. “dusting”

Conclusions NRRA is a powerful technique for understanding cement hydration and it can determine induction period with a precision of  4 minutes or  2% Spatial resolution on the order of 2-3 nm can be achieved A surface layer is formed during the induction period for C 3 S but not for C 2 S Induction period determined by mechanical breakdown of surface layer ~ nm thick. Hydration involves concentration-dependent diffusion process Further work is needed to determine the affects of accelerators and especially of retarders, and to understand hydration of other cement components