Macro-Defect-Free Cement Pastes
M. Berg,* J. F. Young*
University of Illinois

Macro-defect-free (MDF) cement pastes are being studied with the following objectives: (1) optimizing processing parameters, (2) improving resistance to moisture, and (3) developing alternative cement-polymer composites. Flexural strengths up to 300 MPa are achieved in the dry state, with a 0-20% decrease in strength occurring after immersion in water.

Polyelectrolyte Effects on Cement Dispersions
J. A. Lewis,* J. F. Young,* H. Matsuyama, G. Kirby
Asahi Chemical Company, Ltd.

This research focuses on understanding the role of polyelectrolytes (commonly referred to as superplasticizers) on the rheological behavior and dispersion of cement-based dispersions. Model cement powders, beta- and gamma-C2S, have been synthesized for this study. The influence of several acrylate-based polyelectrolytes, obtained commercially, with varying molecular weight, branch lengths, and ionizable side groups have been studied. Experimental observations will be compared to their theoretically predicted stabilization behavior to elucidate the mechanisms by which stability is imparted by this important new class of superplasticizers.

Organoceramics
S. I. Stupp,* P. Osenar
Center for Cement Composite Materials, AFOSR 90-0242

This project investigates the development of new materials we have termed "organoceramics," which are based on the concept of inorganic crystal growth in the presence of polymers and/or monomers. The products of interest are inorganic-organic intercalated structures in which polymers and/or monomers may participate in setting reactions. We have been able to synthesize a number of organocalcium aluminate structures containing poly(alcohols) and cationic polyelectrolytes. Interestingly, we find that the intercalated polymers can modulate the crystal structure, crystal habit, and chemical composition of these cementitious materials.

Chemistry and Composition of DSP Cement Pastes
J. F. Young,* J. Bukowski,* G-K. Sun, H. Ai
NSF Center for Advanced Cement-Based Materials

Strong, dense materials are formed by casting mixtures of calcium silicate (portland) cement and silica fume at very low water contents. The chemistry of the cementitious reactions and development of microstructure are being studied using small-angle x-ray scattering, trimethylsilylation, thermal analysis, and solid-state NMR spectroscopy.

Cement Admixture Interactions
J. A. Lewis,* J. F. Young, H. Matsuyama
Asahi Chemical Co.; NSF Center for Advanced Cement-Based Materials

The interactions between superplasticizing admixtures with portland cement are being studied. Zeta potential measurements will be combined with rheological behavior to determine the mechanism of dispersion.

High-Performance Concretes for Airport Pavements
J. F. Young,* D. A. Lange,* L. J. Struble,* H. Shin
FAA Center of Excellence for Airport Pavement Research (In conjunction with the Department of Civil and Environmental Engineering)

Low-porosity concretes are being evaluated for use as overlays on existing airport pavements. These materials use high additions of silica fume and superplasticizers to provide dense concretes of low permeability, good bonding characteristics, and improved wear resistance. However, cracking caused by thermal and drying shrinkage is a concern. This project examines experimentally the properties of these concretes and models their cracking tendencies. Development of bond with the existing pavement will also be considered.

Synthesis of C-S-H/Polymer Complexes
J. F. Young,* H. Matsuyana
Asahi Chemical Co.; NSF Center for Advanced Cement-Based Materials (In conjunction with Department of Civil and Environmental Engineering)

Synthetic, high molecular weight, linear polymers can be intercalated between the layers of the quasi-crystalline C-S-H structure during its synthesis by precipitation. Nonionic, anionic, and cationic polymers can all be intercalated depending on the composition of the C-S-H and the molecular structure of the polymer. Polymers used as high-range water reducers can also be intercalated. Intercalation also occurs when C-S-H is formed from the hydration of b-Ca2SiO4.

Formation of Hexagonal Anorthite at Low Temperatures
J. F. Young,* R. J. Kirkpatrick* (Geology), S.-H. Hong, P. Yu, J. M. Bukowski
University of Illinois (In conjuction with the Department of Geology)

Hexagonal anorthite has been prepared by hydrothermal treatments at 350°C using mixtures of monocalcium aluminate or calcium aluminate cement with quartz. The purest preparation is made from stoichiometric gels formed by the Pecchini process. Calcining at 900°C produces an intermediate pseudo-hexagonal phase, which converts to triclinic anorthite on heating at 1100°C. Hydrothermal treatment at 350°C of the pseudo-hexagonal phase produces hexagonal anorthite, which converts back to the pseudo-hexagonal phase on heating at 900°C.

Nanostructure of C-S-H
J. F. Young,* R. J. Kirkpatrick* (Geology), G.-K Sun
NSF Center for Advanced Cement-Based Materials (In conjunction with the Departments of Geology and Civil and Environmental Engineering)

The environment of substituent atoms, such as Al and Na, in the structure of quasi-crystalline calcium silicate hydrate (C-S-H) is being studied by solid state NMR spectroscopy. At low Ca/Si molar ratios of C-S-H, Al is in tetrahedral coordination, but at high Ca/Si ratio octohedral coordination is also observed. The effects of concomitant substitution of both Al and Na are also being examined.

Dimensional Changes in DSP Cement Paste
J. F. Young,* H. Ai
NSF Center for Advanced Cement-Based Materials (In conjunction with the Department of Civil and Environmental Engineering)

Low-porosity cement pastes containing silica fume undergo considerable autogenous shrinkage, due both to hydration and the pozzolanic reaction. The amount of drying shrinkage of the hardened paste depends on how much shrinkage has occurred during curing. Thermal expansion and contraction accompanying temperature change is also being studied. On heating, initial expansion is followed by a time-dependent thermal contraction which is attributed to moisture redistribution within the pore system. Both shrinkage and thermal change are being correlated with microstructural parameters.

Thermal Stability of Ettringite
J. F. Young,* Y. Shimada
University of Illinois

The stability of ettringite at temperatures up to 120°C is being studied. At 70°C, the pure solid dehydrates to an amorphous form, which regains its crystallinity on rehydration. When heated in suspension ettringite remains stable in pure water, but partial transformation to the "U-phase" occurs in the presence of sodium hydroxide.