Correlation of Cement Performance Property Measurements with C 3 S/C 2 S Ratio Determined by Solid State 29 Si NMR Measurements Christopher L. Edwards, †,‡ Rickey Morgan, ‡ Lewis Norman, ‡ Gary P. Funkhouser, ‡ and Andrew R. Barron* ,†,§,| Department of Chemistry, Rice UniVersity, Houston, Texas 77005; Halliburton Energy SerVices, Duncan, Oklahoma 73536; Department of Mechanical Engineering and Materials Science, Rice UniVersity, Houston, Texas 77005; and Energy and EnVironmental Systems Institute, Rice UniVersity, Houston, Texas 77005 The physicochemical and engineering performance properties of several API class G and H ordinary Portland cements (OPCs) from various foreign and domestic sources have been investigated in comparison with the tricalcium silicate/dicalcium silicate ratio (C 3 S/C 2 S) as determined by magic angle spinning (MAS) 29 Si nuclear magnetic resonance (NMR) experiments. XRF-derived oxide analysis appears to provide a lower C 3 S/C 2 S ratio than determined by NMR analysis. Furthermore, oxide analysis suggests that all the cements have a C 3 S/C 2 S ratio of 2-5, while our NMR method suggests the actual range is significantly broader. Determination of C 3 S/C 2 S ratios by NMR provides an effective method of analysis for cements, owing to NMR’s direct measurement of the minerals in question. NMR C 3 S/C 2 S ratios demonstrate predictive ability for the determination of engineering performance properties. This is especially the case for prediction of strength development; in keeping with generally accepted understanding of cement hydration behavior, the strength development correlates with increasing C 3 S/C 2 S ratio, i.e., C 3 S content. The observed correlation between NMR-derived silicate ratio and strength development holds for cements in the presence of either a retarder (lignosulfonate) or a fluid loss additive (N,N-dimethylformamide/2-acrylamido-2-methylpropanesulfonic acid copolymer). No significant correlation is observed between C 3 S/C 2 S ratio and the 72 h crush strength. The lack of dependency of either thickening time or Young’s modulus to the C 3 S/C 2 S ratio as determined by MAS 29 Si NMR measurements suggests that these physical properties are independent of the relative silicate composition. No correlations are observed between any physical property and the silicate ratio derived from XRF data. Introduction Cement hydration is a very complex process, not solely dictated by simple solvation and reprecipitation. The prediction of the set kinetics, reaction to inhibitors, and the properties of the set cement is presently not available. Instead of prediction, a series of experiments must be performed on each sample to obtain the property information required. It would be desirable to have a simple analytical method (or short series of methods) that would allow for the prediction of the chemistry of individual samples of cement from various sources. In this regard an attempt was made to correlate data from a wide range of spectroscopic and analytical techniques with experimental data obtained by traditional methods. The ultimate goal of this project is the development of a tool for the prediction of the hydration chemistry of various cements based upon their chemistry. Various attempts in the past have been made to correlate engineering performance properties with more conventional spectroscopic analyses. Barnes and co-workers were able to identify several key factors to the role of gypsum in preventing “flash set” by means of time-resolved in situ X-ray diffraction. 1 Parrott and co-workers applied a series of different tests, including quantitative X-ray diffraction and conduction calo- rimetry, to attempt correlations with degree of hydration. 2 Vlachou and Piau conducted a study of additive response and its correlations with SEM. 3 Ghosh and Handoo reviewed the progress in using infrared and Raman spectroscopies to monitor cement hydration behavior. 4 Coveney, Fletcher, and co-workers were able to build on the existing infrared knowledge base by applying artificial neural net (ANN) analysis to diffuse reflec- tance (DRIFTS) spectra of cements. 5,6 We have recently reported that for the MAS 29 Si NMR of cements the longitudinal relaxation time T 1 of C 3 S and C 2 S is significantly altered because of the paramagnetic Fe 3+ present in the C 4 AF matrix that makes intimate contact with each of the silicate phases. 7 The presence of the paramagnetic C 4 AF matrix thus allows for the rapid collection of spectra of cements. Furthermore, the relative concentration of tricalcium silicate (C 3 S) and dicalcium silicate (C 2 S) within a cement sample (i.e., C 3 S/C 2 S ratio) can be determined using the saturation recovery method, offering the best combination of accuracy, speed, and ease of processing. Our studies showed that the peak intensities are dependent on the relaxation times (τ). As the relaxation time is increased during the 29 Si NMR saturation recovery experi- ment, the volume fraction of the silicate particle (crystallite) being “observed” increases until the entire particle is being sampled (Figure 1). Unfortunately, deconvolution analysis of the resulting spectra does not provide an absolute concentration or weight percentage. However, the processed peak areas attributed to the C 2 S and C 3 S content do allow for an accurate derivation of the C 3 S/C 2 S ratio. 7 Using the data from the longest relaxation times (i.e., after the intensity curve in Figure 1 plateaus) will provide the relative concentrations of C 3 S and C 2 S. Thus, the C 3 S/C 2 S ratio can be calculated by a consider- ation of the intensity ratio at τ values above which the slope in the plot of intensity of the various saturation recovery parameters * To whom correspondence should be addressed. E-mail: arb@ rice.edu. † Department of Chemistry, Rice University. ‡ Halliburton Energy Services. § Department of Mechanical Engineering and Materials Science, Rice University. | Energy and Environmental Systems Institute, Rice University. Ind. Eng. Chem. Res. 2008, 47, 5456–5463 5456 10.1021/ie8000925 CCC: $40.75  2008 American Chemical Society Published on Web 06/24/2008