ABSTRACT The effects of curing time and water-to-cement ratio (W/C) on the pore structure of phosphoaluminate cement (PAC) paste are here presented. Based on the adsorption and condensation theory, the adsorption isotherm of hardened paste was tested using the Brunauer-Emmett-Teller (BET) nitrogen adsorption method. The phase composition and morphology of hydration products cured at different times were analyzed using X-ray diffraction (XRD), and a hydration heat test instrument (HHT) was employed to determine the heat of hydration. The effects of curing time and W/C on the pore structure of PAC are significant. The adsorption isotherm is fitted to the second category based on the Brun-auer- Deming-Deming-Teller (BDDT) classification system. Adsorption volume was found to increase with W/C and then decrease with age. The hysteresis loop of PAC is fitted to the H3 type based on International Union of Pure and Applied Chemistry (IUPAC) guidelines, and the adsorption volume and area enclosed by the hysteresis loop were found to increase with W/C and then decrease with age. BET surface and saturated adsorbed volume of PAC both increase with W/C and decrease with curing time, which is attributable to the greater hydration that produces and changes the characteristics of the pore structure.
Cite this paper
W. Wang, P. Liu, M. Zhang, J. Hu and F. Xing, "The Pore Structure of Phosphoaluminate Cement," Open Journal of Composite Materials, Vol. 2 No. 3, 2012, pp. 104-112. doi: 10.4236/ojcm.2012.23012.
 U. Rattanasak and K. Kendall, “Pore Structure of Cement/Pozzolan Composites by X-Ray Microtomogram- phy,” Cement Concrete Research, Vol. 35, No. 4, 2005, pp. 637- 640. doi:10.1016/j.cemconres.2004.04.022
O. Deo and N. Neithalath, “Compressive Behavior of Pervious Concretes and a Quantification of the Influence of Random Pore Structure Features,” Materials Science and Engineering: A, Vol. 528, No. 1, 2010, pp. 402-412.
M. S. Sumanasooriya and N. Neithalath, “Pore Structure Features of Pervious Concretes Proportioned for Desired Porosities and Their Performance Prediction,” Cement Concrete Composites, Vol. 33, No. 8, 2011, pp. 778-787.
R. Kumar and B. Bhattacharjee, “Porosity, Pore Size Distribution and in Situ Strength of Concrete,” Cement Concrete Research, Vol. 33, No. 1, 2003, pp. 155-164.
W. L. Lai and W. F. Tsang, “Characterization of Pore Systems of Air/Water-Cured Concrete Using Ground Penetrating Radar (GPR) through Continuous Water Injection,” Construction and Building Materials, Vol. 22, No. 3, 2008, pp. 250-256.
A. K. Ladavos, A. P. Katsoulidis, A. Iosifidis, K. S. Triantafyllidis, T. J. Pinnavaia and P. J. Pomonis, “The BET Equation, the Inflection Points of N2 Adsorption Isotherms and the Estimation of Specific Surface Area of Porous Solids,” Microporous and Mesoporous Materials, Vol. 119, No. 4, 2011, pp. 1-8.
H. W. Song and S. J. Kwon, “Permeability Characteristics of Carbonated Concrete Considering Capillary Pore Structure,” Cement Concrete Research, Vol. 37, No. 6, 2007, pp. 909-915. doi:10.1016/j.cemconres.2007.03.011
J. J. Thomas, J. Hsieh and H. M. Jennings, “Effect of Carbonation on the Nitrogen BET Surface Area of Hardened Portland Cement Paste,” Advanced Cement Based Materials, Vol. 3, No. 2, 1996, pp. 76-80.
J. Zhou, Y. E. Guang and K. V. Breugel, “Characterization of Pore Structure in Cement Based Materials Using Pressurization Depressurization Cycling Mercury Intrusion Porosimetry (PDC-MIP),” Cement Concrete Research, Vol. 40, No. 7, 2010, pp. 1120-1128.
J. Kaufmann, R. Loser and A. Leemann, “Analysis of Cement-Bonded Materials by Multi-Cycle Mercury Intrusion and Nitrogen Sorption,” Journal of Colloid and Interface Science, Vol. 336, No. 2, 2009, pp. 730-737.
B. B. Das and B. Kondraivendhan, “Implication of Pore Size Distribution Parameters on Compressive Strength, Permeability and Hydraulic Diffusivity of Concrete,” Construction and Building Materials, Vol. 28, No. 1, 2011, pp. 382-386. doi:10.1016/j.conbuildmat.2011.08.055
M. C. G. Juenger and H. M. Jennings, “The Use of Nitrogen Adsorption to Assess the Microstructure of Cement Paste,” Cement Concrete Research, Vol. 31, No. 6, 2001, pp. 883-892. doi:10.1016/ S0008-8846(01)00493-8
M. Siegwart, J. F. Lyness and B. J. McFarland, “Change of Pore Size in Concrete Due to Electrochemical Chloride Extraction and Possible Implications for the Migration of Ions,” Cement Concrete Research, Vol. 33, No. 8, 2003, pp. 1211-1221. doi:10.1016/S0008-8846(03)00047-4
N. Neithalath, M. S. Sumanasooriya and O. Deo, “Characterizing Pore Volume, Sizes, and Connectivity in Pervious Concretes for Permeability Prediction,” Materials Characterization, Vol. 61, No. 8, 2010, pp. 802-813.
S. Q. Li, J. S. Hu, B. Liu, G. H. Zhang, W. Cao, Q. Wang, et al., “Fundamental Study on Aluminophosphate Cement,” Cement Concrete Research, Vol. 29, No. 10, 1999, pp. 1549-1554. doi:10.1016/S0008-8846(99)00111-8
S. J. Gregg and K. S. W. Sing, “Adsorption Surface Area and Porosity,” Academic Press, London, 1967.
A. C. Mitropoulos, “The Kelvin Equation,” Journal of Colloid and Interface Science, Vol. 317, No. 2, 2008, pp. 643-648. doi:10.1016/j.jcis.2007.10.001
S. Q. Li, B. Liu, J. P. Cheng and J. S. Hu, “Composite Cement of Magnesium Bearing Phosphoaluminate Hydroxyapatite Reinforced by Treated Raw Silk Fiber,” Cement Concrete Composite, Vol. 30, No. 1, 2008, pp. 347-352. doi:10.1016/j.cemconcomp.2007.08.009
L. Z. Xiao and Z. J. Li, “Early Age Hydration of Fresh Concrete Monitored by Non-Contact Electrical Resistivity Measurement,” Cement Concrete Research, Vol. 38, No. 3, 2008, pp. 312-319.