Characterization of Micro-Pore Structure in Novel Cement Matrices
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Characterization of Micro-Pore Structure in Novel Cement Matrices Seyoon Yoon1, Isabel Galan2, Kemal Celik3, Fredrik P. Glasser2and Mohammed S. Imbabi1 1 School of Engineering, Fraser Noble Building, University of Aberdeen, AB24 3UE, UK. 2 Department of Chemistry, Meston Building, University of Aberdeen, AB24 3UE, UK. 3 Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720, USA ABSTRACT Calcium sulfoaluminate (CSA) cements are being developed using a novel processing method having as its objective lowering specific CO2 emissions by ~50% relative to a Portland cement benchmark. We need to be able to measure the properties of the products. Porosity and permeability measurements help define the engineering properties but their quantification is influenced by the choice of experimental protocols. In the present study we used ordinary Portland cement (PC) paste as a benchmark and hydrated ye’elimite, which is a main component of CSA cements, to understand its pore structure. We report on the use of synchrotron-sourced radiation for µCT (Computerized Tomography) and 3D image re-construction of the internal micro-pore structure of PC and ye’elimite-gypsum pastes. As a comparison, porosity and permeability measurements were traditionally obtained using Mercury Intrusion Porosimetry (MIP). The Mori-Tanaka method and the polynomial statistical model were used to analyze the effects of different 3-D micro-pore structures on mechanical properties. The results show that e micro-pore structures differ considerably between PC and ye’elimite pastes and their bulk modulus is significantly affected by the shapes of their micro-pore structures. INTRODUCTION The pores in cement systems have been studied because the content, size and interconnectivity of the pore network influences engineering properties, such as compressive strength and permeation by aggressive agents present in service environments. In Portland cement the smallest nanometer pores are associated with the presence of an open- structured gel while larger pores tend to be extrinsic and related to formulation, fabrication and cure. The pore networks have been studied at all length scales by techniques such as BET gas sorption, low angle X-ray scattering , mercury intrusion porosimetry and recently, by tomography 1-4. But new types of cement, such as calcium sulfoaluminate cements (shorthand, CSA) contain less gel and accordingly may have different pore size distributions and pore structures. We present a status report on the comparison of pore structures of two cements, one CSA, the other Portland, by MIP, microscopy and tomography. EXPERIMENTAL Two type of cement were used for preparing the samples: a commercial PC to CEM I 52.5R (BET surface area of 1.07 m2/g) and lab synthesized ye’elimite, 4CaO.3Al2O3.SO3, (BET surface area of 0.67 m²/g). The Portland cement (PC) was mixed with water in a ratio of 0.32 water/cement. The ye’elimite was first mixed with 50% weight gypsum and sufficient water to achieve a water/binder weight ratio
