X-RAY DIFFRACTION STUDY OF THE STRAINS IN THE TEXTURE OF Ca(OH)2 AT THE TRANSITION ZONE OF CONCRETE. V.S.Haroutyunyan (a), P.J.M.Monteiro (b), H.-R. Wenk (c), E.S.Abovian (a), and V.P.Mkrtchian (a), (a) Dept. of Solide State Physics, Yerevan State University, 375049 Yerevan, Armenia, (b) Dept. of Civil Engineering and (c) Dept. of Geology and Geophysics, University of California, Berkeley, CA 94720
The paper presents theoretical and experimental studies using X-ray diffraction to determine the structural distortions in the texture of Ca(OH)2 that exists at the aggregate-cement paste transition zone (TZ) in portland cement concrete. This problem is of considerable importance because there is a the correlation between the lattice microstrains of the Ca(OH)2 crystallites in the TZ and the deformation state of the concrete, particularly during the development of cracks due to drying shrinkage.
Specimens were prepared with cement paste made with different values of water-cement ratio and with different types of substrates (glass, quartz and marble) in order to study the influence of porosity on the strain of the Ca(OH)2 texture and to study the effects of the morphology of the substrate on the above mentioned strain. The specimens were cured under saturated conditions and then broken at the substrate-cement paste interface. The interface on the cement paste side was analyzed by powder diffractometer and pole figure goniometer. With use of kinematical theory the analytic result for the intensity profile of the diffracted X-ray beam was obtained for the Bragg-Brentano focusing scheme. The average strain in the Ca(OH)2 texture was determined by Fourier analysis. It was observed that there is an inverse relation between porosity and Ca(OH) 2 strain. This result can be explained because there is a higher degree of strain relaxation with a higher concentration of pores.
The transition zone is often considered as the "weak-link" of concrete due the preferred orientation of Ca(OH)2 and the present work provides guidelines for developing better concretes.