Preferred orientation of calcium silicate hydrate and its implication to concrete creep

Abstract

Calcium silicate hydrate (C–S–H) is the primary binding phase of cement-based and alkali-activated materials. The preferred orientation of C–S–H under non-hydrostatic pressure (e.g., uniaxial/biaxial load) is overlooked yet crucial in understanding concrete's multiscale mechanical performance. Here, we unveil the texture formation of C–S–H under compressive deviatoric stress, S, from 0 to ∼200 MPa, using high-pressure X-ray diffraction. Texture initiated at S < 12 MPa: the c-axis (normal to the basal plane) of C–S–H nanocrystallites preferentially re-oriented towards the direction of the principal compressive stress. Below S ∼100 MPa, the preferred orientation intensified through translation and rotation of C–S–H nanocrystallites; above ∼100 MPa, the texture stopped growing then weakened, suggesting internal transformations of C–S–H nanocrystallites. The time-dependence of the preferred orientation development is unveiled by the texture weakening after full unloading. The findings implicate that concrete creep under service loads is contributed by the intergranular preferential re-orientation of C–S–H nanocrystallites, not interlayer sliding or silicate chain breakage.

Additional Information

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory (contract No. DE-AC52-07NA27344). Beamline 12.2.2 and the sample preparation of this research are partially supported by COMPRES, the Consortium for Materials Properties Research in Earth Sciences under NSF Cooperative Agreement EAR 1606856. This work is supported by the US National Science Foundation under Division of Materials Research Ceramics Program, DMR-CER, Grant No. 1935604. We appreciate Dr. Martin Kunz and Dr. Jinyuan Yan at ALS for beamtime support. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. LLNL IM number: LLNL-JRNL-832129.

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