We study the conductive heat transport through calcium silicate hydrate (C-S-H) and organically cross-linked C-S-H via experiments, micromechanical homogenization theory, and molecular simulations. We find that C-S-H's intrinsic thermal conductivity falls below its amorphous limit when cross-linked with short-chain organosilanes. The observed reduction correlates with the alkyl chain length of the bis-organosilane molecule. To understand the underlying fundamental molecular processes accountable for such a reduction, we construct realistic molecular structures of cross-linked C-S-H and validate them against the spectroscopic and pycnometery measurements. The atomistic simulations indicate that the reduction in the contribution of propagons (propagating heat carriers) and diffusons (diffusive heat carriers) to heat transport, and the amplification of locons (localized vibrational modes), are the main driving factors allowing to limit the heat conduction in C-S-H. Presented findings offer new potential directions to nanoengineering novel admixtures for cement composites and resilient lightweight cementitious mesostructures for thermally efficient building envelopes.
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Engineering of high specific strength and low thermal conductivity cementitious composites with hollow glass microspheres for high-temperature high-pressure applications
Lightweight cement-based composites with high specific strength and low thermal conductivity are highly sought in the energy and construction industries. These characteristics are important in designing cement liners for high-temperature, high-pressure (HTHP) wells, in addition to those operating in permafrost. Similar attributes are also desirable in designing cementitious composites for energy efficient building envelopes. This work reports the results of an experimental campaign focused on engineering lightweight cementitious composites with hollow glass microspheres. It is demonstrated that the chemical stability of microspheres at HTHP conditions can be directly controlled by modulating the specific surface area and dissolution rate constant of supplementary siliceous additives. In addition to the stabilizing effect, such additives lead to the pore structure refinement and the enhancement of interfacial transition zone (ITZ). Introduced lightweight composites are capable of delivering significant load bearing capacity when normally cured, which is greatly increased by hydrothermal curing. Such high specific strength composites possess thermal conductivity below 0.3 W/mK at the oven dry density <1000 kg/m3 and cement dosage <400 kg/m3. This class of cementitious composites bears potential to enhance zonal insulation and well integrity, as well as increasing energy efficiency of building envelopes.
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- Award ID(s):
- 1826122
- NSF-PAR ID:
- 10157901
- Date Published:
- Journal Name:
- Cement concrete composites
- Volume:
- 108
- ISSN:
- 0958-9465
- Page Range / eLocation ID:
- 103514
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/https://doi.org/10.1016/j.cemconcomp.2020.103514
