Highly-Dispersed Carbon Nanotube-Reinforced Cement-Based Materials (27146
Cement compositions and processing to enhance mechanical strength and minimize nanoscale crack formation.
ADVANTAGE: Simple process suitable to existing cement fabrication with potential for significant property improvement.
SUMMARY: Most construction cements today are hydraulic, and generally based on Portland cement, composed primarily of limestone, certain clay minerals and gypsum. Effort to mitigate structural failures in cement is a constant endeavor that has employed a range of materials. Although microfiber reinforcement has led to significant improvement of cement mechanical properties, flaws at the nanoscale remain. Carbon nanotubes (CNTs) have been added to cementitious matrices at 0.5 to 1.0 wt% loadings to overcome such defects but suffer from poor dispersion and cost.
Northwestern researchers have discovered a process to utilize multi-walled carbon nanotubes (MWCNTs) at very low levels in conjunction with additives and mixing methods that provide excellent MWCNT dispersion in the cement matrix and afford significant improvement in cured mechanical properties. Thus, an aqueous MWCNT (0.08 wt% cement basis) additive solution, after suitable mixing, is blended into cement under ASTM procedures, cast and cured. Scanning electron microscopy (SEM) analysis of fracture surface specimens after 18 hours reveals isolated MWCNT fibers with a high degree of dispersion in the matrix (Figure 1). The uniform MWCNT distribution contributes to the observed increase in cured cement mechanical properties. Over 80% increase in the 7 day flexural strength is realized at the 0.08 wt% MWCNT loading versus the unmodified control (Figure 2). This modest MWCNT addition inhibits cracking at the nanoscale level and provides a cement matrix essentially “crack free”. The current invention promises a cost effective technology to provide high strength cements in a direct and scalable process.
Surendra Shah, Maria Konsta-Gdoutos and Zoi Metaxa
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