Microstructure and mechanical properties of carbon nanotube reinforced cementitious composites developed using a novel dispersion technique

The present paper reports the first attempt of developing carbon nanotube (CNT) reinforced cement composites through a short dispersion route using Pluronic F-127 as a novel dispersing agent. Optimum concentrations of Pluronic for various types of CNT were determined, and the influences of Pluronic and CNT on the microstructure and mechanical properties of cementitious composites were thoroughly investigated. Pluronic with optimized defoamer concentration significantly improved the bulk density and mechanical properties of cement mortar. Further, dispersion of 0.1% single walled nanotube (SWNT) improved flexural modulus of mortar by 72% and flexural and compressive strengths by 7% and 19%, respectively after 28 days of hydration. Flexural and compressive strengths with functionalized SWNT increased with the hydration period up to 17% and 23% after 56 days, respectively. All CNT reinforced samples exhibited significantly higher stiffness, fracture energy and ductility as compared to plain mortar and composite samples prepared using a common surfactant.The authors also acknowledge Centre for Textile Science and Technology (University of Minho) and FIBRENAMICS PLATFORMfor providing required conditions for this research. Sincere thanks are also due to Mr. Pedro Samuel Leite and Mr. Carlos Jesus for their kind help in sample preparation and testing

The suitability of concrete using recycled aggregates (RAs) for high-performance concrete

The use of recycled construction and demolition waste (CDW) as concrete aggregate has been studied over the recent years, although, there have only been a few attempts to utilize recycled aggregates in the production of high-performance concrete (HPC) due to the limitations imposed by the inherent defects of mentioned aggregates. This chapter describes the influence on the properties of the fresh and hardened state of recycled HPC by different types of recycled aggregates, produced from concrete, ceramic, and mixed waste. It is necessary to employ “high-quality” coarse recycled concrete aggregates in the production of a 100% recycled HPC to obtain similar mechanical and durability properties to those of natural aggregates. It has been determined that the employment of fly ash also improves the durability of recycled HPC. The high water absorption capacity of the ceramic and mixed aggregates, used as fine recycled aggregates caused a beneficial internal curing, reducing shrinkage, and increasing their suitability with respect to those of natural aggregate concrete.Peer ReviewedPostprint (author's final draft

Effect of multiscale reinforcement on the mechanical properties and microstructure of microcrystalline cellulose-carbon nanotube reinforced cementitious composites

The present research investigated for the first time the combined effect of microcrystalline cellulose (MCC) and carbon nanotube (CNT) on the performance of cement composites. Multi-scale or hierarchical composites were developed by dispersing MCC and multi-wall CNT (MWCNT) within the cementitious matrix as reinforcements. Homogeneous suspensions of MCC (0.4 wt% and 1 wt%) and CNTs (0.2 wt% and 0.6 wt%) in water were prepared using two different surfactants, cetyltrimethylammoniumbromide (CTAB) and Pluronic F-127 using ultrasonication energy, and the suspensions were subsequently added to cement-sand mixture to fabricate cementitious composites. The composite samples were stored in water for 28 and 56 days to carry out the hydration process and were next characterized for flexural and compressive properties, dry bulk density, porosity, hydration products and fracture surface morphology. It was observed that the flexural and compressive strengths of cement composites improved significantly due to the MCC - CNT hybrid reinforcement. The highest improvements in flexural strength of 12.3% and 23.2% and compressive strength of 16.3% and 27.9% were achieved with 0.5 wt % MCC-0.3 wt % CNT in 28 and 56 days, respectively. In addition, significant improvements in flexural modulus, flexural strain and fracture energy were also noticed. Positive influence of hybrid reinforcement on the porosity of cementitious composites was also confirmed; the average pore diameter of plain mortar reduced from 47.5 nm to 30 nm. Further, the multi-scale composites exhibited higher bulk density, better hydration and crack bridging by CNTs leading to higher fracture energy.FCT - Fundação para a Ciência e Tecnologia, I.P., within the research unit C-MADE, Centre of Materials and Building Technologies (CIVE-Centro-Covilhã-4082), Universidade da Beira Interior, Portugalinfo:eu-repo/semantics/publishedVersio