Nanotechnology in concrete – A review

Highly dispersed carbon nanotube-reinforced cement-based materials

In this experimental study, the reinforcing effects of graphene oxide (GO) on portland cement paste are investigated. It is discovered that the introduction of 0.03% by weight GO sheets into the cement paste can increase the compressive strength and tensile strength of the cement composite by more than 40% due to the reduction of the pore structure of the cement paste. Moreover, the inclusion of the GO sheets enhances the degree of hydration of the cement paste. However, the workability of the GO-cement composite becomes somewhat reduced. The overall results indicate that GO could be a promising nanofillers for reinforcing the engineering properties of portland cement paste.

Reinforcing effects of graphene oxide on portland cement paste

Graphene oxide (GO) is the product of chemical exfoliation of graphite. Due to its good dispersibility in water, high aspect ratio and excellent mechanical properties, GO is a potential candidate for use as nanoreinforcements in cement-based materials. In this paper, GO was used to enhance the mechanical properties of ordinary Portland cement paste. The introduction of 0.05 wt% GO can increase the GO-cement composite compressive strength by 15-33% and the flexural strength by 41-59%, respectively. Scanning electron microscope imaging of the GO-cement composite shows the high crack tortuosity, indicating that the two-dimensional GO sheet may form a barrier to crack propagation. Consequently, the GO-cement composite shows a broader stress-strain curve within the post-peak zone, leading to a less sudden failure. The addition of GO also increases the surface area of the GO-cement composite. This is attributed to increasing the production of calcium silicate hydrate. The results obtained in this investigation suggest that GO has potential for being used as nano-reinforcements in cement-based composite materials.

Mechanical properties and microstructure of a graphene oxide-cement composite

Permafrost in steep bedrock is abundant in many cold-mountain areas, and its degradation can cause slope instability that is unexpected and unprecedented in location, magnitude, frequency, and timing. These phenomena bear consequences for the understanding of landscape evolution, natural hazards, and the safe and sustainable 
operation of high-mountain infrastructure. Permafrost in steep bedrock is an emerging field of research. Knowledge of rock temperatures, ice content, mechanisms of degradation, and the processes that link warming and destabilization is often fragmental. 
In this article we provide a review and discussion of existing literature and pinpoint important questions. Ice-filled joints are common in bedrock permafrost and possibly actively widened by ice segregation. Broad evidence of destabilization by warming permafrost exists despite problems of attributing individual events to this phenomenon 
with certainty. Convex topography such as ridges, spurs, and peaks is often subject to faster and deeper thaw than other areas. Permafrost degradation in steep bedrock can be 
strongly affected by percolating water in fractures. This degradation by advection is difficult to predict and can lead to quick and deepdevelopment of thaw corridors along 
fractures in permafrost and potentially destabilize much greater volumes of rock than conduction would. Although most research on steep bedrock permafrost originates from the Alps, it will likely gain importance in other geographic regions with mountain permafrost.

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Permafrost in steep bedrock slopes and its temperature‐related destabilization following climate change

The present study investigated the effects of the method of surface decoration on the wetability of multi-walled carbon nanotubes (MWCNTs) and the mechanical properties of the cement paste incorporating these dispersions. The results showed that stable and homogenous dispersions of MWCNTs in water can be obtained by using surface functionalisation combined with decoration using polyacrylic acid polymers. The cement paste specimens incorporating these dispersions revealed good workability and an increase in the compressive strength of nearly 50% even with only a small addition of the MWCNTs, namely 0·045–0·15% of the cement weight. These results indicate the existence of chemical bonds between the OH groups of the functionalised MWCNTs and probably the CSH phase of the cement matrix, which enhanced the transfer of stresses. A second method that was studied included decoration of MWCNTs with polyacrylic acid polymers and gum Arabic. These dispersions appeared to be homogeneous only for approximately 2 h aft...

Surface decoration of carbon nanotubes and mechanical properties of cement/carbon nanotube composites

Aggregate-cement paste transition zone properties affecting the salt-frost damage of high-performance concretes

The pH measurement of concrete and smoothing mortar using a concrete powder suspension

Reactive powder based concretes: Mechanical properties, durability and hybrid use with OPC

Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) are known to possess exceptional tensile strength, elastic modulus and electrical and thermal conductivity. They are promising candidates for the next-generation high-performance structural and multi-functional composite materials. However, one of the largest obstacles to creating strong, electrically or thermally conduc- tive CNT/CNF composites is the difficulty of getting a good dispersion of the carbon nanomaterials in a matrix. Typically, time-consuming steps of purifica- tion and functionalization of the carbon nanomaterial are required. We propose a new approach to grow CNTs/CNFs directly on the surface of matrix particles.

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Vesa Penttala

Papers

Surface decoration of carbon nanotubes and mechanical properties of cement/carbon nanotube composites

Aggregate-cement paste transition zone properties affecting the salt-frost damage of high-performance concretes

The pH measurement of concrete and smoothing mortar using a concrete powder suspension

Reactive powder based concretes: Mechanical properties, durability and hybrid use with OPC

A novel cement-based hybrid material