Zhu Pan

Reinforcing Effects of Graphene Oxide on Portland Cement Paste

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.

Carbon nanotube-cement composites: A retrospect

Although ordinary Portland cement (OPC) is widely used in the construction industry, its weak tensile strength, to some extent, limits its application. A carbon nanotube (CNT), on the other hand, has outstanding mechanical properties with a tensile strength of 63 GPa and Youngs modulus of 1 TPa, making it a candidate as nano-scale reinforcements in OPC. Past research studies have reported improved mechanical and electrical properties of carbonnanotube–ordinary Portland cement (CNT–OPC) composites, which show future promise in practical civilengineering applications. In this study, recent research studies in developing CNT–OPC composites are comprehensively reviewed. Highlighted herein are the considerable efforts been made in the study of fabrication, hydration, porosity and transport properties of the CNT–OPC composites. There are, however, future investigations needed to provide a better understanding in the areas of uniform dispersion of CNTs within the OPC paste, durability, impact, fatigue properties and the theoretical modelling of CNT–OPC interaction.

Damping and microstructure of fly ash-based geopolymers

As environmentally-friendly materials, geopolymers have the potential to replace ordinary Portland cement (OPC) for the construction of railway sleepers and multi-flue chimneys, where the vibration control capabilities of the material must be considered. The critical damping value (ξ) is the main parameter in relation to vibration reduction. In this study, the traditional logarithmic decrement technique was used to measure the ξ of geopolymers. Geopolymers were prepared by activating fly ash using alkali solutions with different SiO2/Na2O ratios. The results show that the ξ of the geopolymers is similar to that of the OPC counterpart. Finite element analysis (FEM) based on the Rayleigh damping model was conducted to replicate the test results, and scanning electron microscopy and mercury-intrusion porosimetry were used to study the microstructure of the geopolymers. A discussion of the possible damping mechanisms based on the microstructural investigation and the FEM analysis is presented.

In Situ Elevated Temperature Testing of Fly Ash Based Geopolymer Composites

In situ elevated temperature investigations using fly ash based geopolymers filled with alumina aggregate were undertaken. Compressive strength and short term creep tests were carried out to determine the onset temperature of viscous flow. Fire testing using the standard cellulose curve was performed. Applying a load to the specimen as the temperature increased reduced the temperature at which viscous flow occurred (compared to test methods with no applied stress). Compressive strength increased at the elevated temperature and is attributed to viscous flow and sintering forming a more compact microstructure. The addition of alumina aggregate and reduction of water content reduced the thermal conductivity. This led to the earlier onset and shorter dehydration plateau duration times. However, crack formation was reduced and is attributed to smaller thermal gradients across the fire test specimen.