Interfacial Engineering of Cement by Graphene Oxide
Presented By: Jing Zhong
Affiliation: Harbin Institute of Technology
Description: Through dissolution-precipitation process, cement bind coarse aggregate, fine aggregate, and other fillers altogether to form concrete. There are numerous interfaces between cement and other concrete components, and these interfaces form a 3-dimensional network in concrete containing pores, water, non-reactive components inside. Graphene oxide, which is a single layer of nanosheet with high flexibility, can be considered as a macro-molecule with a large number of chemical functional groups. Morphologically, graphene oxide is a perfect material for the interfacial nano-engineering since it can be intercalated conformally and effectively at any interface in principle. For the understanding of such nano-engineering capability of graphene oxide, we design a serious of platforms and related techniques to uncover the true effects of graphene oxide. For the illustration of concept, I will show how graphene oxide modify the interfacial transition zones between cement and aggregates, as well as the cement-cement interface. The talk will then highlight the great potential that 2D material, represented by graphene oxide, to control the properties of cementitious material from the perspective of multi-scales design.
Investigating the Effect of Carbon Nanotube on Early-Age Hydration of Cementitious Composites with Isothermal Calorimetry and Fourier Transform Infrared Spectroscopy
Presented By: Zhen Li
Affiliation: Dalian University of Technology
Description: The effects of a range of carbon nanotube (CNT) additions (0.1–0.5% by weight of cement) on the early hydration processes (0–24h) of cementitious composites were investigated by isothermal calorimetry, Fourier transform infrared spectroscopy (FTIR), X-Ray powder diffraction (XRD) analysis and scanning electron microscope (SEM) observation. The addition of CNT can improve the rate of hydration heat of cementitious composites. However, 0.1 wt% CNT obviously decreased the total cumulative hydration heat of cementitious composites. Additionally, the peaks corresponding to (v4) SiO4(4-) vibrations were shifted from 496 cm-1 to higher frequencies (534 cm-1, 534 cm-1 and 546 cm-1) at 24h due to the inclusion of CNT (0.1%, 0.3% and 0.5%). It is hypothesized that CNT with high surface energy can improve the energy of cementitious composites and increase the polymerization of C–S–H. According to the XRD test, CNT didn't affect the types of cement hydration products, but can reduce the orientation index of calcium hydroxide crystal. The microstructure observations demonstrated that CNT can also change the morphologies of hydration products and modify the microstructure of cementitious composites. Such behaviors could be associated with the case that CNT can increase the polymerization degree of C–S–H which was verified by the isothermal calorimetry and FTIR test.
Piezoresistive Properties of Cementitious Composites with Graphene Nanoplates and Graphite Plates
Presented By: Wengui Li
Affiliation: University of Technology Sydney
Description: Graphene nanoplate (GNP) and graphite plate (GP) are promising functional nanofillers for smart cementitious composites. The effects of GNP and GP on physicochemical, mechanical and piezoresistive properties of cementitious composite were investigated in this study. The results show that the cement hydration was accelerated with the increase of GNP and GP because of nucleation effect. The electrical resistivity of GNP-cementitious composites is always lower than that filled with GP at the same concentration. On the other hand, percolation occurs for the GNP/cement composites at the dosages from 2-3% (by weight), while it never happens for the GP/cement composites. Moreover, the GNP/cement composites reached the maximum mechanical strengths when GNP content was 1.0%, while for the GP/cement composites, only minor strength improvement was obtained at a dosage of 0.5% GP. As for the piezoresistivity, the cementitious composites filled with GNP exhibited higher fractional changes of resistivity. Irreversible resistivity generated for 2-3% GP/cement composites subjected to cyclic compression, due to the poor and loose microstructure. Related outcomes can provide an insight into the application of GNP/cement composites and GP/cement composites as cement-based sensors for structural health monitoring.
Ultra-Sensitive Cement Sensor with In-Place Synthesized Carbon Nanotubes
Presented By: Mimi Zhan
Affiliation: The Hong Kong University of Science and Technology
Description: Carbon nanotube cement-based sensors have gathered many interests in the structural health monitoring (SHM) area as they not only perfectly solve the incompatibility of conventional sensors but also possess an outstanding sensitivity that conventional sensors cannot compare. However, the sensitivity to strain (gauge factor) of such materials are limited by the difficulty in dispersing carbon nanotubes (CNTs). Here we synthesized CNTs in situ on the surface of fly ash (FA) to significantly improve the CNT dispersibility and enabled the cement mortar to exhibit an outstanding strain-sensing capability. The mortar with CNT-coated FA (CNT@FA) at 2.0 wt% CNT concentration exhibited a gauge factor of 6544, about one order of magnitude higher than that of mortar with commercial CNTs under the same condition. Its fractional change in electrical resistivity also reached as high as 70% upon compressive loading. This outstanding piezoresistivity was explained by the great dispersion of CNT@FA observed by optical microscopy measurements and indicates the great potential applications of CNT@FA cement sensor in assessing the conditions of civil engineering structures.
The Role of Carbon-Based Nanostructured Materials on the Stress-Strain Sensing and Crack Detection of E-conducting Nanoreinforced Concrete
Presented By: Panagiotis Danoglidis
Affiliation: University of Texas At Arlington
Description: The use of 2d carbon-based materials such as carbon nanotubes, nanofibers, and graphene nanoplatelets, when successfully dispersed in cementitious materials allows us to explore novel functionalities. We have succeeded in obtaining networks of well dispersed CNTs/CNFs and GNPs and develop nano-engineered concrete that exhibits semi-conducting behavior and notable electromechanical impedance sensitivity. In this presentation we will focus on the sensing functionality and the ability to monitoring stress and strain and detecting crack propagation and damage accumulation at all stages of deformation.
Effect of Graphene Oxide on the Properties of a Fly Ash-Based Geopolymer Paste Before and After F/T Damage
Presented By: Zhipeng Li
Affiliation: Washington State University
Description: This laboratory study demonstrates the beneficial effect of admixing trace amount of graphene oxide to the mechanical properties and durability performance of an environment-friendly fly ash-based geopolymer paste. Such a novel cementitious material was fabricated through the use of chemical activators and graphene oxide to upcycle a class C fly ash into a geopolymer binder. A typical mix proportion of the geopolymer binder features the mass ratios of fly ash: waterglass: lime: triisopropanolamine: sodium sulfate: GO at 100:6:3.6:1.2:1:0.02. The compression strength, splitting tensile strength, water absorption, and gas permeability of this nano-modified paste and its none-modified counterpart were tested before and after F/T cycles, to clarify the effect of GO on the macroscopic properties of this geopolymer paste. Two curing regimes were investigated: ambient temperature and and 60 degree C. We employed advanced tools such as scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), 29Si and 27Al Magnetic Resonance (NMR) to shed light on the mechanistic role of GO both during geopolymer hydration and during F/T cycling. The Ca, Si, Al contents and the Ca/Si, Al/Si, Ca/(Al + Si) mole ratios, obtained from energy-dispersive X-ray (EDX) spectroscopy, were statistically compared to elucidate the effects of GO on the hydration products of the geopolymer binder and their F/T durability.