Engineering topics

Zhou, Chunsheng

Publications and source records attributed to Zhou, Chunsheng.

3 records

DOE OSTI2021

Quantifying the anomalous water absorption behavior of cement mortar in view of its physical sensitivity to water

The one-dimensional water absorption into cement-based materials, possibly the simplest case of unsaturated water flow playing a fundamental role in predicting mass transport and durability, is still far from being completely understood due to several puzzling anomalies. Considering the water sensitivity of C-S-H gels (swell upon wetting and contract upon drying), a modified Richards equation (MRE) is proposed to quantify the anomalous water absorption into cement-based materials of changing porosity. Consistent experimental tests on a cement mortar and calculations indicate that the MRE with time-decaying water permeability can quantitatively capture the long-term absorption with two linear stages and a nonlinear transition stage between them. The water sensitivity is validated to be responsible for the anomalous deviation of water absorption from the classical square root of time law. It also partially contributes to the anomalous dependence of sorptivity on the temperature-dependent surface tension and viscosity of water and many organic liquids.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Pore-size resolved water vapor adsorption kinetics of white cement mortars as viewed from proton NMR relaxation

The dynamic pore structure of partially saturated cement-based material is rather essential to quantify its mass transport and many other properties. To clarify the influence of water removal and re-entry, the low-field nuclear magnetic resonance technique is employed to characterize the pore structure of two white cement mortars during isopropanol exchange and water vapor adsorption kinetics. It is found that, after isopropanol replacement the pore structures of mortars become remarkably coarsen due to the significant collapse of C-S-H interlayer pores, which are only partly reversible at water re-saturation. Consistently, water vapor adsorption is not a simple progressively filling process from finer to coarser pores, but accompanied by continuous expansion of C-S-H gel adsorbing water in priority. Furthermore, the irrecoverable contraction of C-S-H gel is the physical root of irreversible shrinkage. The smaller BET surface area using nitrogen than water is also attributed to the collapse of interlayer pores after drying.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Engineering hybrid Co-picene structures with variable spin coupling

We report on the in situ engineering of hybrid Co-picene magnetic structures with variable spin coupling using a low-temperature scanning tunneling microscope. Single picene molecules adsorbed on Au(111) are manipulated to accommodate individual Co atoms one by one, forming stable artificial hybrid structures with magnetism introduced by the Co atoms. By monitoring the evolution of the Kondo effect at each site of Co atom, we found that the picene molecule plays an important role in tuning the spin coupling between individual Co atoms, which is confirmed by theoretical calculations based on the density-functional theory. Our findings indicate that the hybrid metal-molecule structures with variable spin coupling on surfaces can be artificially constructed in a controlled manner.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗