Shengwen Tang

Non-steady state migration of chloride ions in cement pastes at early age

This paper proposes preliminary work to study the diffusion and migration of chloride ions in cement pastes at early age. The non-steady state ion migration coefficients of cement pastes are evaluated from three aspects: (1) electrical rapid ion migration test; (2) non-contact impedance measurement (NCIM) based on a fractal model; and (3) a corresponding simulation of an “I” shape fractal network. The experimental results from electrical rapid ion migration tests and NCIM have good agreement. The influences of water to cement ratio, curing hydration age and addition of mineral admixtures on the performance of ion diffusion/migration in cement pastes are investigated.

New Pore Structure Assessment Methods for Cement Paste

AbstractIn this study, two new approaches for pore structure assessment of cement paste are investigated and compared with mercury intrusion porosimetry (MIP)-based methods. One is based on a status-oriented computer model; the other is based on fractal analysis on the impedance measured by a noncontact impedance measurement system. In the computer model, cement paste microstructure is simulated as a function of cement properties, water-to-cement ratio (w/c), and degree of hydration. With the simulated microstructure, large capillary pores are characterized by image processing. A model developed based on nitrogen adsorption results and physical rules is applied to predict the small capillary pore structure, as a complementation to cover the whole range of capillary pores. In the impedance measurement based approach, fractal dimensions corresponding to specific pore size ranges are determined from the fractal networks and the impedance responses of the material. Then the pore size distribution curves are d...

CONTINUOUS MICROSTRUCTURAL CORRELATION OF SLAG/SUPERPLASTICIZER CEMENT PASTES BY HEAT AND IMPEDANCE METHODS VIA FRACTAL ANALYSIS

This paper presents a preliminary work to evaluate the influence of slag and superplasticizer on the early-age hydration of cement pastes by an innovative non-contact impedance measurement, heat evolution method, compressive strength and setting time tests. Besides, the cumulative pore volume obtained from modulus and phase of impedance in different hydration sections is taken to continuously correlate the cumulative heat releasing of cement pastes via the fractal analysis. Retarded phenomena and mechanism of hydration in cement pastes incorporated with slag and superplasticizer are studied, respectively. It is found that the compressive strength and setting time have a good linear relation with the slag amount in blended cement pastes.

THE EVALUATION OF ELECTRICAL IMPEDANCE OF THREE-DIMENSIONAL FRACTAL NETWORKS EMBEDDED IN A CUBE

This paper presents a preliminary work to evaluate the electrical impedance of three-dimensional pore fractal networks embedded in a cube. The construction and structural parameters of pore and electrical networks are illustrated in detailed. The total impedance response (modulus and phase) of networks is primarily associated with structural parameter of network, pore structure parameter of cube, conductivity of pore and solid phases. The impedance response of cube with the evolution of fractal network is analyzed comprehensively in this work. Besides, the influence of conductivity of pore phase caused by different types of electrolytes, electrical frequencies and conductivity of solid phase on the total impedance response is systematically studied.

Effectiveness of Fabricating High Performance Fiber Reinforced Cementitious Composite (HPFRCC) Using High Volume Steel Slag Powder

In this work, a high performance fiber reinforced cementitious composite (HPFRCC) is fabricated using high volume steel slag powder as a supplementary cementing material. Two water to cementitious materials ratio (w/cm), 0.25 and 0.35 respectively, and four contents of steel slag, namely 0, 30%, 60%, and 80% (percentage of total cementitious materials), are considered. The basic mechanical properties, including compressive strength and flexural toughness of HPFRCC, have been tested. The test results show that when the water cement ratio is 0.25 and steel slag content is 80%, HPFRCC shows a better flexural toughness. This work shows that it is feasible to utilize steel slag to produce HPFRCC, which not only gains a high performance building material, but also reduces industrial waste products.