Monitoring hydration characteristics of cement paste by EMI method
A monitoring system, which employs a piezoelectric ceramic as an active sensing transducer, is proposed for monitoring hydration characteristics of cement paste based on the electromechanical impedance (EMI) method. An impedance analyzer was used to obtain the electrical response of the sensor and the EMI measurements were performed by an online technique. The obtained data were analyzed using root mean square deviation (RMSD), a common statistical algorithm used for comparative processing of EMI spectra. The results show that the developed monitoring system is able to effectively detect physical changes of cement paste during the initial hydration.
CEMENT PASTE AND CONCRETE
This paper outlines the current state of knowledge as regards the chemical and physical aspects of the structure of hardened cement paste, then relates the properties of shrinkage, inelastic behavior, and creep to structure. Some significant recent developments in materials for concrete production are presented. New materials include (a) two types of matrices: expansive cement and regulated set cement, (b) two types of reinforcements: fiber reinforcements and ferrocement, and (c) two types of polymeric additions: polymer latex modified mortar and polymer impregnated concrete. Artificial aggregates including possible use of waste products and special techniques for preparation of extremely high strength cement pastes are also discussed.
Turbulent boundary layer wall‐pressure fluctuations downstream from an abrupt change in surface roughness
Spectra of wall‐pressure fluctuations beneath a turbulent boundary layer have been investigated immediately downstream from an abrupt change in surface roughness, from slightly rough to very rough. Over the measurable frequency band (400 Hz to 7 kHz), the spectra in the first 150 mm scale on wall variables. This indicates that the motions responsible for the pressure fluctuations measured in this region are very close to the wall. Farther downstream this scaling procedure breaks down. It is suggested that the initially thin internal layer behaves independently of the flow external to it until it has grown appreciably and only then interacts with the outer boundary layer. It was found that, for all frequencies measured, the dimensional spectral level decreases initially then rises to a maximum at 250 mm from the roughness change before decreasing once more. The position of the maximum is close to where the internal layer ceases to have a distinct edge.