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.
POF based smart sensor for studying the setting dynamics of cement paste
Fiber optic smart sensors are used to monitor the civil structures. One of the important parameters in civil engineering is the setting characteristics of concrete made of cement. The paper discusses how a simple polymer optical fiber can be used to characterise the setting dynamics of various grades of cement. The results explain the comparative performance of polymer fiber over silica fiber. The basic principle underlying the sensor is that as the cement sets, it exerts a stress on the sensing fiber, which is laid within the cement paste. This stress induces strain on the optical fiber, which can be thought of as a series of aperiodic microbends on the surface of the fiber. This in turn changes the characteristics of the light signal transmitted through the fiber and can be viewed as stress induced modulation of light in the fiber. By monitoring the intensity variation of transmitted light signal with time we can determine the cement setting rate. This can be used as an effective tool for quality testing of commercially available cements of different grades.
A study of the hydration and setting behaviour of OPC-HAC pastes
Abstract An impedance measurement technique was applied to an investigation of the hydration process and setting behaviour of ordinary portland cement-high alumina cement (OPC-HAC) paste systems. Evidence indicates that the impedance and capacitive response are sensitive to ionic concentration changes in the liquid phase and microstructural development of the hydrating pastes. Rapid increases in impedance value occurred at about 30 minutes and 450 minutes hydration. The first impedance increase corresponded to the nucleation of ettringite contributing to fast setting behaviour; the other was attributed to HAC hydration processes. The decrease of matrix impedance at hydration times greater than 450 minutes may be due to the dissolution of calcium hydroxide (CH) generated from C 3 S and C 2 S hydration.