Li Zongjin

Piezoelectric, dielectric, and ferroelectric properties of 0–3 ceramic/cement composites

The sulphoaluminate cement and a piezoelectric ceramic, 0.08Pb(Li1∕4Nb3∕4)O3·0.47PbTiO3·0.45PbZrO3[P(LN)ZT], were used to fabricate 0–3 cement based piezoelectric composites. The piezoelectric, dielectric, and ferroelectric properties of the composites were mainly investigated. The results indicate that the piezoelectric strain factor d33 increases as the P(LN)ZT volume fraction increases, which follows the cube model well. The dielectric constant ex and dielectric loss tan δ show similar trends with the d33. In the frequency range of 40–100 kHz, the dielectric constants of the composites decrease sharply, which is mainly attributed to interfacial polarization in the composite. Above 200 kHz, the cement-based piezoelectric composites exhibit good dielectric-frequency stability. Hysteresis measurements indicate that the composites exhibit typical ferroelectric hysteresis loops at room temperature. The remanent polarization Pr and the coercive field Ec of the composites increase as the P(LN)ZT volume fracti...

The electrical resistivity of cement paste incorporated with retarder

A non-contacting electrical resistivity measurement device was used for measuring the electrical resistivity of cement paste incorporated with retarder. The hydration process was divided into dissolving period, setting period, hardening period. With the increase of the retarder, the dissolution time will increase. The setting time happens between minimum point time and inflexion point time based on the electrical resistivity curve. The strength isoline was proposed to predict the strength trend.

Influence of Calcium Sulfate State and Fineness of Cement on Hydration of Portland Cements Using Electrical Measurement

The influence of calcium sulfate state and fineness of cement on hydration of Portland cement was studied using electrical resistivity measurement. The bulk resistivity curve of the paste from the abnormal cement mainly with hemihydrate had a characteristic abnormal peak and rapid increase in early period. The resistivity measurement technique can be used to discriminate abnormal setting. For normal cement with gypsum, the increase in fineness of the Portland cement decreases the minimum resistivity due to a higher ionic concentration and increases the 24 hour resistivity due to a reduction in macroscopic pore size. The setting time, compressive strength, pore structure of pastes made from different cements were carried out to compare the influence of water to cement ratio, calcium sulfate state and fineness. It is found that the electrical and mechanical properties are strongly affected by the initial porosity, the presence of hemihydrate or gypsum, and the fineness of cement.