By using a newly developed Real-Time AE Spectrum Analyzer, the mechanism of microcracking process and fracture formation of cement mortar was investigated.
This system consists of a newly developed high-speed pipelined FFT (Fast Fourier Transform) processor, and a data acquisition and data compression circuit which is specially designed for the AE signal processing.
The object of AE spectrum analysis is to obtain informations on the microcracking process, and to clarify the relation between microstructure and mechanical properties in cement mortar.
A notched three points bending test by JSME standard was used.
During deformation and fracture process, seven kinds of AE power spectra are detected.
Cracking formation of mortar are shown as follows.
(1) Two kinds of AE events with low energy correspond to debonding at the interface between cement paste and coarse aggregates such as sand particles.
(2) Three kinds of AE events with low-middle energy correspond to the fracture path into cement paste parts by the above mentioned debonding.
(3) The others of two kinds with low-high energy correspond to extension of microcracks through the cement paste parts.

View full abstract

There are many cases observed in the burning zone of rotary cement kiln that wear of the direct-bonded magnesia chrome refractories has been increased due to fuel conversion from oil to coal. Two used bricks taken from the most severest part of the burning zone were analyzed by X-ray deffraction, microscope, chemical composition and thermal expansion respectively.
In addition to the textural changes in the used brick which were commonly observed due to migration of cement components, it was found that alkalis in the used brick played important role in wear mechanism. The brick peeled off with 32 mm thick showed large quantity of K₃Na (SO₄) ₂ and KCl in the range of 20 to 32 mm from the hot face. On the other hand, the brick which remained on the kiln shell contained a lot of K₃Na (SO₄) ₂ and KCl in the range of 0 to 20 mm from the surface as well.
From the thermal expansion test these two layers that contained more alkalis than other layers showed larger thermal expansion with 1. 84% and 1.63% respectively while original brick showed 1.20% at 1100°C.
It was assumed that the crack came out between the two layers due to higher thermal expansion.
From the results, it was learned that well developed direct bond and increase of the density of brick give better characteristic to increase resistance to alkali attack.

View full abstract