"The importance of a suitable material for the laying of bricks in furnace and kiln construction has been recognized by the refractory industry for a long time. It is necessary that a strong bond should develop between the bricks to impart strength to the entire construction work. A weak joint would form the weakest link and dangerously weaken the whole structure.
Such being the importance of the bond, the refractory industry has made quite an effort to develop jointing materials which would produce strong bonds. During the last two decades, due to intensive research and development work, many good bonding materials have been made available. As a result of such development work it becomes necessary to evaluate the strength of such bonds, and hence test methods were developed to measure the bonding strength of mortars. Adequate specifications and standards of testing methods have been provided both by Federal specifications and by The American Society for Testing Materials. Among several tests recommended by them, the test to determine the strength of the joints is one of the most important.
A method has been specified by them by which the strength of joints can be measured at room temperature after air setting or after heat treatment of the joint at several temperatures. According to these methods, a joint after being made, dried at room temperature and at 105⁰ C, is then subjected to the modulus of rupture test. The data indicate the strength of joint which has been attained after air setting. Similarly the strength is determined on the joints which are fired at several temperatures. After firing, the joints are cooled to room temperature, and modulus of rupture is determined as before. Sample results which are recorded as strength of the joints at the specified temperatures are shown in Figure 1 on page 3. This method of measuring bonding strength is now universally practiced by both users and manufacturers of refractory mortars.
By careful study of the bonding strength method, it will be realized that the method for measuring strength at various temperatures is an erroneous one. According to this method, information is collected regarding room temperature strength of joints which had been previously subjected to a heat treatment. The strength at higher temperatures as shown in Figure 1 does not indicate the true strength of joints when maintained at these temperatures. Since furnace linings are expected to withstand stresses at operating temperatures, it becomes necessary to have exact knowledge of the true strength of the joints at working temperatures of the furnace and not at room temperatures. The above described test procedure does not provide such information.
During the literature review it has been noticed that some attempt has been made to determine strength of joints at a few isolated temperatures. This work, though it adds to present information, does not contribute much to the knowledge or strength of joints through the entire range of temperatures. In view of this, the present investigation was undertaken. This investigation is a study of the behavior of refractory mortars as regards to their bonding strengths at elevated temperatures.
During this investigation an attempt has been made to study the strength of joints at elevated temperatures and the effect of various variables of the mortar batch on such strengths. The mortar batches are compounded by varying some of the variables in the batch. These batches are then used to prepare mortar joints. After drying and firing these joints to temperatures ranging from 100⁰ to 1400⁰C, they are then broken at these elevated temperatures to determine the modulus of rupture. Several other tests are also performed to supplement the data. An attempt has been made to determine the factors which caused the change in strength at these temperatures. This was done by petrographic and x-ray methods of investigation. Finally an effort has been made to study the effect of various constituents of the mortar on the strength of the joints at elevated temperatures.
The importance of this problem lies in the fact that by this study one can easily evaluate the temperatures to which the refractory mortars can be used. Also one can develop a mortar composition which will give added strength at high temperatures by varying the proportions of various constituents of the mortar batch"--The problem, pages 1-4.
Planje, Theodore J., 1919-1980
Materials Science and Engineering
Ph. D. in Ceramic Engineering
Missouri School of Mines and Metallurgy
viii, 212 pages
© 1954 Bhikhubhai Mahadeo Sedalia, All rights reserved.
Dissertation - Open Access
Mortar -- Testing
Refractory materials -- Testing
Ceramic materials -- Effect of high temperatures on
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Sedalia, Bhikhubhai Mahadeo, "A study of the bonding by air-setting refractory mortar at elevated temperatures" (1954). Doctoral Dissertations. 983.