Influence of Rate of Temperature Rise during Firing process on Compressive Strength of Mukono Ntawo Ball Clay

Byekwaso Ronald, Enjiku Ben D. D


This study was focused on the effect of varying the rate of temperature rise during firing process on the compressive strength of ball clay slab from Ntawo clay deposit from Mukono District, in central Uganda. The rectangular clay slabs of dimensions of 16cm by 4cm by 1cm were produced of clay particles of  45μm size. They were dried under open shade and fired at varied rate of temperature rise of 20C min-1,30C min-1,40C min-1,50C min-1 and 60C min-1to  firing temperatures of 5000C, 6000C, 7000C. 8000C, 9000C and 1000C and held at the temperatures for one hour. The fired slabs were then cooled to room temperature in the electric  furnace. The chemical composition by percentage weight of the unfired clay sample was determined by x-ray diffraction using RIX 3000 spectrometer. The compressive force of the samples were measured using 500SN-1299417 compressive machine. It was observed  that Ntawo ball clay to contained 67.20% of silica, 18.20% of alumina,2.83% of iron oxide,1.38% of titanium, 0.06% of phosphorous penta-oxide, 0.31% of calcium oxide, 0.98% of potassium oxide and 0.19% of sodium oxide. The compressive strength of the samples decreased with increase in the rate of temperature rise. The null hypothesis that the compressive strength of the fired samples did not depend on the rate of temperature rise during the firing process was rejected at α=0.05 and α=0.01 levels of significance. The decrease of compressive strength  with increase of  the rate of temperature rise between 20C min-1 to 30C min-1 was negligible for all the  firing temperatures. The percentage decrease f compressive strength with the rate f temperature rise was appreciable for firing temperatures 0f 5000C and 10000C of 11%.


Rate of temperature rise; Compressive strength; Firing temperature and Fired clay.

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