Clinker reactivity improvement project which aims at reducing clinker factor in blended cement needs special focus by top level management, writes Dr. SB Hegde.
Performance of cement is governed by the clinker reactivity. The basic characteristics of all types of cement such as setting time and strength development are fulfilling national and international standard frameworks. This is necessary, as requirements of most cement applications in structural engineering are defined by regulations or codes based on standardised cements. To have the required hydraulic properties in cement, the clinker quality always needs special focus on quality control and assurance during process/production.
Clinker reactivity is the resultant of combustion management, which is of prime importance for optimisation and needs special attention on the following:
Why clinker reactivity?
The main objective of clinker reactivity improvement project is to achieve the following:
To reduce clinker factor in blended cement (to add cementitious materials, maximum permissible limit as per IS codes) which will not only increase the life of the limestone deposits, reduce the CO2 emission but also help in imparting higher durability potential to the structures
To optimise the fineness level of cement (to avoid finer grinding) thereby to improve the performance of cement mills which will bring down the power consumption.
To minimise the dose of grinding aid while maintaining the same quality of cement.
To achieve excellence in quality (zero customer complaint, to achieve compatibility of cement with chemical admixtures etc), good reliability factor of kiln and to show good overall plant performance in terms of lower raw mix cost, highest clinker/cement production, lower specific heat consumption and lower power consumption.
Factors governing clinker reactivity Besides raw mix composition
and the kiln design, burning conditions affect the clinker microstructure which will have an impact on properties of cement. Needless to say that the influence of fuel mix, burning zone temperature, flame shape, potential ash absorption, kiln atmosphere and cooling rate needs to be controlled to maintain constant and desired clinker quality (Figure 1 and Table 1 show the details).
Assessment of clinker reactivity
The hydration of portland cement itself is subject to a number of parameters involving clinker reactivity. Basic parameters like lime saturation factor (LSF), silica modulus (SM), alumina modulus (AM) as well as other numbers describing clinker´s chemical composition provide a basis for clinker quality assessment and quality control, and can be measured automatically by XRF. Since the clinker characteristics are a result of more complex influences, additional analytical techniques are necessary to have more information about the reactivity.
Quantification of clinker phases by using XRD by Rietveld method is gaining importance and found useful. Microscopical technique provides morphological features of clinker phases and cement structures (Figure 2).
Cement setting and compressive strength determination can be tested by using appropriate equipment as mentioned in Indian standard specifications. The obtained results will indicate for possible product improvements on the levels of raw material processing, kiln operation, grinding and sulphate optimisation. The governing parameters of clinker reactivity as mentioned in Table 1 should be achieved by adopting various action plans (at different sections of unit operation) in cement plant for the purpose.
Clinker reactivity improvement project needs special focus, attention and seriousness for implementation and the same is to be driven by top level management at cement plant(s) in a time-bound manner to reap the huge benefits in plant performance, quality excellence and ultimately organisation´s profitability.
In order to implement this project, the prerequisite is to assess the present level of performance or result as against each parameter mentioned in Table 1. Once this is ascertained, various action plans are to be formulated in each section of cement plant to achieve the desired result.
The author is Vice President and Functional Head-Quality and Material Development, Reliance Cement Company Pvt Ltd.
The author is thankful to the CEO of Reliance Cement Company for the consent to publish this paper.