Cement Kiln Chemistry 2.1 Introduction

Cement Kiln Process Chemistry Module 2. Cement Clinker Quality and Composition. 2.1 Introduction In module 2 of the course we are going to focus on the quality and composition of cement clinker. Perhaps we should first define quality as it relates to cement clinker. Primarily clinker quality is judged by the hydraulic performance of cement made from the clinker. Hydraulic performance of cement covers strength development, setting characteristics, workability and durability and the consistency of those hydraulic performance characteristics. The clinker quality and composition affects all these hydraulic characteristics of the cement, although setting and workability can be adjusted or controlled in the finish milling of the cement. Durability of concrete made from cement is certainly determined by the clinker quality and composition. The clinker must be combined to a low residual free lime (<2.5%) and not contain more than 5% MgO. However, presuming adequate combination, the strength development of the cement made from the clinker is the primary measure of clinker quality. The strength development of cement, and concrete made from cement, is determined by the silicate content of the cement in the minerals C3S and C2S. The higher the silica modulus (SM) of clinker the greater the silicate content, but we have seen in Module 1 that if the SM exceeds 4.0 then there are difficulties in combining the clinker. The early strength of cement derives primarily from the C3S, the higher the lime saturation (LSF) of the clinker the higher will be the C3S content, up to the maximum of 100% lime saturated.

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Cement Kiln Chemistry 2.1 Introduction

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The raw materials in kiln feed can be proportioned to high LSF and SM targets to maximise silicate and C3S content, but what does lime saturation actually mean? Will the real clinker mineralogy correspond with the target from the proportioning? Will strength development of the C3S and C2S be as expected? Is strength development only dependent on the amount of the C3S and C2S present? Or is the C3S and C2S in some clinkers better at strength development than others? What is the role of minor compounds and constituents in the clinker? How can the strength development of the C3S and C2S be controlled and predicted? These are the questions we will try to answer in this Module 2 of the course. We will certainly not be able to answer these questions without an understanding of CaO-SiO2-Al2O3-Fe2O3 (CSAF) quaternary system. The CaO-SiO2-Al2O3-Fe2O3 (CSAF) quaternary system is where we will start in the next session of the course. There is no exercise associated with this session 1 of module 2, however, I recommend trying Quiz 2.1 to assess your current knowledge before studying the rest of the sessions, then repeating later as self-assessment.