Cement News tagged under: clinker chemistry

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Construction and demolition waste as clinker raw material

09 September 2019, Published under Cement News

The concept of the circular economy encourages the reuse of waste products as raw materials in the production of cement. Arthur Harrisson looks at the use of construction and demolition waste as a raw material for clinker. Initial crushing of concrete produces aggregate containing a significant proportion of mortar Carbon dioxide is produced during cement clinker manufacture from two sources. Firstly, the primary raw material for clinker is limestone, which is predominantly calc...

Belite in Portland clinker

22 July 2019, Published under Cement News

While belite is often represented as a pure dicalcium silicate, in practice the phase contains a range of impurities. Arthur Harrisson highlights the differences in belite composition and examines the causes of such impurities. Type I belite crystals with dark laminations containing exsolved matter The belite phase in Portland cement clinker is often characterised as dicalcium silicate or C 2 S, implying a lime-to-silica ratio of 2:1. The ratio refers to the number of CaO units ...

Alternative clinkers

11 March 2019, Published under Cement News

The drive to lower the carbon footprint of cement has led to the development of alternative cement clinkers to replace Portland cement clinker. Arthur Harrisson examines the potential of carbon reduction in four alternative clinker types, as proposed by Gartner and Sui. Belite in clinker Some years ago in ICR the possibilities for using alternatives to Portland cement clinker were discussed. 1 The particular cements examined were calcium aluminate cement (CAC), calcium sulphoal...

Aluminium and iron in clinker

06 February 2019, Published under Cement News

Aluminium and iron are two of the key components in Portland cement clinker. Varying their presence in clinker can have significant effects on the final clinker. Arthur Harrisson looks at some of the impacts of such variations. Figure 1: light grey aluminate and white ferrite very slowly cooled. The hexagonal blue alite crystal below centre is 30µm across The four essential constituents of Portland cement clinker are usually listed as: • calcium oxide (CaO or, in cement chemi...

Reducing cadmium volatility

19 December 2018, Published under Cement News

A recent news report for the Journal of Engineering described some experimental work that has been carried out in China designed to investigate the behaviour of some heavy metals, especially cadmium, in cement clinker. In particular the work looked at the influence of chalcogens on the volatility of cadmium. The content of cadmium in alternative fuels may be higher than in fossil fuels Chalcogens are a group of elements also known as the oxygen family. It consists of the element...

Sulphate in clinker

26 November 2018, Published under Cement News

The amount of sulphate (SO 3 ) varies widely in cement clinker. Arthur Harrisson discusses the sources of SO 3 and its impact on clinker composition. Figure 1: relationship between the contents of sulphate and aluminate in alite crystals from two cement plants The four main phases in Portland cement clinker are alite (C 3 S), belite (C 2 S), aluminate (C 3 A) and ferrite (C 4 AF). As has frequently been discussed, the chemical compositions suggested in brackets for these compou...

Bringing on the substitutes

18 July 2018, Published under Cement News

As part of its drive to reduce its CO 2 emissions, Votorantim Cimentos is using a range of clinker substitutes to lower its clinker-to-cement ratio. As a result, around 86 per cent of its product portfolio in Brazil has a reduced carbon footprint, lowering its impact on the environment. By Silvia R S S Vieira, Votorantim Cimentos, Brazil. The use of substitute materials such as acidic slags (pictured: maganese slag) and calcined clay is key to reducing a cement plant’s carbon foot...

Alternative fuels and clinker crystal characteristics

30 April 2018, Published under Cement News

Arthur Harrisson examines the effect of alternative fuel use on the characteristics of crystals present in clinker.  Figure 1: difference in alite quantity measured by microscopy and the Bogue calculation when burning increasing quantities of PSP Some four years ago an article was published in International Cement Review about the microscopic effects due to the use of alternative fuels (AFs). 1 In the intervening years the author has examined some 200 clinker sampl...

Modifying the Bogue calculation

31 January 2018, Published under Cement News

The Bogue calculation helps cement chemists to allocate the four main oxides in Portland cement clinker to the four main phases present following the pyroprocess in the cement kiln. While not perfect, it remains an effective guide to the potential relative properties of such clinkers. How much of each phase is there? The Bogue calculation is a means of allocating the four main oxides in Portland cement clinker to the four main phases present after firing in a cement kiln. The ca...

Crystal clusters in clinker

13 December 2017, Published under Cement News

With increasing use of alternative fuels, short homogenisation times in precalciner kiln systems and the requirement for high alite cement, the presence of crystal clusters is not expected to be a thing of the past. While the impact of crystal clusters in clinker on quality is not always clear, some effects can be seen.  Figure 1: brown and lighter blue belite crystals surrounding liquid phase Cement clinker for general-purpose Portland cement is composed essentially of four...