Unusual cement performance (continues...)

Since last month our team started to investigate sample from belt conveyor to Finish mill and carry out microscopic test. And the champion found a visual correlation between low compressive strength (CS). Generally the clinker was under burnt with high porosity and low alite contain ('bad thing happen at the same time').
The message is microscopic observation still play as a great tool to prove that Bouge and freelime (XRD) not always sufficient to provide clear figure of low late CS.
Base on Bouge formula also shows that alite and aluminate contain have good correlation to improve strength . For certain level Blaine cannot improve late strength.

Unusual cement performance

In recent month we found many compressive strength (CS) ASTM results were lower than internal spec. 2 weeks before this happen all parameter looks similar such Blaine, C3S, actual inert additive (IA) and raw meal residue. The IA was increased by 2% after that 2 week seems to reduce the CS lower than 2% respectally to the IA.
Immediate action was to decrease the IA by 2%. Some investigations are carried out e.g ensuring the testing method, equipments and tester consistency.
My opinion; focus to 2% and the ammount of low data. 8 data is enough to make me convince. The clinker microscopy play a role, even if the freelime is only 1%. Alternative fuel(AF) does not effect cement quality directly but clinker. Currently clinker become slighly to very porous with similar freelime. AF itself contains high moisture beside low calor value. High porousity clinker with very small size of alite and belite may resulting a severe low CS at all stages. Slugish CS is caused by belite cluster (remnant of coarse raw meal).

Basic Identification

The main mineral identification is Alite, belite and derivates, ferrite, aluminate (taken from workshop in 2003 paper)

Size almost everything beside the level of content, see table below.

excellent is the most recommended but not easy to achieve. The excellent regime is the highest reactivity, hence can obtain higher cement performance. In many case medium regime is the most occurance, since stability of process is easier.

Common finding is softburnt (almost well burnt)


Under burnt

Underburnt or softburnt clinker has almost the same performance of strength on early stage but has low low strength gain on late stage. Shorther setting time is another impact, the most vurnable is high expansion of freelime (white color on 'underburnt picture' is free lime cluster

Crack is a phenomena of slightly overburnt. 

Workshop

Starting on wednesday (this week) I run a worksop for a internal program (but can be proposed for external) for 3 days instead 4 days for complete workshop.
The objectives is to cascade the knowledges and skills to own area.
The workshop includes, class; benefit of this method, a view clinker formation process by the method, common and special phenomena. Practice includes; Ono method for burnability of kiln feed, mineral other than clinker and polished section.
Enhancement to improve understanding, during the classroom activities are practice to recognize the clinker minerals, mineral other than clinker, find phenomena, root cause.
Final test includes theoritical, observation.

ono method assess clinker

How the method assess clinker quality?
Simply Mr Yoshio Ono the founder describes the main parameters;
- burning rate, rate of heat from calcination to burning zone 850-1450C, the parameter is expressed by alite size, optimum at 20-30 microns.
- birefringence, max temperature that clinker accept at burning zone, optimum at 0.007-0.010.
- burning time, express by belite size is the time length meal at max temperature, optimum at 20-25 microns.
- cooling rate that expressed by belite color is the rate of decreasing temperature from max temperature to 1200C, optimum at clear cooler.

Ono parameters are very important basic method.

Clinker Samples

My team has recieve external sample from several company here are some report examples;



is a hard brown core clinker that is hard to be broken by steel hammer. Hard brown clinker is usually produced by long strong flame with a high temperature at kiln inlet (higher than calcination temp). Hard clinker will reduce finish mill productivity due to its low grindability.

under a microscope pictures;

a basic of clinker investigation method

Fig 1, Polished section method, belite blue, alite brown, liquid phase white color, black clould be voids
















Fig 2, Ono method with gypsum filter, alite in yellow color and (almost)rectangular shape, belite yellow with spherical shape.















Fig 3. SEM more detail













Microscopic analysis can provide information of material quality and controlling for analysis of raw material/raw-mix analysis such as;

• estimation of burn ability,
• mineralogy,
• chemistry of size fractions and individual phases,
• efficiency of grinding and
• homogenization processes

The other information from Clinker and Cement examination by microscopic analysis can provide

• the detail information regarding temperature profile; calcining and burning zones of kiln; rate of heating, max temperature, retention time and rate of cooling.
• Accurate investigation in clinker mineralogy can estimate cement performance better.

Prediction of cement performance also can be determined earlier such as

• grinding potential efficiency, potential strength gain and

Impact on additional mineral component on cement such as limestone & fly ash.

Why Microscopy?

In cement industri, quality control using XRF is common. XRF is a fast, acurate and easy to use tool. Additional equipment such a microscope still rarely use.
Microscopy technique to analyse clinker cement is powerfull but need longer time to have a result.
Appropiate accessoris to gain faster result also became essential.
Advantages of using microscopy technique has abundandly publish in book and internet, this internet link are most recommended;
www.cement.org
www.icma.org
www.struers.com
or certain title could be obtain using www.google.com search
Microscopy in the company where I work (Holcim Indonesia narogong Plant) was already used for weekly testing since 2002.
Mainly for clinker cement in the first application, currently my team tried to develop other method to analyze other material such raw meal or mineral components also tried to widen the service coverage not only for the company in Indonesia but also for regional such Vietnam, Thailand. In Indonesia beside Narogong plan we  serve sister company in Cilacap also  other cement company in Indonesia such Tonasa in Sulawesi.