Cement: Agglomeration and weathering

Agglomeration and weathering

Effects

Agglomeration / weathering

Factors and recommendations

Effects

Poor flow of cement (in dry)

Due to agglomeration,

difficult silo extraction

extractors blockage

loss of silo volume

increased cohesion of powder

bad cement distribution during mixing

change of rheology

longer setting time

reduction of strength

Agglomeration / weathering

Lumps formation : 2 types

Rapid

o weak, easily broken

o strength a little affected

à Agglomeration

Slow

o stronger strength of lumps

o decrease of early strength

o increase of setting time

à Weathering

Factors and recommendations

Agglomeration factors

Alkali content

o eventual ettringite formation (C3A – 3CaSO4 – 32H2O)

o syngenite formation if humidity (CaSO4 – K2SO4 – H2O)

Humidity

Too hot temperatures

o Gypsum dehydration

Recommendations

Avoid too high level of alkali

Against humidity :

o Reduce stock time in winter

o Avoid water injection in the mill and cement cooler

Against Gypsum dehydration

use a mix: anhydrite/gypsum

Agglomeration and weathering : OPC HPR VZ
Air-setting (20 °C – 50 % HR labo)