Their content in Portland pozzolana cement is about 15% ~35%, and gypsum is about 3%-6%.
Pozzolanic materials contain active silica and aluminum and usually do not have any cementitious properties. But when they are mixed with water and lime at ambient temperatures, they will react with calcium hydroxide to form compounds possessing cementitious properties. The commonly used pozzolanic materials can be classified as natural or artificial:
What is Portland Pozzolana cement? The hydraulic cementitious materials made of Portland cement clinker, pozzolanic material, and a proper amount of gypsum are all called Portland pozzolana cement (PPC cement). It is a kind of blended cement that is manufactured by mixing and fine-grinding silicate cement clinker, pozzolanic material, and gypsum.
PPC cement needs a long time for curing, and the curing temperature has a significant influence on its strength development. When the temperature is low, the hardening rate becomes slow. When steam curing or humid heat treatment is used, the hardening is accelerated, so this cement is not suitable for winter construction.
The initial strength of PPC cement is less, but the final strength is high. This is due to the active silica in the pozzolanic material interacting with calcium hydroxide to produce a large amount of hydrated calcium silicate.
The water requirement of PPC cement is large because the mixture material is porous and has fine particles. The water requirement of standard consistency varies with the type and amount of admixture.
The setting time of Portland pozzolana cement is relatively long, the initial setting time needs at least half an hour, and the final setting time needs 10 hours at most.
The drying shrinkage of Portland pozzolana cement should not exceed 0.15%. The fineness of pozzolana cement should not be less than 300m2 /kg.
PPC cement has good compressive strength that can reach 13MPa in 3 days, 22 MPa in 7 days, and 33 MPa in 28 days.
The hydration rate and hydration heat of PPC cement are low, which is related to the variety and quantity of mixed materials.
PPC cement has a high resistance to sulfate attack in acid water and carbonic acid environment.
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