What do you mean by pozzolanic activity?
The pozzolanic activity is a measure for the degree of reaction over time or the reaction rate between a pozzolan and Ca2+ or calcium hydroxide (Ca(OH)2) in the presence of water.
What is calcined pozzolan?
A natural pozzolan is a raw or calcined pozzolan that is found in natural deposits. A material is referred to as “calcined” when it has been heated below the temperature of fusion to alter its composition or physical state.
How is pozzolanic activity measured?
The pozzolanic activity is evaluated by determining the amount of lime consumed by the pozzolanic reaction during the test. In this test a mixture of pozzolan and calcium oxide is kept at 90°C for 16 h in a standard apparatus. Afterwards the amount of calcium oxide that did not react is measured.
Is calcined shale pozzolan?
Natural pozzolan basics The most common natural pozzolans used in concrete applications today include calcined clay, calcined shale and metakaolin.
What are pozzolanic admixtures?
Pozzolanic or Mineral admixtures are basically derived from other substances, not chemically manufactured. Popular examples of mineral admixtures are silica fume, fly ash, blast furnace slag etc. Mineral admixtures have different roles to play in the concrete mix and enhance various properties of the concrete.
What is the common thing in pozzolanic material?
The pozzolanic materials contain aluminosilicate glass phase that reacts with cement hydration product i.e. calcium hydroxide and form different hydration products (C3S2H3, C8AFH26, C3ACSH12, C4AH13) at different stages of curing (Zeng et al.
What’s pozzolanic cement?
Pozzolanic cements are mixtures of portland cement and a pozzolanic material that may be either natural or artificial. The natural pozzolanas are mainly materials of volcanic origin but include some diatomaceous earths. Artificial materials include fly ash, burned clays, and shales.
Which material was responsible for pozzolanic properties in the mix?
Pozzolana and Pozzolanic Cements Owing to the chemical composition of clay and related materials, these artificial pozzolanas are mostly composed of silica and alumina.
What is the common thing in pozzolanic materials?
What are examples of pozzolanic materials?
Examples of pozzolanic materials are volcanic ash, pumice, opaline shales, burnt clay and fly ash. The silica in a pozzolana has to be amorphous, or glassy, to be reactive.
What are the types of pozzolanic material?
Types of Pozzolanic Materials | Admixtures | Concrete Technology
- Natural Pozzolanic Materials: Under this group following materials can be grouped: Calcined diatomaceous earths. Volcanic ash, tuffs and pumicites. Opaline cherts.
- Artificial Pozzolanas: Under this group following substances are grouped: Silica fume. Fly ash.
What are pozzolanic mixtures?
What is the difference between pozzolanic and cementitious materials?
They may or may not be further processed for use in concrete. Some of these materials are called pozzolans, which by themselves do not have any cementitious properties, but when used with portland cement, react to form cementitious compounds. Other materials, such as slag, do exhibit cementitious properties.
Where is pozzolana used?
Pozzolana is abundant in certain locations and is extensively used as an addition to Portland cement in countries such as Italy, Germany, Kenya, Turkey, China and Greece. Compared to industrial by-product pozzolans they are characterized by larger ranges in composition and a larger variability in physical properties.
What are the advantages of pozzolanic materials?
The advantages of using pozzolans in concrete include the following: (1) material cost reduction when a part of the cement is replaced by pozzolans, which are low cost (with some of them being natural or industrial by-products/wastes) and pollution free; (2) environmental cost reduction in relation to reducing the …
What is pozzolanic explain various pozzolanic materials?
Pozzolanic materials are siliceous and aluminous materials, possessing little or no cementitious value by themselves, but in finely divided form and in the presence of moisture react chemically with calcium hydroxide liberated on hydration of cement at ordinary temperature to form compounds, possessing cementitious …
What are pozzolanic materials and what are the advantages of adding pozzolanic material in concrete?
Pozzolans act as extenders, but because they form cementitious compounds by reaction with Portlandite, they also contribute to the compressive strength of the set cement. The most common pozzolans used in well cement systems are artificial pozzolans; mainly fly ashes and high surface area amorphous silica products.
Which is the natural pozzolanic material?
Natural pozzolans include rocks of volcanic origin (e.g. vitreous rhyolites from the Rocky Mountains in the USA or German and Turkish trasses), as well some sedimentary clays and shales. Some may be used as they are, while others undergo a process of thermal activation (e.g. calcined clays).
What are the types of pozzolana and their characteristics?
Types of Pozzolans
- metakaolin.
- silica fume.
- fly ash.
- slag.
- VCAS (vitrified calcium alumino-silicate)