The Effects Of Sugar Cane Bagasse Ash As Suplementary Cementitious Material In Production Of Concrete

2.4.2.3 Setting time
    Setting is a process in which cementitious mixtures of plastic consistency is converted into a set material which has lost its deformability and crumbles under the effect of sufficiently great external force(Hewlett and Lea's, 2004). It is preceded by a stiffening of the paste in which the apparent viscosity of the material increases without losing its plastic character. There are two types of setting time i.e. initial and final setting times. The initial setting time indicates the time at which the paste begins to stiffen considerably and can no longer be molded; while the final setting time indicates the time at which the paste has hardened to the point at which it can sustain some load. Like normal consistency these tests are also used for quality control
 2.5 Pozzolans
    The modern concrete technology uses different types of admixtures in order to enhance the properties of the fresh and hardened concrete. Mineral admixtures are one of these admixtures used in concrete for a variety of purposes. They may be found naturally or artificially. These admixtures can be divided into three main categories, which are pozzolanic, cementitious and non-reactive materials. The first two categories are added at the mixer as supplementary cementing materials. These admixtures interact chemically with the hydrating Portland cement and form a modified paste microstructure. The non-reactive admixtures are on the other hand finely divided materials such as lime-stone, silica flour, hydrated lime, etc, which may sometimes react weakly with the cement. They are blended with Portland cement to form masonry cements which have improved workability. In this research we are concerned with, , cementitious material which are described below.
2.6 Supplementary Cementitious Materials (SCM)
    Alternative cementitious materials are finely divided materials that replace or supplement the use of Portland cement. Their use reduces the cost and/or improves one or more technical properties of concrete. These materials include fly ash, ground granulated blast furnace slag, condensed silica fume, limestone dust, cement kiln dust etc. The use of these cementitious materials in cement offer advantages such as increase cement plant capacity, reduce fuel consumption, low greenhouse gas emissions, control of alkali-silica reactivity etc.
Pozzolanic materials can be divided into two groups: natural pozzolana and artificial pozzolana. Clay and shales, opalinc chert, diatomaceous earth, and volcanic ash are example of natural pozzolans while fly ash, blast furnace slag, silica fume, rice husk ash, and metakaoline are example of artificial pozzolans. Most of the pozzolans in use today are mainly by-product materials that are widely available.  Because of the diversity of pozzolans their chemical composition also varies therefore classifying pozzolans only depending on their chemical composition would be difficult. For this reason ASTM C 618 classifies pozzolans depending on performance basis. ASTM C 618 chemical composition for pozzolans is as shown in Table 2.2.

Chemicals tightness, reduction in the alkali aggregate reaction, resistance to sulfate attack, better workability, and cost efficiency are some of the improvements achieved by using pozzolans blended with Portland cement.