FINENESS TEST OF FLY ASH

Fly ash, also known as flue-ash, is an industrial waste and a material of pazzolanic characteristics occurring due to burning the pulverized coal in thermal power plant.

In construction sector, the fly ash is used in production of cement as an additive –material in production of concrete instead of some of the cement or instead of some of the fine aggregates, as a base and sub-base material in highway construction, as a filling material in dams, in retaining walls.

The fly ash fineness affects the strength, drying shrinkage and the resistance to sulfate solution attack. It is generally agreed that the use of fine fly ash improves the properties of concrete. Sieved fine fly ash increases the strength of mortar as compared to that of mortar made from original coarser fly ash. The different fineness portions of fly ash appear to have a slight but consistent variation in physical and chemical properties. The fly ash with different fineness had a marked effect on the compressive strength as well as drying shrinkage and sulfate resistance. The incorporation of the fine fly ash reduced the water requirement of the mortar mixes. The coarse fly ash portion, lacking both the medium and the fine portions increased the water demand owing to the rougher surface of the coarser particle. The fine fly ash with high surface area was more reactive and results in the increase in strength. The fine fly ash also required less water owing to its spherical shape and smooth surface. Its packing or filling of the voids helped increase the compressive strength of the mortar.

All the fly ashes reduced the shrinkage of the mortars. It is known that the drying shrinkage is influenced by many factors in which water content is the prime factor as the fine fly ash mortars with low W/B exhibited low drying shrinkage and the coarse fly ash mortar with high W/B showed relatively high drying shrinkage.

With regard to the sulfate attack, it is evident that the incorporation of the fine fly ash reduced the expansion of the mortar bars immersed in the sodium sulfate solution. The fine fly ash reduced the W/B of the mortar thus made it denser and stronger. The use of the coarse fly ash resulted in an increase in the expansion as W/B of the FC mortar was rather high.

The method for determination for fineness is recommended by Indian standard specification IS: 4031 Part-3 1999.

Apparatus Required:-

1) Standard balance with 100 gms weighting capacity.2) IS: 90 micron sieve confirming to IS: 460-1962 and a brush.

Procedure:-

a) Break down any air-set lumps in fly ash sample with fingers.b) Weigh accurately 100 gms of fly ash and place it on a standard 90 micron IS sieve.c) Continuously sieve the sample for 15 minutes.d) Weigh the residual left after 15 minutes of sieving. This completes the test.

Readings of Experiment:

Weight of sample(fly ash) 100gWeight of the sieve 295.65gWeight of sieve + sample 311.91gWeight of the residue 16.26g

Results:-

The percentage weight of residue over the total sample is reported.

Percentage Weight of Residue ¿Weight of sampleretained onsieve

Total weight of sample X100

¿16.26100

X100

¿ 16.26%