The chances in compressive strength (Table 6), flexural strength and modulus of elasticity for both types of concrete when immersed in 3 % NaCl and 5 % MgSO₄ solution were observed at 90 and 180 days. The results clearly indicate better durability of flyash added concrete to that of  OPC concrete (4) .

This fly ash concrete mix has been used by M/S Unitech construction India Ltd. for construction of 8 stories residential blocks at Gurgoan, Haryana.

 

Recent construction outside India

 

Bridges and tunnel built between FYN to Sprogo Island and from Sprongo to Zealand had a durability requirement of 100 years service life in Saline environment. This has been built with 50 Mpa concrete containing 300 Kg/m³ cement, 15 to 25 % flyash, 4 to 8 % silica fume using water cementitious ratio between 0.35 to 0.45.

 

Old fly ash added concrete structures

 

Results were obtained using old fly ash cement concrete structures along with various details such as, PFA % used, water/cementitious ratio, workability, 28 day compressive strengths along with carbonation depth and chloride penetration in both types of concrete (9). Following conclusions were drawn from these data and are presented herein.

 

Conclusions

i) For better performance and durability PPC is preferable in construction as it imparts improved workability and less heat of hydration.

ii) Even low-grade plan flyash cement concrete has improved workability and higher strength as well as durability.

iii) Reinforced concrete structures are being built with addition of flyash in concrete for better durability even in aggressive environment.

iv) Observations on old PFA concrete structures indicate

v) PFA concrete had higher strength at longer ages than OPC concrete though,   

      compressive strength of PFA concrete at 28 days was lower than  OPC concrete.

ii)   Equal grade of concrete will carbonate at equal rate.

iii)  PFA concrete will carbonate at higher rate at early ages but rate of    carbonation               

       will reduce at higher ages because of less permeability and    higher strength.

 

5) Chloride permeation is also less in PFA concrete as compared to OPC concrete thereby 

       having a better durability.

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