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Ambuja Cements Limited

Composite Cement is covered under IS: 16415-2015 and presents a good opportunity to produce high strength concrete which is highly durable. Composite cement is a mixture of high quality clinker (IS:16353-2015), fly ash (IS:3812 (Part 1) - 2013), granulated slag (IS:12089-1987) and gypsum. Typical range of these components is clinker (35% to 65%), fly ash (15% to 35%), granulated slag (20% to 50%) and gypsum (3% to 5%).

Scope of study: The study was conducted to understand the effect of Composite Cement into concrete performance in the form of strength, workability and chloride penetration along with PPC. Concrete mixes with 300 Kg/m3, 400 Kg/m3 & 500 Kg/m3 with W/C 0.3, 0.4 & 0.5 were tested to understand the impact on the critical concrete properties. To get desired workability, appropriate chemical admixture was used with fixed dosage for each set of concrete mixes. Workability measurement (initial slump and slump at 60 minutes) and strength measurement at the age of 1, 3,7,28 and 90 days was done. RCPT test was done to ascertain the chloride penetration resistance of concrete mixes.

Workability: The study was conducted with 9 nos. different concrete mixes with varying cement content and water cement ratio. Concrete mixes with lower cement content and relatively higher W/C, PPC offers better workability whereas for richer mixes and lower W/C, Composite Cement offers better workability. The overall concrete rheology with Composite Cement was much better and mix was very cohesive than PPC concrete. The reason behind getting lower slump value with Composite Cement may be due to the crystalline slag particles and its effect of holding entrapped water into the green concrete matrix. We observed that the concrete mixes made with Composite Cement were releasing some water after giving little vibration even after 60 minutes and exhibited more workability than concrete mixes made with PPC.

Compressive Strength: The one day strength pattern shows excellent early strength with Composite Cement Concrete vis-à-vis PPC Concrete of the same plant and same batch. All mix combinations have shown the same pattern though the gap is wider in case of lowest water cement ratio i.e. 0.3 with 300Kg/m3 and 500kg/m3 combinations.

Seven days compressive strength results of all the concrete mixes for PPC and Composite Cement shows at par values, specifically for mixes with lower cement content and higher water to cement ratio. At the same time for concrete mixes with higher cement content and lower W/C, PPC gives slightly better strength in comparison to Composite Cement.

Later-age strength development pattern exhibits better strength with Composite Cement for lower cement content and relatively higher W/C. For moderate cement content and W/C, both the cement gives similar strength. Whereas for richer concrete mixes and lower W/C, PPC gives slightly better strength.

We have observed that concrete mixes with higher cement content and lower W/C gives much workable mix in case of Composite Cement vis-à-vis PPC (at 60 minutes) with the same amount of admixture dosage.  So there is a scope for reduction of water content and hence may achieve better strength with Composite Cement.

Rapid Chloride Penetration Test Results:

RCPT test results shows better resistance to chloride ion penetration in concrete made with Composite Cement vis-à-vis PPC. The concrete mix was selected with moderate cement content i.e. 400kg with variable W/C. Each set consist of both PPC and Composite Cement. Almost in every case, Composite Cement gives better resistance to the chloride ion penetration, hence lower RCPT value.

Conclusion:

Composite Cement offers better opportunity to conserve natural resources in terms of limestone by replacing higher percentage of clinker, having lower carbon footprint without compromising on concrete properties in green and hardened state. The finding of this study might be useful to accept Composite Cement for different concrete applications in construction.