The challenge
The main design focus was the prestressed slabs, chosen for strength, durability, stiffness and serviceability. The specified concrete was M50, with at least 30 MPa after 48 hours. The original mix used 490 kg/m³ of cementitious material, a water cement ratio of 0.36 and an SNF admixture, and took three to four days to reach 30 MPa. The challenge was to reach strength sooner without raising concrete cost per m³ through more cement.
The DCP solution
The DCP technical team proposed Supaflo PC711, a high range polycarboxylate (PC) admixture, for evaluation by Larsen & Toubro. Trials at a water cement ratio of 0.35 with Supaflo PC711 reached the required compressive strength in a shorter time with less cementitious material.
DCP products used
How it was applied
- Original mix: cement and fly ash 490 kg/m³ (415 + 75), free water 175 litres, SNF at 1.2% by weight of cement, CA:FA 60:40, slump 120 mm at 90 minutes.
- Final mix: cement and fly ash 470 kg/m³ (380 + 90), free water 165 litres, Supaflo PC711 at 0.55% by weight of cement, CA:FA 62:38, slump 150 mm at 90 minutes.
- Both mixes: 20 mm and 10 mm aggregate at 60:40, 100% crushed sand.
The result
The required strength was reached after 2 days instead of 3 to 4, the contractor achieved its prestressing cycle and the cost of the concrete fell noticeably.
