Use of Functional Grading to Improve the Early Age Performance of Low Carbon One-Way Slab Strips

Concrete production is responsible for up to 10% of global anthropogenic CO2 emissions. To combat this issue, low carbon concrete (LCC) mixes have been developed. However, LCC may gain strength more slowly than ordinary Portland cement (OPC) concrete. With tight construction schedules often requiring that forms are stripped as quickly as possible after pouring, concrete that gains strength slower could result in construction delays. One solution to this is the use of functionally graded concrete (FGC), which is the layering of different types of concrete in a member to enhance performance or reduce material use. In the current study, the behaviour of FGC slab strips with LCC bottom layers and OPC concrete top layers (in the flexural compression region) were compared to that of control LCC slab strips. Lightly (ρ = 0.33%) and moderately reinforced (ρ = 1%) slab strips were tested for each type of specimen including early age (3 or 4 days after cast) FGC, early age control LCC, and 50 + day control LCC. The six one-way slab strips were tested in four-point bending and monitored with linear potentiometers and distributed fibre optic sensors. It was found that the early age FGC specimens had higher stiffness when compared to the LCC control specimens at the same age (curvatures up to 23% lower and deflections up to 14% lower at service), especially for the moderately reinforced slabs. Furthermore, the moderately reinforced FGC slab had 11% higher capacity at three days versus its LCC counterpart.