1. Optimising Building Design for Sustainability Using High Performance Concrete Doug Jenkins - Interactive Design Services Daksh Baweja – The University of Technology, Sydney. Joanne Portella– DMC Advisory, Melbourne.

2. Introduction Focus of emissions reduction strategies in Australia has been on cement reduction. –Can significant emissions reductions be made with the use of high strength concrete? Outline of study: –Effect of high strength concrete and high supplementary cementitious material (SCM) content on total CO 2 emissions. –Typical flat slab building structure –5 grades of concrete –Reinforced or post-tensioned slab

3. Alternative Concrete Mixes

4. Component Emissions

5. Embodied Energy Calculation

6. Concrete Emissions Analysis Emissions based on emissions of component materials multiplied by material content Cement emissions allow for 5% mineral additions Total mix emissions mainly controlled by cement content Based solely on emissions per cubic metre of concrete, the 25 MPa standard structural mix, and the 40 MPa high SCM mix appear to offer the minimum CO 2 -e emissions.

8. Flat Slab Layout

9. Structural Design Procedure Design to AS 3600 simplified method. Checked to equivalent frame method (Warner et al) Prestress force balanced approx. 85% of dead load Deflections checked with non-linear finite element analysis

10. Slab Sections Reinforced slab depth controlled by deflections: 25 MPa – 300 mm 40 and 65 MPa – 250 mm Prestressed slab depth controlled by punching shear 40 MPa – 180 mm 65 MPa – 170 mm

11. Deflection Analysis Non-linear finite element analysis; 4 node plate-shell elements Stress-strain curve formulated to give correct moment-curvature behaviour, allowing for: Cracking of the concrete Tension stiffening and loss of tension stiffening Long term creep and shrinkage effects

12. Typical FEA Mesh

13. Vertical Deflections, Slab 1-B

14. Vertical Deflections, Slab 1-C

15. Vertical Deflections, Slab 2-C

16. Deflection Results Long term deflection of reinforced slabs greatly increased due to flexural cracking, shrinkage and creep effects Deflections of prestressed slab greatly reduced, and increase in deflection with time much less because the section remains uncracked.

17. Emissions Analysis Results

19. Conclusions The mixes with minimum emissions allowed a small reduction in CO2 emissions for the reinforced slabs, compared with the standard “reference case” concrete. All of the prestressed slabs showed a much more significant reduction in total emissions, in spite of the higher cement content of the concrete used. The high SCM 40 MPa mix gave the lowest overall emissions with a prestressed slab, but the emissions from the 65 MPa mix were only marginally higher.

20. Conclusions Higher strengths allowed the use of a reduced depth of slab, with associated savings in other works. These savings were not included in this analysis. The high SCM mixes had a reduced early-age strength which is likely to impact on the construction program.

21. Conclusions The overall reduction of CO2 emissions was not a simple function of the reduction of Portland cement in the concrete, but was also based on how the material properties of the concretes used influenced the structural efficiency of the design.