Latest Developments in Concrete Research

Size: px

Start display at page:

Download "Latest Developments in Concrete Research"

Hubert Arnold
5 years ago
Views:

1 Latest Developments in Concrete Research Presented by: Elsabe Kearsley University of Pretoria

2 Introduction Background Concrete properties Appropriate test methods and specifications Examples of applications Modelling of reinforced concrete Conclusions Your Organisation

3 Background Historically we assume that concrete: consists of water, cement, sand and stone; needs to contain enough water to make it workable; strength is a function of water/cement ratio; is much stronger in compression than in tension; behaves in a brittle manner.

4 Background Concrete properties can be altered by: optimizing particle size distribution and thus packing density of composite; blending cementitious materials; adding chemicals such as high range water reducing agents; Including high performance fibres.

5 Appropriate test methods and specifications Self-compacting concrete

6 Appropriate test methods and specifications Ultra-thin high strength concrete

7 Appropriate test methods and specifications Compressive strength Flexural strength Tensile strength

8 Appropriate test methods and specifications Post-cracking strength of concrete

9 Appropriate test methods and specifications Concrete strength Fibre 7-day 28-day Content fcu fcu fbt fst E-value kg/m3 MPa MPa MPa Mpa GPa

10 Flexural stress (MPa) Appropriate test methods and specifications Effect of fibre reinforcing kg/m3 115 kg/m3 150 kg/m3 0 kg/m Deformation (mm)

11 Energy absorbed (Nmm) Appropriate test methods and specifications Effect of fibre reinforcing kg/m3 80 kg/m3 115 kg/m3 150 kg/m ,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 2 Deformation (mm)

12 Example of application WRC project on Moveable Lightweight VIP Superstructures Fibre reinforced selfcompacting concrete

13 Example of application WRC project on Moveable Lightweight VIP Superstructures

14 Example of application WRC project on Moveable Lightweight VIP Superstructures

15 Example of application WRC project on Moveable Lightweight VIP Superstructures

16 Ultra Thin Continuously Reinforced Concrete Pavements (UTCRCP) Concrete pavements normally rigid, unreinforced, 250 mm thick with movement joints closely spaced. 2006: South African National Roads Agency requires concrete pavement with life of 25 years without serious maintenance: Ultra Thin Continuously Reinforce Concrete Pavement (UTCRCP): 50 mm thick 90 MPa concrete 50 x 50 x 5.6 mm steel mesh 80 kg/m3 steel fibres No movement joints for kilometres

17 UTCRCP test sections

18 UTCRCP test sections

19 UTCRCP test sections

Full scale pavement testing Heavy Vehicle Simulator (HVS) can place 20 years of heavy

BUT a design method is needed: HVS places only half axle load no hogging.

$Behaviour of concrete can be modelled with fracture mechanics, but response of$

20 Full scale pavement testing Heavy Vehicle Simulator (HVS) can place 20 years of heavy traffic on pavement in 3 months. UTCRCP did not fail under aircraft wheel load. BUT a design method is needed: HVS places only half axle load no hogging. Mechanistic pavement design methods assume linear elastic behaviour of soil layers and use 2D analysis. Behaviour of concrete can be modelled with fracture mechanics, but response of supporting layers can not yet be modelled. Existing pavement models does not predict behaviour.

21 Centrifuge modelling Centrifuge scale models Used to increase soil stresses to realistic values

22 Model pavement construction LOAD mm Concrete layer (800 mm x 350 mm) 15 mm Stabilized base layer (800 mm x 360 mm) 15 mm Subbase layer (800 mm x 390 mm) 15 mm Selected layer (800 mm x 420 mm) 15 mm Backfill layer (800 mm x 450 mm)

23 Model pavement construction

24 Model pavement construction Concrete 8 7 Base 7 5 Subbase Selected Backfill 1

25 Model pavement construction

26 Model pavement construction LOAD mm Concrete layer (800 mm x 350 mm) 15 mm Stabilized base layer (800 mm x 360 mm) 15 mm Subbase layer (800 mm x 390 mm) 15 mm Selected layer (800 mm x 420 mm) 15 mm Backfill layer (800 mm x 450 mm)

27 Reinforcement properties

28 Concrete properties Centrifuge scale models at 10G Material kg/m 3 Cement (Cem II 42.5R) 450 Condensed Silica fume (CSF) 50 Water 210 Dolomite aggregate 1850 HRWRA 16 Micro Steel fibre Up to 80 Polypropylene fibre 2 Property Model Full scale Compressive strength (MPa) Tensile strength (MPa) Flexural strength (MPa) Modulus of elasticity (GPa) Typical sample density (kg/m 3 )

29 Vehicle load

30 Vehicle load

31 UTCRCP test results Concrete 8 7 Base 7 5 Subbase 4 3 Selected 2 1

32 UTCRCP test results (Cycle 29 & 30) Concrete Base Subbase Selected Concrete Base Subbase Selected

33 Preliminary findings Influence zone of wheel load on concrete slab much larger than expected. Relative movement between centre of slab and wheel path significant. Voids develop between concrete slab and soil layers. Stabilized layer beneath concrete slab seems to crack and not distribute load like other layers.

34 Preliminary findings The behaviour of scaled UTCRCP models in a centrifuge is similar to that observed during full-scale testing. Centrifuge modelling could in future be used to optimize UTCRC pavement designs by investigating: Effect of reinforcement spacing and layout Effect of relative layer stiffness Effect of layer thickness Effect of removing stabilized layers Suitable soil structure interaction models that can be used for design purposes.

35 Conclusions The use of cementitious materials in the construction industry can be significantly increased by using modern technology to optimize material properties and mechanical behaviour. Use materials with suitable properties; Optimize material properties; Use appropriate specifications; Use suitable test methods; Measure relevant properties; Cure concrete properly.

The World s First RPC Road Bridge at Shepherds Gully Creek, NSW

The World s First RPC Road Bridge at Shepherds Gully Creek, NSW Brian CAVILL, FIE Aust CPEng, Chief Technical Officer, VSL Prestressing Pty Ltd Gordon CHIRGWIN, BEng, MEngSc. MIE Aust, Manager Bridge Policy,