1 Concrete Pavements for Local Government Forms, reinforcement, joints, dowels & tiebars The quality of the placed Concrete will be no better than the quality of setting the forms, fixing the reinforcement, and installing the joints. For each of these activities, the input of the paving crew is vital. Concrete Pavements for Local Government Forms Setting fixed forms - basic principles Thickness & width Line & level Edge vertical Fixed forms have to withstand forces caused by the fresh Concrete during placing. They need good : Support Bracing Pinning Jointing Basic formwork components Hard smooth edge Form & Brace at Securely base suitable pinned plate spacing Packing if required Supporting ground Connecting forms Firm connection Pins on between forms both sides of join Smooth top Brace on edge across both sides of join in forms!
2 Join Supporting ground Fixed form detailing in the field (M4 1980 De Martin and Gasparini). A very good result using good basic rules Form bracing &. pinning Form join Firm continuous support Good running surface Good timber formwork Simple, low cost - all the right elements in place Limited repeats without a metal running surface Need to keep running surface clean and in good condition Terrible timber formwork No bracing Pegs not sufficient Poor running surface for screed Large gap under forms if Concrete moves, it can't be compacted!
3 Non conforming formwork How can the Concrete be fully compacted ? Non conforming formwork Form face not vertical top edge of the Concrete will spall Concrete Pavements for Local Government Reinforcement Basic principles Three general criteria are important for steel reinforcement in Concrete road Pavements : Reinforcement, where required, is not to prevent cracking but to control cracking which is assumed may occur. The amount of steel used is small and, combined with its location in the base, is insufficient to add to the flexural strength of the pavement .
4 Even in plain Concrete Pavements (PCP), reinforcement is required in certain slabs. Crack formation Cracking is from shrinkage/curling not traffic Crack starts from top and progresses down Reinforcing mesh in jointed Pavements Reinforcement in TOP. third, with the minimum Reinforcement stops cover on drawings, and short of joints - joints supported on chairs must be able to open/close Supporting ground Reinforcement at contraction joints Contraction joint must open and close - no restriction Reinforcement stopped short of joint Only dowels cross the intended line of the joint Reinforcement not to be disturbed during placing They're going to have to walk in there Mesh stability bar chairs on a regular grid of say 1m Often use SL82 even if less required CRCP reinforcement Follows the same principles as for mesh set at
5 Correct height on bar chairs Less likely than mesh to be disturbed much heavier Concrete Pavements for Local Government Joints General jointing principles Plain Concrete design basis Sufficient joints to anticipate cracking Based on experience General joint types Plain Concrete slab size Keep it simple . Square or near square Max 1 : For 200mm thickness, max side / preferable For 150mm thickness, max side / preferable For 125mm thickness, max side / preferable Joint design objectives Control cracking Provide capacity to transfer loads without stepping or faulting' at joint Design joint layout for practical/economical construction Contraction joint PCP.
6 Preferably sawn D/4. PCP-D doweled joint Slab length can be increased a little Joint is dowelled to cater for the additional shrinkage m max Plain Concrete pavement PCP. 5 m max Plain Concrete pavement - dowelled PCP - D. X. Base formats - 1. Jointed reinforced (JRCP). It is often asked - Can I avoid all these joints? . Yes, but once the slab length is more than about 5m, you must expect some cracking To stop crack from further opening, reinforcement is required Basis for JRCP. mesh reinforcement 8 - 15 m typ. Jointed reinforced dowelled Concrete pavement JRCP - D.
7 Bar reinforcement 1 - m typ. Cracking in JRCP. Cracks are expected to happen in JRCP. Cracks do not equal failure . Longitudinal joints Not designed for movement Tied (not doweled). Some allowance for rotation'. Weakened plane (sawn), or formed construction joints Formed longitudinal joint Keyways were discontinued 35 years ago Top of female element is prone to breaking/spalling Replaced by corrugated tied joints Current practice Corrugated joint Longitudinal joint NSW country town street built 1940s No joint down centre so it made its own Isolation joints Isolation joints, not be confused with expansion joints, are required in situations where conflict may arise between two Concrete elements.
8 Two typical situations in a road are: At an intersection. The two intersecting roads will tend to move longitudinally in conflicting directions Where a pit or other road penetration is either at the pavement edge or within the pavement Isolation joints Isolation joint Pit intruding from kerb into pavement Isolate pit from pavement Thickened edge slab reinforced (precaution). Isolation joint Full depth gap, no need for more than about 10mm Filler and sealant No load transfer capacity subgrade beam required Concrete Pavements for Local Government Dowels & tiebars Dowels and tiebars they are different Dowels Joint able to move Short thick smooth Alignment is critical Tiebars Joint tied Long and thin deformed bar for anchorage Alignment important but not critical Dowel support Dowels in transverse contraction joints must be supported by baskets/cages so that.
9 They maintain dowel alignment They are not disturbed by the paving operation from pre-set position Nothing but the dowel crosses the intended joint line to avoid any restriction on joint movement Dowel alignment Joint must be able to open/close Dowel alignment is critical Must be parallel to : Each other Road centreline pavement surface Dowel debonding debonding coating to one half length + min 25mm debonding must debond and stay on during paving debond additional 25mm to allow for construction sawcut tolerance intended joint line Dowels out of line what happens?
10 Joint locked up Crack may form near back-end of dowels, not at joint May have to remove and rebuild whole of this area . not a good move The force applied to dowel cages by Concrete is significant Tiebars in longitudinal joints Long deformed bar for anchorage Thin bar (12mm) to allow some curling'. Located mid depth Same for sawn or formed joint Spacing depends on the width and thickness of the tied slabs Typical tiebar arrangement 200 mm 4 bars @ 1050 mm min 300mm to avoid joint Tiebars in longitudinal joints Good alignment and depth location Tie bars left out near transverse joints to allow them to open and close Now we're ready to start paving!