Section 5: Steel Placement
In this section, only the placement of longitudinal and transverse rebars is described. The placement of other rebars, such as tie bars and dowel bars, is described in Section 7, “Joints.”Anchor: #i1006511
The longitudinal reinforcing steel keeps the naturally occurring transverse cracks in continuously reinforced concrete pavement (CRCP) tight, thereby providing high level of load transfer across cracks. When transverse cracks are kept tight, aggregate interlock also transmits the shear forces across the crack, resulting in reduced wheel load stress and fatigue damage in concrete.
Transverse reinforcing steel is used to provide support for longitudinal steel. It also keeps longitudinal cracks tight if they occur.
ASTM A966 Type R bars may only be used as straight bars and only in concrete pavements. This type of bar is permitted to encourage the use of recycled steel in TxDOT concrete paving projects. It may not meet the “pin” test requirements of ASTM and may not have sufficient strength if bent. If this type of reinforcing steel is used in concrete pavement, care must be taken that these bars are not diverted to other uses on the project.
Only Grade 60 deformed steel bars that meet the requirements of the Item 440 are used. Grade 70/75 steel bars have been used in some TxDOT projects and no pavement performance improvements have been noted. On the other hand, when reduced amount of longitudinal steel was used with Grade 70/75 steel, transverse cracks were wider than those in sections with Grade 60 steel. Cracks with larger widths reduce load transfer across cracks, resulting in larger wheel load stress and poor long-term CRCP performance.
The reinforcing steel should be placed at the locations shown on the plans. As the pavement thickness increases, the amount of steel is increased. For thinner pavements, all the steel is fit into one mat or layer of steel placed at the mid-height of the pavement.
For 14- and 15-in. thick concrete pavements, two layers of steel are necessary. Enough room must be provided between adjacent bars to allow the plastic concrete that is placed on top of the steel mat to pass completely through the steel mat to the lower portion of the concrete placement.Anchor: #i1006546
Storing Reinforcing Steel
The steel must be stored above the surface of the ground upon platforms, skids, or other supports and shall be protected from damage and deterioration. This prevents excessive rusting that would occur if sitting directly on the ground. It also prevents mud and dirt from collecting on the steel.
When placed in the work, reinforcement shall be free from dirt, paint, grease, oil, or other foreign materials. Reinforcement shall be free from defects such as cracks and laminations.Anchor: #i1006561
Splicing Longitudinal Steel
In CRCP, maintaining steel continuity in the longitudinal direction is important in ensuring good performance of the pavement. The length of the reinforcing steel bars is 60 ft. The continuity of the longitudinal steel is achieved by overlapping individual steel bars. Extensive testing shows that as long as the overlapping is more than 33 times bar diameter, stresses in one steel is effectively transferred to the next steel via surrounding concrete. For example, No. 6 bars would need a 25-in. splice for effective stress transfer. Figure 9-14 shows an example of spliced or lapped reinforcing steel.
Figure 9-14. Spliced or Lapped Reinforcing Steel.Anchor: #i1006583
If all the splices occur at the same longitudinal location, transverse cracks that occur at the location could cause steel bonding failure, resulting in wide cracks and performance problems. To make sure that all the splices do not occur at the same transverse location, Item 360 requires staggering splices to avoid having more than 1/3 of the splices within a 2-ft. longitudinal length of each lane of the pavement.
Figure 9-15. Acceptable Splicing Pattern- 33% (4 of the 12 bars) within the box are spliced.
Figure 9-16. Acceptable Splicing Pattern.
Figure 9-17. Acceptable Splicing Pattern.
Figure 9-18. Non-acceptable Splicing Pattern – 66% of bars in the box are being spliced.Anchor: #i1006643
Holding the Reinforcing Steel in Place
Contractors like to keep the steel mat from moving excessively prior to paving due to the paving operation itself or because of temperature changes. Figure 9-19 shows a piece of reinforcing steel being used as a pin. This pin can be left, or can be removed before the concrete pour.
Figure 9-19. Pinning the mat.
Steel depth has an effect on CRCP performance. Design Standards CRCP (1)-03 and CRCP (2)-03 requires the tolerance of longitudinal steel at +/- 1 in. horizontally and +/- 0.5 in. vertically. Figure 9-20 illustrates the checking of the depth of steel.
Figure 9-20. Checking depth of steel.