710 - Waterproofing and Protective Covers
Joint waterproofing is conducted at locations where a concrete joint is located below grade thus creating the potential for leaking or seepage due to infiltration through the soils. An example of a common joint that requires joint waterproofing is the joint between the abutment bridge seat and backwall.
The joint waterproofing material is a preformed membrane that is applied to the back side of the joint to be sealed per the project plans. The membrane is a minimum 18 inches wide and typically requires a prime coat for adhesion per manufacturer’s recommendations. This joint is then covered with backfill as soon as practical to avoid sagging in the membrane. Approved membranes can be found in the Qualified Products List section 914.11.
- A. The integrity of the membrane and its waterproofing capabilities relies upon the bond between the membrane adhesive and the concrete. The membrane is to be applied within 4 hours of removing the form work at the location requiring the waterproofing. The air and concrete temperatures must be greater than 40 degrees prior to beginning surface preparation. The 4 hour requirement may be adjusted accordingly to meet the temperature limitations. The surface of the concrete must be dry, clean and free from sharp edges or intrusions. Ensure the contractor fills any surface with a MDOT approved epoxy mortar, mortar, or concrete. These patches must be cured for 24 hours prior to placement of the membrane. Abrasive blasting with compressed, oil-free air is required to remove all contaminates and prepare the surface for the membrane. The surface is to be prepared and primed 12 inches either side of the joint to accommodate the 18 inch membrane.
- B. Apply the membrane in accordance with the manufacturer’s recommendations and section 710 of the Standard Specifications for Construction. Prior to backfilling the engineer may require the contractor to demonstrate the membrane is adhered to the concrete and free from wrinkles and tears. Any tears in the membrane may be patched with additional membrane material overlapping 6 inches either side of the area to be patched.
Expansion joint waterproofing is used at locations indicated in the plans as expansion joints in the substructure, or at integral and semi-integral backwall abutment locations. Expansion joint waterproofing in applied in similar fashion to the joint waterproofing described in 710.01 of the Construction Manual except that a bond breaker and two layers of membrane will be used.
The beveled surfaces at the expansion joint location will not receive the prime coat and will instead receive a bond breaker to prevent adhesion of the membrane at this location. This allows for rotation, expansion and contraction of the substructure at this location without tearing the membrane. Place the bond breaker at the beveled surfaces, then prime the surface 12 inches either side of the joint. Place the membrane per 710.01 of the Construction Manual ensuring the membrane follows the contour of the beveled surfaces. This “slack” in the membrane allows for the required expansion. A second layer of membrane must then be placed over the first layer. Prime the first layer per manufacturer’s recommendations. A bond breaker is not needed for the second coat. Apply the second layer of membrane and backfill after adhesion amongst the layers and concrete has been demonstrated.
Bridge deck waterproofing with HMA overlay is applied per subsection 710.03.C of the Standard Specifications for Construction. HMA overlays are susceptible to water permeation, and the waterproofing membrane is critical is preserving the concrete deck below the HMA overlay. In this regard care should be taken to adhere to specifications when placing the waterproofing membrane to ensure the membrane is applied correctly and not damaged during placement of the HMA.
Shotcreting is a method of applying latex modified concrete to patch locations by means of pneumatically ejected concrete material mixed with the latex at the nozzle. Shotcrete is typically used for substructure repairs where forming and/or concrete placement by conventional means is difficult.
Shotcrete equipment and materials can be difficult to calibrate and apply to the substrate. In this regard shotcreting is very dependent upon the skill of the operator or “nozzleman”. Test panels are required to demonstrate to the engineer the ability of the nozzleman to provide a satisfactory patch. The test panel should replicate the field placement in terms of thickness and steel reinforcing pattern, but be at least 3 inches thick. After test panel placement, the concrete must be kept continuously wet and above 40 degrees for at least 5 days. Five cores must then be taken from the panel and tested in accordance with subsection 710.03.D.1 of the Standard Specifications for Construction.
- A. Prior to shotcrete placement for concrete patches all loose material must be removed from the patch. Edges surrounding the patch must be saw cut ½ inch. Care should be taken not to damage sound surrounding concrete during removal operations. After concrete removal, the areas to be patch must be blast cleaned with a compressed, oil-free air to remove all contaminates.
- B. Ensure the contractor uses galvanized or epoxy coated reinforcement wire for all patches greater than 2 inches deep. The reinforcement should be placed at mid depth of the repair, or at least 1 inch from the face of the repair. Ensure the contractor uses stainless steel anchors spaced no more than 18 inches on center in each direction.
- C. Immediately prior to shotcrete placement the patch must be wetted with the liquid latex component to be used during the shotcrete operation. Place shotcrete in several passes until the required thickness is met. Large areas may be broken down into smaller sections for placement; however, the final thickness must be achieved prior to moving to the next section. Laminations in the shotcrete should be avoided. The nozzleman must keep the nozzle 2 to 6 feet away from the surface and as near as perpendicular to the surface as possible. Do not apply shotcrete if high winds prevent proper application, the surface temperature of the concrete is less than 45 degrees, or during rain causing washouts or sloughing of the fresh concrete. Place shotcrete in accordance with section 710.03.D.3 of the Standard Specifications for Construction.
- D. Cure shotcrete in accordance with subsection 706.03.N.3 of the Standard Specifications of Construction.
- E. The engineer may require cutting cores from the completed work for compression testing. If tests are order, three samples should be taken and tested in accordance with subsection 710.03.D.1 of the Standard Specifications for Construction.