Chapter 9 – Joint Design, Layout, Construction, Sawing and Sealing
Hot-Poured Joint Sealing
Hot-poured sealants usually consist of some combination of asphalt, coal-tar, and rubber. Be- fore sealing the joints, the contractor needs to demonstrate that the equipment and procedures for preparing and placing the sealant will pro- duce a satisfactory joint seal. The sealant needs to bond to the concrete surface of the joint walls, have no voids, and needs to be tack-free after a specified time period. The key to achieving good joint sealing include:
1. Install the closed-cell backer rod to the appropriate depth to achieve the right shape factor.
2. The backer rod should not bond to the concrete or sealant; bonding induces stress in the sealant.
3. The backer road needs to be compressed about 25% if it is to maintain its position in the joint.
4. Heating kettle needs to be an indirect heating type kettle. Direct heating ele- ments can cause changes in materials properties. The kettle also needs an agi- tator to prevent localized overheating.
Material that is overheated can lose plas- ticity. Any overheated material should be discarded.
5. The application wand needs to be fitted with a re-circulation line. Otherwise, sealant in the hose can drop below appli- cation temperature.
6. Filing the reservoir is accomplished from bottom to top. Care needs to be taken that the sealer is applied such that the material is solid with no entrapped air.
7. It is a good practice to have a trial instal- lation to verify that the sealant is capable of achieving a good bond.
8. The sealant needs to be recessed from the surface to protect it if traffic that needs to use the pavement soon after
Cold-Poured Joint Sealing
Cold-poured sealants are usually polysulfides, polyurethanes, or silicones. The material can be ready to use one component or it can be two- component material requiring mixing at the site.
Before sealing the joints, the contractor should demonstrate that the equipment and procedures for preparing, mixing, and placing the sealant will produce a satisfactory installation. The sealant needs to bond to the concrete surface of the joint walls, have no voids, and needs to be tack-free after a specified time period. The fol- lowing are the key items to consider:
1. Depending on the material, and the rec- ommendation of the manufacturer, the cold-poured materials may be mixed in a paddle wheel or other mixer, or fed from separate containers to a mixing nozzle that is also used to inject the material into the joint.
2. A silicone is either self-leveling or non- self-leveling. These materials cure by a chemical reaction from a liquid state to a solid state.
3. The potential for incompatibility between silicone seals and the concrete aggre- gates must be checked. A silicone sealant that does not develop proper bond with aggregates is going to fail.
PAVING ALERT
Clean Air = Clean Joint Face:
The air stream needs to be free of oil. Many modern compressors automatically insert oil into the air lines to lubricate air-powered tools.
For joint cleaning, this line needs to be dis- connected and an effective oil and moisture trap needs to be installed.
In most cases, the inside of the hose of a lu-
Chapter 9 – Joint Design, Layout, Construction, Sawing and Sealing
4. Aggregate surface moisture at the time of sealing can affect the bond between sili- cone and concrete. The use of a joint primer provided by the manufacturer may need to be considered to ensure that the silicone seal develops satisfactory bond to the joint reservoir face.
5. Cold-poured materials are generally more sensitive to moisture in the reservoir.
Therefore, it is essential to check that the reservoir is dry when the sealant is in- stalled.
6. Cold applied joint sealing compound needs to be applied by means of pres- sure equipment that will force the sealing material to the bottom of the joint and completely fill the joint without spilling the material on the surface of the pavement.
7. Non self-leveling sealants require addi- tional tooling to maintain the required depth of sealant. Tooling of non self-level- ing sealants must be performed before the material cures.
Preformed Joint Sealing
Most preformed seals are made of extruded neoprene rubber. These sealants are also called compression seals. The neoprene mate- rial is compressed and inserted into the joint reservoir. The pre-compression amount is based on the anticipated movement of the joint over the service life of the sealant.
The key aspects of achieving a good preformed sealant application are as follows:
1. For the sealant to be effective during its service life, the sealant material must be maintained in the sealant reservoir at a minimum amount of compression (i.e., it is always in compression).
2. The sealant manufacturer’s recommen- dations are to be followed for sealant siz- ing and installation.
3. The sealant needs to be inserted using a device that uniformly compresses the sealant with nominal stretch.
4. The sealant needs to be lubricated, straight, vertical, and not damaged.
5. The installation device should not stretch the sealant. This reduces the allowable sealant compression and sealant failure can occur. The maximum stretch is 5 percent but 3 to 4 percent is generally specified. The military specifies a maxi- mum of 2 percent stretch.
6. There are two ways to check for stretch- ing.
a. First, insert the sealant in a known length of joint and then remove the material and measure the length ex- tracted.
b. The second method is to pre-mea- sure a length of sealant. A perma- nent mark is placed on the roll. After installation, the length of the installed sealant is measured.
7. If preformed sealants are specified for both longitudinal and transverse joints, the following installation sequence should be used.
a. Install the longitudinal sealants first, b. Cut the longitudinal sealants at the
transverse joint locations, and c. Install the transverse sealant in a
continuous length across the width of the slab.
QUALITY ALERT
Prevent Incompressibles:
Temporary filling of joints with a backer
rod/rope is a good practice to minimize infiltra- tion by construction debris.
Cleanliness of the joint is necessary for per- formance of all sealant materials.