The public works staff has been working on crack filling streets throughout the city. The streets we are concentrating on are; Albright, Auburn, Beulah, Blewett, Cozens, Dawson, Eastchester, Garesche, Hathaway north and south, Hord and Lemont.
Cracking in pavement occurs when a stress is built up in a surface layer that exceeds the tensile or shear strength of the pavement causing a fissure or crack to open. Crack sealing and crack filling are methods which can be used to repair these cracks in pavement surfaces. The cause of the crack and its activity play a dominant role in determining the success of the crack filling operations. Cracking may be associated with various distress mechanisms. Pavement cracking on our streets include;
Fatigue cracking: These cracks form a pattern like an alligator’s skin. They are a result of repetitive traffic loads or high deflections often due to wet bases or sub grades. This type of cracking can also lead to potholes and pavement disintegration. This type of cracking cannot be effectively treated with crack sealants.
Longitudinal cracks: These cracks run longitudinally along the pavement and are caused by thermal stress and/or traffic loadings. They occur frequently at joints between adjacent travel lanes or between a travel lane and the shoulder, where hot mix density is lower and voids are higher. These cracks can be effectively treated with crack sealants.
Block cracking: These cracks form regular blocks and are a result of age hardening of the asphalt coupled with shrinkage during cold weather. They can be effectively treated with crack sealants.
Slippage cracks: These cracks produce a characteristic crescent shape and are caused when the top layer of the asphalt shears, often due to high deflections and poor bond between the layers. This type of cracking cannot be effectively treated with crack sealants.
Crack filling is the placement of materials into nonworking or low movement cracks to reduce infiltration of water and incompressible materials into the crack. Filling is often considered a short-term treatment to help hold the pavement together between major maintenance operations or until a scheduled rehabilitation activity. Two important reasons we need to maintain and repair the cracks is because we don’t want moisture to penetrate under the asphalt surface causing more damage. The second reason we should fill cracks in our asphalt is because vegetation will begin growing in them. As the roots on vegetation get bigger, the plant root can push the pavement up and create even more damage. This breaks the pavement surface and other problems begin occurring.
Crack filling materials are designed to adhere to the walls of the crack, stretch with the movement of the crack over the range of conditions and loads associated with the crack location, and resist abrasion and damage caused by traffic. Sealant is usually elastomeric. This means the material has a low modulus of elasticity and will stretch easily and to high elongations (usually around 10 times its non-strained dimensions) without fracture. Sealants are usually applied at elevated temperatures due to their high viscosity at ambient temperatures and they set or cure by cooling and reforming into complex structures. This is called thermoplastic. Hot application ensures good adhesive bond to the crack walls. Most hot pour materials are rubber-modified asphalt. These materials have excellent abrasion resistance and are useful for trafficked surfaces.