SUB FEATURE
CRACKS , CRACK SEALING EXPLAINED
Causes , culprits , and treatment By Jeff Winke
Folklore and myths survive . Walk down a sidewalk or cross the street with a bunch of friends and observe how many avoid stepping on cracks . When asked , they ’ ll respond that they don ’ t want to break their momma ’ s back or release bad luck from demons that dwell in the underworld beneath .
Asphalt pavement specialists think differently , although there may be a few who avoid stepping on cracks just in case .
“ The three main causes of cracks in asphalt pavement ,” Tom Kelly , senior VP at Crafco , Inc ., DeKalb , Illinois , stated , “ are ( 1 ) thermal movement of the pavement -- i . e ., the expansion and contraction due to temperature changes , sometimes as much as 100 degrees F in a single day , ( 2 ) traffic loads – when cars and trucks pound the pavement , any weakness in the structure of the pavement will fracture or any flaw in the Hot Mix Asphalt ( HMA ) composition may cause premature cracking and pavement failure , and ( 3 ) age and oxidation – - as pavement ages , it loses flexibility and cohesion within the pavement structure , making it more susceptible to the first two causes of cracking .”
Causes for pavement cracks can be grouped in two categories : load-related causes and non-load ( environmental ) causes , reported Ben Thielbar , director of sales , with Cimline , Inc ., Plymouth , Minnesota .
“ Load-related cracks typically occur in the wheel paths in the form of fatigue cracks ,” Thielbar said . “ Non-load causes are from expansion and contraction of the pavement from temperatures ( thermal cycling ), made worse as the material oxidizes and becomes brittle . Damage is also accelerated when water can get into the asphalt and expand and strip or de-densify the material .
“ In other words , in either load-related or non-load related , it ’ s when the stress applied to the layer exceeds the strength of that material .”
There are some interesting industry studies that focus on increasing education and awareness about road center line issues and cracking .
“ We have found research that finds that the center line portion of the pavement typically fails first ,” stated Jeffrey S . Ball , executive director of marketing and communications for Asphalt Materials , Inc ., Indianapolis , Indiana . “ The longitudinal joint is the Achille ’ s Heel of pavements .
“ For example , asphalt ( HMA ) pavements constructed in Minnesota typically have air void contents of about 7 % to 8 % in the mat and often approach or exceed air void contents of 10 % at the longitudinal joints . Higher air void contents at the longitudinal joints can expose the pavement to premature deterioration and , as a result , compromise pavement integrity and performance . In Minnesota , the primary concern during construction is the achievement of high density in the mixture , especially at the longitudinal joints .”
A blog published by NAC Supply , Inc ., Ingleside , Illinois does a good job of capturing the culprits for asphalt pavement cracking : moisture , the sun , and ground movement .
With respect to moisture , the blog stated , “ Asphalt is impressively waterproof , but that doesn ’ t mean it ’ s completely immune to moisture . Moisture will wash away the pavement ’ s gravel and sand base , which can lead the surface layer to shift and break . This shifting and breakage lead to the formation of cracks . Water can affect your pavement ’ s surface , too . It can make its way into crevices , creases , and dents and start exerting pressure on the pavement from above . Adequate drainage will divert water away from your pavement , but if you don ’ t have good drainage , a sealant will also help keep your pavement dry . Since water can pool in any dents or cracks , you ’ ll want to fill them up as soon as possible to avoid further damage .”
www . callape . com [ 28 ] 1.800.210.5923