Form Follows Function

Concrete surfaces with opposing shoulders on both ends, such as the bell and spigot and the modified tongue and groove joints, generally utilize a rubber compound gasket or flexible mastic for leak-resistant, silt-tight and soil-tight sealing. Joints utilizing flexible mastic sealants typically perform as a soil tight system unless higher performance expectations are described in the project specifications. Mortar joints have been used successfully in soil tight applications for decades.

Concrete joints with a groove or offset on the spigot and/or bell utilize a rubber compound gasket, which fits against the shoulder or in the groove of the joint. Rubber compound gasketed concrete pipe joints are frequently used where measurable infiltration/exfiltration and/or internal pressure is a factor in the design. This joint combines great shear strength, excellent water tightness, and flexibility. There are a wide variety of rubber gasket joints from which to choose, but they must meet certain stringent requirements included in ASTM C 443, ASTM C 361, or ASTM C 1628.

Bitumen and butyl sealants are manufactured in accordance with ASTM C 990. The sealant is applied to the tongue or spigot and inserted into the bell or groove. Joints utilizing flexible mastic sealants typically perform as a soil tight system unless higher performance expectations are described in the project specifications. If properly applied, these joints provide a degree of flexibility without impairing water tightness. However, they are not intended to perform under internal pressure.

For mortar joints, a layer of cement paste or mortar is placed in the lower portion of the bell or groove of the installed pipe and on the upper portion of the tongue or spigot of the pipe section to be installed. The tongue or spigot is then inserted into the bell or groove of the installed pipe until the sealant material is squeezed out onto the interior or exterior surfaces. Joints employing mortar joint sealants are rigid. Mortar joints have been used successfully as a soil tight joint for many years.

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