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Aluminum guardrail posts embedded in gypsum containing grout

Aluminum guardrail posts embedded in gypsum containing grout

Aluminum guardrail posts embedded in gypsum containing grout

A project I am reviewing has experienced cracking of the gypsum-containing grout poured in formed sockets in a PT concrete slab to secure aluminum guardrails. The cracks radiate from the rail to the edge of the formed socket. The grout material is also "soft" and can be chipped away with a screwdriver.

Does anyone have experience with an explanation of this failure and are there any publications/code sources which support the conclusions drawn.

RE: Aluminum guardrail posts embedded in gypsum containing grout

S22...gypsum grouts are non-durable for exterior applications.  While they hydrate similarly to portland cement, they are also subject to softening if re-exposed to water.  The inherent bond created by hydration is not as strong as with portland cement.

Gypsum cement sets up very quickly...in a few minutes.

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