diff --git a/src/paveit/datamodels/norm_documents.py b/src/paveit/datamodels/norm_documents.py
index 44283e8..6100045 100644
--- a/src/paveit/datamodels/norm_documents.py
+++ b/src/paveit/datamodels/norm_documents.py
@@ -27,4 +27,7 @@ class NormDocument(Document):
     }
     
 class NormDocumentAggregate(NormDocument):
+    pass
+
+class NormDocumentBitumen(NormDocument):
     pass
\ No newline at end of file
diff --git a/src/paveit/datamodels/norm_specification.py b/src/paveit/datamodels/norm_specification.py
index 2be9627..f72b55b 100644
--- a/src/paveit/datamodels/norm_specification.py
+++ b/src/paveit/datamodels/norm_specification.py
@@ -1,7 +1,7 @@
 from mongoengine import *
 
 from .enumeration import RelationalOperatorsEnum, BitumenCategoryEnum, NormEnum
-
+from .norm_documents import NormDocumentAggregate
 class EnumerateBase(Document):
     
     meta = {
@@ -18,7 +18,7 @@ class EnumerateBase(Document):
 class DeliveryGrain(EnumerateBase):
     name = StringField()
     category = StringField()
-    norm =  EnumField(NormEnum, default=NormEnum.TLGestein2018)
+    norm =  LazyReferenceField(NormDocumentAggregate, required=True)
     
 # Bitumen