Characterization of the Clay Masonry Units and Construction Technique at the Ancient City of Nippur

This paper describes a programme of experimental measurements performed in support of a parallel programme of field investigations to evaluate the construction methods used at the site of the ancient city of Nippur. The experimental programme investigated both the mechanical properties and durability of the ancient clay masonry units used in the construction of buildings at Nippur including tests for dimensional consistency and flatness, density, compressive strength, initial rate of water absorption and thermal properties. The test results have been compared with those for modern brick units available nowadays in Iraq and with hard natural stone samples.
The field investigations showed that the important buildings were constructed using composite walls inclusion firing clay masonry units with two nominal dimensions (30× 30×7) cm and (30× 15× 7) cm (l, w and h). The formulation of working design technique was followed to achieve the member stability under applied loads. Layers of bitumen material were used as a binder for both bed and head joints in order to provide the desired strength level for the masonry wall.
The experimental results show that the ancient brick units and stone samples exceed the tolerance and range of dimensions limits recommended by current EN Standards. Lower density values were recorded for the ancient brick units compared with that for both modern clay brick and stone specimens and these values showed agreement with the modern classification of high density (HD) units. Approximately similar values of compressive strength were observed for both ancient brick units and natural stone samples reaching about 17 MPa, whilst modern clay brick samples showed lower compressive strength value suitable for application of partition walls. The initial rate of water absorption increases with an increase of the soaking time, but tends to decrease after 90 minutes for both ancient and modern brick units. Superior performance in terms of thermal conductivity, thermal resistance and durability under fire action were observed for the ancient brick samples compared with modern clay brick and stone samples.