Test

Testing of 50 year old prestressed concrete railway sleepersDaniel DwyerJune, 2016

What are they?12 x narrow gauge sugar cane railway sleepers

Length = 1220 mmMass = 40 kg

What did we do?Tested the concrete compressive strength

Using a Schmidt hammer

Tested the sleepers in static bending

Displacement control testLoading rate = 0.5 mm per minute

What did we aim to find?How much strength remained in the aged sleepers?

Could they be safely put back into service?

What was the concrete compressive strength after 50 years in service?

What can we interpret from these findings in relation to concrete structures in general?

How did we structure the test?Categorised the sleepers into three groups Bad, Average and Good

Based on visual assessmentMarked the sleepers at specified locations

1234567G stands for Good

The marked sleepers provided Consistent Schmidt hammer test point locations& Reference points to monitor cracking during static bending tests

345

What did we find?The compressive strength was highest at the rail seat locations and visual assessment did prove to be an effective method for the top of sleeper

It was believed that the rails had protected the top concrete surface from environmental exposure which helped maintained strength

The compressive strength was considerably lower for the side of sleeper

Static bending test results were not predictable from the visual assessment method

However, all sleepers easily exceeded the proof bending test requirement of,

no cracking visible to the naked eye at 32.5 kN

Sleeper AB failure video

How did they fail?All sleepers exhibited the same failure method - believed to be shear

Diagonal cracking initiated at the bottom

Although cracking did not initiate at the supports, there was no sign of flexural cracking at the centre span

Flexural cracking was not present

There was only one major crack in each specimen

What did we learn?The prestressing strands were still in very good condition visually but were not tested

Even after 50 years, the sleepers strength was high

They could potentially be put back into service safely