testing of 50 year old prestressed concrete railway sleepers
TRANSCRIPT
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