PT beam crack retification

[struggle66]

Hi all,
For less than 0.5 mm width PT beam cracks, which rectification should I use epoxy injection or just patching back with concrete. Is there code specification for this crack rectification method.

 

[Ingenuity]

Depends. What is the cause of the crack?

If it is deemed structural, then epoxy injection is possibly required. But, there are many PT beams that have controlled flexural cracks that have been in service for a long time without issue - depends if the crack is shear, flexural, combination etc.

Patching with "concrete" for a 0.5mm crack will do absolutely nothing.

For epoxy injection as good specification is ACI 503.7 Specification for Crack Repair by Epoxy Injection.

A good publication of field procedure by ACI is Repair Appliation Procedure RAP - 1: Structural Crack Repair by Epoxy Injection.

Google for both ACI documents. The RAP document is free via download. The specification can be downloaded or hard copy with purchase.

 

[struggle66]

Ingenuity,
Sorry for taking so long to get back
The cracks were occurred during construction stage when they cast the above storey floor as the above floor self weight, form work weight and other unforeseen construction weight is heavier than the allowable design capacity of the storey below. The loading from the above floor which had not done stressing transferred to the PT beams below through form work resulting cracking of those of beams. When the building is in service, such heavy loading is not expected. Now the contractor have propped those beams and rectified with just cementitious grouting so far. Even if we use epoxy injection, structural integrity may not be restored. Is it correct?

 

[struggle66]

The cracks are flexural and thanks for the links.

 

[Ingenuity]

Depending on the PT beam design (amount of prestress and mild steel rebar) and the level of temporary 'overload' the cracked beam/s may be okay without any crack repair.

The contractor should have provided re-shoring (back propping) to this level BEFORE the upper level/s construction.

Cementitious grouting of the cracks is most probably more accurately described as 'cement wash' over the cracks to make them magically disappear from the surface/s only. Cement grouting will not penetrate the cracks for any type of structural repair, unless the cracks are of significant magnitude (>3mm or 1/8").

Epoxy pressure injection (typically <150psi) will often provide 90%+ depth of penetration and generally provide structural re-installment of the crack location. Which, depending one the nature of the loadings and beam design, does not mean the beam will not crack again - if it does crack again, it is usually adjacent to the previous crack, not at the exact same location as the epoxy strength will exceed the adjacent concrete tensile strength.