Repair of Cracks in Concrete Structures

Grouting Procedure for Repair of Cracks in Concrete Structures:

Procedure of grouting for repair of concrete cracks in structures are:

1. Holes  are  drilled  in  structure  along  cracks  and  in  an  around  hollow spots.

2.If  there  are  several  cracks,  holes  can  be  drilled  in  a staggered  manner  at  500  to  750mm  spacing  in  both  directions covering  adequately  the  area  proposed  to  be  grouted.  Holes spacing  can  be  altered  as  per  site  conditions.

3. G.I.  pieces  (12  to  20mm  dia  x  200mm)  with  one  end  threaded  or PVC nozzles are fixed in the holes with rich cement mortar.

4. All  the  cracks  and  annular  space  around  G.I.  pipes  are  sealed  with rich  cement  mortar.

5. All  the  cracks  are  cut  open  to  a  ‘V’  shaped groove, cleaned & sealed with rich cement mortar.

6. All  the  grout  holes  should  be  sluiced  with  water  using  the  same equipment  a  day  before  grouting  as  per  following  sequence;  so  as to saturate the masonry.

All holes are first plugged with proper wooden plugs or locked in the case  of  PVC  nozzles.  The  bottom  most  plug  and  the  two  adjacent plugs  are  removed  and  water  injected  in  the  bottom  most  hole under  pressure.

When  the  clear  water  comes  out  through  the adjacent holes the injection of water is stopped and the plugs in the bottom  most  hole  and  the  one  immediately  above  are  restored.

The  process of grouting of concrete cracks is  repeated  with  other  holes  till  all  the  holes  are covered. On  the  day  of  grouting  all  the  plugs  are  removed  to  drain out excess water and restored before commencing grouting.

The same sequence as described above is adopted for injecting the cement  grout  also.  The  grout  is  kept  fully  stirred/  agitated  under pressure  throughout  the  grouting.

The  grouting  is  carried  out  till refusal  and/  or  till  grout  starts  flowing  from  the  adjacent  hole.  A proper record of the quantity of grout injected into every hole should be maintained.

After grouting, curing should be done for14 days. Tell tales are provided for checking the effectiveness of grouting.

Only such quantities of material for preparing grout should be used, as can be used within 15 minutes of its mixing. Grouting equipment must be cleaned thoroughly after use.

Fig: Grouting Procedure for Concrete Cracks Repair

Precautions during Grouting of Cracks in Concrete :

• During  the  grouting  operation  in  track  or  close  to  it,  speed restrictions  of stop-dead  and  proceed  at  10  kmph  shall  be  imposed at the site of work and same should be continued for a period of 24 hours.
• The restriction  may  then  be  relaxed  to  non-stop  30  kmph  to be  continued  for  a  period  of  another  2-3  days.  However,  speed restrictions indicated above are only guidelines and appropriate  speed restriction at each individual site should be considered.
• Immediately  after  grouting  work,  all  the  grouting  equipment including  the  slurry  and  mixing  drums,  pipes,  nozzles,  etc.  should be  thoroughly  washed  so  that  set  cement  does  not  damage  the equipment.
• After  the  work  has  been  completed,  it  should  be  inspected thoroughly  and  should  be  kept  under observation  for  a  period  of  6  months  to  12  months  for  its  behaviour after  grouting.
• In  case  arch  masonry  of  bridges  is  grouted  to strengthen  the  structure,  some  load  tests  may  be  carried  out  in selected  cases  to  satisfy  that  grouting  has  helped  to  reduce  the deflection  of  crown  and  spread  at  the  springing  to  within permissible limits.