There are various bridges in world which are very old in age but still capable of carrying constant traffic load but it was possible only due to regular maintenance. But how to maintain a bridge?
There are only alternate to maintain a bridge is to repair to it and its wound. In technical term is called Rehabilitation of bridge. There are various symptoms an old bridge may point us to the aging of bridge and need supports. What are these?
These supports are nothing but a long list of repairing processes with help of external products. There are various methods are available in current market out of which these are most familiar one
Sealing of cracks by Injection grouting and Epoxy mortar
Guniting / Shortcreting
Replacement of expansion joints
Replacement of Bridge Bearings
Strengthening with CFRP
Now like human bridges also need through check up to find out its defect and relevant treatment.
Here I going to describe sealing of cracks by Injection grouting with epoxy resin.
Sealing of cracks by Injection grouting and Epoxy mortar
Common reason to use grouting is crack on concrete structure which can be examine either visual inspection or by crack mapping microscope. Cracks may be of two types surface crack and through crack.
Now treatment for above mentioned both cases are independent and totally different.
Epoxy mortar is mix of Sand, epoxy resin and hardener. Sand should be fine quartz sand and typical ratio is 800 (I have experienced with following materials of Hindustan specialty chemical limited in mixing ratio: HSC 7452/HSC 8230/ Quartz Sand-100:50:800). HSC 7452 is low viscosity clear liquid resin and HSC 8230 is medium viscosity polyaminoamide hardener of light amber colour. First of all we have to mix resin and hardener then mix with sand using hand mixing for 5 minutes. This uniform mix is ready to apply on member surface and having pot life of 60 min approximately. Application must be using hand , trowel and float done and not more than thickness of 10 mm in single application. Curing is needed for at least for 7 days. After full curing period of epoxy mortar grouting process is the next step.
Line crack grout treatment
For through crack over important parts of bridges like beam, girder etc. it is needed to inject grout to crack with sealing of crack line only using epoxy mortar or other adhesive mortar. First of all we need to identify each and every individual crack and their path line, need grinding of surface for removing dust, stain oil, grease, tar, asphalt, paint, wax, curing compounds from surface for crystal vision . sometime sand blasting may be needed. Treat each and every crack as separate case. After identification , of crack it also be assured that crack is in single side or appeared in both faces of element if next case the go for same process in another side and go for grouting method only after completion of sealing in both side. Drilling hole to insert nipple is to be taken as next step. Interval of nipple should not be more than the thickness of structural element need for grouting. But if crack is very severe this interval will be very less. Drilling hole should be at least 150 mm to 200m deep depending on member but not so deep respect to member thickness. Put nipple (may be of PVC or Steel ) in to hole and seal it with epoxy putty and seal crack line with mortar (if need crack may be grooved in shallow depth for bonding).
For grouting there are two option namely Cement grouting and epoxy grouting . If cracks are of narrow width (which can be determined from work experience of expertise) then epoxy grouting giving better result because it has less viscosity than cement grouting material. Here we discussed about epoxy grouting as it is a most trendy substitute. Fundamental of epoxy grouting is quite similar to epoxy works that is mixing of resin with hardener.one part of epoxy resin is generally mixed with two part of hardener. Mixing can be done manually by any stirring rod or by any blender. I have personally have the experience of using HSC 7450 resin which is of low viscosity and HSC 8230 as hardener of medium viscosity (For narrow width use HSC 8231 as low viscosity hardener) reactive polyaminoamide.
Grouting can be done either by hand grouting machine or by pressure pump grouting machine. For large work next one is suitable option. Fundamental is to start grout from bottom most point and moving forward for assuring pressure grout. Pressure of grout may be checked by pressure gauge connected to the equipment and generally pressure should be in range of 7-15 kg/Cm2 which can also depend upon targeted structure age and compressive strength of concrete used in target. The main fundamental theory of time upto which process continues in single nipple port until grout material comes out of just next port or if nipple consumes more than 2 ltr of grout .
If next consequence is happening then specification of grout is need to recheck. Some it can be happen due to poor workmanship. Stop grouting just when next port expel out grouting materials and plug both ports and shift to third one. If grout comes out for more than one port and not in sequence then also plugged all of them and start from that first nipple till opened in line from bottom side. After completion whole grouting process left it for 24 hours and cut grouting nipples if of PVC type and seal it with epoxy mortar and left if of metal as it is.
Spider web crack treatment
For surface cracks i.e cracks are not in single line it spreading like spider web then it is to examine the integrity of concrete member by using UPV test that is Ultrasonic Pulse Velocity and if result is come in moderate to poor then we need to inject grout in this case also but pre-treatment is different in this case. We have to use apply epoxy mortar in surface of crack with some extra coverage and after that go for grouting by drilling hole over mortar. Grouting method is same as given above.
Generally I have been seen that by making of grouting material cube of 75mm it has given about 65-70 mpa compressive strength in just 1 day room temp curing.
Please comment below if any enquiry is there.