Concrete Repair-This involves patch work fixing of specific weak zones.
The different kind of weak zones are as follows-
1) Cold joints– Cold joints are formed primarily between two batches of concrete where the delivery and placement of the second batch has been delayed and the initial placed and compacted concrete has started to set. The full knitting together of the two batches of concrete under vibration to form a homogeneous mass is therefore not possible, unlike the compaction of two fresh workable batches of concrete. This could be a potential plane of weakness.
2) Construction Joints-are made where the concrete placement operations end for the day or where one structural element is cast against previously placed concrete. These joints allow some load to be transferred from one structural element to another through the use of keys or (for some slabs and pavement) dowels. Note that the construction joint extends entirely through the concrete element.
3) Honeycomb/voids– develop due to lack of proper compaction.
4) Cracks are a result of improper mixing rations or lack of adequate curing resulting in entry of water.
5) Tie rod Holes– is a result of shuttering boards held together during concrete pour. These are very common spots of leaks.
6) Pin Holes- These are imperfection in the concrete surface caused due to excess air entering the mix or improper de shuttering.
All the above can be rectified/ treated using few simple methods. The course of treatment depends on the intensity of the leakage.
Intensity of moisture entry is classified into 3 major groups-
1) Dampness- in case of dampness i.e., the surface shows slight presence of moisture, a cementitious plug can be used to block the entry of moisture.
2) Seepage-if the surface shows sign of dripping of water at regular intervals with low intensity, this can be arrested by using a combination of cementitious repair plug and cementitious grouting or Epoxy Injection Grouting can also be performed.
3) Leakage– if the surface shows continuous dripping of water with high intensity, then a highly reactive and rapid system is needed to arrest the issue such as PU injection grouting.
Recommended Solution by Aquaseal
1) Cementitious repair mortars-are used to treat all the above-mentioned weak zones when there is no moisture entry from negative side.
a) Polymer modified repair mortar-It can be made using combination of cement sand S.B.R. Latex and water mixed in the ratio of 1 kg Cement + 3 kg sand + 150 ml S.B.R. Latex + 200 ml Water (1C: 3S: 0.15 S.B.R: 0.2W).
Or a free flow grout (GP2) can also be used in the ratio of 25 kg grout + 4.5 Ltrs water. Prior to using the above systems, the surface must be in SSD condition and a bonding primer coat must be provided before starting application. To make bonding primer coat, choose from any S.B.R. latex, the mixing ratio is 1:1 i.e., 1 Part Latex + 1 part cement. To seal the pin holes, use the following mix, 5 parts cement + 500 ml Latex + 500 ml Water.
b) Crystalline repair mortar- these are active systems which combine chemically with water and unhydrated cement to form millions of needle shaped crystals that grow in all directions to fill any capillary pores, cracks and joints that might otherwise allow water to pass. E.g., Krystol Waterstop Grout, Penecrete Mortar.
Mixing ratio is 4-4.5 Parts of Powder + 1 Part Water.
If, repair size is 25*25mm then, coverage is 1-1.5 kg / RMT.
Prior to using the above systems, the surface must be in SSD condition and a primer coat must be provided before starting application. To make primer coat, choose from the slurry coating material respectively, the mixing ratio is 3:1 i.e., 3-part Powder + 1 part Water.
c) Epoxy mortar it is a 3-component repair mortar based on solvent free epoxy resin and quartz aggregate
Mixing ratio is 1:1:1. Coverage is 2 kg / mm / Sqm.
2) Cementitious repair plugs- They are instant setting repair mortars which can be used to stop active leaks
a) Crystalline plug for treating seepage e.g., Penetron-Peneplug – these systems are to be used at the time of active leaks only as they set instantly in the presence of water.
Mixing ratio is 1 kg powder + 250 ml water. Such a system stays for life long, penetrate the concrete.
b) Polymer plug for treating dampness e.g., Fosroc-Renderoc Plug- These are temporary systems that can arrest water some limited duration.
Mixing ratio is 1-part clean water + 3-part plug
3) Cementitious Grouting-This process helps in filling up the void thus blocking entry of water using a cement slurry mixed with an admix and pumping the liquid at a pressure to achieve deep penetration. There are various types of admix which can be used, the 2 typical types are-
1. PRAH (Permeability Reducing Admix for Hydrostatic Condition)
E.g., Penetron-Admix
Mixing Ratio- 1 kg Cement + 500 ml Water + 10 grms of PRAH.
2. PRAN (Permeability Reducing Admix for Non-Hydrostatic conditions)
E.g., Fosroc-Cebex 100
Mixing Ratio- 1 kg Cement + 500 ml Water + 4.5 grms of PRAN.
4) Resin Injection Grouting- used to treat active leaks in a concrete structure. They can be classified into 2 types-
a) PU Injection Grouting– the resin is injected at a very high pressure into the weak locations where active leak are present, the PU instantly reacts with water to block the pores. There are 2 types of systems-
- 1K System e.g., Con Repair-CYH 500
- 2K System e.g., Sika-201 CE
Mixing ratio (1 Part A: 1 Part B) as per manufacturer’s instructions.
b) Epoxy Injection Grouting– this also plugs active leaks but take longer time to cure compared to PU. Generally used for strengthening of the structure.
Once cured forms a hard bond having excellent tensile strength. The material is more plastic in nature. The shortcoming of epoxy is the lack of flexibility.
*Consumption of the resin depends up on the porosity of the concrete structure.