Overview
Concretes based on hydraulic binders such as Ordinary Portland Cement have a common tendency to crack. There may be different type of cracks and various reasons for cracking to take place. The main reason is shrinkage in plastic and hardened stage. Sometimes these cracks are minimal and may be ignored or treated on the surface itself. But when the cracks tend to penetrate deeper, they start affecting the durability of concrete. Cracks may appear in a floor slab, foundation, basement slab, roof slabs a beam or a column.These cracks may affect structural, aesthetical or environmental performance of the utility.This creates a need to treat these cracks carefully, with proper materials and techniques. There are a number of methods and techniques which are developed by the construction industry to such cracks. Crack injection using either Epoxy Resin or Polyurethane resin based grouts, is one of the most efficient and effective techniques. Although not new, these techniques and materials have been getting refined and innovative for quite some time.
Conditions, Considerations, and Materials
In order to decide whether to use crack injection, it is important to understand the cracking in a particular place or structure in detail. There may be different reasons for the cracks to appear. One must know if it is drying shrinkage cracking, cracking due to corroding reinforcements or alkali aggregate reactions are involved. Further need is to understand whether the crack is structural or non-structural i.e. on a non-load bearing element. Some cracks may be still developing. Some cracks might have appeared, due to not sufficient movement joints in the structure and may be moving. Some are due to settlement or due to damages during or after curing period. If the crack is subject to subsequent movement, an epoxy repair may not be suitable.Here we will discuss specifically two types of injection materials. Low Viscosity Epoxy resins and Polyurethane resins. The former being mainly used for structural crack repair and the later mainly finding use in situations, where movement is expected or water leakages have to be stopped quickly. Sometimes a combination of both materials may also be used.
Both Epoxy resins and polyurethanes are sensitive to water. One must understand this aspect, while formulating as well as recommending them. Epoxy resins, have difficulty in setting and developing the desired strength, in presence of water. Some epoxy resin systems are tolerant to a fair amount of damp and some even are used under water. But handling under water epoxy injection resins, could prove more difficult and costlier than the polyurethane resins. Polyurethane resins on the other hand are available in one, two, or three pack systems. One pack resins generally foam in presence of water thus affecting quick stoppage of flowing water through cracks. Two and three pack systems offer either a flexible sealing solution or foam like single pack resins. The foam generated by such systems, are more flexible than the single pack resin.
