Repair mortar

There are different concrete replacement systems available for renovating reinforced concrete structures. They range from sprayed concrete without polymer additions to systems containing conducting polymers (PCC-mortar). Since with the latter alkalinity is lower, more rapid carbonization occurs on weathering [59] and the increased electrical resistivity has to be taken into account, so that with cathodic protection only sprayed concrete should be used as a repair mortar. 

Industrial flooring Protective coatings Repair mortars... 

Caulking sealants Anticarbonation coatings Elastomeric coatings Patch-repair mortars General-purpose adhesives Crack injecting systems... 

Epoxies have an excellent resistance to abrasion. The abrasion resistance of a particular system depends upon the type of formulation and conditions. For example coatings have the capacity to resist abrasion from rubber wheels, whereas screed floorings, repair mortar and self-levelling floors can resist thousands of cycles from steel wheels. 

Acrylic-modified cementitious products excellent bond strength water resistance resistance to ultraviolet radiation low water/cement ratio superior handling and application properties various, depending upon type of product repair mortars floorings tile adhesives renders coatings, etc. 

The formulation of cementitious products with use of powdered acrylics is accomplished through dry blending. After gaining information on cement-modifying acrylics, let us now gain an idea of two broad spec-trums of such acrylics acrylic-cement repair mortars and acrylic-cement protective coatings. These discussions are equally applicable to acrylic emulsions as well as to powdered acrylics. 

Render Cementitious repair mortar cements modified with polymers are included in this category. 

The anodic process can be stopped by applying a coating to the reinforcement that acts as a physical barrier between the steel and the repair mortar. For this purpose only organic coatings, preferably epoxy based, should be used. Protection is entirely based on the barrier between the reinforcement and the mortar, and passivation of steel cannot be achieved because contact with alkaline repair material is prevented. This method should be used to protect depassivated areas of the reinforcement only as a last resort, i. e. when other techniques are not applicable and only for small specific applications [1,4]. It may be used, for instance, when the thickness of the concrete cover is very low and it is impossible to increase it to the proper level, so that the repair material cannot provide durable protection to the embedded steel. 

For the replacement of the original concrete, an alkaline material with high resistance to chloride penetration should be applied with a sufficient cover thickness to prevent corrosion initiation during the design life of the repair (Chapter 19). Effects of possible diffusion of chlorides into the repair mortar from the concrete substrate should also be considered. A chloride resistant coating or mortar layer can also be applied on the concrete surface to limit further chloride penetration (Chapter 14). 

Bonding agents may also be applied in some cases on the concrete surface in order to enhance adhesion of the repair mortar. These may be cementitious systems (cement paste or fine mortars), polymer latex or epoxy systems [4]. Epoxy systems should be used carefully since they create a moisture barrier between the substrate and the repair material, which can result in failure of the repair if moisture is trapped in the concrete. 

Polymer-modified mortars can be obtained by replacing part of the mixing water with a synthetic latex (e. g. styrene butadiene or acrylate) to the mix. Although the binder is still cementitious, and thus alkalinity is guaranteed, the latex may improve the workability, the waterproofness, the carbonation and chloride resistance, the tensile and flexural strength of the repair mortar [8]. It can also reduce the modulus of elasticity, increase the bond to the substrate, reduce the rate of drying out and thus the rate of shrinkage. 

The definition of mix proportions that can fulfil the different properties required for the repair material may be rather difficult. A wide variety of commercial premixed products of proprietary compositions are available that can suit different requirements. Specifications for the repair mortars should, however, be clear in order to allow the selection of an appropriate material. 

Under particular circumstances, the long-term protection given by the repair material may be improved by additional measures that are aimed at prolonging the passivity of the reinforcement In any case, the main objective of the repair work remains passivation of the reinforcement due to the alkahnity of the repair mortar (otherwise other repair methods illustrated in Chapter 18 should be considered). 

Corrosion inhibitors. Corrosion inhibitors may in principle improve the protection of the steel reinforcement. Mixed-in inhibitors added to repair mortar may increase the chloride threshold or delay the chloride penetration in the repair material. Migrating inhibitors appHed on the surface of the original concrete are intended to reduce or stop corrosion and thus make concrete removal and its replacement unnecessary. The role of inhibitors and their effectiveness are discussed in Chapter 13. It is, however, useful to remember that if a corrosion inhibitor is used, the concentration that is needed in the vicinity of the reinforcement should be specified and suitable means for demonstrating that such conditions are actually achieved and maintained for an adequately long time should be proposed [11-... 

Surface treatment of concrete. Surface treatment of concrete may be used in association with conventional repair to achieve the required service life of the repair. A specific type of treatment may be used to delay penetration of carbonation or chlorides or to decrease the moisture content (Chapter 14) either in the original concrete or in the repair mortar. The effect of this treatment can be taken into consideration in the evaluation of the residual service fife of the structure, both in the repaired and unrepaired zones. This can lead to a reduction in the extent of the areas to be repaired or in the thickness of the repair material. 

Coating of rebars. Proprietary products are often applied on the surface of the rebars, to promote adhesion to the repair mortar and to improve the corrosion resistance (often inhibiting properties are also claimed, anti-corrosion coatings ... 

The use of a surface coating on the reinforcement should be carefully evaluated. As far as corrosion of steel reinforcement is concerned they should not be recommended, since the repair mortar is the material intended to protect the reinforcement. Only if it is impossible to provide adequate thickness of repair material cover, so it is locally not possible to provide the required long term protection, may a coating that acts as a physical barrier be useful. In that case, however, it should be clearly understood that the repair principle is locally changed and requirements illustrated in Sections 18.3.3 or 18.4.3 should be fulfilled [10]. 

A. Nanni, CERP strengthening . Concrete International, 1997, 6. prEN 13396-1, Products and systems for the protection and repair of concrete structures — Test methods - Part 1 Measurement of chloride ion ingress by diffusion of repair mortars and concreted 2002. 

Repair materials. Repair materials to be used in areas where current is flowing should have similar electrical resistivity as the parent concrete in order not to disturb uniform current flow. Repair mortars should be tested for resistivity for several months to obtain mature values, preferably in a cHmate that simulates the exposure of the structure [7,8]. A difference of a factor two between mortar and concrete resistivity is considered acceptable [13]. It appears that most cementitious... 

Lambe, et al.l It l reported that repair mortars using redispersible polymer powders for concrete structures show high resistance to the diffusion of chloride ions, oxygen and carbon dioxide, and also low shrinkage. 

Recently, Kobayashi et al. (2010) also studied the chloride penetration into the cracked HPFRCC material. In their study, several concrete beams were prepared, and the bottom layer surrounding the reinforcing steel was repaired using HPFRCC and repair mortar (polymer cement mortar [PCM]). Cracks were introduced in the specimens by uniaxial tension. The maximum crack widths in the HPFRCC repair layer and PCM layer were 0.06 and 0.43 mm, respectively. The specimens were then subjected to saltwater (containing 3% NaCl) spray for 5 min every 6 h and continned for 2 months. Similar to Miyazato and Hiraishi (2005), the AgNOj solution was also sprayed on the fractured surface to measure the chloride penetration depth. Reduced chloride penetration in cracked HPFRCC compared to PCM was reported in their study (Figure 6.10). The above results on the permeability of HPFRCC show that it has very low water and chloride permeability even in the crack state. 

Although not strictly used as prime structural adhesives, polymer latices or dispersions have been included here because of their increasing use as aids to bonding in the patch repair of spalled concrete. They usually take the form of a polymer-cement slurry which is applied to the moistened and prepared concrete surface. In general, the repair mortar must then be applied before a film... 

A typical repair mortar composition might comprise ... 

For the repair of shallow spalls or where the cover to the steel is less than 12 mm repair mortars based on reactive thermosetting resin binders may be more appropriate. Their advantages include ... 

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