Patch and Repair Mortars

Concrete is a very versatile, long-lasting and durable building and construction material if it is applied according to the state of the art. In the past, and even today, unfortunately, repeated disregard of the fundamental principles of concrete and structural concrete apphcation has lead, and, in many cases, still leads to severe and serious damage in the building industry. The cost of the repair of concrete structures has dramatically increased over the last 30 years in ah industrial countries. In Ger- 

SLU surface after abrasion lest with redispersible powder 

SLU surface after abrasion wst without redispersible powder 

The degradation of structural concrete is caused by corrosion of the steel reinforcement due to chemical processes, which often occur over a long period of time. One of the main reasons is the carbonation of concrete. Acidic carbon dioxide (CO2) from the atmosphere and other aggressive media (such as SO2, acid rain) neutralizes the alkalinity of the concrete. Once the alkaline environment of the steel reinforcing no longer exists, the steel starts to corrode and, due to its volume increase, causes splitting of the concrete on top of the steel reinforcement. A secondary cause of corrosion is the penetration of free chloride ions into the concrete, leading to chloride ion attack on the steel. 

In the construction industry concrete repair work can be classified in two types  

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The following paragraphs will describe the most important and most developed application areas for redispersible powders as they are ceramic tile adhesives/ tile grouts, thermal insulation systems (E.I.F.S.), self-leveling underlayments, patch and repair mortars, as well as water proof membranes (sealant slurries). 

Latex-modified mortars and concretes have become promising materials for preventing chloride-induced corrosion and for repairing damaged reinforced concrete structures. In Japan and the USA, latex-modified mortar is widely used as a construction material in bridge deck overlays and patching compounds, and for finishing and repairs [99]. Polymer-cement hydrate-... 

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... 

They are appHed in bridge decking and airport runway apphcations, in repair applications, where the mortar layer can be as much as 5-8 cm thick, in industrial floor screeds, where up to a 5 cm layer is appHed over standard concrete, in fine screeds or patching compounds, where up to 1.5 cm of repair mortar is appHed on floors, in self-leveHng underlayments, where thickness from 2-3 cm to feather edging are common. 

Acrylic polymer concrete and mortars fast curing good chemical properties patch repairs... 

As a concrete repair and as patching mortars they are used to ... 

Protection effect. MacroceU currents can have beneficial effects on rebars that are polarized cathodically. This is indirectly evident for patch repair of chloride-contaminated structures when only the concrete in the corroding areas is replaced with alkaline and chloride-free mortar, but surrounding concrete containing chlorides is not removed. Before the repair, the corroding rebars behave as an anode with respect to those in the surrounding areas, which are polarized cathodically and thus are protected by the macrocell. After the repair, formerly anodic zones no longer provide protection, and corrosion can initiate in the areas surrounding repaired zones (these have been called incipient anodes) [3]. Consequences for repair are discussed in Chapter 18. 

Conventional repair. The most utilised method consists in the removal of carbonated concrete and its replacement with alkaline mortar or concrete. This method is convenient when the corrosion attack is limited to zones of small extent (for example when the thickness of the concrete cover is reduced locally). In that case it is usually called patch repair. Conversely, it may be rather expensive when repair is required on large surfaces. In fact, concrete must be removed in all the zones where carbonation and subsequent corrosion of steel are expected to damage the structure within the design life of the repair. Even structurally sound concrete must be removed where the corrosion rate of the embedded steel is expected to... 

Non-alkaline (polymer) mortars have been used for repairs however, they do not promote repassivation and they are only based on physical effects. Epoj mortors applied as patch repairs have in the past been unsuc-... 

If the disintegration is shallow, it may be possible to use a latex-fortified or an epoxy mortar to patch the area. The mixtures of latex and cement and sand described under Repairing Surfaces of Pavement and Slabs may be used. An epoxy mortar may also be used, but it may not blend readily with the surrounding concrete in color or appearance. 

As described in detail in the RILEM 124 SRC recommendation (RILEM, 1994), the basic repair methods for carbonation induced corrosion consist in repassivation of the steel by a mortar layer or by local repair. The procedure for patch repair is described in the published guidelines (e.g. Bentur et al., 1997). Limitation of the concrete moisture content is another repair principle, its aim is dry out the concrete, e.g. when additional facade elements are mounted to reduce energy consumption. When carbonated concrete is not completely removed in the vicinity of the reinforcement, corrosion occurs after repair when sufficient moisture is present (Schiessl and Breit, 1996). 

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