A TEST METHOD FOR CONCRETE IMPREGNATION

Abstract: A method of determining the presence of and penetration depth for an impregnating agent in concrete at concrete impregnation, wherein a UV fluorescent constituent is incorporated into the impregnating agent and, for establishing presence and penetration depth, holes are taken up in the concrete and the wall of the hole is illuminated with UV light, whereby fluorescence shows penetration depth and presence of impregnating agent, respectively.

Description: A test method for concrete impregnation The present invention relates to a method of controlling concrete impregnation and more specifically a method of determining the presence of the impregnating agent and its penetration depth in concrete. Protective treatment of concrete structures is performed outdoors as well as indoors. Protective treatment of bridge structures is performed in order to minimize the risk of freeze damages and salt penetration causing corrosion of the reinforcement steel. Impregnation of concrete structures indoors, especially floors, is performed primarily in order to eliminate the pro¬ blems giving rise to sick houses. Another field coming into focus is landing field concrete where especially joints are subjected to mechanical as well as moisture related damages. Through impregnation the risk for damages at e.g. joints and cracks in the concrete is reduced. In connection with performing hydrophobic impregnation of different .concrete structures it is desirable to be able to control the quality and effect of the performed impregnation at the site. Today, there are several methods of investigat¬ ing the water repellant effect out in the field. Examples of methods for controlling the result of the impregnation are - the funnel method according to British Standard BS1881, - electrically measuring BASt- ethod, and - high pressure tests with German-equipment. These methods are not intended for or suitable for continuous measurement in the field. On planar and horisontal concrete structures the so called Funnel method can be used. On bridge structures and especially the edge beams and the under side thereof presently it is not possible to control the quality of the impregnation performed with the above mentioned methods. Rational control methods with so called "non-destructive testing" in the field have until now been very restricted. However, there are methods which in com¬ bination with laboratory investigations give reliable results. However, the methods are costly, they give very limited possibilities of controlling the quality of the impregnation performed out in the field and to a judgement of how large part of the effect of the impregnation that remains in a concrete structure having been treated at an earlier time. Further, the above mentioned methods are not suitable for controlling an impregnation open to diffusion which is achie¬ ved when impregnating with alkyl silane based impregnation solutions. The only method which can be used today for this type of control involves taking a core sample out of the concrete structure in question which then has to be analyzed in the laboratory. This is very time consuming and expensive and is not well adapted to industrial purposes. The object of the invention is to provide a method for controlling the quality of concrete impregnation, which is quick and reliable, and which also allows for control of remaining impregnation of previously impregnated concrete structures. This is achieved with the method according to the present invention which is characterized in that a UV fluorescent constituent is introduced into the impregnating agent and that for control holes are taken up in the concrete and the wall of the hole is illuminated with UV light, whereby fluorescence shows the depth of penetration and the presence of impregnating agent, respectively. The method according to the invention is well adapted for use in the field, and thus, all surfaces, which have been treated with the impregnating agent, can be controlled at the site in e.g. final and guarantee inspections of contracts as well as in controlling and following up of the permanence of the impregnation. At the controlling operation UVA light is preferably used, which is completely harmless to humans. According to a preferred embodiment of the invention part of the impregnating agent is modified with a chromophor which gives fluorescence, whereupon a suitable amount of modified impregnating agent is mixed with non-modified impregnating agent. A suitable amount might be about 0.01 - 0.1 %. The impregnating agent is preferably an alkylsilane, such as isobutyl triethoxysilane. A decisive advantage with this course of action is that the chromophore modified molecule takes part in the polymerisation of the impregnating agent and is solidly bound, since it becomes part of the polymer, such as the polysiloxane. Suitable chromophores are molecules with conjugated double bonds, advantageously with an aromatic structure. Examples of chromophores are.naphtalene, anthracene and fluorescein. The choise of chromophore depends on which group of an impregnating molecule that should be changed as well as the wave length emitted by the fluorescing light. According to an alternative embodiment of the invention a fluorescent brightening agent or a corresponding UV fluorescent substance is mixed into the impregnation solu¬ tion. A concentration of 0.01 - 0.1 % is believed to be suitable also in this case. An addition of a fluorescent agent to the impregnating agent works well also in an indoor environment and at small penetration depths. At large penet¬ ration depths the added fluorescent agent results in an underestimation of the penetration depth, since the penetra- tion of this substance is retarded by the concrete. Further, in outdoor applications it could be that the added substance is not stable over the time, hence the embodiment with a chemically bound chromophore is preferred for such applica¬ tions. The object of hydrophobic impregnation of an underlayer is to protect concrete and flow putty, respectively, from future water absorption. The agent used thus should penetrate into a mineral construction material with a low porosity, whereby the small molecules in the agent form a water re- pellant layer on the capillary walls, without the pores and capillaries, respectively, becoming clogged. The structure should thus be completely open to diffusion after performed treatment. In the hydrophobic impregnation the impregnating agent preferably comprises a 100 % active component, such as Dynasalan® BHN, which is based on isobutyl triethoxysilane. The molecules of this product have a dimension of about 1.85 nm (18.5 A), which results in an excellent penetration ability into the composite material such as concrete and flow putty, respectively. The control of the quality of the impregnation is per¬ formed with the method according to the invention. As stated above, the impregnating agent can be mixed with a fluorescent substance such as an fluorescent brightening agent. In an alkylsilane based impregnation solution the fluorescent agent can be fluorescein (2 (3, 6-dihydroxy xantyl) -bensoic acid) or another substance with fluorescent characteristics and a suitable solubility. After finished impregnation the penetra- tion can subsequently be controlled using ultraviolet light by taking up a hole in the concrete and then illuminating the walls of the hole with UV light. By using UVA light, that is UV light where the dangerous wavelengths have been eliminat¬ ed, the method is completely safe. The control method can also be performed on horizontal concrete structures such as for example the under side of bridges and their edge beams, which advantageously can be impregnated in order to prevent uptake of water and salt. When the isobutyl triethoxysilane mentioned above for examplifying purposes is used as impregnating agent the isobutyl group or one of the ethoxy groups is exchanged for the chromophore. Beside the above discussed advantages of using fluorescent silane for hydrophobation of concrete it is essential that the problems with solvent emission are comple¬ tely eliminated when using fluorescent silanes such as Dynasalan®BHN (Hiils AG) containing 100 % active component, Dynasalan®BSM 2000 (Hiils AG) comprising 20 % active com¬ ponent, in the form of isobutyl triethoxy silane. The invention has been examplified with reference to isobutyl triethoxysilane as an impregnating agent, since it has a molecular size favouring penetration into pores in concrete and gives a hydrophobic coating while at the same time the molecules do not clog pores and capillaries in the concrete, but the invention is not limited to only this impregnating agent.

Claims: Claims 1. A method of determining the presence of and penetra¬ tion depth for an impregnating agent in concrete at concrete impregnation, characterized in that a UV fluorescent consti- tuent is incorporated into the impregnating agent and in that, for establishing presence and penetration depth, holes are taken up in the concrete and the wall of the hole is illuminated with UV light, whereby fluorescence shows penet¬ ration depth and presence of impregnating agent, respec- tively. 2. A method according to claim 1, characterized in that part of the impregnating agent is modified with a chromophore which gives fluorescence, whereupon a suitable amount of modified impregnating agent is mixed with non-modified impregnating agent. 3. A method according to claim 2, characterized in that about 0.01 - 0.1 % modified impregnating agent is mixed into the impregnating agent before impregnation. 4. A method according to claim 1, characterized in that the impregnating agent is mixed with a fluorescent brighte¬ ning agent or other UV fluorescent substance before impreg¬ nation. 5. A method according to any of claims 1 - 4, charac¬ terized in that the impregnating agent is an alkylsilane. 6. A method according to claim 5, characterized in that the alkylsilane is isobutyl triethoxysilane. 7. A method according to any of claims 1 - 6, charac¬ terized in that the chromophore is chosen from the group consisting of fluorescein, anthracene, naphtalene.

Inventors: KAENNGAARD BENGT, KRISTENSSON JAN, KAENNGAARD, BENGT, KRISTENSSON, JAN
Applicants: KAENNGAARD BENGT, KRISTENSSON JAN, KAENNGAARD, BENGT, KRISTENSSON, JAN
Application year: 1995
Main classification: G01N21
IPC codes: C04B41, G01N21