METHOD AND APPARATUS FOR CONTROLLING THE RELATIVE HUMIDITY IN CONCRETE AND MASONRY STRUCTURES

Abstract: In a method for eliminating humidity from concrete and masonry structures by means of electroosmosis, current pulses which are supplied in a determined pattern are used. The pulse voltage is limited to +/- 40 V. In order to generate the pulses and feed the electrodes a special electronic control device is used.

Description: METHOD AND APPARATUS FOR CONTROLLING THE RELATIVE HUMIDITY IN CONCRETE AND MASONRY STRUCTURES The invention relates to a method and means for controlling the relative humidity in concrete and masonry, including masonry wherein cement is used as a bonding agent. The structure may be reinforced or not, and the method may also be used in plaster, mortar in stone masonry and light concrete structures. The object of the invention is a directional control of the migration path of the humidity, in or out of a structure by use of a DC current pulse in a determined sequence. Thus it is desired to make a control of the relative humidity content in both small and large concrete structures, for instance to reduce the humidity from 100% to about 70% in order to maintain the most suitable conditions, also for a possible reinforcement and further to keep humidity away from the structure with a regard to fracturing by frost, the occurrence of fungi and wet rot, possibly high air humidity in rooms, so- called cellar odour, limit corrosion, slow down the car- bonatization and vice versa. By start-up of a device according to the invention the relative humidity will be high. By using a high voltage the dehumidifi- cation is accelerated. The relative current drawn and power are high. When 80% relative humidity is approached, the current drawn is reduced. The voltage will still provide a high power due to a reduced conductance. The process ill nevertheless be relatively slower as the relative humidity is reduced. This is caused by the conductance of the concrete structure being reduced. A structure with a supposedly low relative humidity will maintain the achieved condition by the conductance increasing on renewed penetration of liquid. The method is advantageously realized with a device which comprises a hybrid circuit which drives an attached power transistor stage, so that the latter is either wholly conduc- SUBSTITUTE SHEET tive or completely blocking. Also within the scope of the invention is a device wherein transistor stages are replaced by relays or thyristors. The device includes functions such as a monitoring system which informs of circuit breakage, short- circuits, current interruptions, blown fuses and normal operation. The electronic device feeds the anodes (for instance reinforce¬ ment) or anodes provided in the structure with the particular pulse pattern of the invention and thereby creates an osmotic pressure due to said pulse pattern. This pressure drives humidity in the capillaries out of the concrete towards the externally provided ground cathode. The improvement achieved comprises: increased power, a monitoring and alarm system, reduced drift when the tempera¬ ture changes, reduced heat generation.,in the solid state power circuit, improved apparatus housing and power supply certified by the Authorities. In order to optimize the device with regard to powere consump¬ tion, the output stage is constructed as a bridged complemen¬ tary stage, wherein saturation of transistors is made possible by predriver and driver stage having their own power supply, with compensation for voltage reduction in solid state circuitry in a push-pull complementary stage. This stage is bridged with a corresponding push-pull complementary stage. The features characterizing the invention are as follows: 1. Due to safety reasons, a positive and negative pulse of 40 V is used. 2. Salts are driven out with the humidity, something which slows down the carbonatization process. 3. Anodes which are adapted to the pH values and the chemical conditions on the installation site are used. 4. Current and voltage is dependent on and self-regulated in dependence of the conductivity and the humidity of the concrete structure. The current drawn is limited by a predetermined boundary value. 5. The direction of the osmotic pressure is controlled. According to the invention there may for instance be used DC current pulses with a positive pulse fed to the reinforcement of the structure or to an installed anode, the pulse having a controllable duration. Then a negative pulse is fed to the anode for about 1/6 of the duration of the positive pulse, followed by a interval with a duration between 0 and 1/3,5 of the positive pulse. Usually a pulse sequence is applied in start-up phase, which usually takes about two weeks and a pulse sequence for maintenance applied for a duration of five times that period. An increased instantaneous power of 50 times the normal power may also be applied, this in order to handle larger concrete structures.__and_..tc_ achieve.a quick expulsion of humidity, lowering the relative humidity from 100% to 70%, so that carbonatization ceases in structures reinforced with iron bars. Preferably the system makes use of a hybrid circuit which drives an attached power transistor stage, so that the latter may be wholly conductive or completely blocking. The invention is further illuminated by means of the appended drawings which partly show the pulse pattern used and their combinations (Fig. 1) , partly circuitry according to the invention (Fig. 2) and partly examples of embodiments of the invention (Fig. 3-10) , as well as details of the pulse pattern (Fig. 11a, lib) and further details of the electronic device (Fig. 12-15) .

Claims: PATENT CLAIMS 1. A method for expulsion or control of humidity in a concrete and/or masonry structure, one or more electrodes being provided in the concrete or masonry structure, the electrodes being preferably of a non-corrosive material, and connected in series or parallel with the current source, wherein an earth eleectrode is provided adjacent to or on the concrete or masonry structure, so that the electrode or electrodes comprise the anode and the earth electrode the cathode in an electric circuit when they are connected with the respective outputs of the current source, wherein the anode and cathode are provided with a pulse voltage supplied by the current source, and wherein the pulse voltage is delivered sequentially as pulse sequences of a given pattern, c h a r a c t e r i z e d i n that the anode is fed with a pulse sequence generated with a first negative pulse, followed by a neutral interval or a zero voltage interval of a duration being from 0 to 2 times the duration of the negative pulse, followed by a positive pulse, the duration of which is about 6 times the duration of the negative pulse, and that simultaneously the cathode is fed with a corresponding pulse sequence, but with inverted polarity. 2. A method according to claim 1, c h a r a c t e r i z e d i n that the duration of each pulse sequence is regulated within the range 1-20 s, so that the pulse frequencey lies in the range 1-0,05 Hz. 3. A method according to claim 2, c h a r a c t e r i z e d i n that the pulse voltage delivered by the current source has an amplitude of maximum ± 22 V. 4. A method according to claim 3, c h a r a c t e r i z e d i n that the humidity expulsion comprises a first phase for quick reduction of the relative humidity in the concrete or masonry structure, usually with a duration of two weeks, wherein typically a pulse sequence frequency of 1-0,5 Hz is applied, followed by a phase for maintenance of a permanently low humidity content, wherein a pulse sequence frequency of typically 0,2-0,1 times the pulse sequence frequency of the first phase is applied. 5. A method according to any of the preceding claims, c h a r a c t e r i z e d i n that the applied instan¬ taneous power may be regulated by a factor of 50-100, dependent on the structural or material properties of the concrete or masonry structure, the cathode impedance and the initial relative humidity of the concrete or masonry structure. 6. A method according to claim 5, c h a r a c t e r i z e d i n that the maximum instan¬ taneous power is about 2 kW. 7. A method according to any of the preceding claims, c h a r a c t e r i z e d i n that a possible corrosion resistant or corrosion protected reinforcement of the concrete or masonry structure is used as electrode or electrodes. 8. Apparatus for performing the method according to claim 1, the apparatus comprising a controlled power supply (4, Fig. 12) , whose outputs contains pulse voltage lines, a control voltage line and a neutral conductor, c h a r a c t e r i z e d i n that the output of the controlled power supply is connected to the input of puls- width modulators (IC1, IC2; Fig. 14) , whose outputs are connected with the inputs of respective pulse generators (IC3, IC3; IC4, IC4; Fig. 14) , each output of which is connected with a complementary push/pull amplifier stage (Tl, T2; T3, T4; Fig. 14) , the push/pull amplifier stages being bridged for syn¬ chronous feeding of a first electrode with a determined pulse sequence and a second electrode with a corresponding puls sequence, but with reversed polarity. 9. Apparatus according to claim 8, c h a r a c t e r i z e d i n that between the output of the push/pull amplifiers and the electrodes (Tl, T2; T3, T4; Fig. 14) there are provided respective output power amplifiers, preferably in the form of MOSFET drivers (Fig. 15) for further amplification of the power supplied with the pulse sequences to the electrodes. 10. Apparatus according to claim 9, c h a r a c t e r i z e d i n that the puls width modu¬ lators, pulse generators and amplifier stages are designed as a hybrid integrated circuit (MC411, Fig. 13) and that the controlled power supply and the hybrid integrated circuit are mounted on a circuit board. t. 11. Apparatus according to claim 10, c h a r a c t e r i z e d i n that it comprises a manual or an automatic selector adapted for setting a determined pulse pattern, preferably by operating a switch connected to a pattern generator or automatically via a timer with a stored programme. 12. Apparatus according to claim 11, c h a r a c t e r i z e d i n that it comprises a display device (7, Fig. 12) adapted for indicating the selected pulse pattern as well as for indicating the voltage of the pulse voltage lines, preferably being provided with light emitting diodes as indicating means.

Inventors: UTKLEV KJELL, UTKLEV, KJELL
Applicants: ELCRAFT AS, ELCRAFT A/S
Application year: 1990
Main classification: E04B1
IPC codes: B01D61, E04B1