CN102495108A - Method for monitoring water content change in concrete in situ - Google Patents

Abstract

The invention discloses a method for monitoring the water content change in concrete in situ, comprising the following steps: first, directly burying a water content change monitoring sensor in a position to be monitored in the concrete, then transmitting the cork impedance values obtained by the water content change monitoring sensor to a monitoring center to process, calculating the water content in the sensor, and then further inferring the water content change in the monitored concrete. According to the invention, the in situ real-time measurement of the water content change in the concrete can be realized without stable time, wherein the sampling period can be less than 1 ms, and the water content monitoring scope is 0-100 %.

Description

A method for in-situ monitoring of water content changes in concrete

technical field

The invention relates to the technical field of non-destructive monitoring of concrete, in particular to a method for in-situ monitoring of water content changes in concrete.

Background technique

In-situ monitoring of moisture content in concrete is extremely difficult. Although there are many technologies for measuring moisture in porous materials, in-situ moisture monitoring technology that can be used for concrete from pouring to long-term age has not been seen because: (1) There is no sensor that can be directly embedded in fresh concrete , because there are many colloids, many ions in the fresh concrete, and the humidity is 100%, most electrical measuring sensors will fail quickly after being embedded; (2) When measuring relative humidity sensors, a measurement cavity is usually required to meet the vapor-liquid Due to the needs of the balance measurement principle, it is impossible to directly contact the concrete under test; (3) Measurement technologies such as neutron, microwave, optical fiber, TDR, and FDR are expensive and not suitable for large-scale monitoring of large structures.

Viggo Jensen in Norway uses a post-installed Ramin stick as a sensor to intermittently measure the relative humidity in hardened concrete. The sensor consists of a plastic tube with two holes and two sections It is composed of Ramin sticks, and each stick is a sensor. The measurement principle is: form a vapor-liquid balance at the opening of the plastic pipe, and convert the relative humidity of the measured area through the relationship curve between the conductance of the wooden stick and the relative humidity of the air calibrated in advance. Obviously, this sensor is only suitable for hardened concrete. Through the post-installation, pull out intermittently to measure the conductance of the Lamin stick. Due to the characteristics of Ramin wood, the sensor is especially suitable for the measurement of RH80~95%, which is also an area where many commercial humidity sensors are inaccurate. Although the application of the solid structure for as long as 7 years shows that the humidity sensor has good long-term stability, it still has the following disadvantages: (1) non-situ direct measurement; (2) long stabilization time required for measurement, usually 1~ 12hrs; (3) The measurement range is limited; (4) It can only be used for hardened concrete.

Contents of the invention

In order to overcome the above-mentioned shortcomings of the prior art, the present invention provides a method for in-situ monitoring of water content changes in concrete, capable of real-time and in-situ monitoring of water content changes in concrete from freshly mixed to long-aged concrete.

In order to achieve the above object, the technical scheme that the present invention takes is:

A method for in-situ monitoring of changes in water content in concrete, comprising the steps of:

The first step is to directly bury the monitoring sensor for water content change in the concrete at the position to be monitored in the concrete;

The second step is to transmit the cork impedance value measured by the moisture content change monitoring sensor to the monitoring center for processing;

The third step is to calculate the water content in the sensor according to the calibrated cork impedance and its water content function, or to calculate the water content in the sensor according to the measured impedance value when the cork is completely dry and fully saturated with the following linear difference formula. Water quantity:

$\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 100</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 100</span>}<span\; class="notranslate">\; \%</span>$

In the formula: W is the relative water content, R is the monitored cork impedance value, R ₀ is the impedance value when the cork is completely dry, R ₁₀₀ is the impedance value when the cork is completely saturated, and then the water content in the monitored concrete is deduced Variety.

The invention can realize the in-situ real-time measurement of the water content change in the concrete without stabilizing time, the sampling period can be less than 1 ms, and the water content monitoring range is 0-100%.

Description of drawings

Fig. 1 is a schematic diagram of the principle of monitoring the variation of water content in concrete according to the present invention.

Fig. 2 is a diagram of monitoring data in a concrete specimen in a tidal range area according to an embodiment of the present invention.

Fig. 3 is a graph of monitoring data in the concrete specimen in the splash zone according to the embodiment of the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

With reference to Fig. 1, a kind of method for in-situ monitoring moisture content change in concrete, comprises the following steps:

The first step is to directly bury the monitoring sensor P for water content change in the concrete T at the position to be monitored;

In the second step, the impedance value of the cork m measured by the water content change monitoring sensor P through the electrode K and the wire L is transmitted to the monitoring center for processing;

The third step is to calculate the water content in the sensor according to the calibrated cork impedance and its water content function, or to calculate the water content in the sensor according to the measured impedance value when the cork is completely dry and fully saturated with the following linear difference formula. Water quantity:

$\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 100</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 100</span>}<span\; class="notranslate">\; \%</span>$

In the formula: W is the relative water content, R is the monitored cork impedance value, R ₀ is the impedance value when the cork is completely dry, R ₁₀₀ is the impedance value when the cork is completely saturated, and then the water content in the monitored concrete is deduced Variety.

Embodiment one

A method for in-situ monitoring of changes in water content in concrete, comprising the steps of:

In the first step, in a C35 concrete specimen located in the sea tidal range area, as shown in Figure 1, a water content change monitoring sensor was buried at a depth of 5mm from the concrete surface, in which the diameter of the cork was 6mm and the length was 3mm , a pair of gold-plated electrodes, the diameter is 0.15mm, the length is 2.5mm, the electrode spacing is 2.5mm, the sheath is a PP plastic tube with a thickness of 2.5mm, a diameter of 25mm, and a length of 40mm;

The second step is to transmit the cork impedance value measured by the moisture content change monitoring sensor to the monitoring center for processing;

The third step is to directly calculate the water content in the sensor by the following linear difference formula according to the measured impedance values of the cork when it is completely dry and fully saturated:

$\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 100</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 100</span>}<span\; class="notranslate">\; \%</span>$

In the formula: W is the relative water content, R is the monitored cork impedance value, R ₀ is the impedance value when the cork is completely dry, R ₁₀₀ is the impedance value when the cork is completely saturated,

The monitoring sampling period is <1ms, and the monitoring interval is 5min.

Figure 2 is part of the monitoring data of the concrete specimens in the tidal range area. It can be seen that the water content of the concrete surface changes between 98.5 and 99.5% due to the tidal range, which is closely related to the water absorption of the concrete surface mortar and is consistent with the actual The situation is completely consistent, and it can also be seen that the sensor used in the present invention has a fast response and is suitable for on-site real-time monitoring.

Embodiment two

According to the same steps described in Example 1, the same monitoring is carried out in a concrete specimen located in the splash zone C40. Fig. 3 is part of the monitoring data. It can be seen that the water content at the surface of the concrete is basically in a dry state. The splashing effect occasionally varies from 0 to 0.9%, which is exactly in line with the actual situation.

Claims (1)

1. A method for in-situ monitoring of water content variation in concrete, characterized in that, may further comprise the steps: The first step is to directly bury the monitoring sensor for water content change in the concrete at the position to be monitored in the concrete; The second step is to transmit the cork impedance value measured by the moisture content change monitoring sensor to the monitoring center for processing; The third step is to calculate the water content in the sensor according to the calibrated cork impedance and its water content function, or to calculate the water content in the sensor according to the measured impedance value when the cork is completely dry and fully saturated with the following linear difference formula. Water quantity: $\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 100</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 100</span>}<span\; class="notranslate">\; \%</span>$ In the formula: W is the relative water content, R is the monitored cork impedance value, R ₀ is the impedance value when the cork is completely dry, R ₁₀₀ is the impedance value when the cork is completely saturated, and then the water content in the monitored concrete is deduced Variety.

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