CN108398486A - Lossless detection method for the arrangement detection of large-scale Box-shaped Drainage Culvert structure reinforcing bars - Google Patents

Abstract

The invention discloses a kind of lossless detection methods for large-scale Box-shaped Drainage Culvert structure reinforcing bars arrangement detection, it is characterised in that the lossless detection method includes the following steps：Survey line is detected in the surface layout at least one of the Box-shaped Drainage Culvert；It is moved along the detection survey line to be detected to reinforcing bar distribution in the Box-shaped Drainage Culvert below the detection survey line using one or more combinations in ultrasonic mapping device, geological radar, 3-D supersonic imaging instrument.It is an advantage of the invention that：Boring and coring is not needed, the position of Box-shaped Drainage Culvert structure reinforcing bars arrangement can be fast and accurately detected using the method for non-breakage.

Description

Non-destructive testing method for detecting reinforcement arrangement of large drainage box culvert structures

technical field

The invention belongs to the technical field of geotechnical engineering detection and testing, and in particular relates to a non-destructive testing method for detecting the arrangement of steel bars in a large-scale drainage box culvert structure.

Background technique

Large-scale drainage box culvert is an important basic measure of the urban drainage system, which plays an important role in ensuring the collection, transportation and treatment of urban sewage and maintaining the daily operation of the city. With the rapid development of urban construction, traffic is becoming more and more busy, road loads are increasing, road widening and reconstruction, and other surrounding engineering activities are more and more affected, resulting in certain safety hazards in large drainage box culverts that are generally in disrepair at this stage. Among them, leakage of large drainage box culverts occurs from time to time. After excavation, it was found that most of the reasons for the leakage came from the damage to the overall structure of the box culvert, such as being soaked in sewage for a long time, and the surface concrete inside the box culvert was washed by sewage and corroded. , so that the internal structural reinforcement of the box culvert often suffers from severe corrosion.

The internal steel bars of the box culvert maintain the overall structure of the box culvert to a certain extent. If the internal steel bars are seriously corroded, the overall structure of the box culvert will be affected. Daily processing brings adverse effects and seriously endangers the normal operation of the city.

Contents of the invention

The purpose of the present invention is to provide a non-destructive testing method for detecting the arrangement of steel bars in a large-scale drainage box culvert structure according to the shortcomings of the above-mentioned prior art. One or more combinations of an ultrasonic imaging device, a ground radar, and a three-dimensional ultrasonic imager are used to move along the detection line to perform non-destructive detection on the distribution of steel bars in the drainage box culvert below the detection line.

The object of the present invention is realized by the following technical solutions:

A non-destructive testing method for detecting the arrangement of steel bars in a large-scale drainage box culvert, characterized in that the non-destructive testing method includes the following steps: arranging at least one testing line on the surface of the drainage box culvert; using an ultrasonic imaging device, One or more combinations of ground radar and three-dimensional ultrasonic imager move along the detection line to detect the distribution of steel bars in the drainage box culvert below the detection line.

The detection measuring line can be one or both of the main reinforcement detection measuring line and the stirrup detection measuring line; Angle; the stirrup detection measuring line and the arrangement direction of the stirrups in the drainage box culvert form an included angle of 80°-90°.

The detection line is arranged at one or more places on the upper surface and the two side surfaces of the drainage box culvert.

The detection measuring line is composed of a number of measuring points arranged at intervals on the surface of the drainage box culvert.

The detection method of the ultrasonic imaging device is as follows: the ultrasonic imaging device composed of an ultrasonic transmitting probe and an ultrasonic receiving probe is arranged on the first measuring point of the detection line, and the ultrasonic imaging device is used to detect the ultrasonic imaging device. The drainage box culvert at the measuring point is detected, the ultrasonic transmitting probe transmits ultrasonic signals into the drainage box culvert, and the ultrasonic receiving probe receives the ultrasonic reflection signal reflected from the drainage box culvert; The above-mentioned detection measuring line completes the detection at the positions of the remaining measuring points successively, and the obtained ultrasonic reflection signal is obtained after data processing to obtain the section diagram of the ultrasonic imaging method; in the section diagram of the ultrasonic imaging method, the drainage box culvert The location of the steel bars in the box is shown as the ultrasonic reflection signal that is different from the interface with the surrounding concrete medium; the distribution of the steel bars in the drainage box culvert is determined through the section diagram of the ultrasonic imaging method.

The ultrasonic imaging device is composed of the ultrasonic transmitting probe and the ultrasonic receiving probe combined at a fixed distance. When testing, the midpoint of the connection line between the ultrasonic transmitting probe and the ultrasonic receiving probe is located Point.

The detection method of the geological radar is as follows: the geological radar composed of a transmitting antenna and a receiving antenna combined at a fixed distance is arranged on the first survey point of the detection survey line, and the geological radar is used to detect the survey point. The drainage box culvert at the location is detected, and the transmitting antenna transmits a high-frequency electromagnetic wave signal into the drainage box culvert. When the high-frequency electromagnetic wave signal reaches the separation between the steel bar and the surrounding concrete medium inside the drainage box culvert The high-frequency electromagnetic wave reflection signal is generated at the interface and received by the receiving antenna; the detection at the remaining measuring points on it is sequentially completed along the detection line, and the obtained high-frequency electromagnetic wave reflection signal is obtained after data processing. The section diagram of the radar method is used to determine the distribution of steel bars in the drainage box culvert through the section diagram of the ground radar method.

In the sectional view of the geological radar method, the position of the steel bar in the drainage box culvert is shown as a high-frequency electromagnetic wave reflection signal that is different from the interface with the surrounding concrete medium.

The detection method of the three-dimensional ultrasonic imager is as follows: the three-dimensional ultrasonic imager is arranged on the first measuring point of the detection line, and at least two rows of ultrasonic probes are arranged on the three-dimensional ultrasonic imager; A row of the ultrasonic probes in the ultrasonic imager emits ultrasonic signals into the concrete structure of the drainage box culvert, when the ultrasonic signal encounters the interface between the reinforcement in the concrete structure of the drainage box culvert and the surrounding concrete medium When, the ultrasonic reflection signal is generated and received by the ultrasonic probes of the remaining rows on one side of the row of ultrasonic probes in the three-dimensional ultrasonic imager to obtain the ultrasonic reflection signal; After the detection, move the three-dimensional ultrasonic imager along the detection measuring line to complete the detection of the remaining measuring points on it; use the three-dimensional ultrasonic imager to detect each of the detection measuring lines in sequence to obtain ultrasonic reflection signals, and performing data processing on the ultrasonic reflection signal to obtain a result map of the three-dimensional ultrasonic imaging method, and determining the distribution of steel bars in the drainage box culvert through the result map of the three-dimensional ultrasonic imaging method.

In the result map of the three-dimensional ultrasonic imaging method, the position of the steel bar in the drainage box culvert shows a difference in the ultrasonic reflection signal at the interface with the surrounding concrete medium.

The invention has the advantages that no drilling and coring is needed, and the position of the reinforcement arrangement of the drainage box culvert structure can be quickly and accurately detected by using a non-destructive method.

Description of drawings

Fig. 1 is the schematic diagram that utilizes ultrasonic imaging device to arrange main reinforcement detection measuring line along drainage box culvert surface to detect in the present invention;

Fig. 2 is the schematic diagram that utilizes ultrasonic imaging device to arrange stirrup detection measuring line along the drainage box culvert surface to detect in the present invention;

Fig. 3 is the sectional view that utilizes ultrasonic imaging device to detect drainage box culvert in the present invention;

Fig. 4 is the schematic diagram that utilizes geological radar to arrange the main reinforcement detection measuring line along the drainage box culvert surface to detect in the present invention;

Fig. 5 is the schematic diagram that utilizes geological mine to arrange stirrup detection measuring line to detect along drainage box culvert surface in the present invention;

Fig. 6 is the sectional view that utilizes geological radar to detect drainage box culvert in the present invention;

Fig. 7 is the sectional view that utilizes three-dimensional ultrasonic imager to detect drainage box culvert in the present invention;

Fig. 8 is a schematic diagram of using a three-dimensional ultrasonic imager in the present invention to arrange the main reinforcement detection line along the surface of the drainage box culvert for detection;

Fig. 9 is a schematic diagram of arranging stirrup detection and measuring lines along the surface of a drainage box culvert by using a three-dimensional ultrasonic imager for detection in the present invention.

Detailed ways

The features of the present invention and other relevant features are described in further detail below in conjunction with the accompanying drawings through the embodiments, so as to facilitate the understanding of those skilled in the art:

As shown in Figure 1-9, the marks in the figure are: drainage box culvert 1, main reinforcement 2, main reinforcement 2a, main reinforcement 2b, stirrup 3, stirrup 3a, stirrup 3b, detection line 4, ultrasonic transmitting probe 5, ultrasonic Receiving probe 6 , ultrasonic imaging device 7 , ground radar 8 , transmitting antenna 9 , receiving antenna 10 , top concrete structure 11 , bottom concrete structure 12 , three-dimensional ultrasonic imager 13 , and ultrasonic probe 14 .

Embodiment 1: As shown in Figures 1, 2, and 3, this embodiment specifically relates to a non-destructive testing method for detecting the arrangement of steel bars in a large-scale drainage box culvert structure. 1 Carry out non-destructive testing, specifically including the following steps:

(1) As shown in Figures 1 and 2, according to the orientation of the drainage box culvert 1, the general orientation of the internal main reinforcement 2 and stirrup 3 is known, and several detection lines 4 are arranged on the structural concrete surface of the large drainage box culvert 1, The arranged detection and measurement line 4 includes the main reinforcement detection and measurement line 4 and the stirrup detection and measurement line 4. As shown in Figure 1, the main reinforcement detection and measurement line 4 is arranged at an angle of 80°-90° to the direction of the main reinforcement 2 in the drainage box culvert 1. °; as shown in Figure 2, the stirrup detection line 4 is at an angle of 80°-90° with the trend of the stirrup 3 in the drainage box culvert 1 when it is arranged; wherein, each detection line 4 is specifically Arranged by a number of equally spaced measuring points;

(2) Remove the floating dust and residue at each measuring point on the surface of the drainage box culvert 1, and try to ensure that the contact surface is as smooth as possible. An ultrasonic imaging device 7 is arranged at the first measuring point of a certain testing line 4. Specifically, the The midpoint of the line between the ultrasonic transmitting probe 5 and the ultrasonic receiving probe 6 is correspondingly arranged at the first measuring point, and the ultrasonic imaging device 7 is well coupled with the surface of the drainage box culvert 1, and the ultrasonic transmitting probe 5 and the The distance between the ultrasonic receiving probes 6 is fixed; after that, the detection is carried out, and the data collection method adopts the flat measurement method, so that the ultrasonic transmitting probe 5 transmits ultrasonic signals to the interior of the drainage box culvert 1 structure. At the same time, the ultrasonic receiving probe 6 receives signals from the drainage The ultrasonic reflection signal between the steel bar and the concrete interface inside the box culvert 1 is stored and stored. The ultrasonic reflection signal includes the measured waveform, sound time and amplitude; it should be noted that during the detection process, the host is connected to control the ultrasonic imaging device 7, Therefore, when the ultrasonic transmitting probe 5 transmits the ultrasonic signal, the host will also synchronously trigger the ultrasonic receiving probe 6 to start working;

(3) After completing the detection of the first measuring point on the detection line 4, move the ultrasonic imaging device 7 to the next measuring point, and follow the detection method in step (2) to the measuring point Perform detection to obtain the ultrasonic reflection signal at the position of the measuring point; reciprocate in this way, complete the detection of all the measuring points on the detection measuring line 4 in turn; and complete all the detection measuring lines on the surface of the drainage box culvert 1 in the same way 4 detection;

(4) Perform data processing and analysis on the collected ultrasonic reflection signal data at different measuring points on each testing line 4 to form a two-dimensional ultrasonic imaging profile. Of course, when there are main rib testing lines 4 and In the case of the stirrup detection measuring line 4, a three-dimensional detection image can also be combined to form a three-dimensional detection image; then, according to the two-dimensional ultrasonic imaging method profile and the three-dimensional detection image, the exact reinforcement distribution in the drainage box culvert 1 is determined, here The reinforcement specifically refers to the main reinforcement 2 and the stirrup 3. The specific judgment is explained as follows: According to the two-dimensional ultrasonic imaging method section diagram and the three-dimensional detection image, the reinforcement shows strong reflection and diffraction, which are different from the surrounding concrete medium. Based on this, the exact distribution position of the steel bars in the drainage box culvert 1 can be judged, so as to determine the distribution of the structural main bars 2 and stirrups 3 in the large drainage box culvert 1 .

Embodiment 2: As shown in Figures 4-6, this embodiment specifically relates to a non-destructive testing method for detecting the arrangement of steel bars in a large-scale drainage box culvert structure. The non-destructive testing method mainly uses geological radar 8 to conduct Non-destructive testing, specifically includes the following steps:

(1) As shown in Figures 4 and 5, according to the orientation of the drainage box culvert 1, the orientation of the main reinforcement 2 and stirrup 3 is known, and several detection lines 4 are arranged on the structural concrete surface of the large drainage box culvert 1. The arranged detection line 4 includes the main reinforcement detection measurement line 4 and the stirrup detection measurement line 4. As shown in Figure 4, the main reinforcement detection measurement line 4 is arranged at 80°-90° to the direction of the main reinforcement 2 in the drainage box culvert 1. As shown in Figure 5, the stirrup detection line 4 is at an angle of 80°-90° with the direction of the stirrup 3 in the drainage box culvert 1 when it is arranged; wherein, each detection line 4 is specifically composed of It is formed by arranging a number of equally spaced measuring points;

(2) Remove the floating dust and residue at each measuring point on the surface of the drainage box culvert 1, and ensure that the contact surface is as smooth as possible, and arrange a geological radar 8 at the first measuring point of a certain detection line 4. Specifically, it will launch The midpoint of the connection line between the antenna 9 and the receiving antenna 10 is correspondingly arranged at the first measuring point, and the distance between the transmitting antenna 9 and the receiving antenna 10 is fixed; afterward, the detection is carried out so that the transmitting antenna 9 is directed to the drainage box culvert 1. The high-frequency electromagnetic wave signal is emitted inside the structure. When the high-frequency electromagnetic wave signal reaches the interface between the reinforcement (main reinforcement 2 or stirrup 3) in the drainage box culvert 1 and the surrounding concrete medium, there is an obvious difference in dielectric constant between the reinforcement and concrete, so High-frequency electromagnetic wave reflection signals will be generated at the interface between the two and received by the receiving antenna 10;

(3) After completing the detection at the first measuring point on the detection line 4, move the geological radar 8 to the next measurement point along the detection line 4, and follow the detection method in step (2) Detect the measuring point, so as to obtain the high-frequency electromagnetic wave reflection signal at the position of the measuring point; reciprocate in this way, and complete the detection of all the measuring points on the detection measuring line 4 in turn; and complete the drainage box culvert 1 in the same way Detection of all detection lines 4 on the surface;

(4) Perform data processing and analysis on the collected high-frequency electromagnetic wave reflection signal data at different measuring point positions on each detection measuring line 4, and obtain the GPR profile within the coverage of each detection measuring line 4; after that Determine the exact reinforcement distribution in the drainage box culvert 1 according to the obtained georadar section diagram. The reinforcement here refers to the main reinforcement 2 and the stirrup 3. The steel bars in the culvert 1 exhibit reflection phenomena that are different from the surrounding concrete medium, such as strong reflection and diffraction. Based on this, the exact distribution position of the steel bars in the drainage box culvert 1 is determined, and thus the structural main bars 2 and stirrups in the drainage box culvert 1 are determined. 3 distribution.

Embodiment 3: As shown in Figures 7-9, this embodiment specifically relates to a non-destructive testing method for detecting the arrangement of reinforcement bars in a large-scale drainage box culvert structure. The non-destructive testing method mainly uses 13 pairs of drainage box culverts 1 for non-destructive testing, a total of 48 ultrasonic probes 14 are arranged on the three-dimensional ultrasonic imager 13, and every four ultrasonic probes 14 form a row, a total of 12 rows; it should be noted that the ultrasonic probes 14 in this embodiment use The ultrasonic transceiver probe can transmit and receive ultrasonic waves; specifically, it includes the following steps:

(1) According to the orientation of the drainage box culvert 1, the approximate orientation of the internal main reinforcement 2a, 2b and stirrup bars 3a, 3b is known, and several detection lines 4 are arranged on the surface of the concrete structure 11 at the top of the large drainage box culvert 1, The arranged detection measuring line 4 includes the main reinforcement detecting measuring line 4 and the stirrup detecting measuring line 4, the detecting measuring lines 4 of the same type should be kept parallel to each other, and the distance between adjacent detecting measuring lines 4 is 10cm;

As shown in Figure 8, the main reinforcement detection line 4 is arranged at an angle of 80°-90° with the direction of the main reinforcement 2 in the drainage box culvert 1; as shown in Figure 9, the stirrup detection measurement line 4 is arranged at the same time The direction of the stirrup 3 in the drainage box culvert 1 is at an included angle of 80°-90°;

It should be noted that when detecting the distribution of the main reinforcement 4 in the concrete structure 12 at the bottom of the drainage box culvert 1, each detection measuring line 4 should be arranged between adjacent stirrups 3 to obtain a better detection effect; When the stirrups 5 in the concrete structure 12 at the bottom of the box culvert 1 are distributed, each detection line 4 should be arranged between adjacent main reinforcements 2 to obtain better detection results;

(2) Remove the floating dust and residue on the surface of the drainage box culvert 1, and ensure that the contact surface is as smooth as possible; arrange a three-dimensional ultrasonic imager 13 at the first measuring point of a certain testing line 4 and conduct testing. The specific process is : A row of ultrasonic probes 14 in the three-dimensional ultrasonic imager 9 transmits ultrasonic signals to the interior of the concrete structure in the drainage box culvert 1. When the ultrasonic signals reach the interface between the main reinforcement 2a or stirrup 3a in the top concrete structure 11 and the surrounding concrete medium , the ultrasonic reflection signal will be generated and will be received and stored by the ultrasonic probe 14 of the remaining row on the right side of the row of ultrasonic probes in the three-dimensional ultrasonic imager 13; of course, when the ultrasonic signal reaches the main reinforcement 2b in the bottom concrete structure 12 Or when the interface between the stirrup 3b and its surrounding concrete medium, the ultrasonic reflection signal will also be generated and received and stored by the ultrasonic probe 14 of the remaining row on the right side of the row of ultrasonic probes in the three-dimensional ultrasonic imager 13;

Afterwards, move the three-dimensional ultrasonic imager 13 along the detection line 4 and perform a detection at intervals of 10-20 cm;

(3) According to the step (2), reciprocate in this way, use the three-dimensional ultrasonic imager 13 to complete the detection on all detection lines 4 in sequence, and obtain the ultrasonic reflection signals on all detection lines 4, which can be obtained after data processing by the host computer Obtain the results map of the three-dimensional ultrasonic imaging method, including section data, plane data or three-dimensional data; the main reinforcement 2a, 2b and stirrup 3a, 3b in the drainage box culvert 1 will appear to exist with the surrounding concrete medium in the three-dimensional ultrasonic imaging method result map Differential strong reflection phenomenon.

Embodiment 4: As shown in Figures 1-9, this embodiment specifically relates to a non-destructive testing method for detecting the arrangement of steel bars in a large drainage box culvert structure. The non-destructive testing method uses the methods described in Examples 1-3 in sequence Ultrasonic imaging device 7 , ground radar 8 , and three-dimensional ultrasonic imager 13 detect the reinforcement distribution of drainage box culvert 1 , and the specific detection accuracy can be improved through the detection by the three devices in the above-mentioned embodiment.

Claims (10)

1. A non-destructive testing method for the detection of large-scale drainage box culvert structural reinforcement arrangement, characterized in that said non-destructive testing method comprises the following steps: at least one detection line is arranged on the surface of said drainage box culvert; One or more combinations of the device, ground radar, and three-dimensional ultrasonic imager move along the detection line to detect the distribution of steel bars in the drainage box culvert below the detection line. 2. A kind of non-destructive testing method for steel bar arrangement detection of large-scale drainage box culvert structure according to claim 1, it is characterized in that said detection measuring line can be one of main reinforcement detecting measuring line and stirrup detecting measuring line One or two types; the main reinforcement detection measuring line and the arrangement direction of the main reinforcement in the drainage box culvert are at an angle of 80°-90°; the stirrup detection measurement line and the arrangement of the stirrups in the drainage box culvert The direction is at an angle of 80°-90°. 3. A non-destructive testing method for detecting the arrangement of steel bars in a large-scale drainage box culvert according to claim 1 or 2, wherein the detection line is arranged on the upper surface and both sides of the drainage box culvert one or more of the above. 4. A non-destructive testing method for detecting the arrangement of steel bars in a large-scale drainage box culvert structure according to claim 1, wherein the detection line is arranged by a plurality of measuring points distributed at intervals on the surface of the drainage box culvert composition. 5. A kind of non-destructive testing method for steel bar arrangement detection of large-scale drainage box culvert according to claim 1, characterized in that the detection method of the ultrasonic imaging device is: a combination of an ultrasonic transmitting probe and an ultrasonic receiving probe The completed ultrasonic imaging device is arranged on the first measuring point of the detection line, and the ultrasonic imaging device is used to detect the drainage box culvert at the measuring point, and the ultrasonic transmitting probe is directed to the Ultrasonic signals are transmitted in the drainage box culvert, and the ultrasonic receiving probe receives the ultrasonic reflection signal reflected from the drainage box culvert; the detection at the remaining measuring points on it is completed sequentially along the detection line, and the obtained After the ultrasonic reflection signal is processed, the ultrasonic imaging method section diagram is obtained; in the ultrasonic imaging method section diagram, the position of the steel bar in the drainage box culvert is represented by the ultrasonic reflection that is different from the interface with the surrounding concrete medium. signal; determine the distribution of steel bars in the drainage box culvert through the section diagram of the ultrasonic imaging method. 6. A non-destructive testing method for detecting reinforcement arrangement of large-scale drainage box culvert structures according to claim 5, characterized in that the ultrasonic imaging device consists of the ultrasonic transmitting probe and the ultrasonic receiving probe at a fixed distance Combination structure, when testing, the middle point of the connection line between the ultrasonic transmitting probe and the ultrasonic receiving probe is located on the measuring point. 7. A kind of non-destructive testing method for steel bar arrangement detection of large-scale drainage box culvert structure according to claim 1, characterized in that the detection method of the geological radar is: the transmitting antenna and the receiving antenna are combined at a fixed distance The formed geological radar is arranged on the first measuring point of the detection survey line, and the geological radar is used to detect the drainage box culvert at the measuring point, and the transmitting antenna is directed to the drainage box culvert When the high-frequency electromagnetic wave signal reaches the interface between the steel bar inside the drainage box culvert and the surrounding concrete medium, a high-frequency electromagnetic wave reflection signal is generated and received by the receiving antenna; along the detection The survey line completes the detection at the positions of the other survey points in turn, and the obtained high-frequency electromagnetic wave reflection signal is processed to obtain the geological radar method section diagram, and the drainage box culvert is determined through the geological radar method section diagram. distribution of reinforcement. 8. A non-destructive testing method for detecting reinforcement arrangement of large-scale drainage box culvert structure according to claim 7, characterized in that, in the section drawing of the geological radar method, the steel bars in the drainage box culvert The position appears as a high-frequency electromagnetic wave reflection signal that produces a difference at the interface with the surrounding concrete medium. 9. A non-destructive testing method for detecting reinforcement arrangement of large-scale drainage box culvert structures according to claim 1, characterized in that the detection method of the three-dimensional ultrasonic imager is: the three-dimensional ultrasonic imager is arranged in On the first measuring point of the detection line, at least two rows of ultrasonic probes are arranged on the three-dimensional ultrasonic imager; When the ultrasonic signal encounters the interface between the reinforcement in the concrete structure of the drainage box culvert and the surrounding concrete medium, an ultrasonic reflection signal is generated and transmitted by the row of ultrasonic waves in the three-dimensional ultrasonic imager. The ultrasonic probes in the remaining rows on one side of the probe receive the ultrasonic reflection signal; after the detection at the first measuring point is completed, the three-dimensional ultrasonic imager is moved along the detection line to complete the remaining Detection at the position of the measuring point; use the three-dimensional ultrasonic imager to detect each of the detection measuring lines in turn to obtain ultrasonic reflection signals, and perform data processing on the ultrasonic reflection signals to obtain a three-dimensional ultrasonic imaging result map. The distribution of steel bars in the drainage box culvert is determined from the result map of the three-dimensional ultrasonic imaging method. 10. A non-destructive testing method for detecting the arrangement of steel bars in a large-scale drainage box culvert structure according to claim 9, characterized in that in the result map of the three-dimensional ultrasonic imaging method, the steel bars in the drainage box culvert The location appears as a differential ultrasonic reflection signal at the interface with the surrounding concrete medium.