| With the increase of human demand and the development of society,in the construction industry,pile foundation with high bearing capacity has become an important foundation form of high-rise buildings and bridges,among which cast-in-place pile is the most common in engineering.With the continuous development of construction technology,the pile diameter and length of the cast-in-place pile are increasing,because the whole pouring process of the cast-in-place pile can not be intuitively felt,in order to ensure the bearing capacity and quality of the pile,the over pouring of concrete will occur in many cases,resulting in waste.In this paper,the two electrode method is proposed to control the over pouring of concrete,but the effective size and shape of the electrode used need to be studied by model test,and then the effectiveness and practicability of the electrode are verified by the field pouring pile test.The results of this study are as follows:1.Through indoor model test,the stability and reproducibility of measuring concrete resistivity with alternating current are verified;in the test,the width of measuring electrode is respectively 10 mm,20 mm,30 mm,50 mm and 100 mm,and the research results show that when the width of measuring electrode is 30 mm,the dispersion of resistivity value is the smallest.The cement paste with water cement ratio of 0.3,0.4,0.5 and 0.6 was measured by using the above electrodes.The resistivity of cement paste with water cement ratio of 0.3 was about 2 times of that of 0.6.The resistivity of the sample showed a certain linear relationship with the width of the measuring electrode,the slope was greater than 1,the correlation coefficient was above 0.99,and the correlation was good.2.The influence of electrode placement on the measurement results is studied.When the embedding depth of the electrode in liquid concrete and cement slurry is 10 mm,20 mm,30 mm,50 mm and 100 mm respectively,the lower sample of the electrode has a certain influence on the measurement results.Adding different proportion of aggregate into cementpaste with water cement ratio of 0.4,the measurement of resistivity shows that when the buried depth of measuring electrode is 30mm,the effect is the smallest.In the cement paste with water cement ratio of 0.4,adding the same proportion of aggregate,different proportion of sand and stone has little effect on the change of the resistivity value of the sample,which is basically the same.The results show that(1)cement:water:Sand:Stone=1:0.4:1:0.5;(2)cement:water:sand=1:0.4:1;(3)cement:water:sand=1:0.6:1 the resistivity of three different mix proportion samples increases with the increase of the area of measuring electrode.When the area of measuring electrode is 200mm~2,the resistivity of three different mix proportion samples are 52.0Ω·cm and 39.7Ω·cm respectively When the electrode area is900mm~2,the resistivity is 111.7Ω·cm,92.5Ω·cm and 41.20Ω·cm respectively.The results show that when the area of the measuring electrode is 900mm~2,the sample under the measuring electrode has the least influence on the measurement results,and the resolution of different substances is improved.It is found that the resistivity of the sample increases 16%,15%and 19%respectively when the distance between the measuring electrodes is 50 mm,which is more intuitive to distinguish different samples.When the measuring electrodes are all placed in the sample,the measurement results are more stable than one placed in the middle and one placed on one side.3.It is found that the resistivity test results of rod electrode and sheet electrode are in good agreement,and the test results of embedded electrode and post embedded electrode are also in good agreement.It is found that when the length of rod electrode is 30mm,the sample around the electrode has the least influence on its resistivity,which is consistent with the law of sheet electrode.Rod electrode can replace sheet electrode in practical engineering.4.It is found that the rod electrode can be used to distinguish the mud and concrete in the whole process of grouting.It is found that there is a certain time difference between the two electrodes when they enter the turning point. |
