Civil Engineering Tests

Shrinkage limit is defined as the smallest water content at which the soil is saturated. It is also defined as the maximum water content at which a reduction of water content will not cause a decrease in the volume of the soil mass. In other words, at this water content, the shrinkage ceases.

In the below block diagram, stage 1 represents a soil sample which is fully saturated with a water content greater than shrinkage limit. Stage 2 represents soil sample which has water content equal to shrinkage limit. Stage 3 represents the soil sample when it is oven dried, i.e., the water content is removed completely. The total volume V₃ in stage 3 is same as the total volume V₂in stage 2. Let M_sbe the mass of solids.
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Keywords: Pycnometer, specific gravity, density, density bottle, glass jar, dry soil.

The specific gravity of solid particles can be determined in the laboratory using the following methods:
1. Density bottle method
2. Pycnometer method
3. Measuring flask method
4. Gas jar method
5. Shrinkage limit method

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By
KAUSHAL KISHORE
Materials Engineer, Roorkee

Fundamental principle
A pulse of longitudinal vibrations is produced by an electro-acoustical transducer, which is held in contact with one surface of the concrete under test. When the pulse generated is transmitted into the concrete from the transducer using a liquid coupling material such as grease or cellulose paste, it undergoes multiple reflections at the boundaries of the different material phases within the concrete. A complex system of stress waves develops, which include both longitudinal and shear waves, and propagates through the concrete. The first waves to reach the receiving transducer are the longitudinal waves, which are converted into an electrical signal by a second transducer. Electronic timing circuits enable the transit time T of the pulse to be measured.

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By
KAUSHAL KISHORE
Materials Engineer, Roorkee

The examination and compression testing of cores cut from hardened concrete is a well – established method, enabling visual inspection of the interior regions of a member to be coupled with strength estimation. Other properties which can be measured is also given in this paper.

IS: 456-2000 specified that the points from which cores are to be taken and the number of cores required shall be at the discretin of the engineer-in-charge and shall be representative of the whole of concrete concerned in no case, however, shall fewer than three cores be tested. Core shall be prepared and tested as described in IS: 516.

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By
Kaushal Kishore
Materials Engineer, Roorkee

INTRODUCTION
The standard method of determining strength of hardened concrete consists of testing concrete cubes in compression. The quality of entire concrete of a structure cannot be fully assessed by testing a few concrete cubes. The results obtained in testing cubes do not always reflect the actual strength of concrete in construction. In a whole day, concreting work cubes are cast in a few batches, the differences (unintentional and intentional) in the composition are not uncommon, their compaction and their hardening conditions always differ more or less from those of the structure. In addition, the number of test cubes is generally so small that they can only be considered as random tests. Some times, in case of failure of cubes, doubtful concrete, cracks, deterioration of concrete, etc. it becomes necessary to assess the quality and strength of concrete of the structure. As far back as early thirties, the necessity was felt to develop instruments by which in-situ strength of concrete may be obtained. Various non-destructive methods of testing concrete have been developed, which include, Firing method, Skramtayev’s method, Polakov’s method, Magnitostroy method, Fizdel ball hammer, Einbeck pendulum hammer, Ball indentation hammer, Rebound hammer, Pull out techniques, Windsor probe, Ultrasonic pulse velocity methods, Radioactive and nuclear methods, Magnetic and electrical methods. In all these methods of tests, due to simplicity, rebound hammer test based on surface hardness becomes most popular in the world for non-destructive testing of in-situ concrete.

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