Material Testing

Cement we use may go bad during transportation and storage prior to its use in work.We need to test the cement for a good quality and better performance in concrete mixtures. Broadly there are two tests for cement-

• Field Testing
• Laboratory Testing

Field Testing
It is generally done when cement is used for small or minor works. Following are the field tests-

• After opening the bag of cement, we should give a good look, There should not be any visible lumps present in it. Colour of cement should be greenish grey.
• It should give a smooth and gritty feeling when pinch of cement is feel between the fingers.
• If we thrust our hand into the cement bag, it must give a cool feeling.There should not be any lumps inside.
• If we throw some amount of cement into a bucket of water, it should float sometime before sinking.
• A cube made from a stiff paste of 100gm cement and little water is to be put in a glass plate. The glass plate is taken slowly under water in a bucket. The shape of the cube should not be deformed while taking into water. After 24 hours cube should retain its original shape.

If a sample of cement truly satisfies the above tests we may say that the cement is not bad. But the above tests do not really indicate that the cement is really good for important work or big structure. For using cement in important and major structure, it should satisfy the Indian Standard specifications. It is possible only in laboratory testing to confirm the requirements of specified physical and chemical properties.
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By
KAUSHAL KISHORE
Materials Engineer, Roorkee

Most of our construction sites do not have field-testing laboratory. In this paper simple test methods of construction materials are described which could be performed without any machine or special equipments.

1. TEST FOR ORGANIC IMPURITIES IN FINE AGGREGATE
The aggregate must be checked for organic impurities such as decayed vegetations, humus, and coal dust, etc. Colour test is a reliable indicator of the presence of harmful organic matter in aggregates except in areas where there are deposits of lignite.

Procedure:
a) Fill a 350 ml clear glass medicine bottle upto 75 ml mark with a 3% solution of caustic soda or sodium hydroxide.
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The advantages of using Rowe cell over oedometer apparatus are:

(i) It possesses the control facilities for drainage and for the measurement of pore water pressure.

(ii) It is capable of testing larger diameter soil samples. Hence, more reliable data can be provided by using Rowe’s cell because of the relatively smaller effect of structural viscosity in larger specimens.

(iii) Rowe cell uses hydraulic loading system which is less susceptible to the effect of vibration than oedometer apparatus.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

Particle density of soils is defined by the ratio of soil particle mass and soil particle volume. Depending on soil types, the range of variation of soil particle density varies not significantly, i.e. by 4%. Therefore, it may not be worthwhile to order laboratory tests and incur additional expenditure just to determine the particles density by recognizing that the variation of particles density is not significant.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

There are two major techniques of particle size distribution:

(i) Sieve analysis – for soil particles larger than 60?m they can be separated by this method.

(ii) Sedimentation analysis – for soil particles smaller than 60?m, they are too small to be sieved by sieve analysis. Instead, the particle size distribution is worked out from the rate of settlement of soil particles suspended in water by Stoke’s law.

In sedimentation analysis, the soil under testing is firstly boiled with little distilled water to wet and break up the particles. After that, hydrogen peroxide is added to remove any organic material. Then the whole mixture is allowed to stand still for a night and then boiled again to remove hydrogen peroxide.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.