
Field Guidelines

1. CEMENT Field Test:

The following field tests may be conducted to ascertain the quality of cement. a) The colour should be uniform. b) The cement should feel smooth when touched or rubbed in between fingers. c) The Cement should be cool when hand is thrust through inside heap/bag of cement. d) Small quantity of cement thrown over a bucket of water should sink and not float on surface. e) A thin paste of cement with water should feel sticky between fingers. f) The cement should not contain hard lumps. g) A sample of cement is taken and heated on a clean steel plate kept on a stove for about 20 mins. A change in color in cement indicates adulteration with stone dust. h) A sample of cement is put in half glass full of water and stirred well and allowed to settle. It will leave the adulteration in cement to continue to float. Storage of Cement Cement has a tendency to absorb moisture. If the moisture absorption exceeds 5%, the cement becomes useless. Hence cement should be stored as for as possible in air tight containers. It is not advisable to store cement in jute bags for more than 3 months. The cement should be stacked in piles of 10 bags each and 30 cms away from the external wall. Top and bottom of stacks should be covered with tarpaulins. In spite of every precaution taken in storage of cement certain loss of strength with the passing of time is inevitable as shown below: Fresh Cement - 100 % strength After 3 month - 20 % less strength. After 6 month - 30 % less strength. After 12 month - 40 % less strength. After 24 month - 50 % less strength. 2. AGGREGATES 2.1 Fine Aggregate (Sand) Sand is generally obtained from beds of rivers and streams. They are generally found clean and is widely used. Sand is classified according to the size of grains: a. Fine sand passes through a screen of 1.587 mm opening. This is mainly used for plastering. b. Coarse sand passes through a screen of 3.175 mm. This is mainly used for masonry work. c. Gravelly sand passes through a screen of 7.162 mm and is used for concrete works. The following field test can be carried out to ascertain fitness of sand a. A sample of sand is taken and rubbed in hand. If clay content is more, it leaves soil on hand and such sand should be rejected. b. When sand is watered and dried, if it leaves white salt or when tasted salty, the same is not suitable. c. A solution of Sodium Hydroxide or Caustic Soda is added to the sand and stirred. The solution changes its color to brown if organic matter is present. Such sand is not fit for construction. d. The sand shall be clean, coarse and angular and free from vegetable and organic matter. 2.2. Coarse Aggregate Coarse aggregate is the material used as filler in cement concrete mix and are formed by crushed stones either mechanically or manually. a. The crushed stone should consist of clean angular fragments uniform in size. It should be free from elongated pieces, soft or disintegrated stones or clay. b. Rounded particles do not provide good interlocking. Hence they should be rejected. c. Aggregate should not contain harmful materials such as iron pyrites, coal, mica, shale or similar laminated material, clay, alkali, sea shells organic impurities. 3. BRICKS The following visual tests and field tests be carried out to ascertain good quality bricks for use in works. a. Well burnt bricks are copper colored and are free from cracks. b. They posses sharp and square edges. c. They are of uniform color, shape and size as per standard. d. When struck with each other, they produce clear metallic ringing sound. e. Fracture of good bricks show uniform and bright compact structure without any voids. f. They absorb minimum water when immersed in water. The absorption should not be more than 20 % when immersed in water for 24 hours. g. Good bricks are hard on their surface and leave no impression when scratched with nails. h. Good bricks do not break when dropped from 1 m height i. Good bricks when soaked in water and dried, do not show white patches or white deposits on their surface. j. The good quality bricks could be gauged easily by the percentage of bricks that get broken in transit and stacking in the course of ordinary handling (2 to 3%). 4. STEEL The mild steel / TOR steel used in RCC works should be a. Able to develop good bond with concrete b. Should have thermal expansion nearer to concrete. c. Should have high tensile strength. d. Should not get affected by concrete. e. Should afford easy cutting, bending and welding. f. It should be ensured that the bars used are clear and free from dust or rust.