CONTENT

NO TITLE PAGE

1 OBJECTIVE 1

2 THEORY 1

3 APPARATUS 2

4 MATERIAL 2

5 PROCEDURES 3

6 RESULT 4

7 QUESTIONS 5

8 DISCUSSION 6

9 CONCLUSION 7

10 APPENDIX 8

11 REFERENCE 9

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EXPERIMENT : 4

TITLE : SILT TEST FOR SAND

OBJECTIVE : To determine amount and percent of silt in a nature sand

THEORY

Silt is granular material of a size somewhere between sand and clay whose mineral

origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment (also known

as suspended load) in a surface water body. It may also exist as soil deposited at the bottom

of a water body.

Clay, mud, fine, dust or silt will weaken the concrete because the dirt tends to coat the

aggregate and weaken the bond between the aggregate and cement paste thus preventing the

cement from setting. Coarse aggregates should be for cleanliness purposes are inspected by

visual inspection.

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APPARATUS

1. Measuring cylinder 250 ml

2. Rubber hammer

3. Spatula

4. Stirring rod

MATERIAL

1. Water

2. Sand

3. Salt

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PROCEDURE

1. The cylinder was filled up to about 50 ml of salt water solution.

(one tablespoon salt to 1 litre of water)

2. The sand was poured into the cylinder until the level of water reaches 100 ml.

3. More salt water was added until it reaches 150 ml.

4. The cylinders were shakes well.

5. The cylinders were placed on a levelled surface.

6. After 2 hours, the results were recorded.

7. The silt layer was measured on top of the sand. The thickness can be explained as a

percentage of sand level below the layer. The sand considered as clean if the

percentage is not more than 8% of the original volume of the sand.

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RESULT

Calculation on amount of silt using Volume method.

No. DescriptionMeasurement (mm)

Sand inside the lab

Sand outside the lab

1 Height of sand layer (y) 83 mm 80 mm

2 Height of silt (x) 4 mm 5 mm

Percentage of silt in sand = x / y X 100%

=

Standard form : percentage of silt less than

………………………………….%

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QUESTION

1. Why we use salt water in this test?

We use the salt in this test is for separate the water with the sand to measure the silt layer on the top of the sand. If we don’t use the salt, we could not measure it as the water did not float or separate with the sand.

2. What happen to you concrete when we use the sand with silt more than 8%?

If we use sand with silt more than 8%, the concrete will weak and cannot use it for any project. This is because the silt will weaken the bond between aggregates and cement paste.

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DISSCUSSION

Silt is created by a variety of physical processes capable of splitting the generally sand-sized

quartz crystals of primary rocks by exploiting deficiencies in their lattice. These involve

chemical weathering of rock and regulate, and a number of physical weathering processes

such as frost shattering and haloclasty. The main process is abrasion through transport,

including fluvial combinations, Aeolian attrition and glacial grinding. It is in semi-arid

environments that substantial quantities of silt are produced. Silt is sometimes known as

"rock flour" or "stone dust", especially when produced by glacial action. Mineralogical, silt is

composed mainly of quartz and feldspar. Sedimentary rock composed mainly of silt is known

as siltstone.

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CONCLUSION

If the sand contains more than 6% silt, you would have to use more cement and the concrete would shrink more during the hardening process, causing cracks in the product. Silt and clay are not as strong as typical aggregates. They can absorb water and their properties can change because of it. In fresh concrete, I would think that silt and clay would interfere with the bonding of aggregates to cement. In hardened concrete, if the silt and clay come in contact with water in air voids, they can shrink or swell, either building internal pressure (swelling) or leaving larger voids and weakening the concrete (shrinking).

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APPENDIX

Poured salt water into cylinder filled with sand Salt

Stirring salt water Salt water

Glass rod

Spatula

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REFERENCE

http://en.wikipedia.org/wiki/Silt

http://autonopedia.org/buildings_and_shelter/Rural_Building/Aggregates.html

http://sg.answers.yahoo.com/question/index?qid=20100528053325AAfWt4Y

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