BULKING:FINE AGGREGATE



BULKING OF FINE AGGREGATE (FIELD METHOD)

IS: 2386 - Part 3

1. Introduction

Sand brought on to a site or works may contain some amount of moisture. Due to this, when loosely filled into a container, it will occupy a larger volume than if it is dry. If the sand is measured by loose volume, it is necessary in such a case to increase the measured volume of sand, in order that the amount of sand put into the concrete may be the amount intended for nominal mix used, based on dry sand. It will be necessary to increase the volume of sand by the „percentage bulking?. The procedure to be adopted may be varied, but two methods are used.

2. Apparatus

(i) A measuring cylinder, 250 ml.

(ii) Two containers to hold test sand.

(iii) One steel rule.

3. Procedure for method I

a) Put sufficient quantity of the sand loosely into a container until it is about two-third full and level off the top of the sand.

b) Push a steel rule vertically down through the sand at the middle to the bottom and measure the height, h cm.

c) Empty the sand out of the container into another container where none of it will be lost.  

d) Half fill the first container with water

e) Put back about half the sand and rod it with a steel rod, about 6 mm in diameter, so that its volume is reduced to a minimum.  

f) Then add the remaining sand and rod it in the same way.

g) Smooth and level the top surface of the inundated sand and measure its depth at the middle with the steel rule, h’ cm.

4. Calculation

The percentage of bulking of sand due to moisture is calculated from the below formula:  Percentage bulking = [(h/h?)-1] x 100

5.  Procedure for method II

a) Pour the damp sand (consolidated by shaking) into a 250 ml measuring cylinder, until it reaches the 200 ml mark.

b) Then fill the cylinder with water and stir the sand well. (The water shall be sufficient to submerge the sand completely).

c) It will be seen that the sand surface is now below its original level. Suppose the surface is at the mark y ml.

6. Calculation

The percentage of bulking of sand due to moisture is calculated from the formula below:

 Percentage bulking = [(200/y) -1] x 100

7. Reporting of results

Report the percentage bulking of the sand to the nearest whole number.

MEASURING THE MORTAR MAKING PROPERIES OF FINE AGGREGATES 

IS: 2386 - Part 6 

1. Introduction

The mortar-making properties of fine aggregate for concrete are measured by casting cubes in 7.06 cm cube moulds with mortar of a plastic consistency and gauged to a definite watercement ratio. The cubes tested in a compression testing machine of required capacity and average crushing strength determined. The fine aggregate is compared by testing mortar cubes made using sand treated with 3 percent solution of Sodium Hydroxide and mortar cubes made using sand without treatment.

2.  Apparatus

(i) Flow table and flow mould conforming to the requirements specified in 12 of IS: 1727-1960 Methods of test for Pozzolanic materials.  

(ii) A tamper of 12.5 mm x 25 mm cross section 12.5 to 15 cm long of a nonabsorptive, non-abrasive material.

(iii) A trowel having a steel blade 100 to 150 mm long with straight edges.

(iv) Steel moulds of 7.06 cm size.

(v) Tamping rod shall be 10 mm diameter with one end with hemispherical tip, 300 mm long.

(vi) A compression testing machine of suitable capacity.

3. Treatment of sand

a) The sand for preparing mortar is washed with 3 percent of solution of Sodium Hydroxide followed by through rinsing with water.

b) The treatment process shall be repeated till the washed material produces a colour lighter than that of the standard solution described in IS: 2386 (Part 2) - Methods of test for aggregates for concrete: Estimation of deleterious material and organic impurities.

c) Ensure that no fines are lost while washing with sodium hydroxide solution.

d) The rinsed aggregate may be tested using litmus or phenolphthalein to assure that all traces of sodium hydroxide is removed from the sand before preparing mortar.

4. Preparation of mortar

a) Take cement and water in a vessel to get a water-cement ratio of 0.6 by weight. Permit the cement to absorb water by keeping for one minute.

b) Mix with a spoon to make a smooth paste.

c) Add a known weight of sample sand at saturated surface-dry condition to this paste and mix thoroughly to get the desired consistency (Flow 100±5).

d) After mixing for another 30 seconds, determine flow as given in para 5 below.

5. Determination of flow

a) Place the flow mould on the carefully cleaned surface of the flow table.   

b) Immediately after mixing of the mortar, place a layer 25 mm thick and tamp 20 times with the tamper. The tamping pressure shall be just sufficient to ensure uniform filling inside the mould.

c) Fill the mould fully in the same manner as first layer. Cut off the excess mortar from the top of the mould using the straight edge of the trowel.

d) Clean the flow table surface, free of water and spilled mortar.

e) Lift the mould after one minute after completing the mixing. Drop the table 10 times in 6 seconds through a height of 12.5 mm.

f) Measure the dia of the spread mortar mass in four directions and find the average. This expressed as a percentage of the original diameter will give the flow.

g) If the flow is more, add more sand and repeat the process to get a flow of 100±5.

h) If more than two trials are required to get a flow of 100±5 consider it as a trial mortar. Prepare test specimens from a new batch.  

6. Moulding test specimens

a) Immediately after completing the flow test, place the mortar in 7.06 cm cubes in 2 layers, each layer rodded 25 times with tamping road.

b) After rodding is completed, fill the moulds to overflow. Place the moulds in a moist chamber for curing.

c) After 3-4 hours, strike off the excess mortar to make a smooth surface.

d) Remove the specimens from the mould after 20-24 hours and keep in water until tested.

e) The temperature of mixing water, moist closet and water in the curing tank shall be kept at 27±2°C.

7. Testing of specimens

a) Remove the specimens from moist closet (24 hours testing) or from curing tank after the specified period.

b) Surface dry each specimen.

c) Remove any sand particles adhering to the faces. Use soft instruments to clean the cubes.

d) Apply load to the face of the specimen which is in contact with plane surface of the mould.

e) Rate of loading shall be adjusted such that the failure occurs only after 20 seconds but within 80 seconds.

8. Calculation

a) Calculate the average crushing strength of minimum three specimens prepared with the sand sample.

b) Similarly find out the crushing strength of specimens prepared with treated sand.

c) Report the crushing strength of specimens prepared with untreated sand as a percentage of the average crushing strength of specimens made with treated sand. 

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