MANUAL 4 - Construction Industry Development Board

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<strong>MANUAL</strong> 4 – BITUMINOUS PAVEMENT SEALS Notes 1. The cement must be added to the neat aggregate and no attempt must be made to add the dry cement after the emulsion has been added. 2. If, for any reason, extra cement is to be added, it must be added as a slurry of water and cement mixture. When drums of emulsion have been stored for any length of time, the bitumen molecules in the emulsion tend to settle to the bottom of the drum. Therefore it is essential to roll the drum and mix the contents well before use. It is even recommended that the day before the drums are to be used, they are turned upside down before being rolled for the next day’s use. It is recommended that full drums are stored not vertically but horizontally, ready for rolling and mixing and empty drums are stored vertically – apart from mixing by rolling the drums, it facilitates stock taking. • The diluted emulsion must be poured slowly into the mixer and not dumped into the mixer (Photo 4.40). By slowly pouring fluid into the mixer, quicker and more efficient coating of the aggregate will occur, without spillage or splashing of both the emulsion and the slurry. The drum of the mixer must not be in the vertical position when pouring the emulsion. This vertical position is used by the operator to protect him from splash, caused by the dumping of emulsion into the drum. Note that the drum must be just off the horizontal position, and that the emulsion should be poured slowly, deep into the throat of the drum, resulting in very little splash. Pour a little at a time and allow mixing to occur before the next pour is done. Photo 4.40 • Before adding the water, inspect the mix as it may not need much water to get the correct consistency. Carefully add the water in 2,5 litre amounts (Photo 4.41), and allow thorough mixing before adding further water. IMPLEMENTING EMPLOYMENT INTENSIVE ROAD WORKS 63 MODULE 1 2 3 4 5 6 7
MODULE 1 2 3 4 5 6 7 <strong>MANUAL</strong> 4 – BITUMINOUS PAVEMENT SEALS Photo 4.41 • The mixing must produce a consistency which is creamy and although very soft when dropped from the mixer into the wheelbarrow (Photo 4.42), it will fall in similar fashion to fresh cow dung without splashing, with a tendency to flow outwards for some 60 to 70 mm. Photo 4.42 • The inside of the drum must be continually inspected for caking at the bottom of the drum. This will be evident when, after mixing for ± 2 min, a watery mixture of emulsion and aggregate (poorly graded) appears to form. Some of the aggregate will have caked at the bottom of the drum. • This will occur if the operator has kept the drum in the semi-vertical position for extended periods while mixing. To rectify this situation, place the drum in the near horizontal position and tap the base of the drum with a 2 kg hammer. Immediately the cake will be released and the mixture will revert to the creamy smooth mixture. The operator of the concrete mixer is in charge of the discharging operations and must ensure the barrows are correctly placed, so that when discharging of the drum occurs, the slurry falls well within the bowl of the barrow without any wastage or mess taking place (Photo 4.42). Only half barrow loads must be discharged and not full loads. IMPLEMENTING EMPLOYMENT INTENSIVE ROAD WORKS 64
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MANUAL 4: Bituminous pavement seals
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MODULE 1 2 3 4 5 6 7 MANUAL 4 - BIT
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MANUAL 4 - Construction Industry Development Board

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