Understand how to compare a given gradation curve to a set of gradation limits (
ID: 1712451 • Letter: U
Question
Understand how to compare a given gradation curve to a set of gradation limits (i.e. ASTM, etc.) Coarse Aggregate Properties What are some mistakes that would cause the absorption and moisture content values to come out wrong? For each mistake describe how the absorption and moisture content would change (ie, Due to error “X", the computed moisture content would be much higher than the typical range for coarse aggregates) . Your about to mix the concrete but notice, that your coarse aggregate looks a little dry, you decide to quickly check the moisture content and see that its 2% as opposed to the 5% moisture that was specked out. If you were making 1 yd of concrete how much additional water do you need to add if 50% of the mix is coarse aggregate? Fine Aggregate Properties - For the specific gravity procedure you cannot dry a sample of fine aggregate in an oven to SSD. Drying in an oven will not produce the same moisture condition as raking and using a blow-dryer. Discuss why the same moisture condition will not be produced between the two p rocedures. Bulking of sand is a common issue in fine aggregate stockpiles. What is bulking and why does it need to be taken into consideration for a concrete mix? Explain the procedure to calculate bulking Mortar Cubes What is the purpose of submerging the cubes in a lime-water bath after de-molding them? IoD Courses Calendar To Do Notifications MessagesExplanation / Answer
Some common mistakes due to which absorption and moisture content value change are as follows :
(1) The sample is not air dried properly before experiment. This would lead to decrease in water absorption value
(2) The sample is not kept in water for 24 hrs for the experiment. This would lead to decrease in water absorpition and decrease in water content.
(3) The sample is not oven dried. If proper drying is not done absorption content would decrease and moisture content would increase.
(4) Error in weighing balance. This can lead to both increase or decrease in water content depending wether the error in weighing balance is positive or negative.
(5) Impurities are present in sample. This would lead to increase in moisture content and absorption limit as impurities like sand will absorb more water than aggregates
Fine Aggregate Properties
In drying with oven the moisture is evaporated from all particles of fine aggregate, from all the four sides , as a result the drying is better .In case of drying with blow dryer the drying is only done in the upper layer, the lower layer still contains some moisture as a result the moisture remains in the case of blow dryer.
Bulking of sand means that the sand has buldged out from sides due to normal force acting downwards on it. Bulking results in increase in volume of sand. A 4 % moisture increase in sand reults in expansion of volume by 25 to 30 %. It should be taken into account for a concrete mix, because if it happens then less concrete will be produced per bag of cement. As a result the cost of concrete will increse. It will reduce the quantity of fine aggregate in concrete mix as a result the concrete will be difficult to place.
The procedure to calculate bulking can be done as -
% Bulking = ( 200-X/X) * 100
Motor cubes are submerged in lime water so that it becomes easy to take them out while demoulding.
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