concrete yield is term used to describe actual volume of freshly mixed concrete form known quantities of ingredients. Usually concrete is sold on volume basis i.e m3 and batched by weight basis.If the mixture proportions for concrete mixtures are not established for the required unit volume or if concrete ingredients are not batched accurately, the combined materials may produce either more or less than the desired volume.
When actual volume of concrete is greater than desire volume, over yield occurs and vice versa.Therefore it is essential to calculate concrete yield to determine actual volume of concrete received at site.Based on unit weight, yield calculation can be done to decide whether less or more volume that desire volume is received.
under yield concrete problems :
It can impact the composition and resulting properties of the mixture furnished. A 2% under yield may result in 2% higher cementitious content per cubic meter.
It may result in having to deliver clean up or short loads involving additional truck and personnel time at an increased cost.
It can increase the standard deviation of strength tests, thereby impacting quality and increasing the cost of all concrete produced.
It can lead to a potential loss of business if the condition is not corrected quickly.
If yield problem not corrected in time, may lead to potential business loss.
1) When concrete vehicle arrives at site, the batch ticket of concrete shall be collected.
2)calculate total weight of truck load, by adding weight of all ingredients i.e. Cement, fly ash, aggregates, corrected water, admixture etc. by referring the batch ticket.(W)
3) The density of concrete shall be determined out of sample concrete by filling concrete in three layers in Density Pot of 3 to 5 Litre capacity and tamping each layer 30 times. Any extra concrete shall be strike off and the finished surface should be flat. The difference of weight of Density pot filled with concrete and empty density pot shall be divided by volume of container to find out density of concrete (D). The pot should be calibrated with water. The weigh balance should be sensitive to 0.010 kg.
4) The concrete yield (The actual volume of concrete) (V) shall be determined by dividing weight of concrete by density of concrete V = W/D
5) calculate % variation by using following formula
P = (V-V 1)/V 1* 100 where V1 is volume of concrete as per batch ticket.
How to avoid Yield Discrepancies?
1. Calculate yield of concrete as per above procedure and check variation. Repeat this process if problem arises.
2. Take measurement of formwork near the end of large pour and calculate the actual volume require. This calculation should be done when last 2-3 truck load of concrete is remaining so that adjustment can be made in ordering concrete.
3.For large area and shallow depth concreting, check the depth at intervals at varies places to ensure uniform thickness.
4.Periodically check form-work for deflection during concreting and estimate extra quantity required due to deflection of form-work.