4 of 4 3 of 3 Faculty of CA aaiali UAEU Engineering United Arab Emirates Univers

Question

4 of 4 3 of 3 Faculty of CA aaiali UAEU Engineering United Arab Emirates University Properties of Concrete Materials The following are the materials available in the lab to be used in the concrete mix: Crushed stone is available as coarse aggregate. Two sizes are available. You can use either one. The properties are as follows: NMS 4.75 to 19.0mm OR 4.75 to 9.5mm Specific gravity 2.75 Bulk Density 1750 kg/ms Specific gravity 270 Bulk Density 1750 kg/ma ineness Modulus ranges from 2.5 to 30 Ordinary Portland cement (OPC) wil be used. All cast cubes will be moist cured in curing tanks after de-molding and until the test date, NO ADMIXTURE IS ALLOWED Quality Control The quality contro (QC) Very Good Percentage of defects 5% Durability Requirements No durability requirements should be considered Mix Design Each group could perform the mix design by any method or any available software. It is required from each group to submit the quantities by weight for 1ma of concrete. The mix design procedure or steps are needed. In case of using any software, the name of the software should be provided together with its website link and a screen shot of the mix from the used software. After the submission of the mix design, the group cannot change their concrete mix. Mixing, Casting and Testing The concrete mixture for each group will be mixed in the lab, the slump wil be measured and 4 cubes 100x100x1 wil be cast to be tested at 7days of age All mixes will be judged by the achieved slump and average compressive strength of tested cubes. 4 of 3

Explanation / Answer

Solution -

The ordinary portland cement has strength class of 42.5

For 42.5 strength class of cement with a free water-cement ratio of 0.5 , the approximate compressive strength of 7 days age for crushed aggregate is 36 N/mm2

The standard deviation s for fewer than 20 results of test = 8 N/mm2 for 36 N/mm2 compressive strength

The margin & target mean strength is given by -

fm = fc + ks

where fm = target mean strength

fc = specified compressive strength = 36 N /mm2

ks = margin , where s = standard deviation = 8 N/mm2 & k = 1.64 for 5% defectives

So fm = 36 + 1.64 x 8 = 49.12 N/mm2

water-cement ratio for 49.12 N/mm2 compressive strength = 0.32

Let us consider maximum size of aggregate = 10mm

so for 10mm aggregate entrapped air as percent of volume of concrete = 3%

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