A ready mix concrete producer is requested to supply non-air entrained concrete
ID: 1765635 • Letter: A
Question
A ready mix concrete producer is requested to supply non-air entrained concrete for a(n) Based o structure in Melbourne that will be grade based on cylinder specimens is 40 MPa at 28 days b to restrictions, the concrete will be pumped on site. The scope of the project required that one (d) Wha hundred laboratory test results on the controlling mix had to be caried out which resulted in a ) Using the standard deviation of 5.0 MPa. trength an exposed to sea water. The minimum compressive cteristic strength Due (b) What is the tareet strength fem (k L.65) ) Using the tahles provided. what is the recommended stump ased on strength requirement. t is the required water per ky m of concrete? required (f) What is the required cement per kg'm of concrete? (g) What is the wet density of the conerete per ke m ? (h) Determine the amount of sand per kg m of air entrained co (i) Determine the amount of aggregate per ke m of air entra G) You are required to cainy out testing on three Australian Standard cylinders and three Assume that you will be using the following materials General purpose Portland cement: Type A, density 3150 kgm ned concrete Coarse aggregate: crushed granite, maximum size is 20 mm, density 2800 kg'm', and dry rodded density 1600 kgm e volume of concrete needed to manufacture these specimens in the lab. Assume a safety volume factor of 20%. Round the final result to the nearest whole numbe (Hint the eylinder is 200 mm high100 m in dinmeter, the beam is Fine aggregate: density 2700 kg m. fineness modulus-3.0 (k) In order to cast the nmount of concrete in (1), how much cement, water, fine and The approximate amount of accidentally-entrapped air in the fully-compacted concrete should be estimated as 3%. All calculations are based on the British mix design concept. coarse aggregate would you need to have? Round a decimal o the nearest tenth. Il) If the cylinders prepared in ) have average 28 days strengih of 30 MPa, how do you adjust the concrete mixture to satisfy the requirement?Explanation / Answer
a) Characteristics Strength = 40 MPa
b) Target Mean Strength = Characteristics Strenght of Concrete + 1.65*(Standard Deviation)
= 40+8.25
= 48.25 MPa ~ 50 MPa
c) No tables are provided to calculate the slump
d) Assume 160 Kg/m3 of water is needed to prepare the concrete
e) Assuming water to cement ratio of 0.35.
Therefore amount of cement needed: (=160/0.35) = 457 kg/m3
Consider volume of concrete = 1 m3
Air Content = 3%
Therefore, volume of fresh concrete = 1-(3/100)
= 0.97 m3
457 kg of cement corresponds to 0.1450 m3 of cement. (volume = Mass/Density = 457/3150)
Similarly, 160 kg of water corresponds to 0.160 m3 of water. (Volume = Mass/Density = 160/1000)
Subtracting the above amounts from the volume of fresh concrete: 0.97-0.145-0.16
=0.665 m3 is the combined volume of coarse and fine aggregate
Assuming proportion of coarse aggregate to total aggregate to 0.60.
Mass of Coarse aggregate: (Volume of all aggregate) * (Proportion of Coarse aggregate in total aggregate) * (Density of Coarse aggregate)
= (0.665)*(0.60)*2800
= 1117.20 kg
Mass of Sand: (Volume of all aggregate) * (Proportion of fine aggregate in total aggregate) * (Density of Fine aggregate)
(Note: Here fine aggregate corresponds to Sand)
= (0.665)*(0.4)*2700
= 718.20 kg
Mass of materials in per m3 of concrete:
1. Water Content: 160 kg
2. Cement Content: 457 kg
3. Coarse Aggregate: 1117 kg
4. Fine Aggregate: 718 kg
Volume of concrete required for cylinder: 3.14*0.1*0.1*0.2*1.2/4*3 = 0.0565 m3
Volume of concrete required for beam: 0.1*0.1*0.35*1.2 = 0.0042 m3
If the actual strength of concrete is lower than the target mean strength. The water to cement ratio of mix should be reduced in order to get a higher strength.
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