Concrete Cube Molds, 150x150mm used to mold concrete specimens with

uniform compressive strengths for strength testing and set-time calculations in

accordance with ASTM C403/403M, AASHTO T 197/197M, and EN 12390-1
standards. 150x150x150mm (5.9x5.9x5.9in) WxDxH are the internal
measurements for both variants.

my question how is the QC/QA procedure....i mean is there no means

to assure proper procedure?....i wished to know the QC/QA guidelines
or higoch ....compared to cast insitu

It’s a very wide question but let me try to answer it shortly. Let’s start with the
term QA/QC (Quality Assurance/ Quality control) first. QA looks the quality in
production, such as quality of cement, aggregate, sand, water, mix design etc
QC is once the mix arrive to the site which includes time, temperature, slump,
placing etc
For a ready mix concrete,
1. you need to have proper mix design at first; the approved mix shall be
checked for 2hrs in 30min interval, meaning the slump and strength shall be
checked at initial, 30min, 60min, 90min, & 120m and it shall satisfy the
requirements in all levels.
2. The batching plant shall have weight bridge that controls what goes inside
and print computer generated slip for every batch. This way the plant personnel
can’t compromise on quality or quantity. Most of the plants I see in Addis are
hand written
3. The truck need to reach site at least in 1:15 hrs, since we need to cast the
concrete with in the 2hr range (see point 1). If the truck can’t rich site within
that limit, the mix design shall be run for the required hrs such as 3hrs. But the
best decision would be change a plant or cast at night where you have less
traffic
4. Check the slip from the plant and make sure it is the grade you need. Usually
the mix shall have different code for your site
5. Check the temperature of the mix, it generally not need to exceed 35 degree
centigrade
6. Check slump, it shall be with in the mix design range, if not you need to reject
the mix
7. Take random samples for compressive strength and durability, the sampling
frequency shall be in the specification if not you need to take at least one
sample (that is 6 cubes) for ever 50m3
8. Casting: the concrete shall not be thrown in a free fall over 2m and vibrator
need to be operated only perpendicular
The main justification for choosing 150 mm as the standard size is that it is the
Minimum dimension for concrete testing that will exhibit the same strength as
that for any other dimension at the actual site. Because of this, it was
determined that 150mm is the Best MINIMUM DIMENSION that can relate to
actual strength acquired at site after researching various sizes and forms. Due
to the homogeneity of the mix, which will produce repeatable and dependable
results for concrete strength, a 150mm cube is an ideal size for the majority of
concrete mix designs.

Concrete mix design is the process of finding right proportions of cement, sand
and aggregates for concrete to achieve target strength in structures. So,
concrete mix design can be stated as Concrete Mix = Cement:Sand:Aggregates.
The concrete mix design involves various steps, calculations and laboratory
testing to find right mix proportions. This process is usually adopted for
structures which requires higher grades of concrete such as M25 and above and
large construction projects where quantity of concrete consumption is huge..
Benefits of concrete mix design is that it provides the right proportions of
materials, thus making the concrete construction economical in achieving
required strength of structural members. As, the quantity of concrete required
for large constructions are huge, economy in quantity of materials such as
cement makes the project construction economical. Concrete Mix design of M20,
M25, M30 and higher grade of concrete can be calculated from example below.

Concrete Mix Design

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Data Required for Concrete Mix Design

(i) Concrete Mix Design Stipulation
(a) Characteristic compressive strength required in the field at 28 days grade
designation — M 25 (b) Nominal maximum size of aggregate — 20 mm (c)
Shape of CA — Angular (d) Degree of workability required at site — 50-75 mm
(slump) (e) Degree of quality control available at site — As per IS:456 (f) Type of
exposure the structure will be subjected to (as defined in IS: 456) — Mild
(g) Type of cement: PSC conforming IS:455 (h) Method of concrete placing:
pump able concrete

(ii) Test data of material (to be determined in the

laboratory)
(a) Specific gravity of cement — 3.15 (b) Specific gravity of FA — 2.64 (c)
Specific gravity of CA — 2.84 (d) Aggregate are assumed to be in saturated
surface dry condition. (e) Fine aggregates confirm to Zone II of IS - 383
Procedure for Concrete Mix Design of M25
Concrete
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Step 1 — Determination Of Target Strength

Himsworth constant for 5% risk factor is 1.65. In this case standard deviation is
taken from IS:456 against M 20 is 4.0.
ftarget = f + 1.65 x S
ck

= 25 + 1.65 x 4.0 = 31.6 N/mm 2

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Where, S = standard deviation in N/mm2 = 4 (as per table -1 of IS 10262- 2009)

Step 2 — Selection of water / cement ratio:-

From Table 5 of IS 456, (page no 20) Maximum water-cement ratio for Mild
exposure condition = 0.55 Based on experience, adopt water-cement ratio as
0.5. 0.5<0.55, hence OK.

Step 3 — Selection of Water Content

From Table 2 of IS 10262- 2009, Maximum water content = 186 Kg (for Nominal
maximum size of aggregate — 20 mm)

Table for Correction in water content

Values as per Values as per Correction in
Parameters Standard reference Present Departure Water
condition Problem Content

(+3/25) x 25 =
Slump 25-50 mm 50-75 25
+3

Shape of
Angular Angular Nil -
Aggregate

Total +3
Estimated water content = 186+ (3/100) x 186 = 191.6 kg /m 3

Step 4 — Selection of Cement Content

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Water-cement ratio = 0.5 Corrected water content = 191.6 kg /m 3 Cement

content = From Table 5 of IS 456, Minimum cement Content for mild exposure
condition = 300 kg/m3 383.2 kg/m3 > 300 kg/m3, hence, OK. This value is to be
checked for durability requirement from IS: 456. In the present example against
mild exposure and for the case of reinforced concrete the minimum cement
content is 300 kg/m3 which is less than 383.2 kg/m3. Hence cement content
adopted = 383.2 kg/m3. As per clause 8.2.4.2 of IS: 456 Maximum cement
content = 450 kg/m3.

Step 5: Estimation of Coarse Aggregate

proportion:-
From Table 3 of IS 10262- 2009, For Nominal maximum size of aggregate = 20
mm, Zone of fine aggregate = Zone II And For w/c = 0.5 Volume of coarse
aggregate per unit volume of total aggregate = 0.62

Table for correction in estimation of coarse

aggregate proportion
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Values as
Correction
per Values as
in Coarse
Parameter Standard per present Departure Remarks
Aggregate
reference problem
proportion
condition

W/c 0.5 0.5 Nil - See Note 1

pump able
Workability - - -10% See Note 2
concrete

Total -10%
Note 1: For every ±0.05 change in w/c, the coarse aggregate proportion is to
be changed by 0.01. If the w/c is less than 0.5 (standard value), volume of
coarse aggregate is required to be increased to reduce the fine aggregate
content. If the w/c is more than 0.5, the volume of coarse aggregate is to be
reduced to increase the fine aggregate content. If the coarse aggregate is not
angular, the volume of coarse aggregate may be required to be increased
suitably, based on experience. Note 2: For pump-able concrete or congested
reinforcement the coarse aggregate proportion may be reduced up to 10%.
Hence, Volume of coarse aggregate per unit volume of total aggregate = 0.62 x
90% = 0.558 Volume of fine aggregate = 1 – 0.558 = 0.442

Step 6: Estimation of the mix ingredients

a) Volume of concrete = 1 m3 b) Volume of cement = (Mass of cement / Specific
gravity of cement) x (1/100) = (383.2/3.15) x (1/1000) = 0.122 m 3 c) Volume of
water = (Mass of water / Specific gravity of water) x (1/1000) = (191.6/1) x
(1/1000) = 0.1916 m3 d) Volume of total aggregates = a – (b + c ) = 1 – (0.122
+ 0.1916) = 0.6864 m3 e) Mass of coarse aggregates = 0.6864 x 0.558 x 2.84 x
1000 = 1087.75 kg/m3 f) Mass of fine aggregates = 0.6864 x 0.442 x 2.64 x
1000 = 800.94 kg/m3
Concrete Mix proportions for Trial Mix 1
Cement = 383.2 kg/m3 Water = 191.6 kg/m3 Fine aggregates = 800.94
kg/m3 Coarse aggregate = 1087.75 kg/m3 W/c = 0.5 For trial -1 casting of
concrete in lab, to check its properties. It will satisfy durability & economy. For
casting trial -1, mass of ingredients required will be calculated for 4 no's cube
assuming 25% wastage. Volume of concrete required for 4 cubes = 4 x
(0.153 x1.25) = 0.016878 m3 Cement = (383.2 x 0.016878) kg/m3 = 6.47 kg
Water = (191.6 x 0.016878) kg/m3 =3.23 kg Coarse aggregate = (1087.75 x
0.016878) kg/m3 =18.36 kg Fine aggregates = (800.94 x 0.016878) kg/m3
=
13.52 kg

Step 7: Correction due to absorbing / moist

aggregate:-
Since the aggregate is saturated surface dry condition hence no correction is
required.

Step 8: Concrete Trial Mixes:-

Concrete Trial Mix 1:
The mix proportion as calculated in Step 6 forms trial mix1. With this proportion,
concrete is manufactured and tested for fresh concrete properties requirement
i.e. workability, bleeding and finishing qualities. In this case, Slump value = 25
mm Compaction Factor = 0.844 So, from slump test we can say, Mix is cohesive,
workable and had a true slump of about 25 mm and it is free from segregation
and bleeding. Desired slump = 50-75 mm So modifications are needed in trial
mix 1 to arrive at the desired workability.
Concrete Trial Mix 2:
To increase the workability from 25 mm to 50-75 mm an increase in water
content by +3% is to be made. The corrected water content = 191.6 x 1.03 =
197.4 kg. As mentioned earlier to adjust fresh concrete properties the water
cement ratio will not be changed. Hence Cement Content = (197.4/0.5) =
394.8 kg/m3 Which also satisfies durability requirement. Volume of all in
aggregate = 1 – [{394.8/(3.15x1000)} + {197.4/(1 x 1000)}] = 0.6773 m 3 Mass
of coarse aggregate = 0.6773 x 0.558 x 2.84 x 1000 = 1073.33 kg/m 3 Mass of
fine aggregate = 0.6773 x 0.442 x 2.64 x 1000 = 790.3 kg/m 3
Concrete Mix Proportions for Trial Mix 2
Cement = 384.8 kg/m3 Water = 197.4 kg/m3 Fine aggregate =790.3
kg/m3 Coarse aggregate = 1073.33 kg/m3 For casting trial -2, mass of
ingredients required will be calculated for 4 no's cube assuming 25% wastage.
Volume of concrete required for 4 cubes = 4 x (0.15 3 x1.25) = 0.016878
m3 Cement = (384.8 x 0.016878) kg/m3 = 6.66 kg Water = (197.4 x 0.016878)
kg/m3 =3.33 kg Coarse aggregate = (1073.33 x 0.016878) kg/m3 =18.11 kg Fine
aggregates = (790.3 x 0.016878) kg/m3 = 13.34 kg In this case, Slump value =
60 mm Compaction Factor = 0.852 So, from slump test we can say, Mix is very
cohesive, workable and had a true slump of about 60 mm. It virtually flowed
during vibration but did not exhibit any segregation and bleeding. Desired slump
= 50-75 mm So , it has achieved desired workability by satisfying the
requirement of 50-75 mm slump value . Now , we need to go for trial mix-3 .
Concrete Trial Mix 3:
In case of trial mix 3 water cement ratio is varied by +10% keeping water
content constant. In the present example water cement ratio is raised to 0.55
from 0.5. An increase of 0.05 in the w/c will entail a reduction in the coarse
aggregate fraction by 0.01. Hence the coarse aggregate as percentage of total
aggregate = 0.558 – 0.01 = 0.548 W/c = 0.55 Water content will be kept
constant. Cement content = (197.4/0.55) = 358.9 kg/m3 Hence, volume of
all in aggregate
= 1 – [{(358.9/(3.15 x 1000)} + (197.4/1000)] =0.688 m 3

Mass of coarse aggregate = 0.688 x 0.548 x 2.84 x 1000 = 1070.75 kg/m 3 Mass
of fine aggregate = 0.688 x 0.452 x 2.64 x 1000 = 821 kg/m 3
Concrete Mix Proportions of Trial Mix 3
Cement = 358.9 kg/m3 Water = 197.4 kg/m3 FA = 821 kg/m3 CA = 1070.75
kg/m3 For casting trial -3, mass of ingredients required will be calculated for 4
no's cube assuming 25% wastage. Volume of concrete required for 4 cubes = 4
x (0.153 x1.25) = 0.016878 m3 Cement = (358.9 x 0.016878) kg/m3 = 6.06 kg
Water = (197.4 x 0.016878) kg/m3 =3.33 kg Coarse aggregate = (1070.75 x
0.016878) kg/m3 =18.07 kg Fine aggregates = (821 x 0.016878) kg/m3 = 13.85
kg In this case, Slump value = 75 mm Compaction Factor = 0.89 So, from slump
test we can say, Mix is stable, cohesive, and workable and had a true slump of
about 75 mm. Desired slump = 50-75 mm So , it has achieved desired
workability by satisfying the requirement of 50-75 mm slump value . Now , we
need to go for trial mix-4.
Concrete Trial Mix 4:
In this case water / cement ratio is decreased by 10% keeping water content
constant. W/c = 0.45 A reduction of 0.05 in w/c will entail and increase of coarse
aggregate fraction by 0.01. Coarse aggregate fraction = 0.558 +.01 =.568 W/c
= 0.45 and water content = 197.4 kg/m3 Cement content = (197.4/0.45) =
438.7 kg/m3 Volume of all in aggregate = 1 – [{438.7/(3.15 x 1000)} +
(197.4/1000)] = 0.664 m3 Mass of coarse aggregate = 0.664 x 0.568 x 2.84 x
1000 = 1071.11 kg/m3 Mass of fine aggregate = 0.664 x 0.432 x 2.64 x 1000 =
757.28 kg/m3
Concrete Mix Proportions of Trial Mix 4
Cement = 438.7 kg/m3 Water = 197.4 kg/m3 FA = 757.28 kg/m3 CA = 1071.11
kg/m3 For casting trial -4, mass of ingredients required will be calculated for 4
no's cube assuming 25% wastage. Volume of concrete required for 4 cubes = 4
x (0.153 x1.25) = 0.016878 m3 Cement = (438.7 x 0.016878) kg/m3 = 7.4 kg
Water = (197.4 x 0.016878) kg/m3 =3.33 kg Coarse aggregate = (1071.11 x
0.016878) kg/m3 =18.07 kg Fine aggregates = (757.28 x 0.016878) kg/m3
=
12.78 kg A local correction due to moisture condition of aggregate is again
applied on this proportions. With corrected proportions three concrete cubes are
cast and tested for 28 days compressive strength. A summary of all the trial
mixes is given in the following Table.

Recommended mix proportion of

ingredients for grade of concrete M25:
From Compressive Strength vs. c/w graph for target strength 31.6 MPa we get,
W/c = 0.44 water content = 197.4 kg/m3 Cement content = (197.4/0.44) =
448.6 kg/m3 Volume of all in aggregate = 1 – [{448.6/(3.15 x 1000)} +
(197.4/1000)] = 0.660 m3 A reduction of 0.05 in w/c will entail and increase of
coarse aggregate fraction by 0.01. Coarse aggregate fraction = 0.558 +.01
=.568 Volume of fine aggregate = 1 – 0.568 = 0.432 Mass of coarse aggregate
= 0.660 x 0.568 x 2.84 x 1000 = 1064.65 kg/m3 Mass of fine aggregate = 0.660
x 0.432 x 2.64 x 1000 = 752.71 kg/m3