Civil Engineering | Assignment

Civil Engineering
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1. Introduction
1.1 slump test
slump test is conducted to determine the fluidity or the degree of mobility of concrete.
Commonly, it can be stated to as the consistency of concrete. Consistency of concrete is
determined by factors such as surface texture of aggregates, use of admixtures, water cement
ratio, mix proportions as well as sizing of the constituent aggregates. In addition to the slump
value it shows the concrete feature. It is called true slump if the concrete slumps uniformly. It
is called shear slump if one half of the cone slides down.
1.2 compressive strength test.
To determine the cube compressive strengths, cubes of 150 mm sizes were tested at 28 days
cure as per the standards of ACI which requires use of cylinder of height 300 mm and
diameter 150 mm. the results of this test are identified as the characteristic compressive
strength of the concrete sample and is based with not exceeding 5 % f the test results.
1.3 splitting tensile strength test.
This test is key determinant on understanding failure of concrete by means of cracking, that
is the strength of the said concrete to resist tensile forces within it. Concrete is weak in
tension hence the need for reinforcement in structural works. Determine the maximum tensile
strength of a given concrete is key so as to effectively design against any failures that may
result when the resulting tensions is more than the tensile strength of concrete.
1.4 flexural test on concrete.
Concrete flexural test is an indirect evaluation of the concrete splitting tensile strength.
Flexural test evaluates the capacity of unreinforced slab or beam to resist bending. It is
expressed as modulus of rupture MR in psi or MPa.
2. Experimental method/ procedure.
Manufacture of concrete
Concrete is manufactured from a mixture of cement as binder material, coarse aggregates
(gravel) and fine aggregates(sand). Chemical additives such as plasticizers could be added in
some mixes to impart other properties such as increased strengths.

Concrete testing
To test concrete, aspects of compressive strength, tensile strength and flexural strength are tested
for hardened concrete. For fresh concrete, slump test is carried out to evaluate the consistency or
workability of concrete. The following procedures describe these tests;
Mix proportions
Mix proportions implies the ratio of cement, sand and aggregates by weights
For example, for group one: cement: sand: aggregates ratio is
10.5
10.5 = 10
10.5 = 23.2
10.5 which translates ¿1:0.95:2.2 as shown in the table
2.1 Slump test procedure.
See figure 2.1 (a) and (b).
 The mould is
kept damp
and clean
with no
excess
moisture on
its surface.
Position the
mould in a
smooth non-
absorbent,
horizontal, and rigid surface devoid of any shock or vibration.
 The mold is held firmly in place and a scoop is used to fill the mould in three
layers of concrete.
 Each layer is sufficiently tampered upon placement with 25 strokes of
tamping rod to ensure uniform distribution of the test concrete mix over the
Groups cement: sand: aggregates simplified mix ratio
1 10.5:10:23.2 1:0.95:2.2
2 10:10.5:23.2 1:1.05:2
3 9.1:11.1:23.6 1:1.0:2.6
4 8.2:11.7:23.8 1:1.5:3
5 7.6:12.7:23.5 1:1.67:3.1
6 6.9:14.4:23.4 1:2:3.4
7 7:14.4:23.4 1: 2:3.3
8 6.5:15.5:22.2 1:2.4:3.4
9 6.6:15.1:21.7 1:2.3:3.3
10 4.5:12.9:22 1:2.9:4.9

cross-section layer. This should be done carefully such that the tamping road
doesn’t not strike the surface below and that it is not excessively conducted.
 Heap the concrete on top of the mould before tampering the uppermost layer.
 upon sufficient tamping of the top layer, strike off the concrete level with the
mould edge with a rolling and sawing motion of the tamping device. While
still maintaining the mould down, any concrete that have fallen onto the
surface is carefully cleaned.
 Remove the mould from the entire concrete by carefully, vertically and slowly
raising in in such a manner that minimum torsional and lateral movement is
impacted on the concrete.
 Immediately after removing the mould, by use of a rule measure the height of
the mould and that of the highest point of the sample.
Figure 2.1 a) slump test procedure.

Figure 2.1 b) measuring of slump.
2.2 Compressive strength test procedure
See figure 2.2 (a) and (b).
 This is conducted in accordance to IS516:1959.
 The proportion of the concrete aggregates are measured by weight. Test cubes
of dimensions 150mm by 150mm by 150m made immediately after mixing of
concrete and cured after 28 days is used.
 the concrete was fully compacted with neither excessive laitance nor
segregation.
 The concrete is filled in the mould in layers not exceeding 50 mm and placed
in the cube in such a way that symmetrical distribution is achieved in the
cube.
 The test samples are kept in moist air with not less than ninety percent
humidity and no vibrations with temperatures of 27 degree Celsius with a
variation of + or – 3 sustained for a period of 24 hours. Curing is done until 28
days,

Figure 2.2 a) curing of concrete cube specimen.
 The specimen is then capped before testing after 28 days of cure.
 Concrete cube is placed in a clean testing device in such a way that the load
distribution shall be to the opposite sides of the cast cubes and not bottom
down.
 The specimen axis is carefully aligned with the center of the spherically seated
plate.
Figure 2.2 b) compressive strength test set up.
 Without shock, the load is continuously applied at a rate of approximately 140
kg/sq cm/min until the sample fails by breaking.
 Maximum load applied is then noted for analysis and report.

2.3 Splitting tensile strength test procedure.
See figure 2.3 (a), (b) and (c).
 The cured sample is removed from water and wiped clean
 Diametrical lines are drawn on the specimen ends to ensure they achieve the
same axial plane.
 Weigh and dimension of the specimen is taken and recorded.
 The testing machine is then set to the required range.
 The specimen is placed on a plywood base and positioned on the lower plate
of the machine.
 The specimen is aligned so that based on the diametrical lines drawn, a proper
symmetry is achieved in positioning.
 Provide a plywood strip on above the specimen and adjust the upper plate to
touch the plywood strip such that the test specimen is well fitted between the
plates as shown in figure 2.3 a).
Figure 2.3 a) specimen set up.
 At a rate of 0.7 to 1.4 MPa/ min (IS 5816 1999) continuously apply the load
on the specimen without shock.

 Note down the load at failure.
Figure 2.3 b) split cylinder testing machine.
Figure 2.3 (c) bearing strip and load set up.
2.4 Flexural test procedure.
See figure 2.4 (a) and (b).
Center Point Load Test (ASTM C293)
The specimen is immediately tested after curing since surface drying may lead to decline in the
flexural strength.

Figure 2.3 a) Centre point load test set up.

Figure 2.3 b) flexural strength test in progress.
3. Results
3.1 slump test result
water
content
kg
slump
mm
4.2 2
4.2 0
4.2 3.5
4.2 10
4.2 52
4.5 168
4.2 30
4.2 71
4.6 205
4.5 48

Graph 1: slump Vs water content.
As shown in graph 1, slum generally increases with increasing water content until 4.5 kg of
water from where the pattern is non-linear.
Slump= 168 mm (group 6)
3.2 compressive strength test results
Cube tests Cube 1 Mass in air – 1 (g) 2324
Mass in water – 1
(g)
1277
Failure load – 1
(kN)
381
Cube 2 Mass in air – 2 (g) 2379
Mass in water – 2
(g)
1309
Failure load – 2
(kN)
380
Cube 3 Mass in air – 3 (g) 2325
Mass in water – 3
(g)
1278
Failure load – 3 382

(kN)
a. Density of the cubes
density of sample= mass∈ air
mass∈air−mass∈water × 100 %
density of cube−1= 2324
2324−1277 ×1000=2219.7 kg/m3
density f cube−2= 2379
2379−1309 × 1000=2223.4 kg/m3
density of cube−3= 2325
2325−1278 × 1000=2220.6 kg /m3
b. cube compressive strengths
compressive strength= maximum load
cube cross sectional area
cube−1 compressive strength= 381 kN
( 0.15 ×0.15 ) m2 =16933.3 kN / m2=16.93 MPa
cube−2 compressive strength= 380
( 0.15 ×0.15 ) m2 =16888.9 kN / m2=16.89 MPa
cube−3 compressive strength= 382
(0.15 ×0.15)m2 =16977.8 kN /m2=16.98 MPa
From the calculations above, for the rest of the group we come up with the following
tabulated data.

Graph 2: density vs water content.
The water to cement ratio= weight of water divided by
weigh of cement in Kg hence the tabulated results
below.
Gr
ou
compr
essive
wat
er
gro
ups
wat
er
con
tent
kg
den
sity
kg/
m3
1 4.2 224
5
2 4.2 224
0
3 4.2 225
2
4 4.2 224
4
5 4.2 224
4
6 4.5 222
0
7 4.2 223
8
8 4.2 222
9
9 4.6 223
3
10 4.5 223
9

ps strengt
h Mpa
cem
ent
rati
o
1 22.57 0.4
2 23.58 0.42
3 22.17 0.46
4 20.15 0.51
5 18.25 0.55
6 16.93 0.65
7 18.18 0.6
8 16.37 0.65
9 14.24 0.7
10 18.67 0.54
Graph 3: compressive strength vs water to cement ratio.

As depicted in graph 3, compressive strength share an inverse relationship with water
to cement ratio hence the graph curvature.
3.3 splitting tensile strength test results
Splitting tensile strength is given by the formula T = 2 P
πLD where ,
T is splitting tensile strenth∈MPa
P isthe maximum applied load indicated by the testing achine ,
D is diameter f the specimen ∈mm;
L islenth of the specimen∈mm
¿ this case ,
D is given as 100 mm∧L is200 mm while
P is obtained ¿ the recorded result as 99 kN
Therefore ,
Tensile strength T = 2 × 99 kN
3.14 × 0.2 m× 0.1m =3152.9 kN /m2=3.1529 MPa
By same methodology, T is calculated for other groups and the result is tabulated as shown
below;
Groups split tensile strength
Mpa
water cement ratio
1 3.5 0.4
2 3.53 0.42
3 3.5 0.46
4 3.53 0.51
5 3.15 0.55

6 3.15 0.65
7 3.12 0.6
8 3.53 0.65
9 3.06 0.7
10 3.82 0.54
Graph 4: split tensile strength vs water content.
From graph 4, slit tensile strength is higher at low water to cement rati and decreases as the ratio
increases.
3.4 flexural test results
Flexural strength is estimated using Modulus of rupture MR which is derived according
to the equation; MR= 3 PL
2b d2 .
given; b=100 mm , d=100 mm ,
L=300 mm∧Pis obtained fro test result where P=15.5 kN

Hence , MR=3 ×15.5 kN × 0.3 m
2 ×0.1 × 0.12 =6975 kN /m2=7 MPa
Based on flexural test, the bending strength of concrete is estimated as follow;
f b= PL
b d2 where f b denotesbending strength
substituting the parametres we get ; f b = 15.5 kN × 0.3 m
0.1m ×(0.1¿¿ 2) m2=4650 kN / m2 ¿
f b=4.65 MPa
This is calculated from the other groups hence the tabulation and the graph shown below:
Grou
ps
flexural
strength
MPa
water
cement
ratio
1 5.31 0.4
2 5.43 0.42
3 4.29 0.46
4 4.26 0.51
5 4.32 0.55
6 4.65 0.65
7 4.83 0.6
8 3.72 0.65
9 4.11 0.7
10 4.05 0.54

Graph 5: flexural strength vs water to cement ratio.
Similarly, flexural strength is higher at low water to cement ratio and decreases with
increasing water to cement ratio. This is as shown in graph 5 above.
4. Discussion
Generally. The trends noted in this experiment are agreeable as they generally depict the normal
trends when it comes to the relationship between water content and density, water content and
slump as well as the relationships between strengths to water to cement ratio of concrete mixes.
Water cement ratio is acritical parameter when it comes to concrete technology and mix design.
It significantly impacts on concrete durability. When water cement ratio is reduced in concrete
mixes, there is a general reduction in porosity of the concrete which as a result lower its
permeability and higher durability is achieved. Typically, the capillary pores vary between 10-
100 micrometers depending on the water cement ratio with lower capillary porosity. Low water
cement ratio therefore allows the cement particles to be closer together or more proximate to one
another resulting in better bonding hence high strength concrete and increased durability. This
typically explain the trends in graphs 3,4, and 5 on compressive strength, tensile strength and
flexural strengths.
The effect of water cement ratio on concrete durability can be summarized as in the following
equation based on the Feret’s formula as shown;

where
is the constant based on the classification / type of cement .
T is formula clearly indicates the inverse relation between water cement ration and concrete’s
compressive strength. Higher strength in concrete is as well characterized by more resistance to
internal stresses hence high tensile and bending strengths.
Low water cement ratio implies low workability in concrete hence high slump is observable,
water cement ratio and slump therefore share a direct correlation such that at high water cement
ratio there is increased workability of concrete(slump) while at low water cement ratio, the
workability of concrete is reduced hence low slump. This explains the trend noted in graph 1.
The content of cement and the water content of the mix (not the w / c ratio) influence the density
directly a shown in graph 2. All alone the water cement amount has no direct influence on
concrete density. Mix of the same ratio of water cement can be of varying densities. From our
observations in the experiment, the density of the cubes decreases with the decreasing mass of
water in the mix hence the trend in the graph of Density versus water content. This implies that
at low water cement ratio, low density of concrete is achieved and vice versa. This as shown in
the results in the previous section.
Experimental errors and limitations of the experiments.
There are so many of errors in this kind of experimental set up. Some of these consists of
mathematical error as expressive in rounding off of figures as well as errors when taking
measurements or readings. For instance, when measuring height of the slump there could be
errors in attaining exact reading. Also, during preparation of the experiment where compaction is
needed such as in slump cone and cubes/ cylinders for compressive, tensile and flexural strength
concrete there exists possibilities of over compaction. Over compaction interferes with concrete
mix as it results to segregation and settlement hence the ideal slump or strengths cannot be
attained.