Trial mixing concrete .pdf

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STRUCTURAL ENGINEERING LABORATORY
DEPARTMENT OF CIVIL ENGINEERING
FACULTY OF ENGINEERING, SLIIT
BSc ENGINEERING – YEAR 2 SEMESTER 1
LABORATORY ASSIGNMENT
CE2021 – PROPERTIES AND MECHANICS OF MATERIALS
Experiment: Trial Mixing of Concrete
Introduction
A trial mix is used to see if a mix design can produce concrete with the desired strength, workability,
and other characteristics. The workability of concrete may be assessed by performing a slump test
on new concrete, but the compressive and tensile strengths of concrete must be measured using
hardened concrete specimens.
The slump test is the most practical method of determining concrete's workability. A higher slump indicates
that the concrete is more workable. Both cube and cylindrical specimens can be used to evaluate the
concrete's compressive strength, whereas cylindrical examples are required for tensile strength testing.
Objectives
• To determine the slump of the concrete
• To cast cube and cylindrical specimens for hardened concrete testing

3. Apparatus
• Platform scale
Figure 1
• Drum concrete mixer
Figure 2
• Slump test apparatus
Figure 3
• Concrete cylinder molds with
diameter 150 mm and height 300 mm (6)
Figure 4
• Compacting rod
Figure 5
• Scoop
Figure 6

4. • 150 mm x 150 mm x 150 mm concrete cube moulds (3)
Figure 7
• Trowel
Figure 8
Procedure
Step 1.
Calculation of mix amounts

5. Specimen type Unit volume (m3) No of
specimens
Total (m3)
Cube 3.375x10-3
3 0.0101
Cylinder 5.301x10-3 4 0.0212
Total volume 0.0313
Considering 10 % extra for wastages 0.0344
Constituent Weight required per
1m3 (kg)
Volume required (m3) Weight
required (kg)
Coarse aggregate 1019.6 0.0344 35.074
Fine aggregate 868.65 0.0344 29.882
Cement 351.85 0.0344 12.104
Water 190 0.0344 6.536

6. Step 2:
Measuring out constituents
• Required amounts of coarse aggregates, fine aggregates, cement. and water were
measured.
Step 3:
Mixing of concrete
• Half of the Coarse aggregates were added
• All the Fine aggregates were added
• All the Cement was added
• Remaining coarse aggregates were added
• Mixing process started using Drum concrete mixer
• All the water were added withing 30s
• Mixed around 2min to 3min

7. Step 4:
Carrying out the slump test
Tamping rod: 600 mm long; 16 mm diameter; rounded ends
• mould and base plate of the slump test apparatus was dampened
• Mould was kept on the plate and filled in three layers with concrete(each layer 1/3 of the
total height).
• Each layer was compacted with 25 strokes from the tamping rod distributed uniformly
over the entire cross-section of the mould
• After compacting the third layer, the surface was strike offed using the tamping rod
using a sawing and rolling motion.
• Then the mould was lifted steadily and vertically within 5s to 10s and placed it next to
the concrete in an inverted position.
• The tamping rod was placed horizontally on the mould and measured the slump of the
concrete
Figure 9

8. Step 5:
Casting cubes and cylinder specimen Compacting
bar: 380 mm long; 1.8 kg; 25 mm2
face
• The mould was placed on a rigid horizontal surface
• Concrete was placed in layers 50 mm thick using scoop.
• Each layer was compacted with 35 strokes from the compacting rod distributed
uniformly over the entire cross-section of the mould
• Each layer was compacted with 35 strokes from the compacting rod distributed
uniformly over the entire cross-section of the mould. (Cubes-min.35 blows pr layer,
Cylinders- minimum 30 blows per layer)
• After compacting the final layer, smooth offed the top surface and wiped clean the
outside of the mould.
Step 6:
Demoulding and curing
Specimens should be left in the mould for at least 16 hours but not more than 3 days. After
demoulding, cure specimens in water at a temperature of 20 ˚C ± 2 ˚C. Curing must be done until
just before the specimens are tested. Finally, the moulds must be greased up using form oil and
assembled awaiting the next casting.
Observations
• Target slump :30-60mm
• Observed slump:183mm
• Observed slump type:

9. Figure 10 collapsed slump
DISCUSSION
1. What is the purpose of doing a trial mix?
Concrete trial mixes are used to test the strength, workability, density, and other characteristics of
concrete mixtures. When novel ingredients or admixtures are to be employed, trial mixes are frequently
used. Trial mixes are vital for mix optimization since they may help you maximize all of the elements in
the mix.
2. What is the purpose of using a vibrating table/tamping rod?
The vibration table may be tuned to provide the optimal acceleration and frequency for compacting
concrete, resulting in uniform, neat-surfaced concrete products. In secondary concrete product
manufacturers, this compactor may significantly enhance the working environment, product quality,
productivity, and cost.

10. 3. What are the tests you did in the mixing process?
Slump test
Slump testing is a laboratory or on-site method of determining concrete consistency. The slump test
indicates the consistency of concrete in different batches. The shape of the concrete slumps reveals
information about the concrete's workability and quality. A few tamping or blows with a tapping rod on
the base plate can also be used to assess the features of concrete in terms of segregation propensity.
Because of the simplicity of the apparatus and process, this test has been used since 1922. The Slump
cone's form demonstrates concrete's workability.
4. Did you achieve the desired slump value? If no, explain the reasons for the
difference and the remedies that you could use?
All concrete has slump loss, or it would never harden. In the normal slow congealing, we call
‘setting’, the concrete first gradually loses all its slump and then proceeds to harden.
• Time
When identifying and discussing the causes of slump loss, time is sometimes overlooked. It is, in fact, the
most crucial of all of them. From mixing to placement, elapsed time is constantly there and striving to
lessen the slump minute by minute.
Slump loss is purely a function of time in most cases.
Prevention
Remove all potential delays.
Workable concrete must be established by trial and adjustment made as required under
actual job condition
After a satisfactory trial on the project, one key change to make is enough extra slump in
the concrete as mixed to balance typical slump loss and provide adequate time for
transportation and placement.
• TEMPERATURE
When concrete is mixed, handled, or exposed to high temperatures, the rate of slump loss
increases. Whatever additional factors may be at play in a given setting, they appear to be
amplified with greater temperatures.
Prevention
Cooling concrete materials such as aggregate and water (ice, liquid nitrogen)
Slow rate of setting time by retarder or supplementary cementing material
Follow guidelines on Hot-Weather Concreting
1) AGGREGATE

11. Aggregates are often blamed for causing slump loss because they are dry or because they have
latent absorption.
Prevention
Use shading for aggregate
Highly absorption poor aggregate preferably should not be used
Sprinkled to moisten and pre-saturate the aggregate so that it does not absorb water from
the concrete after mixing or during pumping.
5. How did you decide the mixing time for each step?
When determining the mixing time, there are a few elements to consider. These factors include
the mixing drum's rotational speed, the amount of material utilized in the mixture, and the
required workability.
CONCLUSION
Aggregates, Portland cement, and water are all used in the construction of concrete mix designs.
The combinations are widely used to increase concrete strength, improve workability, and
minimize mixing water needs. Concrete proportions are chosen by striking a balance between
cost and needs for strength, durability, density, and beauty. Concrete mix design is the process of
selecting acceptable concrete materials and determining their relative proportions with the goal
of generating a concrete with the requisite strength, durability, and workability as inexpensively
as feasible.
As a result, the attribute of workability becomes critical. The compressive strength of hardened
concrete, which is often used as an indicator of its other attributes, is determined by a variety of
elements including cement quality and amount, water and aggregates, mixing, placement, and
compaction. We performed a concrete mixing experiment to see if a certain mix design might
provide the needed strength, functionality, and other characteristics.
The computations that were necessary were completed. To get an almost flawless concrete mix,
path mixing was done with the greatest precision feasible. Once the mixture is complete, pour it
into molds and set aside for a day to cure. Also soak the shattered concrete for 28 days in water.

12. Bibliography
Hamakareem, M. I. (n.d.). Failed concrete slump test? Retrieved from The constructors:
https://theconstructor.org/
jsssanthoshb. (2020, March 25). SlideShare. Retrieved from Module 4 concrete mix proportioning:
https://www.slideshare.net/jsssanthoshbs/module-4-concrete-mix-proportioning
Marketing, K. (2013, April 25). Snart Concrete. Retrieved from KRYTON:
https://blog.kryton.com/2013/04/three-causes-of-slump-loss/