Expert Answer:Calculations and Graphs For Concrete Mix Design

  

Solved by verified expert:This lab was about concrete mix designs. we did the lab test twice one was after 14 days and the second one was after 28 days. I will upload the results sheet and it will includes 5 teams results my team is ( B2 ). You will need to make 5 graphs based on all teams results, but the rest of the lab will be about my team. please do not use ( we did , I did ) in the lab report. uploaded files :1- results sheet.2- lab manual guide for how to write the lab report.3- how will the lab report will be graded sheet.
lab_guide_manual_for_concret_mixed_111.docx

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IV. Lab #1Concrete Mix Design and Compression Tests
A. Objectives:
1. To familiarize the student with the general characteristics of concrete and
concrete materials and with laboratory methods of manufacture and test of
concrete specimens
2. To determine the effect of varying design mixes and materials (water, cement,
sand, and coarse aggregate) on the consistency of the fresh concrete and on the
strength of the hardened material.
B. References:
ASTM C143-12 Standard Test Method for Slump of Hydraulic-Cement Concrete
ASTM C39-05 Standard Test Method for Compressive Strength of Cylindrical Concrete
Specimens
ACI Committee 211 Standard Practice for Selecting Proportions for Normal,
Heavyweight, and Mass Concrete, ACI 211.1-91, American Concrete Institute, 2002
ACI Committee 214 Evaluation of Strength Test Results of Concrete, ACI 214R-02,
American Concrete Institute, 2002
C. Background:
Portland cement concrete is a widely used building material for many reasons: it can be readily
formed into many shapes; it is both durable and corrosion resistant; it provides fire protection
and water tightness; and has a relatively high compressive strength. Although concrete exhibits
low tensile strength, this disadvantage can be overcome by
reinforcing it, normally with steel.
The properties of concrete, in both the freshly mixed and the hardened state, are closely
associated with the characteristics and relative proportions of its components. The solid
portion of the hardened concrete is composed of the aggregate and a new product which is the
result of a chemical combination of cement with water. The remaining portion of the space
occupied by a given volume of concrete is composed of free water and air voids, with the air
voids usually not occupying more than 1 or 2% of the volume
, unless special chemicals (air entraining admixtures) are used to trap more air voids in the
concrete. After a period of time, the amount of free water depends on the extent of
chemical combination of water and cement, called hydration, and loss from evaporation.
The cement-water paste is the active component in the concrete and the properties of the
water-cement paste depend upon the characteristics of the cement, the relative proportions of
cement and water, and the completeness of the chemical combination or hydration. The
completeness of the hydration requires time, favorable temperatures, and the continued
presence of moisture. The period during which the concrete is definitely subjected to these
conditions is called curing. On construction work, curing may vary from 3 to 10 days; in the
laboratory the common curing period is 28 days. Good curing is essential for the production of
quality concrete.
There are five types of Portland cement, as indicated below:
Type I.
For use in general concrete construction when the special properties specified for
the other four types are not needed
Type II
For use in general concrete construction exposed to moderate sulfate
action, or where moderate heat of hydration is required
Type III
For use when high early strength is required
Type IV
For use when a low heat of hydration is required
Type V
For use when high sulfate resistance is required
All types are made of approximately 60% lime-bearing material and 40% of a clayey material,
which are ground, mixed together, and then heated to fusion. The product is then ground fine
and mixed with about 3% gypsum. A sack of cement contains 1 cubic foot of material and
weighs 94 pounds.
The sand and gravel (fine and coarse aggregate) used in a concrete mixture should be well
proportioned or graded from fine to large particles. Sands generally vary in particle size from
1/4″ down to those that pass a 100 mesh sieve (10,000 openings per square inch). Gravels vary
upward from 1/4″ to 1.5″ and often to 2.5″. If the sand and gravel are well graded, the void
space will be minimized and less cement paste will be needed to produce concrete. Concrete
mix proportions may be based on volume or weight of materials and are stated, for example, as
1-2.5-3.5 mix by volume,
meaning that 1 part of cement, 2.5 parts of sand, and 3.5 parts of gravel, all by volume,
should constitute the mix.
The water-cement ratio (quantity of water divided by quantity of cement used) is the single
most important factor influencing the strength of the final product. The only property of
concrete which improves with a higher water-cement ratio is the workability, or the ease with
which the concrete can be placed. Consistency relates to the state of fluidity of the mix an
d ranges from the driest to the wettest mixtures. The most common test to determine
consistency is the slump test (ASTM C143), which is performed by measuring the subsidence, or
slump (in inches), of a pile of concrete 12″ high, formed in a mold that has the shape of a cone.
The tendency for water to rise to the surface of freshly placed concrete is known as
bleeding, and results from the inability of the material to hold all the mixing water.
Concrete subject to bleeding is not as strong or durable as concrete that does not bleed.
The strength of concrete is taken as an important index of its quality. Strength tests are
commonly made in compression and flexure and occasionally in tension. The compression test
of a 6 by 12-inch (or 4 by 8inch) cylinder at age 28 days, after moist storage at a temperature of
70 of, is a standard ASTM test (ASTM C39).
The compressive strength of concrete, made and tested under standard conditions, ordinarily
varies from 2500 to 6000 psi, although much higher strengths can be obtained by using special
additives. The tensile strength of concrete is roughly 10% of the compressive strength; and the
flexural strength(strength in bending)of plain concrete, as measured by the modulus of rupture,
is about 15 to 20% of the compressive strength.
The principal factors affecting strength are:
1. Water-cement ratio — the higher the water content, the lower the strength.
2. Age — the strength of concrete generally increases with age, although practically
all the strength has been achieved after 28 days.
3. Character of the cement — the finer the cement, the higher the strength.
4. Curing condition — the greater the period of moist storage, the higher the strength.
Evaluation of strength data is required in many situations, such as:
• Evaluation of mixture submittal;
• Evaluation of level of control (typically called quality control); and
• Evaluation to determine compliance with specifications (job – site acceptance testing)
A strength test result is defined as the average strength of all specimens of the same age,
fabricated from a sample taken from a single batch of concrete. A strength test cannot be
based on only one cylinder; a minimum of two cylinders is required for each test. Concrete tests
for strength are typically treated as if they fall into a distribution pattern similar to the normal
frequency distribution curve. A sufficient number of tests are needed to indicate accurately
the variation in the concrete produced and to permit appropriate statistical procedures for
interpreting test results. To satisfy statistically based strength – performance requirements,
the average strength of the concrete fcr′ should be in excess of the specified design
compressive strength fc′. The required average strength fcr′ used in mixture proportioning
depends on the expected variability of test results as measured by the coefficient of variation
or standard deviation. The strength test record used to estimate the standard deviation or
coefficient of variation should represent a group of at least 30 consecutive tests. If the number
of test results available is less than 30, a more conservative approach is needed; and when the
number of strength test results is less than 15, the calculated standard deviation is not
sufficiently reliable to be of use. In those cases, the concrete is proportioned to produce
much higher average strengths fcr′ than the specified design strength fc′.
The strength of concrete in a structure and the strength of test cylinders cast from a sample of
that concrete are not necessarily the same. The strength of the cylinders obtained from that
sample of concrete and used for contractual (job – site) acceptance are to be cured and tested
under tightly controlled conditions. The strengths of these cylinders are generally the primary
evidence of the quality of concrete used in the structure.The engineer specifies the desi red
strength, the testing frequency, and the permitted tolerance in compressive strength. It is
impractical to specify an absolute minimum strength, because there is always the possibility of
even lower strength test results simply due to random variation, even when control is good.
D. Materials:
Type I Portland cement, sand, gravel, and lubricant for molds
E. Equipment:
For mixing: scale for weighing, concrete mixer or mixing pan, shovels, trowel, slump cone, 12″
scale, tamping rod, measuring beakers, mallet, wet towels, plastic, 3” by 6″ or 4” by 8”
cylinder molds (Note: 3 by 6” cylinders are not permissible when testing concrete strength by
ASTM C39). For testing: rigid end caps, and concrete testing machine.
F. Procedure:
This experiment requires several laboratory periods. During the first period, concrete
mixes will be designed and cylinders prepared for testing. Cylinders will be tested at
four weeks (28 days) and either one week (7 days) or two weeks (14 days) after the first period.
Specific instructions regarding the mix design will be given at the time of the experiment, using
ACI 211.1 – 91 Standard Practice for Selecting Proportions for Normal, Heavyweight, and Mass
Concrete. Results will be compiled from all groups, with each group using a different water cement ratio for comparison and analysis.
a. Concrete Mix Preparation
1Design one batch of non-air-entrained concrete, following the guidelines of the
American Concrete Institute. Mix enough concrete to mold four test cylinders and to fill a
slump cone. Mix the materials by first combining the sand and cement, then adding the gravel,
and finally the water. Keep accurate records on the amount (by weight) of each of the
materials used.
2- Once a mix has been prepared, its consistency should be measured with the slump
cone apparatus, which is a truncated cone conforming to ASTM specifications. To make
the slump test(ASTM C143), dampen the slump cone, scoop, tamping rod, and metal
working surface. Holding the cone in position by standing on the foot pieces, fill the
slump cone in three equal layers, rodding each layer 25 times with the tamping rod,
making sure to cover the full area of the concrete with the tamping motion and that
the strokes barely penetrate into the previous layer. For the final layer, pile the
concrete above the top of the cone to account for settlement. If the level settles below
the top of the cone, add additional concrete. Carefully strike off the surface using the
tamping rod. Raise the slump cone by means of the handles, without any twisting or
side motion. Place the cone next to the concrete, with the tamping rod over the cone.
If one side of the concrete falls away or shears off, repeat the test. Measure the slump
to the nearest 1/4″ and classify the mix as wet (over 6″), normal (1-6″), or stiff (under
1″). The slump test is a good field test for consistency and may actually be used to
determine the amount of mixing water. If the mix is outside the “normal slump” range,
mix the concrete again and make adjustments to bring it into the normal range . If the
slump is greater than that required, add more fine and/or coarse aggregates. If the
slump is less than required, water and cement in the appropriate ratio should be
added. Make sure that accurate records are kept of whatever materials are added so
that the actual ratio of materials can be reported.
3. Observe the general characteristics of each mix, making note of its troweling
workability. To determine troweling workability, work the concrete with a trowel. If it
works smoothly and with little effort, the troweling workability may be called good. Rate
as good, fair, or poor.
4. Fill the molds completely in three equal layers, tamping each layer 12 times, and each
time tapping the sides of the mold 5 to 10 times with a mallet to remove air voids. Overfill
the third layer to account for consolidation. Finish the top by striking off with the tamping
rod and troweling it smooth. Cover the top immediately to prevent evaporation.
5. Properly identify samples and clean-up work area, equipment and tools.
6. Arrange for proper curing of your specimens (moisture and temperature). Strip the
molds from the specimens after about a 24 – hour curing time. The samples then should be
submerged in water or stored under wet burlap covered with plastic for 7 days.
b. Compression Testing of Concrete Cylinders
1. Prior to compression testing, measure the diameter of the concrete cylinder using
calipers. Measure the cylinder at mid – height at four different locations around the
circumference of the cylinder.
2. Before testing the compression cylinders they must be capped on the ends to permit
uniform bearing when the load is applied. A cap is a small plane surface of suitable
material, such as gypsum plaster or hardened steel. Wipe clean the bearing faces of the
hardened steel bearing caps and of the test specimen. Insert the test specimen into the
bearing caps.
3. Place the test specimen with bearing caps in place on the table (platen)of the testing
machine directly under the spherically seated (upper) bearing block. Wipe clean the
bearing faces of the upper and lower bearing blocks. Seat the specimen in the testing
machine and close the protective doors.
4. Apply the load continuously and without shock, at a constant rate within the range of 20
to 50 psi per second. During the application of the first half of the estimated maximum
load, a higher rate of loading may be permitted. Do not make any adjustments in the
controls of the testing machine while the specimen is yielding rapidly (immediately before
failure). Increase the load until the specimen fails, and record the maximum load carried by
the specimen during the test. Note the type of failure and the appearance of the concrete
if the break appears to be abnormal. Standard failure modes are shown in Figure 1. MAKE
SURE THE PLATEN DOES NOT RISE ABOVE THE MAXIMUM HEIGHT MARKED ON THE
TESTING MACHINE.
G. Calculations:
1. Record data from all lab groups in your lab section. Develop a data table to record the
details and test results of each cylinder ,including :
Group #
Specimen #
Mix date
Test date
Mix design proportions by weight
Targeted compressive strength
Cylinder size
Slump
Workability
Ultimate load
Ultimate compressive strength, and
Type of fracture.
Data tables will be shared among all groups by posting to shared files on the Campus
Cruiser course web page.
2- The actual compressive strength is calculated as the failure load divided by the crosssectional area of the specimen. Report the strength to the nearest 10 psi.
3- Calculate the average compressive strength and range (difference between maximum
and minimum strengths) for cylinders from the same mix(i.e. by lab groups in your
section) and test date (i.e. same age at testing). Discuss the effect that age at testing has
on compressive strength.
4- Using the average 28 day strengths for the different mix designs, plot a curve showing
the compressive strength has a function of water/cement ratio, and discuss if your curve
follows the expected trend.
5- Did your mix designs produce the strengths you were expecting at 28 days? What are
some reasons why the actual average compressive strengths might not agree with the
targeted compressive strengths from the mix designs?
6- The targeted compressive strength is the strength that is expected to be produced on
average from a mix design. It is also known as the required average strength, fcr′ , but is
NOT the same as the specified strength, fc′ ,engineers use in structural design
calculations. The targeted strength must be larger than the specified structural design
strength, fc′ ; how much larger depends on the quantity of test results available. The
fewer the tests, the larger the amount by which fcr′ must be greater than fc′. For cases
where there are not enough strength tests to establish a standard deviation (i.e. when
there are less than 15 strength tests), the average compressive strength fcr′ must
exceed the design strength fc′ by
fcr′ ≥ fc′ + 1000 when fc′< 3000 psi fcr′ ≥ fc′ + 1200 when fc′ is between 3000 and 5000 psi fcr′ ≥ 1.10 fc′ + 700 when fc′ > 5000 psi
Based on the above, make recommendations for reasonable values for design strength
fc′ for which your concrete mix designs could be used.
CE 206 Lab Report Grading Guide:
Name:
Lab Report:
Date Submitted:
Date Reviewed:
OVERALL GRADING
1. 10% Performance and Preparation for the lab (including quizzes if appropriate)
a. You are expected to be familiar with the objectives and lab procedures prior to the lab and you
may be asked to write them prior to the start of the lab. Unannounced quizzes may be given
prior to the lab to assess your preparation.
2. 90% Technical Content and Technical Writing (approximately equally weighted for lab reports, focus
on technical content for Executive Summaries)
a. Technical Content
i. Tables
ii. Figures
iii. Calculations
iv. Context of the lab (do you understand and can you convey the technical aspects of the
lab)
b. Technical Writing
i. Correct format
ii. Information is in the correct section
iii. Sentence structure
iv. Clarity, etc…
In general, the following outline provides a summary of the information expected for each section of the
report.
CE 206 Lab Report Grading Guide:
Name:
Date Submitted:
Lab Report:
Date Reviewed:
I. Abstract
Does the abstract contain a clear statement of objectives?
Good
OK
Not clear or complete
Does the abstract contain a scope of work that describes the major tasks or activities completed in the lab to get data and
results?
Good
OK
Not clear or complete
Does the abstract contain a summary of results or major findings?
Good
OK Not clear or complete
II. Introduction
Does the introduction contain a background stating the importance of the lab to engineering practice?
Good
OK
Not clear or complete
Does the introduction contain a clear statement of objectives?
Good
OK
Not clear or complete
Does the introduction contain a scope of work that describes the major tasks or activities completed in the lab to get data
and results?
Good OK
Not clear or complete
III. Background
Does the background section contain all pertinent information needed for the reader to understand subsequent section of
the report?
Good OK
Not clear or complete
III. Methods and Procedures (M&P)
Does the M & P contain a description of the types of samples/structures that were tested?
Good
OK
Not clear or complete
Does the M&P contain a description of the procedures used to obtain the required data?
Good
OK
Not clear or complete
Does the M&P contain a discussion of the methods of analysis (calculations, etc) that describes how the data are used to
produce results?
Good
OK
Not clear or complete
IV. Results and Discussion
Are the data presented in a logical/complete order to allow independent confirmation of results (sufficient information is
provided to check the calculations)
Good
OK
Not clear or complete
Are tables or graphs of data and results properly presented?
Good
Are results properly presented and discussed to address objectives? Good
OK Not clear or complete
OK
Not clear or complete
Are there apparent or suspected errors in the results?
NO
Yes- minor
Yes – major
V. Conclusions
Is there a summary of objectives and major results?
Good
OK
Not clear or complete
Are conclusions or recommendations prese …
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