Revised 2024, IA
Datasheet No. 7.3
MOHAWK COLLEGE OF APPLIED ARTS AND TECHNOLOGY
BUILDING AND CONSTRUCTION SCIENCES DEPARTMENT
Concrete Mix Design by Trial and Error
INTRODUCTION:
The purpose of this laboratory procedure is to proportion a concrete mix of specified
water/cement ratio and slump by a trial-and-error procedure. The student will also have an
opportunity to practice performing slump tests, fresh density tests and casting cylinders for
testing. This lab also demonstrates the concept of repeatability in measurements by requiring
two cylinders per batch be cast.
PROCEDURE:
1.
Each group will be assigned a water-cement ratio:
Group:
1
2
3
4
5
6
7
8
9
10
w/c:
0.40
0.43
0.45
0.47
0.50
0.53
0.55
0.57
0.60
0.63
SSD Mass
of Cement:
SSD Mass
of Water:
2.
In this procedure aggregates on the dry side of SSD will be used, since it is much easier to add
water to achieve the SSD state than it is to adjust the cement. Obtain about 12.500 kg of each
“air dried” aggregate and, after mixing separately, take a 500.0 g + 50.0 g moisture sample,
weigh to 0.1 g and dry over a flame. Calculate the moisture correction factors C c and Cf and the
equivalent SSD mass of the aggregate as outlined in Test Procedures and Formulae. If this is
done correctly, the % Moisture Correction for both the CA and FA should be “negative” values.
If it is not, re-check the calculation and check with the instructor.
3.
Prior to weighing of aggregates and mixing of concrete, moisture calculations and “As Is” batch
masses must be checked by instructor.
4.
Add sufficient water to both the coarse and fine aggregate to bring them to the SSD condition
and mix thoroughly (based on the moisture corrections, “Water to Add for SSD”). Weigh the
containers with the aggregate in them and record this weight (Initial SSD Agg. + Pail).
5.
Weigh out 4.500 kg of cement and enough water to yield the water-cement ratio assigned to
your group.
1
6.
After moistening the mixing pan and utensils, place the cement and water in the damp mixing pan
and mix thoroughly to a smooth paste.
7.
From the measured stock of SSD aggregate add CA and FA to achieve a slump of 70 ± 10 mm and
an acceptable ratio of CA to FA.
8.
Slump testing should be started while the mix is on the wet side so that the desired slump point
will not be passed. The optimum ratio of CA to FA is not sharply defined. In general, the
correct amount of sand to be used is that amount which will make enough mortar to fill the
spaces between the CA and leave some excess for workability. This condition can best be
detected by troweling. If a smooth, thin mortar surface can be obtained with three or four
trowel strokes, then proportions are approximately correct. The addition of CA will have a much
smaller effect on the slump than the addition of FA. It is better to keep the mix slightly oversanded as the required slump is approached.
9.
When the mix is satisfactory, weigh the amounts of the SSD CA and FA (in their containers)
remaining (Final SSD Agg. + Pail). Record the slump, perform a fresh density determination, and
cast two cylinders for testing during the next laboratory session.
CALCULATIONS:
1.
The batch proportions are calculated by subtracting the FA and CA left over from the starting
masses.
2.
By referring to the Test Procedures and Formulae calculate:
i) the fresh density,
ii) the proportions per m3 of the mix,
iii) the hardened density and
iv) the compressive strength.
Note: For the following lab session, Datasheet 7.3 should be completed except for the
Hardened Density and Compressive Strength sections.
There will be a “Class Data
Collection Sheet” in the lab where each group will be required to record their information.
After the lab session, the “Class Data” will be posted on MyCanvas to complete the lab
report.
REPORT:
1.
The report should include a title page, the completed Report Form, two graphs as described
below and the completed data sheet 7.3. The proportions per m3 of the mix should be reported.
The masses should be based on SSD aggregates and the water to cement ratio should be
calculated there from and be reported.
2
2.
The above values should be available during (brought to) the subsequent laboratory session, as
each group must record its results on the data collection sheet provided during the lab session in
which the cylinders are tested. The values entered will be evaluated as part of the mark for the
report. A summary of the class results in this same format will be posted on MyCanvas to enable
the performance of the required analysis in the report and the production of the following
graphs:
a)
compressive strength on the Y–axis and water-cement ratio on the X–axis.
b)
hardened density on the Y–axis and water-cement ratio on the X–axis.
Note: Use the Excel Template from Lab 3 posted in MyCanvas to produce the graph.
Note: Refer to Pages 11 to 15, Section 1.6 of the Policy and Procedures posted on MyCanvas
with regards to Laboratory Reports.
Note: Sample calculations not required!
REFERENCES: (Posted in MyCanvas)
MTO LABORATORY TESING MANUAL:
1.
2.
3.
4.
Test Method LS-400: Method of Test for Dry Rodded Density of Coarse Aggregate
Test Method LS-402: Method of Test for Slump of Portland Cement Concrete
Test Method LS-405: Method of Test for Density Yield and Cementing Materials Factor of Plastic
Concrete
Test Method LS-406: Method of Capping Moulded Concrete Cylinders with Sulphur Mortar
ASTM TEST PROCEDURES NOT AVAILABLE:
1.
2.
3.
4.
5.
6.
7.
8.
C31 / C31 M – 12
Standard Practice for Making and Curing Concrete Test Specimens in the Field
C39 / C39 M – 12a
Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens
C94 / C94 M – 13a
Standard Specification for Ready-Mixed Concrete1
C125 – 13a
Standard Terminology Relating to Concrete and Concrete Aggregates
C138 / C138 M – 13
Standard Test Method for Density (Unit Weight), Yield, and Air Content (Gravimetric) of Concrete 1
C143 / C143 M –12
Standard Test Method for Slump of Hydraulic-Cement Concrete1
C172 / C172 M – 10
Standard Practice for Sampling Freshly Mixed Concrete1
C192 / C192 M – 13
Standard Practice for Making and Curing Concrete Test Specimens in the Laboratory 1
3
9.
C617 / C617 M – 12
Standard Practice for Capping Cylindrical Concrete Specimens1
10. C1064 / C1064 M – 12
Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete1
11. Manual of Aggregate and Concrete Testing1
CSA TEST METHODS NOT AVAILABLE:
1. CSA A 23.2 2C
Making Concrete Mixes in the Laboratory
2. CSA A23.2 1C
Sampling Plastic Concrete
3. CSA A23.2 5C
Slump of Concrete
4. CSA A23.2 6C
Density Yield and Cement Factor of Plastic Concrete
5. CSA A23.2 9C
Compressive Strength of Cylindrical Concrete Specimens
4