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					PCC Mix Design
     (Lab 4)




   Ryan Bogan



November 29, 2010
                                  Introduction

       A six-lane bridge is being built over US 431 in Opelika, Alabama and a mix
design for the abutments is needed. The abutments need to have a 7-day
compressive strength at least 75% of the required 28-day compressive strength. For
design the slump and compressive strength of four different mix designs in which
the water-to-cement ratios varied were tested. Cements were also tested for the mix
design by determining the compressive strength of mortar cubes. A secondary
source of water might be required therefore compressive strength tests were also
run on mortar cubes using non-potable water to determine the effect of the
secondary water source on the strength. Based on the performance of the mix
designs and mortar cubes a recommendation was made.

                                      Scope

        Concrete Mixing (ASTM C172) was followed for proper mixing of the
concrete for making cylinders. Slump (ASTM C143) test was performed to measure
if the concrete was at a desired workability range. Making Concrete Cylinders
(ASTM C31) was followed in order to correctly make concrete cylinders for testing.
Compressive Strength of Concrete (ASTM C39) test was run to evaluate the average
compressive strengths for the test cylinders. Mortar Mixing (ASTM C305) is the
standard practice for mechanical mixing of hydraulic cement pastes and mortars of
plastic consistency. Compressive Strength of Mortar (ASTM C109) was run to assess
the average strength of the mortar used and the differences between strengths
when potable and non-potable water is used. Compressive Strength Requirement of
Mortar (ASTM C150) lists the required compressive strengths for types 1-5 and 3, 7,
and 14 day cures of mortar.

                                  Methodology

Preparing Mortar Cubes
ASTM C109M-02
ASTM C305-94
        The mix consisted of 250 grams cement, 687.5 grams sand, and 121
milliliters of water. Three mortar cubes with dimensions of 2x2x2 inches were
created using potable water and three using non-potable water. The molds were
lubricated to allow easier extraction. When the ingredients were mixed, first the
water was placed in the bowl and the cement added to it and mixed on slow for 30
seconds. Over the next 30 seconds the sand was slowly added while mixing on slow.
Then the mixer was turned up to medium and mixing continued for 30 seconds. The
mix was then let stand for 1.5 minutes then mixed at medium for another 1 minute.
The mix was then placed into the molds each in two lifts with each lift being tamped
32 times. The tops of the molds were then screened off and set in the curing room
for 24 hours. After 24 hours the molds were extracted and placed in a lime bath
until testing,
Preparing Test Cylinders
ASTM C31/C31M-03a
       Two test cylinders that were 12 inches in length with a 6-inch diameter were
made for each of the four water-to-cement ratios used. First the amounts of fine
aggregate, coarse aggregate, water and cement were measured out according to the
w/c ratio. These values are listed in Table 1.

Table 1: Raw Material Weights by W/C Ratio
W/C Limestone          Water (lb) Sand (lb)       Cement (lb)
       (lb)
0.40 60.43             12.48        44.16         31.48
0.45 60.43             12.48        47.11         27.98
0.50 60.43             12.48        49.47         25.19
0.55 60.43             12.48        51.40         22.90

Before the mixer was started the coarse aggregate and about half of the water was
added. The mixer was turned to slow until the coarse aggregate is damp then the
rest of the raw materials were added. Mixing continued for three minutes followed
by a three-minute rest and then a final two-minute mix. Next the slump test was
performed on the batch:

       ASTM C 143
       Standard Test Method for Slump of Hydraulic-Cement Concrete
               The cone was dampened and held in place. The mold was filled in 3
       layers tamping each layer 25 times. After cleaning off the excess around the
       mold the mold was raised completely off over 10 seconds. The slump was
       measured by determining the vertical distance from the top of the mold to
       the center of the concrete mixture.

After performing the slump test the cylinders were filled, in three layers, tamping
each layer 25 times and tapping the sides of the cylinder twice on each quarter. The
tamping rod was rolled across the cylinder to remove any excess concrete. The
cylinders were then capped immediately and after sitting out for 24 hours put into
the curing room.

ASTM C109M-02
Standard Test Method for Compressive Strength of Hydraulic Cement Mortars
       The mortar cubes were retrieved after a 14-day cure period and tested one at
a time in a loading frame. With each loading the machine was zeroed out and the top
compressive plate made flush with the mortar cube. A load was continuously
applied at a rate of 300 pounds per second until the specimen broke and the
maximum compressive strength recorded.
ASTM C39-10
Standard Test Method for Compressive Strength of Cylindrical Concrete
Specimens
        The concrete cylinders were tested after a 7-day cure time. The rough end of
the cylinders was ground flat before loading. Baby powder was placed in the bottom
end cap and the cylinder placed in it. The rough edge was on top. Baby powder was
sprinkled on the top end of the cylinder and the other end cap placed on the
cylinder. The specimen with caps was then placed into the loading frame centering
the top with the compressive bearing plate. A load was then applied at a rate of
1000 pounds per second until the specimen broke and the maximum compressive
strength and breakage type recorded.


                            Results and Discussion

Testing of Mortar Cubes
       Mortar cubes were made using both potable and non-potable water sources
and then tested after a 14-day cure period. The average tested compressive
strengths, standard deviations, and coefficients of variation for each water source of
mortar cube is tabulated in Table 2. The compressive strength requirement for Type
1 cement after a 14-day cure according to ASTM C150 is 4000 psi.

Table 2: Strengths of Mortar Cubes
 Potable        Strength (psi)
    P Average      4553.75
    P Std Dev      507.59
        P COV      11.15%
 Non-Potable
  NP Average       4602.92
   NP Std Dev      234.17
      NP COV        5.09%

According to ASTM C150 both the cubes made with potable and non-potable water
sources passed the required compressive strength requirement. The non-potable
water source yielded a higher compressive strength than that of the potable water
source, and the test results were also more consistent. The ASTM C109M spec for
COV is 3.8%, but both of the values exceeded this value. Improper tamping during
the filling of the molds could have caused this or the cube could have been cracked
when extracting, curing, or moving. The requirement for range of values is 10.7%
but again both the mortar cube types exceeded this with the potable being 26.6%
and the non-potable being 13.8%. This is expected for the same reason that the COV
exceeded the required value.
Batch Weights
        Table 3 below lists the calculated batch weights for each of the four water-to-
cement ratios tested. They were calculated using the given material properties listed
in table 4. The total weight of the mix increases when the water-to-cement ratio
decreases. All of the mixes met the minimum cement requirements.

Table 3: Calculated Batch Weights
                                     W/C Ratio
Component
(lb/yd3)               0.4       0.45          0.5      0.55
Coarse Aggregate     1640.02    1640.02      1640.02   1640.02
Fine Aggregate       1203.4     1283.63      1347.15   1399.8
Water                 317.7       317         316.4     315.9
Cement                 850       755.5         680      618.2
Total                4011.12    3996.15      3983.57   3973.92

Table 4: Material Properties for Aggregate
       Property Sand Limestone
        Gsb (dry) 2.652          2.622
           (pcf)      96           97
              FM     2.81             -
   Max Agg Size         -         3/4”
           %Abs       0.1           0.4
  Moist. Content     0.12        0.474
               %

Slumps
       The average slump for each water-to-cement ratio tested is listed in table 5.
The desired slump for this project is 3-4 inches which all of the tests exceeded. The
slump closest to the desired is the 0.5 W/C ratio, which only exceeded desired by
.125 inches. This being so close should allow 0.5 to have a suitable slump for the
project.

Table5: Slumps for given W/C Ratio
    W/C Slump (in)
     0.4        4.75
    0.45        5.25
     0.5      4.125
    0.55         4.5
Compressive Strength
       Table 6 shows the results for the compressive strength tests on the concrete
cylinders cured for 7 days. The last column also lists the break type, which was
determined visually for each test. Table 7 lists the required compressive strengths.
The required compressive strength after 7 days was 75% of the 28-day compressive
strength. From table 7 the required strength after 7 days is 3900 psi. The only test
that did not meet the 3900-psi requirement was the W/C ratio of 0.55. All of the
breaks were some part cone, which is normal.

Table6: Compressive Strengths and Break Types
                         Load
    W/C Specimen          (lbf) Strength (psi)       Break Type
     0.4          1 130830          4627                  Cone
     0.4          2 133290          4714           Cone & Shear
 Average                            4671
    0.45          1 122990          4350           Cone & Shear
    0.45          2 118350          4186            Cone & Split
 Average                            4268
     0.5          1 114800          4060                  Cone
     0.5          2 109210          3863            Cone & Split
 Average                            3961
    0.55          1 101980          3607            Cone & Split
    0.55          2 100350          3549            Cone & Split
 Average                            3578

Table 7: Required Compressive Strengths
            fc' = 4000 psi
           fcr' = 5200 psi
 fcr' @ 7 Days = 3900 psi


                    Conclusions and Recommendations
       From the tests run it is safe to say that use of the non-potable water source is
suitable for this project. It had a higher strength and less variability. It is also
recommended to use the test mix with a water-to-cement ratio of 0.5. This mix
proved to have a high enough 7-day compressive strength and the slump was the
most suitable in this mix. Also by using the 0.5 mix raw material costs will be cut
down since it is the second lightest weight mix, but it is also the lightest mix that
meets strength requirements.
                                 References

American Society for Testing and Materials, “ASTM C109M-02 & ASTM C305-94:
      Preparing Mortar Cubes,” ASTM, 2001.

American Society for Testing and Materials, “ASTM C31/C31M-03a: Preparing Test
      Cylinders,” ASTM, 2001.

American Society for Testing and Materials, “ASTM C 143: Standard Test Method
      for Slump of Hydraulic-Cement Concrete,” ASTM, 2001.

American Society for Testing and Materials, “ASTM C109M-02: Standard Test
      Method for Compressive Strength of Hydraulic Cement Mortars.” ASTM,
      2001.

American Society for Testing and Materials, “ASTM C39-10: Standard Test Method
      for Compressive Strength of Cylindrical Concrete Specimens,” ASTM,
      2001.

				
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