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In the FirstClass Folder

Time to make the concrete!  Students make concrete according to the mix design.    In addition to slump and air content testing, three cylinders and a beam are cast for later testing.

Fresh Concrete in mixer

Safety Info

• Safety glasses are required at all times while equipment is turned on.   Not only are safety glasses a good precaution, they prepare students for industry where they are also required.
• If you are allergic to dusts, cement or any other materials encountered in labs, please see an instructor to make alternative arrangements.
• Cement paste is also a skin irritant - rinse hands after handling cement paste and concrete.
• Long hair must be tied back so it doesn’t get caught in moving equipment.   Avoid wearing jewelry that may also become tangled in equipment.
• You will be working with heavy equipment in this lab. Wear boots and old clothes. No open toed shoes will be allowed in this lab.

• Concrete mixer
• Slump cone
• Air content by pressure method (type B)
• Air content by volumetric method
• Various small tools

Procedure for Mixing Concrete

Use the data sheet from the mix design lab.

1. Weigh out proportions for a 2 cubic foot batch of concrete.
2. Divide your water into two buckets, one with about 3/4 of the water.  Put the air entraining agent in the 3/4 water bucket.
3. Put about half the coarse aggregate and the 3/4 bucket of water with air entraining in the mixer.
4. Start the mixer.
5. Add about half the fine aggregate.
6. Carefully add all the cement with the mixer running.  Try not to make a lot of dust!
7. Mix until all the cement is blended in.
8. Add the rest of the coarse and fine aggregate.
9. Mix for awhile.
10. Add enough water from the final quarter of the water to produce a workable mix.
11. Mix for three minutes, followed by a three minute rest, followed by a two minute final mixing. Cover the mixer opening with a damp towel while not running.
12. Perform a slump test using the procedure given below. If results are satisfactory, skip to the next step.

    * If the slump is less than required, return the concrete to the mixer, add the remaining water, and mix for one minute.

    Perform a second slump test. If results are satisfactory, go on.

    * If the slump is still less than required, return the concrete to the mixer, add additional water, as well as additional portland cement to maintain the desired water/cement ratio (Wt. of PC added = Wt. of water added/WC ratio), and mix for one minute.

    Continue taking slump tests and adding water and cement until the desired slump is obtained.

13. Record the final slump.
14. Record the actual weight of water and cement used
15. Perform an air meter test (Air content by pressure method (type B) or Air content by volumetric method).
16. Record the percent air. In addition, for the pressure method only, record the wet unit weight of concrete.
17. If using superplasticizer, add it to the mixer and mix for one minute.
    Perform another slump test and record the value.
18. Perform the other air meter test, whichever one you have not done yet.
19. Cast 3 cylinders and put the rest of the mix in the beam.

Perform tests and cast samples: (in any order)

Slump test

Air content by pressure method (type B)

Air content by volumetric method

Cast Cylinders

Cast a beam

Sometime TOMORROW (between 20 and 48 hours) the cylinders have to be stripped, relabeled and put in the wet room with the beam.