concrete memo series step 3 of 4.
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 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
- Long hair must be tied back so it doesnt 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.
Procedure for Mixing Concrete
Use the data sheet from
- Weigh out proportions for a 1.6 cubic foot batch of concrete.
- 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.
- Put about half the coarse aggregate and the 3/4 bucket of water with air entraining in
- Start the mixer.
- Add about half the fine aggregate.
- Carefully add all the cement with the mixer running. Try not to make a lot of
- Mix until all the cement is blended in.
- Add the rest of the coarse and fine aggregate.
- Mix for awhile.
- Add enough water from the final quarter of the water to produce a workable mix.
- 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.
- 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
Continue taking slump tests and adding water and cement until the desired slump is
- Record the final slump.
- Record the actual weight of water and cement used
- Perform an air meter test (Air content by pressure method (type B)
- Record the percent air. In addition, record the wet unit
weight of concrete.
- If using superplasticizer, add it to the mixer and mix for one minute.
Perform another slump test and record the value.
- Cast 3 cylinders and put the rest of the mix in the beam.
Perform tests and cast samples: (in any order)
Air content by pressure method (type B)
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.