Mixing the stabiliser with graders 1

[defg]

Dear Sir/Madam
Due to delay to mobilise the pavement equipment on site,the Contractor has requested to temporarly to use graders to mix the approved subbase materials with cement by using graders.As since the approved subbase materials are noncohesive,Shall I allow the Contractor to proceed with the work while awaiting for his stabilizing machine?Or it shall have a big detrimental effect upon the work?

 

[Zambo]

Of course there will be several factors to consider - everyone from client to contractor has deadlines to meet.

You should try to get a few replies rather than just consider mine, but I would think that you would have more success mixing with a payloader (loading shovel) and then placing and grading to level with the graders.

It would also be a good idea to recommend an increase in cement content to compensate for any uneveness of the mixing.

BTW what type of equipment are they supplying a pugmill or a rotovator? They may be able to find a pugmill locally - where are you?

 

[civilperson]

Blending by grader by rolling a berm back and forth is a normal method of mixing. Four passes seems to be sufficient. Split out a sample at random locations and check the gradation and % cement to prove this method.

 

[Zambo]

civilperson,

how do you mix CSM with a grader? From your post I assume you tip from a truck and then form the heaps into a berm with the grader. Then do you spread the cement onto the berm at the required application rate? After that I can't follow what the 4 passes are. I guess you spread the berm out and then reform it into a berm. Is this correct.

I have previously used a payloader because it can lift as well as push the material.

How do you check the % cement? Is this just by sieving and finding the % of fines?

A trial section could be carried out and core tests made along with the density tests.

 

[civilperson]

Grade the native material into a berm equal in volume to the amount required. Drive the cement truck along the berm and deposit cement on top of the berm (sufficient to make the correct % by dry weight). Use grader to roll berm across the subgrade and then shape into triangular berm, (this is one pass), repeat the process to the other side of subgrade and shape into triangular berm, (this is second pass), repeat as necessary for a consistent mix, (by calibrated eyeball judgement). Then grade to limits plus 5% and compact with roller or sheepsfoot. Fine grade to blue top and keep watered for seven days or until strength requirement is obtained. Alternatives to watering are heavy tack coat of emulsified SS-1 or immediate asphalt paving.

 

[Ron]

Absolutely not! It's difficult enough to get good cement distribution when you do it right. The only way the grader method works is to get the cement content so high it doesn't matter much about distribution.

 

[Zambo]

defg,

please give some more info about the job. There may be some assistance than can be offered if we know a few more facts. For example:

1. what is the project, is it a road or yard?
2. where is the material to be stabilised sourced from?
3. is mix in place with rotovator of pre-mixed using a pugmill proposed.
4. what is the specification for strength and density testing?

 

[defg]

Thanks to ALL
The project is a road of 42km found in central part of Tanzania which is going to be upgraded to bituminous standard.The pavement materials are stabilised subbase,crushed stones(CRR)and double surface dressing.
The source of the material to be stabilised are from approved borrowpits
The specification specify that,the mix shall be done by gader,disc harrow,rotary mixer or equivalent plant approved by the Engineer.
The specification for strength and density testng is minimum UCS(1mPa),nominally 97% of MDD BS- heavy compaction

 

[Zambo]

defg,

I don't have any good suggestion. Your spec is interesting "mix shall be done by grader, harrow, rotary mixer or...."

The compressive strength of 1MPa seems low.

Adding additional cement and the frequency of tests carried out may be an option.

 

[LCruiser]

We don't allow mixing by grader - it is too unpredictable. However, if it's still in your specs for that project you should allow it. I'd take it out from now on.