Saurabh Khandelwal

SP dosages are calculated by the percentage of cemetatious materials used in mortar.

e.g. cementatious material in mortar is 300 kg then dosage will be (X) % of 300 kg.

I think you need to study carefully how the dosage is chosen. It is not simply as you stated. You may need to specify the volume of fibers per unit volume of concrete. There are several factors that control your choice. I advise you to see ACI 544.5R-10.

Rheology of FRC concrete depends on the many factors including shape of fibres, aspect ratio, volume of fibres the last two are termed in combined form as reinforced index. As such the exact amount of SP will depend on rheology of FRC concrete which at present is still evolving.

What specific sp are you considering?

Dear William Khulish

I am using Polycarboxylic acid based water reducing agent.

thanks

Liquid or powder?

William Kulish Liquid

I see, so we know that most of your liquid is water. Does the sds say how much? Many of them are over 70%. You must know this because we only care about the solids. All of the above suggestions are very correct.. particle packing.. gradations.. fiber type etc.

If you can tell me either the brand number or solid contents I may be able to at least give you a starting point. w/b ratio is adjusted also.. as you add your hrwr you need to withhold the water within it from your initial water. Is your sand anticular or round.. What's the largest particle... 500 microns?

As far dosing. I recommend always dosing based on a percentage of cementitious only. As others above have correctly mentioned there are many variables that influence how much to add. You need to be careful of the impact adding too much can do. Such as retarding etc.

Once you determine the solids content.. you can test/sample a dose between 1/3 Rd to a maximum of 1% by weight of your cementitious only. That's just the net solid weight and not the water weight.

William Kulish thanks for your answers. I purchased the admixture from a Korean company. The solid content is 50 % and according to the sds the amount should be 0.4-0.6% with to respect to cement. I am using standard sand CEN EN 196-1.

As you suggested I am trying a dosage from 0.3% to 0.5% of cement.

I did not feel any retardation with these dosage but there is an increase in bleeding with vibration/compaction. Is it normal with superplasticizer or still need to reduce the amount ?

I have also attached the datasheet from the company in case if you need more details.

Hi Saurabh,

The goal is to use these least amount of both water and hrwr as to create the slump you are seeking. When fiber is involved, in real world application, the flow has to be able to wrap around rebar and such. I would lower the hrwr to the minimum you need. Not knowing your exact mix design, and not being able to open your pdf, It is a process of elimination. I can only guess a w/b ratio of 25%. Hence I would try keeping your hrwr AR 0.4% and decreasing your water until you see no extra water clinging to the top of your outside edge of your mixing container.

Because you stated mortar, I am assuming your largest particle is less than 600 microns. In this case the fibers, in my opinion (and I must state that most here have much better qualifications than I),.. the fibres become aggregate in some ways being the largest. So aspect ratio, material, whether they absorb water or reject it all need to be considered. 544 will help but additionally I would begin making smaller samples.

Dr. William Kulish provided useful information, many thanks.

I'm not a doctor, but thank you.