Questions regarding Concrete Mix Designs 1

[rahseanj]

I have several questions regarding a Concrete Batch plant inspection, Mix Design review, and Types of concrete mixes.

Questions:

1. What are some of the things I should look for when inspecting a Batch Plant?

2. What are some things I should be concerned about when reviewing a mix design besides water cement ratios (and what range should this ratio be in)?

3. I read in a book that a High-range water reducer is the same thing as a superplasticizer. I always thought plasticizers increased the amount of water in a mix to increase flow. Please clarify?

4. what is the purpose of flyash?

5. Please explain the purpose these concrete types? and what category do plasticizers fall in?

Type A - water-reducing
Type F - high-range water-reducing
Type G - high-range water-reducing and set-retarding

 

[SCPqclabtech]

Hmm.. well to start, you sound pretty new to the industry, so I'll help you out. I was a batch plant operator in Florida for a year at a DOT, ACI, PCI, and CMEC approved facility. If you are inspecting a concrete batchplant, the W/C ratio relates to the desired strength of the concrete, with class V and VI concrete having 6500psi and 8500psi, respectively. They required no higher than .35 and .32 W/C ratios. Consider all cementicious material(flyash, slag, silica fume or slurry) for W/C ratio. When Inspectng a batchplant, verify that all materials originate from the labeled source, check records for inventory receipts, and keep an eye out for anything funny. Check for recent scale calibrations, a treated water source, and depending on state, BP operator certification. Make sure that batch weights are batched within tolerances, often not varying more than 1-3%. Material reciepts in records for items not on an approved mix design can indicate something fishy. A high range water reducer is the same as a superplasticizer, both dramatically reducing the amount of water needed for a high slump, but this comes at a price. The lack of free water can accelerate set times, so a retarder is usually used in conjunction. Flyash is often called a filler, but has cementicious properties. Its fine particles act somewhat as a densifier, reducing permeability on a coulomb test and reducing costs as well(it's cheaper than cement). As far as plasticizers are concerned, look at the manufacturer's labeling on tanks or dispensers, they are often clearly marked as one class or the other, for there are all three types of plasticizers(and sometimes there is more than one type on the same product, like cement can be). You may want to review a few working mix designs from that plant before inspection, just to give you a heads up. Understanding Specific Gravity for items is crucial for uderstanding yield(both theoretical and actual).

I like to talk concrete, as you can see, and I'm ACI field and lab tech certified, as well as PCI level I and II, and various Florida DOT certs(including batch plant operator).

 

[rahseanj]

Thanks for the help.

 

[mporisky]

sounds like hes still got velvet on his horns... young green horn

 

[mporisky]

Actually... some of the questions on here blow... like what is the purpose of fly ash... why dont other eng. know this... i wouldnt even respond to these... just tell them to pick up a book

 

[oneintheeye]

very helpful mporisky

 

[DarthSoilsGuy]

Item 2:

the mix design comes with concrete breaks from all the trial batching. it sounds like you are talking about the batching information that comes on the bottom of the truck ticket? you can compare the batch weights to the submitted mix design if that is what your talking about.

SCP talks refences finding something "fishy". i'll give you an example of something fishy.

Technician performs tests:
Air Content
Fresh Unit Weight
has Batch Tickets (add in the on-site water)

theoretical unit weight can be calculated from the batch ticket weights, the air content, and volume (yards^3 on truck ticket). If theoretical unit weight is consistently close to the Fresh Unit Weight test, then testing, weighing, and actual yards delivered (what they are getting paid $$$$ for!!!) to site should be pretty good.

i didn't start it, but i want to play the guess how rookie game. you are:

1: EI* at a structural firm and you're being shown the ropes by taking care of some annoying trivial Special Inspections duties that one of your bosses is the Structural Engineer of Record.

2: EI* working at a testing company and you have to do the weird services nobody else wants to do for a Special Inspections project to justify sending and billing the field tech.

*may substitute EI for an industry switching PE as an alternate.

i was #2. Play the "new guy card" at the plant visit so you can ask lots of questions. it's not like you're going to find something to bust them on, right

 

[dochardnose]

I have several questions regarding a Concrete Batch plant inspection, Mix Design review, and Types of concrete mixes.

Questions:

1. What are some of the things I should look for when inspecting a Batch Plant?
A. See Ready Mix Concrete Association and PCA manuals.

2. What are some things I should be concerned about when reviewing a mix design besides water cement ratios (and what range should this ratio be in)?
A. Water to cement ratios are rarely applied correctly. The ratio is by weight. water to cement. There is no one answer what the ratio should be, for slabs on ground ACI recommends .47-.53. For high strength high perfomance concrete it might be as low as .40. ACI 212 can help with these questions. Keep in mind that concrete with ratios below about .40 will usually require additional water curing and the addition of High Range Water Reducers.

3. I read in a book that a High-range water reducer is the same thing as a superplasticizer. I always thought plasticizers increased the amount of water in a mix to increase flow. Please clarify?
A. Same products, but the terms imply different application. HRWR are used to reduce the total water content. Reference to superplasticizer is relates increasing the slump of a mix without increasing the water content. Thus, a mix with a water slump of 3" can be placed at a chemical (HRWR) slump of 7" or more.

4. what is the purpose of flyash?
A. Flyash is the term used for pozzolanic materials based on coal combustion waste ash. It is a mineral admixture/supplementary cementitious material. Two types or classes are recognised in the U.S. Class F and Class C. Predominent use is to reduce the cost of concrete by substituting for cement. Proper use is to reduce heat of hydration, slow set times and use "green" material.. Class F ash will also aid in reducing suseptability to Alkali Aggregate Reactivity.

5. Please explain the purpose these concrete types? and what category do plasticizers fall in?

Type A - water-reducing
Type F - high-range water-reducing
Type G - high-range water-reducing and set-retarding
A. These are not concrete types they are admixture types as classified by ASTM C 494. Type A is a "normal" water reducer, expected to permit the reduction of water up to about 7%. F is "normal" set HRWR and Type G is a set retarding HRWR. See ASTM C494.