Naming Concrete Mix Designs

P35DDHGPOne question I am frequently asked is, “What is the best way to name my concrete mix designs?” The simple answer is “the way that works best for you.” Unfortunately most people don’t find that to be a satisfying response. I have my own ideas about the best way to name mix designs, but I decided to turn to the real experts – you. I crowdsourced the question (doesn’t that sound more modern than “put out a survey”) and got 62 responses back from people around the world. What you are about to read is a summary of the results, with some of my own commentary thrown in. I need to warn you in advance, this blog post is much longer than my usually post, but I didn’t want to split it into two posts, so here it is in all its glory.

I know that I am setting myself up as a target of complaints, scorn and ridicule by writing this article. Selecting how to name mix codes is probably one of the most contentious topics in the industry. Every company already has a naming convention and all of them think theirs is the best. I don’t expect companies with current naming conventions to change theirs. However, I do know that companies that are undergoing consolidation are frequently looking for better ways to name their mixes. This article is dedicated to them.

Before we start talking about “mix codes” I want to have a little vocabulary lesson. In technical terms there are two things that receive mix codes – a “mixture design” and “mixture proportions”. A mixture design is the criteria used to define the mix, such as 3000 psi, air entrained, 1” coarse aggregate with 20% fly ash. For you metric junkies out there (which consists of the vast majority of the world) an equivalent would be 25 MPa, air entrained, 25mm coarse aggregate with CEM II. “Mixture proportions” are the quantities of specific materials used to achieve the “mix design”. For concrete producers with multiple sources of materials, “mixture proportions” are often plant-specific, while “mixture designs” are usually generic descriptions used by the salesmen to sell a product. In the vocabulary of Command Alkon, my employer and the host of this blog, a “mixture design” is the same as a “concrete product”, while “mixture proportions” are what we at CA call a “mix design”. Confusing, huh? This is what you get when you let practical business people steeped in 100 years of concrete production culture win out over semantic-fanatics and grammarian-gurus at code and standard meetings. (I just wish there were a way to let practical people take charge in the U.S. Congress.) Anyway, for now I’m going to use the Command Alkon terminology of “concrete product” and “mix design” since the two terms sound totally different and hopefully won’t be confused with each other.

The “mix codes” we are going to discuss primarily relate to a “concrete product”. For the most part “mix designs” are plant specific and to name them we could just attach a plant number to the concrete product code. For example, concrete product code “R35FA1P” from plant #2 could be designated as “R35FA1P-02”. When it comes to batching the concrete, though, the concrete plant code is usually displayed elsewhere on the batch ticket and is usually implied on the mix code on the batch ticket. To try to avoid confusion from now on I am going to use the term “product code” as a substitute for “mix code” or “Mix ID”.

Defining Product Codes

I want to make one thing abundantly clear. There is no need to develop a single product code naming convention and force all concrete producers to use it. For one thing, such a naming convention would require a product code that was too long for most producers to use it in their batching systems. For another, some of the items we are going to discuss aren’t applicable to everyone. For example, in the U.S. we batch fly ash into our concrete separately from the cement. In Europe they typically use cement preblended with fly ash, ground granulated blast furnace slag or powdered limestone. As I understand it, they don’t add fly ash separately. (Correct me if I am wrong, Europeans.)

Concrete producers should take what they need from this document and modify it to fit their needs. All an individual producer needs to insure is that whatever (s)he ultimately decides upon needs to be suitable for all their product naming needs.

Product code survey

About a month ago I posted a survey on the web at https://www.surveymonkey.com/s/NW6W3HF. I am leaving the survey active for now in case anyone wants to add to the database. In all there were 62 responses. Almost 90% of the responses were from the U.S. and Canada, but I did get a few from Europe, Asia and South America. Responses were relatively uniformly distributed from small, medium and large producers, but the most responses came from producers in the 250,000 – 1,000,000 cubic yard/meter per year range. Those who contributed to the survey will be emailed a full copy of the survey analysis.

There are two types of product codes in use: 1) Codes that have no relationship to the concrete product in question. These are often sequentially numbered mixes and are often used by smaller producers. 2) Codes that are related to the composition or performance of the concrete. This second class of code is what we will be talking about in this article.

As part of the survey I asked people what the most common use of the different characters in the product code was. Keep in mind that most of the responses were from the U.S. and will have a heavy emphasis on prescriptive concrete mixes. The results were as follows:

Prescriptive product codes

  • Design strength
  • Air content
  • Cementitious content
  • % Pozzolan
  • Pozzolan type
  • Concrete class (normal, SCC, pervious, grout, paste
  • Maximum aggregate size

Performance concrete products

  • Design strength
  • Air content
  • % Pozzolan
  • Pozzolan type
  • Concrete class
  • Coarse aggregate type (crushed stone, gravel, crushed gravel, blended)
  • Maximum aggregate size

Hybrid prescriptive and performance

  • Design strength
  • Air content
  • % Pozzolan
  • Pozzolan type
  • Concrete class
  • Maximum aggregate size

Number of characters

One thing that will govern what can go into a product code is the number of characters that the producer’s batch or dispatch system can handle. The two primary Command Alkon products can handle 8 or 12 characters, respectively. Survey respondents reported the length of their product codes ranged from 3 characters to 18 characters. The most common responses were 8 (23 respondents), 10 (13 respondents) and 6 (10 respondents). For the examples in this survey I am going to assume we will create an 8 character product code. Ultimately we will be creating a product code that looks like this: R35FEA1P. What follows is my suggestion on how best to name concrete mixes.

Type of concrete products (Char. 1)

This part gets a little tricky, so I hope you can stay with me. There are several different types of concrete products. In the U.S. we typically talk about “prescriptive” concrete and “performance” concrete. Prescriptive concrete is where the project engineer includes requirements for the composition of the concrete, such as “550 minimum pounds of cementitious material”. Performance concrete is specified solely based on criteria that can be tested for, such as 3000 psi. It doesn’t matter hope much or how little cement is used, as long as the concrete can meet the 3000 psi performance criteria. In EN-206 the Eurcode divides products into “prescribed” concrete and “designed” concrete. Prescribed concrete is the same as the U.S. prescriptive concrete, except it usually contains all the mix design weights to be used in production. This approach is not very common in Europe. Designed concrete is the same as performance concrete. One major exception is that in Europe designed concrete mixes can be changed in order to accommodate materials’ variations as long as the performance requirements are met. In the U.S. performance concrete mixes are not typically allowed to change without the approval of the project Engineer.

The problem is that often we have concrete products that are a combination of prescriptive and performance, such as a 3500 psi mix design with a 0.45 maximum water cementitious ratio and a minimum of 550 pounds of cementitious material. Sometimes project requirements can be incompatible with each other. It is extremely difficult to design a concrete with a low modulus of elasticity and at the same time have a low water cementitious ratio.

Proposed product code option: Use the first character of the product code to designate the type of concrete mix, something like this:

  • P – Performance/designed mix design. Proportions of any material can be changed in order to maintain consistent performance
  • R – Prescriptive/prescribed mix design (the R stands for recipe). These exact proportions must always be used.
  • W – Performance mix design where the water cementitious ratio cannot exceed a prescribed value
  • B – Performance mix design where a specified number of “bags” or “sacks” of cementitious material must be used (this is a very common requirement for residential concrete in the U.S.)
  • M – Mortar or grout (no coarse aggregate)
  • Y – Slurry
  • V – Pervious
  • S – Self-consolidating concrete
  • L – Lightweight concrete
  • H – Heavyweight concrete
  • G – Government specified
  • X – Customer-submitted mix design (the same as a prescriptive mix

This code is very important in that it allows for rapid determination whether a mix design can be changed or not. For example, in COMMANDqc, our concrete QC software, a user can perform a mass update on all concrete mixes. If the concrete strengths start to rise, the user can reduce cementitious material by X%. Of course he wouldn’t want to do this for a mix design in categories R, S, G or X. For W mixes cementitious material could only be changed to the point where the maximum w/cm reached the specified maximum w/cm.

Does every concrete producer need to use this code? Of course not. A small producer in the U.S. might not ever use anything other than category R mixes, so why use this code?

Primary performance requirement (Chars. 2 & 3)

The next two characters in our code will designate the primary performance criteria. Typically this will be strength, but it could also be maximum w/cm or specified cementitious content. For example:

  • P35 – This would be a performance mix required to reach 3500 psi or 35MPa (I know the two aren’t equivalent, but most markets won’t cross Imperial and metric units so it doesn’t matter.)
  • W40 – Performance mix with a maximum w/cm of 0.40. Any mix design with a lower water cementitious ratio is acceptable.
  • S55 – Performance mix design containing a cementitious total of 5-1/2 sacks. (Traditionally we use a 94 pound sack of cement, but other countries used other values.)
  • X40 – Customer supplied mix design for 4000 psi, but the producer isn’t responsible for the strength, just batching the submitted mix design.

Binder composition (Char. 4)

The next character would be to designate the binder (or powder) composition and contain the type and quantity of supplementary cementitious material. In this case if the supplementary cementitious material is batched separately we can use a single alphanumeric character to designate both the material type and quantity as follows:

  • A – 10% fly ash
  • B – 15% fly ash
  • C – 20% fly ash
  • D – 25 % fly ash
  • E – 30% fly ash
  • F – 35% fly ash
  • G – 25% GGBFS (ground granulated blast furnace slag)
  • H – 30% ggbfs
  • I – 35% ggbfs
  • J – 40% ggbfs
  • K – 45% ggbfs
  • L – 50% ggbfs
  • M – 55% ggbfs
  • N – 60% ggbfs
  • O-R – combinations I have left out
  • S – 3% microsilica
  • T – 4% microsilica
  • U – 5% microsilica
  • V – 6% microsilica
  • W – 7% microsilica
  • X – 8% microsilica
  • Y – 9% microsilica
  • Z – special combination of cementitious materials

For blended cements used in EN-197 the values would be much simpler

  • 1 – CEM I
  • 2 – CEM II with limestone
  • 3 – CEM II with ggbfs
  • 4 – CEM II with fly ash
  • 5 – CEM III blast furnace cement
  • 6 – CEM IV pozzolanic cement

Maximum aggregate size (Char. 5)

An important designation for all concrete mix designs is the maximum aggregate size. For this example I have started at the smaller aggregates, since as aggregate size increases so does the variability of types of available material.

  • A – 3/8” (9.5 or 10mm) maximum aggregate size (MSA)
  • B – ½” (12.5 mm or 15mm) MSA
  • C – ¾” (19 or 20mm) MSA
  • D – 1” (25mm) MSA
  • E – 1-1/4” (30mm) MSA
  • F – 1-1/2” (37.5mm) MSA
  • G – 2” (50mm) MSA

Air content (Char. 6)

I am using alphanumeric characters for air content for two reasons: 1) sometimes an air content with a ½% is specified and 2) some air mixes are defined with a nominal air content and others with a maximum air content. This approach handles both situations.

Nominal air content (allows for equal plus and minus tolerance)

  • A – 0 to 2% entrapped air (both nominal and maximum air content – non-air entrained)
  • B – 3.0% air
  • C – 3.5% air
  • D – 4.0% air
  • E – 4.5% air
  • F – 5.0% air
  • G – 5.5% air
  • H – 6.0% air
  • I – 6.5% air
  • J – 7.0% air
  • K – 7.5% air
  • L – 8.0% air

Maximum air content (nothing allowed over this amount with a specified minus tolerance)

  • N – 3.0% air
  • O – 3.5% air
  • P – 4.0% air
  • Q – 4.5% air
  • R – 5.0% air
  • S – 5.5% air
  • T – 6.0% air
  • U – 6.5% air
  • V – 7.0% air
  • W – 7.5% air
  • X – 8.0% air

Slump or Workability (Char. 7) (These values also allow for nominal and maximum values.)

Nominal slump (allows for equal plus and minus tolerance)

  • A – 0 inch (0mm) (both nominal and maximum slump)
  • B – 1” slump (25mm)
  • C – 2” slump (50mm)
  • D – 3” slump (75mm)
  • E – 4” slump (100mm)
  • F – 4-1/2” slump (112mm)
  • G – 5” slump (125mm)
  • H – 5-1/2” slump (137mm)
  • I – 6” slump (150mm)
  • J – 6-1/2” slump (162mm)
  • K – 7” slump (175mm)
  • L – 8” – 9” slump (200 – 225 mm)

Maximum slump (nothing allowed over this amount with a specified minus tolerance)

  • M – 1” slump (25mm)
  • N – 2” slump (50mm)
  • O – 3” slump (75mm)
  • P – 4” slump (100mm)
  • Q – 4-1/2” slump (112mm)
  • R – 5” slump (125mm)
  • S – 5-1/2” slump (137mm)
  • T – 6” slump (150mm)
  • U – 6-1/2” slump (162mm)
  • V – 7” slump (175mm)
  • W – 8” – 9” slump (200 – 225 mm)

Slump Flow (self-consolidating concrete where the first character is “S”)

  • X – 22” – 24” (550 – 600 mm)
  • Y – 24” – 26” (600 – 650 mm)
  • Z – 26” -28” (650mm – 700mm)

Viewer’s choice (Char. 8)

The final character I am going to leave up to the individual concrete producer. There are several things that could go in here:

  • Type of aggregates (crushed stone, gravel, natural sand, manufactured sand)
  • Use of fibers, pigments or other additives
  • Weight category by weight range (i.e. 100-105 pcf, or 2000 kg/m^3)
  • Exposure class (this could be a biggie for Europe)
  • Mix family category (usually based on character 4)
  • Admixture type

The important thing is to designate what is important to the concrete being sold. For those with more than 8 characters available you can choose several items to report.

Summary

Here is the final tally of what should go into a concrete product code:

  • 1 – Type of Concrete
  • 2&3 – Primary Performance Criteria
  • 4 – Binder composition
  • 5 – Maximum Aggregate Size
  • 6 – Air content
  • 7 – Slump or Workability
  • 8 – Viewer’s choice (I tend to prefer most restrictive exposure class)

Using the example above we could create concrete product P35DDHGP to designate a performance concrete mix with a 3500 psi mix design, 25% fly ash in the binder, 1” maximum coarse aggregate, 6% air, a 5” slump and a severe exposure to sulfate (I just made that up for the P designation for exposure class).

I hope this article helps. If you have any comments, complaints or other observations, please feel free to post them.

Until next time.

Jay Shilstone
Concrete Technologist
Command Alkon, Inc.

About Jay Shilstone

I am a concrete technologist for Command Alkon, Inc. and have been in the concrete industry for over 35 years. For 28 of those years I have been working on quality control software for the concrete industry. I am a Fellow of the American Concrete Institute and a member of multiple ACI, ASTM and NRMCA committees. I look forward to talking about concrete mix design and quality control with everyone.

Roy Keck

Good information, Jay. Anyone can take this and decide how they want to set up their codes, using their own preferences. There is a typo in the slump section where you use the word air when you meant slump. (“maximum air” should read “maximum slump”) My advice would be to put aggregate size after strength since that is a key factor in daily batch plant operation. Thanks for your work in putting this together.

Randy James

Good Info, we had a similar numeric code with some letter that worked well. The more information the better, but some people that use the codes never catch on! The weak link theory?

Frank A Kozeliski

Jay, this does make a lot of sense. as a small producer that went to a computer this was the hardest item I faced. Then I got out. But the method you have is pretty simple. you just need to carry a cheat sheet to figure what you want and how to number it. thanks for the work.

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