Mortar Workability Competition Questions

Questions from the Mortar Workability Webinar 2024:

Q: You said 60% by mass or volume for admixtures?

A: 60% of the mass of the liquid admixtures is considered water.

Q: Where can we find the template for the cost Excel?

A: Cost and GWP are included in the mixture design Excel sheet, available on the Mortar Workability webpage.

Q: How much time are we going to have for the mixture?

A: Weighing of solid materials (pre-bagged at correct weight) and determining sand moisture condition will be done by the judges. This does not count toward any time. Preparing water and admixtures needs to be done within 5 minutes. Within 10 minutes of inserting a material in the mixer or turning the mixer on, the team needs to deliver the mortar to the judges. The 10 min. can start after the preparation of water and admixtures.

Q: If we are using two types of aggregate, we should take them to the competition in separately weighed bags?

A: Yes. Make sure none of them are above SSD.

Q: Can natural clay be used as a material?

A: Yes. Although dependent on the particle size, it will most likely be considered a mineral filler. If the clay is not calcined, cost and GWP are not included in Appendix C of the rules, so the team will be responsible for including cost and GWP for the clay and cost and GWP for cement found in the same area. Just watch out if you use nano-clay, as that will be considered a nano-material (safety!!).

Q: Would we get disqualified if our aggregate is dry, even if we don't add additional water?

A: You cannot be directly disqualified for using dry aggregates (in fact, it is a safe approach). However, make sure that the mass % of the used sand is still at least 60% of the total mortar mass, and that the volume of material remains within the requirements.

Q: Can the sand passed through a certain sieve be used complying with ASTM C33?

A: As long as the (combined) aggregate gradation meets all requirements from ASTM C33 (and 100% passes the #4 sieve), you are allowed to use this sand. Watch out for requirements on each sieve (including #200 requirements in ASTM C33 — most strict requirement applies), as well as differences between the amount of material passing between successive sieves.

Q: Most of natural sands that can be accessed in our country sometimes are not provided with information of the material source specifically since we got it from local material store, is it allowed to be used in the competition since we have to include it in the Excel file of the mortar design?

A: Try to give us as much information as you can find. For cement, SCMs, admixtures, judges want to be able to classify the material themselves. For sand, if it is a product that is normally used, if the exact source is not known, there is no issue. For example, the sand we use in our institute is “Missouri River Sand.” We don’t know where it is dredged in the Missouri River, and that is no problem to compete.

Q: I am seeking clarification regarding the Mortar Workability Competition rules, specifically section A.10 ii, which mentions that alternative unit costs can be accepted with appropriate references. Could you please confirm if this flexibility also extends to the unit Global Warming Potential (GWP) of materials?

A: Alternative unit cost (and GWP) can be accepted with the following information:

  1. Provide unit cost and GWP for the material used (with justification).
  2. Provide unit cost and GWP for a portland cement used in the region (with justification).

We will calculate a new unit cost and GWP based on the information provided.

However, this only applies to materials that cannot be classified in the existing material categories listed in the Appendix. If the material is listed there, the values for cost and GWP will be retained. The judges will look into this and adjust cost and GWP if necessary.

Q: I am unable to locate the DWG file for the ACI mold:

A: A drawing of the mold is available in Appendix B in the Mortar Workability Rules.

Q: Considering the significance of the mining industry in Chile, a major global copper exporter, we are interested in proposing a sustainable mortar that uses mine tailings as a substitute for cement. Mine tailings, as we understand, are a byproduct or waste from copper production. However, upon reviewing the competition guidelines, we did not find specifications regarding the feasibility of using this material. We would like to inquire whether it would be possible to incorporate chemically treated floated mine tailings into our mixture. If so, what aspects should we consider, such as whether the material cost is considered zero due to its waste nature?

A: Mine tailings would indeed be a material that is not included in the list, so additional information would be requested. However, their classification will depend on their size. If they are smaller than the #200 sieve, they will be considered as a mineral filler. If they are larger than the #200 sieve, they will be considered as part of the sand. If they are considered as sand, please see the answer on the % retained on the #200 sieve question. Concerning cost and CO2 emissions, making them equal to zero would be a little too optimistic. The value will depend on processing required. Fly ash is also a waste product and still incurs cost (although higher than the mine tailings) and CO2 emissions. Although we require you to list cost and CO2 emissions of the product and a Type I Portland cement in the area, we understand that this may not be possible. In this case, try to document as much as possible the process from raw materials to use in concrete in an Appendix in the report (it does not count towards the length limit), so the judges can make an estimate, which will not be open to appeal.

Q: In our mixture, we are using rounded aggregate, and a question arises regarding the classification of sand retained on the #200 sieve. Should we consider it as filler, or conversely, is the sand passing through the #200 sieve the one considered filler? Furthermore, if it is considered a filler, would it be categorized as supplementary cementitious material and therefore be included within the allowable 50% replacement? If not, should it be considered part of the aggregate?

A: Rules section 2.h states that any fine aggregate passing the #200 sieve will be counted as part of the aggregate. Please do note that the combined aggregates need to comply with the gradation requirements from ASTM C33, which includes a requirement on the #200 sieve. If you feel you have too many fines, you can manually sieve them off from the aggregates, bag them separately and label them as a mineral filler. In that case, they will be considered as a part of the powder.

Q: Concerning the saturated surface dry (SSD) condition of aggregates, should the water percentage it contains be considered part of the water/cement (w/c) ratio, or is only the free water added to the mixture taken into account?

A: Your mixture design reported in the Excel spreadsheet should be in SSD conditions (rule 2.h). The w/c ratio is calculated based on the aggregates being in SSD conditions. We will evaluate the moisture condition of the sand through ASTM C128, but we will not correct for the lack of moisture compared to SSD (rule 2.i). The water calculated comes from the added water, water in the admixtures, and water in the nanomaterials, if applicable. The SSD is a go/no-go test during competition (with disqualification if the sand is still standing in a pile after consolidating). Warning: If you design at exactly 60% sand quantity, with the sand in SSD, and the sand is drier at competition (no longer in SSD), you may be disqualified due to insufficient sand content.

Q: Finally, we would like confirmation on whether there would be any issue in using quartz powder as a fine aggregate, sourced from the same quarry as our rounded aggregate.

A: There is no issue with using quartz powder as a source of fine aggregate, as long as the requirements from ASTM C33 are met with the combined grain size distribution.

Q: We are writing due to uncertainties on how to properly define the concept of segregation and what exactly should be interpreted as the occurrence of this phenomenon for the ACI Mortar Workability Competition. The other topic that brings us questions refers to alternative (noncanonical) ingredients.

As is known, segregation is not a very strictly specified term, and there are many factors that have an impact on it, taking very different forms. It is vastly important for us to have a solid starting point in a stability test score estimation; hence, we would be more than pleased if you could provide any further explanation or examples, especially focusing on the following questions:

How is visible, separated water, shown in the picture, being considered?

A: Based on what is shown, without a clear visual of the sample, it would be placed at 236 or 238 mL. The purpose of the sedimentation test is to evaluate bleeding and segregation. It seems the shown sample is showing segregation.

During the competition, judges will have clear instructions on what to evaluate, they will ask for clarification from the head judge if needed, and pictures of the samples will be evaluated afterward by other members of the competition committee.

Q: How is a liquid cementitious base being considered?

A: The lowest line that can be interpreted as a separation.

Q: Should segregation be tested as a separation of water/relatively colorless liquid or, after 30 minutes, a pouring out of liquids/liquid cementitious/cement wash?

A: The sedimentation test is a visual assessment of the lowest line that can be interpreted as a separation. This does not necessarily need to be a clear water versus paste separation. There will be no removal of parts of the sample.

If the team has a suggestion to modify any test methods for upcoming competitions, they can be proposed to the ACI Mortar Workability Competition Committee (ACI Subcommittee 238-A, Student Workability), meeting on Tuesday, March 26, from 10:00 – 11:30 am.

Q: What makes a reading of a solid-liquid separation line in the cylinder reliable—what is being focused on during the procedure?

A: The lowest line that can be interpreted as a separation. As mentioned before, a group of judges and committee members will evaluate all pictures afterward and reassess scores if needed. This is how we can make the assessment as reliable as possible.

Q: We desire information about other (noncanonical) ingredients and fillers:

What rules should we follow when adding alternative ingredients, for example, multivitamin juice, and how should we calculate Global Warming Potential (GWP) in this case?

A: Refer to Rule 4(f)(iv) on alternative materials and what is required.

Q: What documents shall we provide for alternative/other materials whose GWP cannot be easily defined? What should we reference?

A: When teams choose to use alternative materials, they are responsible for finding the appropriate documentation. The judges will revise and adjust if necessary.

Q: Are fillers, such as polystyrene granulate and foam glass, being considered as aggregates?

A: They are considered aggregates for the mixture design requirements if they pass the No. 200 sieve and if the combined grain-size distribution of all aggregates still meets the requirements of ASTM C33. However, for cost and GWP calculations, they are considered as alternative materials; therefore, Rule 4(f)(iv) needs to be considered. It should also be kept in mind that in the case of lightweight materials, if there is floating of lightweight particles, this will be assessed in the sedimentation test.

Q: Rule 2(i) in the rulebook states that the aggregate needs to be delivered below saturated surface-dry (SSD) condition at the moment of the competition. Are we able to deliver bone-dry aggregate that is below SSD?

A: Yes, you are allowed to bring oven-dry (or bone-dry) aggregates. The aggregates will be visually inspected by a judge, and if necessary, the assessment procedure for SSD from ASTM C128 will be used. Bone-dry aggregates should be fine.

Just take into consideration that the mixture design sheet available online requires entering the aggregates in SSD conditions. If the team decides to design right at 60% sand content with the SSD aggregates and bring oven-dry aggregates to competition, they may no longer meet the 60% requirement as some mass may no longer be there due to water loss. The masses of all materials will be determined on site.

Q: I have a question regarding the submission of the written report for the ACI Competition. Seeing that it is due at the end of this month, am I correct in concluding that we can’t make any adjustments to our mix design in the weeks leading up to the competition? (After submission of the report.)

A: Correct, that is not permitted as February 29 is the final deadline.

Q: Can the mixing procedures be different from what is written in the report? For example, in the report, we stated that we will mix the sand and cement separately in the mixing bowl. But in the competition, we mix them first in a container, then into the mixing bowl.

A: While we would prefer you adhere as much as possible to your mixing procedure in the report, we know that changes can happen due to the adjusted dosage of the chemical admixture. We do not task the judges with comparing your procedure during competition to what is written in the report.

Q: Is a funnel required when pouring the mixture into the ACI mold? From our own experiment, we found that the mortar would clogged the funnel.

A: The flow test will be performed by the judges, and they will utilize the funnel. The purpose of the funnel is that it contains all materials prior to opening the bottom.

Q: If the usage funnel is required, are we allowed to poke the funnel with a small stick (for example a chopstick) if it is clogged with mortar? We understand that only gravity should be used to help the mixture fill the ACI mold, but we think that the poking doesn't count as extra forces since we only poke the funnel and not the mold.

A: The flow test is performed by the judges and they will not poke the funnel to undo a clogging. If the material clogs in the funnel, it does not fully reflect the objectives of the competition.

Q: Is the mixing procedures stated in the report and on the competition will be scored? If yes, are there any preferable mixing procedures? For example, the method stated in ASTM to make a mortar.

A:The scores for the competition are based on the results of the flow test, the sedimentation test, the GWP and cost per m3, and for the overall category, the report as well. There will be no separate scoring for selecting a mixing procedure during competition. The description of the procedure in the report will be scored as part of the report judging.

Q: In our mix design, we have encountered the presence of aggregate passing through the #200 sieve. We are uncertain whether this material should be considered as part of the sand by weight or if it should be treated as mineral filler.

A: Rules section 2.h states that any fine aggregate passing the #200 sieve will be counted as part of the aggregate. Please do note that the combined aggregates need to comply with the gradation requirements from ASTM C33, which includes a requirement on the #200 sieve. If you feel you have too many fines, you can manually sieve them off from the aggregates, bag them separately and label them as a mineral filler. In that case, they will be considered as a part of the powder.

Q: For the Mix Design excel sheet, we are designing for 1000L, (or 1,000,000 mL), so do we simply scale all of our percentages used for our mix design (650 mL +/- 100 mL) up to 1000 mL +/- 100 mL then multiply them by 1000 for the excel sheet?

A: Yes, you can simply scale up every individual volume to get to 1 m3.

Q: Also, are we expected to calculate our own specific gravities for each component or can we use the given value from the manufacturer or a number within the range of common values (I.e., Cement = 3.15)

A: The assessment of specific gravities is a task that will impact the risk the team wants to take to be compliant with the rules, especially the volume requirements. Ideally, teams determine the specific gravity of their constituents. Taking the numbers from the manufacturer can induce some more variation, but should be a good indication of specific gravity. If the team desires to use a common value, there is a larger chance for error, which could throw off volume. Remember, during competition, we measure the total mass of mortar mixed, and we determine the density of the material as well, so we can precisely calculate volume.

Q: In the 3rd sheets of the official mix and design cost, the fifth sections point 1 describe that the total volume (yield) has to be in the range of 1000 +- 10 liters. But in the Rules 4a. it is stated that the materials shall provide 650 +- mL. We are confused by this. We would be pleased if you could explain our confusion.

A: The sheet asks you to give the full mix design for 1000 liters, as cost and GWP are calculated based on a volume of 1 m3. Once you have the full mix design, you can simply downscale to 650 mL.

Q: Since the fine aggregate has been designed in SSD conditions, but we plan to deliver it oven-dry, are we allowed to make adjustments, such as increasing the amount of sand or adjusting the water content we bring to compensate for the absorption that the aggregate may experience while mixing?

For example, if we design for 1390kg/m^3 (SSD) but are bringing oven dry, can we use the correction factor of:

Mass Batched = Mass(SSD) x (1+MC)/1+ABS) = 1428.5kg/m^3 Sand

W(Corrected) = Mass(SSD) x (ABS-MC)/(1+ABS) = +38.5kg/m^3 Water

A: No adjustments are allowed. If you design for 1390 kg/m3 of sand in SSD condition, you should bring that amount of sand. We are aware that the mass can decrease as the materials are drying. We will not disqualify or deduct points directly if the mass of sand is (slightly) different due to drying (but see a little further below!). However, and this is important, you should not correct for the amount of water, because we don’t know the exact moisture content of the sand. So, in the question, the 38.5 kg/m3 of water cannot be added. If the team would decide to do so, the total amount of water added to the mixture will count towards w/p.

However, there is 1 important consequence: if the team designs for the 1390 kg/m3 of sand, and that is exactly (or very slightly above) 60% sand in the mixture, the drying of the sand will decrease the mass. In your example, it should be 1352.5 kg/m3, which could bring the total sand mass below 60% of the mixture. If this happens during competition, the team will be disqualified. Insufficient sand in the mixture during competition was the main reason teams were disqualified in the Spring of 2019. The rules will be strictly enforced.

Q: We can however design for x amount of SSD sand and then bring that same weight of sand in oven dry sand, correct?

A: Yes, they bring the amount of sand they design for. They can bring it in any moisture condition, as long as it is not above SSD. Oven dry is fine, but it does not have to be.

Q: Currently, we are contemplating a 3% entrapped air and 0% entrained air, as we are not using any air-entraining agent. However, we are not sure if the 3% entrapped air for the mix design is correct or if we should adhere to a different standard value. Additionally, we are unsure about how to input these values into the online mixture design sheet, as it only mentions "design air content" without specifying whether it refers to entrapped air or entrained air.

A: We cannot advocate whether certain values are correct or whether other values should be chosen. We are aware that air is a tricky component, and that air contents can turn out different during competition. The mix design sheet does not distinguish between entrained and entrapped air, so please put your estimated (or measured) value in that specific design air content cell.

Q: If we are utilizing 2 different admixtures, are we allowed to introduce them into the mixer at different times? For example, if we are using an air entrainer and a water reducer, are we allowed to add the air entrainer into our mixing water, and then add our water reducer at a later stage?

A: Yes, you are allowed to introduce your admixtures at different times, split admixture additions, etc. There is no problem with that. As long as you report every addition to the judges and you finish the mixing process within 10 min.

Q: Will we be allowed to turn off the mixer once the mixing process has begun and scrape the sides of the bowl for any material that may be located there, to reintroduce it to the mixture?

A: Yes, that is allowed, but please bring your own tools, as we do not have any. If you want to scrape the sides of the bowl, the mixer HAS TO BE turned off.

Q: We are a team from Mexico, and since the materials we are using are from local companies, we wanted to ask if there is any problem if we submit our cement's mill certificate and technical data sheets in Spanish?

A: Feel free to submit your documents in Spanish if no English version is available.

Q: We are writing to clarify if in case of alternative materials direct data from manufacturer is required or will scientific papers, if shown credible, be taken as reliable.

A: For cost, direct data from the manufacturer is required. For CO2, we understand this can be a little more difficult. If information from the manufacturer is available, that will be preferred. If not, we can take the scientific papers, but know the judges may adjust your values.

Q: Are we allowed to use silica fume in a liquid form? Or does it has to be in its powder form?

A: Silica fume needs to be delivered in powder form. Please bring the appropriate PPE to protect your team members.

Q: We did our mixture design for 1m3 in SSD condition. However, for our actual 650mL of mixture, we performed moisture correction, due to the actual state of the aggregates, which is drier than the SSD condition. This reflects in a higher dosage of water and less aggregate. Is it okay if we use the corrected quantities at the competition? They are a little bit different from the ones that the Mix and Cost Worksheet automatically calculates because those are in SSD condition.

A: This is not ok, as you may have less aggregates than required (60%) and a higher w/p (0.50) than allowed. The rules state that we will check whether the sand is above SSD or not, and that no correction can be performed to account for the absorbed water when the sand is below SSD. We will re-evaluate all mix designs made on-site, with the “at or below SSD” sand quantity and the total amount of water added to the mixture on-site.

Q: It is stated in the rules A.5 v. that we need to submit calculation of GWP and cost calculation using the excel template. What does "Submit the mix design and cost and GWP calculation using the template excel file" mean? Are we only allowed to use the template given by the official?

A: Correct, you need to submit using the Mixture Design File spreadsheet on the Mortar Workability page.

Q: My team is confused if only the water added to the mixer is counted towards the w/p ratio? Or do we have to calculate the water in the aggregate due to moisture content as well?

A: During competition, only the water added to the mixer, the water in the admixtures and the water in the nanomaterials, will be counted towards the w/p. There is no correction performed and no correction needed for the moisture content of the aggregates. The only requirement on the aggregates is that they cannot be above SSD and that the mass of sand weighed during competition is at least 60% of the total mass of the mixture.

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