Concrete Technologies - Science topic

Thanks @Padmanabhan

Krishna Subedi and Thank you sir for your reply. Actually in my concrete structures no any issues of cracking and shrinkage have appeared till now(It's almost 4-5 months but nothing happened) but some people are telling that cracks and shrinkage may appear in long term duration. So that thing i want to confirm whether it's like that or not.

Achieving a significant portion of the concrete's design strength (around 100% strength) within 7 days is considered favorable, especially for early-age applications or when early formwork removal is desired. However, it's important to note that the strength gain beyond 7 days and up to 28 days is also crucial for the long-term durability and performance of the concrete. A typical strength gain pattern involves a relatively rapid initial strength development, followed by a gradual increase. While achieving the full design strength within 7 days is advantageous, it is also desirable to see additional strength gain between 7 days and 28 days. A strength increment of around 5 MPa during this period is generally acceptable and can be considered a normal development. However, it's essential to evaluate the specific project requirements, structural considerations, and any relevant design codes or specifications for the piling concreting application.

The History of Ferrock Ferrock was actually invented by accident in the early 2000s. Dr David Stone, the founder of Iron Shell Media Technologies and former University of Arizona PhD student, was researching ways to prevent iron from rusting and hardening when he accidentally created Ferrock.

Iron Shell is a start-up material science company founded in 2012 which produces Ferrock, an environmentally friendly cement substitute utilizing waste steel dust. This technology is carbon-negative, absorbs environmental toxins, and has substantial structural advantages over traditional cement.

David Stone Founder and CTO at Iron Shell Material Technologies

More information might be in this link

This is a good question.

I would like to recommend Silicone Rubber Compounds - RTV 2 components which perform the ability of high thermal conductivity and adhesive. Some famous brand names which you can refer ShinEtsu, Momentive, or Dow-Corning.

References:

1) https://www.shinetsusilicone-global.com/catalog/pdf/rubber_e.pdf

2) https://www.dow.com/en-us/product-technology/pt-silicone-hybrids-silanes.html

Best regards.

Yes it's possible, bet definitely, it's going to cost you time, a whole new experience from process to traditional Engineering. It's worthwhile as new technologies are bound to be developed from analysis of materials.

Dear Waldemar Łasica

Nanoparticles are used in concrete for various reasons. The most important one is to increase concrete mechanical properties, such as its compressive strength.

Nano-materials like Nano-silica, Carbon Nanotubes by filling nanopores in concrete and preventing the spread of cracks, respectively, increase the strength of concrete.

There are lots of published articles in this regard.

Dear Mheran there are many chemical admixtures (superplasticizers) use to modify the properties of fresh concrete. The best approach is to perform a test using various types of superplasticizer and select the best one. An empirical selection is not always efficient.

Dear Kunal . ,

You can use steel fibres or rubber strips and so on to increase the tensile strength of concrete.

I think international concrete codes take these details into account. But, here we must provide an adequate running length for rebar that no debondind happen! And keeping tension force path as efficient as possible. For interaction zone, the amount of longitudinal reinforcement always doubled and no failure reported for this region in some literature That I read. Thank you that was good question.

If you are interested in concrete model for explicit solver (VUMAT), you can use this link to download it

Ecofriendly concrete bricks could be produced globally by using less of cement but more of pozzollanic ashes from industrial and agro activities. But most brick makers will first consider acceptance from consumers alongside the financial implications. Standards and other logistical challenges are other factors affecting it's global acceptance and adoption.

Bhautesh Mistry I am very much interested in the question you have raised. I also have a cement mill nozzle which keeps blocking especially when there is a power failure. Have you found a solution to your problem? if yes, please do share. Also is there a special type of nozzle that helps prevent this blockage? How efficient is the use of grinding aid in the nozzle in preventing this blockage and improving overall grinding efficiency? Thank you.

You will find in this link:

I've been using these molds for a while in my studies. It's really difficult to respond your question without considering the parameters contributing in the study. However, since the focus of my studies are in the assessment of the impact of the environmental conditions and curing practice on the cracking behaviour of this type of shrinkage, based on my experience so far, I can admit that your doubt toward these molds is justifiable and reasonable and I personally have already thought about it.

Mr.Muneeb,

I feel the main important one in all over the world is population increase and no space available for developing infrastructure relative to increase in population. so the construction activities have taken place as closer to an existing structure. In view of this, the stability analysis of existing structure adjacent to new construction in terms of excavation, embankment, tunneling or pile driving is a serious problem. As a geotechnical engineer we need to come out with design idea to protect the existing structure due to the effect of new construction.

Another important issue is we don't have excellent supporting ground for the new construction. So, in this case we need to develop economical ground improvement technique to support the load. Ground improvement technique alternate to conventional method is catching up among researcher . ok all the best in your research..

Thanks. I will look into your suggestion

Re-tempering with chemical admixture (need proper mixing after re-tempering, at east 70 revolutions in 2/3 minutes in transit trucks) is not harmful. It increases slump and concrete can be pumped and compacted with less efforts. Re-tempering by addition of water is always harmful as it reduces strength of concrete drastically.

High performance concrete with advanced properties like high density, low density, high water resistance, chemical resistance, weather resistance, fire resistance, radiation resistance, ductility, durability, etc customised as per project requirements

Hi, I had the same problem, and after checking that both damage values and crushing strain values were all positive and in ascending order, I removed all the values of the damage parameter greater than 0.98, and the error message disappeared. Also try to ensure that the diference between two consecutive values of the damage is greater than 0.001

I agree with @Jessly Rajan

maybe recycled aggregates

The term "geopolymer" is widely used for slag cements and alkali-activated (slag) cements, too. The production and handling of those systems (without any Ordinary Portland Cement OPC) are neither "difficult to create", have not to be "premixed only" nor "sensitive" at all. Major and fundamental research work and applications have been performed in Russia, China, Ukrania, Japan, India, Spain, Germany and Tschechia since 1990. Intense research about this very competitive product to OPC has been done and patented by P. Krivenko, F. Skvara and J. Gebauer& L. Ko{HOLCIM} and other international cement producers.

Most important is a constant quality of the components for geopolymers:

- Homogenous slags or ashes of consistent/constant quality with high glassy phases

- Proper adjustment of desired slag/ash with alkali source (Sodium or Lithium Sulfate, Sodium Silicates( "water glass"), Sodium Metasilicate, Alkali Hydroxides, Calcium Oxide and/or Hydroxide etc.

Since the constant quality of slag/ash component is necessary, geopolymer production is especially economically in those countries with/or close to a strong heavy metal industry. Geopolymers have a much improved ecological balance (less Carbon Dioxide and dust emissions compared to OPC), very good to excellent compressive strength and much better chemical resistance/durability in comparison to OPC.

The major draw-backs of geopolymers are the lack of standardisation, the strong lobby of the OPC producers....and the still lax legislation on CO2 reduction...but the time for geopolymers will come!

Please check my answer at

Hoping that it is helpful

Grid provides you the pattern of cracking and directions to allow you to study the detailing of reinforcement required in the joint.

Polycarboxylates are linear polymers with a high molecular mass (Mr ≤ 100 000) and with many carboxylate groups. They are polymers of acrylic acid or copolymers of acrylic acid and maleic acid.

You may find some information in this regard at NIST website

In ansys you can use CZM material with identifying the debonding parameters as an input. The contact should be bonded with pure penalty or augmented lagrange formulation.

see https://www.rilem.net/images/publis/119303.pdf

I agree with D.K. Mishra.

You can also see paper attached here.

Dear Anil Kumar Thakur ... Thanks for answering..

So did you think that precast concrete could be considered energy efficient?

There is some developing research that utilises surface water flow to predict concrete permeability and durability characteristics. This research determines the relative covercrete skin permeability which can be standardised for various concrete parameters such as strength, porosity, and durability. You can get an idea of how it works from this link (at least through the images). http://wdnsword.iis.u-tokyo.ac.jp/research/IISopen/Kikuchi_2012.pdf

S.M. Iqbal S. Zainal … Please check references below.. hope it will be helpful for you…

Regards…

Cnt

1. Act as nano fibers arresting the cracks at their initial propagation.

2. Nucleation sites for the cement hydration gels helping increasing stregnth.

3. Nano fillers to the nano and microscale pores and consequently increasing the packing level of the cement matrix

Hello Dear

the main purpose of adding SP is to improve the workability of concrete.. but there's a limitation of the SP mount added to the concrete mixture, otherwise that may effect in the mechanical properties of concrete such as compressive strength, tensile and flexure..

the range of SP amount used is almost 2-4 % kg/m3 of concrete.

hi Rasheed Babatunde Isa

Factors affecting the strength and durability of concrete

1-Water to cement ratio

2- Wet care of concrete :

Concrete without moisture control 50% reduction in compressive strength 28 days.

Concrete with 3 days of wet care 75% resistance in conditions 28 Day of wet care.

With 28 days of wet care we will have 100% resistance.

3- Type of cement used.

4- Time factor in compressive strength :

The compressive strength of concrete should increase over time

Forecast of concrete strength growth according to ACI 209 standard As follows: f(t)=f(28)(t/4+0.85t)

5- Effect of temperature on concrete strength

Yes and no. Innovations are slow to transfer from the lab to the field. There are a number of reasons for this, but in my mind there are 2 primary reasons. Firstly, there is far more academic kudos in writing papers than in influencing practice. Consequently, academia is set up to support grant/journal writing far more than support for technical input. Secondly, industry is very conservative. This means that standards are often a long way behind the latest research findings (there may well be other, commercially influenced, reasons for this). The conservative nature of construction (and the low profit margins) means that industrial and academic timelines are not necessarily aligned.

I'm both sure what the solution is. But academia should encourage technology transfer while industry should put their hands in their pockets and recognise that not all research yields immediate returns.

Geopolymer Concrete

Please find the attached file. This file is explaining the behavior of SCC under high temperature. I hope it can help you to find the best answer. The main reason of seeing this phenomena is transforming water to vapor and entrapping in the concrete can cause an increase in internal pressure.

Interesting discussion!

interested

I have some serious issues about modelling element for pre-stressing steel tendon. 

Truss Element (T3D2) is supposed to be used for tendon (having axial stress only) but it does not have any cross-sectional shape and surface, so it is not possible to apply surface base cohesion with concrete surface and tie (with end plate) at end. 

If solid element is used, everything is fine (surface base cohesion with concrete and tie at end) but there is an unwanted flexural effect on beam from the tendon, it also acts as rio bars. You can imagine the effects when a 26 mm dia bar with 1000 MPa pre-stress exerts as a  flexural member. This results a lots of damage in surrounding concrete. 

Is there is any other suitable options? Any elements can acts in axial tension/compression only but having cross-sectional area and shape?

Thank you.

Hi Venkatesh

In attached spreadsheet, you can find Modified-Kent Park formula and Saatcioglu and Razvi formula. Hopefully, this can help you in your work.

Good luck!

Considering the cost of fabricating motor is low, you can try to use various content of admixture with less sand! Ensure the quality of raw materials and enough vibration, the problem is easy to be found!

Alex,

Your problem is bigger than you think. Concrete is not like metals. Not only do you have to worry about getting a grip on the sample, because concrete is such a brittle substance that gets more brittle as it gets stronger, you also have to take care not to introduce extra moments through misalignments, potentially in both x and y, that can lead to inconsistent or erroneous results. Something like the opposite of loading a compression sample through a ball is needed. I suggest this can be done through chains or cables depending on loads, attached to plates glued or bolted to your specimens. Be very careful because such attachments can fly around at failure. Even with such a system, aligning the top and bottom along the intended axis is also necessary. For this I sometimes used two lasers.

Direct tension testing of concrete is very hard. If you are looking for loading curves going from zero through the peak and back to zero, it is even harder than that. As always, the question: why do you want this value? Maybe the question is already answered. Maybe there is another test to get you the information you need, Brazilian or flexural test perhaps.

Petr Konečný, Can you provide an example of the whole process? An excel sheet maybe?

I think X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and Brunner−Emmet−Teller (BET) may be helpful for you. XRD and XPS can clarify the particle binding type (crystal or amorphous; valence state) .  And BET can present porosity and specific surface area.

The ASTM has designated five types of portland cement, designated Types I-V.  Physically and chemically, these cement types differ primarily in their content of C3A and in their fineness.  In terms of performance, they differ primarily in the rate of early hydration and in their ability to resist sulfate attack.  

pl. follow the link to compare the properties

Concrete is not a homogeneous material even at macroscopic level, thus, it is not easy to define a definite border for the segregated concrete and accepteble concrete. This is why the data on the segregation or degree of homogeneity of concrete is very limited. Obviously the lack of proper test method(s) to evalute segragation plays a important role in this subject.   

Thank you Sina Dadsetan for your answer. I cannot access that standard from my university. I have ASTM C 1611. My question is related with increment rate of VSI not cone orientation. I think the standards refer the same VSI rating values (0, 1, 2 and 3). But I want to express the values with 0.5 increment rate as 0.0, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0. I cannot find any materials (article, report etc.) for the rating. 

You may be interested to hear that I investigated an example of severe static segregation where, in the worst case, coarse aggregate had sunk over 5m from the top of a 55m deep pile (not true self-compacting concrete but high flow concrete that consolidates under its own weight with no vibration). The site records showed no evidence of dynamic segregation problems through VSI in any of approx. 300 batches.

I think that the issue is mainly a phase misID. Since you have calcite in your system, its quite likely that the peak that you're assigning to Gypsum at latter ages corresponds to hemicarboaluminte or monocarboaluminate (both are AFm phases), both have their main peak around this position. In fact, the main peak of Mc matches perfectly your data, as you can see in the attached image (you've not only one Mc peak, but all of them, always remember that a good phase ID require the presence of all the main peaks of the candidate phase, unless you suspect strong texture). Hope this would be helpful for you :)

Thank you professor for your suggestion. I dowloaded the software. The program is seen very useful for structural members in hardened state. I' m researching the concrete in fresh state as a liquid. I want to dynamically model the segregation of aggregates by depending on reinforcing bar blocking and aggregates amount/size etc. in flowing of the concrete . 

regards

Dear Lincy,

There is no need to estimate quantities of "C3S, C2S, C3A, C4AF" in fly ash because there are no such minerals in fly ash. Fly ash consists of mostly amorphous phases. Ideally, the major component is amorphous silica (in class F fly ash). Usually, some content of lime (CaO), which in class C fly ash can be high. Maybe some alumina, sulfate, and alkali. You may have some minor contaminating compounds too. As crystalline phases in fly ash, you may have mullite and quartz in relatively small amounts (depending on the source of fly ash), but most phases are amorphous (that is why you will not be able to identify them by XRD). The most important components from the viewpoint of cement reactivity are amorphous silica, lime, and alumina. I hope this will help you.

But they were recorded using an ATR?

Once you have made trial mixes and tested the required responses such as compressive test and other tests of interest ,you can then apply surface response methodology to optimize the mixes otherwise you will be forced to conduct several tests to come up with an"optimized mix"

really interesting answer Fernando

you can check it ..either by traditional method like bitumen retained penetration after 5 hrs thin film oven test or by more scientific approach  viscosity test (AR). regards

How can I Create a Model of Bow and arrow and Associated Frequencies

Thank you very much for replying Dhirendra Singhal . This information of yours is really helpful. Also, thank you very much for your inputs.

Thank you very much for replying Saad Sarsam. This information of yours is really helpful. Also, thank you very much for your inputs.

Dear Nadim,

I agree with Rytis and I would like to add the following; In case you want to identify failure mechanisms (matrix cracking, fibre breakage etc) in composites you may need to use resonant sensors in order to amplify your resolution in a specific narrow band frequency.

In our software ATENA (http://www.cervenka.cz/products/atena) this can be accomplished easily by assigning special parameters along with bond properties to our reinforcement model.

See for instance: