Concrete Technologies - Science topic
Concrete Technologies are one of the most crucial ways to reach the sustainability and development of the world in the future is to work and research on Concrete Technology. The concerns will be to enhance structural strength and durability of the concrete. Actually, what is the boundary for concrete strength? 2000 kg/cm2, 5000 kg/cm2 or more. How long will our concrete design and implementation continue to be utilized? 50 years, 100 years or more. In this group, we strongly appreciate your new ideas to be submitted for mix designs of the concrete, QC of the concrete, implementation of the concrete and so on.
Questions related to Concrete Technologies
Is there any chances of shrinkage or any other types of cracks formation in concrete if concrete attains its 110% strength in 7 days and little bit increment around 5mpa in 28 days by using admixtures? Its actually M40 grade concrete in which 7days strength is 44Mpa and 28days strength is around 52-56Mpa.
Can anyone please clear my one doubt sir, Is it good or not if concrete attains its full 100% strength in 7 days and little bit increment around 5mpa in 28 days by using admixtures?/
I have attached the file herewith. It's M40 grade concrete used for piling concreting.
In wide RC beams, the shear reinforcement (stirrups) are distributed along the beam length and across its width. There are limits for the longitudinal spacing of stirrup legs (SL) in the current Codes of Practice. But, Do these Code have provisions for the stirrup legs spacing in the transverse direction (Sw) of these wide RC beam? Only EC2 Code deals with Sw, where it assumes that Sw = SL = 0.75d.
As far as FRP is concerned, there are two documents in North America for the design and detailing of RC structures, i.e., CSA S806-12 and ACI 440.1R-15. I have been trying to find any similar documents in Europe but it seems there is no unified European document so far. Any clues?
I have stadium stairs made of concrete, and i need to pick an adhesive material that give a good bonding strength and can resist some environmental factors such as hot and cold weather without peeling off. ( ceramic- polymer composite).. I can،t wait to read your esteemed answers.
Is it possible to switch major from petroleum engineering to civil engineering? Specially related to basic concrete technology, concrete releted products and materials?
We know that superplasticizers' properties vary in terms of PH, Density, Mass average molecular weight, Sidechain density of carboxylic acid groups, Impeller rotational velocity, Viscosity cP, and so on.
I wonder which type of superplasticizer can disperse Nano-SiO2 in water in the best way possible to make concrete?
Furthermore, is there any test that shows how well the nanoparticles dispersed in water?
I have seen that tensile strength of concrete is always lower than compressive strength values (generally 10-12 folds). How can we enhance the tensile strength of the concrete? Is it possible to enhance up to levels similar to compressive strength values either by addition of some SCMs, pozzolanic materials, admixtures, superplasticizers etc. or do we have to change the grade of concrete i.e. M20, M30....... M60 ....so on .., SCC, etc.?
Obviously, it is impossible to use continuous reinforcement concrete bars; thus, several splicing methods are available to tackle the problem. Among them, overlap with tie wire, coupling, and welding methods are the common ones.
The question that has been on my mind is: What is the force transmission mechanism difference between these methods?
In the overlap splicing method, there is inherent space between the center of the bars. It means that there is a discontinuity in force transmission in this method. On the other hand, in mechanical splicing (coupling), the rebars' center is in precisely the same direction. Several tensile tests in this method have shown us that the rupture will never happen in place of the patch (beneath the coupling). While in the overlap splicing method, a fracture could occur anywhere along the rebar.
The question is that, has the force transmission mechanism taken into account for splicing rebars? Or overlap splicing method exists just to keep the rebars in their place for concreting?
Because the mentioned methods are acting quite differently in terms of the force transmission mechanism.
Thank you so much for your attention and participation.
Concrete block bricks companies are marketing that their products are eco-friendly, as they are not emitting carbon dioxide and not using soil. At that viewpoint, they are right.
But,in their manufacturing process, they are largely using cement and sand. Cement manufacturers also badly polluting environment by particulate matters and others emissions activities. Overconsumption of natural resources as well as sand extraction can cause environmental damage.
My question is, how much eco-friendly concrete block bricks is?
Cement mill with spray nozzles are being used since many years. Experience suggests that it sometime helps in preventing unnecessary increase of mill temperature which in turn gives no harm to cement quality. On the other side, sometime spray nozzle does not work properly due to coating formation on it and also causes unnecessary stoppages of cement mill due to high temperature. What should be the soluton to avoid coating fornmation on spray nozzle.
I am using ASTM C1579 standard mold to investigate plastic shrinkage crack in concrete. Unfortunately I cannot find any crack on the concrete surface while the contraction on the mold edges can easily be seen. So, I believe the mold is not restrained enough. I wonder if anyone else has the same experience.
Dear RG Community,
I intend to ask you that what are some classical examples of Geotechnical Engineering related problems, for example differential settlement in Leaning Tower of Pisa was/is considered one of the fine problem. Also if you could help me with some of the case studies which you consider will be helpful in understanding the fundamentals and core of Geotechnical Engineering.
i have a master of science degree in the field of construction engineering and management and i went to continue my PHD degree in the field of concrete technology or construction materials so i need some suggestion form other researchers about research idea or title.
Have you come across this error-"DURING THE CONVERSION FROM CRUSHING TO PLASTIC STRAIN Abaqus FOUND NEGATIVE AND/OR DECREASING VALUES OF PLASTIC STRAIN. VERIFY THAT THE DEGRADATION DATA UNDER *CONCRETE COMPRESSION DAMAGE IS CORRECT?"
DURING THE CONVERSION FROM CRACKING TO PLASTIC STRAIN Abaqus FOUND NEGATIVE AND/OR DECREASING VALUES OF PLASTIC STRAIN. VERIFY THAT THE DEGRADATION DATA UNDER *CONCRETE TENSION DAMAGE IS CORRECT
How to overcome this error , I was trying to replicate the problem as mentioned in the attached paper
Due to its fined microstructure, HSC possesses different mechanical properties compared to normal strength concrete. One common characteristic is its increased brittleness. Many approaches have been used to judge the material brittleness. One method is using the ratio between the tension strength to compressive strength: the lower the ratio, the more brittle. Another is the linear portion in the stress-strain curve observed in uniaxial compressive concrete. The larger the linear portion, the more brittle. In fracture mechanics, some brittleness quantifiers have been defined according to different models In fictitious crack model (FCM), a characteristic length (lch) that is defined by combining the fracture energy (Gf) with elastic modulus E and the tensile strength of material (ft). The smaller the value lch, the more brittle the material. Another common used brittleness indicator is the critical crack extension length (ac). the larger the value ac, the less brittle. When it decreases with an increase in compressive strength, we can say the brittleness increases with strength. Apart from these, what are the other approaches that can be used to define brittleness of HSC?
I am aware about autoclave, heating, using accelerator agents, Type III cements, polymer modification, and lower W/C ratios. But I am wondering if you can introduce other techniques, as well.
I am referring to achieve a compressive strength of at least 20 MPa in 1 day or less.
In the research I conduct, I would like to compare the number of multi-family buildings erected in prefabricated concrete technology with other technologies. What did the situation look like in individual countries 20 years ago and now. In Poland, such data is collected by the Central Statistical Office. I couldn't find such statistics in the statistical offices of other countries. Does anyone know the source where they can be published?
What do you think how important, for segregation coefficient of SCC, could be very small superplasticizer overlaps during the process of making SCC? I made some observations in my work:
According to the previous studies [1-3], an increase in the S/C ratio within the range of 0.5 to nearly 2.25 results in a gradual increase in the compressive/flexural strength while the S/C ratio higher than 2.25 can reduce the compressive/flexural strength of the cement mortar. My mix-design consists of general-purpose cement, silica fume, superplasticizer, viscosity modifying agent, and washed high purity silica sand with a maximum particle size of 600 µm and fineness modulus of 1.29. all the proportion including the water/cement =0.35 kept constant except the S/C which changed from 0.8 to 1.0 and 17% reduction observed in compressive strength.
Moreover, the addition of Sand resulted in a lower density and all the compressive and flexural strength were measured after 28 days of curing.
Can this phenomenon be explained by the fineness modulus (particle size distribution) and/or changes in the porosity of the mixes?
Are there any standards applying a 25mm(thickness) X 100mm(width) X 350mm(span) for concrete flexural strength test? Or maybe any possible formula could explain this?
Extra info: 3point load test, tested for a fibre reinforced lightweight foam concrete. I really need a clear explanation about this. Thank you very much in advance.
We are investigating the mechanical properties of coir fiber reinforced concrete, and following some recommendations from previous research, we decided to reduce the alkalinity of concrete to prevent premature aging of coir fibers. We are using an OPC concrete mix with a pH of 12.5 to 13. To reduce the pH, we have incorporated into the concrete mix amounts of micro-silica and gypsum. However, no significant changes were recorded (pH of 12 to 12.2). Does anyone know an effective and practical method to reduce the pH of an OPC concrete and obtain values of 11 of less?
Concrete strength measured using concrete cubes produce a results different than concrete cylinders. Conservative estimates put concrete cylinders at 80% of concrete cubes, for high-strength concrete some say the percentage is near 100%.
Does anyone have experience using a cube strength in place of a cylinder's or vise-versa? Would anyone use a "translated" cube strength specification for design? Would anyone use a translated cube strength in place of a cylinder test for acceptance?
I'm working on the Fly Ash & GGBFS based geopolymer mortars in Lab. Can we consider the specifid weight of this mortars as 2000kg/m3? And when we use GGBFS instead of Fly ash, shall we reduce the content of ggbfs because of these higher specific weight?
it is well known the reasons behind cracks at early age,like natural concrete shrinkage combined with outer boundary conditions restraint this volume changes. in addition changing the properties of materials with time
the standards codes and committees work to solve this issue. unfortunately this issue still not solved yet.
The question: is it this standers and committees not understand clearly this phenomenon?
or need more improvement ?
note : we talking about the through cracks not surface cracks .
OPC is the 2nd largest generator of CO2 after automobile industries. Researchers have claimed that geopolymer based concrete is more stronger , durable,versatile and eco friendly but unfortunately it has not been widely utilized in practice. I wanted to know its limitations and if there is any possible health hazards related to it. I have also heard that it has some sorts of toxic effects. Is it just a hoax?
I am modeling the debonding between concrete and CFRP subjected to tangential loading using ANSYS Workbench, I used (CZM/VCCT) techniques to model the debonding. as you know with workbench you can't choose the element type directly. you have to insert commands for Solid65. or use the default solid186.
- For pure tangential force applied on the plate. is it suitable to use solid65 element for concrete in this case. bearing in mind that in some failure modes in experimental there is a lump concrete attached to the plate after separation (Failure). and in others the concrete is intact (just debonding failure).
- I tried different element types, but when I use the SOLID 65 command, my model lose convergence too early. If I remove cracking and crushing capability (Suppress the command), the solution runs fine without any convergence problems. (is this due to cracking feature associated with solid65). how can I get the model to converge.
- in meshing,If the mid-side nodes are set to "dropped" for the default solid186 (20 nodes), will I get similar behavior as solid65 (8 nodes) (3 DOF/node for both).
I already tried the following to get my model to converge for solid65 in workbench:
1- Refining the mesh.
2- Reducing the normal stiffness of the contact region
3- Use newton Raphson residuals.
4- Playing with steps and sub-steps (applying displacement in small intervals).
Any help or suggestions will be highly appreciated.
Thanks in advance.
Was it to physically identify crack orientation/inclination and differentiate it between lateral, flexural, shear cracks etc? Or is it for some other function i dont know about.
I will like to model the microstructure of concrete/mortar, is there any software to model the resulting products?
I have used CONTACT 173 and TARGET 170 element. The shear bond strength of brick-mortar is 0.005 MPa, coefficient of friction for bed joint is 1.2 and head joint is 0.85. Does it works if i use ''bonded always'' contact pair?
One of the apparatus required for freeze and thaw test according to ASTM C666 is the dynamic testing apparatus. This apparatus is used to obtain the relative dynamic modulus of elasticity and durability factor of the concrete.
However, in case where the apparatus is not available, what other apparatus or parameter can be used ?
Few studies have used UPV as an alternative, but i'm still seeking for alternative methods.
PVA fibers are modified with oiling agents to reduce bonding between the fiber and the cementitious matrix.
What is the best type of oiling agent and method of application is most suitable?
Also, how can PVA fiber be tested whether its coated or not
Similar to a project I have recently seen "Nest Hilo Roof" I am going to do a Master's thesis in a CONCRETE ROOF OVER A TEXTILE MESH. I am starting to work on the literature review and it's being complicated to find other examples done before.
Thank you for your help in advance. Any literature advise would be welcome.
As there is no universal standards for the determination of the axial tensile stress of fiber reinforced composites, they exist various suggestions by different studies.
What is the best specimen dimension and shape (i.e. dogbone or prism) to be used in assessing the tensile stress of FRCs
Non destructive tests equipment for concrete are quite expensive and not readily available. Is there any non destructive test that can be improvised or built with commonly available materials to determine the strength or/and permeability properties of concrete and other cementitious composites?
Does it have any relevance with M50 and C50 concrete strength? In terms of designing it, will using a normal concrete design method achieving 50MPa considered a B50 grade? Thanks in advance.
I am wondering if someone can explain the positive role of superplasticizer on concrete compressive strength of constant w/c ratio?
Hi dear colleagues
Do the research projects that are continuously being published by researchers to reduce the depletion of resources and to enhance the environment are applied in practice?
For example, in the field of concrete technology, there are a lot of studies have used alternatives to cement (to reduce CO2 emission during cement industry) and natural aggregates for the above-mentioned purposes. Are such studies applied practically?
As we know water absorption of RCA is more than the natural aggregate...so how do we manage it in case of partial replacement..
There are several specifications that provide equations to consider the effect of creep and shrinkage on the estimation of prestress loss. As some of the references state, creep and shrinkage equations for precast segmental concrete bridges differ from that for the other types of concrete bridges. For example, one of the references states that the creep factor for precast construction is normally around 1.6, while for in situ construction this factor would normally be between 2.0 and 2.5. Since most of the references are related to the bridges other than segmentally constructed ones, I would really appreciate it if you kindly provide me with some guidance and references related to the following points:
1. Equations for creep and shrinkage calculation in precast concrete.
2. Equations for prestress loss estimation in precast concrete bridges.
Thank you in advance.
I have used truss element to model the tendon. But to model it as UNBONDED, should i be embedding it in concrete as the normal reinforcement is embedded.
Calculation of the confined concrete properties is necessary for non linear analysis. I am using Manders model.
Do anyone have the already built up code of excel sheet for it?
Also can anyone share the pdf file regarding information on Manders model?
Thanks in advance
I have a problem of a test setup to do the direct tensile test in a universal testing machine. The machine jaws cannot be applied directly to grip the test specimens because of local damage and slip around the jaws. I want to do a fabrication by attaching metal plates to the specimens and my problem is what kind of adhesive of sufficient bond strength will I use to bond the plates to the concrete?
The surface chloride content data is missing, but the concrete was ponded with 3% NaCl solution for 30 days.
There is commonly some missing information in the scientific studies researching some properties of the special concretes such as lightweight, heavyweight, self-consolidating, pre-placed aggregate, pervious etc. Are the concretes more tend to segregate (also including bleeding) than ordinary workable concrete becuase of their complex nature?
Although modified VSI test with 0.5 increment rate was used in several studies, there is no any accessible document to evaluate visual segregation of SCC.
Although VSI test is commonly known as static segregation evaluation method for self-compacting concrete, it is rarely expressed as dynamic segregation method in some studies. Can the both phenomenons (static and dynamic assessments) express with the test method.
I have a mix design of cement flyash blend. After doing rietveld refinement I have found that the ettringite percentage that was 1.57% at 7 days reduced to 0.85% at 28days. The gypsum content that was 0.67% at 7 days increased to 2.52% at 28days. Not sure, if I have identified the peak of gypsum correctly. Based on the past literature, ettringite normally converts into AFm phase but not back to gypsum.
I am quantifying the samples using external standard method and value of factor "G" which i'm using is 1890.29. The formula, which i'm using for the calculation of phases is (S * ρ * V2 * µ)/G. Where S=scale factor; ρ = density of a particular phase; V2= square of the volume of unit cell of the same phase; µ = absorption coefficient of the mix.
The scale factors were:
Ettringite @ 7day = 0.00000632 Gypsum @ 7day = 0.00004583
Ettringite @ 28day = 0.00000341 Gypsum @ 28day = 0.00014414
Ettringite density = 1.79 g/cm3 and unit cell volume = 2306.04 pm3
Gypsum density = 2.32 g/cm3 and unit cell volume = 493.34 pm3
µ = absorption coefficient of the mix = 49.29 cm2/g
The data was collected at Brukers D4 Endevor with the following settings:Cu ka Anode, Stepsize 0.013 deg, time per step 1 sec, 40 Kv and 40 mA
I have attached the jpeg images of the refined samples for both 7 and 28days and have also attached .raw files. I would highly appreciate if someone could have a look and suggest if the identification is correct or there is something wrong in that.
There are some commercial softwares to model the SCC in fresh state in point of segregation with coupled restrainments (aggregate and reinforcing bar) . e.g. Flow3D, Fluent, etc. What are their advantages and disadvantages relative to each other in terms of convenience, inputs, outputs, assessment etc.
Like Bogue's equation for compound composition (C3S, C2S, C3A and C4AF) estimation of Portland cement based concrete, Is there any method/equation available for the estimation of the same for fly ash?
In an FTIR analysis of cementitious materials (Fly ash and cement combination) from 3 hours to 28 days of hydration, the peaks were identified only at upsilon (2&3) vibrations of H2O. No other peaks were observed at any other region (for eg. corresponding to Ca(OH)2). What could be the possible reasons?! or only two peaks should be expected for such a study?!
What do the bandwidth shift and increase in peak intensity of an FTIR spectrum of cementitious materials indicate?!
I have just finished casting 36 geopolymer mortar mix designs. Several variables were set in my work. Nanosilica replacement dosage (0, 2, 4% of slag weight), microsilica replacement dosage (0, 5, 7.5 and 10% of slag weight), chemical activator type (2 types), solution to base material ratio (2 levels).
I am asking about the best approaches to determine optimized mix designs for further tests.
In the first stage the compressive strength and flowability of mortars were evaluated.
I am doing a project on pre and post yielding behaviour of normal, standard and high strength concrete, we did tests on aggregate and sand according to IS codes and we are in the stage of casting the concrete but i am confused as to what literature do I refer for the project? I have been referring only the code books till now. Can anyone help me?
While carring on the mix design by means of doing Marshall method, the binder was prepared at specified mixing temperature in the heating instrument. However, the binder was aged with heating time increasing. Anyone knows what the best way to estimate the aged degree of the binder during mixing process to avoid binder aged phenomenon.
concrete mix are of many types ,generally for domestic construction we use M20 grade of concrete where 'M' is the mix
of ingredients such as cement, agrregates(fine and coarse) and water and '20'refers to compressive strength of concrete for 28 days of curing with water.
steps invovlved in concrete mix are
1)collecting raw materials such as cement (43 grade or 53 grade),fine agrregate(sand)and coarse aggregate(gravel or stone)
2)batching:-weighing of all the raw materials the ratio of M20 grade of concrete should be (1:1.5:3) which means 1 part of cement,one and half part of sand and three parts of gravel with water by water cement ratio.
3)the water cement ratio should be 0.45 of all mix
4)mix the all ingredients such as cement ,affregates and water.
5)after mixing the freshly mixed concrete should be used for its application .the initial setting time of concrete is 30 mins and final setting time sholud be less than 10 hrs.
so this was about the mix design for M20 concrete.
In the calculation of the water/cement ratio and of mix proportions in general, the volume of the liquid superplasticizer must be taken into account.