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.
It is not clear from your question what type of admixture have been used, however, these days cement are much finer and therefore the 7 days strength may reach 75-80% of 28 days . If you are using superplasticizers and mix is having low water cement ratio, then this is possible.
Om Prakash Chhangani Hello sir, thanks for your reply. Here we had used Water reducing agent. w/c ratio is also low around 0.37 and cement cotent used here is 431kg/m3 , we are getting 7days strength as 44Mpa and 28days strength as 52-55Mpa.
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.
Wengler Nunes do Prado Actually sir For M40 concrete, i am getting around 44-45 Mpa in 7 days and around 52-56 in 28 days, so is it okay??
The benefits and the disadvantages of early strength concrete using admixture in projects should be analyze based on the Quality, time, cost & type of Projects. In general, the design mix of getting the design strength in 7 days using water reducing admixtures may cost around 7-8% increased cost over normal 28 days concrete design and if the pile is precast pile, due to the high strength development beyond 7 days, brittleness will increase and possibility for develop cracks in sudden loads (when pile driving) due to brittleness, but as per the specifications the pile design was done to accommodate this, the above issue can be avoided. If it is a bored pile, only issue is cost and the benefits are time and quality.
Gajendran Suntharalingam Sir Can you please elaborate relationship between brittleness and high strength development beyond 7 days in case of precast pile in detail sothat it will be helpful for me??
If you get cube strength For M40 concrete, as 44-45 Mpa in 7 days and around 52-56 in 28 days is ok, but you have retrospect about testing procedure you follows while casting the cubes as per the relevant standards.
sometimes error in proportioning, over compaction, loading during testing etc. leads to higher results.
May Shrinkage and other types of cracks will apper because of this early strength gain within 7days??
Give description for Shrinkage and other types of cracks that are appear on surface... as many other factors like temperature, humidity, water-cement ratio, mix proportions, curing etc. will affect cracks at different time. It may not be due to early strength gain within 7days.
As long as moisture is present in the capillaries of concrete and in the interlayers the shrinkage will take place irrespective of concrete strength. Sometime temperature regime can enhance the strength of the concrete. Are you curing properly the specimen.
it is depend on the mix design , and the economic value , using admixture raise the early strength of the concrete , but not the targeted compressive strength.
so it will be useful if you in a fast track project , you need early strength to can DE shutter the form work , anther less no useful
There should not be any harm getting 100% strength at early age. You can get the benefit of using higher strength. Moreover, you see your 7 day result is like 86% of 28 day result, it's good.
Using proper type and dosed of admixture is always good for durability concept. If you are confident enough with results for consecutive testing and statistical analysis, you may reduce the target strength.
No harm in getting high early which is helpful in fast track constructions unless 28 days strength and beyond is not affected .with due regards to durability of the structure. Points to be considered are type of structure,purpose,curing procedure adopted,mix design,SP dosage,QC etc.
Since the use is in Pile, there is no problem in gaining early strength i.e., 7days. The pile is actually designed for entire superstructure load. So, we can start the "Pile cap construction" after 7days and actual load on piles will anyways come after 28days.
Anyways, it's a costly affair to use admixures and need to see the benifits w.r.t to money invested Vs Early Project completion benifits.
There's no harm. It actually helps you in the sense that projects can progress faster without having to wait for the 28 day curing period to elapse.
It also means if you find the strength quite high, you can redo the mix design with a lower target strength to reduce the amount and subsequent cost of cement to help offset the cost of admixtures where price of materials would be an issue
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