Dear Saurabh,

Please provide more details. What was the calculated flexular strength? What was the way of mixing - was it the same for all of the samples? How the samples were stored? What were the curing conditions? Without these information it is not possible to answer.

Best regards

Łukasz

Dear Lukasz Sadowski

Thanks for answering my question. The additional information is here:

Sample 1: 1.7705

Sample 2: 3.2932

Sample 3: 0.8826

Sample 4: 3.8768

Sample 5: 3.5646

2. Mortar mixer is used for mixing the raw materials having low speed (140 rpm) and high speed (285 rpm) through following steps.

• Pour measured water in the mixer.
• Add cement and start mixer at low speed for 30 seconds.
• Sand was added in the mixer steadily from 30 s to 60 s.
• Mixer was switched to higher speed and mixing continues for another 30 s.
• After 1 min 30 sec, mixer was off for 15 seconds and mortar adhering to the wall and bottom part was scrape off.
• Mixing was continued at high speed for 60 seconds.
• After mixing, the samples were molded and vibrate for 2 minutes (same vibration frequency every time).
• And then samples were stored in a covered plastic box for 24 hours.
• The steps of mixing is same every time.

3. Curing:

• Temperature (10 ° C),
• Closed plastic container,
• humidity-15 to 20%.

Thank you. I think that the differences may be caused by curing conditions. I suggest you to repeat the experiment and store the samples in water and in the temperature about 20C. Then, you will probably get results with lower scatter.

I wish you all the best.

Regards

Łukasz

Dear Sourabh,

Please mention the size of specimen sample you tested. Flexural strength at 24 hours curing period is very sensitive. More care is is required for Handling of samples. Type of cement is not mentioned.

Dear Ishwar Sonar

Thanks. The beam specimen size is 20 X 20 X 100 mm and the cement is OPC type I.

Regards

saurabh khandelwal

When was the testing machine calibrated, sometimes out of calibration also cause inconsistency in results other reasons are described in many answers as above

follow

I agree with @Ytyo and other answers. I think that you are able to receive repeatable results with next experiments.

Regards

Łukasz

The cross section of the samples is small. Any variation of the height, could be affect too much to the results. I would suggest measurement with a caliber the real cross section of each sample to do the right calculations of flexural strength. In addition, I would suggest make bigger samples to decrease the effect of potential small defects. 40x40x160 mm could be a good option.

Depending on the maximum size of your aggregate, the size of the specimen could be too much small. If your maximum size of the aggregate is high, most likely, you will get high variability of results if you use small samples.

In summary, my advice is making bigger samples to reduce the variability of results due to small defects.

Dear Mirian Velay-Lizancos

Thank you for suggesting large sample size but my Instron has 10 Kilo Newton load cell and I am not sure whether I could test my sample of 40 X 40 X 160 mm for 28 days flexural test.

Regards

Saurabh Khandelwal

I agree with Mirian. In my opinion, size 80 m x 80mm x 500 mm will give better results. If you know approximately flexural strength then considering capacity of machine ( 10 kN) one can workout dimensions of beam for the given span say 400 mm or 500 mm, assuming approximate load of 7 kN ,

For cement concrete or cement mortar very small specimens may give variable results. size of aggregate is important.

Hello everyone,

thanks to all the researchers for suggesting the solution of my question. I repeated my experiments with

• Increased vibration time (4 minutes),
• With controlled humidity for 24 hour sample and
• Measurement of cross section with vernier caliper.

Now the data has low scatter.

Regards

saurabh

Dear Saurabh,

Congratulations. It will be beneficial if you take all of the comments into account. I hope that the results after 28 days will be also satisfied for you.

Best regards

Łukasz

The size you have selected (40 X 40 X 160 mm ) will prove to be very small. As suggesyed by Dr. I P Sonar sir you have to go for bigger size. Also rate of loading will play an important role in the testing.

Following...

40x40x160 mm could be a good option