Importing standard sand for cement tests is becoming unnecessarily expensive. Why can't we use local sands which have been blended to approximate the grading of the 'standard sand'. Would there be a significant difference in test results?
the importance of standard silica sand for cement mortar are:
1-standard silica sand is composed of 97 to 100% quratz (crystaline silica) there is no possibility of reaction between cement aggregate (alkali silica reaction)
2-standard graded silica sand is naturally round aggregate that helps to produce workable mortar. many cement mortar test like compressive, flextural and drying shrinkage rests needs mortar that produce a flow of 110+-5% based on ASTM C1437. crushed sand needs more water to produce such mortar and may produce more voids in mortar structure.
3-the water absorption of standard graded silica is near 0/25 % that is
negligible. you only should prepare 500 cement,1375 sand and 242 gr water without any correction to water. consider that round river sand can absorb water to 2.5 %.
4- standard graded sand posses well graded gradation with low voids and well compact.
if you do not access to standard graded silica sand i propose river sand with consideration of water absorption, sand dune, sand molded casting may be working well.
good luck
The main thing is the quality of the sand you use. There is research evidence that says that you can achieve the desired/comparable strength using non-standard sand as that using standard sand.
See this article:
http://www.ijetsr.com/images/short_pdf/1433922786_anjali_ijetsr.pdf
The main reason for using standard sand is to eliminate its effect on the reported strength of the mortar cubes. With a standard sand, the only variable will be the cement which you are trying to quantify its properties (assuming the water used is potable water). So if you report the strength of the cement, you can compare it to other cements produced elsewhere. If you use different sands, then the difference might be caused by the sand and not the produced cement.
As A Loulizi mentions, using the standard sand eliminates one variable (or experimental noise) and leaves only the cement properties as the independent variable. I think the Portland cement industry follows the procedure so to stamp their products with the standard compliance
Some additional considerations:
a) Standard sand is crazy expensive. It is not complicated to grade (using sieves) the particle size of local sands to match that of the standard sand. Have irregular-angular particles of your local sand? Get them rolling in a ballmill-like container with no grinding media, so to round the edges.
b) The type of sand can have a large effect on the evaluation of cements, depending on the type of cements. In some cements the standard sand gives awful results, while limestone works wonderfully.
c) Once tests are performed with the standard sand, there is no guarantee on the actual field performance when local sands are used.
We only use local sands in the lab, sometimes we grade them.
In our company, we try to change sand to local sand but we face problems of fluctuation of testing. Even if with the standard sand, different lot of sands provide different results due to different shapes and gradation of sand.
This is because the standard sand (ennore sand) is free from any impurities which may alter the strength activity index.
to ensure that the result of test is resulting from cement effect only
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