I need to quantify crack in concrete beam/ slab. Is it possible by any simple method (not with sensor etc.) to do so? I need to compare volume of the crack with one mix-design to another.
It is possible to quantify cracks in concrete, and for this there are different methods with differing degrees of ease and accuracy. One such methods is optical fluorescent microscopy, which is basically an image analysis. A number of papers have been published on this (for example A. Litorowicz). There is also the use of X-ray (for example Takea and Otsuka). In my view, the use of sensors gives better accuracy (for example Hughi and Marzouk).
Any of these methods is fine, but the deciding factor is accuracy.
The best method is to go for X-ray computed tomography. You can obtain a 3dimensional model showing crack locations and sizes across the whole specimen. You can even quantify the cracks
It is going to be difficult to be able to determine the volume of cracks in a concrete beam without a sensor. Surface crack widths can easily be determined without sensors but cracks within the concrete have so far best been determined using CT scans (also X-ray computer tomography) as indicated by Rajeev Roychand. The scans can quantify the volume of the cracks.
If you do not want to use any sensors, it will be laborious. One method I can recommend you is that. Measure the length of the cracks using a flexible string (thin rope), also measure the width of crack at particular intervals (say 2 cm) throughout the length. Do this for all the cracks. Hope this will help you to quantify the cracks on different mixes.
Using X-ray computed tomography on big specimens is rather impractical. I would suggest to use DIC: Digital image correlation. It is a method that tracks and registers changes in images. Cracks can easily be seen. You only need to apply a speckle pattern and use a high-definition camera.