What is in the cube register?
One sheet with 400 ready rows, one row for each set of three cubes, and a short “How to use” sheet. White columns are for you to type; grey columns calculate. Counters at the top show how many sets are due today and how many are overdue, and the sheet prints on A4 landscape with the header on every page.
| You type | The sheet works out |
|---|---|
| Lab ID, client, site or structure, grade (dropdown M10 to M60) | |
| Date of casting and age (dropdown: 1, 3, 7, 14, 28, 56, 90 days) | Due date, highlighted yellow on the day and red when overdue |
| Cube sides (150 or 100 mm, or measured) and the average weight of the three cubes | Loaded area and density (kg/m³) |
| Maximum load of each of the three cubes (kN) | Strength of each cube and the average, to the nearest 0.5 N/mm² |
| Date tested, tested by, remarks | Largest deviation from the average, and a warning when a cube is more than 15% away |
Two example rows show how it works. They are fictitious: delete them before you start.
How does the sheet calculate cube strength?
IS 516 (Part 1/Sec 1):2021 clause 3.6 says compressive strength is the maximum load divided by the loaded area, reported to the nearest 0.5 N/mm². A 150 mm cube has an area of 22,500 mm², so a cube that fails at 720 kN has a strength of 720,000 ÷ 22,500 = 32.0 N/mm².
Use the nominal size only if the cube's actual dimensions are within the IS 10086 tolerances; otherwise enter the measured sides. Ages are counted from the time water was added to the dry ingredients (clause 3.3), so cubes cast on 5 January are due on 12 January for 7 days and on 2 February for 28 days.
The 15 percent rule, worked through
| Cube | Load (kN) | Strength (N/mm²) |
|---|---|---|
| 1 | 720 | 32.0 |
| 2 | 765 | 34.0 |
| 3 | 740 | 33.0 (32.9 before rounding) |
| Average | 741.7 | 33.0, largest deviation 3.1%: OK |
Now say the third cube had failed at 560 kN (24.9 N/mm²). The average drops to 30.5 N/mm² and that cube is about 18 percent below it, so the sheet shows a warning. IS 516 says repeat the test; if no further cube is available, take the average of the two closest values. IS 456 clause 15.4 is stricter: if any cube varies by more than 15 percent, the test result of that sample is invalid. Agree with your client which rule applies, and write it in the remarks.
What the register does not do
- It does not judge acceptance of the concrete. That is done on 28-day strength under IS 456 clauses 15.1.1 and 16.
- It is not a validated system. ISO/IEC 17025 clause 7.11.2 expects you to check any calculation tool before relying on it, so test the formulas against a few results you have worked out by hand.
- It keeps no audit trail. Anyone can overwrite a cell, which is a common NABL finding for Excel registers.
For setting up the whole lab, see how to start a construction material testing lab. For tests on existing structures, see concrete NDT tests under IS 516 Part 5.
Where Tanush LIMS fits
When the register outgrows Excel: in Tanush LIMS you enter the date of casting at inward, the 7- and 28-day tests take their due dates from it, and the Home screen lists the specimens to test today. The analyst types the dimensions, weight and maximum load and the strength calculates; results lock once approved, so nobody overwrites them later. Construction materials are in the built-in library, and the NABL symbol and ULR print on your accredited scope. It runs on your lab's own PC, even without internet, or in the cloud. See Tanush LIMS or book a demo.
Sources
- BIS, IS 516 (Part 1/Sec 1):2021, Hardened concrete: methods of test, compressive, flexural and split tensile strength, clauses 3.3 and 3.6.
- BIS, IS 456:2000, Plain and reinforced concrete: code of practice, clauses 15.1.1, 15.4 and 16.
- BIS, IS 10086:2021, moulds for use in tests of cement and concrete.