1. Grade Designation (Required Grade of Concrete)
2. Types of Work (RCC, PCC)
3. Maximum Nominal Size of Aggregate
4. Shape of Coarse Aggregate
5. Workability
6. Slump
7. Compaction Factor (C.F.)
8. Fine Aggregate confirming grading zone
9. Exposure Condition
10. Type of Cement
11. Grade of Cement
12. Specific Gravity of Cement, Coarse Aggregate, Fine Aggregate
13. Free moisture content of fine aggregate and coarse aggregate
14. Water Absorption for fine aggregate and coarse aggregate
15. Fineness Modulus of Fine Aggregate and coarse aggregate
16. Dose of Admixture
17. Reduction in water content due to admixture

If you need excel sheet of concrete mix design, you can email me.

• Water Curing
  • Immersion – Precast
  • Ponding – slabs, pavements
  • Sprayings – plasters, vertical concrete
  • Wet-covering (saw-dust, sand, jute, etc) – vertical surface, concrete in difficult position

• Membrane Curing
  • Concrete covered with thin membrane to prevent evaporation loss.Generally used after 2-3 days of water-curingUseful in inaccessible areasA thin impervious layer is created on the surface of the concrete.
  • Example Bitumen, polyethylene, water-proof paper, rubber compounds, etc.

• Application of Heat
  • Steam curing gives uniform temperature – no differential expansion crack
  • Fast method, and useful in congested area.
  • Useful in pre-cast industry
  • Heat increases the rate of hydration as-well.

• Miscellaneous
  • Chemicals like calcium chloride are used as surface coating. It absorbs moisture from atmosphere as stays wet for longer period.

• Shielding of wind in the working area and insulating the plant with insulators.
• The site shall be well managed for quick delivery, finishing and covering of the concrete with insulator like straw, jute sacks, plastic sheets, water-proof paper, etc.
• The material for concrete can be pre-heated. Water can be easily heated in a container. Coarse aggregate can be heated with closed steam coils under stock pile, or by steam or hot air, if stored in a room. Sand can be heated over steel plates, while cement shall not be heated.
• The form-work or sub-grade can also be heated (to the temperature of concrete) so that heat of concrete is not absorbed by them.
• Special type of cement like rapid hardening cement, high alumina cement, etc. can be used that have higher heat of hydration and keeps the concrete warm.
• Accelerating admixtures is also commonly used that increases the rate of hydration. Calcium chloride is a good accelerator, but use in higher amount increases the corrosion in steels embedded in RCC.
• Where possible, electrical heating can also be adopted for curing (maintaining the temperature) of the concrete by passing alternating current through it.
• Where caging is possible, especially in pre-cast industry, low pressure steam (or hot air) circulation maintains the temperature thus accelerating the hydration

1. Management of Materials
   • Aggregates shall be stock-piled in shade.
   • Regular sprinkling of water to aggregate.
   • Arrangement for circulation of cold air in aggregates.
   • Using cold water (up to 5^oC)
   • Low heat cement can be used.
   • Retarding admixtures are also helpful in delaying the setting process.
2. Management of Concreting Work:
   • Scheduling the concreting work in evening (but with sufficient lighting)
   • Use of more masons for quickly finishing the work.
   • Transporting the concrete in deep containers.
   • Covering of concrete with moist materials as early as possible.
3. Curing of Concrete:
   • The concrete shall be cured with cold water.
   • The surface shall be continuously made wet either by ponding, or using water absorbing materials in surface like cloth, jute, sand, etc.
   • If possible, shade shall be maintained on the concrete.

Check Acceptance Criteria

• If 28th days concrete cube test results fail checks if the result of all 7 days’ cubes is the same. If even one passes the acceptable criteria you are sure that the concrete mix is OK.
• Even if one of the cubes is OK wait for a 28 Day result.
• If 28 days’ result fails, then again there is a possibility that cubes are not filled properly or they were not cured properly in the first 7 days. But it is possible that slab concrete is OK. Go for the Hammer test.
• If the hammer test is also as per failed cube result then go for core cutter and test it to get actual strength of laid concrete.
• There are many options to strengthen a weak concrete member if concrete cube fails in test (Strengthening Techniques)

For more details: https://civiconcepts.com/blog/what-next-if-concrete-cube-fails-in-test

• If the on-site slump test fails, the site engineer may use his/her contractual power and reject the concrete and suspend the concreting process.
• However, it is believed that a slump test is just a measure of concrete consistency, and it may not cause the reduction of concrete strength. So, the site engineer can allow the contractor to continue concreting work, but proper slump adjustments should be made.
• If the concreting process is permitted to be finished, the contractor still needs to prove that the finished work complies with other contractual requirements, such as a compression test.
• Engineers should be aware that the workability is related to both strength and durability of concrete. If the concrete attains the designated strength, the durability may still get affected.
• If the concrete slump value is too high, the site engineer may allow the mixer to revolve for 8 to 10 minutes to reduce the slump. If the test still fails, one may add cement to the concrete mix to minimize slump value.

For more details: https://theconstructor.org/concrete/site-slump-test-fails/176167/

Concrete gains strength with time after casting. It takes much time for concrete to gain 100% strength and the time for same is still unknown. The rate of gain of concrete compressive strength in higher during the first 28 days of casting and then it slows down. In 28 days, concrete gains almost 99% of its strength. So, we test the concrete compressive strength on 28 days.

For more details: https://theconstructor.org/concrete/why-we-test-concrete-strength-after-28-days/6060/

It is found that cylinder specimen gives lower strength compared to cube specimen. Also, cylinder test gives more uniform strength than cube test. It may be because,

• The cylinder strength is less affected by the friction at loading surface.
• The slenderness ratio for cylinder will be more than that of cube (Approximately double, For Cylinder = 300/150 = 2 and for cube 150/150). So, the cylinder has less compressive strength.

Honeycomb is the space or void inside the concrete.

Causes

• Improper compaction as well as mixing of ingredients.
• Due to too stiff (Hard) concrete.
• When large size aggregate is used.
• Due to Segregation of ingredients of concrete
• Caused if there is not adequate gap between steel rods to enter concrete mix into it.

Effects

• Reduce Strength of Concrete
• Generally, occur in beam, slab, column etc. which may cause collapse of whole structure.
• Dangerous for earthquake structure
• Easy corrosion of Rebar.

Remedies

• Mix concrete materials properly.
• Use standard size aggregate
• Use vibrator for compaction of concrete. (Too much compaction of concrete with vibrator leads to segregation in concrete)

For more details: