Detailed Cement Concrete Specification :
The detailed cement concrete specification give information about quality and the quantity of the materials, proportion of mortar, workmanship, method of preparation and execution of work etc. The cement concrete specification is properly prepared which makes it easy on site for execution of cement concrete work.
Coarse Aggregates :
Course aggregate shall be of broken stones of granite or similar stones. They shall be free from dust, dirt and other foreign matters. Size of the stones should be 20 mm and down all should be retained on 5 mm square mesh and well graded such that it should not have voids more than 42 %.
Fine Aggregates :
Fine aggregates shall be of coarse sand and should have hard, sharp and angular grains. The grains should pass the screen of 5 mm square mesh. The sand should be of standard specification and should be free from dust, silt and it should not be obtained from sea.
Cement used fro the construction should be fresh and it should not be too old. It should be of good quality and should meet all the standard specifications. The minimum compressive strength of cement should be 175 kg/ m².
Water should be clean and free from alkaline and other acidic matter. It should be suitable for drinking purpose.
The proportion of the cement concrete should be 1:2:4 or as prescribed. For the proportion of 1:2:4 the quantity of materials goes as one part of cement, two parts of sand and four parts of aggregates.
Hand Mixing :
Hand mixing is done on masonry platform or iron sheet tray. For the proportion of 1:2:4 first of all 2 boxes of sand and one bag of cement shall be properly and thoroughly mixed. Then 4 boxes of aggregates are added into the mix and then it is again properly mixed. The mixture should be dry mixed till all the materials are mixed together. Water is then added gradually along with turnings of the mixture. Generally 25-30 liters of water per bag of cement is used to obtain plastic mix of required workability and water cement ratio.
Machine Mixing :
In machine mixing for the proportion of 1:2:4 first of all 2 boxes of sand are dumped into the cement concrete mixer then one bag of cement and four boxes of aggregates are gradually added and rotated for dry mix to obtain required colour and then required quantity of water is added by water can. While being mixed, generally 25-30 lit of water per bag of cement is used to obtain required workability and water cement ratio.
Slump Test :
Regular slump test shall be carried out to control the addition of water and to maintain the water cement ratio. Generally a slump of 75 – 100 mm is allowed for building construction and 30 – 40 mm for road works.
Formwork centering and shuttering shall be provided as per the specifications. The internal surface of the formwork should be properly oiled before the application so that at the time of removal of formwork the concrete does not get stuck to it. The base of the formwork should be properly watered. Generally form work is not removed before 14 days. They should be properly removed without disturbing concrete material.
Laying of Concrete :
Concrete should be laid gently and properly and should not exceed 150 mm. The concrete should not be dropped from a great height. Proper compaction should be done with the help of rods and tamping should be done by tamping rods until dense concrete is obtained. In case of mass concreting compaction should be done with the help of mechanical vibrators. Needle vibrators are used in case of compacting in deeper sections.
When the concrete gets hardened (generally after 3-5 hours of laying) wet gunny bags are placed on the concrete surface to keep the surface damp till 24 hours. The next day onward the concrete surface is flooded with water for 15 days for proper curing.
Also Read : Index Properties of Soil and Its Formation