Concrete specimens are a cast and tested under the action of compressive loads to determine the strength of concrete. In very simple words, compressive strength is calculated by dividing the failure load with the area of application of load, usually after 28 days of curing.Pouring Concrete vs Pouring Rain.If the rain occurs when the concrete is fresh (about 2-4 hours after mixing), the surface should be protected from the rain. If the finishing process was recently completed, rainwater may not cause damage as long as it is not worked into the surface and the slab is left untouched.Slump. Slump is a basic parameter which must be specified. Slumps that can be specified range from 20 to 120 mm in 10-mm increments. The higher the value, the more workable the concrete is likely to be for ease of placement and compaction.In making concrete strong, these ingredients should usually be mixed in a ratio of 1:2:3:0.5 to achieve maximum strength. That is 1 part cement, 2 parts sand, 3 parts gravel, and 0.5 part water.Concrete hardens as a result of a chemical reaction, called hydration, between cement and water, not because it dries.Concrete continues to gain strength after pouring for as long as it retains moisture, but the longer it moist-cures, the slower the rate of strength gain.Concrete finishers here tell me that a slab poured outside on a hot day won’t cure properly unless it’s kept wet.It simply makes the concrete set more slowly, which would actually make curing more critical. For concrete to reach its full strength, it needs water to hydrate the cement.When measuring the workability and consistency of a batch of concrete, a concrete slump test must be performed for each batch of fresh concrete.The cone is filled with concrete, and then removed. The shape of the concrete after the cone removal is then assessed to determine the workability.
Mix design can be defined as the process of selecting suitable ingredients of concrete and determining their relative proportions with the object of producing concrete of certain minimum strength and durability as economically as possible.Since workability of concrete is achieved by more water, it reduces the strength of concrete.For mass concrete where and lightly reinforced concrete structures, low degree of workability can be used.The mix design as per IS 10262:2009 is in line with ACI 211.1. The code permits the use of 1. supplementary materials such as chemical and mineral admixtures. Provisions of IS 456:2000 are applicable for durability requirements with all types of exposure.A ground line pump can reach over 150 meters, with possible extensions if required. A boom pump can extend up to 72 meters. with possible extensions if required.Standard Codes for Concrete Admixtures. As per ACI 212.3R-10, Concrete admixture is a material other than water, aggregates, hydraulic cement, and fiber reinforcement used as an ingredient of concrete or mortar, and added to the batch immediately before or during its mixing.
Very dry mixes having slump 0 – 25 mm are typically used in road making, low workability mixes having slump 10 – 40 mm are typically used for foundations with light reinforcement, medium workability mixes with slump 50 – 90 mm, are typically used for normal reinforced concrete placed with vibration, high workability .Increased porosity also results in more efflorescence, causing the color of the surface to be less intense or whitish. Excessive slump also can result from accidentally adding too much water-reducing admixtures or super-plasticizers to a mix. This can result in aggregate segregation and a serious loss of strength.The slump test is a means of assessing the consistency of fresh concrete. It is used, indirectly, as a means of checking that the correct amount of water has been added to the mix. The test is carried out in accordance with BS EN 12350-2, Testing fresh concrete.Slump is the measure of concrete consistency and fluidity. It shows the flow and overall workability of freshly mixed concrete. Simply put, the higher the slump, the wetter the mix. Four-inch (4”) slump is very common with normal weight concrete and is a good for pumping.Concrete slump test or slump cone test is to determine the workability or consistency of concrete mix prepared at the laboratory or the construction site during the progress of the work. Concrete slump test is carried out from batch to batch to check the uniform quality of concrete during construction.In simple words, workability means the ease of placement and workable concrete means the concrete which can be placed and can be compacted easily without any segregation. Workability is a vital property of concrete and related with compaction as well as strength.