Compressive Strength of Concrete

By | January 14, 2020

The concrete slump test measures the consistency of fresh concrete before it sets. It is performed to check the workability of freshly made concrete, and therefore the ease with which concrete flows.The slump test is used to ensure uniformity for different loads of concrete under field conditions.Place the cone next to the mound of wet concrete and put the steel bar level on top of it, extending over the top of the mound. Immediately measure the distance between the bottom of the steel bar and the top of the concrete mound. The distance, measured to the nearest 1/4 inch is the concrete slump.There are three types of slump that may occur in a slumps test, namely, true slump, shear slump and collapse slump. True slump refers to general drop of the concrete mass evenly all around without disintegration.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.Slump test is the most commonly used method of measuring consistency of concrete which can be employed either in laboratory or at site of work.In case of a shear slump, the slump value is measured as the difference in height between the height of the mould and the average value of the subsidence.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.

Adding just 1 gallon of water per cubic yard can: Increase slump 1 inch, decrease compressive strength 150 to 200 psi, waste about 1/4 bag of cement, and increase shrinkage by 10%. But water isn’t the only way to adjust slump. Consider adding a superplasticizer at the site to increase slump.The workability of pumped concrete in general has an average slump of between 50 mm and 100 mm. A concrete of less than 50 mm slump is impractical for pumping, and slump above 125 mm should be avoided.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.Workability is a property of raw or fresh concrete mixture. 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.High slump or “flowing” concrete mixes are economical ready mix products that allow maximum flowability without sacrificing strength by adding water at the jobsite. These high slump, high strength properties are attained through the use of high range water reducing admixtures (superplasticizers).Shear slump indicates lack of cohesion in the concrete mix. Shear slump may occur in the case of a harsh mix.


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.Plasticizers are also often used when pozzolanic ash is added to concrete to improve strength.Adding an excessive amount of plasticizer will result in excessive segregation of concrete and is not advisable. Depending on the particular chemical used, use of too much plasticizer may result in a retarding effect.The lower the amount of water in a traditional concrete mix, the lower its slump. Low slump values in traditional mixes generally mean higher quality concrete. The additional ingredients in modern concrete mixes make it impossible to determine concrete quality from slump, however.The common way to slow the hardening of concrete is to employ an admixture termed a retarder.Retarders are primarily intended to counteract the harmful results of heat on the concrete mix; they lower the water/cement ratio only as a side effect. Just remember, don’t use retarders in cold weather.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.

Leave a Reply

Your email address will not be published. Required fields are marked *