Fresh Concrete Properties PDF

Workability Fresh Concrete Segregation Properties Bleeding Main Text: Properties of Concrete, A.M. Neville, Longman, 1995 Concrete: Mic...

Workability Fresh Concrete Segregation Properties Bleeding Main Text: Properties of Concrete, A.M. Neville, Longman, 1995 Concrete: Microstructure, Properties and Materials, Mehta & Monteiro, McGraw-Hill, 2006 Advanced Concrete Technology, Zongjin LI, John Wiley & Sons, 2011 1  Fresh Concrete Concrete mixture that has not lost its plasticity. Covers the hydration Final set is regarded as the start of stages I and II. complete loss of plasticity, hardening. Initial set indicates the beginning of a ❖ Formation of hydration noticeable stiffening products over the time leads to: Provides time for transportation, placing, compaction and ▪Stiffening ▪Setting finishing. ▪Hardening (strength gain)  Importance of Compaction Compaction is the process which expels entrapped air from fresh concrete and packs the aggregate particles together to increase the density of concrete. Important to compact fully because the air voids affect the strength of concrete. Difficult to compact and the strength reduces Thus, it is vital the fresh concrete to be workable. The potential strength and durability of concrete dependent on the degree of its ## the fresh concrete influences the properties compaction of hardened concrete. Workability 4  Workability The fresh concrete property, that indicate the ease with which a concrete mixture can be handled without segregation. Consistency Cohesiveness This property including consistency and cohesiveness. – Consistency is to indicate the degree of mobility or the degree of fluidity. It indicates the wetness of the mix, a major factor in determine the workable concrete. Workable – Cohesiveness is a measure of compactibility and finishability. 5  Workability Factors Primary Water Factors Content Weather Aggregate Condition Properties Workability Admixture Grading Aggregate- Sand- Secondary Cement Aggregate Factors Sources: Properties of Concrete, A.M. Neville, Longman, 1995 Concrete: Microstructure, Properties and Materials, Mehta & Monteiro, McGraw-Hill, 2006 Advanced Concrete Technology, Zongjin LI, John Wiley & Sons, 2011 6 Water Content Water plays a role of lubricant in the fresh concrete Higher the water content, the higher will be the fluidity of concrete. Lower water content means less water, or more cement and lower workability. workability becomes low, the concrete becomes difficult to compact and the strength reduces Excess of water in concrete also has some disadvantages: – Strength of concrete may reduced. – Cause bleeding in concrete – Segregation, where cement slurry may pass through the joints of formwork. 7 8  Aggregate Properties Size Shape Texture The bigger the size of The shape of aggregates Rough textured aggregate aggregate, less is the have great influence on has more surface area than surface area. Hence, less workability. smooth textured rounded water is required for Rounded shaped aggregate of same volume. wetting the surface and aggregates requires Hence, smooth textured less paste is required to comparatively less paste aggregate will show better lubricate the surface of for lubrication and gives workability while rough aggregates. better workability. Less textured aggregate will give However, if the volume of friction resistance. poor workability. coarse aggregate is large, Angular aggregates, having minimum void space is more surface area, requires available, minimum paste more paste for lubrication Further, smooth textured available, thus the fresh and reduces workability. aggregate, less frictional concrete is likely to be Similarly, flakiness and resistance and contributes to harsh and unworkable. elongation of aggregates higher workability. also reduces workability. 9  Grading The grading of aggregate has greater effect on workability of concrete. A better grading has less void in it. Less void, more paste is available Well-graded for a better lubricating effect. has a gradation of particle sizes from the finest to the coarsest. A slice of a core of well-graded More paste, the mixture becomes aggregate concrete shows a packed field of many different particle sizes. cohesive, which prevents Poorly graded aggregate is characterized by small variations in size. This means that the particles segregation of particle and less pack together, leaving relatively large voids in the amount of compacting is concrete. Gap-graded aggregate consists of coarse required. aggregate particles that are similar in size but A well graded aggregate is one significantly different in size from the fine aggregate. Gap-graded concrete shows a fine which has the least amount of aggregate interspersed with slightly isolated, large aggregate pieces embedded in the fine voids in a given volume. aggregate. 10 Sand-Aggregate ratio If the proportion of fines is increased in relation to the coarse aggregate, the overall aggregate surface area will increase. If the surface area of the aggregate has increased, more surface area and more contact area causing more resistance. the water demand will also increase, the water cement ratio will increase. Increase in water cement ratio, the compressive strength will decrease. Smaller CA, high ratio of S/A are needed 11 Aggregate-Cement ratio High A/C ratio, less workability due to less cement. Less cement mean less water, so the paste is stiff. 12  Admixtures Weather Condition Chemical admixtures Workability is reduced at higher Use of plasticizers and super temperatures. plasticizers greatly improve the If temperature is high, evaporation workability. increases, workability decreases. Use of air entraining agent produces If wind is moving with greater air bubbles which acts as a sort of velocity, the rate of evaporation also ball bearing between particles and increase. This reduces the amount of increases mobility and workability water and ultimately reducing workability. Mineral admixtures The fine particles of pozzolan materials increase the surface area, however: glassy particles provide better lubricating effects and improve workability. 13 Measurement of Fresh Concrete Slump Test Consistency Flow Test Cohesiveness Compacting Factor Test Vebe Test Bleeding Test Other ….. …… 14  Slump Test Definition A slump test is most widely used. A method used to determine the consistency or fluidity of concrete. Consistency or fluidity of concrete is an important component of workability and refers in a way to the wetness of the concrete. Slump Test is related with the ease with which concrete flows during Measure the slump by determining the vertical difference placement between the top of the mold and the displaced original center of the top surface of the specimen Principle The slump test result is a measure of the behavior of a compacted inverted cone of concrete under the action of gravity. It measures the consistency or the wetness of concrete. 15 Type of Slump ❖ Collapse Slump A collapse slump where the concrete collapses completely, which means that the mix is too wet or high workability mix, for which slump test is not appropriate. ❖ Shear Slump A shear slump the top portion of the concrete shears off and slips sideways. OR If one-half of the cone slides down an inclined plane. ▪ If the shear slump persists, as may the case with harsh mixes, this is an indication of lack of cohesion of the mix. ▪ If a shear or collapse slump is achieved, a fresh sample should be taken and the test is repeated. ❖ True Slump In a true slump the concrete keeping more or less to shape. ▪ This is the only slump which is used in various tests. ▪ Mixes of stiff consistence have a Zero slump, so that in the rather dry range no variation can be detected between mixes of different workability. 16 Slump (mm) 0 - 20 20 - 40 40 - 120 120 - 200 200 - 220 Consistency Dry Stiff Plastic Wet Sloppy EN 206-1:2000 identifies five classes of slump 17 18  Flow Test Definition The flow table test or flow test is a method to determine the consistence of fresh concrete.  If the consistence is not correct, the concrete will not have the desired qualities once it has set, particularly the desired strength.  If the concrete is too wet, it may result in cavities within the concrete which leads to corrosion. Cavities will also lower the stress the concrete is able to support. Principle This test gives the ability of concrete to flow under the gravitational force. 19 Percent of 0 – 20 20 – 60 60 – 100 100 – 120 – Flow % % % 120 % 150 % Consistency Dry Stiff Plastic Wet Sloppy 20 Compacting Factor Test The test is measure the degree of compaction. The test required measurement of the weight of the partially and fully compacted concrete and the ratio the partially compacted weight to the fully compacted weight, which is always less than one, is known as compacted factor. For the normal range of concrete the compacting factor lies between 0.8 - 0.92 21 Workability Slump (mm) C.F Uses Very Low 0 - 25 0.78 Roads - Pavements Low 25 - 50 0.85 Foundations Concrete Medium 25 - 100 0.92 Reinforced Concrete Reinforced Concrete High 100 - 175 0.95 (High Reinforcement) 22 Vebe Test 23  Self Compacting Concrete Self compacted concrete is highly engineered concrete with much higher fluidity without segregation and is capable of filling every corner of formwork under its self- weight. Thus SCC eliminates the vibration for the compaction without affecting its https://www.youtube.com/watch?v=JIa7hhDgLUc engineering properties. 24 Self-Compacting Concrete – Fresh Properties ❑ Filling ability (excellent deformability) - Flows easily at suitable speed into formwork ❑ Passing ability (ability to pass reinforcement without blocking) -passes through reinforcements without blocking ❑ High resistance to segregation - the distribution of aggregate particles remains homogeneous in both vertical and horizontal directions ▪ Static segregation due to gravity, vertical direction ▪ Dynamic segregation due to flow, horizontal direction 25 Method- Properties 26  Flow Tests of SCC L-Box Test Slump J-Ring Flow Test Test V- Orimet Funnel Test Test U-Box Test 27 Classification 28 Thank You 29 30