Transcript
WORKABILITY AND STRENGTH CHARACTERSTICS OF SUPERPLASTICIZED CONCRETE T. P. Meikandaan Department of Civil Engineering Bharath Uniuversity Chennai 73 ABSTRACT The superplasticizers are a special category of water reducer agent in that they are formulated from materials that allow much greater water reductions. This is achieved without undesirable side effects such as excessive air entrainment or set retardation. The aim of this project is to study the workability and strength characteristics of superplasticized concrete. The investigation is carried out using workability test, compressive test, indirect tensile test and modulus of elasticity test. There are total six batches of concrete mixes, consist of 0% to 4.5% of superplasticizer of each batch. For each batch 6 cubes, 2 beams and 2 cylinders have been cast and cured for test. From the test results it is concluded that what should be the appropriate percentage of superplasticizer that should be added to the concrete so that the compressive strength, tensile strength and flexural strength is increased. 1. Introduction Concrete, in some form or the other, has been in use for more than 6000 years. Babylonians and Assyrians first used a mixture of clay, lime and water. Later civilizations developed these initial mixes. In 1824, Joseph Aspdin invented the Portland cement (PC). But it was only when concrete has been brought into the laboratory that it became the building material of this century. The correlation between the strength of a concrete to its water content by Abram and Power s in the year 1964 studies linking the porosity, the water cement ratio and degree of hydration of the cement to its strength, greatly improved knowledge of the concrete and set the basis for its wide spread use. In the past main objective in production of the concrete was to achieve High Strength Quality. Today, the name of the game is High Performance concrete. There is a distinct difference between the two. The difference is durability. The superplasticizers are a special category of water-reducing agents in that they are formulated from materials that allow much greater water reductions. Or alternatively extreme workability of concrete in which they are incorporated. This is achieved without undesirable side effects such as excessive air entrainment or set retardation. The three major types of raw materials used in superplasticizer. SNF, SMF, and polyacrylates, which also illustrates the three different types of polyacrylates. Minor amounts of other materials are often added such as triethanolamine (to counteract retardation). Tribally phosphate (to cut down excessive air entrainment) and hydroxycarboxylic acid can be blends of two of the main ingredients. ISSN: Page 56 A.Magnin et al. (Dec. 2004) stated that the friction does not follow Coulomb s Law for the specimens tested for studying fresh concrete friction. The principle consists in pressing fresh concrete samples against a moving metal surface and measuring the tangential force. Abel et al. (Dec. 2000) studied about the variability of the setting behavior of concrete and on the relationship between setting of concrete and concrete and the setting of mortar. A sample test is introduced for monitoring setting behaviour of concrete in the field. The method was inspired by the ASTM C 403 penetration resistance method for mortar setting time. CF.Ferraris et al. (Dec. 1998) stated that the ease of placement of concrete depends upon at least two physical properties, the yield stress and plastic viscosity. Currently the most common field test is the slump test and it is related only to yield stress. To determine plastic viscosity the time necessary for the upper surface of the concrete in the standard slump cone 100mm was measured. The apparatus and the test procedure are described. Uchikawa et al. (1995) linked the improvement in fluidity of concretes with later addition of superplasticizers to the increased availability of the admixture in solution. They also found that SNF based chemicals were more sensitive to delayed addition compared to PCE and linosulphonates. DJ.Lawrence (Jan. 1994) studied about the methods to determine the water and cement content in fresh concrete. The subject of determining the cement or water content in fresh concrete was not covered in previous editions of ASTM STP 169. It has been derived from ASTM Test Method. Whiting and Dziedzic (1989) studied that one problem associated with using a high range water reducer in concrete is slump loss. Second generation high range water reducer are claimed not to suffer as much from the slump loss phenomenon as the first generation conventional water reducers do. However, slump loss of flowing concrete was found to be less severe, especially for newly developed admixtures based on copolymeric formulation. 2.Materials and Method Procedure For Compaction Factor Test Weight the empty cylinder accurately and note it. Weight and fix it to the base of the compaction factor apparatus. Weight the following material to prepare concrete for testing. 2.5kg of cement, ISSN: Page 57 4kg of sand and 8.25kg of coarse aggregate. Add water at the rate of 52% by weight of cement to it and mix them thoroughly on a platform. Place the sample of concrete to be tested in the upper hopper, up to the brim. After the concertinas come to rest open the trap door of the lower hopper and allow the concrete to fall into the cylinder. This brings concrete into stranded compaction. Trim off the excess concrete remaining above the top level of the cylinder. Wipe off the outside of the cylinder. Weight the cylinder full of concrete. Take this weight as the weight of partially compacted concrete. Empty the cylinder, after that, and again fill the cylinder with concrete in five layers. The layers being rammed heavily so as to obtain full compaction. Strike off the compacted excess concrete above the top of the cylinder carefully and weight the cylinder with concrete. Take this weight as fully compacted concrete. Compacting factor = weight of partially compacted / weight of fully compacted concrete. Procedure For Vee-Bee Consistometer Test Place the sheet metal slump cone in the cylindrical container of the consistometer. Fill the cone in 4 layers, each approximately one quarter of height of the cone. Tamp each layer with 25 strokes of the rounded end of the pumping rod. The stroke are distributed in a uniform manner over the inner surface of the cone and for 2 and subsequent layer the tamping bar should penetrate into the under laying layer. After the top layer has been rode, level the concrete with trowel so that the cone is exactly filled. More the glass disc attached to the swivel arm and places it just on the top of the slump cone in cylindrical container. Adjust the glass dies so as to touch the top of the concert cone and note the initial reading on the graduate rod. Remove the cone from the concrete from the cone immediately by raising it slowly and carefully in the vertical direction lower the transparent disc on the top of concrete. Note down the reading on the graduated rod. Determine the slump by taking the difference between the readings on the graduated rod recorded. Switch on the electrical vibrations and start the stopwatch. Allow the concrete to re-mould by spreading out in the cylindrical container. The vibrations are continued until the concrete is completely re-moulding i.e. the surface become horizontal and the whole surface adheres uniformly to the transparent disc. Record the time required for complete remolding in seconds which measures the workability expressed as the no. of vee-bee seconds. TESTS ON HARDENED CONCRETE Procedure For Compressive And Tensile Strength Test Preparation Of Cubes And Cylinder Fill in the concrete into the mould of known size and compact it. The concrete using tamping rod or vibrating table. In case of the cylindrical specimens the top surface of the specimens should be capped with a cement past of stiff consistency, the method adopted for this is as follows. Leave the concrete in the cylindrical mould for about 2 to 4 hours. Scrap the top surface of the concrete little and apply on it the cement paste of stiff consistency (also prepared 2 to 4 hours earlier). Place the steel cover plate on the cylinder and press hard with the taming motion till it rests on the mould and leave it there after 24 hrs or till the time specimen is taken out of the mould. Submerge the specimen (after taking out from the mould) in clean, fresh water and leave there till just prior to test i.e., 7days and 28 days. Remove the specimen from the water and wipe it clean. Note down the dimensions of the specimen to the nearest 0.2mm and weight it accurately. Cleaning the bearing surfaces of the testing machine and place the specimen in such a manner that the load shall be applied to opposite sides of cube as cast and not to the top and ISSN: Page 58 bottom. After aligning the axis of the specimen carefully apply the load slowly at approx. 140 kg/sq.cm/min. till the cube breaks. Record the maximum load and appearance of load failure. Procedure For Flexural Strength Test The specimen is prepared and after curing it shall be placed in the experimental setup in such a manner that the load shall be applied to the uppermost surface. The axis of the specimen shall be carefully aligned with the axis of the loading device no packing shall be used between the bearing surface of the specimen and the rollers. The loading shall be applied without shock and it shall be increasing continuously such that the extreme fiber stress increases at approx. 7kg/sq.cm/min that is at the rate of 18 N/min for 100mm specimen. The loading shall be increased until the specimen fails and the maximum load applied to the specimen during the test shall be recorded. The flexural strength of the specimen shall be expressed as modulus of recapture which, if a equals to the distance between the line of fracture and the nearer support measured on the center line of the tensile side of the specimen in cm, shall be calculated to the nearest 0.5kg/sq.cm as: When, a 200mm for 150 mm specimen. A 133mm for 100mm specimen there f.b = (p x l)/(b x d 2 ). When, 170mm a 200mm for 150mm specimen. 110mm a 133mm for 100mm specimen. Then f.b = (3p x a)/(b x d 2 ). Where, b = measured with in mm of the specimen. d = measured depth in mm of the specimen at the point of failure. l = length in mm of the span on which the specimen is supported. p = maximum load in N applied to the specimen. When, a 170mm for 150mm specimen. a 110mm for 100 mm specimen, then the results of the test shall be discarded. 3.Results and discussion The values of compaction factor for the specimens with different percentage of super plasticizers have been tabulated in table 1. The graph is drawn between dosage of superplasticizer vs compaction factor and represented in figure 1. ISSN: Page 59 TABLE 1.Values Of Compaction Factor SL.NO. PERCENTAGE OF SUPERPLASTICIZER ADDED INTO THE NORMAL CONCRETE COMPACTION FACTOR 1. 0% of superplasticizer % of superplasticizer % of superplasticizer % of superplasticizer % of superplasticizer % of superplasticizer Fig1.Graphical representation of compaction factor value vs percentage of superplasticizer added ISSN: Page 60 The values of vee-bee test for the specimens with different percentage of super plasticizers have been tabulated in table 2. The graph is drawn between dosage of superplasticizer vs vee-bee test and represented in figure 2. Table 2 Values Of Vee-Bee Test SL.NO. PERCENTAGE OF SUPERPLASTICIZER ADDED INTO THE NORMAL CONCRETE TIME REQUIRED (IN SEC.) 1. 0% of superplasticizer % of superplasticizer % of superplasticizer % of superplasticizer % of superplasticizer % of superplasticizer 23 Fig 2.Graphical representation of vee-bee test value vs percentage of superplasticizer added ISSN: Page 61 The values of 7days Compressive Strength of Concrete for the specimens with different percentage of super plasticizers have been tabulated in table 3. The graph is drawn between dosage of superplasticizer vs Compressive Strength and represented in figure 3. Table 3. 7days Compressive Strength Of Concrete SL. NO. PERCENTAGE OF SUPERPLASTICIZER ADDED INTO THE NORMAL CONCRETE COMPRESSIVE STRENGTH (N/mm²) 1. 0% of superplasticizer % of superplasticizer % of superplasticizer % of superplasticizer % of superplasticizer % of superplasticizer ISSN: Page 62 Fig 3.Graphical representation of 7days compressive strength vs percentage of superplasticizer added ISSN: Page 63 The values of 28 days Compressive Strength of Concrete for the specimens with different percentage of super plasticizers have been tabulated in table 4. The graph is drawn between dosage of superplasticizer vs Compressive Strength and represented in figure 4. Table 4. 28days Compressive Strength Of Concrete SL. NO. PERCENTAGE OF SUPERPLASTICIZER ADDED INTO THE NORMAL CONCRETE COMPRESSIVE STRENGTH (N/mm²) 1. 0% of superplasticizer % of superplasticizer % of superplasticizer % of superplasticizer % of superplasticizer % of superplasticizer ISSN: Page 64 Fig 4. Graphical representation of 28days compressive strength vs percentage of superplasticizer added The values of 7days Flexural Strength Test for the specimens with different percentage of super plasticizers have been tabulated in table 5. The graph is drawn between dosage of superplasticizer vs Flexural Strength and represented in figure 5. ISSN: Page 65 Table.5 7days Flexural Strength Test SL. NO. PERCENTAGE OF SUPERPLASTICIZER ADDED INTO THE NORMAL CONCRETE FLEXURAL STRENGTH (N/mm²) 1. 0% of superplasticizer % of superplasticizer % of superplasticizer % of superplasticizer % of superplasticizer % of superplasticizer Fig 5.Graphical representation of 7days flexural strength vs percentage of superplasticizer added ISSN: Page 66 The values of 7days Flexural Strength Test for the specimens with different percentage of super plasticizers have been tabulated in table 6. The graph is drawn between dosage of superplasticizer vs Flexural Strength and represented in figure 6. Table 6. 28days Flexural Strength Of Concrete SL. NO. PERCENTAGE OF SUPERPLASTICIZER ADDED INTO THE NORMAL CONCRETE FLEXURAL STRENGTH (N/mm²) 1. 0% of superplasticizer % of superplasticizer % of superplasticizer % of superplasticizer % of superplasticizer % of superplasticizer Fig. 6. Graphical representation of 28days flexural strength vs percentage of superplasticizer added ISSN: Page 67 The values of 7days Tensile Strength Of Concrete for the specimens with different percentage of super plasticizers have been tabulated in table 7. The graph is drawn between dosage of superplasticizer vs Tensile Strength and represented in figure 7. Table 7. 7days Tensile Strength Of Concrete SL. NO. PERCENTAGE OF SUPERPLASTICIZER ADDED INTO THE NORMAL CONCRETE TENSILE STRENGTH (N/mm²) 1. 0% of superplasticizer % of superplasticizer % of superplasticizer % of superplasticizer % of superplasticizer % of superplasticizer ISSN: Page 68 Fig.7 Graphical representation of 7days tensile strength vs percentage of superplasticizer added ISSN: Page 69 The values of 28days Tensile Strength Of Concrete for the specimens with different percentage of super plasticizers have been tabulated in table 8 The graph is drawn between dosage of superplasticizer vs Tensile Strength and represented in figure 8. Table.8 28days Tensile Strength Of Concrete SL. NO. PERCENTAGE OF SUPERPLASTICIZER ADDED INTO THE NORMAL CONCRETE TENSILE STRENGTH (N/mm²) 1. 0% of superplasticizer % of superplasticizer % of superplasticizer % of superplasticizer % of superplasticizer % of superplasticizer ISSN: Page 70 Fig. 8 Graphical representation of 28days tensile strength vs percentage of superplasticizer added ISSN: Page 71 3.Conclusion The following conclusions are observed from the test results. The workability of the concrete such as compaction factor and vee-bee degree increases with increase in percentage of superplasticizer (at 1.5%).The compressive strength of the concrete increases by 56.95% that to conventional concrete at 2.5% of superplasticizer added.the flexural strength of the concrete increases by 1.01% that to conventional concrete at 3.5% of superplasticizer added. The tensile of the concrete is increases by 9.54% that to conventional concrete at 1.5% and 2.5% of superplasticizer added. In general the properties of fresh concrete such as compaction factor and vee-bee degree are increasing with increase in percentage of superplasticizer (at 1.5%).In general the properties of hardened concrete such as compressive strength, Tensile strength and Flexural strength are increasing with increase in percentage of superplasticizer (at 2.5%). It is observed that the optimum dosage of superplasticizer to be used is 1.5%. REFERENCES [1] IS: 2386 (Part I IV) , Methods of Test for Aggregates for Concrete, Bureau of Indian Standard, [2] IS: , Coarse and fine aggregate from natural sources for concrete, Indian Standards Institution, [3] IS: , recommended guidelines for concrete mix design, Indian Standards Institution, [4] IS: (Reaffirmed 1999) Methods of Sampling and Analysis of Concrete, Bureau of Indian Standards, [5] IS: (Reaffirmed 1999) Edition 1.2 ( ) Methods of tests for strength of Concrete, Bureau of Indian Standards, [6] Concrete Technology by M L GAMBHIR. Tata McGraw-Hill Company Limited New Delhi. [7] Sachithanantham P,2011 Experimental study on the Effect of Retempering on Properties of Cement Concrete, Bharath University, Selaiyur, Chennai [8] Magnin.A, Vanhove.Y and Djelal.C, 2004 A device for studing fresh concrete friction, volume 26, page 7. [9] Abel J.D, Hover.KC, Field study of the setting behavior of fresh concrete volume 22, page 8. [10] Ferraris.CF, de Larrard.F Modified slump test to measure rheological parameters of fresh concrete volume 20, page 7. [11] Lawrence.D Evaluation of selected procedures of the rapid analysis of fresh concrete [12] Uchikawa, Hanehara and Sawaki, 1995, The role of steric repulsive force in the dispersion of cement particles in fresh paste preparation with organic admixture, cement and concrete research, volume 27, page ISSN: Page 72
