STUDY OF MIX DESIGN FOR HIGH PERFORMANCE CONCRETE

Transcription

1 STUDY OF MIX DESIGN FOR HIGH PERFORMANCE CONCRETE SACHIN PATIL Abstract In present research work a thorough study and analysis of Mix Design of High Performance Concrete has been done. Initially VSI Coarse Aggregate ( having size 20 & 10 mm ) and VSI Crushed Stone Sand, Pozzocrete-100 and Pozzocrete-60 Fly Ash Samples and Microsilica 920 D are collected. In the first phase of research study, for High Performance Concrete Mix design, total 27 trial mixes have been carried out by using 10 mm VSI aggregate along with 75%,70%,65% Cement and fly ash replaced in three different percentage i.e. 25, 30 & 35 % and microsilica replaced in two different percentage i.e. 5% & 10%. In second phase using combination of 20 mm and 10 mm VSI aggregate, 8 trial mixes has been carried out. In Second phase P-60 & P-100 type of fly Ash and microsilica is utilized in different percentage to achieve the targeted strength (M-80). Initially aggregate proportioning was done on maximum density approach. Trial mixes were carried out to fix the water content, sand percent and required slump. After finalizing the water content, sand percent and slump, final mixes were run and specimens casted. Cubical specimens of size 150 mm X 150 mm were cast for compressive strength, 150 mm X 150 mm cylinders for permeability test. The specimens were tested at 7 & 28 days age for Compressive strength and 28 days age for Permeability test. Results of all the tests were thoroughly studied and analyzed. Keywords Fly ash, Microsilica, Aggregate. I. INTRODUCTION American Concrete Institute defines High Performance Concrete as Concrete meeting special combination of performance and uniformity requirements that cannot always be achieved routinely using conventional material and normal mixing, placing and curing method. High Performance Concrete can be termed as concrete having grade greater than M-45 (As IS: caters for the concrete up to the grade M- 40). Also it has to perform satisfactorily on properties like strength, permeability, workability, durability and cohesive mix which give a response to long term environmental effects. As far as Water Resources Department is concerned, mostly dams are designed as solid gravity dam. Therefore High Performance Concrete with greater strength may not be required while designing solid gravity dams. However different parts of dam (Spillway Bridge) and big structure on canal attract High Performance Concrete for thinner and economical sections. In view of the above it was thought of to develop a mix having characteristic strength of 80 MPa. II. OBJECTIVES 1) To find the optimum % of mineral admixture like fly ash and microsilica this is to be used in High Performance Concrete mix for given cementious content. 2) To develop M-80 grade of concrete within cement consumption limit set by IS: (maximum cement is 450 kg/cum). 3) To make ready reference for various grades of concrete above M-45 grade of Concrete. 4) To make a database of High Performance Concrete, this will be useful for further High Performance Concrete research studies. III. METHODOLOGY 1) Collection of materials. 2) Testing of materials for their physical & chemical properties. 3) Proportioning of aggregates on maximum density approach. 4) Mix design calculations for given cementitious content by blending of fly ash and microsilica in different percentage. 5) Finding water content for a given mix. 6) Calculating fine aggregate ( crushed sand ) %. 7) Fixing the % of various sizes of coarse aggregate ( i.e , mm ) based on maximum density approach. 8) Carry out trial mixes to get required slump & homogenous concrete mix without honeycombing & segregation. 9) Casting of samples for various cementitious contents with different percentage of fly ash and microsilica. 10) Testing of samples at 7 & 28 days age. 11) Results and discussions. IV. MATERIALS 1) Cementitious materials: It is a combination of cement and fly ash, micro silica in certain specified %. 2) Cement: Ultratech OPC 53 grade cement is used in this study. It is tested for physical properties as per IS : 12269: ) Fly ash: P-100 and P-60 type of Fly ash were used in High Performance Research 104

2 Study. The physical & chemical properties are tested as per IS : 3812: ) Microsilica: 920 D Densified microsilica were used in High Performance Concrete Research Study. 5) Fine Aggregate (Crushed sand): For all the High Performance Concrete mixes 100 % VSI crushed sand was used. This materials are tested for physical properties as per IS : 383 : ) Coarse Aggregate: VSI Coarse aggregate having size 20 mm and 10 mm was used and tested for physical properties as per IS : 383 :1970. Coarse aggregates were graded using maximum density approach and final proportion are as follows; 20 mm to 10 mm : 60 % 10 mm to 4.75 mm : 40 % 7) Admixture : In High Performance Concrete research study water cement ratio is very low, to achieve the desired workability and strength, a powerful retarding admixture (Super Plasticizer) Master Glenium Sky 8855 was used, It satisfies requirements of IS 9103 & ASTM C494 : Type B & D. 8) Water : Potable water is used for mixing the concrete which is free from injurious amounts of oil, acids, alkalis, salts, sugar, organic materials or other substances that may be deleterious to High Performance Concrete. V. MIX DESIGN It was required to make a concrete of grade M-80. The slump required was to the tune of 75 to 100 mm. 1) In this research study mix proportions of different water cement ratio viz, 0.15, 0.20, 0.22, 0.25 and 0.30 included. 2) For every water cement ratio cement is replaced by fly ash and microsilica is on weight basis keeping cement in the limit 450 kg/m 3 as per IS: ) For above study the proportion of coarse aggregate and fine aggregate was determined in the laboratory by running trial mixes for various combinations. 4) The amount of coarse and fine aggregate used were 60% and 40% by mass of total aggregates and the amounts of different ingredients were determined by using the solid volume formulas. 5) Based on various trial mixes, super plasticizer dosage by weight of cement is used to yield desired slump of concrete varied 75 to 100 mm. The dosage has been kept in the range of 0.5 to 1.5 % of Cementitious content. (In lieu of limit of 2 % respectively by weight of cementitious materials as per IS: VI. TESTING OF SPECIMENS 1) The specimens cast for various tests were of size, Compressive strength test: 15 cm x 15 cm cubes. Permeability test: 15 cm dia x 15 cm ht. Cylinders. 2) The specimens were cast in three equal layers of concrete each layer being compacted on a vibrating table. Mixing time for every mix was kept as 3 minutes to get uniform mix. Then the specimens were cured in curing tank until the day of testing. Compressive Strength Test ( as per IS ) Permeability Test ( as per IS : ) VI. OBSERVATIONS DURING HPC STUDY 3) There is a little variation in water content for all the mixes. 4) Mix Using P-100, P-60 Fly Ash and Microsilica is flowy and homogeneous. 5) The Pozzocrete 100 mix and Pozzocrete was found to be highly cohesive and easy to work. 6) Mix using combination of P-100 & P-60 with microsilica is harsh and sticky. 7) Specimens casting using P-100, P-60 & microsilica have best surface finish. 8) At every trial mix, constant flow measured in the range mm. 9) The Water Demand increases as the microsilica added in the mix. 10) Specimen show cup and cone appearance after failure for compressive strength. VII. RESULT AND DISCUSSIONS Abstract for test results are shown in table 1 and analysis of the test results are as below: 105

3 Table 1. Abstract of Test Details For Various Trial Mixes 8.1 Compressive Strength 1) From graph of 7 D & 28 Days Compressive Strength vs. water cement ratio the Compressive Strength increases as % of cement in cementitious content decreases. 2) All the combinations ( Type A, Type B & Type C ) shows 28 days compressive strength greater than 70 Mpa with a maximum of 78 Mpa for water cement ratio ) For 0.20 water cement ratio 28 days compressive strength lies between 65 Mpa and 75 Mpa as well as for 0.25 water cement ratio 28 days compressive strength lies between 64 Mpa and 68 Mpa. 4) From graph of 7 Days Compressive Strength vs. water cement ratio the increase in % of microsilica (from 5 % to 10 % ) increase in compressive strength is noticed. 5) From Graph of 28 Days Compressive Strength vs. water cement ratio, Mix F shows the compressive strength is greater than 78 Mpa for 0.20 w/c ratio and for w/c ratio 0.25c ompressive strength is greater than 75 Mpa. 6) Mix D and E Shows compressive strength greater than 75 Mpa for 0.20 water cement ratio which however drops up to 67 Mpa for water cement ratio ) Mix A, B and C shows compressive Strength greater than 66 Mpa at water cement ratio ) From graph of 28 Days Compressive Strength vs. cementitious material, the target of 80 Mpa the laboratory strength work put to 89 Mpa. The maximum strength with fly ash (P-60 and P-100) is 85 Mpa and that with blending of fly ash and Microsilica is 87 Mpa. 106

4 These laboratory strength shows the field strength with fly ash is 78 Mpa and that with blending with fly ash and Microsilica is 80 Mpa which is not equal or closer to the target strength. It can be said that these mixes (A & B ) will give a field strength 75 Mpa ( 94 % of targeted strength i.e 89 Mpa ). Mixes F & G will give a field strength 78 Mpa (97 % of targeted strength i.e 89 Mpa). 107

5 8.2 Permeability 1) Permeability is very important test of any water retaining structure. Permeability is also indirectly related to the durability of concrete. 2) All the HPC mixes are very encouraging as for a pressure of 10 Kg/cm 2 there is absolutely no leakage from none of the samples for cementitious content. CONCLUSIONS 1) Addition Of processed Fly Ash improves the compressive strength of the Concrete. Percentage of compressive strength gain from 7 days to 28 days of concrete mix A, B and C is 8 %, 9% and 10 % respectively. 2) Keeping the quantum of cement (450 Kg/m 3 ) in permissible limits High Grade Concrete can be produced. 108

6 3) Use of VSI metal & artificial sand clubbed with a powerful chemical admixture like Master Glenium 8855 provides freedom to the producer of concrete to limit water content in the mix and at the same time keeping water cement ratio as low as ) The aforesaid combination also provides required flow for pumpable concrete. 5) Addition of High Grade Concrete in the structural design will reduce the size of the members and thereby reducing quantum of cement and aggregate in the mix. This will eventually reduce carbon footprints. 6) The present study inspires to explore further in this direction. Therefore as sequel of this study will shortly be in hand. 7) It is observed that these mixes have adequate flow and with some improvement and addition can be converted in to self compacting concrete. As everybody knows applicability of self compacted concrete is increasing at tremendous rate. In case of secondary concrete for radial gates and other gates in dams this type of self compacted concrete may prove effective and more useful. REFERENCES [1] Mix Design Report No. 13/ Of Grade M-50 ( 20 MSA ). [2] Indian Standard: Plain and Reinforced Concrete- Code Of Practice. [3] Indian Standard: Guidelines for Concrete Mix Design. [4] Indian Standard: Specifications for Coarse and Fine aggregate. [5] Indian Standard: 1489 ( Part-I ) 1991Specifications for Portland Pozzolana Cement. [6] Indian Standard : Specification For Concrete Admixtures [7] Concrete Technology: Author M.S. Shetty [8] Properties Of Concrete by A.M. Neville. 109