SUPER POZZOLANS :RICE HUSK ASH & MICROSILICA.

High Performance Concrete. Concrete having High Workability and Very High Early strength. Concrete having High Workability and Long Term Durability High early strength is not necessary , but high ultimate strength is an additional feature of these concrete mixtures

Effect Of MS & RHA. The incorporation of fine particles of MS and RHA even in small amounts (5% to 10% cement replacement ) 1) Enhance Workability 2) Improve strength 3) Provide protection against Chemical Attack 4) Prevent Reinforcement Corrosion Thus the overall Durability of concrete is enhanced.

Mechanism by which MS & RHA particles enhance Workability & Impermeability. The MS & RHA particles segment the Bleed Water channels thus controlling 1)Segregation 2)Bleeding hence improve the workability. Impermeability The pozzolonic reaction (conversion of calcium hydroxide to calcium hydride silicates ) fills up the empty spaces &causes densification (pore refinement or conversion of open pore structure to closed pore structure. ) and strengthening of the microstructure. At 10% replacement levels 100nm size pores in Hydrated cement paste get reduced to 1-10nm thus improving the impermeability.

IS 456:2000 5.2.1.2 Silica Fume Silica Fume conforming to a standard approved by the deciding authority may be used as part replacement of cement provided uniform blending with cement is ensured. 5.2.1.3 Rice Husk Ash Rice Husk Ash giving required performance and uniform characteristics may be used with the approval of the deciding authority.

Micro silica:Sources & Characteristics MS is a by product of the induction arc furnaces in the Silicon metal & Ferro Silicon alloy industries. Reduction of Quartz mineral to Silicon at a Temp up to 2,000 deg C produces SiO vapors at low temp oxidize & condense into tiny spherical particles of non crystalline Silica. Avg. Particle size 0.1 micron meter. Surface Area 20 –25 m2 / gm. It is available in 3 forms a)Powder Form b)Compacted or Granulated c)Liquid Slurry.

The MS under consideration was obtained from Elkem Industries The MS under consideration was obtained from Elkem Industries. The specifications of which are as under:- CHARACTERICTICS MICRO SILICA (MS) Chemical composition in percentage SILICA 84.9 CARBON 1-2 ALKALIES 0.5-2 MINERALOGY CRYSTALLINITY Non-Crystalline PARTICLE CHARACTERISTICS AVERAGE PARTICLE SIZE 0.1 – Micron Meter. SHAPE & TEXTURE Agglomerated Spheres.

Rice Husk Ash :-Sources & Characteristics Rice Husks are the shells produced during the dehusking operation of paddy rice and when burnt under controlled condition give RHA which is highly pozzolonic & suitable for use in lime –pozzolona mixes & for portland cement replacement. Rice Husk burnt at a controlled temperature of 500-600 deg C gives amorphous silica . 200 kg of Husk yields approximately 40 kg of highly siliceous ash. Also the Hard burnt Ash obtained from the parboiling mills also gives reactive siliceous ash when ground for 7 hrs.

The RHA under consideration was obtained from-ORISSA The RHA under consideration was obtained from-ORISSA.During the manufacturing process it was treated for moisture content and was ground to 25 micron particle size. The specifications are as under. The Lime Reactivity for the ash was found to be 4.3 Mpa.

CHARACTERISTICS RICE HUSK ASH Chemical composition in % SILICA 88.44 CARBON 5.06 ALKALIES 5 MINERALOGY CRYSTALLINITY NON CRYSTALLINE PARTICLE CHARACTERISTICS AVERAGE PARTICLE SIZE 25 MICRON SHAPE & TEXTURE. IRREGULAR, CELLULAR.

Trials and Tests. About 150 cubes were cast during the trial with the following MIX Details Aggregate Cement ratio (A/C) = 4.2 Coarse Aggregate 1 = 20% Coarse Aggregate 2 = 30% Fine Aggregate = 50% Admixture = 1% (Forsoc-SRV 430) MS percentages 5% and 10% RHA percentages 5% and 10% Target Slump 100 mm 50 cubes of 150*150 mm were cast from each mix .

Tests The cubes have been tested for compressive strength at 7, 28 ,56 and 90 days. Water Permeability test (DIN 1048 Part 5)at 28 days Chloride Penetration test (ASTM Standard Method C 1202) Heat of Hydration test.

DISCUSSION OF RESULTS

Compressive Strength

Compressive Strength

Water Permiability (at 28 days) Opc + 10% Rha Opc + 5% Rha Opc + 10% Ms Opc + 5% Ms Opc

RCPT At 90 Days 3791 1535 1162 OPC+10%RHA

Heat of Hydration Temp In Deg C Time in sec