MEASURING PERMEABILITY OF CONCRETE - THE CHALLENGES AND

SOLUTIONS IN THE RESEARCH EXPERIENCE

ByNarain Hariharan

Aishwarya Baranikumar

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Outline of the presentation

Research objective Purpose of the Paper Importance of Permeability in Concrete Experiment procedure Challenges in Various Stages of Research Results and Discussion Conclusion

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Research Objective Measure the permeability of Cement paste

(w/c=0.45 and 0.40) @ 7 days after mixing, using the Hollow Cylinder Dynamic Pressurization (HDP) test.

Compare and test the results of the 2 cases for statistical significance.

Establish the importance and impact of w/c ratio on permeability.

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Purpose of the Paper

To discuss the results obtained in the research study.

To elaborate on the various challenges faced during the experimental process.

Discuss the solutions and measures adopted to tackle the challenges.

Bring to light the importance of precision and accuracy in performing laboratory tests.

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Importance of Permeability in Concrete

Diffusion, osmosis, adsorption, permeability- all affect durability of concrete.

Permeability- seepage of water through the pores in concrete.

Results in loss of durability. Main reason why concrete is taken out of

service. Early age permeability of concrete- very low but

critical. Accurate measurements required.

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Experiment procedure Mold details

• Hollow cylindrical mold• Diameter- 2 in.• Height - 8 in.• Batch 1: w/c=0.40• Batch 2: w/c=0.45• 0.20 in. diameter plastic rods in center to make hollow samples.

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Sample details Batch 1: w/c = 0.4 , Type III OPC Batch 2: w/c = 0.5 , Type III OPC Mixed in accordance with ASTM C305-99. Samples demolded 15-18 hrs. after mixing. Immediately placed in water @ room temperature

till testing. Tested for Permeability using HDP after 7 days.

Pressure – 920-1000 psi Test time – 24 hrs. Gives relaxation time Ʈ from strain-time history

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HDP Test Apparatus

Reference: Correlation of Radial Flow-Through and Hollow CylinderDynamic Pressurization Test for Measuring PermeabilityChristopher A. Jones and Zachary C. Grasley

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Challenges in Various Stages of Research Mold Preparation

Combined two 2”x4.2” standard molds Cut open the closed end of one mold and

combined with another mold using duct tape to get 2”x8” mold

Hollow mold?? Reflector sticks drilled through center of base To hold the stick in place– Aluminum plate same

dimensions as base used at top To remove stick – cut longer than 8”

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Sample Demolding Process Removing the reflector stick – critical; after initial

set and before final set ( 3-4 hrs.) Blowing compressed air- ineffective for hollow

geometry Removing the duct tape and separating the two

molds by twisting/shearing – breaks the sample, weak zone at interface

Hence, the mold was cut vertically after removing the tape and the two molds were bent out without damaging the sample

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HDP Test Setup Sample glued to steel caps using epoxy Height adjustments made by threading and

bending the steel rod having LVDT setup LVDT extremely sensitive – challenge to position

the core and coil in line Very important for accurate measurements.

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HDP Testing Risks associated with High Pressure Pressure range in HDP - High (1000 psi) Pressure Removal dangerous Can result in leaks and spills Damage the specimen

Precautions – Step-wise depressurization; minimum 3 levelsSecurely check and fasten all connections

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Other Scope of Errors

Presence of entrapped air Insufficient saturation at time of testing Variation in time of performing test.(+/- 2-3hrs.) Minor variation in specimen height as a result of

cutting open the existing 2”x4” mold LVDT- zero error

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Results and Discussion Permeability is then calculated using the following

relation:

where,k- permeability in units of length squareRo, Ri are respectively the outer and inner radii of the sampleKp , M and Ƞl are material properties of the sampleƮ is the relaxation time (obtained from HDP test)

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Cement paste (w/c=0.40 @ 7 days)

Note: x-axis represents time and y-axis represents micro-strain.

1 10 100 1000 10000 1000000

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60

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160

180 stain-time-paste1curve-fit

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Summary of results

Statistically significant increase in permeability with higher w/c ratio.

w/c ratio impacts permeability of early age cement paste.

Batch Relaxation time (s)

Permeability k (nm2)

1 (w/c = 0.4) 20000 0.005

2 (w/c = 0.5) 17000 0.015

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Conclusion

Discussed the various challenges encountered during the research study.

Highlighted the importance of perfection and precision in execution of research tasks.

Understood the significance of research in education.

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REFERENCES

Jones, C.A. and Grasley, Z.C. (2009) Correlation of Radial Flow-Through and Hollow Cylinder Dynamic Pressurization Test for measuring Permeability.

Grasley, Z.C. (2006) Measuring and modeling the time-dependent response of cementitious materials to internal stresses.

Vichit-Vadakan, Scherer, G.W. and Grutzeek, M. (2002) Measuring permeability of rigid materials by a beam-bending method.

Jones, C.A. and Grasley, Z.C. (2010) Correlation of hollow and solid cylinder dynamic pressurization Test for measuring permeability.

Comments/Questions?? Thank you