Suvash Chandra Paul

PhD Candidate in Civil Engineering, Stellenbosch University

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Telephone: +27820933439

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Research topic: Role of chloride and cracks in corrosion of reinforced strain hardening cement-based composite (R/SHCC)

Status:On-going since 2012

Project description:

1. Objectives

2. Mix design of PVA-SHCC

3. Direct tensile testing on SHCC dumbbell specimens

4. Set-up for corrosion testing of R/SHCC specimens

5. Corrosion activities in cracked R/SHCC specimens

6. Chloride profile in cracked R/SHCC specimens

7. Conclusion

Selected publications:

Paul, S.C., and van Zijl, G.P.A.G. (2014). “Crack Formation and Chloride Induced Corrosion in Reinforced Strain Hardening Cement-Based Composite (R/SHCC)”, Journal of Advanced Concrete Technology, Vol. 12, p: 340-351.

Paul, S.C., and van Zijl, G.P.A.G. (2013). “Mechanically Induced Cracking Behaviour in Fine and Coarse Sand Strain Hardening Cement Based Composites (SHCC) at Different Load Levels”, Journal of Advanced Concrete Technology, Vol. 11, p: 301-311.

Paul, S.C., Ebell, G., van Zijl, G.P.A.G., and Schmidt, W. (2014). Cracked and uncracked SHCC specimens under different exposure conditions, In proceeding of the SHCC3 3rd RILEM conference on Strain Hardening Cementitious Composite, Dordrecth, Netherland, Schlangen et al. (eds), © 2014 RILEM – Tous droits reserves, ISBN:978-2-35158-150-6, p:25-32.

Paul, S.C., Theunissen, A.I., and van Zijl, G.P.A.G. (2013).“Chloride Induced Corrosion in Cracked Reinforced Strain Hardening Cement-Based Composite (R/SHCC)”, In proceeding of International Conference onSustainable Construction Materials & Technologies (SCMT3), Kyoto, Japan (received best paper award).

Paul, S.C.,and van Zijl, G.P.A.G. (2013). “Strain Hardening Cement Based Composite (SHCC) with fine and coarse sand under tensile load and chloride attack”, In proceeding of 8th International Conference on Fracture Mechanics of Concrete and Concrete Structures (Framcos), Toledo, Spain, J.G.M. Van Mier, G. Ruiz, C. Andrade, R.C. Yu and X.X. Zhang (eds).

Paul, S.C., and van Zijl, G.P.A.G. (2013). “Mechanical behaviour of strain hardening cement-based composites (SHCC) based on micromechanical design” In proceeding of International Conference on Advances in Cement and Concrete Technology in Africa (ACCTA), Johannesburg, South Africa (received best paper award).

Prizes:

  • The young researchers prize of the German South African year of science for the best junior scientist’s paper from South African affiliation at the ACCTA conference, Johannesburg, South Africa, January 2013 (with GPAG van Zijl).
  • Best paper award at the International Conference on Sustainable Construction Materials & Technologies (SCMT3), Kyoto, Japan, August 2013 (with GPAG van Zijl & Andrew Theunissen).

1. Objectives

  • To establish whether a crack width threshold exists, and what the crack threshold level is in SHCC specimens, below which insignificant ingress rates occur but beyond which rates are accelerated (as has been shown by for instance Sahmaran et al. 2007).
  • To determine chloride permeability in virgin and cracked SHCC specimens under service conditions.
  • To evaluate chloride-induced corrosion protection in virgin and cracked R/SHCC specimens.
  • To determine the rate of corrosion in un-cracked (virgin) and cracked R/SHCC specimens at loaded and un-loaded states.

2. Mix design of SHCC

Table 1: SHCC mix composition in kg/m3

Type / Cement / Water / Fly Ash / Sand / Fibre (%) / SP / VMA / AEA
SHCC / 392 / 392 / 674 / 553 / 2.01% / 1.99 / 0.54 / 0.54

Note: PVA fibre (Lf= 12 mm and df= 0.4 mm) SP = super plasticizer, VMA = viscosity modifying agent and AEA = air entraining agent.

3. Direct tensile testing on SHCC dumbbell specimens

Figure 1: Dumbbell size and setup for direct tensile testing

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Figure 2: Preparation of specimen for measuring cracks data by using ARAMIS

Figure 3: Tensile cracks in 14 days age of FS11 specimen at different strain (%) level

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4. Set-up for corrosion testing of R/SHCC specimens

Figure 4: (a) Reinforced SHCC specimens under sustained loads, (b) specimens for corrosion testing in chloride exposure by means of ponding and (c) corrosion rate measuring technique using coulostatic technique.

5. Corrosion activities in cracked R/SHCC specimens

Figure 5: Estimated corrosion depth in different cover depths of R/SHCC specimens with single steel bar (B1).

Figure 6. Relationship between dc and cover depth

Figure 7. Corrosion inspection in R/FS-SHCC C15B1 steel by destruction and non-destruction (CT scan) method at 580 days

Figure 8. Different corroded steel bars after cleaning with HCl

6. Chloride profile in in cracked R/SHCC specimens

Figure 9. Chloride penetration profile in different cover depths of cracked R/SHCC specimens

Figure 10. Total and free chloride content in R/SHCC specimens

Figure 11. Relationship between total and free chloride content in R/SHCC specimen

7. Conclusions

  • Corrosion rates measurements for cracked R/SHCC specimens are variable in time, most likely due to variations in moisture content and temperature. However, when integrated to obtain corrosion depth, smooth corrosion curves are obtained which clearly indicate higher corrosion rate for steel with a cover of 15 mm than for 25 and 35 mm. It appears that a threshold cover depth between 15-25 mm exists for the materials tested here, beyond which cover no significant reduction in corrosion rate is observed.
  • Removal of the rebars from specimens after extended periods of accelerated corrosion confirmed corrosion damage to rebars from R/SHCC specimens.
  • A correlation was found between average pitting corrosion depth and loss of yield resistance force of rebars. However, the data set was small and should be extended for meaningful conclusions to be drawn.
  • The localised nature of corrosion damage in R/SHCC specimens complicates corrosion damage prediction from corrosion rate measurements. Although more significant corrosion pitting damage could be observed by visual inspection of the bars with 15 mm cover than for rebars with 25 and 35 mm covers, which agrees with the higher measured corrosion rates for these C15 specimens, the loss in rebar yield resistance was not the highest for the C15 rebars.
  • After 620 days of accelerated chloride-induced corrosion, relatively little corrosion damage was found in the R/SHCC specimens. Average and maximum pitting depths in the ranges 0.2 – 0.3 mm and 0.3 – 0.6 mm respectively were found, and a maximum loss of tensile yield resistance of 13.2%.
  • Significant amounts of chloride penetrate to the steel bar surface in R/SHCC specimens. From a limited study, no correlation could be found between the total amount of chloride at the rebar surface and the total or average crack width, number of cracks, or cover depth.

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