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“Use of post-installed screws in the compressive strenght assessment of in-situ concrete” presented at IALCCE2018 by Sha Nur Sourav


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In the structural evaluation of existing concrete structures, concrete strength is an important parameter that influences the quality of the overall assessment. Non-destructive tests (NDTs) allows the inspection of larger areas of concrete at lesser cost and time than coring and provides more reliable information than visual inspection. The low reliability of common NDTs in the assessment of compressive strength of concrete limits the use of NDTs in the practical field. A new technique, post-installed screw pullout (PSP) test, based on the modified pullout of post-installed screw, is presented in this paper. The screw transfers the load to the concrete through bearing on the threads. During the complete pullout failure mode, the failure pattern involves local crushing of concrete under the threads. The PSP test was investigated in mortar and concrete to study different factors; compressive strength, presence of aggregates, and the types of aggregate. Mortar was considered to be a homogenous material and thus taken as a baseline for comparing the effect of aggregate type. Experimental studies showed that aggregates play a significant role in the assessment of compressive strength by PSP test, and a better correlation with compressive strength was observed when concretes with different aggregates were analysed separately. In the strength assessment, the degree of variability of the PSP test in terms of R-squared value, standard deviation, coefficient of variation, and RMSE for mortar and concrete with brick chips and lightweight aggregates was found to be low; however concrete with limestone aggregate showed higher variability in the test results. The study confirms that the PSP test is a viable test method with the potential to be reliable and reasonably accurate, yet cost-effective; it can also contribute to the reduction of the uncertainty in the assessment of compressive strength of in-situ concrete.

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“Use of post-installed screws in the compressive strenght assessment of in-situ concrete” presented at IALCCE2018 by Sha Nur Sourav

  1. 1. Reducing Uncertainty in Structural Safety Special Session SS6 Ghent, Belgium 28-31 October 2018
  2. 2. Md Shah Nur Alam Sourav, Salam Al-Sabah and Ciaran McNally Use of post-installed screws in the compressive strength assessment of in-situ concrete
  3. 3. Outline of the paper • Bond strength of deformed rebar • Post-installed screw in concrete • Post-installed Screw Pullout (PSP) test • Experimental investigation • Statistical properties of the PSP test • Factors influencing the PSP test • Strength assessment and reliability
  4. 4. Research Background • In-situ compressive strength of concrete • Core testing • Non-destructive tests (NDTs) • Indirect approach and uncontrolled factors • Core testing + NDTs • Empirical relationships • Accuracy and confidence level • Time and costs
  5. 5. Bond strength of rebar Adhesion and friction Bearing Load Complete Pullout Failure 0 10 20 30 40 0 20 40 60 80 100 Bondstrength(MPa) Compressive strength (MPa)
  6. 6. Post-installed screw in concrete • Screw cuts threads in the wall of the hole • Load transfer by bearing mechanism of screw threads • Mechanism is similar to bond action of deformed rebar Screw installed in concrete Wall of the drilled hole Bearing Mechanism of screw in concrete
  7. 7. Post-Installed Screw Pullout (PSP) test Concrete cone failure Complete pullout failure
  8. 8. Post-Installed Screw Pullout (PSP) test • Newly developed • Partially destructive in nature • HUS3-H8- a product of Hilti • Inner diameter-7.70 mm • Outer diameter-10.40 mm • Hole diameter-9.0 mm • Hole depth-70 mm
  9. 9. Post-Installed Screw Pullout (PSP) test Experimental set up Crushed concrete in between the threads
  10. 10. Post-Installed Screw Pullout (PSP) test Factors studied • Compressive strength • Aggregate type • Cement content • Water-cement ratio • Aggregate content • Particle size distribution
  11. 11. Post-Installed Screw Pullout (PSP) test Load-displacement curve Zone 1 Zone 2 Zone 3 Zone 4
  12. 12. Post-Installed Screw Pullout (PSP) test
  13. 13. Effect of aggregate type Damage on the threads
  14. 14. Post-Installed Screw Pullout (PSP) test Statistical properties Aggregates R-sq Mean Residual (MPa) RMSE (MPa) Mortar (No aggregate) 0.90 3.24 4.47 Limestone 0.80 4.98 6.29 Brick chips 0.83 3.40 3.33 Lightweight 0.87 1.90 2.28 All 0.73 5.26 6.83 All except mortar 0.75 4.70 6.13
  15. 15. Conclusion • Cost effective in compared to core test and other NDTs • High strength correlation when considering the aggregate types • Load carrying behaviour affected by aggregate type • Harder the aggregate, higher the variation in results • High repeatability and reliability in concrete with softer aggregates • Potential to be reasonably accurate and reliable
  16. 16. The TRUSS ITN project ( has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 642453 Thanks for your attention