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.
“Use of post-installed screws in the compressive strenght assessment of in-situ concrete” presented at IALCCE2018 by Sha Nur Sourav
1. Reducing Uncertainty in Structural Safety
Special Session SS6
Ghent, Belgium
28-31 October 2018
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. 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. 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. 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. 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
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
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. 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. The TRUSS ITN project (http://trussitn.eu) 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
