# HOW TO DETERMINE OF BOND STRENGTH BETWEEN STEEL & CONCRETE? [PULL OUT TEST]

## Theory

Bond strength is a measure of the effectiveness of the flue between concrete and steel and there is no standard quantitative definition. In pull out tests on plain bars, the maximum load typically represents the bond strength that can be developed between the concrete and the steel. With plain bars the maximum load does not differ much from the load at the first visible slip, but in the case of deformed bars, the maximum load may correspond to a large slip that was not achieved in practice before other types of failure occurred. can go. It is therefore preferable to compare the plain and deformed bars to determine not only the maximum load but also the load at an arbitrary amount of slip and also plot the full load slip curve for the plain and deformed bars under comparison. One such basis of comparison is the load on the relative motion (slip) between steel and concrete of 0.125 mm at the free end of the bar in the pull out test.

## Objective

To determine the bond strength between ordinary mild steel bars and cement concrete.

• In a reinforced concrete beam with overlapping reinforcement
• by pullout test

## Device

• Beam Mold (100mm x 150mm x 1830mm)
• Cylinder mold (diameter=150mm and height=300mm)
• Aligned Stand
• 50 kN (5 ton) transverse test machine or loading reaction frame
• 100 KN (10 Ton) Universal Testing Machine With Pullout Testing System
• dial gauge
• tamping bar
• trowels
• platform weight balance
• concrete mixer
• table vibrator

## Process

1. Prepare 1:2:4 concrete mix and water cement ratio equal to 0.6. For this, take 17 kg cement, 34 kg sand, 68 kg coarse aggregate and 10.2 kg water.
2. Cast concrete beams of size 100 m x 150 mm x 1830 mm. Using two 10mm bars having an effective cover of 12.5mm and overlapping 200mm in between. The four pieces of bars will only have hooks on one end. Cast three cubes along the beam to find out the crushing capacity of the concrete.
3. Cast three cylinders to a height of 200 mm with a 10 mm diameter rod placed in the center of the cylinder.
4. After 24 hours, remove the samples from the molds and put them in water. Test the beam after 27 days of wet curing by slowly applying a load on a 50 kN transverse testing machine or loading reaction frame. Test three cubes in compression.
5. At 28 days of age, perform the pull out test on a 100 kN Universal Testing Machine using the pull out test attachment.
6. Attach a dial gauge to find the slip between steel and concrete and plot the curve between load and slip.
7. Note the load at a slip of 0.125 mm and the failure of the bond.

## observation and calculation

Record the observations in the table below.

 RC Beam Test Load at first crack (N) final load on bond failure, P (n) Max BM (Nm) at first crack Max BM at failure (Nm) Actual Effective Depth (mm) Crushing Strength of Concrete (N/mm.)2, final bond tension

Calculate the final binding using the following formula

IOdour =pb ,xdxl)

where,

= ultimate bond tension

d = bar. diameter of

L = bar length (in this case it is 200 mm)

 pull out test 0.125 mm slip-on load (p.)1, load on bond failure (P2, Average bond strength at 0.125 mm slip (N/mm.)2, Average bond strength at failure (N/mm2,

Average bond strength at 0.125 mm slip = P1 ,*D*L)

Average bond strength at failure = P2 ,*D*L)

## precaution

• Use an aligned stand when casting the cylindrical specimen to hold the bars in a vertical position.
• The beam and cylinder samples will be tested only after they are removed from the curing tank.

Er. Mukesh Kumar

Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.