My question concerns the hole sizing and embedment depth of post installed rebar which is secured with epoxy mortar into a hole in a reinforced concrete slab.
Hole diameter sizing
My assumption #1 is that the minimum and maximum size of the hole depends on the minimum and maximum thickness of the epoxy mortar. Playing around with the Adhesive Anchor Volume Calculator on the Hilti website suggests the following hole sizes:
+----------------+----------------+
| Rebar diameter | Hole size |
+----------------+----------------+
| 10 mm | 9/16" (14 mm) |
| 15 mm | 3/4" (19 mm) |
| 20 mm | 1" (25 mm) |
| 25 mm | 1 1/4" (32 mm) |
| 30 mm | 1 1/2" (38 mm) |
+----------------+----------------+
For the purposes of this example consider HIT-HY 200 Injection Mortar.
Question 1 - what deviation from these hole sizes is permitted? If a 16 mm hole is accidentally drilled then can the 10 mm rebar still be used with full strength?
Hole depth sizing
My assumption #2 is that the required embedment depth of a rebar dowel depends on the bond strength of the epoxy mortar and the load that the rebar is required to carry.
Conservatively consider that M10 rebar is required to have a pull-out resistance equal to the force that would yield it at 500 N/mm².
Rebar area $= π \times 5^2 = 78.5 \text{ mm}^2$
Rebar circumference $ = 2 π \times 5 = 31.4 \text{ mm}^2$
Conservative pull-out force $= 500 \text{ N/mm}^2 \times 78.5 \text{ mm}^2 = 39.25 \text{ kN}$
For C25/30 concrete the design bond strength of HIT-HY 200 Injection Mortar for any rebar diameter is given by $2.7\,\text{N}/\text{mm}^2$
Bond-strength per mm of M10 rebar $= 2.7 \times 31.4 = 84.78 \text{ N/mm}$
Required embedment depth $= 39250 \text{ N} ÷ 84.78 \text{ N/mm} = 463 \text{ mm}$
Question 2 - Is this a conservative methodology for determining the required embedment depth? Will an embedment depth of 463 mm provide full strength in the case of M10 rebar secured with HIT-HY 200 Injection Mortar in C25/30 concrete?
