Installing a shotcrete lining requires a somewhat dry substrate and certainly is not compatible with running water. The water needs to be blocked or diverted.
A means of blocking the inflow is to inject a swellable urethane grout through the openings in the existing pipe. The grout, if done properly, will expand upon contact with water and seal the outside of the pipe. Another means of diverting the water is to install drainage material over the inflowing area to collect the water and remove it from the pipe. The shotcrete can then be applied over the drainage material.
I have a newly constructed in-ground pool in which shotcrete was used. The pool has been holding dirty water since just after the shotcrete cured. Does the shotcrete have to be cleaned and/or treated before an overlay is applied?
To ensure a good bond between the shotcrete shell and the overlay, the surface should be cleaned and allowed to dry before application of the overlay material.
What are the common standard test methods to measure or assess the permeability of shotcrete?
Boiled absorption and volume of permeable voids testing (ASTM C642) may be required for structures that need enhanced liquid-tightness or resistance to aggressive environmental exposures. The test is sometimes used to provide an overall indication of the quality of the shotcrete mixture, particularly in dry-mix. However, many factors, including admixtures and aggregate, as well as shotcrete placing, can affect the porosity of shotcrete, so it should not be considered an absolute measure of shotcrete quality. When required, the mean average of tests on three specimens from a test panel, or from in-place shotcrete, should be less than or equal to the specified boiled absorption and/or specified volume of permeable voids limits at the specified test age with no single test greater than the specified boiled absorption plus 1%.
The Los Angeles City Bulletin states that no bars over No. 8 (No. 25) shall be used. The structural engineer has No. 10 (No. 32) bars in the columns. I am being told the test panel will get this approved but my City Inspector is balking a little. Is there a publication or code somewhere that allows the test panel to supersede the LADBS Bulletin?
The International Building Code (IBC), Section 1913, allows for larger bars as long as it is demonstrated in a Preconstruction Test Panel. However, the Local Building Code likely takes precedence over the IBC. You may want to present IBC Section 1913, which requires anything over a No. 5 (No. 16) bar to be proven in a Preconstruction Test Panel.
There have been many projects shot in Los Angeles County subject to the LADBS with bar sizes larger than No. 8 bars. ASA is not in a position to give you project references, but perhaps our local members can.
Properly encasing No. 10 (No. 32) bars can be challenging, and should only be attempted by qualified contractors using ACI Certified Nozzlemen who have previous successful experience doing this type of work. You may use our online Buyers Guide to find an ASA corporate member consultant or contractor to assist you.
I am doing an owner/builder pool. The shotcrete company I hired left an approximately 4 x 4 in. (102 x 102 mm) hole in the deep end of the pool on the side wall. What is the proper way to patch this hole prior to plastering? (The shotcrete was applied a month ago.)
The normal repair is to pressure wash with at least 3000 psi (21 MPa) of water pressure to remove any dirt and laitance on the surface of the concrete. Given the rather small size of the hole, it can be hand-patched with a nonshrink hydraulic cement with at least 4000 psi (28 MPa) 28-day compressive strength to plug the hole. After the patch is completed, roughen the surface that will receive the plaster.
What is the fire rating information for shotcrete?
Shotcrete is concrete, pneumatically applied. So the same fire ratings for concrete would apply to shotcrete. The standard is ACI 216.1, “Code Requirements for Determining Fire Resistance of Concrete and Masonry Construction Assemblies.”
I am looking for some technical assistance concerning temperature guidelines for shooting gunite pools. Is there a suggested range of air temperature and humidity that is recommended? Thanks for your help!
Shotcrete is a method of placing concrete. The basic guidelines for placing concrete or shotcrete can be found in documents ACI 305R-10, “Guide to Hot Weather Concreting,” and ACI 306R-10, “Guide to Cold Weather Concreting.” There are some basic “rules of thumb,” such as 40°F (4°C) and rising for starting concrete/shotcrete operations and 40°F (4°C) and falling for stopping concrete/shotcrete operations. With proper planning and procedures, concrete or shotcrete can be placed at below-freezing temperatures and at very hot temperatures, but only with proper planning, procedures, and likely at some cost.
We are working on a project with a wall that requires additional capacity due to increased loading requirements. We are contemplating shotcrete with additional reinforcing to provide additional thickness for the wall. Is it possible to achieve a composite wall to design for a thicker section for bending, using the bond of the existing concrete and shotcrete along with a reinforcing bar hook anchor epoxied into the existing wall? Any information you can provide would be appreciated.
Shotcrete is often used in similar applications. The question of bending is a structural engineering question. Shotcrete is a method of placing concrete and the properties of shotcrete are similar if not the same as cast concrete. To achieve a composite wall, you must ensure that the existing surface is properly prepared to maximize the potential bond between the overlay shotcrete and the existing wall. Shotcrete placed against a properly prepared existing wall should achieve great bonding strength without the use of bonding agents. Drilled and grouted dowels also contribute to the system, working as a composite wall.
We are in the process of building a shotcrete pool and are required to wet-test the pool before set, waterproofing, and tile. What is the expected water-loss percentage? We are required to achieve 1%.
We are not aware of a specific standard for pools. However, ACI 350.1-10, “Specification for Tightness Testing of Environmental Engineering Concrete Containment Structures,” specifies a volume loss of 0.05% of volume per day conducted over a 72-hour test period for “hydrostatic tightness testing of open liquid containment structures. Specifics of conducting the test can be found in the ACI 350.1-10 document.
It should be noted that the pool should be filled and allowed to saturate for 3 days before beginning the measurements.
Can shotcrete be used to help seal a leaking pond? We have a 1.5 acre (6070 m²) pond that we are in the process of completing. We spread 90,000 lb (40,823 kg) of bentonite in, but the bentonite washed off the steep banks and now we are stuck with a half-full pond. Would shotcrete be a practical solution for our problem?
Properly designed shotcrete (both concrete materials and reinforcing are important in the design) placed by an experienced shotcrete contractor can certainly be used to provide a somewhat watertight lining for your pond that will be serviceable, durable, and require little to no maintenance for decades to come. We would suggest you consult with an engineer or shotcrete contractor experienced in this type of shotcrete work. You may use our online Buyers Guide to find an ASA corporate member consultant or contractor to assist you.