Water World Water
Park Denver, CO
Water World Water
Park Denver, CO
This is a two level below grade parking garage that Restruction Corporation is currently working on in Phoenix Arizona. Some of the repairs included full depth and partial depth structural concrete removal and replacement along with installation and welding of the new re-enforced rebar which was then coated with an anti-corrosive agent. You may also be able to see in the photo that we also installed a cathodic anode protection system.
Increasing Concrete Resistance to Reduce Rebar Corrosion
Many large scale properties utilize concrete steam tunnels, distributing heat from a central boiler plant to outlying buildings. This practice used at hospitals, government complexes and universities. The steam tunnels are typically constructed with reinforced concrete foundation and wall systems and are located below grade. Depending upon the age, quality of damp-proofing and soil moisture content, reinforcing steel in the concrete walls is subject to corrosion activity. The corrosion will cause concrete deterioration, eventually leading to structural capacity degradation.
Recently Restruction Corporation proof tested curtain wall grouting to reduce corrosion activity in reinforced concrete walls of a steam tunnel. Fifty linear feet of wall, 4 feet tall was selected for testing. Holes were drilled through the wall and urethane resin material was injected behind the wall. This method commonly used, forms a positive side waterproofing membrane at the wall. Installation of the waterproofing is from the negative side, eliminating costly soil excavation to access the wall.
Irrigation of the lawn above the steam tunnel walls supplied excess moisture. The moisture was absorbed by the concrete wall allowing rebar corrosion to initiate. Reducing the moisture content, measured by concrete resistance, would reduce corrosion rates.
Concrete resistance measurements were completed prior to urethane injection. Two weeks after injection concrete resistance measurements were replicated.A 10% increase in concrete resistance was measured with tighter standard deviation of the data. Cost of the project was approximately $25,000.
Concrete Resistance Prior to Wall Injection
Concrete Resistance Post Urethane Wall Injection
A Contractor’s View on Getting Qualified to Weld Rebar
By Mike Lutonsky, VP Field Operations Restruction Corporation.
What I would like to do is give you some pointers based on some of the failures and successes we have gone through to qualify ourselves. (For specifics go to the rebar welding qualification in section-6 of the AWS D1.4 code for Structural Welding Reinforcing Steel). I’ll describe some basics of what is required for a company and a welder to get qualified to weld rebar. Unlike the structural welding certification which is relatively simple. Rebar welding and testing requirements can be very confusing and difficult which can make it easy to make a mistake when testing. If you put some thought to it and look ahead at what you might be required to weld you can save yourself time and money by doing it right once.
There are three processes described in the code; SMAW-shielded metal arc welding, GMAW- gas metal arc welding and FCAW- flux cored arc welding. The process we use for rebar is SMAW (stick welding) so for this paper I will be referencing SMAW.
Qualifying under the AWS D1.4 code there are two primary areas you need to focus on:
1) The Welding Procedure Specification (WPS) (AWS D1.4-6.2) this is twofold; the weld test (see photo 1) conducted and passed by a company which sets the standard for all of the welders to follow and the written document that lays out the parameters of that test. The written document will include; date of test, process used, position(s), groove type, technique, electrical characteristics, base metal material specifications, filler metal AWS specifications, filler metal AWS classification, shielding, preheat temperature, inter pass temperature, number of passes, electrode diameter, amperage range, voltage range and the contractor information. Once the WPS is done it does not have to be done again unless you are required to weld rebar that does not fall within the perimeters of the WPS.
For the WPS test it is important to use the appropriate materials and procedures to meet the needs you will be faced with when welding production in the field. Test with the highest grade of bar, the largest bar you expect to weld, the largest rod you expect to use, the highest strength rod you will be required to use, the highest carbon equivalent content bar you will be required to weld, all the positions you will be required to weld and the type of joint you will be required to weld in production.
For example if a job has #8 ASTM A615 grade 60 bar that you are required to weld horizontally and you generated a WPS by testing with a #7 ASTM A706 grade 60 bar using SMAW 7018 in a vertical position. You would not be qualified to weld on that job. You did not test with the 90XX SMAW rod required which is required when welding A615, you tested on bar that was smaller than the bar on the job and you tested in the vertical position not horizontal.
WPS testing can be very time consuming and expensive but if you select some broad perimeters and only have to do it once it is worth doing. Using the example above pick the worst case scenario and set your limits to test within. Our experience is in structural repair so for us we are faced with most grades of rebar up to grade 60, most of the bar sizes are #9 and smaller, we weld in all positions and usually have lap splices. So after evaluating our perimeters we chose to test with #10 A615 grade 60 rebar, we tested in all positions using SMAW 5/32” diameter 9018 rod and used the Indirect Butt Joint assembly. Remember if the job requirements are less than your WPS test you will be qualified to weld because you can go down in bar size, grade of bar, strength of rod and size of rod but you can’t go up in any of these from where your WPS was generated. You can find this information in the PQR Essential Variable Table Changes Requiring WPS Re-qualification 6.2 of D1.4. Using the #7 bar example from above we would qualify to weld for that job based on the parameters of our WPS.
Follow all the preheating, tacking, rod storage and other welding processes required in the AWS D1.4 code. For assembly configurations refer to AWS D1.4-126.96.36.199, 188.8.131.52 and 6.2.5. You can see a sample assembly of an Indirect Butt Joint in photo 1. For joint type details refer to AWS D1.4 figures 3.1, 3.2, 3.3, 3.4 and 3.5. You will need a minimum of two test assemblies for every position you will test in. When testing, make notes of all the particulars which you will need for generating your written WPS document. And when your samples are complete send them to your qualified testing company where they will perform a full section tension test for tensile strength that must meet the strength of the bar you are welding and macroetch test for soundness.
2) The Welder Qualification Test (AWS D1.4-6.1) which is a weld test each person welding rebar must perform individually following the WPS as a guideline.
Unlike the WPS, the welder qualification test requires the welder to weld with the smallest bar size to be welded in production which qualifies that welder for welding that bar size and any larger size. Additionally some of the test positions qualify a welder for multiple positions for example in AWS D1.4-184.108.40.206 Indirect Butt Joint Weld Test the 3G vertical test qualifies you for three positions- flat, horizontal and vertical positions, the 4G overhead test also qualifies you for three positions- flat, overhead and horizontal positions. Yet if you test in the 1G flat position it only qualifies you for two positions -flat and horizontal. You need to understand what you will be welding in production and test according to what will be required in the field. When we test our guys we do two positions 3G vertical and 4G overhead when combined this qualifies us for all positions by only performing tests in two positions.
Other important information:
When purchasing your rebar for testing it is very important to get it from a reputable supplier that can provide you with Mill Test Certifications from the manufacturer to ensure you are testing with the right product. It is also a good idea not required but a good idea to sample the carbon equivalency and perform your own tensile strength test to ensure you didn’t get a bad batch. If you will be spending time, money and effort on this test you want it to be right.
Once you are qualified be aware of ‘Period of Effectiveness’ which is designed to ensure a welder stays in tune with the skills they had when they tested. If a welder is not engaged in the rebar welding process for a period of 6 months or more or if there is a question about the welder’s ability he may be required to retest.
American Welding Society D1.4/D1.4M: 2011
About the Author;
Mr. Lutonsky has 24 years’ experience in structural repair and strengthening, and construction management with Restruction Corporation. He has managed highly complex structural repair projects for Restruction Corporation as a superintendent, project manager and field manager. As operations manager, he manages a very talented and diverse group of field supervisors that are considered the leaders in the industry of structural repair. He is a certified pipe and structural welder. He has several safety training certifications and is trained in repair procedures and materials. He is responsible for the training of all field personnel in the Colorado division of Restruction Corporation.
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Polymer Overlays, installed per ACI Committee 548 and AASHTO guidelines, provide protection for and give durability to reinforced concrete parking and bridge decks. The overlays provide a high skid resistant “new” wearing surface and keep de-icing salts from penetrating the concrete. De-icing materials will initiate rebar corrosion and create expensive structural damage. The polymer materials are typically a urethane extended epoxy material designed for low modulus (moderately elastic) properties. Restruction Corporation typically applies these overlays using a “broom and seed” method and will utilize a variety of aggregates dependent upon project specific conditions. Restruction Corporation has utilized silica sand, course flint rock and copper slag aggregate. We have completed numerous projects for Utah Department of Transportation, Town of Telluride Colorado, Colorado Department of Transportation and numerous private companies.