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Concrete Rehabilitation with Fiber-Reinforced Composites at an Air Force Base

Kelly Air Force Base (KAFB), the oldest military airfield in the United States, is the home of the Air Logistics Center and the Air Force Electronic Security Command in San Antonio, Texas. The building housing the Air Force Electronic Security Command exhibited distress in the concrete flat slab which resulted in concerns regarding its performance and adequacy for its intended use. CA performed a building condition assessment, identified the cause of distress, and replicated the in-place conditions in a finite element model of the building. The results from the structural analysis were further used to locate the problem areas in the building and they were confirmed by comparing the model predicted distress to the observed distress in the structure. CA designed a fiber reinforced composite repair system for the rehabilitation of the concrete structure.

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Structural Evaluation and Testing of a Parking Structure

Work performed on a parking structure located in Plano, Texas, encompassed a two phase investigation. Phase I consisted of investigating the cause of cracking occurring in the precast, prestressed double tee beams which resulted in the repair or replacement of several double tees. The forensic structural engineering investigation included a condition assessment of the parking garage structure, evaluation of the double tees removed from the structure, sampling of the concrete, non-destructive testing, petrographic examination, and analytical testing. Phase II consisted of investigating the cause of distress in the architectural precast concrete elements by performing a condition assessment and evaluation of the architectural precast elements in-place. It involved determining the adequacy of the erection details, connections, and the overall structural integrity of the precast architectural members.  CA’s forensic consulting work on this project involved performing a structural analysis, sampling, testing, and petrographic examination of the concrete, the review of concrete production and construction practices, and the development of recommendations for rehabilitation and maintenance of the parking garage structure.

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Heat Flow Analysis of Mass Concrete

CA has conducted heat flow analyses of mass concrete structures. These have included evaluating the effect of the concrete placement sequence, structural specifications, ambient conditions, and concrete materials and their mix proportions on the cumulative heat generation and internal temperature of the mass concrete construction and thus, on the quality of the in-place concrete. The heat flow analysis and the predicted temperature profiles were later confirmed by field measurements during actual construction. The information developed by CA was instrumental in determining the concrete curing, early age protection, and form removal practices followed by the contractor in the job. CA has also investigated the cause(s) of cracking as a result of thermal induced stresses in other facilities such as mass concrete foundations and precast/prestressed concrete highway structures.

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Litigation Support: Slab-On-Grade Distress at an Industrial / Manufacturing Facility

This manufacturing facility consisted of an approximately 200,000 sq. ft. cast-in-place reinforced concrete industrial warehouse floor used for manufacturing and distribution of manufactured products. CA performed a comprehensive condition survey, sampling, petrographic examination, and assessment of the condition and serviceability of the slab-on-grade floor in order to serve as a construction expert witness for this project.  CA’s condition survey included determining the cause of the observed distress in the form of random cracking, delaminations, and control joint deterioration. CA’s litigation support also included, among other things, evaluating the engineering design and specifications, plans and drawings, construction procedures, quality control practices, and concrete materials and their proportions.

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Emmet Shelton Bridge Structural Analysis and Rehabilitation

CA performed a four phase investigation of an existing 1940’s composite steel and concrete bridge spanning the Colorado River in Austin, Texas. Phase I consisted of  full-scale instrumentation and load testing, including performing a preliminary structural analysis and providing  consulting engineering services related to the emergency transport of heavy loads across the bridge well in excess of the rated capacity of the structure. Phase II included a condition survey of the superstructure and substructure which involved photographic documentation of the existing structural conditions, testing of the existing concrete, underwater inspection of the bridge foundation, installation of strain gauge monitoring devices, and addressing safety issues regarding traffic. Phase III involved the continued monitoring of the in-service behavior of the bridge in addition to performing a life-cycle analysis of the structure in its present condition based on the field data obtained in Phase II. Phase IV consisted of the design of repairs for the superstructure and substructure and construction administration and inspection of the implementation of the rehabilitation.

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Non-Destructive Testing Services at Dos Hermanos Bridge

The Dos Hermanos Bridge structure, built in 1981, is one of the two ground-level links between the Islands of San Juan and Puerto Rico. As a result of the severe marine environment exposure conditions, a few years after its completion, the bridge showed signs of early deterioration including severe corrosion of the concrete reinforcement in both the cast-in-place and the precast, prestressed structural members. CA performed a field condition survey and assessment of the structural integrity and safety of the structure including, among other things, destructive and non-destructive concrete testing, chloride ion content testing to determine the chloride ion penetration into the concrete, and cover meter scanning to determine the location of existing reinforcement. Furthermore, a service life cost estimate analysis and predicted service life expectancy was prepared based on various modeling techniques considering the in-service conditions, the implementation of different concrete restoration and rehabilitation techniques, and the actual properties, characteristics, and performance of the concrete.

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Concrete Finish Discoloration

The investigation consisted of determining the cause(s) of discoloration in the hard-troweled finished surface of the elevated structural slab in a high rise building. CA performed a visual inspection of the facility, extracted samples from the concrete surface, and performed a petrographic examination. The discolorations were found to be very shallow. The concrete samples did not indicate the presence of any deficiencies in the concrete requiring any further action other than the removal of the discoloration through very light polishing in order to restore consistency in the appearance of the finish of the elevated slab.

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Architectural Concrete Quality Control and Quality Assurance Program at the Mexican-American Cultural Center

This project was a joint effort between the City of Austin and Desarrollo Integral de Inmuebles, S.A. de C.V. in Mexico. Construction consisted of white precast architectural concrete panels produced in Mexico and white cast-in-place architectural concrete cast in Austin, Texas. Initially, CA was retained to investigate the cause of concrete cracking and failure of some architectural precast panels upon delivery and/or erection of the panels in the project. CA determined that the cause of the cracking was related to the reinforcement and anchorage details associated with the lifting hooks. CA evaluated and tested the anchorage detail and visited the contractor in Mexico to help implement changes. In addition, CA worked with the owner in the development and implementation of the quality control and quality assurance procedures during the construction of the project. CA was also retained to determine the cause of inconsistencies in the color and appearance of the cast-in-place architectural concrete. CA developed recommendations to achieve the specified quality of the architectural concrete construction restoring the uniformity within the architectural concrete in the project in addition to facilitating the progress of the construction activities. Of great significance, CA’s work resulted in alternatives and recommendations to adequately fabricate and install the architectural precast panels meeting the needs of the contractor to achieve the specified project requirements.

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Assessment of a Cast-In-Place Post-Tensioned Concrete Parking Garage

A four story, cast-in-place concrete parking garage consisting of an elevated pan-joist slab system framed by post-tensioned concrete beams provided a parking area and a structural frame foundation for a three story commercial office building. The elevated ramps for the parking garage exhibited distress in the form of full depth cracking in the elevated slabs parallel and adjacent to the post-tensioned beams and perpendicular to the longitudinal direction of the intermediate joists allowing for moisture migration and efflorescence to form on the underside of the elevated slab along the length of the cracks. CA performed, among other things, a detailed condition assessment of the structure, including crack maps of the entire parking structure, a review of drawings and plans, and a structural analysis of the post-tensioned beam and joist framing system accounting for their support and restraint conditions. CA determined the causes of the observed distress and developed recommendations for concrete crack repair and remediation of the reinforced concrete structure.

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Best Practice Recommendations for Storage of Manufactured Aggregate

CA was retained for the investigation into the alleged environmental damage caused by the handling and storage of manufactured aggregate in the Dominican Republic. All of the material testing reported by the different independent testing agencies confirmed that the raw materials were nonhazardous, non-toxic, and did not represent a danger or hazard to the environment. Visual inspection of the alleged affected areas at the ports of Manzanillo and Arroyo Barril revealed no evidence of distress to the adjacent waters including mangroves and bay shoreline, nor to the adjacent vegetation. CA concluded that manufactured aggregate being stored and/or used at the ports of Manzanillo and Arroyo Barril was non-hazardous. However, there were some deficiencies in the handling, storage, and/or installation of this material at both facilities that needed to be addressed to comply with industry standards for these activities. CA recommended that, in order to ensure the long-term benefit of the cargo storage and truck parking/staging area, the entire area be compacted, re-graded, surface sealed, and that a granular wear course be installed to prevent excessive surface wear and provide and act as a dust suppressant during traffic.