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Forensic Structural Engineering: Fly Ash Silo Unit

The project involved a roof failure of a fly ash silo unit, which consisted of 12 inch thick cylindrical cast-in-place reinforced concrete walls and 7 inch minimum thickness cast-in-place concrete roof placed over metal decking and supported by steel beams. CA was hired to investigate the concrete cracking and spalling caused by the structural failure, design and provide guidelines and recommendations for the repair, and monitor the repairs to ensure that they were performed as per the product manufacturers’ guidelines and acceptable industry standards. CA’s investigation included, among others, site visits, non‐destructive testing services, photo documentation, detailed condition survey, and review of plans and drawings.  CA also designed and developed guidelines, recommendations, and specifications for the repair, and communicated with client and owner representatives. CA’s failure analysis included determining the limits of the distressed area of the silo roof and determining the areas of the silo roof that could be repaired and those that needed to be removed and replaced.

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Slab-on-Grade and Pavement Distress Investigation and Remediation

This project consisted of a 67,500 square foot warehouse distribution facility supported by concrete slab on grade and exterior Portland Cement Concrete (PCC) and Hot Mix Asphalt (HMA) pavement areas to accommodate truck traffic and storage yard areas. Several weeks after the facility was in service, the owner noticed water seeping out at several locations along the construction joint between the PCC and HMA pavement areas. Additional distress was observed in the HMA pavement in the next year. CA was retained to assess the existing condition of the HMA pavements and warehouse concrete slab-on-grade to determine the cause(s) and/or contributing factors of the observed distress, and to provide recommendations, if needed, for any remedial actions to restore its service life to that intended in the design. CA’s forensic engineering investigation into the cause of the problems included a detailed condition survey of the HMA pavement areas, analysis of results from soil borings, materials sampling, water level measurements from monitoring wells, comprehensive review and evaluation of construction related documents, and review of relevant industry standards and literature. Through its forensic engineering investigation CA was able to develop an economical plan to divert the water away from the slabs, and restore service life to the slabs through remedial action.

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Evaluation of an Asphalt USAF Radar Landing Pad

A radar landing pad in Lajas, PR serves vehicles that are used to deploy a blimp carrying surveillance equipment. The landing pad is a large circular, paved area with a diameter of approximately 200 m. Most of the landing pad is paved with asphalt, with the exception of a centered circular area, with a diameter of about 55 m, which is paved with concrete. As a result of age, the asphalt concrete portion of the landing pad was rehabilitated in early 2010. The rehabilitation involved milling and resurfacing with asphalt, along with some full-depth asphalt repair. A few months after the rehabilitation project was completed, the surface of the asphalt exhibited distress in the form of surface shear, or tearing. Carrasquillo Associates (CA) was hired to characterize the pavement distress and to review the rehabilitation design and construction records. CA performed independent pavement design calculations using the design and current heavy forklift traffic conditions. CA also reviewed the contractor’s asphalt mixture design and quality control records, which included mixture property characteristics and compaction data. The distress was indicative of heavy forklift traffic exceeding the design loading for the pavement. A rehabilitation option using a rigid pavement surface, of either portland cement concrete or resin-modified pavement was also evaluated.

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Condition Assessment of a Storm Water Detention Vessel

The project consisted of a storm water detention vessel with a precast concrete double-tee girder roof deck that also served as a parking lot for a local grocery store in Houston, Texas. CA was retained to perform a visual condition assessment to address concerns regarding the integrity of the structure and the condition of existing repairs. CA performed several site visits and achieved detailed photographic documentation of the structure. Special attention was given to areas exhibiting signs of distress and the quality of precast concrete double-tee girders. CA’s investigation identified areas of concern for further structural evaluation and repair.

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Alkali-Silica Reaction (ASR) in Slab-on-Grade Driveways

CA performed a forensic engineering investigation to determine the cause(s) of the distress observed in the exterior concrete slab-on-grade driveways and sidewalks of numerous homes in a single family residential neighborhood. The observed distress consisted of surface discoloration, pop outs, and peeling of the membrane coating, which was installed on several driveways in an attempt to remediate the distress. CA’s forensic investigation included, among others, visual inspections of more than 100 installations, concrete core sampling, and testing of the bond strength between the membrane coating and the concrete substrate. In addition, CA directed petrographic examination of several concrete cores sampled from the distressed and non-distressed locations in order to investigate any alkali aggregate reaction in the concrete. CA determined that alkali-silica reaction in the concrete was one of the cause(s) of the observed distress and developed recommendations for the concrete surface repair and remediation of the in-place concrete pavement.

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Evaluation of a Shopping Center Flooring System

An expansion to the second story of a commercial retail shopping center consisted of the addition of an elevated slab supported by several different types of framing systems, including a post-tensioned concrete beam and pan joist system, a composite flooring system consisting of metal decking and reinforced concrete, and a reinforced concrete slab and beam system. The flooring system of the second floor expansion contained limestone tile as the final floor finish, which exhibited signs of isolated distress in the form of random map cracking. CA performed, among other things, a detailed condition survey of the flooring system and its distress, a review of drawings and plans, an examination of the materials utilized in the flooring system, and a structural evaluation of the flooring system and its individual components. Testing conducted during the site investigations included bond pull-off tests, ground penetrating radar (GPR) mapping, concrete core sampling, and elevation surveys.  CA determined the cause of the distress exhibited by the tile flooring, provided recommendations for the repair and remediation of the flooring system, and developed guidelines to reduce the progression of the distress.

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Investigation into the Cause of Cracking in Precast Post-Tensioned Concrete Beams

The construction of Highway 10 in Puerto Rico has been one of the largest and longest highway projects in the island. This highway runs through Puerto Rico’s scenic mountains and was expected to be completed in 2015. Cracking in the precast, post-tensioned concrete beams manufactured on-site resulted in concerns to the public authorities requiring immediate action. CA provided construction consulting services during construction of various post-tensioned concrete beams and sections of Highway 10. CA inspected many of the beams where cracking was observed, visited the concrete production facilities on-site, observed casting operations, and evaluated field data including, but not limited to, internal concrete temperatures of the concrete beams. In addition, CA’s investigation included a review of concrete mixture proportions, material information, concrete quality control testing results, curing, and demolding practices to determine the causes of the concrete cracking observed and propose remediation procedures.

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Precast Concrete Welded Connections

A six (6) story parking garage for a residential building consisted of precast, pre-topped double-tee beams and pre-cast wall panels. A concern regarding life safety was expressed due to the observed distress consisting of spalling of the concrete beneath the welded connections along the flange of adjacent double-tee beams. In addition, concrete cracking in the vertical panels of the pre-cast walls was observed. CA’s investigation focused on determining the cause of the distress and included, but was not limited to, a detailed condition survey and visual inspections of over 1,600 welded connections and a review of the construction drawings and plans. CA determined the cause of the observed distress and developed recommendations for repair and rehabilitation of the concrete structure, including design of repair procedures, materials selection, and quality control/assurance procedures during and after implementation of the repairs.

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Industrial Parking Lot Concrete Pavement Design

The project consisted of the rehabilitation of two concrete pavement parking lots in an industrial park in Laredo, Texas, including the removal and replacement of distressed areas as well as repairs at the expansion joints in concrete slabs. CA performed a detailed condition assessment of both parking lots to observe the distress and developed repair recommendations pertaining to concrete properties, concrete pavement thickness design, expansion joint transfer details, expansion joint sealant, drainage, preparation, material, and base and subgrade preparation.

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Indoor Concrete Topping Placement Recommendations

Construction at a university recreation and wellness center required a concrete topping slab in the main entrance and lobby areas. CA provided structural engineering consulting services including, but not limited to, improvements to the concrete placement activities and incorporation of necessary measures to reduce the potential for drying shrinkage cracking. CA’s experience with concrete toppings and understanding of concrete placement fundamentals contributed to successfully addressing the project’s needs and its unique conditions. CA provided recommendations for the concrete placement including reducing structural restraint and bond, implementing drying shrinkage cracking control and appropriate curing methods, and using proper joint design and layout.