Residential Structure Investigations for Vibrations from Subsurface Drilling

CA investigated whether the alleged distress at 28 residences located in Peñitas, Texas was the result of drilling operations which occurred in the area between 2007 and 2011. The investigation included a detailed condition survey of each residence as well as an elevation survey of each residence’s slab-on-grade foundation. CA reviewed applicable industry standards and relevant published literature regarding ground vibrations and damage to existing structures. The investigation did not produce any evidence to support the conclusion that the alleged distress in the residences was the result of ground vibrations from the drilling operations. CA determined that the observed distress in the residences was most likely caused by one or a combination of the following: dimensional movement of the structure due to temperature and humidity cycles, drying shrinkage stresses, foundation movement, and/or deficient construction.

Retrofit of Reinforcement Concrete Cantilevered Seating Structure

CA investigated the structural adequacy of an as-built cast-in-place concrete cantilever seating structure in two levels of a sports venue’s grandstand. The cantilever section consisted of an almost 4-foot overhang. Sometime after placement, it was discovered that the cantilever’s tensile reinforcement was placed incorrectly. CA used ground penetrating radar scans to determine the actual reinforcement position, performed a structural analysis to determine the as-built capacity of the cantilever, and designed a retrofit to restore the capacity. CA performed a load test on the first section of repair to document the effectiveness of the retrofit solution. CA maintained a full-time field engineer to oversee and document the entirety of the grandstand repairs.

Industrial Asphalt Pavement Investigation

Carrasquillo Associates investigated pavement distress in a shipping container terminal in Jacksonville, Florida. The pavement consisted of a 7-to-12-inch thick asphalt pavement over an 8-inch thick base consisting of a mixture of limestone, hydrated fluidized bed ash, and fly ash from a local coal combustion electric plant. Approximately one year after completion of the project, the terminal operator noticed certain areas of the asphalt pavement adjacent to concrete drains and concrete crane turning pads exhibiting up to 4.5 inches of heave.  CA’s investigation included, but was not limited to, reviewing construction documents such as quality control test reports of the base material, extracting cores of the base material from areas of distress and non-distress for petrographic examination and chemical exposure testing to determine if the base material was exhibiting any residual expansion after installation. CA’s investigation determined that the presence of expansive compounds and poor quality control during mixing and hydration of the base material led to the delayed expansion of the pavement when exposed to moisture penetrating the joints between the asphalt and concrete pavement sections.

Evaluation and Repair of Concrete Slab Placed in Inclement Weather

Carrasquillo Associates investigated and characterized the surface distress occurring at an elevated post-tensioned concrete slab in a parking garage that is part of a high-rise building under construction in downtown Austin, Texas. CA’s investigation included an examination of the extent of distress or unsound concrete in an area within one level of the parking garage equal to approximately 10,000 square feet, where rain had affected the fresh concrete surface soon after it had been placed. CA conducted a site visit to the parking garage to perform a visual examination and condition survey, and to obtain core samples from the concrete deck. The cores were studied by a concrete petrographer, who determined the extent of rain damage within the depth of each core. CA utilized this determination in developing a repair plan for the affected concrete surface to restore its serviceability and long-term durability. This project provides an example of CA’s expertise in recognizing a structural or materials problem and its root cause, assessing how it will affect the structure, and offering a repair solution that efficiently and reliably restores the structure.

Cold Weather Concrete, Post-Tensioned Slab Blowout

CA investigated allegations that the characteristics of the concrete mixture and properties of the as-delivered concrete caused numerous post-tensioning blowouts and delays during construction of a seven-level parking garage. CA’s investigation focused on investigating the concrete mixture design’s conformance with the design requirements, the quality and suitability of the as‐delivered concrete for its intended purpose, and if the concrete caused and/or contributed to the alleged delays and blowouts experienced during construction. CA determined that the ready-mix supplier’s concrete mix design submittal was in compliance with the design requirements for the construction of the parking garage and was approved by the engineer of record. CA’s investigation into the materials, proportioning, production, mixing, and delivery of the fresh concrete and its characteristics and performance did not reveal any evidence to support the allegation that the concrete produced and delivered was the cause of or a contributing factor to the alleged delays and blowouts during post‐tensioning. CA found that the blowouts were the result of any one or a combination of the following deficiencies within the responsibilities of the general contractor: in‐place concrete early‐age protection and curing during cold weather, curing and handling of field‐cured cylinders, concrete placement quality, and installation of reinforcement.

Convention Center CMU Wall Repair

Carrasquillo Associates designed repairs for a 50 ft. tall exterior concrete masonry unit (CMU) wall. During construction, it was discovered that the wall was constructed without the proper amount of reinforcement, essentially making it unreinforced. CA computed the loads acting on the wall from self-weight, cladding, and wind. Multiple wall sections were considered due to the varying cladding, geometry, and parapet details. Nearly the entirety of the wall was overstressed due to the wind load. CA’s repair involved adding a steel structural support to reduce the wall’s span and thus reduce flexural demands. This significantly reduced the overstressed areas such that localized areas could be strengthened with fiber reinforced polymer sheets. While developing the repair, CA collaborated with the Structural Engineer of Record to ensure that the added steel support would not overload the existing steel columns and braced frames.

Municipal Water Tank Roof Failure

CA investigated the structural integrity of a 275,000 gallon municipal water tank in Vermont. The water tank consisted of a cast-in-place concrete foundation slab, cast-in-place concrete walls, and a precast, hollow-core plank roof with a continuous cast-in-place concrete topping slab over the planks. After only about ten years in service, distress was noted on the underside of the precast, hollow-core planks in the form of cracking and fractured and fallen sections of concrete. CA investigated the distress and alleged failure of the water tank. CA focused on the structural system, construction, and condition of the water tank as well as determining the cause(s) of the observed distress. CA reviewed construction documents, construction specifications, previous engineering and petrographic summary reports, and relevant published literature and industry standards. CA’s field observations, sampling, and petrographic examination revealed that the overall tank structure was in good condition and that the distress in the roof structure was due to an internal sulfate attack mechanism. CA determined that the distress mechanism emanated from planks’ manufacturing process.

As-Built Construction Investigation of Concrete Water-Retaining Structures

Carrasquillo Associates investigated leaking and cracking in multiple concrete structures which occurred several months after construction of a municipal drinking water treatment plant. CA’s investigation focused on determining if the distress observed in the concrete structures resulted from deficiencies in the installation of the steel reinforcement, as well as evaluating the findings and recommendations of the investigations performed by other parties.

Pavement Construction and Possible Overload Investigation

Several new structures for an oil-field equipment servicing company were constructed in 2012 in Houston, TX.  The structures were surrounded by three large reinforced concrete drive lanes utilized for delivery and pick-up of the large-size oil equipment parts.  Shortly after construction, the reinforced concrete pavement exhibited distress in form of spalled joints at dowel locations, pumping, and localized panel failures.  CA was retained to determine the cause(s) of the distress and provide repair recommendations.  CA’s field work included soil sampling and testing, non-destructive testing of the concrete pavement, including the use of ground penetrating radar, and relative elevation surveys to verify surface drainage patterns.  In addition to the field work, CA also performed an analysis of the pavement design to determine its structural adequacy as-designed considering the actual forklift and truck traffic.  CA’s investigation revealed numerous design deficiencies relating to the base material and pavement thickness considering the actual pavement loads. Certain construction deficiencies exacerbated the observed distress as well. CA provided a repair plan for the pavement.

Burnished Concrete Floor Finish Investigation

Carrasquillo Associates reviewed a 150,000 square foot interior slab-on-ground for a big box retailer in Cibolo, TX. The project specifications for the slab-on-ground finish incorporated strict aesthetic requirements.  Shortly after burnishing and cleaning the finished floor surface, the contractor was notified that the floor was unacceptable due to various aesthetic issues on the surface of the floor. CA extracted concrete core samples for petrographic examination of the concrete and finished surface. CA determined that the concrete floor was structurally adequate, but identified various deficiencies in the burnishing and/or cleaning operations which affected the initial hard trowel finish leaving a dull appearance and exposed aggregate at localized areas.