By Carrasquillo Associates 0 Comments

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.

By Carrasquillo Associates 0 Comments

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.

By Carrasquillo Associates 0 Comments

Concrete Repairs under Severe Exposure at Wastewater Treatment Plant

The Govalle Tunnel is an approximately 8-mile long, 96-inch diameter, cast-in-place concrete tunnel at an average depth of 100 feet that conveys wastewater generated in central and southeast Austin, Texas to the South Austin Regional Wastewater Plant. Inspections performed by the City of Austin in 2002 identified rehabilitation needs for the tunnel system. Rehabilitation work included structural repair of large diameter and deep shafts and laterals using a cementitious repair material followed by the application of an epoxy protective system. The purpose of these repairs was to remediate the impacts of concrete deterioration due to exposure to sulfates and steel reinforcement corrosion and to protect from future deterioration. CA was retained by the City of Austin to determine the cause(s) and/or contributing factors resulting in the failure of the rehabilitation work using an approved repair mortar. Among the most relevant issues investigated were the quality of the substrate surface preparation, repair materials characteristics and properties, repair practices, and behavior, performance and curing requirements of the repair mortar at different temperatures.

By Carrasquillo Associates 0 Comments

Cementitious Underlayment Deficiencies in Hospital Operating Rooms

CA investigated the quality of a cementitious underlayment installed as part of the finish out of the 11th and 12th floors of an existing 33-story hospital building. The elevated concrete structural slabs of these floors were covered with a variable thickness cementitious underlayment material, with the intent to achieve an adequate floor surface that would later receive final floor finishes such as tile or carpet. The owner observed that this underlayment exhibited an inconsistent appearance, variable color, a dusty/powdery surface, and a poor bond with the finished flooring. CA evaluated the underlayment and assessed the expected performance of the floor, specifically its integrity and ability to resist wear due to long-term loading from wheeled medical equipment. CA’s investigation included a walk-through, visual condition assessment, core sampling, petrographic examination, and bond pull-off testing. CA’s analysis resulted in the removal and replacement of the underlayment to ensure a quality long-term floor system in the operating rooms and associated support rooms.

By Carrasquillo Associates 0 Comments

Inspection and Rehabilitation of Underground Tunnel System

The Govalle Tunnel is an approximately 8 mile long, 96-inch diameter, cast-in-place concrete tunnel at an average depth of 100 feet that conveys wastewater generated in central and southeast Austin, Texas to the South Austin Regional Wastewater Plant. Inspections performed by the City of Austin in 2002 identified rehabilitation needs for the tunnel system. Rehabilitation work included structural repair of large diameter and deep shafts and laterals using a cementitious repair material followed by the application of an epoxy protective system. The purpose of these repairs was to remediate the impacts of concrete deterioration due to exposure to sulfates and steel reinforcement corrosion and to protect from future deterioration. CA was retained by the City of Austin to determine the cause(s) and/or contributing factors resulting in the failure of the rehabilitation work using an approved repair mortar. Among the most relevant issues investigated were the quality of the substrate surface preparation, repair materials characteristics and properties, repair practices, and behavior, performance and curing requirements of the repair mortar at different temperatures.