Specification:Concrete properties and in-kind replacement

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=GENERAL=

DESCRIPTION
 This specification provides guidance for identifying concrete deterioration and appropriate general repair methods. This specification has been developed for use on historic properties (defined as any district, site, building, structure, or object that is listed in or eligible for listing in the National Register of Historic Places) and provides an overview of accepted practices. All work described herein and related work must conform to the Secretary of the Interior’s Standards for the Treatment of Historic Properties. The Contractor shall provide all labor, materials, equipment, and operations required to complete the rehabilitation work indicated herein. All work described herein and related work must have the approval of a Cultural Resources Manager, Conservator, Historic Architect, or other professional who meets the standards outlined in the Secretary of the Interior’s Standards – Professional Qualifications Standards pursuant to 36 CFR 61. Such person is referred to in this document as the Architect. The Architect will provide site-specific specifications, when appropriate. 

SECTION INCLUDES
 Concrete Properties</li> Causes of Concrete Deterioration</li> Methods of Investigation</li> </ol>

RELATED SECTIONS
<ol type="A"> 03710.01 – Cleaning and Testing of Atmospheric Soiling, Graffiti, Staining and Biogrowth</li> 03732.01 – Composite and Mechanical Concrete Repair</li> 04100 – Historic Mortar</li> 04500 – Masonry Restoration</li> 04720 – Historic Cast Stone</li> </ol>

DEFINITIONS
<ol type="A"> Concrete: Concrete encompasses any of a number of material compositions consisting of sand, gravel, crushed stone, or other coarse material, bound together with various kinds of cementitious materials, such as Portland cement, lime, or natural hydraulic cements. When mixed with water, the composition hardens due to the chemical interaction of the constituent parts.</li> Cement/Portland Cement: A hydraulic cement made by heating a limestone and clay mixture in a kiln and pulverizing the resulting material. Portland cement consists of a properly proportioned mixture of three minerals: lime, silica, and alumina.</li> Unreinforced Concrete: Concrete composed simply of cement and aggregate. While very strong in compression, unreinforced concrete lacks significant tensile strength and is unsuitable for applications that are subject to bending forces such as those formed in beams.</li> Reinforced Concrete: Concrete strengthened by embedding metal (typically steel) bars. The addition of metal bars (which are very strong in tension) allows concrete to be used in applications that are subject to bending forces.</li> Cast-in-place Concrete: Concrete poured onsite into a previously erected formwork that is removed after the concrete has set. Precast Concrete: Concrete structural components cast in molds and finished offsite. Components are then shipped to the project site and fastened together using embedded clips and anchors.</li> </ol>

SUBMITTALS
<ol type="A"> Detailed Schedule: Submit a detailed schedule to architect for approval of the survey and evaluation of materials, construction methods, cause and extent of deterioration.</li> Historic concrete analysis: Submit laboratory report from completed mortar analysis. Complete concrete analysis prior to beginning test panel preparation. Analysis shall be limited to wet chemical and microscopic analysis to characterize the insoluble aggregate, determine binder-aggregate ratio, prepare a mix design for replacement concrete and identify appropriate sources for sand aggregate.</li> Mix Design: Submit mix design for new concrete to architect. Mix design shall include concrete strength, cement type, aggregates and admixtures (including pigments), and shall indicate conformance to referenced standards.</li> Samples: Where color and texture match is a requirement, submit three cured samples of the proposed concrete for evaluation by the Architect. Samples shall be a minimum of 12 inches by 12 inches with a minimum thickness of two inches. Samples shall be finished/tooled in the same manner as the final installation to match the original concrete. Inspect the samples for color, texture, composition, and other visual characteristics. Multiple batches of replacement concrete samples may be required to be acceptable for approval. The Contractor shall prepare up to five such sample batches without further compensation. Approved samples shall become part of the work and shall serve as the quality standard for all similar work.</li> <li>Shop Drawings: Submit shop drawings for reinforcing steel sizing and layout for all structural work. Show bar size and length, piece numbers, overlap, etc.</li> </ol>

QUALITY ASSURANCE
<ol type="A"> <li>The Contractor shall have a minimum of seven years experience in repair and restoration of historic concrete and masonry. He/She shall have successfully completed at least three concrete restoration projects of similar scope within the previous five years. He/She shall demonstrate a working knowledge of the Secretary of the Interior’s Standards for the Treatment of Historic Properties.</li> <li>Material, design, and placement of concrete shall comply with ACI 318.</li> </ol>

DELIVERY, STORAGE AND HANDLING
<ol type="A"> <li>Store reinforcing materials off the ground and covered to limit corrosion. Store in such a manner as not to interfere with the daily use and maintenance of the building.</li> <li>Deliver reinforcing steel to job site bearing identification indicating size and grade in accordance with the drawings.</li> <li>Deliver concrete materials for immediate placement on site. Notify Owner at least 24 hours in advance of scheduled concrete deliveries.</li> <li>Waste, debris and excess concrete shall be removed from the site immediately and disposed of in accordance with local, state and federal environmental regulations.</li> </ol>

PROJECT / SITE CONDITIONS
<ol type="A"> <li>The normal temperature range for the work of this Section shall be air and surface temperatures of 40 degrees F and rising or less than 90 degrees F and falling. When temperatures are expected to fall outside this range, the Contractor shall employ hot or cold weather procedures as published by the American Concrete Institute.</li> <li>The Contractor is responsible for protecting existing adjacent materials and surfaces during the execution of the work. Provide all necessary protection and work procedures to prevent damage to existing material assemblies not a part of the work in the Section. <ol> <li>Protect the adjacent vegetation and lawns from damage during delivery and placement of concrete. The Contractor shall repair any damage to the surrounding lawns.</li> <li>Provide protective barriers around trees and tree driplines to prevent damage to mature trees through compression of root system.</li> <li>Protect adjacent building surfaces from concrete spatter and staining. Remove any concrete spatter on adjacent surfaces immediately before setting.</li> </ol> </li> <li>Provide visible barriers and/or warning tape around the perimeter of the work area for visitor protection. Protect nearby vehicles and adjacent structures from damage during the course of the work.</li> <li>The Contractor shall coordinate concrete replacement with the other trades involved in the work including, but not limited to, concrete/masonry cleaning, masonry, structural steel, painting, and rough carpentry.</li> </ol> =PRODUCTS=

CONCRETE PROPERTIES AND PROBLEMS
<ol type="A"> <li>Concrete Properties <ol> <li>Concrete has good compressive strength but limited tensile strength. It requires reinforcement in order to be practical and economical as a building material.</li> <li>Concrete absorbs and draws moisture. Therefore, it is subject to deterioration from exposure to moisture, freeze-thaw cycles and contaminants.</li> <li>The composition of concrete varies greatly according to date of construction, location, and influence of building traditions.</li> <li>Early concrete consisted of “lime and gravel” mixtures sometimes referred to as gravel walls or mud buildings. Around the mid-nineteenth century, concrete buildings generally had thick monolithic walls. These concretes were not standardized and often included contaminants that resulted in condition problems years later.</li> <li>The earliest buildings of reinforced concrete in the United States date from the 1860s. The use of reinforced concrete continued to increase through the end of the nineteenth century. Improved reinforcement techniques eventually allowed concrete structural members to become more structurally efficient and streamlined.</li> <li>At the start of the twentieth century in the United States, acceptance of Portland cement (due to its high strength), refinements in cement production, and innovations in concrete construction facilitated its use both as a primary building material and in conjunction with steel-frame construction.</li> </ol> </li> <li>Causes of Concrete Deterioration <ol> <li>Environmental factors: Even years after initial curing, concrete continues to react with the surrounding environment. Concrete absorbs moisture readily, creating problems with leaching and migration of soluble salts and freeze-thaw damage. Historic concrete is often more susceptible to thermal factors because of the absence of expansion/contraction joints. Atmospheric carbon dioxide and sulfur can cause deterioration by reacting with the cement at the surface.</li> <li>Materials and Workmanship: Most notably, early concrete has potential for problems arising from the methods of formulation and construction, and particularly the types of aggregates included in the formulation. <li>The addition of cinders and certain crushed brick can make the concrete weak.</li> <li>Alkali-aggregate reactions within the concrete create cracking and staining.</li> <li>Poorly consolidated and weaker concrete might be formed when aggregates with similarly size particles were used.</li> <li>The addition of salts, whether intentionally or inadvertently (through the use of seawater or beach sand), causes efflorescence and surface disfigurement.</li> <li>Poor placement practices contribute to deterioration in aging concrete. Placement in small batches allows cold joints to form where one batch sets prior to the placement of the subsequent batch. Cold joints may leave spaces or planes of weakness that can allow water or dirt infiltration and subsequent deterioration.</li> <li>Failure to consolidate the concrete after pouring often leaves voids or spaces (called “honeycombs) within the material, providing passage for moisture. Poor consolidation often leaves reinforcing bars unprotected and reduces the tensile strength of the member.</li> </ol> </li> <li>Improper Maintenance: Deferred maintenance can lead to prolonged exposure to water or woisture, leading to long-term deterioration. Similarly, improper maintenance, such as incompatible repairs and the use of sealants, can promote deterioration of concrete. </li> </ol> </li><li>Methods of Investigation: <ol> <li>Document Review: Review historical materials such as plans, permits, photographs, specifications, records of previous repairs, and news reports for information about the original construction.</li> <li>Field Survey: Note the condition of the concrete and the building. Identify and record the location, type, extent, and severity of any stress, deterioration or damage. Also note the cause of deterioration and any necessary repairs. Document through any areas that are anticipated to be replaced through narratives and photographs.</li> <li>Petrographic analysis to identify the composition of the concrete: This type of analysis includes microscopic examination and chemical testing of samples extracted from the structure. Problems such as poor aggregate, alkali-aggregate reaction and the presence of soluble salts may be identified through petrographic analysis.</li> <li>Other types of testing include, but are not limited to: <li>Compressive strength: Core samples of cured concrete are compressed to the point of fracture to determine the ultimate strength of the material.</li> <li>Load testing: Concrete structures may be loaded with weights in situ to assess structural performance.</li> <li>Potential testing: The flow of electricity through the concrete is used to determine the extent of deterioration in embedded reinforcing metal.</li> <li>Thermography: The use of thermographic imaging may assist in detecting areas of moisture infiltration and eventual deterioration.</li> <li>Sonic testing: The ability of sound pulses to travel through concrete may be used to identify cracks and areas of delamination.</li> </ol> </li> <li>Evaluation of survey and test results in conjunction with documentation to determine the nature and causes of deterioration. Results of the investigations are used to plan types of intervention needed, formulate appropriate maintenance schedules, and formulate proper remediation measures.</li> </ol> </li> </ol>

EQUIPMENT
<ol type="A"> <li>Equipment for removal of deteriorated concrete: Power saws and chisels as approved by the Architect.</li> <li>Equipment for mixing and fabrication, molds, and forms. <ol> <li>Paddle or drum type mixers.</li> <li>Wood (free of dirt and contaminants).</li> <li>Molds and Forms: Shall be free from dirt and contaminants.</li> <li>Trowels, hoe.</li> </ol> </li> <li>Equipment for installation: <ol> <li>Paddle or drum type mixers.</li> <li>Wood: shall be free from dirt and contaminants.</li> <li>Molds and Forms: Shall be free from dirt and contaminants.</li> <li>Trowels, hoe</li> </ol> </li> </ol>

CONCRETE MATERIALS
<ol type="A"> <li>Ready-mix concrete, if its properties are analyzed and approved by the Architect, shall comply with ASTM C 94, with proportions of cement, aggregates and water to provide the required strength at 28 days. Concrete slump shall not exceed four inches. </li> <li>Concrete design strength shall be 4000 psi for structural components such as footers, slabs, beams and pads.</li> <li>Concrete strength for all other applications shall be as noted on the Drawings.</li> </ol>

ADMIXTURES
<ol type="A"> <li>Air entrainment (for exterior concrete only) shall be six percent (plus or minus one percent).</li> <li>No anti-freeze or calcium chloride additives shall be used in any concrete.</li> <li>Mortar colorant, if required to match the color of the existing mortar, shall be a standard alkali-resistant, non-fading, approved product .</li> </ol>

REINFORCING
<ol type="A"> <li>Deformed Reinforcing Bars and Dowels: ASTM A 615, Grade 60, epoxy coated.</li> <li>Supports for Reinforcement: Bolsters, chairs, spacers, and other devices for spacing, supporting, and fastening reinforcing bars in place.</li> <li>Epoxy adhesive for embedding anchors and dowels shall be a high modulus epoxy resin conforming to ASTM C-881, Type I, II, IV and V, Grade 3 epoxy resin adhesives.</li> </ol>

FORMS
<ol type="A"> <li>Forms for concrete shall be plywood, metal, metal-framed plywood faced, or other acceptable panel-type materials to provide straight, smooth surfaces when removed.</li> <li>Form release agent shall be approved by the Architect.</li> </ol> =EXECUTION=

GENERAL
<ol type="A"> <li>The extent of the concrete replacement shall be reviewed and approved by the Architect on site prior to beginning operations. Historic concrete will be removed only where it is structurally unstable or where it will cause further deterioration. Contractor shall submit a schedule, including methods and materials to be used.</li> <li>Submit a detailed schedule of concrete analysis, preparation and installation, including curing procedures and finishing techniques, to the Architect for review. Schedule and required samples must be approved by the Architect prior to start of work.</li> <li>The type of substrate, where applicable, must be identified prior to concrete replacement. The chosen concrete composition must be compatible with the substrate.</li> <li>The Contractor shall complete a survey of the condition of the existing concrete (where applicable). <ol> <li>Document existing general concrete failures and coordinate with other scheduled repairs prior to work.</li> <li>Analyze concrete type, color and composition. The extent and type of analysis shall be determined by the Architect.</li> </ol> </li> <li>If work is found to be unacceptable by the Architect, all work shall cease without additional cost to the Owner until deficiencies in tools, workmanship, or methodology have been corrected to the Architect’s satisfaction.</li> </ol>

CLEAN-UP
<ol type="A"> <li>Excess concrete shall be removed from the site. Do not dump on site.</li> <li>Immediately remove any mortar spatters from adjacent surfaces to prevent staining. Do not allow concrete to harden on adjacent surfaces.</li> </ol>

FINAL REPORT
<ol type="A"> <li>After the new concrete has cured at least one week, revisit the site to compare the finish and color of the repair to see if the desired effect has been achieved.</li> <li>Document the finished product with photographs.</li> <li>Provide a written summary of the project and results upon final inspection and approval. Outline steps taken or new findings not specified in the initial documentation.</li> </ol>