ACI 305R PDF

R Hot Weather Concreting. ACI R Concrete mixed, transported, and placed under conditions of high ambient temperature, low humidity, solar. Temperature, volume changes, and cracking problems associated with mass concrete are treated more thoroughly in ACI R, R, and R. ACI Committee defines hot weather as any combination of high ambient temperature, high concrete temperature, low relative humidity, wind speed and.

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The several volumes are arranged to group related material together and maybe purchased individually or in setS. AC1 Committees prepare standards and reports in the general areas of materials and properties of concrete, construction practices and inspection, aco and slabs, structural design and analysis, structural specifications, and special products and processes.

A complete catalog of all AC1 publications is available without charge. American Concrete Institute P. AC1 certification programs identify craftsmen, technicians, and inspectors who have demonstrated their qualifications. The 35r programs are administered by AC1 to fulfill the growing demand in the industry for certified workers: Enhancement of 035r Documents The technical committees responsible for AC1 committee reports and standards strive to avoid ambiguities, omissions, and errors in these documents.

In spite of these efforts, the users of AC1 documents occasionally find information or requirements that may be subject to more than one interpretation or may be incomplete or incorrect.

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To assist in the effort for accuracy and clarity, the Technical Activities Committee solicits the help of individuals using AC1 reports and standards in identifying and eliminating problems that may be associated with their use. Users who have suggestions for the improvement of AC1 documents are requested to contact the AC1 Engineering Department in writing, with the following information: Title and number of the document containing the problem and specific section in the document; 2.

Concise description of the problem; 3. If possible, suggested revisions for mitigating the problem. Members as well as nonmembers of the Institute are encouraged to assist in enhancing the accuracy and usefulness acl AC1 documents. If not, suggested 035r specifications are available on request from the AC1 Certification Department. Ryan Chairman Muwnfaq A. Abu-hid Bijan Ahmadi J. Gene Daniel Richard D.

Moore Dan Ravina John M. Zein Al-Abidien Concrete mixed, transported, und placed under conditions of high ambient temperature, low humidity, solar rudiution. This committee report defines hot weuther. A selected bibliogruphy is included. These revisions involve un editorial ai of the document. Copyright OAmerican Concrete Institute. All rights reserved including rights of reproduction and use in any form or by any means,includingthemaking of copies by anyphoto process.

AC1 CommitteeReports,Guides,StandardPractices,and Commentaries are intended for guidance aaci, designin ing, executing, and inspecting construction. This document is intended for the use 305 individuals who are competent to evaluate the significance and limitations of its content and recommendations and who will accept responsibility for the application of the material it contains. The American Concrete Institute disclaims any and ail responsibility for the stated principles.

The Institute shall be liable for any loss not or damage arising therefrom. Reference to this document shall not be made in contract documents. If items found in this document are desired by the ArchitectEngineerto bea part of the contract axi, they shallbe restated in mandatory language for incorporation by the ArchitectEnaineer.

Download Aci R Guide To Hot Weather Concreting

These problems can adversely affect the properties and serviceability of the concrete. Most of these problems relate to the increased rate zci cement hydration at higher temperature and increased evaporation rate of moisture from xci freshly mixed concrete. The rate of cement hydration is dependent on concrete temperature, cement composition andfineness, and admixtures used. This report will identify problems created by hot weather concreting and describe practices that will alleviate these potential adverse effects.

These practices include suggested preparations and procedures for use in general types of hot weather construction, such as pavements, bridges, and buildings. Temperature, volume changes, and cracking problems associated with massconcrete are treated more thoroughlyin AC1 IR and AC1 R.

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Concrete durability is a general term that is difficult to quantify, but it is perceived to meanresistance of the concrete to weathering AC1 Generally, if concrete strengths are satisfactory and curing practices are sufficient to avoid undesirabledrying of surfaces, durability of hot weather concrete will not differ greatly from similar concrete placed at normal temperatures. The presence of a desirable air-void system is needed if the concrete is going to be exposed to freezing cycles.

Download Aci 305R 10 Guide To Hot Weather Concreting

If an acceptable record of field tests is not available, concrete proportions may be determined by trial batches AC1 and AC1 Trial batches should be made at temper1 atures anticipatedin the work and mixed following of the one procedures describedin Section 2. The concrete supplier and contractor are generally responsible for determining concrete proportions to producetherequired quality of concrete unless specified otherwise. If thecylinders are allowed to dry at early ages, strengths will bereducedeven further Cebeci Therefore, proper fabrication, curing, and testing of the test specimens during hot weather is critical, and steps should be taken to ensure that the specified procedures are followed.

High ambient temperature; High concrete temperature; Low relative humidity; Wind speed; and Solar radiation. The potential problems of hot weather concreting may occur at any time of the year in warm tropical or arid climates, and generally occur during the summer season in other climates.

Early cracking due to thermal shrinkage is generally more severe in the spring and fall. This is because the temperature differential for each h 24 period is greater during these times the year. Precautionary of measures required on a windy, sunny day will be more strict than those requiredon a calm,humid day, even if air temperatures are identical.

Increased water demand; Increased rate of slump loss and corresponding tendency to add water the job site; at Increased rate of setting, resulting in greaterdifficulty with handling, compacting, and finishing, and a greater risk of cold joints; Increasedtendency for plastic-shrinkage cracking; and Increaseddifficulty in controlling entrainedaircontent.

Increasedtendency for drying shrinkage and differential thermal cracking from either cooling of the overall structure, or from temperature differentials within the cross section of the member; Decreased durability resulting from cracking; Greater variability of surface appearance, such as cold joints or color difference, due to different rates of hydration or different water-cementitious material ratios wkm ; Increased potential for reinforcing steel corrosionmaking possible the ingress of corrosive solutions: The following list of practices and measures to reduce or avoid the potential problems of hot weather concreting are discussed in detail in Chapters 23and 4: Select concrete materials and proportions with satisfactory records in hot weather conditions; Cool the concrete; Use a concrete consistency that permits rapid placement and effective consolidation; Minimize the time to transport, place, consolidate, and finish the concrete; Plan the job to avoid adverse exposure of the concrete to the environment; schedule placing operations during times of the day or night when weather conditions are favorable; Protect the concrete from moisture loss during placing and curing periods; and Schedule a preplacement conference to discuss the requirements of hot weather concreting.

Use of cements with increased rate of hydration; Use of high-compressive-strength concrete, which requires higher cement contents; Design of thin concrete sections with correspondingly greater percentages of steel, which complicate placing and consolidation of concrete; Economic necessity to continue work in extremely hot weather: Harmful effects are minimized by control procedures outlined in this report. Strength, impermeability, dimensional stability, and resistance of the concrete to weathering, wear, and chemical attack all depend on the following factors: Good judgment is necessary to select the concrete producedandcured at lower temperatures, but most appropriate compromise of quality, economy, and strengths are generally lower at 28 days and later ages.

The procedures selected will depend on: Some bient temperature, high concrete temperatures, low relative researchers conclude that a relatively more uniform microhumidity, wind speed, and solar radiation. Last-minute improvisations are rarely successful. Specimens molded and purchasing, and coordination of all phasesof work. Precautions to avoid plastic-shrinkage specimens moist-cured at 73 F 23 C 28 days.

The longer for cracking are important. The potential for thermal cracking, the delay between casting the cylinders and placing into staneither from overall volume changes or from internal redard moist storage, the greater the strength reduction. The straint, should be anticipated. Methods to control cracking data illustrate that inadequate curing in combination with include: The tests were made on plain concrete steel or fibers, limits on concrete temperature, reduced without admixtures or pozzolans that might have improved cement content, low-heat-of-hydration cement, increased its performance at elevated temperatures.

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Other researchers form-stripping time, and selection and dosage of appropriate determined that insufficient curing is more detrimental than chemical and mineral admixtures. High concrete temperatures, high wind speed, and low humidity, alone in or combination, cause rapid evaporation of surface water. The rate of bleeding, other the hand, on depends on concrete mixture ingredients depth and proportions, the on of member the being cast, and on the type of consolidation and finishing.

Because surface drying is initiated when evaporation rate exrate, ceeds bleeding of plastic-shrinkage 8 whenever cracking therefore increases 1E conditions increase evaporation, or when the concrete has a For mixtures incorreduced bleeding rate.

The table is based on the assumption of a 10 mph 16 k m h wind speed and an air temperatureof 10 F 6 C cooler than the concrete temperature. The nomograph in Fig. It occurs in exposed concrete, primarily in flatwork, but also in beams and footings, and maydevelop in other climates when thesurface of freshly cast concrete dries and subsequently shrinks. Surface dryingisinitiatedwhenevertheevaporation rate is greater than the rate at which water risesthe surface of reto cently placed concrete by bleeding.

A method to estimate logical methods for estimating the rate of evaporation waof ter from lakes and reservoirs, is and therefore the most accurate when estimating the rate of evaporation from the surface of concrete while that surface is covered with bleed water.

When the concrete surface is not covered with bleed water, the nomograph and its underlying mathematical expression tends to overestimate the actual rate of water loss from theconcrete surface by as much as a factor of 2 or more Al-Fadhala The method is therefore the most useful in estimating the evaporation potentialof the ambient conditions, and not as an estimator of the actual rate of water loss from the concrete.

Early in the bleeding process, however, and at rates of evaporation less than or equal to 0. The probability for plastic-shrinkage cracks to occurmay be increased if the setting time of the concrete is delayed due to the use of slow-setting cement, an excessive dosage of retarding admixture, fly ash as a cement replacement, or cooled concrete.

Fly ash is also likely to reduce bleeding and may thereby contribute to a cracking tendency AC1 Plastic-shrinkage cracks are difficult to close once they have occurred see Section 4. Other adverse effects are listedin Section 1.

The amount of the water required to produce a given slump increases with the time. Xci constant mixing time, the amount of water required to produce a given slump also increases with the temperature, as shown in Fig. This cause thermal cracking AC1 may A maximum ambient or concrete temperature that will serve a specific case may be unrealistic in others.

Accordingly, the committee can only provide information about the effects of higher temperatures in concrete as mentioned in Sections 1.

Practices for hot weather concreting should be discussed during the preplacement conference. Trial batches of concrete for the job should be made at the limiting temperature selected, or at the expected job site high temperature, rather than the68 to 86 F 20 to 30 Zci range given in ASTMC Procedures for testing of concrete batches at temperatures higher than approximately 70 F 21 C are given in Section 2.

I b -Effect of temperature increase on the water requirement of concrete U. Bureau o Reclamation Because bleeding rates vary from zero to over 0. The most commonlyquoted value is 0. Construction specifications for the State of New York and the City 30r Cincinnati are intermediate evaporation rates of O.

High water temperatures cause higher concrete temperatures, and as the concrete temperature increases, morewaterisneededtoobtain the same slump.