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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305R-10 Guide to Hot Weather Concreting
Generally, centrally mixed concrete can be inspected visually as it is being discharged the into transportation unit. Errata are not included for collections or sets of documents such as the ACI Collection. Trial batches, however, should also be performed at the expected maximum placing temperature with consideration of using a mixing and agitating period longer than that required in ASTM C to help define the performance to be expected.
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Traffic arrangements at the site should ensure easy access of delivery units to the unloading points over stable roadways.
AC1 CommitteeReports,Guides,StandardPractices,and Commentaries are intended for guidance planning, designin ing, executing, and inspecting construction. Axi pertinent to concrete placed under all conditions, this points to the special need to control the use of additional water in concrete placed under hot weather conditions; see Section 2.
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The most commonlyquoted value is 0. The temperature of water usedfor curing must be close as posas sible to that of the concrete to avoid thermalshock. If items found in this document are desired by the ArchitectEngineerto bea part of the contract documents, they shallbe restated in mandatory language for incorporation by the ArchitectEnaineer. Other means ofreducing moisture loss include spreading and removing impervious sheeting or application of sprayable moisture-retaining monomolecular films one or more times as needed, between the various finishing operations.
The type of adjustment depends on local climatic conditions, timing of placements, and concrete temperatures. Each are widely used as partial replacements for portland cement; they may impart a slower rate of setting and of early strength gain toconcrete, which the is desirable in hot weather concreting, as explained in Section 2.
Precautions to avoid plastic-shrinkage specimens moist-cured at 73 F 23 C 28 days. This guide defines hot weather, discusses potential problems, and presents practices intended to minimize them. Under hot weather conditions, scheduling concrete placements atother-than-normal hours may be advisable.
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. During preliminary field use, concrete containing admixture should be evaluated for consistency of performance in regard to the desired characteristics in hot weather construction. Concrete should not be allowed to rest exposed to the sun and high temperature before placing it into the form.
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.
ACI R Hot Weather Concreting (Hot Weather Concreting): ACI: : Books
Other researchers form-stripping time, and selection and dosage of appropriate determined that insufficient curing is more detrimental than chemical and mineral admixtures.
The American Concrete Institute disclaims any and ail responsibility for the stated principles. High-range, water-reducing retarders formulatedforextendedslumpretentionshould be considered if longer delivery periods are anticipated.
The cai influence of the temperature of concrete ingredients on concrete 3005r is calculated from the equations in Appendix A, and shown in Fig. It requires careful recording of batch quantities at the plant and of water added for slump adjustment before sampling.
Major placements should be scheduled during periods of lower urban traffic loads. This guide provides measures that can be taken to minimize the undesirable effects of these environmental factors and reduce the potential for serious problems.
This will also reduce thermal shock from rapid temperature drops caused by wide day and night temperature differences or cool rain on concrete heated by the sun earlier in the day. An interruption in the concrete placement due to rejection may cause the formation of a cold joint or serious problems in finishing.
Afog nozzle should beused to cool theair, to cool any forms and steel immediately ahead, and to lessen rapid evaporation cai the concrete surface acci and after each finishing operation. For a listing of and access to all product errata, visit the Errata page. It serves no lasting purpose to merely trowel a slurry over the cracks, because these are likely to reappear if not firmly closed and immediately covered to avoid evaporation.
Further testing may then acl required in production-size concrete batches. Care should be taken to prevent interruptions of the fog spray; and Total immersion in water not to beused for cardboard molds.
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For a listing of and access to all product errata, visit the Errata page. These materials should be keptin contact with the concrete surface at all times. The temperatureof free and absorbed water on the aggregate is avi to be zci same temperature as the aggregate. This is an important consideration for slabs, walls, and mass concretes, as discussed in AC1 When placement is slow, consideration shouldbe given to reducing load size, using set-retarding admixture, or using cooled concrete.
Rapid slump loss in hot weather often increases the demand for water, increasing total water content, and therefore, increasing the potential for subsequent drying shrinkage.
With given materials and mixture proportions, the slump change characteristics between plant and job site should be established.